In Situ Anchoring Ultrafine ZnS Nanodots on 2D MXene Nanosheets for Accelerating Polysulfide Redox and Regulating Li Plating

2D/3D hierarchical Zinc@Ti3C2Tx-MXene composite-coated copper foil as dendrite-free lithium host for stable lithium metal batteries

Lithium metal, with its ultrahigh theoretical capacity (3860 mAh g-1) and the lowest redox potential among metallic anodes (-3.04 V vs. SHE), is regarded as the ultimate anode for next-generation high-energy-density batteries. However, rampant dendrite growth and unstable solid electrolyte interphase (SEI) formation critically hinder its practical adoption. Herein, we design a hierarchical 2D/3D Zinc@MXene (Zn@M) composite-coated Cu current collector to stabilize lithium metal anodes. The MXene nanosheets (Ti3C2Tx) function as lithium-philic conductive channels to homogenize Li+ flux, while micrometer-sized Zn particles construct a porous scaffold that mitigates MXene restacking and provides preferential nucleation sites for lithium deposition. Benefiting from the strong interfacial bonding between MXene and Zn, the composite forms a robust dual-phase architecture with enhanced mechanical integrity and ion/electron transport efficiency. This synergy enables dendrite-free Li plating/stripping, as evidenced by the Li||Zn@M half-cell achieving a high average coulombic efficiency of 97.6 % over 450 cycles (1 mA cm-2/1 mAh cm-2) and symmetrical cells sustaining stable operation for 3300 h (1 mA cm-2/1 mAh cm-2). Remarkably, when paired with a high-loading LiFePO4 cathode (12.7 mg cm-2) in anode-free configuration, the Zn@M/Cu current collector demonstrates exceptional full-cell cyclability with 70 % capacity retention after 50 cycles. This work provides a universal interface engineering strategy for realizing dendrite-suppressive lithium hosts, paving the way toward practical high-energy lithium-metal batteries.

Superior performance lithium-ion battery anode based on Co9S8 nanoparticles layered in-situ growth with capacitive synergy

Identifying new anode materials that possess high energy density, outstanding cycling stability, and superior rate capability has emerged as a pivotal research focus in the development of lithium-ion batteries (LIBs). Herein, we successfully synthesized a novel Co9S8-MoB MBene heterostructure. This innovative material was developed through a space-confined growth process, wherein Co9S8 nanoparticles were incorporated within the interstitial layers of MoB MBene, thereby creating a unique composite with enhanced electrochemical properties. The Co9S8-MoB MBene electrode showed excellent performance, retaining 756.34 mAh/g capacity after 200 cycles at 100 mA/g (initial capacity 828.67 mAh/g), with an impressive retention rate of 91.27 %. Even at a high current density (800 mA/g), the specific capacity of 632.1 mAh/g was maintained with a retention rate of 79.83 % after 700 cycles, and the Coulombic efficiency was consistently around 99 %. The excellent cycling stability and rate performance are attributed to the two-dimensional layered structure of conductive MoB MBene. Density functional theory (DFT) calculations reveal that MoB MBene's low lithium diffusion barrier significantly decreases the Co9S8's lithium binding energy, through rapid kinetic charge transfer, improving the efficiency of lithium-ion insertion and extraction. The incorporation of MoB MBene restricts the volume expansion of Co9S8 during lithiation and delithiation, and facilitates the formation of surface capacitance and the development of diffusion-controlled pseudocapacitors. The excellent electrochemical performance suggests that the Co9S8-MoB MBene materials designed in this work can be a rational approach to be applied for high-performance LIBs anodes.

Thermoelectric Field Enhanced Sulfur Evolution Kinetics for High Performance Lithium-Sulfur Batteries

The practical deployment of lithium-sulfur (Li-S) batteries has been impeded by the shuttle effect and sluggish kinetics of lithium polysulfide (LiPSs) conversion. Here, Bi0.5Sb1.5Te3/carbon nanotubes (BST/CNT) interlayer is designed to enhance the durability of Li-S batteries by providing extensive adsorption sites and generating a thermoelectric field from BST thermoelectric material. Experimental and density functional theory investigations confirm the superior adsorption properties of BST. Additionally, analyses using Gibbs free energy and cyclic voltammetry robustly demonstrate that the thermoelectric field significantly accelerates the conversion kinetics of LiPSs. The electrochemical performance of cells equipped with a 20% BST interlayer is exceptional, showing remarkable stability over 500 cycles at 1 C with a minimal capacity decay rate of 0.05% per cycle. Most importantly, the thermoelectric field substantially improves the conversion kinetics of LiPSs, allowing the cell to maintain a discharge capacity of 594 mAh g-1 even at 10 C. Furthermore, under conditions of high sulfur loading (7.0 mg cm-2) and low electrolyte-to-sulfur ratio (6.1 µL mg-1), the cell achieves an areal capacity of 5.9 mAh cm-2. This research not only evidences the effectiveness of the thermoelectric field in enhancing the conversion kinetics of LiPSs but also shows its potential to boost the performance of Li-S batteries.

Niobium Phosphide-Induced Sulfur Cathode Interface with Fast Lithium-Ion Flux Enables Highly Stable Lithium-Sulfur Catalytic Conversion

Research on the Li-S catalytic chemistry primarily focus on the development of high-performance catalysts and the exploration of their reaction mechanisms, with limited attention given to the impact on the interface at the cathode. Moreover, regulating the Li+ flux at the cathode interface can enhance Li2S conversion kinetics without compromising the intrinsic catalytic activity of catalyst. This work presents a paradigm that employs interface regulation to enhance Li-S battery (LSB) cycling stability. A novel phosphorus doped carbon supported niobium phosphide nanocrystals (NbP/PC) catalyst is developed and demonstrates exceptional intrinsic activity for lithium polysulfide conversion while it facilitates lithium salt dissociation through intermolecular hybridization. The NbP-induced functional interface layer with abundant LiF and Li3N provides efficient Li+ transport channel for Li2S decomposition, which further mitigates the passivation of active sites. In consequence, the assembled LSB exhibits a capacity retention rate of 0.04 % per cycle after 1100 cycles at a 1 C. Furthermore, the pouch battery with an energy density of 451 Wh kg-1 maintains stable performance over 20 cycles. This strategy addresses the limitations of traditional catalytic material design in the chemical regulation of the cathodic interface for promising future of LSBs.

Synergistic Catalysts for Lithium-Sulfur Batteries: Ni Single Atom and MoC Nanoclusters Composites

The practical application of sulfur (S) cathodes in lithium-sulfur (Li-S) batteries is hindered by the shuttling of soluble lithium polysulfides (LiPSs) and sluggish sulfur redox kinetics. Addressing these challenges requires advanced catalytic host materials capable of trapping LiPSs and accelerating Li-S redox reactions. However, single-site catalysts struggle to effectively mediate the complex multi-step and multi-phase sulfur conversion processes. In this study, we present a novel dual-site catalyst, Ni-MoC-NC, featuring nickel single atoms anchored to nitrogen sites (Ni-N4) within a carbon nitride (NC) matrix and molybdenum carbide (MoC) nanoclusters. Experimental and theoretical analyses reveal that MoC sites efficiently catalyze the reduction of long-chain LiPSs (Li₂S₈ to Li₂S₄), while Ni-N4 sites drive the reduction of short-chain LiPSs (Li₂S₄ to Li₂S), resulting in a synergistic enhancement of the complete Li-S redox process. When incorporated as a coating on the cathode side of a commercial polypropylene (PP) separator, the Ni-MoC-NC catalyst enhances sulfur utilization, suppresses LiPSs shuttling, and facilitates a uniform Li+-ion distribution, effectively mitigating the uncontrolled growth of lithium dendrites. Thereby, Li-S batteries employing an S/Ni-MoC-NC cathode and a Ni-MoC-NC@PP separator demonstrate outstanding performance, including an initial capacity of 1624 mAh g⁻¹ at 0.2C and 1142 mAh g⁻¹ at 1C, retaining 590 mAh g⁻¹ after 800 cycles. At a sulfur loading of 8.3 mg cm⁻2 and an electrolyte/sulfur ratio of 6 µL mg⁻¹, the system achieves an initial areal capacity of 9.57 mAh cm⁻2 at 0.1C, showcasing significant promise for practical applications.

Bifunctional NiCoP nanofiber arrayed on carbon cloth for fast polysulfide conversion and uniform lithium deposition in lithium sulfur batteries

The severe polysulfides shuttling and irregular lithium dendrites impede the widespread adoption of lithium-sulfur (Li-S) batteries. Here, a sulfiphilic/lithiophilic NiCoP nanofiber arrayed on carbon cloth (NiCoP@CC) as the sulfur/lithium host is reported, providing a dual solution for both cathode and anode issues. Both theoretical calculations and experiments confirm that NiCoP@CC enhances the cycling stability of sulfur cathode and lithium anode by facilitating polysulfides conversion and homogenizing lithium deposition. Additionally, the unique structure of NiCoP nanofiber-decorated carbon cloth provides ample space to accommodate active materials and ensures even distribution of sulfur and lithium. Consequently, Li-S half cells containing NiCoP@CC exhibit an outstanding cycling life of 900 cycles at 1 C. Moreover, the Li@NiCoP@CC electrode achieves a stable, long cycling performance for 3000 h at 1 mA cm-2. Notably, Li-S full cells show enhanced cycling performance, maintaining stability over 750 cycles with a decay rate of 0.04 % per cycle at 1 C and a low N/P (negative/positive capacity) ratio of 2.4. A high areal capacity of 7.75mAh cm-2 is obtained at a high sulfur loading of 8.6 mg cm-2. This study presents a new strategy for designing bimetallic phosphides as bifunctional materials to overcome difficulties in practical Li-S batteries.

High-Sensitivity Room-Temperature Detection of H2S Using ZnO/Ti3C2TX Nanocomposite: Potential Applications in Exhaled Gas Monitoring

The detection of hydrogen sulfide (H2S) in exhaled breath at room temperature is essential for health monitoring and disease diagnosis. This study investigates a ZnO/Ti3C2TX nanocomposite synthesized by combining ZnO nanoparticles, prepared by a hydrothermal method, with Ti3C2TX MXene. Experimental results demonstrate that the ZnO/Ti3C2TX nanocomposite sensors exhibit excellent H2S detection performance at room temperature with high sensitivity, rapid response time, and robust recovery capability. Specifically, the ZnO/Ti3C2TX-1.0 wt % nanocomposite sensor shows a response of 85.116 at 5 ppm of H2S, which is 14-fold and 35-fold greater than that of pure ZnO and Ti3C2TX MXene, respectively. The sensor exhibits a rapid response (50 s) and recovery time (115 s) at 100 ppb of H2S. Additionally, it shows exceptional sensitivity to H2S at low concentrations, with a detection limit as low as 1 ppb. Based on the excellent sensing performance, oral exhaled gas detection demonstrates that the sensor effectively differentiates H2S levels in healthy and patient breath samples. These findings highlight the potential of the ZnO/Ti3C2TX nanocomposite in exhaled H2S detection at room temperature, offering new insights for developing ultrasensitive biogas sensors.

In Situ Assembly Engineering-Induced 3D MOF-Driven MXene Framework for Highly Stable Na Metal Anodes

Sodium metal, with its high theoretical capacity, low redox potential, and cost-effectiveness, presents a promising anode candidate for next-generation high-energy-density batteries. However, the development of Na metal anodes is significantly challenged by issues such as uncontrolled dendrite growth, uncontrolled volume expansion, and associated safety concerns. Designing and developing advanced materials to enhance the conductivity of sodium metal anodes and promote uniform sodium ion deposition are of urgent importance. Herein, a MXene-based hybrid material was developed by integrating MOF-derived Zn, Co, N, and C dopants with Ti3C2Tx MXene to serve as a hosting substrate for the Na metal anode. The MXene provided a conductive framework, while the MOF-derived dopants introduced sodiophilic sites, promoting uniform Na deposition and mitigating volume expansion. The optimized material demonstrated an average Coulombic efficiency of 99.99% over 3000 cycles and stable cycling for over 5000 h in symmetrical cells and maintained over 80% capacity retention at 3 C after 500 cycles in full-cell tests, highlighting its potential as a robust Na metal anode material.

Active MXene-Based Electrode Interface Chemistry for High Performance Li-S Battery: Design Strategies and Prospects

Lithium-sulfur (Li-S) battery with high capacity and energy density is a promising next-generation energy storage device. However, the shuttle effect of polysulfides causes the low utilization of sulfur and the side reactions at the electrode interface. The electrode/electrolyte interface determines the chemical activity of electrode and electrochemical reversibility as well as the cycling stability of battery. Therefore, the ideal electrode interface in Li-S battery depends on the sulfur loading, the fast ion diffusion, the effective utilization of active intermediates, and the uniform deposition of lithium ion on anode. MXene with two dimension layer structure, good conductivity, and abundant terminal groups can serve as the active interface carrier layer to load sulfur, anchor polysulfides, and accelerate ion transfer. This review summarizes three strategies of active MXene-based electrode interfaces including sulfur host interface, functional separator interface, and lithium anode interface based on the electrochemical principles and challenges of Li-S battery. In addition, the interfacial regulation and application of MXene-based materials focus on the electrochemical activity and reversibility of polysulfides in electrochemical process are also presented. Finally, the further prospective and challenges of MXene in Li-S battery are also discussed.

Zinc-Doping-Induced Electronic States Modulation of Molybdenum Carbide: Expediting Rate-Determining Steps of Sulfur Conversion in Lithium-Sulfur Batteries

Enhancing Li2S deposition and oxidation kinetics in lithium-sulfur batteries, especially the potential-limiting step under lean electrolyte, can be effectively achieved by developing conductive catalysts. In this study, by using ZnMoO4 as precursors, Zn-doped molybdenum carbide microflowers (Zn-Mo2C) composed of speared porous sheets are fabricated with a hierarchically ordered structure. Density functional theory calculations indicate that Zn doping shifts the d-band center on Mo atoms in Mo2C upward, promotes the elevation of certain antibonding orbitals in Mo─S bonds above the Fermi level, enhances d-p interaction between lithium polysulfides (LiPSs) and catalysts, weakens both S─S and Li─S bonds of LiPSs. Incorporating Zn significantly reduces the Gibbs free energy barrier for the rate-limiting step of the Li2S2 → Li2S conversion, from 0.52 eV for Mo2C to just 0.05 eV for Zn-doped Mo2C. Thus, the synthesized Zn-Mo2C demonstrates impressive bifunctional electrocatalytic performance, significantly advancing sulfur reduction and Li2S decomposition. Moreover, this modification enhances charge transfer within the Zn-Mo2C/LiPSs system, synergistically accelerating the kinetics of Li2S4 to Li2S reduction and Li2S oxidation. The Zn-Mo2C/S cathode demonstrates impressive electrochemical performance, achieves remarkable cycling stability with a minimal capacity decay of 0.021% per cycle over 1000 cycles at 5 C, underscoring its potential for high-energy applications.

Three-dimensional hollow ZnS/MXene heterostructures with stable Ti-O-Zn bonding for enhanced lithium-ion storage

An effective way to improve the cycling performance of metal sulfide materials is to blend them with conductive materials. In this paper, three-dimensional (3D) hollow MXene/ZnS heterostructures (ZnSMX) were prepared via a two-step process involving hydrothermal and template methodologies. The formation of Ti-O-Zn bonds enables the firm bonding between ZnS nanoparticles and the MXene substrate at heterogeneous interfaces, which can act as "electron bridges" to facilitate electron and charge transfer. Additionally, 3D hollow ZnSMX not only enhances the conductivity of ZnS, enabling rapid charge transfer, but also effectively show restacking of MXene nanosheets to maintain structural stability during the charge/discharge process. More importantly, the 3D porous structure provides ultrafast interfacial ion transport pathways and extra surficial and interfacial storage sites, thus boosting excellent storage performances in lithium-ion battery applications. The 3D ZnSMX exhibited a high capacity of 782.1 mA h g-1 at 1 A g-1 current, excellent cycling stability (providing a high capacity of 1027.8 mA h g-1 after 350 cycles at 2 A g-1), and excellent rate performance. This indicates that 3D ZnS/MXene heterostructures can potentially be highly promising anode materials for high-multiplication lithium-ion batteries.

Controllable Synthesis of Heterogeneous ZnS/SnS2 Encapsulated in Hollow Nitrogen-Doped Carbon Microcubes as Anode for High-Performance Li-ion Capacitors

Li-ion capacitors (LICs) integrate the desirable features of lithium-ion batteries (LIBs) and supercapacitors (SCs), but the kinetic imbalance between the both electrodes leads to inferior electrochemical performance. Thus, constructing an advanced anode with outstanding rate capability and terrific redox kinetics is crucial to LICs. Herein, heterostructured ZnS/SnS2 nanosheets encapsulated into N-doped carbon microcubes (ZnS/SnS2@NC) are successfully fabricated. The sufficient ZnS/SnS2 heterostructure possesses abundant active sites, and the built-in electric field formed at the heterojunction interface can facilitate electron/ion migration. The interconnected hollow carbon layers could reduce the electron transfer resistance effectively and accommodate the volume change of SnS2, thereby maintaining the structural stability. Due to the synergy between multi-components, the ZnS/SnS2@NC anode demonstrates impressive Li storage performance with an excellent cyclic durablity (690 mAh g-1 at 0.5 A g-1 after 600 cycles) and considerable rate capability. Moreover, when matched with active carbon, the ZnS/SnS2@NC based LIC device delivers an admirable energy density of 134.1 Wh kg-1 and a high power output of 11,250 W kg-1, as well as remarkable capacity retention of 73.2 % after 6,000 cycles at 1.0 A g-1. The experimental results demonstrate the significance of optimized heterointerface engineering toward construction of electrode materials with high-performance for Li storage.

Sandwich-Structured ZnO/MXene Heterojunction for Sensitive and Stable Room-Temperature Ammonia Sensing

2D metal carbides/nitrides (MXenes) have attracted considerable interest in NH3 sensing due to their high electrical conductivity and abundant terminal groups. However, the strong interlayer interactions between MXene nanosheets result in challenges related to recovery and rapid response decay in MXene-based sensors. Here, a one-step hydrothermal strategy is developed that anchors Zn atoms and grows ZnO polycrystals on the Ti vacancies of Ti3C2Tx layers, forming a sandwich-structured ZnO/Ti3C2Tx heterojunction. At room temperature, the NH3 sensitivity of ZnO/Ti3C2Tx is a remarkable 45-fold higher than that of Ti3C2Tx, with a low detection limit of 138 ppb and a rapid recovery time of 39 s. Furthermore, the heterojunction exhibits exceptional long-term stability, maintaining a consistent response over 21 days. The results confirm that in situ intercalation of the ZnO polycrystals effectively solves the recovery problem in MXene substrates by completely exfoliating the Ti3C2Tx nanosheets. Meanwhile, the room-temperature sensing performance and recovery speed of the sandwich-structured ZnO/Ti3C2Tx is enhanced by rapid electron conduction. This straightforward and effective route for in situ exfoliation and intercalation of MXene layers promises the expanded use of 2D material heterojunctions in sensing applications.

In situ construction of 3D 1T-VS2/V2C heterostructures for enhanced polysulfide trapping and catalytic conversion in lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries represent a promising next-generation energy storage solution, yet their performance is hindered by the insulating nature of sulfur and the detrimental shuttle effect. This study presents the in-situ synthesis of metal-phase 1T-VS2 as a modified separator material on a two-dimensional Mxene substrate V2C (VSC). The synergistic effect of strong adsorption by V2C and highly conductive catalysis provided by 1T-VS2 significantly enhances the transport of ions and electrons between lithium polysulfide and the interface. The combinations of experimental data and density functional theory (DFT) indicate that 1T-VS2, which is characterized by its high density of defective active sites and high conductivity, not only effectively improves the adsorption of lithium polysulfides, but also dramatically lowers the redox energy barrier of Li2S, thereby accelerating the chemical reaction kinetics. As a result, the Li-S cells assembled by the VSC-modified separator exhibit an impressive initial capacity of 1131 mAh/g at 1 C with a capacity decay rate of only 0.05% per cycle. In addition, even after 100 cycles and at a high sulfur loading of 5.6 mg cm-2, the cells maintain a discharge capacity of 817 mAh/g. Impressively, the VSC continues to deliver excellent cycling and rate performance even when the environmental temperature is reduced to 0 °C. These findings offer valuable insights into the potential for the advancement of highly practical Li-S batteries.

Optimized K+ Deposition Dynamics via Potassiphilic Porous Interconnected Mediators Coordinated by Single-Atom Iron for Dendrite-Free Potassium Metal Batteries

Potassium metal batteries are emerging as a promising high-energy density storage solution, valued for their cost-effectiveness and low electrochemical potential. However, understanding the role of potassiphilic sites in nucleation and growth remains challenging. This study introduces a single-atom iron, coordinated by nitrogen atoms in a 3D hierarchical porous carbon fiber (Fe─N-PCF), which enhances ion and electron transport, improves nucleation and diffusion kinetics, and reduces energy barriers for potassium deposition. Molten potassium infusion experiments confirm the Fe─N-PCF's strong potassiphilic properties, accelerating adsorption kinetics and improving potassium deposition performance. According to the Scharifker-Hills model, traditional carbon fiber substrates without potassiphilic sites cause 3D instantaneous nucleation, leading to dendritic growth. In contrast, the integration of single-atom and hierarchical porosity promotes uniform 3D progressive nucleation, leading to dense metal deposition, as confirmed by dimensionless i2/imax 2 versus t/tmax plots and real-time in situ optical microscopy. Consequently, in situ X-ray diffraction demonstrated stable potassium cycling for over 1900 h, while the Fe─N-PCF@K||PTCDA full cell retained 69.7% of its capacity after 2000 cycles (72 mAh g-1), with a low voltage hysteresis of 0.876 V, confirming its strong potential for high energy density and extended cycle life, paving the way for future advancements in energy storage technology.

Efficient mitigation of lithium dendrite by two-dimensional A-type molecular sieve membrane for lithium metal battery

Uneven lithium deposition poses a primary challenge for lithium-ion batteries, as it often triggers the growth of lithium dendrites, thereby significantly compromising battery performance and potentially giving rise to safety concerns. Therefore, the high level of safety must be guaranteed to achieve the large-scale application of battery energy storage systems. Here, we present a novel separator design achieved by incorporating a two-dimensional A-type molecular sieve coating onto the polypropylene separator surface, which functions as an effective lithium ion redistribution layer. The results demonstrated that even after undergoing 1000 cycles, the cell equipped with a two-dimensional A-type molecular sieve-Polypropylene (2D-A-PP) separator still maintains an impressive capacity retention rate of 70 %. In contrast, cells equipped with Polypropylene (PP) separators exhibit capacity retention rates below 50 % after only 500 cycles. Additionally, the incorporation of a two-dimensional molecular sieve enhances the mechanical properties of the PP separator, thereby bolstering battery safety. This study proposes a novel concept for the design of lithium-ion battery separator materials, offering a fresh perspective on the development of separators with exceptional thermal stability, enhanced porosity, superior electrolyte affinity, and effective inhibition of lithium dendrite formation.

Synergistically Inducing Ultrafast Ion Diffusion and Reversible Charge Transfer in Lithium Metal Batteries Using Bimetallic Molybdenum-Titanium MXenes

Metal batteries have captured significant attention for high-energy applications, owing to their superior theoretical energy densities. However, their practical viability is impeded by severe dendrite formation and poor cycling stability. To alleviate these issues, a 3D-structured bimetallic-Mo2Ti2C3Tx based fiber electrode was fabricated in this study and analyzed experimentally and computationally. The bimetallic Mo-Ti composition of MXenes synergistically achieved low binding and formation energies with lithium. In particular, the minimal lattice mismatch between the deposited Li metal and the Mo2Ti2C3Tx MXene anode substrate led to improved Li formation energy with respect to the MXene surface. Moreover, the synergy of the bimetallic Mo-Ti composition of the Mo2Ti2C3Tx MXene fiber substrate helped to amplify ion diffusion and reversible charge transfer. Consequently, the bimetallic MXene electrode exhibited an impressive Coulombic efficiency (99.08%) even at a high current density (5 mA cm-2) and a fixed cutoff capacity of 1 mA h cm-2 with prolonged cycle life (650 cycles). This report highlights a promising advancement in addressing the critical challenges facing metal battery operation, thereby offering an approach to improving performance for high-energy applications.

A Versatile Metal-Organic-Framework Pillared Interlayer Design for High-Capacity and Long-Life Lithium-Sulfur Batteries

Developing high-performance lithium-sulfur batteries is a promising way to attain higher energy density at a lower cost beyond the state-of-the-art lithium-ion battery technology. However, the major issues impeding their practical applications are the sluggish kinetics and the parasitic shuttling reactions of sulfur and polysulfides. Here, pillaring the multilayer graphene membrane with a metal-organic framework (MOF) demonstrates the substantial impact of a versatile interlayer design in tackling these issues. Unlike regular composite separators reported so far, the participation of tri-metallic Ni-Co-Mn MOF as pillars supports the construction of an ion-channel interconnected interlayer structure, unexpectedly balancing the interfacial concentration polarization, spatially confining the soluble polysulfides, and vastly affording the lithiophilic sites for highly efficient polysulfide sieving/conversion. As a demonstration, we show that the MOF-pillared interlayer structure enables outstanding capacity (1634 mAh g-1 at 0.1 C) and longevity (average capacity decay of 0.034 % per cycle in 2000 cycles) for lithium-sulfur batteries. Besides, the multilayer separator can be readily integrated into the high-nickel cathode (LiNi0.91Mn0.03Co0.06O2)-based lithium-ion batteries, which efficiently suppresses the undesired phase evolution upon cycling. These findings suggest the potential of "gap-filling" materials in fabricating multi-functional separators, bringing forward the pillared interlayer structure for energy-storage applications.

Accelerated Ion-Electron Transport in Bi-Heterostructures Constructed Based on Ohmic Contacts for Efficient Bi-Directional Catalysis of Lithium-Sulfur Batteries

Although lithium-sulfur batteries have satisfactory theoretical specific capacity and energy density, they are difficult to further commercialize due to the shuttle effect of soluble polysulfides and slow sulfur oxidation kinetics. Based on this, in this work, the catalyst MXene-VS4-SnS2 (MVS), a dual heterostructured catalyst with ohmic contacts, is prepared by a one-step hydrothermal method and electrostatic self-adsorption for lithium-sulfur battery cathode materials. Experimental and theoretical results show that the ohmic contact induces spontaneous charge rearrangement, resulting in the formation of a fast charge transfer pathway at the MVS heterojunction interface, which helps to reduce the energy barrier for polysulfide reduction and Li2S oxidation during the discharge/charge process. In addition, the inherent sulfophilicity of VS4 and SnS2 promotes the conversion of S species, while the pleated MXene nanosheets not only provide a highly conductive network for the active sulfur but also retain a rich internal space to maintain the integrity of the cathode structure during the continuous cycling process. As a result, the MVS cathode exhibits excellent electrochemical performance even under high sulfur loading. The integration of excellent performance with a facile synthesis process provides a promising approach for designing highly efficient electrocatalysts suitable for the energy field.

Heterostructuring Uniform 2D CdS on Ru/Ti3C2-TiO2 via In situ Oxidized Ru-Loaded MXene for Boosting Photocatalytic H2 Production

Building heterojunctions and exposing more catalytic active sites are effective strategies to enhance the photocatalytic hydrogen evolution activity. Herein, TiO2 nanosheets are oxidized in situ on Ru-loaded MXene as carriers and subsequently loaded with uniform 2D CdS via hydrothermal method to obtain 2D Ru/Ti3C2-TiO2/CdS composite photocatalysts that integrate heterojunctions and cocatalysts. The formation of heterojunction between CdS and TiO2 is conducive to promoting the separation and transfer of photogenerated charges, simultaneously, Ru/Ti3C2 with the fully exposed Ru and Ti3C2 can act as effective active sites of photocatalytic hydrogen production reaction. The composite photocatalyst exhibits an improved hydrogen production rate with 5479 µmol g-1 h-1, which is 5, 3, and four times more than that of pristine CdS, CdS loaded Ti3C2-TiO2 and CdS loaded Ru-TiO2 respectively. The results reveal that the notable enhancement in performance can primarily be ascribed to the introduction of the TiO2/CdS heterojunction and the efficient cocatalysts of Ru/Ti3C2. Moreover, the 2D Ti3C2 with high conductivity as carriers can increase charge transfer, and its 2D structure can serve as a template for growing 2D photocatalysts with higher activity. The interface engineering with multiple interfaces can offer novel insights for the advancement of efficient hydrogen evolution reaction catalysts.

Multifunctional Ultrathin Ti3C2Tx MXene@CuCo2O4 /PE Separator for Ultra-High-Energy-Density and Large-Capacity Lithium-Sulfur Pouch Cells

The shuttling of lithium polysulfides (LiPSs), sluggish reaction kinetics, and uncontrolled lithium deposition/stripping remain the main challenges in lithium-sulfur batteries (LSBs), which are aggravated under practical working conditions, i.e., high sulfur loading and lean electrolyte in large-capacity pouch cells. This study introduces a Ti3C2Tx MXene@CuCo2O4 (MCC) composite on a polyethylene (PE) separator to construct an ultrathin MXene@CuCo2O4/PE (MCCP) film. The MCCP functional separator can deliver superior LiPSs adsorption/catalysis capabilities via the MCC composite and regulate the Li+ deposition through a conductive Ti3C2Tx MXene framework, enhancing redox kinetics and cycling lifetime. When paired with sulfur/carbon (S/C) cathode and lithium metal anode, the resultant 10 Ah-level pouch cell with the ultrathin MCCP separator achieves an energy density of 417 Wh kg-1 based on the whole cell and a stable running of 100 cycles under practical operation conditions (cathode loading = 10.0 mg cm-2, negative/positive areal capacity ratio (N/P ratio) = 2, and electrolyte/sulfur weight ratio (E/S ratio) = 2.6 µL mg-1). Furthermore, through a systematic evaluation of the as-prepared Li-S pouch cell, the study unveils the operational and failure mechanisms of LSBs under practical conditions. The achievement of ultrahigh energy density in such a large-capacity lithium-sulfur pouch cell will accelerate the commercialization of LSBs.

Zinc Tellurium with Anionic Vacancies Anchored on Ordered Macroporous Carbon Skeleton Enabling Accelerated Polysulfide Conversion for Lithium-Sulfur Batteries

Lithium-sulfur batteries (LSBs) showcase great promise for large-scale energy storage systems, however, their practical commercialization is seriously hindered by the sluggish redox reaction kinetics and detrimental shuttle effect of soluble polysulfides. Herein, small ZnTe1- x nanoparticles with anionic vacancies firmly anchored on 3D ordered macroporous N-doped carbon skeleton (3DOM-ZnTe1- x@NC) are elaborately constructed as a high-efficiency electrocatalyst for LSBs. The ordered macroporous carbon skeleton not only greatly increases the external surface area to expose sufficient active sites but also facilitates the electrolyte penetration. Additionally, the experimental studies combined with theoretical calculations confirm the presence of Te vacancies optimizes the electronic structure to enhance the intrinsic catalytic activity and chemical absorption. Consequently, LSBs assembled with the 3DOM-ZnTe1- x@NC modified separators exhibit high specific discharge capacity, as well as superior rate performance and good long-term cycling stability. Even under a high sulfur loading of 6.5 mg cm-2 and lean electrolyte, an impressive areal capacity of 5.28 mAh cm-2 is achieved at 0.1 C after 100 cycles. More significantly, the 3DOM-ZnTe1- x@NC based pouch cells are also fabricated to demonstrate its potential for practical applications. This work highlights that the rational combination of 3DOM architecture and vacancy engineering is important for designing advanced Li-S electrocatalysts.

Balanced d-Band Model: A Framework for Balancing Redox Reactions in Lithium-Sulfur Batteries

Managing the redox reactions of polysulfides is crucial for improving the performance of lithium-sulfur batteries (LSBs). Herein, we introduce a progressive theoretical framework: the balanced d-band model, which is based on classical d-band center theory. Specifically, by optimizing the position of the d-band center in the middle between the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of each sulfur species, balanced and fast oxidation and reduction reactions of the sulfur species can be achieved simultaneously. To validate this theory, we synthesized a catalyst featuring an in situ phosphorized heterostructure (NOP) based on nickel oxide (NiO), which effectively optimizes the d-band center at the middle between the HOMO and LUMO of each sulfur species. Aided by the balanced oxidation and reduction kinetics of the sulfur species, the NOP-based cell achieved a high reversible capacity, superior cycling stability, and prolonged cycle life. This study extends the conventional d-band center theory and introduces an innovative theoretical model to expand our understanding of the internal reaction mechanisms in LSBs.

In Situ Built ZnS/MXene Heterostructure by a Mild Method for Inhibiting Polysulfide Shuttle in Li-S Batteries

With high specific surface area, excellent polysulfide conversion activity, and fast electron/ion transfer at the interface, MXene-derived heterostructures can be employed as catalysts for lithium-sulfur (Li-S) batteries to accelerate sulfur redox kinetics and suppress shuttle effect. However, the preparation of MXene-derived heterostructures often requires high-temperature reactions, which can easily lead to the oxidation of MXene and sacrifice the electrical conductivity. Herein, a catalytic two-dimensional heterostructure (ZnS/MXene) was successfully synthesized via a mild method. The MXene skeleton retains the original nanosheet structure without oxidation. The in situ-grown ZnS nanospheres prevent the restacking of MXene nanosheets, which not only increases the active sites, but also guarantees channels for the fast passage of lithium ions. The interfacial built-in electric field further promotes electron/ion migration, thereby expediting the polysulfide conversion and suppressing the shuttle effect. Consequently, the batteries using ZnS/MXene modified separators exhibit a high initial discharge capacity of 1230 mAh g-1 at 0.1 C and a low decaying rate of 0.082 % per cycle after 500 cycles at 0.5 C. This work offers a reference for the fabrication of MXene-based heterostructure in Li-S batteries.

Breaking the Passivation Effect for MnO2 Catalysts in Li-S Batteries by Anion-Cation Doping

Transition metal oxides (TMOs) are recognized as high-efficiency electrocatalyst systems for restraining the shuttle effect in lithium-sulfur (Li-S) batteries, owing to their robust adsorption capabilities for polysulfides. However, the sluggish catalytic conversion of Li2S redox and severe passivation effect of TMOs exacerbate polysulfide shuttling and reduce the cyclability of Li-S batteries, which significantly hinders the development of TMOs electrocatalysts. Here, through the anion-cation doping approach, dual incorporation of phosphorus and molybdenum into MnO2 (P,Mo-MnO2) was engineered, demonstrating effective mitigation of the passivation effect and allowing for the simultaneous immobilization of polysulfides and rapid redox kinetics of Li2S. Both experimental and theoretical investigations reveal the pivotal role of dopants in fine-tuning the d-band center and optimizing the electronic structure of MnO2. Furthermore, this well-designed configuration processes catalytic selectivity. Specifically, P-doping expedites rapid Li2S nucleation kinetics by minimizing reaction-free energy, while Mo-doping facilitates robust Li2S dissolution kinetics by mitigating decomposition barriers. This dual-doping approach equips P,Mo-MnO2 with robust bi-directional catalytic activity, effectively overcoming passivation effect and suppressing the notorious shuttle effect. Consequently, Li-S batteries incorporating P,Mo-MnO2-based separators demonstrate favorable performance than pristine TMOs. This design offers rational viewpoint for the development of catalytic materials with superior bi-directional sulfur electrocatalytic in Li-S batteries.

Versatile Separators Toward Advanced Lithium-Sulfur Batteries: Status, Recent Progress, Challenges and Perspective

Lithium-sulfur batteries (LSBs) have recently gained extensive attention due to their high energy density, low cost, and environmental friendliness. However, serious shuttle effect and uncontrolled growth of lithium dendrites restrict them from further commercial applications. As "the third electrode", functional separators are of equal significance as both anodes and cathodes in LSBs. The challenges mentioned above are effectively addressed with rational design and optimization in separators, thereby enhancing their reversible capacities and cycle stability. The review discusses the status/operation mechanism of functional separators, then primarily focuses on recent research progress in versatile separators with purposeful modifications for LSBs, and summarizes the methods and characteristics of separator modification, including heterojunction engineering, single atoms, quantum dots, and defect engineering. From the perspective of the anodes, distinct methods to inhibit the growth of lithium dendrites by modifying the separator are discussed. Modifying the separators with flame retardant materials or choosing a solid electrolyte is expected to improve the safety of LSBs. Besides, in-situ techniques and theoretical simulation calculations are proposed to advance LSBs. Finally, future challenges and prospects of separator modifications for next-generation LSBs are highlighted. We believe that the review will be enormously essential to the practical development of advanced LSBs.

Construction of Ordered and Fast Lithium Ion Channels in Gel Electrolytes for Li-SPAN Batteries

As one of the most promising battery systems, the lithium sulfur battery is expected to be widely used in fields of high energy density demands. Owing to the unique solid-solid conversion mechanism, there is no shuttle effect for the Li-SPAN (sulfurized polyacrylonitrile) battery. However, the compatibility between Li anode and carbonate electrolyte has not been resolved, which prevents the SPAN from practical applications. Herein, an organic-inorganic gel carbonate electrolyte is proposed to stabilize interphases and structures of both the anode and cathode, where polyimide (PI) is used for electrolyte gelation, which can assist in the uniform distribution of inorganic components at the electrolyte interface. Furthermore, ZnS nanodots loaded on two-dimensional MoS2 flakes provide abundant Li-ion diffusion paths, improve the transfer kinetic of Li ions, and induce uniform nucleation and deposition of Li. This gel electrolyte ensures Li symmetric cells a long-term cycle life of more than 900 h under the condition of deep lithium plating/stripping at 5 mAh cm-1. Li∥Cu cells exhibit a prolonged lifespan of 800 h with a CE of 98.3%. Furthermore, the Li-SPAN battery shows stability of more than 850 cycles, with the capacity retention of 85.1%. This work provides an approach for high-energy Li-SPAN batteries with carbonate-based electrolytes.

Pushing Theoretical Potassium Storage Limits of MXenes through Introducing New Carbon Active Sites

Surface-driven capacitive storage enhances rate performance and cyclability, thereby improving the efficacy of high-power electrode materials and fast-charging batteries. Conventional defect engineering, widely-employed capacitive storage optimization strategy, primarily focuses on the influence of defects themselves on capacitive behaviors. However, the role of local environment surrounding defects, which significantly affects surface properties, remains largely unexplored for lack of suitable material platform and has long been neglected. As proof-of-concept, typical Ti3C2Tx MXenes are chosen as model materials owing to metallic conductivity and tunable surface properties, satisfying the requirements for capacitive-type electrodes. Using density functional theory (DFT) calculations, the potential of MXenes with modulated local atomic environment is anticipated and introducing new carbon sites found near pores can activate electrochemically inert surface, attaining record theoretical potassium storage capacities of MXenes (291 mAh g-1). This supposition is realized through atomic tailoring via chemical scissor within sublayers, exposing new sp3-hybridized carbon active sites. The resulting MXenes demonstrate unprecedented rate performance and cycling stability. Notably, MXenes with higher carbon exposure exhibit a record-breaking capacity over 200 mAh g-1 and sustain a capacity retention higher than 80% after 20 months. These findings underscore the effectiveness of regulating defects' neighboring environment and illuminate future high-performance electrode design.

Construction of an Ohmic Contact Cathode by Two Metal Sulfides for efficient Capture and Catalysis of Polysulfide

The slow reaction kinetics and severe shuttle effect of lithium polysulfide make Li-S battery electrochemical performance difficult to meet the demands of large electronic devices such as electric vehicles. Based on this, an electrocatalyst constructed by metal phase material (MoS2) and semiconductor phase material (SnS2) with ohmic contact is designed for inhibiting the dissolution of lithium polysulfide with improving the reaction kinetics. According to the density-functional theory calculations, it is found that the heterostructured samples with ohmic contacts can effectively reduce the reaction-free energy of lithium polysulfide to accelerate the sulfur redox reaction, in addition to the excellent electron conduction to reduce the overall activation energy. The metallic sulfide can add more sulfophilic sites to promote the capture of polysulfide. Thanks to the ohmic contact design, the carbon nanotube-MoS2-SnS2 achieved a specific capacity of 1437.2 mAh g-1 at 0.1 C current density and 805.5 mAh g-1 after 500 cycles at 1 C current density and is also tested as a pouch cell, which proves to be valuable for practical applications. This work provides a new idea for designing an advanced and efficient polysulfide catalyst based on ohmic contact.

Revisiting porous foam Cu host based Li metal anode: The roles of lithiophilicity and hierarchical structure of three-dimensional framework

Lithium (Li) metal anode (LMA) is one of the most promising anodes for high energy density batteries. However, its practical application is impeded by notorious dendrite growth and huge volume expansion. Although the three-dimensional (3D) host can enhance the cycling stability of LMA, further improvements are still necessary to address the key factors limiting Li plating/stripping behavior. Herein, porous copper (Cu) foam (CF) is thermally infiltrated with molten Li-rich Li-zinc (Li-Zn) binary alloy (CFLZ) with variable Li/Zn atomic ratio. In this process, the LiZn intermetallic compound phase self-assembles into a network of mixed electron/ion conductors that are distributed within the metallic Li phase matrix and this network acts as a sublevel skeleton architecture in the pores of CF, providing a more efficient and structured framework for the material. The as-prepared CFLZ composite anodes are systematically investigated to emphasize the roles of the tunable lithiophilicity and hierarchical structure of the frameworks. Meanwhile, a thin layer of Cu-Zn alloy with strong lithiophilicity covers the CF scaffold itself. The CFLZ with high Zn content facilitates uniform Li nucleation and deposition, thereby effectively suppressing Li dendrite growth and volume fluctuation. Consequently, the hierarchical and lithiophilic framework shows low Li nucleation overpotential and highly stable Coulombic efficiency (CE) for 200 cycles in conventional carbonate based electrolyte. The full cell coupled with LiFePO4 (LFP) cathode demonstrates high cycle stability and rate performance. This work provides valuable insights into the design of advanced dendrite-free 3D LMA toward practical application.

Porous Organic Framework Materials (MOF, COF, and HOF) as the Multifunctional Separator for Rechargeable Lithium Metal Batteries

The separator is an important component in batteries, with the primary function of separating the positive and negative electrodes and allowing the free passage of ions. Porous organic framework materials have a stable connection structure, large specific surface area, and ordered pores, which are natural places to store electrolytes. And these materials with specific functions can be designed according to the needs of researchers. The performance of porous organic framework-based separators used in rechargeable lithium metal batteries is much better than that of polyethylene/propylene separators. In this paper, the three most classic organic framework materials (MOF, COF, and HOF) are analyzed and summarized. The applications of MOF, COF, and HOF separators in lithium-sulfur batteries, lithium metal anode, and solid electrolytes are reviewed. Meanwhile, the research progress of these three materials in different fields is discussed based on time. Finally, in the conclusion, the problems encountered by MOF, COF, and HOF in different fields as well as their future research priorities are presented. This review will provide theoretical guidance for the design of porous framework materials with specific functions and further stimulate researchers to conduct research on porous framework materials.

Enhancing Lithium-Sulfur Battery Performance with MXene: Specialized Structures and Innovative Designs

Established in 1962, lithium-sulfur (Li-S) batteries boast a longer history than commonly utilized lithium-ion batteries counterparts such as LiCoO2 (LCO) and LiFePO4 (LFP) series, yet they have been slow to achieve commercialization. This delay, significantly impacting loading capacity and cycle life, stems from the long-criticized low conductivity of the cathode and its byproducts, alongside challenges related to the shuttle effect, and volume expansion. Strategies to improve the electrochemical performance of Li-S batteries involve improving the conductivity of the sulfur cathode, employing an adamantane framework as the sulfur host, and incorporating catalysts to promote the transformation of lithium polysulfides (LiPSs). 2D MXene and its derived materials can achieve almost all of the above functions due to their numerous active sites, external groups, and ease of synthesis and modification. This review comprehensively summarizes the functionalization advantages of MXene-based materials in Li-S batteries, including high-speed ionic conduction, structural diversity, shuttle effect inhibition, dendrite suppression, and catalytic activity from fundamental principles to practical applications. The classification of usage methods is also discussed. Finally, leveraging the research progress of MXene, the potential and prospects for its novel application in the Li-S field are proposed.

Insights into the Optimization of Catalytic Active Sites in Lithium-Sulfur Batteries

ConspectusLithium-sulfur batteries (LSBs), recognized for their high energy density and cost-effectiveness, offer significant potential for advancement in energy storage. However, their widespread deployment remains hindered by challenges such as sluggish reaction kinetics and the shuttle effect of lithium polysulfides (LiPSs). By the introduction of catalytic materials, the effective adsorption of LiPSs, smooth surface migration behavior, and significantly reduced conversion energy barriers are expected to be achieved, thereby sharpening electrochemical reaction kinetics and fundamentally addressing the aforementioned challenges. However, driven by practical application targets, the demand for higher loadings and reduced electrolyte parameters inevitably exacerbates the burden on catalytic materials during their service. Additionally, given that catalytic materials contribute negligible electrochemical capacity, their incorporation inevitably increases the mass of nonactive components for reducing the energy density of LSBs. A meticulous insight into the lithium-sulfur catalytic reaction reveals that the conversion of LiPSs is dominated by active sites on the surfaces of catalytic materials. These microregions provide the necessary electron and ion transport for the conversion reaction of LiPSs, with their efficacy and quantity directly impacting the conversion efficiency. In light of these considerations, the strategic optimization of active sites emerges as a paramount pathway toward promoting the performance of LSBs while concurrently mitigating unnecessary mass. Here, we outline three strategies developed by our group to optimize active sites of catalytic materials: (1) Augmenting active sites by customizing structural modulation and precise dimensional control to maximize exposure. Emphasis has been placed on the approaches for material synthesis and the essence of reactions for achieving this strategy. (2) Regulating the microenvironment of active sites by integrating the coordination refinement, long-range atomic interactions, metal-support interactions, and other electronic regulation strategies, thereby providing an elevation in the intrinsic catalytic performance. (3) Implementing a self-cleaning mechanism for active sites to counteract deactivation by designing a tandem adsorption-migration-transformation pathway of sulfur contained within the molecular domain. Throughout this process, the intrinsic mechanisms driving performance enhancement through active site optimization strategies have been prominently emphasized, which encompass aspects such as electronic structure, atomic composition, and molecular configuration and significantly expand the comprehension of Li-S catalytic chemistry. Subsequently, considerations demanding heightened attention in future processes of active site optimization for catalytic materials have been delineated, including the in situ evolution patterns and resistance to the poisoning of active sites. It is noteworthy that given the similarity between Li-S catalysis chemistry and traditional electrocatalytic processes, this Account elucidates the concept of active site optimization by drawing insights from representative works and our own works in the field of electrocatalysis, which is relatively rare in previous reviews of LSBs. The proposed insights contribute to uncovering the intrinsic mechanisms of Li-S catalysis chemistry and introducing innovative ideas into active site optimization, ultimately advancing energy density and stability in LSBs.

Construction of High-Performance Anode of Potassium-Ion Batteries by Stripping Covalent Triazine Frameworks with Molten Salt

Covalent triazine frameworks (CTFs) are promising battery electrodes owing to their designable functional groups, tunable pore sizes, and exceptional stability. However, their practical use is limited because of the difficulty in establishing stable ion adsorption/desorption sites. In this study, a melt-salt-stripping process utilizing molten trichloro iron (FeCl3) is used to delaminate the layer-stacked structure of fluorinated covalent triazine framework (FCTF) and generate iron-based ion storage active sites. This process increases the interlayer spacing and uniformly deposits iron-containing materials, enhancing electron and ion transport. The resultant melt-FeCl3-stripped FCTF (Fe@FCTF) shows excellent performance as a potassium ion battery with a high capacity of 447 mAh g-1 at 0.1 A g-1 and 257 mAh g-1 at 1.6 A g-1 and good cycling stability. Notably, molten-salt stripping is also effective in improving the CTF's Na+ and Li+ storage properties. A stepwise reaction mechanism of K/Na/Li chelation with C═N functional groups is proposed and verified by in situ X-ray diffraction testing (XRD), ex-situ X-ray photoelectron spectroscopy (XPS), and theoretical calculations, illustrating that pyrazines and iron coordination groups play the main roles in reacting with K+/Na+/Li+ cations. These results conclude that the Fe@FCTF is a suitable anode material for potassium-ion batteries (PIBs), sodium-ion batteries (SIBs), and lithium-ion batteries (LIBs).

Achieving a smooth "adsorption-diffusion-conversion" of polysulfides enabled by MnO2-ZnS p-n heterojunction for Li-S battery

The commercial application of lithium-sulfur batteries is primarily impeded by the constant shuttling of soluble polysulfides and sluggish redox kinetics. Nowadays, the discovery of the heterojunction, which combines materials with diverse properties, offers a new perspective for overcoming these obstacles. Herein, a functional coating separator for the lithium-sulfur battery is designed using a MnO2-ZnS p-n heterojunction with a spontaneous built-in electric field (BIEF). The MnO2 nanowire provides suitable adsorption capacity for polysulfides, while the abundant reactive sites brought by ZnS ensure efficient conversion. Moreover, the BIEF significantly facilitates the migration of electrons and polysulfides at the MnO2-ZnS interface, enabling a smooth "adsorption-diffusion-conversion" reaction mechanism. By serving as both the adsorption module and catalytic sites, this BIEF allows batteries utilizing separators modified with MnO2-ZnS heterojunction to achieve an impressive initial capacity of 1511.1 mAh g-1 at 0.1C and maintain a capacity decay rate of merely 0.048% per cycle at 2.0C after 1000 cycles. Even when increasing sulfur loading to 9.4 mg cm-2 in lean electrolyte (5.4 μL mg-1), the battery still exhibits an ultrahigh areal capacity of 6.0 mAh cm-2 after 100 cycles.

One-step growth of ultrathin CoSe2 nanobelts on N-doped MXene nanosheets for dendrite-inhibited and kinetic-accelerated lithium-sulfur chemistry

The practical application of lithium-sulfur (Li-S) batteries is inhibited by the shuttle effect of lithium polysulfides (LiPSs) and slow polysulfide redox kinetics on the S cathode as well as the uncontrollable growth of dendrites on the Li metal anode. Therefore, both cathode and anode sides must be considered when modifying Li-S batteries. Herein, two-dimensional (2D) ultrathin CoSe2 nanobelts are in situ grown on 2D N-doped MXene nanosheets (CoSe2@N-MXene) via one-step solvothermal process for the first time. Owing to its unique 2D/2D structure, CoSe2@N-MXene can be processed to crumpled nanosheets by freeze-drying and flexible and freestanding films by vacuum filtration. These crumpled CoSe2@N-MXene nanosheets with abundant active sites and inner spaces can act as S hosts to accelerate polysulfide redox kinetics and suppress the shuttle effect of LiPSs owing to their strong adsorption ability and catalytic conversion effect with LiPSs. Meanwhile, the CoSe2@N-MXene film (CoSe2@NMF) can act as a current collector to promote uniform Li deposition because it contains lithiophilic CoSe2 and N sites. Under the systematic effect of CoSe2@N-MXene on S cathode and Li metal anode, the electrochemical and safety performance of Li-S batteries are improved. CoSe2@NMF also shows excellent storage performances in flexible energy storage devices.

Two-Dimensional Transition Metal Phosphides As Cathode Additive in Robust Lithium-Sulfur Batteries

The development of advanced cathode materials able to promote the sluggish redox kinetics of polysulfides is crucial to bringing lithium-sulfur batteries to the market. Herein, two electrode materials: namely, Zr2PS2 and Zr2PTe2, are identified through screening several hundred thousand compositions in the Inorganic Crystal Structure Database. First-principles calculations are performed on these two materials. These structures are similar to that of the classical MXenes. Concurrently, calculations show that Zr2PS2 and Zr2PTe2 possess high electrical conductivity, promote Li ion diffusion, and have excellent electrocatalytic activity for the Li-S reaction and particularly for the Li2S decomposition. Besides, the mechanisms behind the excellent predicted performance of Zr2PS2 and Zr2PTe2 are elucidated through electron localization function, charge density difference, and localized orbital locator. This work not only identifies two candidate sulfur cathode additives but may also serve as a reference for the identification of additional electrode materials in new generations of batteries, particularly in sulfur cathodes.

Anchoring Carbon Spheres on Titanium Dioxide Modified Commercial Polyethylene (PE) Separator to Suppress Lithium Dendrites for Lithium Metal Batteries

Lithium dendrites are easily generated for excessively-solved lithium ions (Li+) inside the lithium metal batteries, which will lead serious safety issues. In this experiment, carbon spheres (CS) are successfully anchored on TiO2 (CS@TiO2) in the hydrothermal polymerization, which is filtrated on the commercial PE separator (CS@TiO2@PE). The negative charge in CS can suppress random diffusion of anions through electrostatic interactions. Density functional theory (DFT) calculations show that CS contributes to the desolvation of Li+, thereby increasing the migration rate of Li+. Furthermore, TiO2 exhibits high affinity to liquid electrolytes and acts as a physical barrier to lithium dendrite formation. CS@TiO2 is a combination of the advantages of CS and TiO2. As results, the Li+ transference number of the CS@TiO2@PE separator can be promoted to 0.63. The Li||Li cell with the CS@TiO2@PE separator exhibits a stable cycle performance for more than 600 h and lower polarization voltage (17 mV) at 1 mA cm-2. The coulombic efficiency (CE) of the Li||Cu cells employe the CS@TiO2@PE separator is 81.63% over 130 cycles. The discharge capacity of LiFePO4||Li cells based on the CS@TiO2@PE separator is 1.73 mAh (capacity retention = 91.53% after 260 cycles). Thus, the CS@TiO2 layer inhibits lithium dendrite formation.

M4X3 MXenes: Application in Energy Storage Devices

MXene has garnered widespread recognition in the scientific community due to its remarkable properties, including excellent thermal stability, high conductivity, good hydrophilicity and dispersibility, easy processability, tunable surface properties, and admirable flexibility. MXenes have been categorized into different families based on the number of M and X layers in Mn+1Xn, such as M2X, M3X2, M4X3, and, recently, M5X4. Among these families, M2X and M3X2, particularly Ti3C2, have been greatly explored while limited studies have been given to M5X4 MXene synthesis. Meanwhile, studies on the M4X3 MXene family have developed recently, hence, demanding a compilation of evaluated studies. Herein, this review provides a systematic overview of the latest advancements in M4X3 MXenes, focusing on their properties and applications in energy storage devices. The objective of this review is to provide guidance to researchers on fostering M4X3 MXene-based nanomaterials, not only for energy storage devices but also for broader applications.

Ordered Vacancies as Sodium Ion Micropumps in Cu-Deficient Copper Indium Diselenide to Enhance Sodium Storage

Unordered vacancies engineered in host anode materials cannot well maintain the uniform Na+ adsorbed and possibly render the local structural stress intense, resulting in electrode peeling and battery failure. Here, the indium is first introduced into Cu2Se to achieve the formation of CuInSe2. Next, an ion extraction strategy is employed to fabricate Cu0.54In1.15Se2 enriched with ordered vacancies by spontaneous formation of defect pairs. Such ordered defects, compared with unordered ones, can serve as myriad sodium ion micropumps evenly distributing in crystalline host to homogenize the adsorbed Na+ and the generated volumetric stress during the electrochemistry. Furthermore, Cu0.54In1.15Se2 is indeed proved by the calculations to exhibit smaller volumetric variation than the counterpart with unordered vacancies. Thanks to the distinct ordered vacancy structure, the material exhibits a highly reversible capacity of 428 mAh g-1 at 1 C and a high-rate stability of 311.7 mAh g-1 at 10 C after 5000 cycles when employed as an anode material for Sodium-ion batteries (SIBs). This work presents the promotive effect of ordered vacancies on the electrochemistry of SIBs and demonstrates the superiority to unordered vacancies, which is expected to extend it to other metal-ion batteries, not limited to SIBs to achieve high capacity and cycling stability.

Complementary Weaknesses: A Win-Win Approach for rGO/CdS to Improve the Energy Conversion Performance of Integrated Photorechargeable Li-S Batteries

Integrating solar energy into rechargeable battery systems represents a significant advancement towards sustainable energy storage solutions. Herein, we propose a win-win solution to reduce the shuttle effect of polysulfide and improve the photocorrosion stability of CdS, thereby enhancing the energy conversion efficiency of rGO/CdS-based photorechargeable integrated lithium-sulfur batteries (PRLSBs). Experimental results show that CdS can effectively anchor polysulfide under sunlight irradiation for 20 minutes. Under a high current density (1 C), the discharge-specific capacity of the PRLSBs increased to 971.30 mAh g-1, which is 113.3 % enhancement compared to that of under dark condition (857.49 mAh g-1). Remarkably, without an electrical power supply, the PRLSBs can maintain a 21 hours discharge process following merely 1.5 hours of light irradiation, achieving a breakthrough solar-to-electrical energy conversion efficiency of up to 5.04 %. Ex situ X-ray photoelectron spectroscopy (XPS) and in situ Raman analysis corroborate the effectiveness of this complementary weakness approach in bolstering redox kinetics and curtailing polysulfide dissolution in PRLSBs. This work showcases a feasible strategy to develop PRLSBs with potential dual-functional metal sulfide photoelectrodes, which will be of great interest in future-oriented off-grid photocell systems.

Rapid Growth of Bi2Se3 Nanodots on MXene Nanosheets at Room Temperature for Promoting Sulfur Redox Kinetics

Li-S batteries are hampered by problems with their cathodes and anodes simultaneously. The improvement of Li-S batteries needs to consider both the anode and cathode. Herein, a Bi2Se3@MXene composite is prepared for the first time by rapidly growing Bi2Se3 nanodots on two-dimensional (2D) MXene nanosheets at room temperature through simply adding high-reactive hydroxyethylthioselenide in Bi3+/MXene aqueous solution. Bi2Se3@MXene exhibits a 2D structure due to the template effect of 2D MXene. Bi2Se3@MXene can not only facilitate the conversion of lithium polysulfides (LiPSs) but also inhibit their shuttling in the S cathode due to its catalytic effect and adsorption force with LiPSs. Bi2Se3@MXene can also be used as an interfacial lithiophilic layer to inhibit Li dendrite growth in the Li metal anode. Theoretical calculations reveal that Bi2Se3 nanodots in Bi2Se3@MXene can effectively boost the adsorption ability with LiPSs, and the MXene in Bi2Se3@MXene can accelerate the electron transport. Under the bidirectional regulation of Bi2Se3@MXene in the Li metal anode and S cathode, the Li-S battery shows an enhanced electrochemical performance.

Multi-heterostructured MXene/NiS2/Co3S4 with S-Vacancies to Promote Polysulfide Conversion in Lithium-Sulfur Batteries

The severe shuttle effect of polysulfides (LiPSs) and the slow liquid-solid phase conversion are the main obstacles hindering the practical application of lithium-sulfur (Li-S) batteries. Separator modification with a high-activity catalyst can boost LiPSs conversion and suppress their shuttle effect. In this work, multi-heterostructured MXene/NiS2/Co3S4 with rich S-vacancies was constructed facilely with a hydrothermal and high-temperature annealing strategy for separator modification. The MXene sheet not only provides a physical barrier but also ensures a high conductivity and adsorption capacity of the catalyst; the dual active centers of NiS2 and Co3S4 catalyze LiPSs conversion. In addition, the vacancies and heterostructures can modulate the electronic structure of the catalyst, improve its intrinsic activity, and reduce the polysulfides reaction barrier, thus facilitating ion/electron transport and inhibiting the shuttle effect. Benefiting from these advantages, the Li-S battery with MXene/NiS2/Co3S4 modified separator exhibits exciting discharge capacities (1495.4 mAh g-1 at 0.1C and 549.0 mAh g-1 at 6C) and an excellent ultra-long cycle life (average capacity decay rate of 0.026% for 2000 cycles at 2C); at a high sulfur loading of 10.0 mg cm-2, the battery operates for nearly 80 cycles at 0.2C, giving a capacity retention rate of 75.76%. This work provides a high-activity catalyst for Li-S batteries.

Fundamentally Manipulating the Electronic Structure of Polar Bifunctional Catalysts for Lithium-Sulfur Batteries: Heterojunction Design versus Doping Engineering

Heterogeneous structures and doping strategies have been intensively used to manipulate the catalytic conversion of polysulfides to enhance reaction kinetics and suppress the shuttle effect in lithium-sulfur (Li-S) batteries. However, understanding how to select suitable strategies for engineering the electronic structure of polar catalysts is lacking. Here, a comparative investigation between heterogeneous structures and doping strategies is conducted to assess their impact on the modulation of the electronic structures and their effectiveness in catalyzing the conversion of polysulfides. These findings reveal that Co0.125Zn0.875Se, with metal-cation dopants, exhibits superior performance compared to CoSe2/ZnSe heterogeneous structures. The incorporation of low Co2+ dopants induces the subtle lattice strain in Co0.125Zn0.875Se, resulting in the increased exposure of active sites. As a result, Co0.125Zn0.875Se demonstrates enhanced electron accumulation on surface Se sites, improved charge carrier mobility, and optimized both p-band and d-band centers. The Li-S cells employing Co0.125Zn0.875Se catalyst demonstrate significantly improved capacity (1261.3 mAh g-1 at 0.5 C) and cycle stability (0.048% capacity delay rate within 1000 cycles at 2 C). This study provides valuable guidance for the modulation of the electronic structure of typical polar catalysts, serving as a design directive to tailor the catalytic activity of advanced Li-S catalysts.

In situ construction of robust artificial solid-electrolyte interphase layer on lithium-metal anode by a facile one-step solution route

Development of high energy density lithium-metal batteries (LMBs) is markedly hindered by the interfacial instability on lithium-metal anode side. Solid-electrolyte interphase (SEI) is a fundamental factor to regulate dendrite growth and enhance the stability of lithium-metal anodes. Here, trithiocyanuric acid, a triazine derivative with sulfhydryl groups, is used as an efficient promoter to favor the construction of a robust artificial SEI layer on the lithium metal surface, which greatly benefits the stability and efficiency of LMBs. With the assistance of trithiocyanuric acid facilely introduced on the Li surface via a one-step solution route, a highly uniform artificial SEI layer rich in Li2S and Li3N is formed, which efficiently facilitates uniform lithium deposition and suppresses lithium dendrite growth. Remarkably, the Li|Li cell displays stable lithium plating/stripping cycling over 800 h at 0.5 mA cm-2, 1 mAh cm-2, and the Li|LFP cells exhibit prolonged lifespan over 700 cycles at 3 C and superior rate performance from 2 to 20 C. This work provides a facile design strategy for constructing a superb artificial SEI layer for high-performance LMBs.

Difunctional Ag nanoparticles with high lithiophilic and conductive decorate on core-shell SiO2 nanospheres for dendrite-free lithium metal anodes

Lithium metal is an attractive and promising anode material due to its high energy density and low working potential. However, the uncontrolled growth of lithium dendrites during repeated plating and stripping processes hinders the practical application of lithium metal batteries, leading to low Coulombic efficiency, poor lifespan, and safety concerns. In this study, we synthesized highly lithiophilic and conductive Ag nanoparticles decorated on SiO2 nanospheres to construct an optimized lithium host for promoting uniform Li deposition. The Ag nanoparticles not only act as lithiophilic sites but also provide high electrical conductivity to the Ag@SiO2@Ag anode. Additionally, the SiO2 layer serves as a lithiophilic nucleation agent, ensuring homogeneous lithium deposition and suppressing the growth of lithium dendrites. Theoretical calculations further confirm that the combination of Ag nanoparticles and SiO2 effectively enhances the adsorption ability of Ag@SiO2@Ag with Li+ ions compared to pure Ag and SiO2 materials. As a result, the Ag@SiO2@Ag coating, with its balanced lithiophilicity and conductivity, demonstrates excellent electrochemical performance, including high Coulombic efficiency, low polarization voltage, and long cycle life. In a full lithium metal cell with LiFePO4 cathode, the Ag@SiO2@Ag anode exhibits a high capacity of 133.1 and 121.4 mAh/g after 200 cycles at rates of 0.5 and 1C, respectively. These results highlight the synergistic coupling of lithiophilicity and conductivity in the Ag@SiO2@Ag coating, providing valuable insights into the field of lithiophilic chemistry and its potential for achieving high-performance batteries in the next generation.

Hyphae Carbon Coupled with Gel Composite Assembly for Construction of Advanced Carbon/Sulfur Cathodes for Lithium-Sulfur Batteries

The design and fabrication of novel carbon hosts with high conductivity, accelerated electrochemical catalytic activities, and superior physical/chemical confinement on sulfur and its reaction intermediates polysulfides are essential for the construction of high-performance C/S cathodes for lithium-sulfur batteries (LSBs). In this work, a novel biofermentation coupled gel composite assembly technology is developed to prepare cross-linked carbon composite hosts consisting of conductive Rhizopus hyphae carbon fiber (RHCF) skeleton and lamellar sodium alginate carbon (SAC) uniformly implanted with polarized nanoparticles (V2O3, Ag, Co, etc.) with diameters of several nanometers. Impressively, the RHCF/SAC/V2O3 composites exhibit enhanced physical/chemical adsorption of polysulfides due to the synergistic effect between hierarchical pore structures, heteroatoms (N, P) doping, and polar V2O3 generation. Additionally, the catalytic conversion kinetics of cathodes are effectively improved by regulating the 3D carbon structure and optimizing the V2O3 catalyst. Consequently, the LSBs assembled with RHCF/SAC/V2O3-S cathode show exceptional cycle stability (capacity retention rate of 94.0% after 200 cycles at 0.1 C) and excellent rate performance (specific capacity of 578 mA h g-1 at 5 C). This work opens a new door for the fabrication of hyphae carbon composites via fermentation for electrochemical energy storage.

Constructed MXene matrix composites as sensing material and applications thereof: A review

Most studies on MXene matrix composites for sensor development have primarily focused on synthesis and application. Nevertheless, there is currently a lack of research on how the introduction of different materials affects the sensing properties of these composites. The rapid development of MXene has raised intriguing questions about improving sensor performance by combining MXene with other materials such as polymers, metals and inorganic non-metals. This review will concentrate on the construction of MXene-based composites and explore ways to enhance their sensor applications. Specifically, this review describes why the introduction of materials to the system brings the advantage of low concentration and high sensitivity assays, as well as the MXene-based frameworks that have been recently investigated. Lastly, in order to capture the current trend of MXene-based composites in sensor applications and identify promising research directions, this review will critically evaluate the potential applications of newly developed MXene systems.

MXene-Based Current Collectors for Advanced Rechargeable Batteries

As an indispensable component of rechargeable batteries, the current collector plays a crucial role in supporting the electrode materials and collecting the accumulated electrical energy. However, some key issues, like uneven resources, high weight percentage, electrolytic corrosion, and high-voltage instability, cannot meet the growing need for rechargeable batteries. In recent years, MXene-based current collectors have achieved considerable achievements due to its unique structure, large surface area, and high conductivity. The related research has increased significantly. Nonetheless, a comprehensive review of this area is seldom. Herein the applications and progress of MXene in current collector are systematically summarized and discussed. Meanwhile, some challenges and future directions are presented.

Enhancing Lithium-Sulfur Battery Performance by MXene, Graphene, and Ionic Liquids: A DFT Investigation

The efficacy of lithium-sulfur (Li-S) batteries crucially hinges on the sulfur immobilization process, representing a pivotal avenue for bolstering their operational efficiency and durability. This dissertation primarily tackles the formidable challenge posed by the high solubility of polysulfides in electrolyte solutions. Quantum chemical computations were leveraged to scrutinize the interactions of MXene materials, graphene (Gr) oxide, and ionic liquids with polysulfides, yielding pivotal binding energy metrics. Comparative assessments were conducted with the objective of pinpointing MXene materials, with a specific focus on d-Ti3C2 materials, evincing augmented binding energies with polysulfides and ionic liquids demonstrating diminished binding energies. Moreover, a diverse array of Gr oxide materials was evaluated for their adsorption capabilities. Scrutiny of the computational outcomes unveiled an augmentation in the solubility of selectively screened d-Ti3C2 MXene and ionic liquids-vis à vis one or more of the five polysulfides. Therefore, the analysis encompasses an in-depth comparative assessment of the stability of polysulfide adsorption by d-Ti3C2 MXene materials, Gr oxide materials, and ionic liquids across diverse ranges.