Ultrathin Nanosheet Assembled Sn0.91Co0.19S2 Nanocages with Exposed (100) Facets for High‐Performance Lithium‐Ion Batteries

Ultrathin 2D inorganic nanomaterials are good candidates for lithium‐ion batteries, as well as the micro/nanocage structures with unique and tunable morphologies. Meanwhile, as a cost‐effective method, chemical doping plays a vital role in manipulating physical and chemical properties of metal oxides and sulfides. Thus, the design of ultrathin, hollow, and chemical doped metal sulfides shows great promise for the application of Li‐ion batteries by shortening the diffusion pathway of Li ions as well as minimizing the electrode volume change. Herein, ultrathin nanosheet assembled Sn_0.91Co_0.19S₂ nanocages with exposed (100) facets are first synthesized. The as‐prepared electrode delivers an excellent discharge capacity of 809 mA h g^?1 at a current density of 100 mA g^?1 with a 91% retention after 60 discharge–charge cycles. The electrochemical performance reveals that the Li‐ion batteries prepared by Sn_0.91Co_0.19S₂ nanocages have high capacity and great cycling stability.     

Anionic Se‐Substitution toward High‐Performance CuS1−xSex Nanosheet Cathode for Rechargeable Magnesium Batteries

Rechargeable magnesium batteries (rMBs) are promising as the most ideal further energy storage systems but lack competent cathode materials due to sluggish redox reaction kinetics. Herein, developed is an anionic Se‐substitution strategy to improve the rate capability and the cycling stability of 2D CuS_1?xSe_x nanosheet cathodes through an efficient microwave‐induced heating method. The optimized CuS_1?xSe_x (X = 0.2) nanosheet cathode can exhibit high reversible capacity of 268.5 mAh g^?1 at 20 mA g^?1 and good cycling stability (140.4 mAh g^?1 at 300 mA g^?1 upon 100 cycles). Moreover, the CuS_1?xSe_x (X = 0.2) nanosheet cathode can deliver remarkable rate capability with a reversible capacity of 119.2 mAh g^?1 at 500 mA g^?1, much higher than the 21.7 mAh g^?1 of pristine CuS nanosheets. The superior electrochemical performance can be ascribed to the enhanced reaction kinetics, enriched cation storage active sites, and shortened ion diffusion pathway of the CuS_1?xSe_x nanosheet. Therefore, tuning anionic chemical composition demonstrates an effective strategy to develop novel cathode materials for rMBs.     

Interlayer‐Spacing‐Regulated VOPO4 Nanosheets with Fast Kinetics for High‐Capacity and Durable Rechargeable Magnesium Batteries

Owing to the low‐cost, safety, dendrite‐free formation, and two‐electron redox properties of magnesium (Mg), rechargeable Mg batteries are considered as promising next‐generation secondary batteries with high specific capacity and energy density. However, the clumsy Mg²⁺ with high polarity inclines to sluggish Mg insertion/deinsertion, leading to inadequate reversible capacity and rate performance. Herein, 2D VOPO₄ nanosheets with expanded interlayer spacing (1.42 nm) are prepared and applied in rechargeable magnesium batteries for the first time. The interlayer expansion provides enough diffusion space for fast kinetics of MgCl⁺ ion flux with low polarization. Benefiting from the structural configuration, the Mg battery exhibits a remarkable reversible capacity of 310 mAh g^?1 at 50 mA g^?1, excellent rate capability, and good cycling stability (192 mAh g^?1 at 100 mA g^?1 even after 500 cycles). In addition, density functional theory (DFT) computations are conducted to understand the electrode behavior with decreased MgCl⁺ migration energy barrier compared with Mg²⁺. This approach, based on the regulation of interlayer distance to control cation insertion, represents a promising guideline for electrode material design on the development of advanced secondary multivalent‐ion batteries.     

High‐Energy/Power and Low‐Temperature Cathode for Sodium‐Ion Batteries: In Situ XRD Study and Superior Full‐Cell Performance

Sodium‐ion batteries (SIBs) are still confronted with several major challenges, including low energy and power densities, short‐term cycle life, and poor low‐temperature performance, which severely hinder their practical applications. Here, a high‐voltage cathode composed of Na₃V₂(PO₄)₂O₂F nano‐tetraprisms (NVPF‐NTP) is proposed to enhance the energy density of SIBs. The prepared NVPF‐NTP exhibits two high working plateaux at about 4.01 and 3.60 V versus the Na⁺/Na with a specific capacity of 127.8 mA h g^?1. The energy density of NVPF‐NTP reaches up to 486 W h kg^?1, which is higher than the majority of other cathode materials previously reported for SIBs. Moreover, due to the low strain (≈2.56% volumetric variation) and superior Na transport kinetics in Na intercalation/extraction processes, as demonstrated by in situ X‐ray diffraction, galvanostatic intermittent titration technique, and cyclic voltammetry at varied scan rates, the NVPF‐NTP shows long‐term cycle life, superior low‐temperature performance, and outstanding high‐rate capabilities. The comparison of Ragone plots further discloses that NVPF‐NTP presents the best power performance among the state‐of‐the‐art cathode materials for SIBs. More importantly, when coupled with an Sb‐based anode, the fabricated sodium‐ion full‐cells also exhibit excellent rate and cycling performances, thus providing a preview of their practical application.     

Ultrathin Anatase TiO2 Nanosheets for High‐Performance Photocatalytic Hydrogen Production

An ethanol solvothermal route has been developed to prepare ultrathin anatase TiO₂ nanosheets with dominant {001} facets (≈97%), a thickness of ≈2.5 nm, and a side length of ≈200 nm. The introduction of ethanol solvent significantly enhances the content of surface chemisorbed F^? on the TiO₂ nanosheet, which has a higher stability and further lowers the surface energy of {001} facets, giving rise to the large percentage of active {001} facets. Adopting well‐defined morphology, such nanosheets loaded with 1 wt% Pt exhibit an H₂ evolution rate as high as 17.86 mmol h^?1 g^?1, and the corresponding apparent quantum efficiency has been determined to be 34.2%.     

Ultrathin 2D Mesoporous TiO2/rGO Heterostructure for High‐Performance Lithium Storage

Lithium‐ion batteries (LIBs) have been widely applied and studied as an effective energy supplement for a variety of electronic devices. Titanium dioxide (TiO₂), with a high theoretical capacity (335 mAh g^?1) and low volume expansion ratio upon lithiation, has been considered as one of the most promising anode materials for LIBs. However, the application of TiO₂ is hindered by its low electrical conductivity and slow ionic diffusion rate. Herein, a 2D ultrathin mesoporous TiO₂/reduced graphene (rGO) heterostructure is fabricated via a layer‐by‐layer assembly process. The synergistic effect of ultrathin mesoporous TiO₂ and the rGO nanosheets significantly enhances the ionic diffusion and electron conductivity of the composite. The introduced 2D mesoporous heterostructure delivers a significantly improved capacity of 350 mAh g^?1 at a current density of 200 mA g^?1 and excellent cycling stability, with a capacity of 245 mAh g^?1 maintained over 1000 cycles at a high current density of 1 A g^?1. The in situ transmission electron microscopy analysis indicates that the volume of the as‐prepared 2D heterostructures changes slightly upon the insertion and extraction of Li⁺, thus contributing to the enhanced long‐cycle performance.     

尖晶石型Li1-xMgxMn2O4正极材料的制备和性质

采用高温固相分段反应法制备了尖晶石LiMn2O4和Mg2 掺杂的Li1-xMgxMn2O4(x=0.05、0.1)材料,对材料进行了XRD结构分析和电化学性能等测试,结果表明:Mg2 掺杂样品Li1-xMgxMn2O4(x=0.05、0.1)仍保持尖晶石相Fd3m结构;循环性能明显改善,室温条件下50次循环后,样品Li0.9Mg0.1Mn2O4的放电容量为100mAh/g,容量保持率为9.9%,而LiMn204容量衰减率仅为18.1%.     

Recent Progress in the Design of Advanced Cathode Materials and Battery Models for High‐Performance Lithium‐X (X = O2, S,Se, Te,I2, Br2) Batteries

Recent advances and achievements in emerging Li‐X (X = O₂, S, Se, Te, I₂, Br₂) batteries with promising cathode materials open up new opportunities for the development of high‐performance lithium‐ion battery alternatives. In this review, we focus on an overview of recent important progress in the design of advanced cathode materials and battery models for developing high‐performance Li‐X (X = O₂, S, Se, Te, I₂, Br₂) batteries. We start with a brief introduction to explain why Li‐X batteries are important for future renewable energy devices. Then, we summarize the existing drawbacks, major progress and emerging challenges in the development of cathode materials for Li‐O₂ (S) batteries. In terms of the emerging Li‐X (Se, Te, I₂, Br₂) batteries, we systematically summarize their advantages/disadvantages and recent progress. Specifically, we review the electrochemical performance of Li‐Se (Te) batteries using carbonate‐/ether‐based electrolytes, made with different electrode fabrication techniques, and of Li‐I₂ (Br₂) batteries with various cell designs (e.g., dual electrolyte, all‐organic electrolyte, with/without cathode‐flow mode, and fuel cell/solar cell integration). Finally, the perspective on and challenges for the development of cathode materials for the promising Li‐X (X = O₂, S, Se, Te, I₂, Br₂) batteries is presented.     

Highly Electrochemically‐Reversible Mesoporous Na2FePO4F/C as Cathode Material for High‐Performance Sodium‐Ion Batteries

As promising cathode materials, iron‐based phosphate compounds have attracted wide attention for sodium‐ion batteries due to their low cost and safety. Among them, sodium iron fluorophosphate (Na₂FePO₄F) is widely noted due to its layered structure and high operating voltage compared with NaFePO₄. Here, a mesoporous Na₂FePO₄F@C (M‐NFPF@C) composite derived from mesoporous FePO₄ is synthesized through a facile ball‐milling combined calcination method. Benefiting from the mesoporous structure and highly conductive carbon, the M‐NFPF@C material exhibits a high reversible capacity of 114 mAh g^?1 at 0.1 C, excellent rate capability (42 mAh g^?1 at 10 C), and good cycling performance (55% retention after 600 cycles at 5 C). The high plateau capacity obtained (>90% of total capacity) not only shows high electrochemical reversibility of the as‐prepared M‐NFPF@C but also provides high energy density, which mainly originates from its mesoporous structure derived from the mesoporous FePO₄ precursor. The M‐NFPF@C serves as a promising cathode material with high performance and low cost for sodium‐ion batteries.     

Freestanding 1T‐MnxMo1–xS2–ySey and MoFe2S4–zSez Ultrathin Nanosheet‐Structured Electrodes for Highly Efficient Flexible Solid‐State Asymmetric Supercapacitors

Fabrication of hierarchical nanosheet arrays of 1T phase of transition‐metal dichalcogenides is indeed a critical task, but it holds immense potential for energy storage. A single‐step strategy is employed for the fabrication of stable 1T‐Mn_xMo_1–xS_2–ySe_y and MoFe₂S_4–zSe_z hierarchical nanosheet arrays on carbon cloth as positive and negative electrodes, respectively. The flexible asymmetric supercapacitor constructed with these two electrodes exhibits an excellent electrochemical performance (energy density of ≈69 Wh kg^?1 at a power density of 0.985 kW kg^?1) with ultralong cyclic stability of ≈83.5% capacity retention, after 10 000 consecutive cycles. Co‐doping of the metal and nonmetal boosts the charge storage ability of the transition‐metal chalcogenides following enrichment in the metallic 1T phase, improvement in the surface area, and expansion in the interlayer spacing in tandem, which is the key focus of the present study. This study explicitly demonstrates the exponential enhancement of specific capacity of MoS₂ following intercalation and doping of Mn and Se, and Fe₂S₃ following doping of Mo and Se could be an ideal direction for the fabrication of novel energy‐storage materials with high‐energy storage ability.     

Strategies toward High‐Performance Cathode Materials for Lithium–Oxygen Batteries

Rechargeable aprotic lithium (Li)–O₂ batteries with high theoretical energy densities are regarded as promising next‐generation energy storage devices and have attracted considerable interest recently. However, these batteries still suffer from many critical issues, such as low capacity, poor cycle life, and low round‐trip efficiency, rendering the practical application of these batteries rather sluggish. Cathode catalysts with high oxygen reduction reaction (ORR) and evolution reaction activities are of particular importance for addressing these issues and consequently promoting the application of Li–O₂ batteries. Thus, the rational design and preparation of the catalysts with high ORR activity, good electronic conductivity, and decent chemical/electrochemical stability are still challenging. In this Review, the strategies are outlined including the rational selection of catalytic species, the introduction of a 3D porous structure, the formation of functional composites, and the heteroatom doping which succeeded in the design of high‐performance cathode catalysts for stable Li–O₂ batteries. Perspectives on enhancing the overall electrochemical performance of Li–O₂ batteries based on the optimization of the properties and reliability of each part of the battery are also made. This Review sheds some new light on the design of highly active cathode catalysts and the development of high‐performance lithium–O₂ batteries.     

Strong Coupling of MoS2 Nanosheets and Nitrogen‐Doped Graphene for High‐Performance Pseudocapacitance Lithium Storage

Layered material MoS₂ is widely applied as a promising anode for lithium‐ion batteries (LIBs). Herein, a scalable and facile dopamine‐assisted hydrothermal technique for the preparation of strongly coupled MoS₂ nanosheets and nitrogen‐doped graphene (MoS₂/N‐G) composite is developed. In this composite, the interconnected MoS₂ nanosheets are well wrapped onto the surface of graphene, forming a unique veil‐like architecture. Experimental results indicate that dopamine plays multiple roles in the synthesis: a binding agent to anchor and uniformly disperse MoS₂ nanosheets, a morphology promoter, and the precursor for in situ nitrogen doping during the self‐polymerization process. Density functional theory calculations further reveal that a strong interaction exists at the interface of MoS₂ nanosheets and nitrogen‐doped graphene, which facilitates the charge transfer in the hybrid system. When used as the anode for LIBs, the resulting MoS₂/N‐G composite electrode exhibits much higher and more stable Li‐ion storage capacity (e.g., 1102 mAh g^?1 at 100 mA g^?1) than that of MoS₂/G electrode without employing the dopamine linker. Significantly, it is also identified that the thin MoS₂ nanosheets display outstanding high‐rate capability due to surface‐dominated pseudocapacitance contribution.     

Recent Development in Separators for High‐Temperature Lithium‐Ion Batteries

Lithium‐ion batteries (LIBs) are promising energy storage devices for integrating renewable resources and high power applications, owing to their high energy density, light weight, high flexibility, slow self‐discharge rate, high rate charging capability, and long battery life. LIBs work efficiently at ambient temperatures, however, at high‐temperatures, they cause serious issues due to the thermal fluctuation inside batteries during operation. The separator is a key component of batteries and is crucial for the sustainability of LIBs at high‐temperatures. The high thermal stability with minimum thermal shrinkage and robust mechanical strength are the prime requirements along with high porosity, ionic conductivity, and electrolyte uptake for highly efficient high‐temperature LIBs. This Review deals with the recent studies and developments in separator technologies for high‐temperature LIBs with respect to their structural layered formation. The recent progress in monolayer and multilayer separators along with the developed preparation methodologies is discussed in detail. Future challenges and directions toward the advancement in separator technology are also discussed for achieving remarkable performance of separators in a high‐temperature environment.     

Ultrathin VSe2 Nanosheets with Fast Ion Diffusion and Robust Structural Stability for Rechargeable Zinc‐Ion Battery Cathode

The realizing of high‐performance rechargeable aqueous zinc‐ion batteries (ZIBs) with high energy density and long cycling life is promising but still challenging due to the lack of suitable layered cathode materials. The work reports the excellent zinc‐ion storage performance as‐observed in few‐layered ultrathin VSe₂ nanosheets with a two‐step Zn²⁺ intercalation/de‐intercalation mechanism verified by ex situ X‐ray diffraction (XRD) and X‐ray photoelectron spectroscopy (XPS) characterizations. The VSe₂ nanosheets exhibit a discharge plateau at 1.0–0.7 V, a specific capacity of 131.8 mAh g^?1 (at 0.1 A g^?1), and a high energy density of 107.3 Wh kg^?1 (at a power density of 81.2 W kg^?1). More importantly, outstanding cycle stability (capacity retention of 80.8% after 500 cycles) without any activation process is achieved. Such a prominent cyclic stability should be attributed to its fast Zn²⁺ diffusion kinetics (D_Zn²⁺ ≈ 10^?8 cm^?2 s^?1) and robust structural/crystalline stability. Density functional theory (DFT) calculation further reveals a strong metallic characteristic and optimal zinc‐ion diffusion pathway with a hopping energy barrier of 0.91 eV. The present finding implies that 2D ultrathin VSe₂ is a very promising cathode material in ZIBs with remarkable battery performance superior to other layered transitional metal dichalcogenides.     

Few‐Layered Tin Sulfide Nanosheets Supported on Reduced Graphene Oxide as a High‐Performance Anode for Potassium‐Ion Batteries

Anodes involving conversion and alloying reaction mechanisms are attractive for potassium‐ion batteries (PIBs) due to their high theoretical capacities. However, serious volume change and metal aggregation upon potassiation/depotassiation usually cause poor electrochemical performance. Herein, few‐layered SnS₂ nanosheets supported on reduced graphene oxide (SnS₂@rGO) are fabricated and investigated as anode material for PIBs, showing high specific capacity (448 mAh g^?1 at 0.05 A g^?1), high rate capability (247 mAh g^?1 at 1 A g^?1), and improved cycle performance (73% capacity retention after 300 cycles). In this composite electrode, SnS₂ nanosheets undergo sequential conversion (SnS₂ to Sn) and alloying (Sn to K₄Sn₂₃, KSn) reactions during potassiation/depotassiation, giving rise to a high specific capacity. Meanwhile, the hybrid ultrathin nanosheets enable fast K storage kinetics and excellent structure integrity because of fast electron/ionic transportation, surface capacitive‐dominated charge storage mechanism, and effective accommodation for volume variation. This work demonstrates that K storage performance of alloy and conversion‐based anodes can be remarkably promoted by subtle structure engineering.