Achieving a Deeply Desodiated Stabilized Cathode Material by the High Entropy Strategy for Sodium-ion Batteries.

Manganese-based layered oxides are currently of significant interest as cathode materials for sodium-ion batteries due to their low toxicity and high specific capacity. However, the practical applications are impeded by sluggish intrinsic Na+ migration and poor structure stability as a result of Jahn-Teller distortion and complicated phase transition. In this study, a high-entropy strategy is proposed to enhance the high-voltage capacity and cycling stability. The designed P2-Na0.67Mn0.6Cu0.08Ni0.09Fe0.18Ti0.05O2 achieves a deeply desodiation and delivers charging capacity of 158.1 mA h g-1 corresponding to 0.61 Na with a high initial Coulombic efficiency of 98.2%. The charge compensation is attributed to the cationic and anionic redox reactions conjunctively. Moreover, the crystal structure is effectively stabilized, leading to a slight variation of lattice parameters. This research carries implications for the expedited development of low-cost, high-energy-density cathode materials for sodium-ion batteries.

Perspective on High-Stability Single-Crystal Li-Rich Cathode Materials for Li-Ion Batteries.

Benefiting from anionic and cationic redox reactions, Li-rich materials have been regarded as next-generation cathodes to overcome the bottleneck of energy density. However, they always suffer from cracking of polycrystalline (PC) secondary particles and lattice oxygen release, resulting in severe structural deterioration and capacity decay upon cycling. Single-crystal (SC) design has been proven as an effective strategy to relieve these issues in traditional Li-rich cathodes with PC morphology. Herein, we first reviewed the main synthesis routes of SC Li-rich materials including solid-state reaction, molten salt-assisted, and hydrothermal/solvothermal methods, in which the differences in grain morphology, electrochemical behaviors, and other properties induced by various routes were analyzed and discussed. Furthermore, the distinct characteristics were compared between SC and PC cathodes from the aspects of irreversible capacity, structural stability, capacity/voltage degradation, and gas release. Besides, recent advances in layered SC Li-rich oxide cathodes were summarized in detail, where the unique structural designs and modification strategies could greatly promote their structural/electrochemical stability. At last, challenges and perspectives for the emerging SC Li-rich cathodes were proposed, which provided an exceptional opportunity to achieve high-energy-density and high-stability Li-ion/metal batteries.

Integrating Lithium Sulfide as a Single Ionic Conductor Interphase for Stable All-Solid-State Lithium-Sulfur Batteries.

As a very prospective solid-state electrolyte, Li10GeP2S12 (LGPS) exhibits high ionic conductivity comparable to liquid electrolytes. However, severe self-decomposition and Li dendrite propagation of LGPS will be triggered due to the thermodynamic incompatibility with Li metal anode. Herein, by adopting a facile chemical vapor deposition method, an artificial solid electrolyte interphase composed of Li2S is proposed as a single ionic conductor to promote the interface stability of LGPS toward Li. The good electronic insulation coupled with ionic conduction property of Li2S effectively blocks electron transfer from Li to LGPS while enabling smooth passage of Li ions. Meanwhile, the generated Li2S layer remains good interface compatibility with LGPS, which is verified by the stable Li-plating/stripping operation for over 500 h at 0.15 mA cm-2. Consequently, the all-solid-state Li-S batteries (ASSLSBs) with a Li2S layer demonstrate superb capacity retention of 90.8% at 0.2 mA cm-2 after 100 cycles. Even at the harsh condition of 90 °C, the cell can deliver a high reversible capacity of 1318.8 mAh g-1 with decent capacity retention of 88.6% after 100 cycles. This approach offers a new insight for interface modification between LGPS and Li and the realization of ASSLSBs with stable cycle life.

Consummating ion desolvation in hard carbon anodes for reversible sodium storage.

Hard carbons are emerging as the most viable anodes to support the commercialization of sodium-ion (Na-ion) batteries due to their competitive performance. However, the hard carbon anode suffers from low initial Coulombic efficiency (ICE), and the ambiguous Na-ion (Na+) storage mechanism and interfacial chemistry fail to give a reasonable interpretation. Here, we have identified the time-dependent ion pre-desolvation on the nanopore of hard carbons, which significantly affects the Na+ storage efficiency by altering the solvation structure of electrolytes. Consummating the pre-desolvation by extending the aging time, generates a highly aggregated electrolyte configuration inside the nanopore, resulting in negligible reductive decomposition of electrolytes. When applying the above insights, the hard carbon anodes achieve a high average ICE of 98.21% in the absence of any Na supplementation techniques. Therefore, the negative-to-positive capacity ratio can be reduced to 1.02 for full cells, which enables an improved energy density. The insight into hard carbons and related interphases may be extended to other battery systems and support the continued development of battery technology.

Water Catchers within Sub-Nano Channels Promote Step-by-Step Zinc-Ion Dehydration Enable Highly Efficient Aqueous Zinc-Metal Batteries.

Zinc metal suffers from violent and long-lasting water-induced side reactions and uncontrollable dendritic Zn growth, which seriously reduce the coulombic efficiency (CE) and lifespan of aqueous zinc-metal batteries (AZMBs). To suppress the corresponding harmful effects of the highly active water, a stable zirconium-based metal-organic framework with water catchers decorated inside its sub-nano channels is used to protect Zn-metal. Water catchers within narrow channels can constantly trap water molecules from the solvated Zn-ions and facilitate step-by-step desolvation/dehydration, thereby promoting the formation of an aggregative electrolyte configuration, which consequently eliminates water-induced corrosion and side reactions. More importantly, the functionalized sub-nano channels also act as ion rectifiers and promote fast but even Zn-ions transport, thereby leading to a dendrite-free Zn metal. As a result, the protected Zn metal demonstrates an unprecedented cycling stability of more than 10 000 h and an ultra-high average CE of 99.92% during 4000 cycles. More inspiringly, a practical NH4V4O10//Zn pouch-cell is fabricated and delivers a capacity of 98 mAh (under high cathode mass loading of 25.7 mg cm-2) and preserves 86.2% capacity retention after 150 cycles. This new strategy in promoting highly reversible Zn metal anodes would spur the practical utilization of AZMBs.

Hybrid-Electrolytes System Established by Dual Super-lyophobic Membrane Enabling High-Voltage Aqueous Lithium Metal Batteries.

Aqueous electrolytes and related aqueous rechargeable batteries own unique advantage on safety and environmental friendliness, but coupling high energy density Li-metal batteries with aqueous electrolyte still represent challenging and not yet reported. Here, this work makes a breakthrough in "high-voltage aqueous Li-metal batteries" (HVALMBs) by adopting a brilliant hybrid-electrolytes strategy. Concentrated ternary-salts ether-based electrolyte (CTE) acts as the anolyte to ensure the stability and reversibility of Li-metal plating/stripping. Eco-friendly water-in-salt (WiS) electrolyte acts as catholyte to support the healthy operation of high-voltage cathodes. Most importantly, the aqueous catholyte and non-aqueous anolyte are isolated in each independent chamber without any crosstalk. Aqueous catholyte permeation toward Li anode can be completely prohibited without proton-induced corrosion, which is enabled by the introduction of under-liquid dual super-lyophobic membrane-based separator, which can realize the segregation of the most effective immiscible electrolytes with a surface tension difference as small as 6 mJ m-2. As a result, the aqueous electrolyte can be successfully coupled with Li-metal anode and achieve the fabrication of HVALMBs (hybrid-electrolytes system), which presents long-term cycle stability with a capacity retention of 81.0% after 300 cycles (LiNi0.8Mn0.1Co0.1O2 || Li (limited) cell) and high energy density (682 Wh kg-1).

Solvation-Tailored PVDF-Based Solid-State Electrolyte for High-Voltage Lithium Metal Batteries.

Poly(vinylidene fluoride) (PVDF)-based polymer electro-lytes are attracting increasing attention for high-voltage solid-state lithium metal batteries because of their high room temperature ionic conductivity, adequate mechanical strength and good thermal stability. However, the presence of highly reactive residual solvents, such as N, N-dimethylformamide (DMF), severely jeopardizes the long-term cycling stability. Herein, we propose a solvation-tailoring strategy to confine residual solvent molecules by introducing low-cost 3 Šzeolite molecular sieves as fillers. The strong interaction between DMF and the molecular sieve weakens the ability of DMF to participate in the solvation of Li+, leading to more anions being involved in solvation. Benefiting from the tailored anion-rich coordination environment, the interfacial side reactions with the lithium anode and high-voltage NCM811 cathode are effectively suppressed. As a result, the solid-state Li||Li symmetrical cells demonstrates ultra-stable cycling over 5100 h at 0.1 mA cm-2, and the Li||NCM811 full cells achieve excellent cycling stability for more than 1130 and 250 cycles under the charging cut-off voltages of 4.3 V and 4.5 V, respectively. Our work is an innovative exploration to address the negative effects of residual DMF in PVDF-based solid-state electrolytes and highlights the importance of modulating the solvation structures in solid-state polymer electrolytes.

Dual-ion conductors: from liquid to solid.

The traditional working principle within lithium-ion batteries relies on Li+ shuttling between the cathode and anode, namely the rocking-chair mechanism. A single working ion constrains the possibilities for battery design and the selection of electrode materials, while realizing multiple working ions offers the potential to break through the fundamental principles of traditional battery construction. Accordingly, it is necessary to develop dual-ion conductors to enable the migration of multiple working ions. This focus article starts by introducing traditional dual-ion batteries based on liquid electrolytes and their pros and cons. Then, solidifying liquid dual-ion conductors is expected to overcome these drawbacks, so the development of solid dual-ion conductors is discussed in detail. Specifically, basic design principles of solid dual-ion conductors are briefly proposed, including constructing continuous ion transport channels and choosing appropriately sized ion carriers. The potential applications of solid dual-ion conductors are also summarized, such as stabilizing the electrode/electrolyte interface and activating additional redox couples. The goal of this article is to inspire researchers in the development of dual-ion conductors and to contribute to the advancement of all-solid-state batteries.

A solid-state lithium-ion battery with micron-sized silicon anode operating free from external pressure.

Applying high stack pressure (often up to tens of megapascals) to solid-state Li-ion batteries is primarily done to address the issues of internal voids formation and subsequent Li-ion transport blockage within the solid electrode due to volume changes. Whereas, redundant pressurizing devices lower the energy density of batteries and raise the cost. Herein, a mechanical optimization strategy involving elastic electrolyte is proposed for SSBs operating without external pressurizing, but relying solely on the built-in pressure of cells. We combine soft-rigid dual monomer copolymer with deep eutectic mixture to design an elastic solid electrolyte, which exhibits not only high stretchability and deformation recovery capability but also high room-temperature Li-ion conductivity of 2×10-3 S cm-1 and nonflammability. The micron-sized Si anode without additional stack pressure, paired with the elastic electrolyte, exhibits exceptional stability for 300 cycles with 90.8% capacity retention. Furthermore, the solid Li/elastic electrolyte/LiFePO4 battery delivers 143.3 mAh g-1 after 400 cycles. Finally, the micron-sized Si/elastic electrolyte/LiFePO4 full cell operates stably for 100 cycles in the absence of any additional pressure, maintaining a capacity retention rate of 98.3%. This significantly advances the practical applications of solid-state batteries.

A P2/P3 Biphasic Layered Oxide Composite as a High-Energy and Long-Cycle-Life Cathode for Potassium-Ion Batteries.

Layered transition metal oxides are extensively considered as appealing cathode candidates for potassium-ion batteries (PIBs) due to their abundant raw materials and low cost, but their further implementations are limited by slow dynamics and impoverished structural stability. Herein, a layered composite having a P2 and P3 symbiotic structure is designed and synthesized to realize PIBs with large energy density and long-term cycling stability. The unique intergrowth of P2 and P3 phases in the obtained layered oxide is plainly characterized by X-ray diffraction refinement, high-angle annular dark field and annular bright field-scanning transmission electron microscopy at atomic resolution, and Fourier transformation images. The synergistic effect of the two phases of this layered P2/P3 composite is well demonstrated in K+ intercalation/extraction process. The as-prepared layered composite can present a large discharge capacity with the remarkable energy density of 321 Wh kg-1 and also manifest excellent capacity preservation after 600 cycles of K+ uptake/removal.

Chelating Additive Regulating Zn-Ion Solvation Chemistry for Highly Efficient Aqueous Zinc-Metal Battery.

Aqueous zinc-metal batteries (AZMBs) usually suffered from poor reversibility and limited lifespan because of serious water induced side-reactions, hydrogen evolution reactions (HER) and rampant zinc (Zn) dendrite growth. Reducing the content of water molecules within Zn-ion solvation sheaths can effectively suppress those inherent defects of AZMBs. In this work, we originally discovered that the two carbonyl groups of N-Acetyl-ϵ-caprolactam (N-ac) chelating ligand can serve as dual solvation sites to coordinate with Zn2+, thereby minimizing water molecules within Zn-ion solvation sheaths, and greatly inhibit water-induced side-reactions and HER. Moreover, the N-ac chelating additive can form a unique physical barrier interface on Zn surface, preventing the harmful contacting with water. In addition, the preferential adsorption of N-ac on Zn (002) facets can promote highly reversible and dendrite-free Zn2+ deposition. As a result, Zn//Cu half-cell within N-ac added electrolyte delivered ultra-high 99.89 % Coulombic efficiency during 8000 cycles. Zn//Zn symmetric cells also demonstrated unprecedented long life of more than 9800 hours (over one year). Aqueous Zn//ZnV6O16 ⋅ 8H2O (Zn//ZVO) full-cell preserved 78 % capacity even after ultra-long 2000 cycles. A more practical pouch-cell was also obtained (90.2 % capacity after 100 cycles). This method offers a promising strategy for accelerating the development of highly efficient AZMBs.

A rechargeable calcium-oxygen battery that operates at room temperature.

Calcium-oxygen (Ca-O2) batteries can theoretically afford high capacity by the reduction of O2 to calcium oxide compounds (CaOx) at low cost1-5. Yet, a rechargeable Ca-O2 battery that operates at room temperature has not been achieved because the CaOx/O2 chemistry typically involves inert discharge products and few electrolytes can accommodate both a highly reductive Ca metal anode and O2. Here we report a Ca-O2 battery that is rechargeable for 700 cycles at room temperature. Our battery relies on a highly reversible two-electron redox to form chemically reactive calcium peroxide (CaO2) as the discharge product. Using a durable ionic liquid-based electrolyte, this two-electron reaction is enabled by the facilitated Ca plating-stripping in the Ca metal anode at room temperature and improved CaO2/O2 redox in the air cathode. We show the proposed Ca-O2 battery is stable in air and can be made into flexible fibres that are weaved into textile batteries for next-generation wearable systems.

From Oxygen Redox to Sulfur Redox: A Paradigm for Li-Rich Layered Cathodes.

The utilization of anionic redox chemistry provides an opportunity to further improve the energy density of Li-ion batteries, particularly for Li-rich layered oxides. However, oxygen-based hosts still suffer from unfavorable structural rearrangement, including the oxygen release and transition metal (TM)-ion migration, in association with the tenuous framework rooted in the ionicity of the TM-O bonding. An intrinsic solution, by using a sulfur-based host with strong TM-S covalency, is proposed here to buffer the lattice distortion upon the highly activating sulfur redox process, and it achieves howling success in stabilizing the host frameworks. Experimental results demonstrate the prolonged preservation of the layered sulfur lattice, especially the honeycomb superlattice, during the Li+ extraction/insertion process in contrast to the large structural degeneration in Li-rich oxides. Moreover, the Li-rich sulfide cathodes exhibited a negligible overpotential of 0.08 V and a voltage drop of 0.13 mV/cycle, while maintaining a substantial reversible capacity upon cycling. These superior electrochemical performances can be unambiguously ascribed to the much shorter trajectories of sulfur in comparison to those of oxygen revealed by molecular dynamics simulations at a large scale (∼30 nm) and a long time scale (∼300 ps) via high-dimensional neural network potentials during the delithiation process. Our findings highlight the importance of stabilizing host frameworks and establish general guidance for designing Li-rich cathodes with durable anionic redox chemistry.

Molecular Engineering Enabling High Initial Coulombic Efficiency and Rubost Solid Electrolyte Interphase for Hard Carbon in Sodium-Ion Batteries.

Hard carbon (HC) as a potential candidate anode for sodium-ion batteries (SIBs) suffers from unstable solid electrolyte interphase (SEI) and low initial Coulombic efficiency (ICE), which limits its commercial applications and urgently requires the emergence of a new strategy. Herein, an organic molecule with two sodium ions, disodium phthalate (DP), was successfully engineered on the HC surface (DP-HC) to replenish the sodium loss from solid electrolyte interphase (SEI) formation. A stabilized and ultrathin (≈7.4 nm) SEI was constructed on the DP-HC surface, which proved to be simultaneously suitable in both ester and ether electrolytes. Compared to pure HC (60.8 %), the as-designed DP-HC exhibited a high ICE of >96.3 % in NaPF6 in diglyme (G2) electrolyte, and is capable of servicing consistently for >1600 cycles at 0.5 A g-1 . The Na3 V2 (PO4 )3 (NVP)|DP-HC full-cell with a 98.3 % exceptional ICE can be cycled stably for 450 cycles, demonstrating the tremendous practical application potential of DP-HC. This work provides a molecular design strategy to improve the ICE of HC, which will inspire more researchers to concentrate on the commercialization progress of HC.

Boosting a practical Li-CO2 battery through dimerization reaction based on solid redox mediator.

Li-CO2 batteries offer a promising avenue for converting greenhouse gases into electricity. However, the inherent challenge of direct electrocatalytic reduction of inert CO2 often results in the formation of Li2CO3, causing a dip in output voltage and energy efficiency. Our innovative approach involves solid redox mediators, affixed to the cathode via a Cu(II) coordination compound of benzene-1,3,5-tricarboxylic acid. This technique effectively circumvents the shuttle effect and sluggish kinetics associated with soluble redox mediators. Results show that the electrochemically reduced Cu(I) solid redox mediator efficiently captures CO2, facilitating Li2C2O4 formation through a dimerization reaction involving a dimeric oxalate intermediate. The Li-CO2 battery employing the Cu(II) solid redox mediator boasts a higher discharge voltage of 2.8 V, a lower charge potential of 3.7 V, and superior cycling performance over 400 cycles. Simultaneously, the successful development of a Li-CO2 pouch battery propels metal-CO2 batteries closer to practical application.

Molecular Engineering toward Robust Solid Electrolyte Interphase for Lithium Metal Batteries.

Lithium-metal batteries (LMBs) with high energy density are becoming increasingly important in global sustainability initiatives. However, uncontrollable dendrite seeds, inscrutable interfacial chemistry, and repetitively formed solid electrolyte interphase (SEI) have severely hindered the advancement of LMBs. Organic molecules have been ingeniously engineered to construct targeted SEI and effectively minimize the above issues. In this review, multiple organic molecules, including polymer, fluorinated molecules, and organosulfur, are comprehensively summarized and insights into how to construct the corresponding elastic, fluorine-rich, and organosulfur-containing SEIs are provided. A variety of meticulously selected cases are analyzed in depth to support the arguments of molecular design in SEI. Specifically, the evolution of organic molecules-derived SEI is discussed and corresponding design principles are proposed, which are beneficial in guiding researchers to understand and architect SEI based on organic molecules. This review provides a design guideline for constructing organic molecule-derived SEI and will inspire more researchers to concentrate on the exploitation of LMBs.

Solid-State Electrolytes and Electrode/Electrolyte Interfaces in Rechargeable Batteries.

Solid-state batteries (SSBs) are considered to be one of the most promising candidates for next-generation energy storage systems due to the high safety, high energy density and wide operating temperature range of solid-state electrolytes (SSEs) they use. Unfortunately, the practical application of SSEs has rarely been successful, which is largely attributed to the low chemical stability and ionic conductivity, ineluctable solid-solid interface issues including limited ion transport channels, high energy barriers, and poor interface contact. A comprehensive understanding of ion transport mechanisms of various SSEs, interactions between fillers and polymer matrixes and the role of the interface in SSBs are indispensable for rational design and performance optimization of novel electrolytes. The categories, research advances and ion transport mechanism of inorganic glass/ceramic electrolytes, polymer-based electrolytes and corresponding composite electrolytes are detailly summarized and discussed. Moreover, interface contact and compatibility between electrolyte and cathode/anode are also briefly discussed. Furthermore, the electrochemical characterization methods of SSEs used in different types of SSBs are also introduced. On this basis, the principles and prospects of novel SSEs and interface design are curtly proposed according to the development requirements of SSBs. Moreover, the advanced characterizations for real-time monitoring of interface changes are also brought forward to promote the development of SSBs.

High Entropy-Induced Kinetics Improvement and Phase Transition Suppression in K-Ion Battery Layered Cathodes.

Layered oxides are widely accepted to be promising cathode candidate materials for K-ion batteries (KIBs) in terms of their rich raw materials and low price, while their further applications are restricted by sluggish kinetics and poor structural stability. Here, the high-entropy design concept is introduced into layered KIB cathodes to address the above issues, and an example of high-entropy layered K0.45Mn0.60Ni0.075Fe0.075Co0.075Ti0.10Cu0.05Mg0.025O2 (HE-KMO) is successfully prepared. Benefiting from the high-entropy oxide with multielement doping, the developed HE-KMO exhibits half-metallic oxide features with a narrow bandgap of 0.19 eV. Increased entropy can also reduce the surface energy of the {010} active facets, resulting in about 2.6 times more exposure of the {010} active facets of HE-KMO than the low-entropy K0.45MnO2 (KMO). Both can effectively improve the kinetics in terms of electron conduction and K+ diffusion. Furthermore, high entropy can inhibit space charge ordering during K+ (de)insertion, and the transition metal-oxygen covalent interaction of HE-KMO is also enhanced, leading to suppressed phase transition of HE-KMO in 1.5-4.2 V and better electrochemical stability of HE-KMO (average capacity drop of 0.20%, 200 cycles) than the low-entropy KMO (average capacity drop of 0.41%, 200 cycles) in the wide voltage window.

A prototype of dual-ion conductor for all-solid-state lithium batteries.

All-solid-state batteries (ASSBs) represent a promising battery strategy to achieve high energy density with great safety. However, inadequate kinetic property and poor interfacial compatibility remain great challenges, which impede their practical application. A prototype of dual-ion conductor of Li+ synchronized with Cu+ unlocks a four-electron redox reaction with high reversibility and fast kinetics. As a result, the constructed ASSB exhibited a high reversible capacity of 603.0 mA·hour g-1 and an excellent cycling retention of 93.2% over 1500 cycles. Moreover, because of the ion highway connecting active materials and catholytes constructed by dual-ion conductor, remarkable temperature tolerance (-60°C) and excellent rate performance (231.6 mA·hour g-1 at 20 mA cm-2) were achieved. The superior electrochemical performance can be ascribed to the migration pathway with small energy barrier and low tortuosity once the Cu+ introduced into Li6PS5Cl. This work creates a unique perspective of ASSBs with dual-ion conducting strategy, thus inspiring a potential developing strategy of state-of-the-art ASSBs.