MOFs-Derived Flower-Like Hierarchically Porous Zn-Mn-Se/C Composite for Extraordinary Rate Performance and Durable Anode of Sodium-Ion and Potassium-Ion Batteries

Confining CoSe/MoSe2 Heterostructures in Interconnected Carbon Polyhedrons for Superior Potassium Storage

Metal selenides hold promise as feasible anode materials for potassium-ion batteries (PIBs), but still face problems such as poor potassium storage kinetics and dramatic volume expansion. Coupling heterostructure engineering with structural design could be an effective strategy for rapid and stable K+ storage. Herein, CoSe/MoSe2 heterojunction encapsulated in nitrogen-doped carbon polyhedron and further interconnected by three-dimensional nitrogen-doped carbon nanofibers (CoMoSe@NCP/NCFs) is ingeniously constructed. The abundant CoSe/MoSe2 heterointerfaces equipped with built-in electric fields and unique interconnected carbon polyhedrons (convenient electron/ion transfer pathway and robust mechanical buffer) promote the reaction kinetics and bolster the structural robustness. Accordingly, the CoMoSe@NCP/NCFs composite exhibits outstanding cycle life, with a capacity of 206 mAh g-1 preserved after 2500 cycles at 2 A g-1. Besides, CoMoSe@NCP/NCFs also achieves decent rate performance with 161 mAh g-1 at 10 A g-1. This research demonstrates a viable approach for constructing superior PIB anodes with both fast kinetics and high stability.

WS2@NC Square Hexahedral Nanosheets with Na+-DME-Solvent Cointercalation Mechanism for Fast and Durable Sodium Ion Storage

Sodium-ion batteries (SIBs) face challenges in practical applications due to substantial volume expansion of anode materials and unstable solid-electrolyte interphases (SEIs), limiting their cycling life, rate performance, and reaction kinetics. Here, we report the successful synthesis of unique N-doped carbon-coated WS2 hexahedral nanoporous core-shell structures (WS2@NC) combined with a Na+-solvation strategy for high capacity and long-life sodium storage. Nanoporous architecture facilitates sufficient electrolyte infiltration and buffers volume expansion. The uniform N-doped carbon shell improves the conductivity, the stable inorganic-rich SEI improves the cycle stability, and the Na+-solvent cointercalation partially avoids the desolvation process and realizes the rapid reaction kinetics. Unique structural design and excellent compatibility with electrolytes give the WS2@NC electrode unprecedented long cycling life and rate capability in SIBs (207.7 mAh g-1 after 10,000 cycles at 20 A g-1 and 343 mAh g-1 at 50 A g-1). This work provides critical insights into performance enhancement mechanisms, offering a crucial theoretical basis for SIB applications.

Li-Si alloy pre-lithiated silicon suboxide anode constructing a stable multiphase lithium silicate layer promoting Ion-transfer kinetics

Enhancing the initial Coulombic efficiency (ICE) and cycling stability of silicon suboxide (SiOx) anode is crucial for promoting its commercialization and practical implementation. Herein, we propose an economical and effective method for constructing pre-lithiated core-shell SiOx anodes with high ICE and stable interface during cycling. The lithium silicon alloy (Li13Si4) is used to react with SiOx in advance, allowing for improved ICE of SiOx without compromising its reversible specific capacity. The pre-lithiated surface layer contains uniform multiphase lithium silicates (L2SiO3, Li4SiO4, and Li2Si2O5) in the nanoscale. This multiphase lithium silicate layer exhibits mechanical robustness against variation of micro-stress, which can act as a buffer layer to relieve volume variation. In addition, analysis of dynamic electrochemical impedance spectroscopy (dEIS) and distribution of relaxation time (DRT) confirm that the multiphase lithium silicate layer enhances Li-ion diffusion kinetics and contributed to constructing stable SEI. As a result, the optimal L10-850 anode shows a high ICE of 85.3 %, together with a high specific capacity of 1771.5mAh mg-1. This work gives a perspective strategy to modify SiOx anodes by constructing a pre-lithiated surface layer with practical application potentials.

Hybrid supercapacitors using metal-organic framework derived nickel-sulfur compounds

HYPOTHESIS

Metal-organic frameworks (MOFs) are highly suitable precursors for supercapacitor electrode materials owing to their high porosity and stable backbone structures that offer several advantages for redox reactions and rapid ion transport.

EXPERIMENTS

In this study, a carbon-coated Ni9S8 composite (Ni9S8@C-5) was prepared via sulfuration at 500 ℃ using a spherical Ni-MOF as the sacrificial template.

FINDING

The stable carbon skeleton derived from Ni-MOF and positive structure-activity relationship due to the multinuclear Ni9S8 components resulted in a specific capacity of 278.06 mAh·g-1 at 1 A·g-1. Additionally, the hybrid supercapacitor (HSC) constructed using Ni9S8@C-5 as the positive electrode and the laboratory-prepared coal pitch-based activated carbon (CTP-AC) as the negative electrode achieved an energy density of 69.32 Wh·kg-1 at a power density of 800.06 W·kg-1, and capacity retention of 83.06 % after 5000 cycles of charging and discharging at 5 A·g-1. The Ni-MOF sacrificial template method proposed in this study effectively addresses the challenges associated with structural collapse and agglomeration of Ni9S8 during electrochemical reactions, thus improving its electrochemical performance. Hence, a simple preparation method is demonstrated, with broad application prospects in supercapacitor electrodes.

Towards metal selenides: a promising anode for sodium-ion batteries

Metal selenides have garnered significant attention as promising anode materials for sodium-ion batteries, thanks to their high theoretical capacity, excellent conductivity, and natural abundance. However, their potential is hampered by disappointing capacity retention and unsatisfactory lifespan, primarily attributed to volume expansion and unwanted structural collapse resulting from the insertion and extraction of relatively large Na+ ions during the charge and discharge processes. This feature article provides a brief overview of our endeavors to address the challenges associated with metal selenide-based anode materials, aiming to achieve high-performance electrode materials for sodium-ion batteries. Our strategy encompasses nanostructure design, materials composite engineering, heteroatoms doping, and topography and interface engineering. Additionally, future research directions are also outlined.

Synergistically Coupling Atomic-Level Defect-Manipulation and Nanoscopic-Level Interfacial Engineering Enables Fast and Durable Sodium Storage

Through inducing interlayer anionic ligands and functionally modifying conductive carbon-skeleton on the transition metal chalcogenides (TMCs) parent to achieve atomic-level defect-manipulation and nanoscopic-level architecture design is of great significance, which can broaden interlayer distance, optimize electronic structure, and mitigate structural deformation to endow high-efficiency battery performance of TMCs. Herein, an intriguing 3D biconcave hollow-tyre-like anode constituted by carbon-packaged defective-rich SnSSe nanosheet grafting onto Aspergillus niger spores-derived hollow-carbon (ANDC@SnSSe@C) is reported. Systematically experimental investigations and theoretical analyses forcefully demonstrate the existence of anion Se ligand and outer-carbon all-around encapsulation on the ANDC@SnSSe@C can effectively yield abundant structural defects and Na+-reactivity sites, accelerate rapid ion migration, widen interlayer spacing, as well as relieve volume expansion, thus further resolving the critical issues throughout the charge-discharge processes. As anticipated, as-fabricated ANDC@SnSSe@C anode contributes extraordinary reversible capacity, wonderful cyclic lifespan with 83.4% capacity retention over 2000 cycles at 20.0 A g-1, and exceptional rate capability. A series of correlated kinetic investigations and ex situ characterizations deeply reveal the underlying springheads for the ion-transport kinetics, as well as synthetically elucidate phase-transformation mechanism of the ANDC@SnSSe@C. Furthermore, the ANDC@SnSSe@C-based sodium ion full cell and hybrid capacitor offer high-capacity contribution and remarkable energy-density output, indicative of its great practicability.

Recent advances in rational design for high-performance potassium-ion batteries

The growing global energy demand necessitates the development of renewable energy solutions to mitigate greenhouse gas emissions and air pollution. To efficiently utilize renewable yet intermittent energy sources such as solar and wind power, there is a critical need for large-scale energy storage systems (EES) with high electrochemical performance. While lithium-ion batteries (LIBs) have been successfully used for EES, the surging demand and price, coupled with limited supply of crucial metals like lithium and cobalt, raised concerns about future sustainability. In this context, potassium-ion batteries (PIBs) have emerged as promising alternatives to commercial LIBs. Leveraging the low cost of potassium resources, abundant natural reserves, and the similar chemical properties of lithium and potassium, PIBs exhibit excellent potassium ion transport kinetics in electrolytes. This review starts from the fundamental principles and structural regulation of PIBs, offering a comprehensive overview of their current research status. It covers cathode materials, anode materials, electrolytes, binders, and separators, combining insights from full battery performance, degradation mechanisms, in situ/ex situ characterization, and theoretical calculations. We anticipate that this review will inspire greater interest in the development of high-efficiency PIBs and pave the way for their future commercial applications.

Unveiling the bifunctional roles of Cetyltrimethylammonium bromide in construction of Nb2CTx@MoSe2 heterojunction for fast potassium storage

Exploring robust electrode materials which could permit fast and reversible insertion/extraction of large K+ is a crucial challenge for potassium-ion batteries (PIBs). Smart interfacial design could facilitate electron/ion transport as well as assure the integrity of electrode. Herein, Cetyltrimethylammonium bromide (CTAB) was found to play bifunctional roles in construction of Nb2CTx@MoSe2 heterostructure. Firstly, functionalization of CTAB on the surface of Nb2CTx could influence the subsequent growth of MoSe2 by electrostatic effect, stereochemical effect and the synergetic Lewis acid-base interaction, leading to the formation of Nb2CTx@MoSe2 with tiled heterostructure. Secondly, the interlayer spacing of Nb2CTx was expanded from 0.77 to 1.21 nm owing to the pillar effect of CTAB. As excepted, the capacity retention was 80 % from 100 mA g-1 (406 mA h g-1) to 1000 mA g-1 concerning rate capability and the specific capacity maintained at 240 mA h g-1 (at 2000 mA g-1) over 300 cycles. The calculated DK values from Galvanostatic intermittent titration technique (GITT) measurement of the titled C-T-Nb2CTx@MoSe2@C electrode is two orders of magnitude larger than the traditional T-Nb2CTx@MoSe2@C electrode, further confirming intimate interface between MoSe2 and Nb2CTx could provide convenient potassium-ion transport channels and fast diffusion kinetics. Finally, ex-situ characterizations at different charging and discharging voltage stages, including ex-situ XRD/Raman/HRTEM/XPS have been carried out to reveal the potassium storage mechanism. This work provides a facile strategy for the regulation of interface engineering by the assist of CTAB which could extend to other MXenes-TMDs (Transition metal dichalcogenides) hybrid electrodes.

Reduced Graphene Oxide Modulated FeSe/C Anode Materials for High-Stable and Long-Life Potassium-Ion Batteries

Reduced graphene oxide (rGO) has been demonstrated to effectively enhance the potassium storage performance of transition metal selenides due to its robust mechanical properties and high conductivity. However, the impact of rGO on the electrode-electrolyte interface, a crucial factor in the electrochemical performance of potassium-ion batteries (PIBs), requires further exploration. In this study, we synthesized a seamless architecture of rGO on FeSe/C nanocrystals (FeSe/C@rGO). Comparative analysis between FeSe/C and FeSe/C@rGO reveals that the rGO layer exhibits robust adsorption energies towards EC and DEC, inducing the formation of organic-rich solid-electrolyte interphase (SEI) without damage to the structural integrity. Furthermore, incorporating rGO triggers K+ -ions into the double electrode layer (EDL), markedly improving the transport of K+ -ions. As a PIB anode, FeSe/C@rGO exhibits a reversible capacity of 332 mAh g-1 at 200 mA g-1 after 300 cycles, along with excellent long-term cycling stability, showcasing an ultralow decay rate of only 0.086 % per cycle after 1900 cycles at 1000 mA g-1 .

A self-sacrificing template strategy: In-situ construction of bimetallic MOF-derived self-supported CuCoSe nanosheet arrays for high-performance supercapacitors

Transition metal selenides (TMSs) are viewed as a prospective high-capacity electrode material for asymmetric supercapacitors (ASCs). However, the inability to expose sufficient active sites due to the limitation of the area involved in the electrochemical reaction severely limits their inherent supercapacitive properties. Herein, a self-sacrificing template strategy is developed to prepare self-supported CuCoSe (CuCoSe@rGO-NF) nanosheet arrays by in situ construction of copper-cobalt bimetallic organic framework (CuCo-MOF) on rGO-modified nickel foam (rGO-NF) and rational design of Se2- exchange process. Nanosheet arrays with high specific surface area are considered to be ideal platforms for accelerating electrolyte penetration and exposing rich electrochemical active sites. As a result, the CuCoSe@rGO-NF electrode delivers a high specific capacitance of 1521.6 F/g at 1 A/g, good rate performance and an excellent capacitance retention of 99.5% after 6000 cycles. The assembled ASC device has a high energy density of 19.8 Wh kg-1 at 750 W kg-1 and an ideal capacitance retention of 86.2% after 6000 cycles. This proposed strategy offers a viable strategy for designing and constructing electrode materials with superior energy storage performance.

Spatially Confined Fe7S8 Nanoparticles Anchored on a Porous Nitrogen-Doped Carbon Nanosheet Skeleton for High-Rate and Durable Sodium Storage

Iron sulfides are widely explored as anodes of sodium-ion batteries (SIBs) owing to high theoretical capacities and low cost, but their practical application is still impeded by poor rate capability and fast capacity decay. Herein, for the first time, we construct highly dispersed Fe₇S₈ nanoparticles anchored on a porous N-doped carbon nanosheet (CN) skeleton (denoted as Fe₇S₈/NC) with high conductivity and numerous active sites via facile ion adsorption and thermal evaporation combined procedures coupled with a gas sulfurization treatment. Nanoscale design coupled with a conductive carbon skeleton can simultaneously mitigate the above obstacles to obtain enhanced structural stability and faster electrode reaction kinetics. With the aid of density functional theory (DFT) calculations, the synergistic interaction between CNs and Fe₇S₈ can not only ensure enhanced Na⁺ adsorption ability but also promote the charge transfer kinetics of the Fe₇S₈/NC electrode. Accordingly, the designed Fe₇S₈/NC electrode exhibits remarkable electrochemical performance with superior high-rate capability (451.4 mAh g^-1 at 6 A g^-1) and excellent long-term cycling stability (508.5 mAh g^-1 over 1000 cycles at 4 A g^-1) due to effectively alleviated volumetric variation, accelerated charge transfer kinetics, and strengthened structural integrity. Our work provides a feasible and effective design strategy toward the low-cost and scalable production of high-performance metal sulfide anode materials for SIBs.

Bonding iron chalcogenides in a hierarchical structure for high-stability sodium storage

Owing to price-boom and low-reserve of Lithium ion batteries (LIBs), cost-cutting and well-stocked sodium ion batteries (SIBs) attract a lot of attention, aiming to develop an effective energy storage and conversion equipment. As a typical anode for SIBs, Iron sulfide (FeS) is difficult to maintain the high theoretical capacity. Structural instability and inherent low conductivity limit the cyclic and rate performance of FeS. Herein, hierarchical architecture of FeS-FeSe₂ coated with nitrogen-doped carbon (NC) is obtained by single-step solvothermal method and two-stage high-temperature treatments. Specifically, lattice imperfections provided by heterogeneous interfaces increase the Na⁺ storage sites and fasten ion/electron transfer. Synergistic effect induced by the hierarchical architecture effectively enhances the electrochemical activity and reduces the resistance, which contributes to the transfer kinetics of Na⁺. In addition, the phenomenon that heterogeneous interfaces provide more active site and extra migration Na⁺ path is also proved by density functional theory (DFT). As an anode for SIBs, FeS-FeSe₂/NC (FSSe/C) delivers highly reversible capacity (704.5 mAh·g^-1 after 120 cycles at 0.2 A·g^-1), excellent rate performance (326.3 mAh·g^-1 at 12 A·g^-1) and long-lasting durability (492.3 mAh·g^-1 after 1000 cycles at 4 A·g^-1 with 100 % capacity retention). Notably, the full battery, assembled with FSSe/C and Na₃V₂(PO₄)₃/C (NVP/C), delivers reversible capacity of 252.1 mAh·g^-1 after 300 cycles at 1 A·g^-1. This work provides a facile method to construct a hierarchical architecture anode for high-performance SIBs.

Graphene supported FeS2 nanoparticles with sandwich structure as a promising anode for High-Rate Potassium-Ion batteries

Pyrite FeS₂ now emerges as a promising anode for potassium-ion batteries (PIBs) due to its low cost and high theoretical capacity. However, the significant volume expansion, low electrical conductivity, and the ambiguous mechanism related to potassium storage severely hinder its development for PIBs anodes. Herein, FeS₂ nanostructures are skillfully dispersed on the graphene surface layer by layer (FeS₂@C-rGO) to form a sandwich structure by using Fe-based metal organic framework (Fe-MOF) as precursors. The unique structural design can improve the transfer kinetics of K⁺ and effectively buffer the volume expansion during cycling, thereby enhancing the potassium storage performance. As a result, the FeS₂@C-rGO delivers a high capacity of 550 mAh/g at a current density of 0.1 A/g. At a high rate of 2 A/g, the capacity can maintain 171 mAh/g even after 500 cycles. Moreover, the electrochemical reaction mechanism and potassium storage behavior are revealed by in-situ X-ray diffractionand density functional theory calculations. This work not only provides a novel insight into the structural design of electrode materials for high-performance PIBs, but also proposes a valuable understanding of the potassium storage mechanism of the FeS₂-based anode.