Boosting Dual-Directional Polysulfide Electrocatalysis via Bimetallic Alloying for Printable Li–S Batteries

The rational design of electrocatalyst has readily stimulated a burgeoning interest in expediting polysulfide conversion and hence essentially restricting the “shuttle effect” in Li–S systems. Nevertheless, seldom efforts have been devoted to probing the dual-directional polysulfide electrocatalysis to date. Herein, a CoFe alloy decorated mesoporous carbon sphere (CoFe-MCS) serving as a promising mediator for Li–S batteries is reported. Such bimetallic alloying boosts dual-directional electrocatalytic activity toward effective polysulfide conversion throughout detailed electroanalytic characterization, theoretical calculation, and operando instrumental probing. Accordingly, the S@CoFe-MCS cathode harvests a stable cycling with a low capacity decay rate of 0.062% per cycle over 500 cycles at 2.0 C. More encouragingly, benefiting from the optimized redox kinetics and delicate grid architecture, printable S@CoFe-MCS cathode achieves an excellent rate performance at a sulfur loading of 4.0 mg cm⁻² and advanced areal capacity of 6.0 mAh cm⁻² at 7.7 mg cm⁻². This work explores non-precious metal alloy electrocatalysts in printable cathodes toward dual-directional polysulfide conversion, holding great potential in the pursuit of Li–S commercialization.     

Visualizing Lithium Ion Transport in Solid-State Li–S Batteries Using 6Li Contrast Enhanced Neutron Imaging

The elucidation of lithium ion transport pathways through a solid electrolyte separator is a vital step toward development of reliable, functional all-solid-state batteries. Here, advantage has been taken of the significantly higher neutron attenuation coefficient of one of the most abundant stable isotopes of lithium, ⁶Li, with respect to that of naturally occurring lithium isotope mixture, to perform neutron imaging on a purpose built all-solid-state lithium–sulfur battery. Increasing the ⁶Li content in the anode while using natural lithium in the solid electrolyte separator and the cathode enhances the contrast such that it is possible to differentiate, during the initial discharge, between the mobile lithium ions diffusing through the cell from the anode and those that are initially located in the solid electrolyte. The sensitivity of neutrons to the different lithium isotopes means that operando neutron radiography allows demonstration of the lithium ion diffusion through the cell while in situ neutron tomography has permitted presentation, in three dimensions, of the distribution of the trapped lithium ions inside the cell in charged and discharged states.     

Transition Metal Compounds Family for Li–S Batteries: The DFT-Guide for Suppressing Polysulfides Shuttle

Lithium–sulfur batteries (LSBs) are considered as one of the best candidates for the next generation of high-energy-density storage devices owing to their superior theoretical energy density, high specific capacity, and sufficient sulfur reservoirs. However, the shuttle effect of soluble polysulfides and sluggish LiPSs redox kinetics restrict the further application of LSBs. The polysulfides shuttle effect can be efficiently alleviated and LiPSs conversion kinetics be accelerated by designing optimal transition metal compounds (TMCs) as multifunctional catalyst materials. Herein, recent advances about TMCs in LSBs are systematically summarized and analyzed. First of all, the intrinsic structural characteristics of TMCs and relevant application on their works to the adsorption energies studies are described in detail. Second, the bonding manners and structural properties are analyzed by density functional theory (DFT)-guided calculations, focusing on the adsorption and diffusion behavior between TMCs and LiPSs. Furthermore, the mechanism of LiPSs redox reaction conversion is studied from kinetics aspects, thus developing the continuous dynamic analysis on “adsorption–diffusion–conversion” toward LiPSs. Eventually, this study particularly highlights the importance of modification engineering and provides a forward-looking overview for its further application prospects by introduction of the previous advanced studies in LSBs.     

Boosting Catalytic Activity by Seeding Nanocatalysts onto Interlayers to Inhibit Polysulfide Shuttling in Li–S Batteries

The shuttling of soluble lithium polysulfides (LiPSs) is one of the main bottlenecks to the practical use of Li–S batteries. It is reported that in situ synthesized ultrasmall vanadium nitride nanoparticles dispersed on porous nitrogen-doped graphene (denoted VN@NG) as a catalytic interlayer solves this problem. The ultrasmall size of VN particles provide ample triple-phase interfaces (the reactive interfaces among VN nanocatalyst, NG conductive substrate, and electrolyte) for accelerating LiPS conversion and Li₂S deposition, which greatly reduces the accumulation of LiPSs in the electrolyte and therefore inhibits the shuttle effect. Their high catalytic activity is confirmed by a reduced activation energy of the Li₂S₄ conversion step based on temperature-dependent cyclic voltammetric (CV) measurements and the reduced shuttle effect is detected by in situ Raman spectra. With the VN nanocatalyst, Li–S batteries have an outstanding cycling performance with a low capacity decay rate of 0.075% per cycle over 500 cycles at 2 C. A high capacity retention of 84.5% over 200 cycles at 0.2 C is achieved with a high sulfur loading of 7.3 mg cm⁻².     

Sieve Tube-Inspired Polysulfide Cathode with Long-Range Ordered Channels and Localized Capture-Catalysis Microenvironments for Efficient Li–S Batteries

Accelerating the conversion of soluble lithium polysulfides (LiPSs) to solid Li₂S₂/Li₂S through single-atom cathodes has emerged as a promising strategy for realizing high-performance lithium–sulfur batteries. However, rationally optimizing the conversion effects and spatial capture abilities of LiPSs intermediates on the atomic catalytic sites is extremely required but still faces enormous challenges. Here, inspired by the delicate structure of sieve tubes in plants, Fe single-atom cathode (channel-Fe_SAC) equipped with long-range ordered channels and localized capture-catalysis microenvironments towards efficient LiPSs conversion is reported on designing. Benefiting from the individual and stable catalytic areal for localized capture and migration inhibition abilities on LiPSs and fully confined triple-phase boundaries between atomic catalytic centers, conductive carbon, and electrolytes, the channel-Fe_SAC can effectively convert polysulfides, thus eliminating the shuttle effects and generation of inactive LiPSs. It is also elucidated that the channel-Fe_SAC exhibits superior migration inhibition of polysulfide and accelerates Li₂S deposition/conversion kinetics compared with bowl-Fe_SAC and flat-Fe_SAC. The outstanding areal capacity and cycling stability under high sulfur loading and low electrolyte/sulfur ratio verify that the channel-Fe_SAC holds great potential as cathodes for high-performance cathodes. This work offers vital insights into the essential roles of bioinspired fully confined channels and catalytic microenvironments in polysulfide catalysis for efficient lithium–sulfur batteries.     

A Multifunctional Catalytic Interlayer for Propelling Solid–Solid Conversion Kinetics of Li2S2 to Li2S in Lithium–Sulfur Batteries

The theoretically high-energy-density lithium–sulfur batteries (LSBs) are seriously limited by the disadvantages including the shuttle effect of soluble lithium polysulfides (LiPSs) and the sluggish sulfur redox kinetics, especially for the most difficult solid–solid conversion of Li₂S₂ to Li₂S. Herein, a multifunctional catalytic interlayer to improve the performance of LSBs is tried to introduce, in which Fe_1–xS/Fe₃C nanoparticles are embedded in the N/S dual-doped carbon network (NSC) composed by nanosheets and nanotubes (the final product is named as FeSC@NSC). The well-designed 3D NSC network endows the interlayer with a satisfactory LiPSs capture-catalytic ability, thus ensuring fast redox reaction kinetics and suppressing LiPSs shuttling. The density functional theory calculations disclose the catalytic mechanisms that FeSC@NSC greatly improves the liquid–solid (LiPSs to Li₂S₂) conversion and unexpectedly the solid–solid (Li₂S₂ to Li₂S) one. As a result, the LSBs based on the FeSC@NSC interlayer can achieve a high specific capacity of 1118 mAh g⁻¹ at a current density of 0.2 C, and a relatively stable capacity of 415 mAh g⁻¹ at a large current density of 2.0 C after 700 cycles as well as superior rate performance.     

Lithium Tritelluride as an Electrolyte Additive for Stabilizing Lithium Deposition and Enhancing Sulfur Utilization in Anode-Free Lithium–Sulfur Batteries

Despite the potential to become the next-generation energy storage technology, practical lithium–sulfur (Li–S) batteries are still plagued by the poor cyclability of the lithium-metal anode and sluggish conversion kinetics of S species. In this study, lithium tritelluride (LiTe₃), synthesized with a simple one-step process, is introduced as a novel electrolyte additive for Li–S batteries. LiTe₃ quickly reacts with lithium polysulfides and functions as a redox mediator to greatly improve the cathode kinetics and the utilization of active materials in the cathode. Moreover, the formation of a Li₂TeS₃/Li₂Te-enriched interphase layer on the anode surface enhances ionic transport and stabilizes Li deposition. By regulating the chemistry on both the anode and cathode sides, this additive enables a stable operation of anode-free Li–S batteries with only 0.1 m concentration in conventional ether-based electrolytes. The cell with the LiTe₃ additive retains 71% of the initial capacity after 100 cycles, while the control cell retains only 23%. More importantly, with high utilization of Te, the additive enables significantly better cyclability of anode-free pouch full-cells under lean electrolyte conditions.     

In Situ Reconstruction of Electrocatalysts for Lithium–Sulfur Batteries: Progress and Prospects

The current research of Li–S batteries primarily focuses on increasing the catalytic activity of electrocatalysts to inhibit the polysulfide shuttling and enhance the redox kinetics. However, the stability of electrocatalysts is largely neglected, given the premise that they are stable over extended cycles. Notably, the reconstruction of electrocatalysts during the electrochemical reaction process has recently been proposed. Such in situ reconstruction process inevitably leads to varied electrocatalytic behaviors, such as catalytic sites, selectivity, activity, and amounts of catalytic sites. Therefore, a crucial prerequisite for the design of highly effective electrocatalysts for Li–S batteries is an in-depth understanding of the variation of active sites and the influence factors for the in situ reconstruction behaviors, which has not achieved a fundamental understanding and summary. This review comprehensively summarizes the recent advances in understanding the reconstruction behaviors of different electrocatalysts for Li–S batteries during the electrochemical reaction process, mainly including metal nitrides, metal oxides, metal selenides, metal fluorides, metals/alloys, and metal sulfides. Moreover, the unexplored issues and major challenges of understanding the reconstruction chemistry are summarized and prospected. Based on this review, new perspectives are offered into the reconstruction and true active sites of electrocatalysts for Li–S batteries.     

Anchoring Polysulfides and Accelerating Redox Reaction Enabled by Fe-Based Compounds in Lithium–Sulfur Batteries

The synergetic mechanism of chemisorption and catalysis play an important role in developing high-performance lithium–sulfur (Li–S) batteries. Herein, a 3D lather-like porous carbon framework containing Fe-based compounds (including Fe₃C, Fe₃O₄, and Fe₂O₃), named FeCFeOC, is designed as the sulfur host and the interlayer on separator. Due to the strong chemisorption and catalytic ability of FeCFeOC composite, the soluble lithium polysulfides (LiPSs) are first adsorbed and anchored on the surface of the FeCFeOC composite and then are catalyzed to accelerate their conversion reaction. In addition, the Fe_xO_y in Fe-based compounds can spontaneously react with LiPSs to form magnetic FeS_x species with a larger size, further blocking the penetration of LiPSs cross the separator. As a result, the assembled Li–S cells show excellent long-term stability (748 mAh g⁻¹ over 500 cycles at 1.0 C, and ≈0.036% decay per cycle for 1000 cycles at 3.0 C), a superb rate capability with 659 mAh g⁻¹ at 5.0 C, and lower electrochemical polarization. This work introduces a feasible strategy to anchor and accelerate the conversion of LiPSs by designing the multifunctional Fe-based compounds with high chemisorption and catalytic activity, which advances the large-scale application of high-performance Li–S batteries.     

Morphology Control of Li2S Deposition via Geometrical Effect of Cobalt-Edged Nickel Alloy to Improve Performance of Lithium–Sulfur Batteries

Rechargeable lithium–sulfur batteries operate based on the interconversion between sulfur and Li₂S. Due to its insoluble and insulated nature, Li₂S deposition is kinetically sluggish, which has an important effect on performance of lithium–sulfur batteries. In this work, cobalt-edged nickel alloy is designed and used as host material of sulfur cathodes to manipulate the behavior and morphology of Li₂S deposition. It is found that Co and Ni have different catalytic kinetic characteristics for Li₂S deposition reactions, and the difference in nucleation and growth rates of Li₂S and geometrical effect of Co-edged Ni alloy can cause a well-spaced morphology to prevent premature surface passivation, thereby improving sulfur utilization and rate capability of the cathodes. As a result, the thick sulfur cathode using cobalt-edged nickel as host material with a sulfur loading of 4.0 mg cm⁻² shows an initial capacity of 1229.3 mA h g⁻¹ at electrolyte/sulfur ratio of 8 µL mg⁻¹, as well as high capacity retention of 92.2% at 0.2 C during 100 cycles. These results provide an alternative perspective not only for developing new mixed host materials for lithium–sulfur batteries, and also for further understanding the existing works using composite host materials.     

Advanced Engineering for Cathode in Lithium–Oxygen Batteries: Flexible 3D Hierarchical Porous Architecture Design and Its Functional Modification

Modern technology constantly requires smaller, more efficient lithium–oxygen batteries (LOBs). To meet this need, a chemical vapor deposition (CVD) method is used to create an innovative cathode design with both a hierarchical porous nanostructure and a 3D flexible macroscopical morphology. This method employs architectural optimization to further improve cathodic ORR and OER performance via heteroatom doping, surface-sprouted carbon nanofibers (CNFs) grafting, and boundary exposing. The cathode consists of a 3D hierarchical porous graphene foam (PGF), along with RuO₂ nanoparticles impregnated and nitrogen doped CNFs (RuO₂@NCNFs), where the PGF serves as a structural support and cathodic current collector, and the RuO₂@NCNFs work as a superior bi-functional catalyst. The cathode delivers an outstanding discharge capacity of 8440 mAh g_cathode⁻¹ while maintaining a recharge plateau at ≈4.0 V, and can cycle for over 700 rounds without obvious degeneration under a fixed capacity. Notably, this free-standing cathode can be directly used in LOBs without the need for additional substrates or current collectors. Therefore, the current densities and capacities herein are calculated based on the total weight of the cathodes. These results demonstrate the RuO₂@NCNFs-PGF cathode's remarkable potential for LOB applications, and this rational cathodic structure may be extended to other highly efficient catalyst applications.     

TiO2-Induced Conversion Reaction Eliminating Li2CO3 and Pores/Voids Inside Garnet Electrolyte for Lithium–Metal Batteries

Garnet Li₇La₃Zr₂O₁₂ (LLZO) is regarded as a promising solid electrolyte due to its high Li⁺ conductivity and excellent chemical stability, but suffers from grain boundary resistance and porous structure which restrict its practical applications in lithium–metal batteries. Herein, a novel and highly efficient TiO₂-induced conversion strategy is proposed to generate Li ion-conductive Li_0.5La_0.5TiO₃, which can simultaneously eliminate the pre-existing pores/voids and contamination Li₂CO₃. The Li/LLZTO-5TiO₂/Li symmetric cell exhibits a high critical current density of 1.1 mA cm⁻² at 25°C, and the long-term lithium cycling stability of over 1500 h at 0.1 mA cm⁻². More importantly, the excellent performance of LLZTO-5TiO₂ electrolyte is verified by LiCoO₂/LiFePO₄ coupled full cells. For example, The LiCoO₂ coupled full cell exhibits a significant discharge rate capacity of 108 mAh g⁻¹ at 0.1 C, and a discharge capacity retention rate of 91.23% even after 150 cycles of charge and discharge. COMSOL Multiphysics and density functional theory calculation reveal that LLZTO-5TiO₂ electrolyte has a strong lithium affinity and uniform Li ions distribution, which can improve the cycle stability of Li–metal batteries by preventing dendrite growth.     

Combined Defect and Heterojunction Engineering in ZnTe/CoTe2@NC Sulfur Hosts Toward Robust Lithium–Sulfur Batteries

Lithium–sulfur batteries (LSBs) are feasible candidates for the next generation of energy storage devices, but the shuttle effect of lithium polysulfides (LiPSs) and the poor electrical conductivity of sulfur and lithium sulfides limit their application. Herein, a sulfur host based on nitrogen-doped carbon (NC) coated with small amount of a transition metal telluride (TMT) catalyst is proposed to overcome these limitations. The properties of the sulfur redox catalyst are tuned by adjusting the anion vacancy concentration and engineering a ZnTe/CoTe₂ heterostructures. Theoretical calculations and experimental data demonstrate that tellurium vacancies enhance the adsorption of LiPSs, while the formed TMT/TMT and TMT/C heterostructures as well as the overall architecture of the composite simultaneously provide high Li⁺ diffusion and fast electron transport. As a result, v-ZnTe/CoTe₂@NC/S sulfur cathodes show excellent initial capacities up to 1608 mA h g⁻¹ at 0.1C and stable cycling with an average capacity decay rate of 0.022% per cycle at 1C during 500 cycles. Even at a high sulfur loading of 5.4 mg cm^–2, a high capacity of 1273 mA h g⁻¹ at 0.1C is retained, and when reducing the electrolyte to 7.5 µL mg⁻¹, v-ZnTe/CoTe₂@NC/S still maintains a capacity of 890.8 mA h g⁻¹ after 100 cycles at 0.1C.     

In Situ Deformation Topology of COFs with Shortened Channels and High Redox Properties for Li–S Batteries

Covalent organic frameworks (COFs) with various topologies are typically synthesized by selecting and designing connecting units with rich shapes. However, this process is time-consuming and labour-intensive. Besides, the tight stacking of COFs layers greatly restrict their structural advantages. It is crucial to effectively exploit the high porosity and active sites of COFs by topological design. Herein, for the first time, inducing in situ topological changes in sub-chemometric COFs by adding graphene oxide (GO) without replacing the monomer, is proposed. Surprisingly, GO can slow down the intermolecular stacking and induce rearrangement of COFs nanosheets. The channels of D- [4+3] COFs are significantly altered while the stacking of periodically expanded framework is weakened. This not only maximizes the exposure of pore area and polar groups, but also shortens the channels and increases the redox activity, which enables high loading while enhancing host-guest interactions. This topological transformation to exhibit the structural features of COFs for efficient application is an innovative molecular design strategy.     

A Robust Ternary Heterostructured Electrocatalyst with Conformal Graphene Chainmail for Expediting Bi-Directional Sulfur Redox in Li–S Batteries

Designing high-performance electrocatalysts for boosting aprotic electrochemistry is of vital importance to drive longevous Li–S batteries. Nevertheless, investigations on probing the electrocatalytic endurance and protecting the catalyst activity yet remain elusive. Here, a ternary graphene-TiO₂/TiN (G-TiO₂/TiN) heterostructure affording conformal graphene chainmail is presented as an efficient and robust electrocatalyst for expediting sulfur redox kinetics. The G-TiO₂/TiN heterostructure synergizes adsorptive TiO₂, catalytic TiN, and conductive graphene armor, thus enabling abundant anchoring points for polysulfides and sustained active sites to allow smooth bi-directional electrocatalysis. Encouragingly, in situ crafted graphene chainmail ensures favorable protection of inner TiO₂/TiN to retain their catalytic robustness towards durable sulfur chemistry. As expected, sulfur cathodes mediated by ternary G-TiO₂/TiN harvest an impressive rate capability (698.8 mAh g⁻¹ at 5.0 C), favorable cycling stability (a low decay of 0.054% per cycle within 1000 cycles), and satisfactory areal capacity under elevated loading (delivering 8.63 mAh cm⁻² at a sulfur loading of 10.4 mg cm⁻²). The ternary heterostructure design offers an in-depth insight into the electrocatalyst manipulation and protection toward long lifespan Li–S batteries.     

Integrating Energy Band Alignment and Oxygen Vacancies Engineering of TiO2 Anatase/Rutile Homojunction for Kinetics-Enhanced Li–S Batteries

The inferior shuttle effect of intermediate lithium polysulfides and the sluggish kinetics of sulfur redox reaction are two serious puzzles for the application of lithium–sulfur batteries. Herein, energy band alignment is combined with oxygen vacancies engineering to obtain TiO₂ anatase/rutile homojunction (A/R-TiO₂) with effective immobilization and high-efficiency catalytic conversion of polysulfides. Theoretical calculations and experiments reveal that the near perfect energy band alignment in A/R-TiO₂ is conducive to fluent charge transfer and high catalytic activity, while the rich oxygen vacancies are engineered to provide abundant active sites for anchoring and accelerating conversion of soluble polysulfides. As a result, a battery with A/R-TiO₂-modified separator delivers a marked sulfur utilization (1210 mAh g⁻¹ at 0.1 C and 689 mAh g⁻¹ at 1 C, 3.75 mg cm⁻²) and a high capacity retention of 63% over 300 cycles at 0.5 C (3.25 mg cm⁻²). More importantly, the A/R-TiO₂-modified separator endows the pouch cell with a high capacity of 128.5 mAh at 0.05 C with a lean electrolyte/sulfur ratio for practical application (S loading: 4 mg cm⁻²).     

Expediting Stepwise Sulfur Conversion via Spontaneous Built-In Electric Field and Binary Sulfiphilic Effect of Conductive NbB2-MXene Heterostructure in Lithium–Sulfur Batteries

Fabricating metal boride heterostructures and deciphering their interface interaction mechanism on accelerating polysulfide conversion at atomic levels are meaningful yet challenging in lithium–sulfur batteries (LSBs). Herein, novel highly-conductive and binary sulfiphilic NbB₂-MXene heterostructures are elaborately designed with spontaneous built-in electric field (BIEF) via a simple one-step borothermal reduction strategy. Experimental and theoretical results reveal that Nb and B atoms can chemically bond with polysulfides, thereby enriching chemical anchor and catalytic active sites. Meanwhile, the spontaneous BIEF induces interfacial charge redistribution to make more electrons transferred to surface NbB₂ sites, thereby weakening its strong adsorption property yet accelerating polysulfide transfer and electron diffusion on hetero-interface, so providing moderate polysulfide adsorb-ability yet decreasing sulfur-species conversion energy barriers, further boosting the intrinsically catalytic activity of NbB₂-MXene for accelerated bidirectional sulfur conversion. Thus, S/NbB₂-MXene cathode presents high initial capacity of 1310.1 mAh g⁻¹ at 0.1 C, stable long-term lifespan with 500 cycles (0.076% capacity decay per cycle) at 1 C, and large areal capacity of 6.5 mAh cm⁻² (sulfur loading: 7.0 mg cm⁻² in lean electrolyte of 5 µL mg_s⁻¹) at 0.1 C. This work clearly unveils the mechanism of interfacial BIEF and binary sulfiphilic effect on accelerating stepwise sulfur conversion at atomic levels.     

Vacancy-Defect Topological Insulators Bi2Te3−x Embedded in N and B Co-Doped 1D Carbon Nanorods Using Ionic Liquid Dopants for Kinetics-Enhanced Li–S Batteries

Lithium–sulfur (Li–S) batteries are hindered by the shuttle effect and the sluggish redox kinetics of polysulfides. In this study, topological insulators (TIs) Bi₂Te_3−x with abundant Te vacancies embedded in N and B co-doped carbon nanorods (Bi₂Te_3−x@NBCNs) are synthesized and used as sulfur host composites for high-performance Li–S batteries. Bi₂Te_3−x@NBCNs effectively enhance the intrinsic conductivity, strengthened the chemical affinity, and accelerated the redox kinetics of polysulfides. 1D carbon nanorods with N and B co-doped heteroatoms endowed with abundant polar sites improve the chemical affinity of polysulfides, while the embedded Bi₂Te_3−x nanoparticles further promote the nucleation and electrodeposition of Li₂S₂/Li₂S. In situ Raman spectroscopy confirms that Bi₂Te_3−x@NBCNs effectively reduced cathode-side accumulation of polysulfides and suppressed the shuttle effect. Owing to the extraordinary synergistic effects of rich heteroatom polar sites and conductive topological surface states, Bi₂Te_3−x@NBCN-based cells exhibit a high initial specific capacity of 1264 mAh g⁻¹ at 0.2 C and ultra-long lifetime (>1000 cycles, with a degradation rate of 0.02% per cycle at 1.0 C). The fundamental insights offered by this work are likely to enable improvement of the electrochemical performance of Li–S batteries based on TI materials.     

Bi-Metallic Coupling-Induced Electronic-State Modulation of Metal Phosphides for Kinetics-Enhanced and Dendrite-Free Li–S Batteries (Adv. Funct. Mater. 14/2023)

Lithium–sulfur (Li–S) batteries are considered as next-generation promising batteries, yet suffer from severe capacity decay and low-rate capability. Transition metal compounds can solve these problems due to their unique electronic band structure, good chemical adsorption ability, and exceptional catalytic capability. Unraveling the essence of electronic states of metal compounds can fundamentally guide their structure design and promote Li–S battery performance. Herein, bi-metallic coupling-induced electronic-state modulation of metal phosphides is reported for kinetics-enhanced and dendrite-free Li–S batteries. Bimetallic phosphides nanoparticles-anchored N, P-co-doped porous carbons (NiCoP–NPPC) are facilely constructed via a laser-induced micro-explosion strategy. Theoretical calculations reveal that the electronic-state can be modulated via Ni Co coupling, leading to lower polysulfides/Li⁺ diffusion and conversion barriers. As a result, the assembled Li–S full cells based on NiCoP–NPPC exhibit greatly improved capacity (1150 mAh g^-1 at 0.5 C) and cycle stability (84.3% capacity retention after 1000 cycles). Furthermore, they can be operated even under lean electrolyte (5.2 µL mg^-1) with a high sulfur loading (6.9 mg cm^-2), achieving a high areal capacity of 6.8 mAh cm^-2 at 0.5 C. This study demonstrates that bi-metallic coupling-induced electronic-state modulation is an effective approach for developing high-performance Li–S batteries.     

Cationic–Anionic Redox Chemistry in Multivalent Metal-Ion Batteries: Recent Advances,Reaction Mechanism,Advanced Characterization Techniques,and Prospects

Rechargeable multivalent metal-ion batteries (MMIBs) have garnered a surge of attention as competitive candidates for large-scale energy storage applications owing to their high capacity, abundant resources, and good security. However, their practical implementation is still stuck at the prototype stage, mainly plagued with the lack of suitable cathode materials capable of reversible insertion/extraction of multivalent ions and the intrinsically complicated redox reaction mechanism. Recently, anionic redox chemistry has shown to be an effective strategy to increase energy density, providing a new research direction for the next generation of high-energy rechargeable batteries. Unfortunately, anion redox chemistry has not received sufficient attention in MMIBs so far. Here, the fundamental principle and mechanism of anionic redox reactions in MMIBs are discussed and the recent advances regarding cathode materials based on cooperative cationic–anionic redox (CCAR) mechanism are summarized. Additionally, various advanced characterization techniques for studying the anionic redox process are highlighted, aiming to effectively illustrate the underlying reaction mechanism. Finally, challenges and perspectives for the future research on cationic–anionic redox chemistry in MMIBs are proposed. Insight into the significance of CCAR chemistry is provided here in MMIBs, presenting a new avenue for the development of high-energy-density cathode materials for MMIBs.