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Highlights: A molecular-sieving electrode coating towards low-concentrated aqueous sodium-ion batteries is constructed by applying a composite of NaX zeolite and NaOH-neutralized Nafion. Resulting from a molecular sieving effect of zeolite channels and size-shrunken ionic domains in Nafion, the as-prepared coating layer reject hydrated Na+ ions and allow fast dehydrated Na+ permeance. 200 cycles of Na2MnFe(CN)6//NaTi2(PO4)3 full cells can be achieved in a practically feasible 2 m aqueous electrolyte. Aqueous sodium-ion batteries are known for poor rechargeability because of the competitive water decomposition reactions and the high electrode solubility. Improvements have been reported by salt-concentrated and organic-hybridized electrolyte designs, however, at the expense of cost and safety. Here, we report the prolonged cycling of ASIBs in routine dilute electrolytes by employing artificial electrode coatings consisting of NaX zeolite and NaOH-neutralized perfluorinated sulfonic polymer. The as-formed composite interphase exhibits a molecular-sieving effect jointly played by zeolite channels and size-shrunken ionic domains in the polymer matrix, which enables high rejection of hydrated Na+ ions while allowing fast dehydrated Na+ permeance. Applying this coating to electrode surfaces expands the electrochemical window of a practically feasible 2 mol kg–1 sodium trifluoromethanesulfonate aqueous electrolyte to 2.70 V and affords Na2MnFe(CN)6//NaTi2(PO4)3 full cells with an unprecedented cycling stability of 94.9% capacity retention after 200 cycles at 1 C. Combined with emerging electrolyte modifications, this molecular-sieving interphase brings amplified benefits in long-term operation of ASIBs. [ABSTRACT FROM AUTHOR]

Hydrogel electrolytes hold great promise in developing flexible and safe batteries, but the presence of free solvent water makes battery chemistries constrained by H2 evolution and electrode dissolution. Although maximizing salt concentration is recognized as an effective strategy to reduce water activity, the protic polymer matrices in classical hydrogels are occupied with hydrogen‐bonding and barely involved in the salt dissolution, which sets limitations on realizing stable salt‐concentrated environments before polymer‐salt phase separation occurs. Inspired by the role of protein methylation in regulating intracellular phase separation, here we transform the "inert" protic polymer skeletons into aprotic ones through methylation modification to weaken the hydrogen‐bonding, which releases free hydrogen bond acceptors as Lewis base sites to participate in cation solvation and thus assist salt dissolution. An unconventionally salt‐concentrated hydrogel electrolyte reaching a salt fraction up to 44 mol % while retaining a high Na+/H2O molar ratio of 1.0 is achieved without phase separation. Almost all water molecules are confined in the solvation shell of Na+ with depressed activity and mobility, which addresses water‐induced parasitic reactions that limit the practical rechargeability of aqueous sodium‐ion batteries. The assembled Na3V2(PO4)3//NaTi2(PO4)3 cell maintains 82.8 % capacity after 580 cycles, which is the longest cycle life reported to date. [ABSTRACT FROM AUTHOR]

Aqueous zinc batteries (AZBs) show promising applications in large-scale energy storage and wearable devices mainly because of their low cost and intrinsic safety. However, zinc metal anodes suffer from dendrite issues and side reactions, seriously hindering their practical applications. Two-dimensional (2D) materials with atomic thickness and large aspect ratio possess excellent physicochemical properties, providing opportunities to rationally design and construct practically reversible zinc metal anodes. Here, we systematically summarize the recent progress of 2D materials (e.g., graphene and MXene) that can be used to enable dendrite-free zinc metal anodes for AZBs. Firstly, the construction methods and strategies of 2D materials/Zn hybrid anodes are briefly reviewed, and are classified into protecting layers on Zn foils and host materials for Zn. Secondly, various 2D material/Zn hybrid anodes are elaborately introduced, and the key roles played by 2D materials in stabilizing the Zn/Zn2+ redox process are specially emphasized. Finally, the challenges and perspectives of advanced 2D materials for advanced Zn anodes in next-generation AZBs are briefly discussed. [ABSTRACT FROM AUTHOR]

Rechargeable aqueous Zn/MnO2 batteries are very potential for large-scale energy storage applications owing to their low cost, inherent safety, and high theoretical capacity. However, the MnO2 cathode delivers unsatisfactory cycling performance owing to its low intrinsic electronic conductivity and dissolution issue. Herein, we design and synthesize a Ag-doped sea-urchin-like MnO2 material for rechargeable zinc-ion batteries (ZIBs). Doping Ag was found to reduce charge transfer resistance, increase the redox activity, and improve the cycling stability of MnO2. The unique sea-urchin-like structure maintains rich active sites for charge storage. As a result, the Ag-doped MnO2-based ZIB presents a high reversible specific capacity to 315 mA h g−1 at 50 mA g−1, excellent rate performance, and a capacity retention of 94.4% when cycling over 500 cycles. An ex situ TEM test demonstrates the low-dissolution property of Ag-doped MnO2. A flexible quasi-solid-state ZIB is successfully assembled using Ag-doped MnO2 on graphite paper, which shows a stable specific capacity of 171 mA h g−1 at 1 A g−1 when cycled over 600 cycles. Our investigation demonstrates the significant role played by Ag doping in enhancing the ZIB performance of MnO2, and gives some insight into developing advanced active materials by heteroatom doping. [ABSTRACT FROM AUTHOR]

Aqueous sodium‐ion batteries are promising candidates for grid‐scale energy storage due to their high safety and low cost. However, the constant dissolution of vanadium‐based electrodes and protective solid‐electrolyte interphase (SEI) in aqueous electrolytes severely limits the cycle life. Herein, using adiponitrile as a functional co‐solvent, we designed a super‐concentrated aqueous sodium electrolyte (Na+/H2O=1, molar ratio) to confine almost all water molecules within the primary solvation shell of Na+ with decreased activity. Such a unique solvation structure not only expands the electrochemical stability window of the electrolyte to 2.75 V, but also greatly alleviates the dissolution of vanadium‐based electrodes and NaF‐rich SEI. The assembled Na3V2(PO4)3/NaTi2(PO4)3 battery delivers an average Coulombic efficiency of 99.6 % with 71 % capacity retention after 1000 cycles at 5 C. In addition, the freezing point of the electrolyte could be reduced −79 °C while retaining appreciable low‐temperature conductivity due to the disrupted hydrogen bond among water molecules. [ABSTRACT FROM AUTHOR]

Electrolyte/electrode heterointerfaces activated by unhindered charge transfer play an important role in solid‐state and flexible batteries. However, continuous electrochemical cycling and mechanical deformations cause structural dislocation and unwanted reactions. An important challenge is to ensure enduring accurate contact between the battery components. The customization of a highly viscoelastic polyamide (PA, nylon)‐based solid electrolyte to address this key issue is presented. The approach involves the use of concentrated aqueous solutions of bis(trifluoromethane)sulfonimide lithium (LiTFSI) to structurally "unzip" and relink pristine hydrogen‐bonded PA chains by bridged cation–anion association. This elaborately tailored crosslinking technique confers upon the resultant electrolyte a combination of the preferred mechanical characteristics including high viscoelasticity and reversible stretchability, together with outstanding electrochemical performance represented by high ion conductivity (2.7 × 10−4 S cm−1) and high anodic stability (>3 V vs Zn/Zn2+). Flexible batteries with a well‐integrated configuration in which synchronous electrolyte/electrode movement guarantees intimate and compatible interfaces even during extreme deformations and electrochemical stimulations, are further demonstrated. These results reveal a promising opportunity to overcome the bottleneck caused by interfacial defects for next‐generation solid batteries by reconstituting the structure of classical polymers and developing functional electrolytes. [ABSTRACT FROM AUTHOR]

Flexible batteries are essential for wearable electronic devices. To meet practical applications, they need to be mechanically robust and stable. However, strong or multiple bending may sever the interfacial contact between electrode and electrolyte, causing capacity fading or even battery failure. Herein we present a new cooling-recovery concept for flexible batteries, which involves a temperature-sensitive sol-gel transition behavior of the thermoreversible polymer hydrogel electrolyte. Once a battery has suffered from strong mechanical stresses, a simple cooling process can refresh the electrode-electrolyte interface. The energy-storage capability can be recovered with a healing efficiency higher than 98 %. It is believed that this study not only offers new valuable insights, but also opens up new perspectives to develop functional wearable devices. [ABSTRACT FROM AUTHOR]