Selective S/Li2S Conversion via in-Built Crystal Facet Self-Mediation: Toward High Volumetric Energy Density Lithium-Sulfur Batteries

In Situ Electrochemical Evolution of Amorphous Metallic Borides Enabling Long Cycling Room-/Subzero-Temperature Sodium-Sulfur Batteries

Room temperature sodium-sulfur batteries (RT Na-S) have garnered significant attention for their high energy density and cost-effectiveness, positioning them as a promising alternative to lithium-ion batteries. However, they encounter challenges such as the dissolution of sodium polysulfides and sluggish kinetics. Introducing high-activity electrocatalysts and enhancing the density of active sites represents an efficient strategy to enhance reaction kinetics. Here, an amorphous Ni-B material that undergoes electrochemical evolution to generate the NiSx phase within an operational sodium-sulfur battery, contrasting with the crystalline NiB counterpart is fabricated. Electrochemical cycling facilitated the establishment of an interface between the amorphous Ni-B and NiSx, leading to heightened catalytic activity and improved reaction kinetics. Consequently, batteries utilizing the amorphous Ni-B showcased a notable initial specific capacity of 1487 mAh g-1 at 0.2 A g-1, exhibiting exceptional performance under high current densities of 5 A g-1, in low-temperature conditions (-10 °C), with high sulfur loading, and in pouch cell configurations.

Manipulating Atomic-Coupling in Dual-Cavity Boride Nanoreactor to Achieve Hierarchical Catalytic Engineering for Sulfur Cathode

The catalytic process of Li2S formation is considered a key pathway to enhance the kinetics of lithium-sulfur batteries. Due to the system's complexity, the catalytic behavior is uncertain, posing significant challenges for predicting activity. Herein, we report a novel cascaded dual-cavity nanoreactor (NiCo-B) by controlling reaction kinetics, providing an opportunity for achieving hierarchical catalytic behavior. Through experimental and theoretical analysis, the multilevel structure can effectively suppress polysulfides dissolution and accelerate sulfur conversion. Furthermore, we differentiate the adsorption (B-S) and catalytic effect (Co-S) in NiCo-B, avoiding catalyst deactivation caused by excessive adsorption. As a result, the as-prepared battery displays high reversible capacity, even with sulfur loading of 13.2 mg cm-2 (E/S=4 μl mg-1), the areal capacity can reach 18.7 mAh cm-2.

2D Tungsten Borides Induced Interfacial Modulation Engineering Toward High-Rate Performance Zinc-Iodine Battery

Aqueous zinc-iodine batteries are promising candidates for large-scale energy storage due to their high energy density and low cost. However, their development is hindered by several drawbacks, including zinc dendrites, anode corrosion, and the shuttle of polyiodides. Here, the design of 2D-shaped tungsten boride nanosheets with abundant borophene subunits-based active sites is reported to guide the (002) plane-dominated deposition of zinc while suppressing side reactions, which facilitates interfacial nucleation and uniform growth of zinc. Meanwhile, the interfacial d-band orbits of tungsten sites can further enhance the anchoring of polyiodides on the surface, to promote the electrocatalytic redox conversion of iodine. The resulting tungsten boride-based I2 cathodes in zinc-iodine cells exhibit impressive cyclic stability after 5000 cycles at 50 C, which accelerates the practical applications of zinc-iodine batteries.

In Situ-Constructed Multifunctional Composite Anode with Ultralong-Life Toward Advanced Lithium-Metal Batteries

Metallic lithium is the most competitive anode material for next-generation high-energy batteries. Nevertheless, the extensive volume expansion and uncontrolled Li dendrite growth of lithium metal not only cause potential safety hazards but also lead to low Coulombic efficiency and inferior cycling lifespan for Li metal batteries. Herein, a multifunctional dendrite-free composite anode (Li/SnS2) is proposed through an in situ melt-infusion strategy. In this configuration, the 3D cross-linked porous Li2S/Li22Sn5 framework facilitates the rapid penetration of electrolytes and accommodates the volume expansion during the repeated Li-plating process. Meanwhile, the lithiophilic Li2S phases with a low Li+ transport barrier ensure preferential Li deposition, effectively avoiding uneven electron distribution. Moreover, the Li22Sn5 electron conductors with appropriate Li+ bonding ability guarantee rapid charge transport and mass transfer. Most importantly, the steady multifunctional skeleton with sufficient inner interfaces (Li2S/Li22Sn5) in the whole electrode, not only realizes the redistribution of the localized free electron, contributing to the decomposition of Li clusters, but also induces a planar deposition model, thus restraining the generation of Li dendrites. Consequently, an unprecedented cyclability of over 6 500 h under an ultrahigh areal capacity of 10 mAh cm-2 and a current rate of 20 mA cm-2 is achieved for the prepared Li2S/Li22Sn5 composite anode. Moreover, the assembled Li/SnS2||LiFePO4 (LFP) pouch full-cells also demonstrate remarkable rate capability and a convincing cycling lifespan of more than 2 000 cycles at 2 C.

Toward robust lithium-sulfur batteries via advancing Li2S deposition

Lithium-sulfur batteries (LSBs) with two typical platforms during discharge are prone to the formation of soluble lithium polysulfides (LiPS), leading to a decrease in the cycling life of the battery. Under practical working conditions, the transformation of S8 into Li2S is cross-executed rather than a stepwise reaction, where the liquid LiPS to solid Li2S conversion can occur at a high state of charge (SOC) to maintain the current requirement. Therefore, advancing Li2S deposition can effectively reduce the accumulation of LiPSs and ultimately improve the reaction kinetics. Herein, a "butterfly material" GeS2-MoS2/rGO is used as a sulfur host. Rich catalytic heterointerfaces can be obtained via the abundant S-S bonds formed between GeS2 and MoS2. MoS2 (left wing) can enhance LiPS adsorption, while the lattice-matching nature of Fdd2 GeS2 (right wing) and Fm3̄m Li2S can induce multiple nucleation and regulate the 3D growth of Li2S. Li2S deposition can be advanced to occur at 80% SOC, thereby effectively inhibiting the accumulation of soluble LiPSs. Attributed to the synergistic effect of catalytic and lattice-matching properties, robust coin and pouch LSBs can be achieved.

Rechargeable Metal-Sulfur Batteries: Key Materials to Mechanisms

Rechargeable metal-sulfur batteries are considered promising candidates for energy storage due to their high energy density along with high natural abundance and low cost of raw materials. However, they could not yet be practically implemented due to several key challenges: (i) poor conductivity of sulfur and the discharge product metal sulfide, causing sluggish redox kinetics, (ii) polysulfide shuttling, and (iii) parasitic side reactions between the electrolyte and the metal anode. To overcome these obstacles, numerous strategies have been explored, including modifications to the cathode, anode, electrolyte, and binder. In this review, the fundamental principles and challenges of metal-sulfur batteries are first discussed. Second, the latest research on metal-sulfur batteries is presented and discussed, covering their material design, synthesis methods, and electrochemical performances. Third, emerging advanced characterization techniques that reveal the working mechanisms of metal-sulfur batteries are highlighted. Finally, the possible future research directions for the practical applications of metal-sulfur batteries are discussed. This comprehensive review aims to provide experimental strategies and theoretical guidance for designing and understanding the intricacies of metal-sulfur batteries; thus, it can illuminate promising pathways for progressing high-energy-density metal-sulfur battery systems.

Applications, prospects and challenges of metal borides in lithium sulfur batteries

Although the lithium-sulfur (Li-S) battery has a theoretical capacity of up to 1675 mA h g-1, its practical application is limited owing to some problems, such as the shuttle effect of soluble lithium polysulfides (LiPSs) and the growth of Li dendrites. It has been verified that some transition metal compounds exhibit strong polarity, good chemical adsorption and high electrocatalytic activities, which are beneficial for the rapid conversion of intermediate product in order to effectively inhibit the "shuttle effect". Remarkably, being different from other metal compounds, it is a significant characteristic that both metal and boron atoms of transition metal borides (TMBs) can bind to LiPSs, which have shown great potential in recent years. Here, for the first time, almost all existing studies on TMBs employed in Li-S cells are comprehensively summarized. We firstly clarify special structures and electronic features of metal borides to show their great potential, and then existing strategies to improve the electrochemical properties of TMBs are summarized and discussed in the focus sections, such as carbon-matrix construction, morphology control, heteroatomic doping, heterostructure formation, phase engineering, preparation techniques. Finally, the remaining challenges and perspectives are proposed to point out a direction for realizing high-energy and long-life Li-S batteries.

Boosting Polysulfide Redox Kinetics by Temperature-Induced Metal-Insulator Transition Effect of Tungsten-Doped Vanadium Dioxide for High-Temperature Lithium-Sulfur Batteries

The practical application of Li-S batteries is still severely restricted by poor cyclic performance caused by the intrinsic polysulfides shuttle effect, which is even more severe under the high-temperature condition owing to the inevitable increase of polysulfides' solubility and diffusion rate. Herein, tungsten-doped vanadium dioxide (W-VO2 ) micro-flowers are employed with first-order metal-insulator phase transition (MIT) property as a robust and multifunctional modification layer to hamper the shuttle effect and simultaneously improve the thermotolerance of the common separator. Tungsten doping significantly reduces the transition temperature from 68 to 35 °C of vanadium dioxide, which renders the W-VO2 easier to turn from the insulating monoclinic phase into the metallic rutile phase. The systematic experiments and theoretical analysis demonstrate that the temperature-induced in-suit MIT property endows the W-VO2 catalyst with strong chemisorption against polysulfides, low energy barrier for liquid-to-solid conversion, and outstanding diffusion kinetics of Li-ion under high temperatures. Benefiting from these advantages, the Li-S batteries with W-VO2 modified separator exhibit significantly improved rate and long-term cyclic performance under 50 °C. Remarkably, even at an elevated temperature (80 °C), they still exhibit superior electrochemical performance. This work opens a rewarding avenue to use phase-changing materials for high-temperature Li-S batteries.

Modulating d-Band Electronic Structures of Molybdenum Disulfide via p/n Doping to Boost Polysulfide Conversion in Lithium-Sulfur Batteries

Polysulfide shuttle effect and sluggish sulfur reaction kinetics severely impede the cycling stability and sulfur utilization of lithium-sulfur (Li-S) batteries. Modulating d-band electronic structures of molybdenum disulfide electrocatalysts via p/n doping is promising to boost polysulfide conversion and suppress polysulfide migration in lithium-sulfur batteries. Herein, p-type V-doped MoS2 (V-MoS2 ) and n-type Mn-doped MoS2 (Mn-MoS2 ) catalysts are well-designed. Experimental results and theoretical analyses reveal that both of them significantly increase the binding energy of polysulfides on the catalysts' surface and accelerate the sluggish conversion kinetics of sulfur species. Particularly, the p-type V-MoS2 catalyst exhibits a more obvious bidirectional catalytic effect. Electronic structure analysis further demonstrates that the superior anchoring and electrocatalytic activities are originated from the upward shift of the d-band center and the optimized electronic structure induced by duplex metal coupling. As a result, the Li-S batteries with V-MoS2 modified separator exhibit a high initial capacity of 1607.2 mAh g-1 at 0.2 C and excellent rate and cycling performance. Moreover, even at a high sulfur loading of 6.84 mg cm-2 , a favorable initial areal capacity of 8.98 mAh cm-2 is achieved at 0.1 C. This work may bring widespread attention to atomic engineering in catalyst design for high-performance Li-S batteries.

Manipulating Sulfur Conversion Kinetics through Interfacial Built-In Electric Field Enhanced Bidirectional Mott-Schottky Electrocatalysts in Lithium-Sulfur Batteries

Efficient electrocatalysts and catalytic mechanisms remain a pressing need in Li-S electrochemistry to address lithium polysulfide (LiPS) shuttling and enhance conversion kinetics. This study presents the development of multifunctional VO2@rGO heterostructures, incorporating interfacial built-in electric field (BIEF) enhancement, as a Mott-Schottky electrocatalyst for Li-S batteries. Electrochemical experiments and theoretical analysis demonstrate that the interfacial BIEF between VO2 and rGO induces self-driven charge redistribution, resulting in accelerated charge transport rates, enhanced LiPS chemisorption, reduced energy barriers for Li2S nucleation/decomposition, and improved Li-ion diffusion behavior. The Mott-Schottky electrocatalyst, combining the strengths of VO2's anchoring ability, rGO's metallic conductivity, and BIEF's optimized charge transport, exhibits an outstanding "trapping-conversion" effect. The modified Li-S battery with a VO2@rGO-modified separator achieves a highly reversible capacity of 558.0 mAh g-1 at 2 C over 600 cycles, with an average decay rate of 0.048% per cycle. This research offers valuable insights into the design of Mott-Schottky electrocatalysts and their catalytic mechanisms, advancing high-efficiency Li-S batteries and other multielectron energy storage and conversion devices.

Highly stable lithium sulfur batteries enhanced by flocculation and solidification of soluble polysulfides in routine ether electrolyte

Lithium-sulfur batteries (LSBs) are among the most promising next-generation high energy density energy-storage systems. However, practical application has been hindered by fundamental problems, especially shuttling by the higher-order polysulfides (PSs) and slow redox kinetics. Herein, a novel electrolyte-based strategy is proposed by adding an ultrasmall amount of the low-cost and commercially available cationic antistatic agent octadecyl dimethyl hydroxyethyl quaternary ammonium nitrate (SN) into a routine ether electrolyte. Due to the strong cation-anion interaction and bridge-bonding with SN, rapid flocculation of the soluble polysulfide intermediates into solid-state polysulfide-SN sediments is found, which significantly inhibited the adverse shuttling effect. Moreover, a catalytic effect was also demonstrated for conversion of the polysulfide-SN intermediates, which enhanced the redox kinetics of Li-S batteries. Encouragingly, for cells with only 0.1 % added SN, an initial specific capacity of 783.6 mAh/g and a retained specific capacity of 565.7 mAh/g were found at 2C after 200 cycles, which corresponded to an ultralow capacity decay rate of only 0.014 % per cycle. This work may provide a simple and promising regulation strategy for preparing highly stable Li-S batteries.

Steering Bidirectional Sulfur Redox via Geometric/Electronic Mediator Comodulation for Li-S Batteries

Mediator design has stimulated ever-increasing attention to help tackle a surge of detrimental caveats in Li-S realms, mainly pertaining to rampant polysulfide shuttling and sluggish redox kinetics. Nevertheless, universal designing philosophy, despite being highly sought-after, remains still elusive to date. Herein, we present a generic and simple material strategy to allow the target fabrication of advanced mediator toward boosted sulfur electrochemistry. This trick is done by the geometric/electronic comodulation of a prototype VN mediator, where the interplay of its triple-phase interface, favorable catalytic activity, and facile ion diffusivity is conducive to steering bidirectional sulfur redox kinetics. In laboratory tests, the thus-derived Li-S cells manifest impressive cyclic performances with a capacity decay rate of 0.07% per cycle over 500 cycles at 1.0 C. Moreover, under a sulfur loading of 5.0 mg cm^-2, the cell could sustain a durable areal capacity of 4.63 mAh cm^-2. Our work is anticipated to lay a theory-to-application foundation for rationalizing the design and modulation of reliable polysulfide mediators in working Li-S batteries.

Interface Engineering Toward Expedited Li2 S Deposition in Lithium-Sulfur Batteries: A Critical Review

Lithium-sulfur batteries (LSBs) with superior energy density are among the most promising candidates of next-generation energy storage techniques. As the key step contributing to 75% of the overall capacity, Li₂ S deposition remains a formidable challenge for LSBs applications because of its sluggish kinetics. The severe kinetic issue originates from the huge interfacial impedances, indicative of the interface-dominated nature of Li₂ S deposition. Accordingly, increasing efforts have been devoted to interface engineering for efficient Li₂ S deposition, which has attained inspiring success to date. However, a systematic overview and in-depth understanding of this critical field are still absent. In this review, the principles of interface-controlled Li₂ S precipitation are presented, clarifying the pivotal roles of electrolyte-substrate and electrolyte-Li₂ S interfaces in regulating Li₂ S depositing behavior. For the optimization of the electrolyte-substrate interface, efforts on the design of substrates including metal compounds, functionalized carbons, and organic compounds are systematically summarized. Regarding the regulation of electrolyte-Li₂ S interface, the progress of applying polysulfides catholytes, redox mediators, and high-donicity/polarity electrolytes is overviewed in detail. Finally, the challenges and possible solutions aiming at optimizing Li₂ S deposition are given for further development of practical LSBs. This review would inspire more insightful works and, more importantly, may enlighten other electrochemical areas concerning heterogeneous deposition processes.

Zinc-Assisted Cobalt Ditelluride Polyhedra Inducing Lattice Strain to Endow Efficient Adsorption-Catalysis for High-Energy Lithium-Sulfur Batteries

Developing a conductive catalyst with high catalytic activity is considered to be an effective strategy for improving cathode kinetics of lithium-sulfur batteries, especially at large current density and with lean electrolytes. Lattice-strain engineering has been a strategy to tune the local structure of catalysts and to help understand the structure-activity relationship between strain and catalyst performance. Here, Co_0.9 Zn_0.1 Te₂ @NC is constructed after zinc atoms are uniformly doped into the CoTe₂ lattice. The experimental/theoretical results indicate that a change of the coordination environment for the cobalt atom by the lattice strain modulates the d-band center with more electrons occupied in antibonding orbitals, thus balancing the adsorption of polysulfides and the intrinsic catalytic effect, thereby activating the intrinsic activity of the catalyst. Benefiting from the merits, with only 4 wt% dosages of catalyst in the cathode, an initial discharge capacity of 1030 mAh g^-1 can be achieved at 1 C and stable cycling performances are achieved for 1500/2500 cycles at 1 C/2 C. Upon sulfur loading of 7.7 mg cm^-2 , the areal capacity can reach 12.8 mAh cm^-2 . This work provides a guiding methodology for the design of catalytic materials and refinement of adsorption-catalysis strategies for the rational design of cathode in lithium-sulfur batteries.

A Zn8 Double-Cavity Metallacalix[8]arene as Molecular Sieve to Realize Self-Cleaning Intramolecular Tandem Transformation of Li-S Chemistry

Toward the well-explored lithium-sulfur (Li-S) catalytic chemistry, the slow adsorption-migration-conversion kinetics of lithium polysulfides on catalytic materials and Li₂ S deposition-induced passivation of active sites limit the rapid and complete conversion of sulfur. Conceptively, molecular architectures can provide atom-precise models to understand the underlying active sites responsible for selective adsorption and conversion of LiPSs and Li₂ S₂ /Li₂ S species. Here, an octanuclear Zn(II) (Zn₈ ) cluster is presented, which features a metallacalix[8]arene with double cavities up and down the Zn₈ ring. The central Zn₈ ring and the specific double cavities with organic ligands of different electronegativity and bonding environments render active sites with variable steric hindrance and interaction toward the sulfur-borne species. An intramolecular tandem transformation mechanism is realized exclusively by Zn₈ cluster, which promotes the self-cleaning of active sites and continuous electrochemical reaction. Notably, the external azo groups and internal Zn/O sites of Zn₈ cluster in sequence stimulate the adsorption and conversion of long chain Li₂ S_x (x ≥ 4) and short chain Li₂ S/Li₂ S₂ , contributing to remarkable rate performance and cycling stability. This work pioneers the application of metallacalix[n]arene clusters with atom-precise structure in Li-S batteries, and the proposed mechanism advances the molecule-level understanding of Li-S catalytic chemistry.

Crystal Facet Engineering of MXene-Derived TiN Nanoflakes as Efficient Bidirectional Electrocatalyst for Advanced Lithium-Sulfur Batteries

The design of nanomaterials with grain orientation structure by crystal facet engineering is of great significance for boosting the catalytic ability and electrochemical properties, but the controllable synthesis is still a challenge. Here, TiN nanoflakes with exposed (001) facets are prepared using 2D Ti₃ C₂ MXene as the initial reactant and applied as a bidirectional electrocatalyst for the reduction and oxidation process in lithium-sulfur batteries (LSBs). The (001) facet-dominated TiN nanoflakes have a strong adsorption capacity for soluble lithium polysulfides (LiPSs). More importantly, theoretical calculations and experiment results confirm the (001) facet-dominated TiN nanoflakes catalyze the conversion of soluble LiPSs to Li₂ S₂ /Li₂ S to induce the Li₂ S uniform deposition in the discharge process and decrease the delithiation barrier of Li₂ S in the charge process. Therefore, the excellent electrochemical properties of LSBs are achieved, which demonstrates a high discharge capacity of 949 mAh g^-1 at 1 C and maintains high capacity reversibility with a decay rate of 0.033% per cycle after 800 cycles.

Direct-Chemical Vapor Deposition-Enabled Graphene for Emerging Energy Storage: Versatility, Essentiality, and Possibility

The direct chemical vapor deposition (CVD) technique has stimulated an enormous scientific and industrial interest to enable the conformal growth of graphene over multifarious substrates, which readily bypasses tedious transfer procedure and empowers innovative materials paradigm. Compared to the prevailing graphene materials (i.e., reduced graphene oxide and liquid-phase exfoliated graphene), the direct-CVD-enabled graphene harnesses appealing structural advantages and physicochemical properties, accordingly playing a pivotal role in the realm of electrochemical energy storage. Despite conspicuous progress achieved in this frontier, a comprehensive overview is still lacking by far and the synthesis-structure-property-application nexus of direct-CVD-enabled graphene remains elusive. In this topical review, rather than simply compiling the state-of-the-art advancements, the versatile roles of direct-CVD-enabled graphene are itemized as (i) modificator, (ii) cultivator, (iii) defender, and (iv) decider. Furthermore, essential effects on the performance optimization are elucidated, with an emphasis on fundamental properties and underlying mechanisms. At the end, perspectives with respect to the material production and device fabrication are sketched, aiming to navigate the future development of direct-CVD-enabled graphene en-route toward pragmatic energy applications and beyond.

Balancing Electrolyte Donicity and Cathode Adsorption Capacity for High-Performance LiS Batteries

LiS batteries with high theoretical capacity are attracting attention as next-generation energy storage systems. Much effort has been devoted to the introduction of cathode materials with strong adsorption to sulfide species, but it is presented that this selection should be refined in the application of high donicity electrolytes. The oxides with different adsorption capacities are explored while controlling the electrolyte donicity, confirming the trade-off effect between the donicity and the adsorption capacity for sulfur conversion. Specifically, a cathode substrate containing oxide nanoparticles of MgO, NiO, Fe₂ O₃ , Co₃ O₄ , and V₂ O₅ is prepared with spectra in adsorption capacity as well as low and high donicity electrolytes by controlling the concentration of LiNO₃ salt. Strong adsorbent oxides such as Co₃ O₄ and V₂ O₅ cause competitive adsorption of electrolyte salts in high donicity electrolytes, resulting in poor cell performance. High cell performance is achieved on weakly adsorbing oxides of MgO or NiO with high donicity electrolytes; the MgO-containing cathode cell delivers a high discharge capacity of 1394 mAh g^-1 at 0.2 C. It is believed that understanding the interactions between electrolytes and adsorbent substrates will be the cornerstone of high-performance LiS batteries.

Niobium Diboride Nanoparticles Accelerating Polysulfide Conversion and Directing Li2S Nucleation Enabled High Areal Capacity Lithium-Sulfur Batteries

The shuttle effect of polysulfides and Li₂S sluggish nucleation are the major problems hampering the further development of lithium-sulfur batteries. The reasonable design for sulfur host materials with catalytic function has been an effective strategy for promoting polysulfide conversion. Compared with other types of transition metal compounds, transition metal borides with high conductivity and catalytic capability are more suitable as sulfur host materials. Herein, a niobium diboride (NbB₂) nanoparticle with abundant and high-efficiency catalytic sites has been synthesized by facile solid-phase reaction. The NbB₂ with both high conductivity and catalytic nature could regulate 3D-nucleation and growth of Li₂S, decrease the reaction energy barrier, and accelerate the transformation of polysulfides. Thus, the NbB₂ cathode could retain a high capacity of 1014 mAh g^-1 after 100 cycles. In addition, the high initial specific capacities of 703/609 mAh g^-1 are also achieved at 5 C/10 C and could run for 1000/1300 cycles within a low decay rate of 0.057%/0.051%. Even with a high sulfur loading up to 16.5 mg cm^-2, an initial areal capacity of 17 mAh cm^-2 could be achieved at 0.1 C. This work demonstrates a successful method for enhancing the kinetics of polysulfide conversion and directing Li₂S nucleation.

Low concentration electrolyte with non-solvating cosolvent enabling high-voltage lithium metal batteries

Developing low cost, yet high-voltage electrolyte is significant to improve the energy density and practicability of lithium metal batteries (LMBs). Low concentration electrolyte has significant merits in terms of cost and viscosity; however, their poor compatibility with high-voltage LMBs hinders its applications. Here, we develop a diluted low concentration electrolyte by replacing solvating cosolvent with a non-solvating cosolvent to facilitate the interaction between BF₄ ^- and Li⁺, resulting in optimized interfacial chemistry and suppressed side reaction. Thus, the high-loading Li-LiCoO₂ full cells (20.4 mg cm^-2) deliver outstanding cycling stability and rate performance at a cutoff voltage of 4.6 V. More impressively, a Li-LiCoO₂ pouch cell achieves an energy density of more than 400 Wh kg^-1 under practical conditions with thin Li (50 μm) and lean electrolyte (2.7 g Ah^-1). This work provides a rational approach to design a low concentration electrolyte, which can be extended to other high voltage battery systems.

Dual-Functional MgO Nanocrystals Satisfying Both Polysulfides and Li Regulation toward Advanced Lithium-Sulfur Full Batteries

Lithium-sulfur battery (LSB) is regarded as a preferential option for next-generation energy-storage system, but the lithium polysulfides (LiPSs) shuttling effect and the uncontrollable growth of dendritic Li in the anode impede its commercial viability. To address both of the issues simultaneously, a well-designed hybrid of MgO ultrafine nanocrystals dispersed on graphene-supported carbon nanosheets (MCG) is developed via a facile self-template strategy as dual-functional host for both sulfur and lithium. Relying on the coordination of strong LiPS-capturing capability, the shuttling effect is inhibited. Furthermore, the lithiophilic configuration with high specific surface area induce homogenous Li deposition, thus preventing the formation of disordered lithium dendrite. Integrating all these advantages, a full cell based on S@MCG cathode and Li@MCG@Cu anode exhibits a stable capacity at 0.5 C for 150 cycles with a low capacity fading rate. Furthermore, the full cell achieves a high capacity retention of 85.5% at a high S areal loading of 3.82 mg cm^-2 under the condition of a low electrolyte/sulfur ratio (E/S) of 6.5 µL mg^-1 and negative/positive capacity ratio (N/P) of 3. This strategy satisfying both cathode and anode host provides a viable approach to realize high-energy-density and dendrite-free LSBs.

The Interfacial Electronic Engineering in Binary Sulfiphilic Cobalt Boride Heterostructure Nanosheets for Upgrading Energy Density and Longevity of Lithium-Sulfur Batteries

High gravimetric, areal and volumetric capacities together with long lifetime are key indexes for the applications of lithium-sulfur (Li-S) batteries in compact space. The sulfur host materials play pivotal roles in the practical deployment. Herein, one type of new heterostructure nanosheets composed of cobalt boride (CoB) on nitrogen, boron-codoped porous carbon (NBC), which is constructed through molten salt-assisted strategy using ZIF-67-encapsulated ZIF-8 as precursors is reported on. Benefiting from strong interfacial electronic interactions between binary sulfiphilic CoB and porous NBC, the CoB/NBC-S electrode exhibits the excellent cycling stability with low average capacity decay of 0.013% in ultralong 1500 cycles at high rate of 5 C. Remarkably, the electrode with high sulfur content of 82 wt% and high sulfur loading of 5.8 mg cm^-2 delivers gravimetric capacity of 1309 mA h g^-1 , areal capacity of 7.59 mA h cm^-2 , and volumetric capacity of 1355 mA h cm^-3 at 0.1 C. The favorable electrochemical performance can rival with the state-of-the-art of those in the reported nanosheets-based sulfur cathodes. This study provides new methodology for the design of heterostructure nanosheets of metal borides to achieve energy density and longevity of Li-S batteries.

Hierarchical Assembly of CNTs-VSe2-VOx/S for Flexible Lithium-Sulfur Batteries

Constructing highly conductive compact sulfur cathode composites with shorter ion diffusivity lengths is vital for achieving comprehensively superior electrochemical performance under a high mass loading condition. Guided by computerization modeling, we, herein, report self-supporting CNTs-VSe₂-VO_x/S assembly with balanced tortuosity and porosity for flexible Li-S batteries. The resultant hybrid sulfur cathode with a tortuosity of 2.42 and a porosity of 0.44 delivers prominent rate performance and cycling stability with a medium sulfur loading. More importantly, we demonstrate that the pouch cells with a high sulfur loading of 6.0 mg cm^-2 and a low electrolyte to sulfur ratio of 4.2 μL mg^-1 could synchronously deliver high gravimetric/volumetric energy densities of 424.1 Wh kg^-1 and 469.2 Wh L^-1, as well as decent cycling behavior under arbitrary bending conditions, which provides a ponderable reference for future flexible and wearable electronic devices.

Electrocatalytic NiCo2O4 Nanofiber Arrays on Carbon Cloth for Flexible and High-Loading Lithium-Sulfur Batteries

Lithium-sulfur batteries have ultrahigh theoretical energy densities, which makes them one of the most promising next-generation energy storage systems. However, it is still difficult to achieve large-scale commercialization because of the severe lithium polysulfide (LiPS) shuttle effect and low sulfur loading. Here, we report a flexible lithium-sulfur battery of a high sulfur loading with the assistance of NiCo₂O₄ nanofiber array grown carbon cloth. The NiCo₂O₄ nanofibers are ideal electrocatalysts for accelerating LiPS conversion kinetics through strong chemical interactions. Therefore, the composite cathode delivers a high specific capacity of 1280 mAh g^-1 at 0.2 C with a sulfur loading of 3.5 mg cm^-2, and it can maintain a high specific capacity of 660 mAh g^-1 after 200 cycles, showing a good cycle stability. The "layer-by-layer" stacking strategy enables the Li-S battery with a high S loading of ∼9.0 mg cm^-2 to deliver a high areal capacity of 8.9 mAh cm^-2.

To Promote the Catalytic Conversion of Polysulfides Using Ni-B Alloy Nanoparticles on Carbon Nanotube Microspheres under High Sulfur Loading and a Lean Electrolyte

Despite their high theoretical energy density, the application of lithium-sulfur batteries is seriously hindered by the polysulfide shuttle and sluggish kinetics, especially with high sulfur loading and under low electrolyte usage. Herein, to facilitate the conversion of lithium polysulfides, nickel-boron (Ni-B) alloy nanoparticles, dispersed uniformly on carbon nanotube microspheres (CNTMs), are used as sulfur hosts for lithium-sulfur batteries. It is demonstrated that Ni-B alloy nanoparticles can not only anchor polysulfides through Ni-S and B-S interactions but also exhibit high electrocatalytic capability toward the conversion of intermediate polysulfide species. In addition, the intertwined CNT microspheres provide an additional conductive scaffold in response to the fast electrochemical redox. The enhanced redox kinetics is beneficial to improve the specific capacity and cycling stability of the sulfur cathode, based on the fast conversion of lithium polysulfides and effective deposition of the final sulfide products. Conclusively, the S/Ni-B/CNTM composite delivers a high specific capacity (1112.7 mAh g_s^-1) along with good cycle performance under both high sulfur loading (8.3 mg cm^-2) and a lean electrolyte (3 μL mg_s^-1). Consequently, this study opens up a path to design new sulfur hosts toward lithium-sulfur batteries.

Hierarchical Nanoreactor with Multiple Adsorption and Catalytic Sites for Robust Lithium-Sulfur Batteries

Developing high-performance cathode host materials is fundamental to solve the low utilization of sulfur, the sluggish redox kinetics, and the lithium polysulfide (LiPS) shuttle effect in lithium-sulfur batteries (LSBs). Here, a multifunctional Ag/VN@Co/NCNT nanocomposite with multiple adsorption and catalytic sites within hierarchical nanoreactors is reported as a robust sulfur host for LSB cathodes. In this hierarchical nanoreactor, heterostructured Ag/VN nanorods serve as a highly conductive backbone structure and provide internal catalytic and adsorption sites for LiPS conversion. Interconnected nitrogen-doped carbon nanotubes (NCNTs), in situ grown from the Ag/VN surface, greatly improve the overall specific surface area for sulfur dispersion and accommodate volume changes in the reaction process. Owing to their high LiPS adsorption ability, outer Co nanoparticles at the top of the NCNTs catch escaped LiPS, thus effectively suppressing the shuttle effect and enhancing kinetics. Benefiting from the multiple adsorption and catalytic sites of the developed hierarchical nanoreactors, Ag/VN@Co/NCNTs@S cathodes display outstanding electrochemical performances, including a superior rate performance of 609.7 mAh g^-1 at 4 C and a good stability with a capacity decay of 0.018% per cycle after 2000 cycles at 2 C. These properties demonstrate the exceptional potential of Ag/VN@Co/NCNTs@S nanocomposites and approach LSBs closer to their real-world application.