Atomic-scale regulation of anionic and cationic migration in alkali metal batteries

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.

Electrochemical coupling in subnanometer pores/channels for rechargeable batteries

Subnanometer pores/channels (SNPCs) play crucial roles in regulating electrochemical redox reactions for rechargeable batteries. The delicately designed and tailored porous structure of SNPCs not only provides ample space for ion storage but also facilitates efficient ion diffusion within the electrodes in batteries, which can greatly improve the electrochemical performance. However, due to current technological limitations, it is challenging to synthesize and control the quality, storage, and transport of nanopores at the subnanometer scale, as well as to understand the relationship between SNPCs and performances. In this review, we systematically classify and summarize materials with SNPCs from a structural perspective, dividing them into one-dimensional (1D) SNPCs, two-dimensional (2D) SNPCs, and three-dimensional (3D) SNPCs. We also unveil the unique physicochemical properties of SNPCs and analyse electrochemical couplings in SNPCs for rechargeable batteries, including cathodes, anodes, electrolytes, and functional materials. Finally, we discuss the challenges that SNPCs may face in electrochemical reactions in batteries and propose future research directions.

Fluorine Chemistry in Rechargeable Batteries: Challenges, Progress, and Perspectives

The renewable energy industry demands rechargeable batteries that can be manufactured at low cost using abundant resources while offering high energy density, good safety, wide operating temperature windows, and long lifespans. Utilizing fluorine chemistry to redesign battery configurations/components is considered a critical strategy to fulfill these requirements due to the natural abundance, robust bond strength, and extraordinary electronegativity of fluorine and the high free energy of fluoride formation, which enables the fluorinated components with cost effectiveness, nonflammability, and intrinsic stability. In particular, fluorinated materials and electrode|electrolyte interphases have been demonstrated to significantly affect reaction reversibility/kinetics, safety, and temperature tolerance of rechargeable batteries. However, the underlining principles governing material design and the mechanistic insights of interphases at the atomic level have been largely overlooked. This review covers a wide range of topics from the exploration of fluorine-containing electrodes, fluorinated electrolyte constituents, and other fluorinated battery components for metal-ion shuttle batteries to constructing fluoride-ion batteries, dual-ion batteries, and other new chemistries. In doing so, this review aims to provide a comprehensive understanding of the structure-property interactions, the features of fluorinated interphases, and cutting-edge techniques for elucidating the role of fluorine chemistry in rechargeable batteries. Further, we present current challenges and promising strategies for employing fluorine chemistry, aiming to advance the electrochemical performance, wide temperature operation, and safety attributes of rechargeable batteries.

Introduced Hierarchically Ordered Porous Architecture on a Separator as an Efficient Polysulfide Trap toward High-Mass-Loading Li-S Batteries

The severe shuttle effect and the depletion of active sulfur result in performance deterioration, presenting two formidable issues that must be overcome to achieve high-mass-loading lithium-sulfur batteries. Herein, we reported a composite separator by introducing carbon photonic crystals with a hierarchically ordered porous structure on a commercial separator. The ordered structure and interconnected hierarchical macro-meso-micropore network of the composite separator facilitate efficient trapping of polysulfides and rapid transport of lithium ions. The high ion diffusivity promotes the conversion of polysulfides enhancing sulfur utilization and mitigating the occurrence of "dead sulfur" on the surface of the separator. Impressively, under a high sulfur loading of 3 mg cm-2, the lithium-sulfur battery with the composite separator displayed a high reversible capacity of 1582 mA h g-1 at 0.1 C and an excellent long-term cycling performance with a decay rate of as low as 0.033% per cycle over 1500 cycles at 1 C. Surprisingly, the battery represented a high reversible capacity of 935 mA h g-1 at 0.2 C even at a sulfur loading of 6.71 mg cm-2. The design of the composite separator underscores the pivotal role of carbon architecture in improving battery performance and brings a bright prospect to enable the commercialization of high-mass-loading lithium-sulfur batteries.

Bio-inspired Double Angstrom-Scale Confinement in Ti-deficient Ti0.87 O2 Nanosheet Membranes for Ultrahigh-performance Osmotic Power Generation

Osmotic power, a clean energy source, can be harvested from the salinity difference between seawater and river water. However, the output power densities are hampered by the trade-off between ion selectivity and ion permeability. Here we propose an effective strategy of double angstrom-scale confinement (DAC) to design ion-permselective channels with enhanced ion selectivity and permeability simultaneously. The fabricated DAC-Ti0.87 O2 membranes possess both Ti atomic vacancies and an interlayer free spacing of ≈2.2 Å, which not only generates a profitable confinement effect for Na+ ions to enable high ion selectivity but also induces a strong interaction with Na+ ions to benefit high ion permeability. Consequently, when applied to osmotic power generation, the DAC-Ti0.87 O2 membranes achieved an ultrahigh power density of 17.8 W m-2 by mixing 0.5/0.01 M NaCl solution and up to 114.2 W m-2 with a 500-fold salinity gradient, far exceeding all the reported macroscopic-scale membranes. This work highlights the potential of the construction of DAC ion-permselective channels for two-dimensional materials in high-performance nanofluidic energy systems.

Compressible and Elastic Reduced Graphene Oxide Sponge for Stable and Dendrite-Free Lithium Metal Anodes

Dendritic Li deposition, an unstable solid-electrolyte interphase (SEI), and a nearly infinite relative volume change during cycling are three major obstacles to the practical application of Li metal batteries. Herein, we introduce a compressible and elastic reduced graphene oxide sponge (rGO-S) to simultaneously eliminate Li dendrite growth, stabilize the SEI, and accommodate the volume change. The volume change is contained by compressing and expanding the rGO-S anode, which effectively releases the Li plating-induced stress during cycling. The smooth and dense Li metal is deposited on rGO-S without dendrites, which preserves the SEI, reduces consumption of the electrolyte, and prevents the formation of Li debris. The half-cells employing rGO-S show a steady and high Coulombic efficiency. The Li@rGO-S symmetric cells demonstrate excellent cycling stability over 1200 cycles with a low overpotential. When paired with LiFePO4 (LFP), the Li@rGO-S||LFP full cells exhibit a high specific capacity (150.3 mAh g-1 at 1C), superior rate performance, and good capacity retention.

Cationic Defect-Modulated Li-Ion Migration in High-Voltage Li-Metal Batteries

Li metal exhibits high potential as an anode material for next-generation high-energy density batteries. However, the nonuniform transport of Li+ ions causes Li-dendrite growth at the metal electrode, leading to severe capacity decay and a short cycling life. In this study, negatively charged lithiophilic sites (such as cationic metal vacancies) were used as hosts to regulate the atomic-scale Li+-ion deposition in Li-metal batteries (LMBs). As a proof of concept, three-dimensional (3D) carbon nanofibers (CNFs) decorated with negatively charged TiNbO4 grains (labeled CNF/nc-TNO) were confirmed to be promising Li hosts. Cationic vacancies caused by the carbothermal reduction of Nb5+ and Ti4+ ions generated a negatively charged fiber surface and strong electrostatic interactions that guided the Li+-ion flux to the shadowed areas underneath the fiber and throughout the fibrous mat. Consequently, circumferential Li-metal plating was observed in the CNF/nc-TNO host, even at a high current density of 10 mA cm-2. Moreover, CNF/nc-TNO asymmetric cells delivered a significantly more robust and stable Coulombic efficiency (CE) (99.2% over 380 cycles) than cells comprising electrically neutral CNFs without cationic defects (which exhibits rapid failure after 20 cycles) or Cu foil (which exhibits rapid CE decay, with a CE of 87.1% after 100 cycles). Additionally, CNF/nc-TNO exhibited high stability and low-voltage hysteresis during repeated Li plating/stripping (for over 4000 h at 2 mA cm-2) with an areal capacity of 2 mAh cm-2. It was further paired with high-voltage LiNi0.8Co0.1Mn0.1 (NCM811) cathodes, and the full cells showed long-term cycling (220 cycles) with a CE of 99.2% and a steady rate capability.

Enhancement of Pt-O Synergistic Sites through Titanium Vacancies for Low-Temperature Nitrogen Oxide Reduction

Improving the reaction rate of each step is significant for accelerating the multistep reaction of NO reduction by H2. However, simultaneously enhancing the activation of different gaseous reactants using single-atom catalysts remains a challenge to maximize the activity. Herein, we propose a strategy that utilizes titanium-vacancy-regulated electronic properties of single atoms and defective support (Pt1/d-TiO2) to facilitate electron transfer from edge-share O atoms (OTi) to adjacent Pt single atoms. This leads to the formation of low-valence Pt and unsaturated-charge OTi sites, which causes the catalytic reaction to follow a synergistic mechanism. Specifically, experimental and theoretical analyses demonstrate that low-valence Pt sites finely tune the adsorption of H2 molecules, consequently lowering the dissociation energy from 0.15 to as low as 0.01 eV. Moreover, using quasi-in situ spectroscopy, we clearly observe NO molecules being adsorbed on interfacial oxygen sites of a defective support. Then, the bond energy of the N-O bond is weakened through an electron acceptance-donation mechanism between unsaturated-charge OTi sites and NO, thereby facilitating NO activation. The designed single-atom catalysts with synergistic sites exhibit unmatched activity at low temperatures (above 90% NOx conversion at 100 °C), along with higher turnover frequency value (0.74 s-1) and superior stability, making them potentially suitable for industrial applications.

Chaotropic Electrolyte Enabling Wide-Temperature Metal-Free Battery

Metal-free aqueous batteries are promising candidates for grid-scale energy storage owing to their inherent safety, low cost, and cost effectiveness. The battery chemistry based on fast NH4+ diffusion kinetics avoids unfavorable generation of inactive metallic byproducts. However, their practical applications have been impeded by electrolyte instability and the intrinsic drawbacks of current electrodes. Herein, we propose an aqueous ammonium-iodine battery by using a chaotropic electrolyte, 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) anode, and iodine composite (I2@CC) cathode. Experimental investigations and theoretical calculations reveal that the chaotropic electrolyte not only enhances electrolyte stability through modulating the H-bond structure but also facilitates the formation of a hydrophobic cationic sieve (HCS) on the anode, which ensures the electrolyte/electrode stability and high reversibility of the anode. Additionally, the Cl--containing electrolyte can support the consecutive I+/I0 reaction on the cathode by forming [IClx]1-x interhalogen. The as-assembled aqueous ammonium-iodine batteries (AIBs) based on NH4+ accommodation at the anode and I+/I0 redox reaction at the cathode can deliver superior electrochemical performance at room temperature and low temperature (-20 °C). This study provides a strategic insight into developing metal-free aqueous batteries with electrolyte modulation.

Electrochemical molecular intercalation and exfoliation of solution-processable two-dimensional crystals

Electrochemical molecular intercalation of layered semiconducting crystals with organic cations followed by ultrasonic exfoliation has proven to be an effective approach to producing a rich family of organic/inorganic hybrid superlattices and high-quality, solution-processable 2D semiconductors. A traditional method for exfoliating 2D crystals relies on the intercalation of inorganic alkali metal cations. The organic cations (e.g., alkyl chain-substituted quaternary ammonium cations) are much larger than their inorganic counterparts, and the bulky molecular structure endows distinct intercalation and exfoliation chemistry, as well as molecular tunability. By using this protocol, many layered 2D crystals (including graphene, black phosphorus and versatile metal chalcogenides) can be electrochemically intercalated with organic quaternary alkylammonium cations. Subsequent solution-phase exfoliation of the intercalated compounds is realized by regular bath sonication for a short period (5-30 min) to produce free-standing, thin 2D nanosheets. It is also possible to graft additional ligands on the nanosheet surface. The thickness of the exfoliated nanosheets can be measured by using atomic force microscopy and Raman spectroscopy. Modifying the chemical structure and geometrical configuration of alkylammonium cations results in different exfoliation behavior and a family of versatile organic/inorganic hybrid superlattices with tunable physical/chemical properties. The whole protocol takes ~6 h for the successful production of stable, ultrathin 2D nanosheet dispersion in solution and another 11 h for depositing thin films and transferring them onto an arbitrary surface. This protocol does not require expertise beyond basic electrochemistry knowledge and conventional colloidal nanocrystal synthesis and processing.

Recent Progress for Concurrent Realization of Shuttle-Inhibition and Dendrite-Free Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries have become one of the most promising new-generation energy storage systems owing to their ultrahigh energy density (2600 Wh kg-1 ), cost-effectiveness, and environmental friendliness. Nevertheless, their practical applications are seriously impeded by the shuttle effect of soluble lithium polysulfides (LiPSs), and the uncontrolled dendrite growth of metallic Li, which result in rapid capacity fading and battery safety problems. A systematic and comprehensive review of the cooperative combination effect and tackling the fundamental problems in terms of cathode and anode synchronously is still lacking. Herein, for the first time, the strategies for inhibiting shuttle behavior and dendrite-free Li-S batteries simultaneously are summarized and classified into three parts, including "two-in-one" S-cathode and Li-anode host materials toward Li-S full cell, "two birds with one stone" modified functional separators, and tailoring electrolyte for stabilizing sulfur and lithium electrodes. This review also emphasizes the fundamental Li-S chemistry mechanism and catalyst principles for improving electrochemical performance; advanced characterization technologies to monitor real-time LiPS evolution are also discussed in detail. The problems, perspectives, and challenges with respect to inhibiting the shuttle effect and dendrite growth issues as well as the practical application of Li-S batteries are also proposed.

Ultrasmooth and Dense Lithium Deposition Toward High-Performance Lithium-Metal Batteries

Lithium (Li)-metal batteries (LMBs) with stable solid electrolyte interphase (SEI) and dendrite-free formation have great potential in next-generation energy storage devices. Here, vertically aligned 3D Cu₂ S nanosheet arrays are fabricated on the surface of commercial Cu foils, which in situ generate ultrathin Cu nanosheet arrays to reduce local current density and Li₂ S layers on the surfaces to work as an excellent artificial SEI. It is found that Li presents a 3D-to-planar deposition model, and Li₂ S layers are reversibly movable between the 3D nanosheet surface and 2D planar surface of Li during long-term cycling. This enables ultrasmooth and dense Li deposition at 1 mA cm^-2 , presenting an average thickness of ≈53.0 µm at 10 mAh cm^-2 , which is close to the theoretical Li foil thickness and is highly reversible at different cycles. Thus, 1150 stable cycles with high Coulombic efficiency (CE, 99.1%) at ether-based electrolytes and 300 stable cycles with high CE (98.8%) at carbonate electrolytes are realized in half-cell with a capacity of 1 mAh cm^-2 at 1 mA cm^-2 . When coupled with commercial cathodes (LiFePO₄ or LiNi_0.8 Co_0.1 Mn_0.1 O₂ ), the full cells present substantially enhanced cyclability under high cathode loading, limited (or zero) Li excess, and lean electrolyte conditions, even at -20 °C.

Pivotal Role of the Granularity Uniformity of the WO3 Film Electrode upon the Cyclic Stability during Cation Insertion/Extraction

Delicate design and precise manipulation of electrode morphology has always been crucial in electrochemistry. Generally, porous morphology has been preferred due to the fast kinetic transport characteristics of cations. Nevertheless, more refined design details such as the granularity uniformity that usually goes along with the porosity regulation of film electrodes should be taken into consideration, especially in long-term cation insertion and extraction. Here, inorganic electrochromism as a special member of the electrochemical family and WO₃ films as the most mature electrochromic electrode material were chosen as the research background. Two kinds of WO₃ films were prepared by magnetron sputtering, one with a relatively loose morphology accompanied by nonuniform granularity and one with a compact morphology along with uniform particle size distribution, respectively. Electrochemical performances and cyclic stability of the two film electrodes were then traced and systematically compared. In the beginning, except for faster kinetic transport characters of the 50 W-deposited WO₃ film, the two electrodes showed equivalent optical and electrochemical performances. However, after 5000 CV cycles, the 50 W-deposited WO₃ film electrode cracked seriously. Strong stress distribution centered among boundaries of the nonuniform particle clusters together with the weak bonding among particles induced the mechanical damage. This discovery provides a more solid background for further delicate film electrode design.

Fluorinated Covalent Organic Framework-Based Nanofluidic Interface for Robust Lithium-Sulfur Batteries

To realize the practical application of lithium-sulfur (Li-S) batteries, there is a need to inhibit uncontrolled Li deposition by facilitating Li-ion migration, and suppress the irreversible consumption of cathodes by preventing polysulfide shuttling. However, a permselective artifical membrane or interlayer which features fast ion transport but low polysulfide crossover is elusive. Here, we report the design and synthesis of a fluorinated covalent organic framework (4F-COF)-based membrane with a high permselectivity and increased battery lifespan. Combining density functional theory calculation, molecular dynamic simulation, and in situ Raman analysis, we demonstrate that fluorinated COF eliminates polysulfides shutting and dendritic lithium formation. Consequently, Li symmetrical cells demonstrate Li plating/stripping behaviors for 2000 h under 1 mA cm^-2. More importantly, Li-S batteries based on the 4F-COF/PP separator achieve cycling retention of 82.3% over 1000 cycles at 2 C, rate performance of 568.0 mA h g^-1 at 10 C, and an areal capacity of 7.60 mA h cm^-2 with a high sulfur loading (∼9 mg cm^-2). This work demonstrates that functionalizing nanochannels in COFs can impart permselectivity for energy storage applications.

A Polymer Network Layer Containing Dually Anchored Ionic Liquids for Stable Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries with high sulfur utilization, long-cycle life, and dendrite-free features hold great promise for the development of next-generation energy storage devices of high energy density. Considerable efforts have been committed to solving the polysulfide shuttle problem toward highly stable Li-S batteries. Here, a unique polymer network containing dually anchored ionic liquids (DA-PIL) is devolped to improve the cycling performance and coulombic efficiency of Li-S batteries. This DA-PIL electrolyte incorporates the amphiphilicity of both the polysulfides anion and lithium cation, creating an ionic function layer on polypropylene separator. Noteworthily, the DA-PIL network is "clean" in the sense that no free ionic specifies are introduced to the electrolyte system. The DA-PIL layer not only enables strong supression against polysulfide shuttling but simultaneously allows fast lithium transportation owing to cooperate electrostatic interaction among anchored cations and anions. The DA-PIL layer functionalized on a polypropylene separator can boost excellent stability of Li-S battery with >1600 h cycling test at 0.25 mA cm^-2 . The Li-S cell with DA-PIL layer delivers a higher discharge capacity of 827.4 mAh g^-1 at 1C. A discharge capacity of 630.6 mAh g^-1 is retained after 1000 cycles.

Dynamic Intercalation-Conversion Site Supported Ultrathin 2D Mesoporous SnO2/SnSe2 Hybrid as Bifunctional Polysulfide Immobilizer and Lithium Regulator for Lithium-Sulfur Chemistry

The practical application of lithium-sulfur batteries is impeded by the polysulfide shuttling and interfacial instability of the metallic lithium anode. In this work, a twinborn ultrathin two-dimensional graphene-based mesoporous SnO₂/SnSe₂ hybrid (denoted as G-mSnO₂/SnSe₂) is constructed as a polysulfide immobilizer and lithium regulator for Li-S chemistry. The as-designed G-mSnO₂/SnSe₂ hybrid possesses high conductivity, strong chemical affinity (SnO₂), and a dynamic intercalation-conversion site (Li_xSnSe₂), inhibits shuttle behavior, provides rapid Li-intercalative transport kinetics, accelerates LiPS conversion, and decreases the decomposition energy barrier for Li₂S, which is evidenced by the ex situ XAS spectra, in situ Raman, in situ XRD, and DFT calculations. Moreover, the mesoporous G-mSnO₂/SnSe₂ with lithiophilic characteristics enables homogeneous Li-ion deposition and inhibits Li dendrite growth. Therefore, Li-S batteries with a G-mSnO₂/SnSe₂ separator achieve a favorable electrochemical performance, including high sulfur utilization (1544 mAh g^-1 at 0.2 C), high-rate capability (794 mAh g^-1 at 8 C), and long cycle life (extremely low attenuation rate of 0.0144% each cycle at 5 C over 2000 cycles). Encouragingly, a 1.6 g S/Ah-level pouch cell realizes a high energy density of up to 359 Wh kg^-1 under a lean E/S usage of 3.0 μL mg^-1. This work sheds light on the design roadmap for tackling S-cathode and Li-anode challenges simultaneously toward long-durability Li-S chemistry.

A High-Energy and Safe Lithium Battery Enabled by Solid-State Redox Chemistry in a Fireproof Gel Electrolyte

Recent years have witnessed thriving efforts in pursuing high-energy batteries at an unaffordable cost of safety. Herein, a high-energy and safe quasi-solid-state lithium battery is proposed by solid-state redox chemistry of polymer-based molecular Li₂ S cathode in a fireproof gel electrolyte. This chemistry fully eliminates not only the negative effect of extremely reactive Li metal and oxygen species on cell safety but also the damage of electrode reversibility by soluble redox intermediates. The molecular Li₂ S cathode exhibits an exceptional lifetime of 2000 cycles, 100% Coulombic efficiency, high capacity of 830 mA h g^-1 with ultralow capacity loss of 0.005-0.01% per cycle and superior rate capability up to 10 C. Meanwhile, it shows high stability in the carbonate-involving electrolyte for maximizing the compatibility with carbonate-efficient Si anode. The optimized cell chemistry exerts high energy over 750 W h kg^-1 for 500 cycles with fast rate response, high-temperature adaptability, and no self-discharge. A fire-retardant composite gel electrolyte is developed to further strengthen the intrinsic safe redox between the Li₂ S cathode and the Si anode, which secures remarkable safety against extreme abuse of overheating, short circuits, and mechanical damage in air/water or even when on fire.

Synergetic Anion Vacancies and Dense Heterointerfaces into Bimetal Chalcogenide Nanosheet Arrays for Boosting Electrocatalysis Sulfur Conversion

Vacancy and interface engineering are regarded as effective strategies to modulate the electronic structure and enhance the activity of metal chalcogenides. However, the practical application of metal chalcogenides in lithium-sulfur (Li-S) batteries is limited by their low conductivity, rapid decline in catalytic activity, and large volume variation during the discharging/charging process. Herein, bimetal sulfide (CoZn-S) nanosheet arrays with sulfur vacancies and dense heterointerfaces are proposed to accelerate sulfur conversion and improve the performance of Li-S batteries. Systematic investigations reveal that sulfur-vacancy and build-in interfacial field in CoZn-S facilitate the electron transfer and regulate the electronic structure. The well-designed 3D nanosheet array structures shorten the ion-transport pathway and inhibit the volume fluctuation of CoZn-S during the electrocatalysis process. Density functional theory studies confirm that the built-in interfacial field and sulfur vacancy can promote the thermodynamic formation and decomposition of Li₂ S, thus improving their intrinsic activity.

P-Doped NiTe2 with Te-Vacancies in Lithium-Sulfur Batteries Prevents Shuttling and Promotes Polysulfide Conversion

Lithium-sulfur (Li-S) batteries have been hindered by the shuttle effect and sluggish polysulfide conversion kinetics. Here, a P-doped nickel tellurium electrocatalyst with Te-vacancies (P⊂NiTe_{2- x} ) anchored on maize-straw carbon (MSC) nanosheets, served as a functional layer (MSC/P⊂NiTe_{2- x} ) on the separator of high-performance Li-S batteries. The P⊂NiTe_{2- x} electrocatalyst enhanced the intrinsic conductivity, strengthened the chemical affinity for polysulfides, and accelerated sulfur redox conversion. The MSC nanosheets enabled NiTe₂ nanoparticle dispersion and Li⁺ diffusion. In situ Raman and ex situ X-ray absorption spectra confirmed that the MSC/P⊂NiTe_{2- x} restrained the shuttle effect and accelerated the redox conversion. The MSC/P⊂NiTe_{2- x} -based cell has a cyclability of 637 mAh g^-1 at 4 C over 1800 cycles with a degradation rate of 0.0139% per cycle, high rate performance of 726 mAh g^-1 at 6 C, and a high areal capacity of 8.47 mAh cm^-2 under a sulfur configuration of 10.2 mg cm^-2 , and a low electrolyte/sulfur usage ratio of 3.9. This work demonstrates that vacancy-induced doping of heterogeneous atoms enables durable sulfur electrochemistry and can impact future electrocatalytic designs related to various energy-storage applications.

Energy-Saving Synthesis of Functional CoS2/rGO Interlayer With Enhanced Conversion Kinetics for High-Performance Lithium-Sulfur Batteries

Lithium sulfur (Li-S) battery has exhibited great application potential in next-generation high-density secondary battery systems due to their excellent energy density and high specific capacity. However, the practical industrialization of Li-S battery is still affected by the low conductivity of sulfur and its discharge product (Li₂S₂/Li₂S), the shuttle effect of lithium polysulfide (Li₂S_n, 4 ≤ n ≤ 8) during charging/discharging process and so on. Here, cobalt disulfide/reduced graphene oxide (CoS₂/rGO) composites were easily and efficiently prepared through an energy-saving microwave-assisted hydrothermal method and employed as functional interlayer on commercial polypropylene separator to enhance the electrochemical performance of Li-S battery. As a physical barrier and second current collector, the porous conductive rGO can relieve the shuttle effect of polysulfides and ensure fast electron/ion transfer. Polar CoS₂ nanoparticles uniformly distributed on rGO provide strong chemical adsorption to capture polysulfides. Benefitting from the synergy of physical and chemical constraints on polysulfides, the Li-S battery with CoS₂/rGO functional separator exhibits enhanced conversion kinetics and excellent electrochemical performance with a high cycling initial capacity of 1,122.3 mAh g⁻¹ at 0.2 C, good rate capabilities with 583.9 mAh g⁻¹ at 2 C, and long-term cycle stability (decay rate of 0.08% per cycle at 0.5 C). This work provides an efficient and energy/time-saving microwave hydrothermal method for the synthesis of functional materials in stable Li-S battery.

Structural and Compositional Characteristics of Ball-Milled Lepidocrocite Alkali Titanate and the Correlation to Its Surface Acidic-Basic Properties

The studies on mechanical treatments of layered alkali metal oxides are limited despite their diverse compositions/structures and potential for property tuning. In this work, we vibratory mill Cs_0.7Zn_0.35Ti_1.65O₄, K_0.8Zn_0.4Ti_1.6O₄, and Cs₂Ti₆O₁₃ for up to 4 h, during which the lepidocrocite-type structure and the plate-like morphology are well preserved. X-ray diffraction (XRD) indicates a tiny (≤0.6 Å) interlayer expansion accompanied by the enhancement of the preferred orientation along the stacking direction. Chemical analyses across multiple length scales suggest Cs deintercalation, elemental redistributions, and bulk-to-surface (or crystal edge) Cs migration. This ball-milling-induced Cs-rich moiety partially blocks the surface acid sites, although the solids still show a dominating acidic character. The ball-milled samples Cs_0.7-pZn_0.35-qTi_1.65O_4-δ contain vacancies between the sheets (p) and at the sheets (q and δ). It is deduced from Sanderson's electronegativity equalization principle and experimentally verified by X-ray photoelectron spectroscopy (XPS) that ball milling increases (decreases) the partial charge at the surface acidic Ti⁴⁺/Zn²⁺ (basic O^2-) sites. These nonporous solids (≤20 m²·g^-1) contain water sorbed on the external surface as high as 1.1 mol·mol^-1, which is comparable to that in a water-intercalated sample. Our work expands the current understanding of the reactivity vs robustness in layered alkali titanates under physically demanding conditions, complementing knowledge gathered via the soft chemistry approach.