A Room-Temperature Self-Healing Liquid Metal-Infilled Microcapsule Driven by Coaxial Flow Focusing for High-Performance Lithium-Ion Battery Anode

Liquid metals have attracted a lot of attention as self-healing materials in many fields. However, their applications in secondary batteries are challenged by electrode failure and side reactions due to the drastic volume changes during the "liquid-solid-liquid" transition. Herein, a simple encapsulated, mass-producible method is developed to prepare room-temperature liquid metal-infilled microcapsules (LMMs) with highly conductive carbon shells as anodes for lithium-ion batteries. Due to the reasonably designed voids in the microcapsule, the liquid metal particles (LMPs) can expand freely without damaging the electrode structure. The LMMs-based anodes exhibit superior capacity of rete-performance and ultra-long cycling stability remaining 413 mAh g-1 after 5000 cycles at 5.0 A g-1. Ex situ X-ray powder diffraction (XRD) patterns and electrochemical impedance spectroscopy (EIS) reveal that the LMMs anode displays a stable alloying/de-alloying mechanism. DFT calculations validate the electronic structure and stability of the room-temperature LMMs system. These findings will bring some new opportunities to develop high-performance battery systems.

Unique insights into the design of low-strain single-crystalline Ni-rich cathodes with superior cycling stability

Micro-sized single-crystalline Ni-rich cathodes are emerging as prominent candidates owing to their larger compact density and higher safety compared with poly-crystalline counterparts, yet the uneven stress distribution and lattice oxygen loss result in the intragranular crack generation and planar gliding. Herein, taking LiNi0.83Co0.12Mn0.05O2 as an example, an optimal particle size of 3.7 µm is predicted by simulating the stress distributions at various states of charge and their relationship with fracture free-energy, and then, the fitted curves of particle size with calcination temperature and time are further built, which guides the successful synthesis of target-sized particles (m-NCM83) with highly ordered layered structure by a unique high-temperature short-duration pulse lithiation strategy. The m-NCM83 significantly reduces strain energy, Li/O loss, and cationic mixing, thereby inhibiting crack formation, planar gliding, and surface degradation. Accordingly, the m-NCM83 exhibits superior cycling stability with highly structural integrity and dual-doped m-NCM83 further shows excellent 88.1% capacity retention.

Hierarchically Interconnected 3D Catalyst Structure of Porous Multi-Metal Oxide Nanofibers for High-Performance Li-O2 Batteries

Non-aqueous lithium-oxygen batteries (LOBs) have emerged as a promising candidate due to their high theoretical energy density and eco-friendly cathode reaction materials. However, LOBs still suffer from high overpotential and poor cycling stability resulting from difficulties in the decomposition of discharge reaction Li2 O2 products. Here, a 3D open network catalyst structure is proposed based on highly-thin and porous multi-metal oxide nanofibers (MMONFs) developed by a facile electrospinning approach coupled with a heat treatment process. The developed hierarchically interconnected 3D porous MMONFs catalyst structure with high specific surface area and porosity shows the enhanced electrochemical reaction kinetics associated with Li2 O2 formation and decomposition on the cathode surface during the charge and discharge processes. The uniquely assembled cathode materials with MMONFs exhibit excellent electrochemical performance with energy efficiency of 82% at a current density of 50 mA g-1 and a long-term cycling stability over 100 cycles at 200 mA g-1 with a cut-off capacity of 500 mAh g-1 . Moreover, the optimized cathode materials exhibit a remarkable energy density of 1013 Wh kg-1 at the 100th discharge and charge cycle, which is nearly four times higher than that of C/NMC721, which has the highest energy density among the cathode materials currently used in electric vehicles.

Rational Design of Ni-Doped V2O5@3D Ni Core/Shell Composites for High-Voltage and High-Rate Aqueous Zinc-Ion Batteries

Aqueous zinc-ion batteries (ZIBs) have significant potential for large energy storage systems because of their high energy density, cost-effectiveness and environmental friendliness. However, the limited voltage window, poor reaction kinetics and structural instability of cathode materials are current bottlenecks which contain the further development of ZIBs. In this work, we rationally design a Ni-doped V2O5@3D Ni core/shell composite on a carbon cloth electrode (Ni-V2O5@3D Ni@CC) by growing Ni-V2O5 on free-standing 3D Ni metal nanonets for high-voltage and high-capacity ZIBs. Impressively, embedded Ni doping increases the interlayer spacing of V2O5, extending the working voltage and improving the zinc-ion (Zn302+) reaction kinetics of the cathode materials; at the same time, the 3D structure, with its high specific surface area and superior electronic conductivity, aids in fast Zn302+ transport. Consequently, the as-designed Ni-V2O5@3D Ni@CC cathodes can operate within a wide voltage window from 0.3 to 1.8 V vs. Zn30/Zn302+ and deliver a high capacity of 270 mAh g-1 (~1050 mAh cm-3) at a high current density of 0.8 A g-1. In addition, reversible Zn2+ (de)incorporation reaction mechanisms in the Ni-V2O5@3D Ni@CC cathodes are investigated through multiple characterization methods (SEM, TEM, XRD, XPS, etc.). As a result, we achieved significant progress toward practical applications of ZIBs.

Recent Progress of Transition Metal Compounds as Electrocatalysts for Electrocatalytic Water Splitting

Hydrogen has enormous commercial potential as a secondary energy source because of its high calorific value, clean combustion byproducts, and multiple production methods. Electrocatalytic water splitting is a viable alternative to the conventional methane steam reforming technique, as it operates under mild conditions, produces high-quality hydrogen, and has a sustainable production process that requires less energy. Electrocatalysts composed of precious metals like Pt, Au, Ru, and Ag are commonly used in the investigation of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Nevertheless, their limited availability and expensive cost restrict practical use. In contrast, electrocatalysts that do not contain precious metals are readily available, cost-effective, environmentally friendly, and possess electrocatalytic performance equal to that of noble metals. However, considerable research effort must be devoted to create cost-effective and high-performing catalysts. This article provides a comprehensive examination of the reaction mechanism involved in electrocatalytic water splitting in both acidic and basic environments. Additionally, recent breakthroughs in catalysts for both the hydrogen evolution and oxygen evolution reactions are also discussed. The structure-activity relationship of the catalyst was deep-going discussed, together with the prospects of current obstacles and potential for electrocatalytic water splitting, aiming at provide valuable perspectives for the advancement of economical and efficient electrocatalysts on an industrial scale.

Covalently bridged bond assembly of MoS2lamellae onto a graphene sheet: an outstanding electrode for high rate and long-life lithium/sodium-ion batteries

The practical application of Molybdenum sulphide (MoS2) electrodes has been hindered by its structural instability, and poor electrical conductivity. To enhance the cycle stability and rate performance of MoS2in lithium/sodium-ion batteries (LIBs/SIBs), we synthesized a graphene-supported MoS2composite (MoS2@rGO) with affluent covalent bridged bonds through a facile and scalable hydrothermal and annealing process. The covalent bridged bonds of Mo-S-C, Mo-O-C and C-O-S provide an effective charge transfer path between MoS2and graphene, facilitating fast charge hopping and improving rate performance. As anode materials for LIBs, the MoS2@rGO exhibited exceptional long-term cycle life (906 mAh g-1at 1.0 A g-1after 400 cycles) and outstanding rate capability (1267.7/314.7 mAh g-1at 0.1/6.5 A g-1). Additionally, the MoS2@rGO electrode demonstrated a stable reversible capacity of 521.7 mAh g-1at 1.0 A g-1after 700 cycles and excellent rate capabilities of 665.1 and 326.3 mAh g-1at 0.1 and 10.0 A g-1in SIBs. The edge Mo of MoS2is directly coupled with the oxygen of the functional group on rGO, achieved by adjusting the pH value of the solution to tune the surface charge feature, can effectively enhance the structural stability of electrode even under higher current density.

Inhabiting Inactive Transition by Coupling Function of Oxygen Vacancies and Fe─C Bonds achieving Long Cycle Life of an Iron-Based Anode

Fe-based battery-type anode materials with many faradaic reaction sites have higher capacities than carbon-based double-layer-type materials and can be used to develop aqueous supercapacitors with high energy density. However, as an insurmountable bottleneck, the severe capacity fading and poor cyclability derived from the inactive transition hinder their commercial application in asymmetric supercapacitors (ASCs). In this work, driven by the "oxygen pumping" mechanism, oxygen-vacancy-rich Fe@Fe3 O4 (v) @Fe3 C@C nanoparticles that consist of a unique "fruit with stone"-like structure are developed, and they exhibit enhanced specific capacity and fast charge/discharge capability. Experimental and theoretical results demonstrate that the capacity attenuation in conventional iron-based anodes is greatly alleviated in the the Fe@Fe3 O4 (v) @Fe3 C@C anode because the irreversible phase transition to the inactive γ-Fe2 O3 phase can be inhibited by a robust barrier formed by the coupling of oxygen vacancies and Fe─C bonds, which promotes cycle stability (93.5% capacity retention after 24 000 cycles). An ASC fabricated using this Fe-based anode is also observed to have extraordinary durability, achieving capacity retention of 96.4% after 38 000 cycles, and a high energy density of 127.6 W h kg-1 at a power density of 981 W kg-1 .

Whole-Voltage-Range Solid-Solution Reaction in Layered Oxide Cathode of Sodium-Ion Batteries

Layered manganese-based oxides (LMOs) are promising cathode materials for sodium-ion batteries (SIBs) due to their versatile structures. However, the Jahn-Teller effect of Mn3+ induces severe distortion of MnO6 octahedra, and the resultant low symmetry is responsible for the gliding of MnO2 layers and then inferior multiple-phase transitions upon Na+ extraction/insertion. Here, hexagonal P2-Na0.643 Li0.078 Mn0.827 Ti0.095 O2 is synthesized through the incorporation of Li and Ti into the distorted orthorhombic P'2-Na0.67 MnO2 to function as a phase-transition-free oxide cathode. It is revealed that Li in both the transition-metal and Na layers enhances the covalency of Mn-O bonds and allows degeneracy of Mn 3d eg orbitals to favor the formation of hexagonal phase, and the high strength of Ti-O bonds reduces the electrostatic interaction between Na and O for suppressed Na+ /vacancy rearrangements. These collectively lead to a whole-voltage-range solid-solution reaction between 1.8 and 4.3 V with a small volume variation of 1.49%. This rewards its excellent cycling stability (capacity retention of 90% after 500 cycles) and rate capability (89 mAh g-1 at 2000 mA g-1 ).

La-Doped Ultrahigh-Nickel Layered Oxide Cathode with Enhanced Cycle Stability for Li-Ion Batteries

Currently, ultrahigh-nickel layered oxide is one of the most promising cathodes for lithium-ion batteries, with the advantages of high theoretical capacity and low cost. However, some problems in ultrahigh-nickel layered oxides are more serious, such as irreversible structural transformation, particle cracking, and side reactions at the electrode/electrolyte interface, resulting in the fast decay of the discharge capacity and midpoint potential. In this work, La doping is introduced into ultrahigh-nickel layered LiNi_0.9Co_0.1O₂ oxide to improve the cycle stability on both discharge capacity and midpoint potential. As demonstrated, La can be doped successfully into the subsurface of LiNi_0.9Co_0.1O₂ oxide, and the morphology of the oxide microspheres is not changed obviously by La doping. Compared with the pristine sample, the La-doped sample presents improved electrochemical performance, especially good cycle stabilization on both discharge capacity and midpoint potential. In addition, after a long-term cycle, the La-doped sample still maintains a relatively complete spherical morphology. It means that the pillaring effect of La with a large radius is helpful in accommodating the volume change caused by the insertion/extraction of Li ions, thus easing the anisotropic stress accumulation and microcrack growth inside the microspheres of the La-doped sample.

Highly Reversible Chevrel Phase Mo6Se8 Cathode with Low Voltage Hysteresis for Rechargeable Aluminum Batteries

Rechargeable aluminum (Al) batteries have attracted considerable interest as potential large-scale energy storage technologies due to the abundance, high theoretical capacity, and high safety of Al. We report here a highly reversible Al-Mo₆Se₈ prototype cell with low discharge-charge hysteresis (approximately 50 mV under 30 mA g^-1 at 50 °C), ultra-flat discharge plateau, and exceptional cycle stability: the reversible capacity retaining at a steady 77 mA h g^-1 after more than 1800 cycles. The Al intercalation-extraction mechanism is probed with ex situ and operando XRD techniques, revealing the reversible intercalation reaction from Mo₆Se₈ to Al_4/3Mo₆Se₈. The stable electrochemical performance and unambiguous intercalation mechanism of the Al-Mo₆Se₈ system provide an alternative for beyond-lithium battery technologies.

Electrospun Sandwich-like Structure of PVDF-HFP/Cellulose/PVDF-HFP Membrane for Lithium-Ion Batteries

Cellulose membranes have eco-friendly, renewable, and cost-effective features, but they lack satisfactory cycle stability as a sustainable separator for batteries. In this study, a two-step method was employed to prepare a sandwich-like composite membrane of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP)/cellulose/ PVDF-HFP (PCP). The method involved first dissolving and regenerating a cellulose membrane and then electrospinning PVDF-HFP on its surface. The resulting PCP composite membrane exhibits excellent properties such as high porosity (60.71%), good tensile strength (4.8 MPa), and thermal stability up to 160 °C. It also has exceptional electrolyte uptake properties (710.81 wt.%), low interfacial resistance (241.39 Ω), and high ionic conductivity (0.73 mS/cm) compared to commercial polypropylene (PP) separators (1121.4 Ω and 0.26 mS/cm). Additionally, the rate capability (163.2 mAh/g) and cycling performance (98.11% after 100 cycles at 0.5 C) of the PCP composite membrane are superior to those of PP separators. These results demonstrate that the PCP composite membrane has potential as a promising separator for high-powered, secure lithium-ion batteries.

CoNi Alloys Encapsulated in N-Doped Carbon Nanotubes for Stabilizing Oxygen Electrocatalysis in Zinc-Air Battery

Alloy-based catalysts with high corrosion resistance and less self-aggregation are essential for oxygen reduction/evolution reactions (ORR/OER). Here, via an in situ growth strategy, NiCo alloy-inserted nitrogen-doped carbon nanotubes were assembled on a three-dimensional hollow nanosphere (NiCo@NCNTs/HN) using dicyandiamide. NiCo@NCNTs/HN exhibited better ORR activity (half-wave potential (E_1/2) of 0.87 V) and stability (E_1/2 shift of only -13 mV after 5000 cycles) than commercial Pt/C. NiCo@NCNTs/HN displayed a lower OER overpotential (330 mV) than RuO₂ (390 mV). The NiCo@NCNTs/HN-assembled zinc-air battery exhibited high specific-capacity (847.01 mA h g^-1) and cycling-stability (291 h). Synergies between NiCo alloys and NCNTs facilitated the charge transfer to promote 4e^- ORR/OER kinetics. The carbon skeleton inhibited the corrosion of NiCo alloys from surface to subsurface, while inner cavities of CNTs confined particle growth and the aggregation of NiCo alloys to stabilize bifunctional activity. This provides a viable strategy for the design of alloy-based catalysts with confined grain-size and good structural/catalytic stabilities in oxygen electrocatalysis.

Revealing the Effect of High Ni Content in Li-Rich Cathode Materials: Mitigating Voltage Decay or Increasing Intrinsic Reactivity

Li-rich layered oxides are considered as one of the most promising cathode materials for secondary lithium batteries due to their high specific capacities, but the issue of continuous voltage decay during cycling hinders their market entry. Increasing the Ni content in Li-rich materials is assumed to be an effective way to address this issue and attracts recent research interests. However, a high Ni content may induce increased intrinsic reactivity of materials, resulting in severe side reactions with the electrolyte. Thus, a comprehensive study to differentiate the two effects of the Ni content on the cell performance with Li-rich cathode is carried out in this work. Herein, it is demonstrated that a properly dosed amount of Ni can effectively suppress the voltage decay in Li-rich cathodes, while over-loading of Ni, on the contrary, can cause structural instability, Ni dissolution, and nonuniform Li deposition during cycling as well as severe oxygen loss. This work offers a deep understanding on the impacts of Ni content in Li-rich materials, which can be a good guidance for the future design of such cathodes for high energy density lithium batteries.

Adsorption-Assisted Redox Center in Porous Organic Frameworks for Boosting Lithium Storage

Due to the designable structure and capacity, organic materials are promising candidates for lithium-ion batteries. Herein, we report a novel type of porous organic frameworks (POFs) based on the coupling reaction of diazonium salt as the anodes for lithium ion storage. The active center containing an azo group and the adjacent lithium-philic adsorption site is constructed to investigate the electrochemical behaviors and reaction mechanism. As synthesized POF material (named as POF-AN) exhibits high reversible lithium storage capacities of 523 mAh g^-1 at 0.5 A g^-1 and 445 mAh g^-1 at 2.0 A g^-1 after 1500 cycles, showing excellent cycle stability and rate performance. The detailed characterizations reveal that the azo group can act as an electrochemical active site that reversibly bonds with Li-ions, and the adjacent oxygen atoms can electrostatically adsorb with Li-ions to promote the lithium storage reaction. This adsorption-assisted three-atom redox center is beneficial to synergistically enhance the adsorption and intercalation of lithium ions, which can further improve the capacity and cycle stability. By replacing the precursor, it is also facile to synthesize more similar structure types. The reversible redox chemistry of the adsorption-assisted three-atom active center provides new opportunities for the development of long lifespan and high-rate organic anodes.

Achieving Ultrahigh Energy-Density Aqueous Supercapacitors via a Novel Acidic Radical Adsorption Capacity-Activation Mechanism in Ni(SeO3 )/Metal Sulfide Heterostructure

Transitional metal chalcogenide (TMC) is considered as one promising high-capacity electrode material for asymmetric supercapacitors. More evidence indicates that TMCs have the same charge storage mechanism as hydroxides, but the reason why TMC electrode materials always provide higher capacity is rare to insight. In this work, a Ni_x Co_y Mn_z S/Ni(SeO₃ ) (NCMS/NSeO) heterostructure is prepared on Ni-plated carbon cloth, validating that both NCMS and NSeO can be transformed into hydroxides in electrochemical process as accompanying with the formation of SeO₃ ^2- and SO_x ^2- in confined spaces of NCMS/NSeO/Ni sandwich structure. Based on density functional theory calculation and experimental results, a novel space-confined acidic radical adsorption capacity-activation mechanism is proposed for the first time, which can nicely explain the capacity enhancement of NCMS/NSeO electrode materials. Thanks to the unique capacity enhancement mechanism and stable NCMS/NSeO/Ni sandwich structure, the optimized electrodes exhibit a high capacity of 536 mAh g^-1 at 1 A g^-1 and the impressive rate capability of 140.5 mAh g^-1 at the amazing current density of 200 A g^-1 . The assembled asymmetric supercapacitor achieves an ultrahigh energy density of 141 Wh Kg^-1 and an impressive high-rate capability and cyclability combination with 124% capacitance retention after 10 000 cycles at a large current density of 50 A g^-1 .

Composite Electrolytes Prepared by Improving the Interfacial Compatibility of Organic-Inorganic Electrolytes for Dendrite-Free, Long-Life All-Solid Lithium Metal Batteries

Compared with simplex ceramic or polymer solid electrolytes, composite solid electrolyte (CSE) is more promising for its better interfacial compatibility to electrode and high ionic conductivity simultaneously. Further, the interfacial compatibility within ceramic and polymer is considered to be more and more critical to the overall performance of solid-state batteries. Avoiding the agglomeration of ceramic particles at high loadings can improve the whole intrinsic characteristic and electrochemical performance of CSEs. Herein, we designed a CSE (EO@LLZTO-PEO), which consists of composite particles (EO@LLZTO) as a filler and polyethylene oxide (PEO) as polymer matrix. EO@LLZTO was prepared by chemically grafting polyethylene glycol monomethyl ether methacrylate (MPEG-MAA) on the micro-sized Li_6.4La₃Zr_1.4Ta_0.6O₁₂ (LLZTO) particles. By introducing of polymer containing EO segments onto LLZTO, the interfacial compatibility between LLZTO and PEO matrix is highly enhanced, and the intrinsic Li⁺ complexation capability of MPEG-MAA is improved, even at the high loading of garnet. EO@LLZTO-PEO shows a high ionic conductivity (1.91 mS cm^-1), a broad electrochemical window (∼5.2 V vs Li/Li⁺), and a high lithium ion transference number (0.72). The Li/EO@LLZTO-PEO/Li battery also exhibits a long cycle stability (over 1200 h of cycling). Moreover, all-solid-state batteries with LiFePO₄ and LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) cathodes exhibit excellent cycling stability and rate performance. Consequently, enhancing the interfacial compatibility between organic and inorganic electrolytes is identified to be one of the crucial strategies for commercial solid-state lithium batteries.

A Study on the Effect of Graphene in Enhancing the Electrochemical Properties of SnO2-Fe2O3 Anode Materials

To enhance the conductivity and volume expansion during the charging and discharging of transition metal oxide anode materials, rGO-SnO₂-Fe₂O₃ composite materials with different contents of rGO were prepared by the in situ hydrothermal synthesis method. The SEM morphology revealed a sphere-like fluffy structure, particles of the 0.4%rGO-10%SnO₂-Fe₂O₃ composite were smaller and more compact with a specific surface area of 223.19 m²/g, the first discharge capacity of 1423.75 mAh/g, and the specific capacity could be maintained at 687.60 mAh/g even after 100 cycles. It exhibited a good ratio performance and electrochemical reversibility, smaller charge transfer resistance, and contact resistance, which aided in lithium-ion transport. Its superior electrochemical performance was due to the addition of graphene, which made the spherical particle size distribution more uniform, effectively lowering the volume expansion during the process of charging and discharging and improving the electrochemical cycle stability of the anode materials.

MgCr2O4-Modified CuO/Cu2O for High-Temperature Thermochemical Energy Storage with High Redox Activity and Sintering Resistance

Metal oxides as high-temperature thermochemical energy storage systems with high energy density based on the gas-solid reaction are a critical demand for the future development of concentrated solar power plants. A copper-based system has high enthalpy change and low cost, but its serious sintering leads to poor reactivity. In this study, MgCr₂O₄ is decorated on the CuO/Cu₂O surface to effectively increase the sintering temperature and alleviate the sintering problem. The re-oxidation degree is increased from 46 to 99.9%, and the reaction time is shortened by 3.7 times. The thermochemical energy density of storage and release reach -818.23 and 812.90 kJ/kg, respectively. After 600 cycles, the oxidation activity remains 98.77%. Material characterization elucidates that nanosized MgCr₂O₄ is uniformly loaded on the surface of CuO/Cu₂O during the reversible reaction, and there is a strong interaction between metal oxides and prompter. Density functional theory (DFT) calculation further confirms that CuO/Cu₂O-MgCr₂O₄ has large binding energy and the formation energy of copper vacancy increases, which can effectively inhibit sintering. The modification mechanism of CuO/Cu₂O by MgCr₂O₄ is revealed, which can provide guidance for the reasonable design of thermochemical energy storage materials with sintering resistance and redox activity.

Long Shelf-Life Efficient Electrolytes Based on Trace l-Cysteine Additives toward Stable Zinc Metal Anodes

The unstable anode/electrolyte interface (AEI) triggers the corrosion reaction and dendrite formation during cycling, hindering the practical application of zinc metal batteries. Herein, for the first time, l-cysteine (Cys) is employed to serve as an electrolyte additive for stabilizing the Zn/electrolyte interface. It is revealed that Cys additives tend to initially approach the Zn surface and then decompose into multiple effective components for suppressing parasitic reactions and Zn dendrites. As a consequence, Zn|Zn symmetric cells using trace Cys additives (0.83 mm) exhibit a steady cycle life of 1600 h, outperforming that of prior studies. Additionally, an average Coulombic efficiency of 99.6% for 250 cycles is also obtained under critical test conditions (10 mA cm^-2 /5 mAh cm^-2 ). Cys additives also enable Zn-V₂ O₅ and Zn-MnO₂ full cells with an enhanced cycle stability at a low N/P ratio. More importantly, Cys/ZnSO₄ electrolytes are demonstrated to be still effective after resting for half year, favoring the practical production.

Topology Optimized Prelithiated SiO Anode Materials for Lithium-Ion Batteries

Silicon monoxide (SiO)-based materials have great potential as high-capacity anode materials for lithium-ion batteries. However, they suffer from a low initial coulombic efficiency (ICE) and poor cycle stability, which prevent their successful implementation into commercial lithium-ion batteries. Despite considerable efforts in recent decades, their low ICE and poor cycle stability cannot be resolved at the same time. Here, it is demonstrated that the topological optimization of the prelithiated SiO materials is highly effective in improving both ICE and capacity retention. Laser-assisted atom probe tomography combined with thermogravimetry and differential scanning calorimetry reveals that two exothermic reactions related to microstructural evolution are key in optimizing the domain size of the Si active phase and Li₂ SiO₃ buffer phase, and their topological arrangements in prelithiated SiO materials. The optimized prelithiated SiO, heat-treated at 650 °C, shows higher capacity retention of 73.4% and lower thickness changes of 68% after 300 cycles than those treated at other temperatures, with high ICE of ≈90% and reversible capacity of 1164 mAh g^-1 . Such excellent electrochemical properties of the prelithiated SiO electrode originate from its optimized topological arrangement of active Si phase and Li₂ SiO₃ inactive buffer phase.

Face-lifting the surface of LiNi0.8Co0.15Al0.05O2cathode via Y(PO3)3to form anin situtriple composite Li-ion conductor coating layer with the enhanced electrochemical performance

Due to the assets such as adequate discharge capacity and rational cost, LiNi_0.8Co_0.15Al_0.05O₂(NCA), a high-nickel ternary layered oxide, is regarded to be a favorable cathode contender for lithium-ion batteries. However, the superior commercial application is restricted by the surface residual alkaline lithium salt (LiOH or/and Li₂CO₃) of nickel-rich cathode materials, which will expedite the disintegration of the structure and the engendering of gas (CO₂). Therefore, in this paper, we devise and fabricate a Y(PO₃)₃modified LiNi_0.8Co_0.15Al_0.05O₂(NCA), intending to optimize the surface residual alkaline lithium salt (antecedent deportation of H₂O and CO₂) while forming anin situtriple composite Li-ion conductor coating (Y(PO₃)₃-Li₃PO₄-YPO₄) to enhance the electrochemical behavior. Under this method, the 2 mol% Y(PO₃)₃modified NCA electrode reveals exceptional rate capability (5 C/156.3 mAh g^-1) and extraordinary cycle stability after 200 cycles (2 C/88.3%), whereas the original sample is only 5 C/123.1 mAh g^-1and 2 C/71.2% after 200 cycles. Conspicuously, even under the draconian circumstances of the high temperature and the high rate at 55 °C/1 C, the 2 mol% Y(PO₃)₃modified NCA electrode sustains a high reversible capacity, with an admirable capacity retention rate of 89.4% after 100 cycles. These contented results signify that the surface remodeling tactic presents a viable scheme for ameliorating high-nickel materials' performance and appropriateness.

High-performance K-ion half/full batteries with superb rate capability and cycle stability

SignificanceThe present work might be significant for exploring advanced K-ion batteries with superb rate capability and cycle stability toward practical applications. The as-assembled K-ion half cell exhibits an excellent rate capability of 428 mA h g^-1 at 100 mA g^-1 and a high reversible specific capacity of 330 mA h g^-1 with 120% specific capacity retention after 2,000 cycles at 2,000 mA g^-1, which is the best among those based on carbon materials. The as-constructed full cell delivers 98% specific capacity retention over 750 cycles at 500 mA g^-1, superior to most of those based on carbon materials that have been reported thus far.

LiNi0.6Co0.2Mn0.2O2 Cathodes Coated with Dual-Conductive Polymers for High-Rate and Long-Life Solid-State Lithium Batteries

High-energy density and safe solid lithium batteries call for cathodes with high capacity and good kinetic properties. In this work, LiNi_0.6Co_0.2Mn_0.2O₂ (NCM622) cathodes are coated with the ionic-electronic dual-conductive polymers composed of poly(ethylene glycol) (PEG)-doped polyaniline (PANI). Scanning electron microscopy, transmission electron microscopy, Fourier transform infrared, and thermogravimetric analysis reveal that the dual-conductive polymers are homogeneously coated on the surfaces of NCM622 cathodes with a thickness of approximately 10 nm. The solid-state lithium batteries consisting of the NCM622 cathodes coated with PANI-PEG show a specific capacity of 158 mA h g^-1 and a retention rate of 88% after 100 cycles at the rate of 0.1 C and room temperature, which are superior to the discharge capacity of 153 mA h g^-1 and capacity retention of 59% after 100 cycles for the batteries with the pristine NCM622 cathodes. Moreover, the cells with the coated cathodes display a better rate performance of 84 mA h g^-1 at 1 C than those with the uncoated ones which show a rate performance of 11 mA h g^-1 at 1 C.

Bio-Inspired Binder Design for a Robust Conductive Network in Silicon-Based Anodes

Due to the severe volume variations during electrochemical processes, Si-based anodes suffer from poor cycling performance as the result of a collapsed conductive network. In this regard, a key strategy for fully exploiting the capacity potential of Si-based anodes is to construct a robust conductive network through rational binder design. In this work, a bio-inspired conductive binder (PFPQDA) is designed by introducing dopamine-functionalized fluorene structure units (DA) into a conductivity enhanced polyfluorene-typed copolymer (PFPQ) to enhance its mechanical properties. Through constructing hierarchical binding networks and resilient electron transportations within both nano-sized Si and micro-sized SiOx electrodes via interweaved interactions, the PFPQDA successfully suppresses the electrode expansion and maintains the integrity of conductive pathways. Consequently, owing to the favorable properties of PFPQDA, Si-based anodes exhibit improved cycling performance and rate capability with an areal capacity over 2.5 mAh cm-2 .

Improving Cycling Stability of the Lithium Anode by a Spin-Coated High-Purity Li3PS4 Artificial SEI Layer

Controlling the composition and microstructure of the solid electrolyte interphase (SEI) layer is critical to improving the cycling stability of the high-energy-density lithium-metal electrode. It is a quite tricky task to control the properties of the SEI layer which is conventionally formed by the chemical reactions between a Li metal and the additives. Herein, we develop a new route to synthesize a lithium-compatible sol of the sulfide electrolyte Li₃PS₄, so that a Li₃PS₄ artificial SEI layer with a controllable nanoscale thickness and high phase purity can be prepared by spin-coating. The layer stabilizes the lithium/electrolyte interface by homogenizing the Li-ion flux, preventing the parasitic reactions, and alleviating concentration polarization. Consequently, a symmetrical cell with the Li₃PS₄-modified lithium electrodes can achieve stable lithium plating/stripping for 800 h at a current density of 1 mA cm^-2. The Li-S batteries assembled with the Li₃PS₄-protected Li anodes show better capacity retention than their bare Li counterparts, whose average decay rate from the 240th cycle to the 800th cycle is only 0.004%/cycle. In addition, the Li₃PS₄ layer improves the rate capacity of the batteries, significantly enhancing the capacity from 175 to 682 mA h g^-1 at a 2 C rate. The spin-coated Li₃PS₄ artificial SEI layer provides a new strategy to develop high-performance Li metal batteries.

Modified KBBF-like Material for Energy Storage Applications: ZnNiBO3(OH) with Enhanced Cycle Life

Not only are new and novel materials sought for electrode material development, but safe and nontoxic materials are also highly being intensively investigated. Herein, we prepare ZnNiBO₃(OH) (ZNBH), a modified and Be-free KBe₂BO₃F₂ (KBBF) family member as an effective electrode material. The novel ZNBH resembles the KBBF structure but with reinforced structure and bonding, in addition to well-incorporated conductive metals benefiting supercapacitor applications. The enhanced electronic properties of ZNBH are further studied by means of density functional theory calculations. The as-prepared ZNBH electrode material exhibits a specific capacity of 746 C g^-1 at a current density of 1 A g^-1. A hybrid supercapacitor (HSC) device is fabricated and successfully illuminated multiple color LEDs. Interestingly, even after being subjected to long charge-discharge for 10 000 cycles, the ZNBH//AC HSC device retains 97.2% of its maximum capacity, indicating the practicality of ZNBH as an electrode material.

Sulfur-Bridged Bonds Boost the Conversion Reaction of the Flexible Self-Supporting MnS@MXene@CNF Anode for High-Rate and Long-Life Lithium-Ion Batteries

Manganese sulfide (MnS) has been found to be a suitable electrode material for lithium-ion batteries (LIBs) owing to its considerable theoretical capacity, high electrochemical activity, and low discharge voltage platform, while its poor electrical conductivity and severe pulverization caused by volume expansion of the material limit its practical application. To improve the rate performance and cycle stability of MnS in LIBs, the structure-control strategy has been used to design and fabricate new anode materials. Herein, the MnS@MXene@CNF (MMC, CNFs means carbon nanofibers) electrode has been prepared by electrospinning and a subsequent high-temperature annealing process. The MMC electrode exhibits excellent cyclic stability with a capacity retention rate close to 100% after 1000 cycles at 1000 mA/g and an improved rate performance with a specific capacity up to 500 mAh/g at a high current density of 5000 mA/g, much higher than the 308 mAh/g of the MnS@CNF (MC) electrode. The elevated electrochemical performance of the MMC electrode not only benefits from the unique structure of MnS nanoparticles evenly dispersed in the well-designed flexible self-supporting three-dimensional (3D) CNF network but, more importantly, also benefits from the formation of sulfur-bridged Mn-S-C bonds at the MnS/MXene interface. The newly formed bonds between MnS and MXene nanosheets can stabilize the structure of MnS near the interfaces and provide a channel for fast charge transfer, which notably increase both the reversibility and the rate of the conversion reaction during the charge/discharge process. This work may pave a new path for designing stable and self-supporting anodes for high-performance LIBs.

Lithium Storage Mechanism and Application of Micron-Sized Lattice-Reversible Binary Intermetallic Compounds as High-Performance Flexible Lithium-Ion Battery Anodes

A strategy of lattice-reversible binary intermetallic compounds of metallic elements is proposed for applications in flexible lithium-ion battery (LIB) anode with high capacity and cycling stability. First, the use of metallic elements can ensure excellent electronic conductivity and high capacity of the active anode substance. Second, binary intermetallic compounds possess a larger initial lattice volume than metallic monomers, so that the problem of volume expansion can be alleviated. Finally, the design of binary intermetallic compounds with lattice reversibility further improves the cycle stability. In this work, the feasibility of this strategy is verified using an indium antimonide (InSb) system. The volumetric expansion and lithium storage mechanism of InSb are investigated by in situ Raman characterization and theoretical calculations. The active material utilization is significantly improved and the growth of In whiskers is inhibited in the micron-sized ball-milled and carbon coated InSb (bInSb@C) anode, which exhibits a reversible capacity of 733.8 mAh g^-1 at 0.2 C, and provides a capacity of 411.5 mAh g^-1 after 200 cycles at 3 C with an average Coulombic efficiency of 99.95%. This strategy is validated in pouch cells, illustrating the great potential of lattice-reversible binary intermetallic compounds for use as commercial flexible LIB anodes.

A Comparative Evaluation of Sustainable Binders for Environmentally Friendly Carbon-Based Supercapacitors

Environmentally friendly energy storage devices have been fabricated by using functional materials obtained from completely renewable resources. Gelatin, chitosan, casein, guar gum and carboxymethyl cellulose have been investigated as sustainable and low-cost binders within the electrode active material of water-processable symmetric carbon-based supercapacitors. Such binders are selected from natural-derived materials and industrial by-products to obtain economic and environmental benefits. The electrochemical properties of the devices based on the different binders are compared by using cyclic voltammetry, galvanostatic charge/discharge curves and impedance spectroscopy. The fabricated supercapacitors exhibit series resistance lower than a few ohms and values of the specific capacitance ranged between 30 F/g and 80 F/g. The most performant device can deliver ca. 3.6 Wh/kg of energy at a high power density of 3925 W/kg. Gelatin, casein and carboxymethyl cellulose-based devices have shown device stability up to 1000 cycles. Detailed analysis on the charge storage mechanisms (e.g., involving faradaic and non-faradaic processes) at the electrode/electrolyte interface reveals a pseudocapacitance behavior within the supercapacitors. A clear correlation between the electrochemical performances (e.g., cycle stability, capacitance retention, series resistance value, coulombic efficiency) ageing phenomena and charge storage mechanisms within the porous carbon-based electrode have been discussed.

Constructing a Resilient Hierarchical Conductive Network to Promote Cycling Stability of SiOx Anode via Binder Design

Despite exhibiting high specific capacities, Si-based anode materials suffer from poor cycle life as their volume change leads to the collapse of conductive network within the electrode. For this reason, the challenge lies in retaining the conductive network during electrochemical processes. Herein, to address this prominent issue, a cross-linked conductive binder (CCB) is designed for commercially available silicon oxides (SiO_x ) anode to construct a resilient hierarchical conductive network from two aspects: on the one hand, exhibiting high electronic conductivity, CCB serves as an adaptive secondary conductive network in addition to the stiff primary conductive network (e.g., conductive carbon), facilitating faster interfacial charge transfer processes for SiO_x in molecular level; on the other hand, the cross-linked structure of CCB shows resilient mechanical properties, which maintains the integrity of the primary conductive network by preventing electrode deformation during prolonged cycling. With the aid of CCB, untreated micro-sized SiO_x anode material delivers an areal capacity of 2.1 mAh cm^-2 after 250 cycles at 0.8 A g^-1 . The binder design strategy, as well as, the relevant concepts proposed herein, provide a new perspective toward promoting the cycling stability of high-capacity Si-based anodes.

High-Performance Potassium-Ion Batteries with Robust Stability Based on N/S-Codoped Hollow Carbon Nanocubes

Currently, a big challenge for the practical use of potassium-ion batteries (PIBs) is their intrinsically poor cycling stability, due to the relatively large radius of K⁺ and sluggish kinetics for intercalation/deintercalation. Here we report the scalable fabrication of N/S-codoped hollow carbon nanocubes (NSHCCs), which have the potential as an electrode for advanced PIBs with robust stability. Their discharge and charge specific capacities are ∼560 mA h g^-1 and 310 mA h g^-1 at a current density of 50 mA g^-1, respectively. Meanwhile, they exhibit 100% specific capacity retention after 620 cycles over 9 months at a low current density of 50 mA g^-1, which is state-of-the-art among carbon materials. Moreover, they demonstrate nearly no sacrifice in specific capacities with 99.9% retention after 3000 cycles over 4 months under a high current density of 1000 mA g^-1, superior to most carbon analogues for potassium storage previously reported. The improved electrochemical performance of NSHCC can be mainly attributed to the unique hollow carbon nanocubes with incorporated N and S dopants, which can expand the carbon layer spacing, facilitate K⁺ adsorption, and relieve the volume change during the intercalation/deintercalation of K⁺ ions.

Robust high-temperature potassium-ion batteries enabled by carboxyl functional group energy storage

The popularly reported energy storage mechanisms of potassium-ion batteries (PIBs) are based on alloy-, de-intercalation-, and conversion-type processes, which inevitably lead to structural damage of the electrodes caused by intercalation/de-intercalation of K⁺ with a relatively large radius, which is accompanied by poor cycle stabilities. Here, we report the exploration of robust high-temperature PIBs enabled by a carboxyl functional group energy storage mechanism, which is based on an example of p-phthalic acid (PTA) with two carboxyl functional groups as the redox centers. In such a case, the intercalation/de-intercalation of K⁺ can be performed via surface reactions with relieved volume change, thus favoring excellent cycle stability for PIBs against high temperatures. As proof of concept, at the fixed working temperature of 62.5 °C, the initial discharge and charge specific capacities of the PTA electrode are ∼660 and 165 mA⋅h⋅g^-1, respectively, at a current density of 100 mA⋅g^-1, with 86% specific capacity retention after 160 cycles. Meanwhile, it delivers 81.5% specific capacity retention after 390 cycles under a high current density of 500 mA⋅g^-1 The cycle stabilities achieved under both low and high current densities are the best among those of high-temperature PIBs reported previously.

Advances and Prospects of High-Voltage Spinel Cathodes for Lithium-Based Batteries

Insertion compounds have been dominating the cathodes in commercial lithium-ion batteries. In contrast to layered oxides and polyanion compounds, the development of spinel-structured cathodes is a little behind. Owing to a series of advantageous properties, such as high operating voltage (≈4.7 V), high capacity (≈135 mAh g^-1 ), low environmental impact, and low fabrication cost, the high-voltage spinel LiNi_0.5 Mn_1.5 O₄ represents a high-power cathode for advancing high-energy-density Li⁺ -ion batteries. However, the wide application and commercialization of this cathode are hampered by its poor cycling performance. Recent progress in both the fundamental understanding of the degradation mechanism and the exploration of strategies to enhance the cycling stability of high-voltage spinel cathodes have drawn continuous attention toward this promising insertion cathode. In this review article, the structure-property correlations and the failure mode of high-voltage spinel cathodes are first discussed. Then, the recent advances in mitigating the cycling stability issue of high-voltage spinel cathodes are summarized, including the various approaches of structural design, doping, surface coating, and electrolyte modification. Finally, future perspectives and research directions are put forward, aiming at providing insightful information for the development of practical high-voltage spinel cathodes.

Yttrium Surface Gradient Doping for Enhancing Structure and Thermal Stability of High-Ni Layered Oxide as Cathode for Li-Ion Batteries

The high-nickel layered oxides are potential candidate cathode materials of next-generation high energy lithium-ion batteries, in which higher nickel/lower cobalt strategy is effective for increasing specific capacity and reducing cost of cathode. Unfortunately, the fast decay of capacity/potential, and serious thermal concern are critical obstacles for the commercialization of high-nickel oxides due to structural instability. Herein, in order to improve the structure and thermal stability of high-nickel layered oxides, we demonstrate a feasible and simple strategy of the surface gradient doping with yttrium, without forming the hard interface between coating layer and bulk. As expected, after introducing yttrium, the surface gradient doping layer is formed tightly based on the oxidation induced segregation, leading to improved structure and thermal stability. Correspondingly, the good capacity retention and potential stability are obtained for the yttrium-doped sample, together with the superior thermal behavior. The excellent electrochemical performance of the yttrium-doped sample is primarily attributed to the strong yttrium-oxygen bonding and stable oxygen framework on the surface layer. Therefore, the surface manipulating strategy with the surface gradient doping is feasible and effective for improving the structure and thermal stability, as well as the capacity/potential stability during cycling for the high-Ni layered oxides.

Dual-Redox System of Metallo-Supramolecular Polymers for Visible-to-Near-IR Modulable Electrochromism and Durable Device Fabrication

Dual-redox metallo-supramolecular polymers with a zigzag structure (polyFe-N and polyRu-N) were successfully synthesized by 1:1 complexation of a redox-active Fe(II) or Ru(II) ion and 4,4-bis(2,2:6,2-terpyridinyl)phenyl-triphenylamine (L_TPA) as a redox-active ligand. The polymers had high solubility in methanol, and the polymer solutions showed dark brown (polyFe-N) or orange-red (polyRu-N) coloration. UV-vis spectra of the polymers displayed a strong metal-to-ligand charge transfer (MLCT) absorption in the visible region. Cyclic voltammograms of the polymer films exhibited two pairs of reversible redox waves. The first redox at ∼0.5 V versus Ag/Ag⁺ was assigned to the redox in the triphenylamine (TPA) moiety of L_TPA, and the second redox at 0.8 V versus Ag/Ag⁺ (polyFe-N) or 0.9 V versus Ag/Ag⁺ (polyRu-N) was given to the redox of Fe(II)/(III) or Ru(II)/(III), respectively. Upon applying a positive potential of more than 0.5 V versus Ag/Ag⁺ to the polymer films, a new absorption at ∼820 nm in the near-infrared (NIR) region appeared with wide tailing to the longer wavelength. It is considered that the new absorption in the NIR region is caused by the polaron band of the oxidized ligand in the polymers. When the applied potential was increased to 1.0 V versus Ag/Ag⁺ (polyFe-N) or 1.1 V versus Ag/Ag⁺ (polyRu-N), the maximum wavelength of the new absorption in the NIR region shifted to 885-900 nm and the absorbance was further enhanced with disappearance of the MLCT absorption. Eventually, the original colors of the polymers were faint to light green. This visible-to-NIR electrochromism was reversible, and maximum optical contrast (ΔT) reached 52% in the visible region and 80% in the NIR region. A prototype solid-state device with the polymer was fabricated for practical utilization, exhibiting excellent cycle stability of >4000 cycles with maintaining high optical contrast from the visible-to-NIR range.

High-Efficiency Electrolyte for Li-Rich Cathode Materials Achieving Enhanced Cycle Stability and Suppressed Voltage Fading Capable of Practical Applications on a Li-Ion Battery

Li-rich cathodes have been in considerable attention for their high reversible capacity. However, they have serious problems like poor cycling with intense capacity decay and voltage fading, which restrict their access to practical applications. In this work, a facile and efficient strategy is proposed to alleviate these intrinsic issues with a high-efficiency electrolyte system. This special electrolyte enables Li-rich cathodes to deliver superior integrated performance with a high initial discharge capacity of 301 mAh·g^-1, outstanding cycling stability with a capacity retention of 88% at 0.5 C over 500 cycles, and a remarkable rate capability of 136 mAh·g^-1 at 5 C, respectively. What is more, the voltage fading is largely suppressed. Physical and electrochemical characterizations demonstrate that the robust CEI film formed on the cathode surface contributes to the improved electrochemical performance. This work provides a new approach to surmount defects of Li-rich materials and will largely promote their practical applications on Li-ion batteries.

Polydopamine Coated Lithium Lanthanum Titanate in Bilayer Membrane Electrolytes for Solid Lithium Batteries

The demand for solid lithium batteries with high energy density and safety boosts the development of solid-state electrolytes in which composite membrane electrolytes consisting of polymers and ceramic fillers are attractive. As the common ceramic filler, perovskite-structured Li_0.33La_0.557TiO₃ (LLTO) has great advantage on cost and environmental friendliness by using earth-abundant raw materials in the production. Nevertheless, the chemical instability of LLTO against Li-metal hinders its application. Herein, LLTO particles are coated by biodegradable polydopamine (PDA) layers and united with poly(vinylidene fluoride) (PVDF) to prepare composite electrolytes which perform superior stability against Li-metal. Besides, PVDF:LLTO membranes are assembled at cathode sides and show high voltage tolerance. The Li/Ni_0.6Mn_0.2Co_0.2O₂ cells with bilayer membrane electrolytes can deliver the specific capacity of 158.2 mAh g^-1 and maintain 83% capacity after 100 cycles at 0.1 C. Furthermore, based on the bilayer membranes with outstanding flexibility and stretchability, the cells can even survive under several extreme conditions, such as bending, twisting, crimping, and stretching. This study offers an environmentally friendly strategy to improve the stability of LLTO against Li and sheds light on the development of cost-effective solid electrolytes.

Polydopamine-Coated Garnet Particles Homogeneously Distributed in Poly(propylene carbonate) for the Conductive and Stable Membrane Electrolytes of Solid Lithium Batteries

Flexible membrane electrolytes consisting of Li_6.4La₃Zr_1.4Ta_0.6O₁₂ (LLZTO) fillers in poly(propylene carbonate) (PPC) are considered promising for developing solid lithium batteries with high energy density and safety. However, LLZTO particles tend to agglomerate owing to their high surface energy, especially concerning their distribution in PPC that has low surface energy. Moreover, basic LLZTO particles attack PPC, resulting in its decomposition. Such problems make it difficult to achieve membrane electrolytes of PPC/LLZTO with high conduction and stability. In this work, continuous polydopamine (PDA) layers with a thickness of 4 nm are coated on LLZTO particles. Characterized by synchrotron X-ray microtomography and scanning electron microscopy, the PDA-coated LLZTO particles show homogeneous dispersion in PPC, which is attributed to the reduced surface energy of the LLZTO particles. Besides, this coating hinders the reaction between LLZTO and PPC, which improves the chemical stability of the membrane electrolytes. Consequently, the cells based on membrane electrolytes with PDA-coated LLZTO particles in PPC show improved electrochemical performance and cycling stability. These results demonstrate that the strategy of coating basic LLZTO particles is powerful for enhancing their usability in the high-performance membrane electrolytes for solid lithium batteries.

Dynamic Changes in Charge Transfer Resistances during Cycling of Aprotic Li-O2 Batteries

Various electrolyte components have been investigated with the aim of improving the cycle life of lithium-oxygen (Li-O₂) batteries. A tetraglyme-based electrolyte containing dual anions of Br^- and NO₃^- is a promising electrolyte system in which the cell voltage during charging is reduced because of the redox-mediator function of the Br^-/Br₃^- and NO₂^-/NO₂ couples, while the Li-metal anode is protected by Li₂O formed via the reaction between Li metal and NO₃^-. To maximize the potential of this system, the fundamental factors that limit the cycle life should be clarified. In the present work, we used nondestructive electrochemical impedance spectroscopy to analyze the temporal change of the charge transfer resistances during cycles of Li-O₂ batteries with dual anions. The charge transfer resistance at the cathode was revealed to exhibit good correlation with the reduction of the discharge voltage. These results, combined with the results of electrode surface inspections, revealed that irreversible accumulation of insulating deposits such as Li₂O₂ and Li₂CO₃ on the cathode surface was a major cause of the short cycle life. Furthermore, the analyses of the time course of the solution resistance suggested that diminished reactivity between the redox mediators and Li₂O₂ was a critical factor that led to the irreversible accumulation of the less-reactive Li₂O₂ on the cathode and eventually to a shortened cycle life. These findings indicated that increasing the reactivity between Br₃^- and Li₂O₂ is essentially important for improving the cycle stability of Li-O₂ batteries and the reactivity can be nondestructively assessed by tracking the dynamic changes in the solution resistance.

Rational Tuning of a Li4SiO4-Based Hybrid Interface with Unique Stepwise Prelithiation for Dendrite-Proof and High-Rate Lithium Anodes

Lithium metal batteries (LMBs) are among the most promising candidates for high energy-density batteries. However, dendrite growth constitutes the biggest stumbling block to its development. Herein, Li₄SiO₄-dominating organic-inorganic hybrid layers are rationally designed by SiO₂ surface modification and the stepwise prelithiation process. SiO₂ nanoparticles construct a zigzagged porous structure, where a solid electrolyte interface (SEI) has grown and penetrated to form a conformal and compact hybrid surface. Such a first-of-this-kind structure enables enhanced Li dendrite prohibition and surface stability. The interfacial chemistry reveals a two-step prelithiation process that transfers SiO₂ into well-defined Li₄SiO₄, the components of which exhibits the lowest diffusion barrier (0.12 eV atom^-1) among other highlighted SEI species, such as LiF (0.175 eV atom^-1) for the current artificial layer. Therefore, the decorated Li allows for an improved high-rate full-cell performance (LiFePO₄/modified Li) with a much higher capacity of 65.7 mAh g^-1 at 5C (1C = 170 mAh g^-1) than its counterpart with bare Li (∼3 mAh g^-1). Such a protocol provides insights into the surface architecture and SEI component optimization through prelithiation in the target of stable, dendrite-proof, homogenized Li⁺ solid-state migration and high electrochemical performance for LMBs.

Synthesis of Hierarchical Porous Ni1.5Co1.5S4/g-C3N4 Composite for Supercapacitor with Excellent Cycle Stability

In this work, the hierarchical porous Ni1.5Co1.5S4/g-C3N4 composite was prepared by growing Ni1.5Co1.5S4 nanoparticles on graphitic carbon nitride (g-C3N4) nanosheets via a hydrothermal route. Due to the self-assembly of larger size g-C3N4 nanosheets as a skeleton, the prepared nanocomposite possesses a unique hierarchical porous structure that can provide short ions diffusion and fast electron transport. As a result, the Ni1.5Co1.5S4/g-C3N4 composite exhibits a high specific capacitance of 1827 F g-1 at a current density of 1 A g-1, which is 1.53 times that of pure Ni1.5Co1.5S4 (1191 F g-1). In particular, the Ni1.5Co1.5S4/g-C3N4//activated carbon (AC) asymmetric supercapacitor delivers a high energy density of 49.0 Wh kg-1 at a power density of 799.0 W kg-1. Moreover, the assembled device shows outstanding cycle stability with 95.5% capacitance retention after 8000 cycles at a high current density of 10 A g-1. The attractive performance indicates that the easily synthesized and low-cost Ni1.5Co1.5S4/g-C3N4 composite would be a promising electrode material for supercapacitor application.

Water-Based Dual-Cross-Linked Polymer Binders for High-Energy-Density Lithium-Sulfur Batteries

High-mass-loading electrodes with long-term stability have long been a great challenge for lithium-sulfur batteries (LSBs), since the conventional binders are unable to cope with the shuttling of lithium polysulfides and the structural damage in an electrode. Here, a novel water-based polymer, polyphosphate acid cross-linked chitosan ethylamide carbamide (PACEC), is developed as a binder to construct high-energy-density sulfur cathode and flexible LSBs. With a dual-cross-linked network, the PACEC shows excellent affinity with lithium polysulfides to relieve the shuttle effect and robust mechanical properties to stabilize the electrode. The sulfur cathode based on PACEC demonstrates a high sulfur loading of 14.8 mg cm^-2, the areal initial capacity of 17.5 mAh cm^-2, and Coulombic efficiency of 99.3%, while the amount of electrolyte is strictly limited to 6 μL mg^-1. More importantly, a robust pouch cell with an area of 6 cm² and only 177% oversized lithium can successfully integrate the energy density of 6.5 mAh cm^-2 with the cycling retention per cycle of 99.74% during 270 cycles and flexibility at a curvature of 3 mm. This study provides inspirations for the design of eco-friendly polymer binders and paving new ways for the development of LSBs.

Delayed Phase Transition and Improved Cycling/Thermal Stability by Spinel LiNi0.5Mn1.5O4 Modification for LiCoO2 Cathode at High Voltages

Increasing the upper cutoff voltage is capable of achieving higher charge capacity, whereas this strategy always causes a dramatic degradation of cycling and thermal stability. In this study, we first report spinel LiNi_0.5Mn_1.5O₄-modified LiCoO₂ (LiCoO₂@LiNi_0.5Mn_1.5O₄) as an outstanding cathode material. LiCoO₂@LiNi_0.5Mn_1.5O₄ retains capacity retention of 81.4% in a full cell between 4.45 and 3.00 V after 400 cycles at 0.5 C and is superior to 55.3% of pure LiCoO₂. In situ X-ray diffraction at an upper cutoff voltage of 4.75 V in combination with differential capacity curve reveals that the promoted cycling performance is ascribed to a delay of O3 → H1-3 → O1 phase transitions and a suppression of cobalt dissolution-induced side reactions. Moreover, LiNi_0.5Mn_1.5O₄ modification improves the thermal stability of LiCoO₂ by depressing the release of oxygen and the formation of cobalt dendrites.

LiF Protective Layer on a Li Anode: Toward Improving the Performance of Li-O2 Batteries with a Redox Mediator

The high charging overpotential and insulating/insoluble Li₂O₂ discharge products have seriously hindered the development of Li-O₂ batteries. Here, we report a highly concentrated 5.0 M lithium nitrate (LiNO₃) in N,N-dimethylacetamide (DMA) with 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) as a redox mediator (RM) and with the LiF layer by adding N,N-dimethyltrifluoroacetamide (DMTFA) to the electrolyte, which reduces the charge voltage (3.6 V over 65 cycles) and allows stable cycling for 100 cycles without noticeable fading in capacity. The Li plating/stripping test and electrochemical impedance of the Li/Li symmetric cell results reveal that a Li/Li symmetric cell with DMTFA is stable due to the formation of a LiF protective layer on the Li metal, which suppresses the RM shuttle effect, improving the interface stability of Li and the electrolyte and also restraining the growth of dendrite during cell cycling. This work may provide a novel strategy for designing a protective layer for Li anodes in Li-O₂ batteries when using an RM.

A High-Performance Primary Nanosheet Heterojunction Cathode Composed of Na0.44 MnO2 Tunnels and Layered Na2 Mn3 O7 for Na-Ion Batteries

Owing to its large capacity and high average potential, the structure and reversible O-redox compensation mechanism of Na₂ Mn₃ O₇ have recently been analyzed. However, capacity fade and low coulombic efficiency over multiple cycles have also been found to be a problem, which result from oxygen evolution at high charge voltages. Herein, a Na_0.44 MnO₂ ⋅Na₂ Mn₃ O₇ heterojunction of primary nanosheets was prepared by a sol-gel-assisted high-temperature sintering method. In the nanodomain regions, the close contact of Na_0.44 MnO₂ not only supplies multidimensional channels to improve the rate performance of the composite, but also plays the role of pillars for enhancing the cycling stability and coulombic efficiency; this is accomplished by suppressing oxygen evolution, which is confirmed by high-resolution (HR)TEM, cyclic voltammetry, and charge/discharge curves. As the cathode of a Na-ion battery, at 200 mA g^-1 after 100 cycles, the Na_0.44 MnO₂ ⋅Na₂ Mn₃ O₇ heterojunction retains an 88 % capacity and the coulombic efficiency approaches 100 % during the cycles. At 1000 mA g^-1 , the Na_0.44 MnO₂ ⋅Na₂ Mn₃ O₇ heterojunction has a discharge capacity of 72 mAh g^-1 . In addition, the average potential is as high as 2.7 V in the range 1.5-4.6 V. The above good performances indicate that heterojunctions are an effective strategy for addressing oxygen evolution by disturbing the long-range order distribution of manganese vacancies in the Mn-O layer.

Reversible Alloying of Phosphorene with Potassium and Its Stabilization Using Reduced Graphene Oxide Buffer Layers

High specific capacity materials that can store potassium (K) are essential for next-generation K-ion batteries. One such candidate material is phosphorene (the 2D allotrope of phosphorus (P)), but the potassiation capability of phosphorene has not yet been established. Here we systematically investigate the alloying of few-layer phosphorene (FLP) with K. Unlike lithium (Li) and sodium (Na), which form Li₃P and Na₃P, FLP alloys with K to form K₄P₃, which was confirmed by ex situ X-ray characterization as well as density functional theory calculations. The formation of K₄P₃ results in high specific capacity (∼1200 mAh g^-1) but poor cyclic stability (only ∼9% capacity retention in subsequent cycles). We show that this capacity fade can be successfully mitigated by the use of reduced graphene oxide (rGO) as buffer layers to suppress the pulverization of FLP. We studied the performance of rGO and single-walled carbon nanotubes (sCNTs) as buffer materials and found that rGO being a 2D material can better encapsulate and protect FLP relative to 1D sCNTs. The half-cell performance of FLP/rGO could also be successfully reproduced in a full-cell configuration, indicating the possibility of high-performance K-ion batteries that could offer a sustainable and low-cost alternative to Li-ion technology.

Amorphous Mo-Ta Oxide Nanotubes for Long-Term Stable Mo Oxide-Based Supercapacitors

With a large-scale usage of portable electric appliances, a high demand for increasingly high-density energy storage devices has emerged. MoO₃ has, in principle, a large potential as a negative electrode material in supercapacitive devices due to high charge densities that can be obtained from its reversible redox reactions. Nevertheless, the extremely poor electrochemical stability of MoO₃ in aqueous electrolytes prevents a practical use in high capacitance devices. In this work, we describe how to overcome this severe stability issue by forming amorphous molybdenum oxide/tantalum oxide nanotubes by anodic oxidation of a Mo-Ta alloy. The presence of a critical amount of Ta oxide (>20 at. %) prevents the electrochemical decay of the MoO₃ phase and thus yields an extremely high stability. Due to the protection provided by tantalum oxide, no capacitance losses are measureable after 10,000 charging/discharging cycles.

Cathode Interfacial Layer Formation via in Situ Electrochemically Charging in Aqueous Zinc-Ion Battery

The issue of material dissolution is common in aqueous batteries, leading to serious performance deterioration. However, it is difficult to be solved so far. In this study, a single component cathode solid electrolyte interface (SEI) layer (CaSO₄·2H₂O) is observed via in situ electrochemically charging process, as demonstrated in a Ca₂MnO₄ cathode for an aqueous zinc-ion battery. Density functional theory calculation confirms its electronic insulation and ionic conductor properties, indicating that it is an appropriate SEI film. The material dissolution seems to be effectively suppressed by the presence of the SEI layer on the cathode side. Meanwhile, this in situ formed interface layer is advantageous for lowering impedance, ameliorating interface, and reducing activation energy. As a result, significantly superior rate performance and cycle stability are exhibited. The observation of a protective SEI layer in an aqueous system may provide an insight into the development of high stability aqueous batteries.

Surface-Functionalized Coating for Lithium-Rich Cathode Material To Achieve Ultra-High Rate and Excellent Cycle Performance

Although the lithium-rich cathode material Li_1.2Mn_0.54Ni_0.13Co_0.13O₂, as a promising cathode material, has a high specific capacity, it suffers from capacity decay and discharge voltage decay during cycling. In this work, the specific capacity and discharge voltage of Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ are stabilized by surface-functionalized LiCeO₂ coating. We have conducted LiCeO₂ coating via a mild synchronous lithium strategy to protect the electrode surface from electrolyte attack. This optimized LiCeO₂ coating has high Li⁺ conductivity and abundant oxygen vacancies. The results demonstrate that 3% LiCeO₂-coated Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ exhibits the highest capacity retention rate at 1, 2, and 5 C after 200 cycles, which were 84.3%, 85.4%, and 86.3%, respectively. The discharge specific capacity was almost 1.3, 1.4, and 1.4 times that of the pristine electrode. In addition, the 3% LiCeO₂ electrode exhibited the least voltage decay of 0.409, 0.497, and 0.494 V at 1, 2, and 5 C, which was only about half of the pristine electrode. It should not be overlooked that the 3% LiCeO₂ electrode still exhibits a high capacity at high current densities of 1250 mA g^-1 (5 C) and 2500 mA g^-1 (10 C), and its specific discharge capacities are 190.5 and 160.6 mAh g^-1, respectively. These outstanding electrochemical properties benefit from surface-functionalized LiCeO₂ coatings. To better understand the mechanism of oxygen loss of lithium-rich materials, we propose the lattice oxygen migration path of the LiCeO₂-coated electrodes during the cycle. Our research provides a possible solution to the poor rate capability and cycle performance of cathode materials through surface-functionalized coatings.

MOF-Derived FeS/C Nanosheets for High Performance Lithium Ion Batteries

In recent years, transitional metal sulfides have received much attention as lithium ion batteries (LIBs) anode. In this paper, FeS/C nanosheets are prepared through Fe-based metal organic frameworks (Fe-MOFs) as a precursor. The electrochemical performance of FeS/C nanosheets has been obviously improved due to the synergistic effect of the oxygen doped carbon and the special flake morphology. When the test current density is 0.1 A/g, the initial discharge capacities of FeS/C nanosheets is up to 1702 mAh/g and can retain reversible capacities of about 830 mAh/g over 150 cycles with the voltage ranging from 0.01 V to 3 V. Moreover, these composite materials are proved to have a good rate performance and the capacities reach 460 mAh/g even at a higher current density of 5 A/g. This work suggests that FeS/C nanosheets are excellent anode materials for LIBs.