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Solid polymer electrolytes (SPEs) have the potential to meet evolving Li‐ion battery demands, but for these electrolytes to satisfy growing power and energy density requirements, both transport properties and electrochemical stability must be improved. Unfortunately, improvement in one of these properties often comes at the expense of the other. To this end, a "hybrid aqueous/ionic liquid" SPE (HAILSPE) which incorporates triethylsulfonium‐TFSI (S2,2,2) or N‐methyl‐N‐propylpyrrolidinium‐TFSI (Pyr1,3) ionic liquid (IL) alongside H2O and LiTFSI salt to simultaneously improve transport and electrochemical stability is studied. This work focuses on the impact of HAILSPE composition on electrochemical performance. Analysis shows that an increase in LiTFSI content results in decreased ionic mobility, while increasing IL and water content can offset its impact. pfg‐NMR results reveal that preferential lithium‐ion transport is present in HAILSPE systems. Higher IL concentrations are correlated with an increased degree of passivation against H2O reduction. Compared to the Pyr1,3 systems, the S2,2,2 systems exhibit a stronger degree of passivation due to the formation of a multicomponent interphase layer, including LiF, Li2CO3, Li2S, and Li3N. The results herein demonstrate the superior electrochemical stability of the S2,2,2 systems compared to Pyr1,3 and provide a path toward further enhancement of HAILSPE performance via composition optimization. [ABSTRACT FROM AUTHOR]

Nowadays, electrolytes for commercial batteries are mostly liquid solutions composed of solvent and salt to migrate the ions. However, solvents of the electrolyte bring several inherent limitations, either the electrochemical window, working temperature, volatility or flammability. Herein, we report polyphosphoric acid as a solvent-free protic liquid electrolyte, which excludes the demerits of solvent and exhibits unprecedented superiorities, including nonflammability, wider electrochemical stability window (>2.5 V) than aqueous electrolyte, low volatility and wide working temperature range (>400 °C). The proton conductive electrolyte enables MoO3/LiVPO4F rocking-chair battery to operate well in a wide temperature range from 0 °C to 250 °C and deliver a high power density of 4975 W kg−1 at a high temperature of 100 °C. The solvent-free electrolyte could provide a viable route for the stable and safe batteries working under harsh conditions, opening up a route towards designing wide-temperature electrolytes. It is challenging to prepare electrolyte that could achieve wide electrochemical window, broad working temperature, non-inflammability, and fast ion transport simultaneously. Here the authors report a rocking-chair proton battery utilizing a solvent-free protic liquid electrolyte, which could operate in a broad temperature range from 0 to 250 celsius degree. [ABSTRACT FROM AUTHOR]

Water‐in‐salt (WIS) electrolytes using super‐concentrated organic lithium (Li) salts are of interest for aqueous Li‐ion batteries. However, the high salt cost, high viscosity, poor wettability, and environmental hazards remain a great challenge. Herein, we present a localized water‐in‐salt (LWIS) electrolyte based on low‐cost lithium nitrate (LiNO3) salt and 1,5‐pentanediol (PD) as inert diluent. The addition of PD maintains the solvation structure of the WIS electrolyte, improves the electrolyte stability via hydrogen‐bonding interactions with water and NO3− molecules, and reduces the total salt concentration. By in situ gelling the LWIS electrolyte with tetraethylene glycol diacrylate (TEGDA) monomer, the electrolyte stability window can be further expanded to 3.0 V. The as‐developed Mo6S8|LWIS gel electrolyte|LiMn2O4 (LMO) batteries delivered outstanding cycling performance with an average Coulombic efficiency of 98.53 % after 250 cycles at 1 C. [ABSTRACT FROM AUTHOR]

Aqueous Zn batteries promise high energy density but suffer from Zn dendritic growth and poor low‐temperature performance. Here, we overcome both challenges by using an eutectic 7.6 m ZnCl2 aqueous electrolyte with 0.05 m SnCl2 additive, which in situ forms a zincophilic/zincophobic Sn/Zn5(OH)8Cl2⋅H2O bilayer interphase and enables low temperature operation. Zincophilic Sn decreases Zn plating/stripping overpotential and promotes uniform Zn plating, while zincophobic Zn5(OH)8Cl2⋅H2O top‐layer suppresses Zn dendrite growth. The eutectic electrolyte has a high ionic conductivity of ≈0.8 mS cm−1 even at −70 °C due to the distortion of hydrogen bond network by solvated Zn2+ and Cl−. The eutectic electrolyte enables Zn∥Ti half‐cell a high Coulombic efficiency (CE) of >99.7 % for 200 cycles and Zn∥Zn cell steady charge/discharge for 500 h with a low overpotential of 8 mV at 3 mA cm−2. Practically, Zn∥VOPO4 batteries maintain >95 % capacity with a CE of >99.9 % for 200 cycles at −50 °C, and retain ≈30 % capacity at −70 °C of that at 20 °C. [ABSTRACT FROM AUTHOR]

Aqueous rechargeable nickel‐zinc batteries (NZBs) have the advantages of economical cost and reliable safety. Despite reports of success in achieving high‐utilization and stable Zn anodes, the practical application of NZBs has been plagued by the restrictive capacity density and degradation of the Ni‐based cathode. Herein, it is reported that nickel‐ligand coordination grids (NCGs) with a high theoretical capacity of 128.12 mAh g−1 offer a fast faradic reaction while maintaining good reversibility due to the abundant open metal sites and flexible network structures. In situ and ex situ characterizations demonstrate that the graphene nanosheet (GN) modification of NCGs supramolecular substantially boosts surface charge and reducing the work function of supramolecular compounds. A Ni//Zn battery using such a graphene organic‐inorganic material (G‐NCGs) achieve a high gravimetric capacity of 113.8 mAh g−1 at 0.5 A g−1 with 50% of its initial capacitance retained after 2000 cycles and an exceptional rate capacity of 43.3 mAh g−1 even at the current density of 5.0 A g−1. [ABSTRACT FROM AUTHOR]

Aqueous Zn batteries are challenged by water decomposition and dendrite growth due to the absence of a dense Zn‐ion conductive solid electrolyte interphase (SEI) to inhibit the hydrogen evolution reaction (HER). Here, we design a low‐concentration aqueous Zn(OTF)2‐Zn(NO3)2 electrolyte to in situ form a robust inorganic ZnF2‐Zn5(CO3)2(OH)6‐organic bilayer SEI, where the inorganic inner layer promotes Zn‐ion diffusion while the organic outer layer suppresses water penetration. We found that the insulating Zn5(OH)8(NO3)2⋅2 H2O layer is first formed on the Zn anode surface by the self‐terminated chemical reaction of NO3− with Zn2+ and OH− generated via HER, and then it transforms into Zn‐ion conducting Zn5(CO3)2(OH)6, which in turn promotes the formation of ZnF2 as the inner layer. The organic‐dominated outer layer is formed by the reduction of OTF−. The in situ formed SEI enables a high Coulombic efficiency (CE) of 99.8 % for 200 h in Ti∥Zn cells, and a high energy density (168 Wh kg−1) with 96.5 % retention for 700 cycles in Zn∥MnO2 cells with a low Zn/MnO2 capacity ratio of 2:1. [ABSTRACT FROM AUTHOR]

Aqueous rechargeable zinc metal batteries promise attractive advantages including safety, high volumetric energy density, and low cost; however, such benefits cannot be unlocked unless Zn reversibility meets stringent commercial viability. Herein, we report remarkable improvements on Zn reversibility in aqueous electrolytes when phosphonium‐based cations are used to reshape interfacial structures and interphasial chemistries, particularly when their ligands contain an ether linkage. This novel aqueous electrolyte supports unprecedented Zn reversibility by showing dendrite‐free Zn plating/stripping for over 6400 h at 0.5 mA cm−2, or over 280 h at 2.5 mA cm−2, with coulombic efficiency above 99 % even with 20 % Zn utilization per cycle. Excellent full cell performance is demonstrated with Na2V6O16⋅1.63 H2O cathode, which cycles for 2000 times at 300 mA g−1. The microscopic characterization and modeling identify the mechanism of unique interphase chemistry from phosphonium and its functionalities as the key factors responsible for dictating reversible Zn chemistry [ABSTRACT FROM AUTHOR]

Rechargeable multivalent metal (e.g., Ca, Mg or, Al) batteries are ideal candidates for large–scale electrochemical energy storage due to their intrinsic low cost. However, their practical application is hampered by the low electrochemical reversibility, dendrite growth at the metal anodes, sluggish multivalent–ion kinetics in metal oxide cathodes and, poor electrode compatibility with non–aqueous organic–based electrolytes. To circumvent these issues, here we report various aqueous multivalent–ion batteries comprising of concentrated aqueous gel electrolytes, sulfur–containing anodes and, high-voltage metal oxide cathodes as alternative systems to the non–aqueous multivalent metal batteries. This rationally designed aqueous battery chemistry enables satisfactory specific energy, favorable reversibility and improved safety. As a demonstration model, we report a room–temperature calcium-ion/sulfur| |metal oxide full cell with a specific energy of 110 Wh kg–1 and remarkable cycling stability. Molecular dynamics modeling and experimental investigations reveal that the side reactions could be significantly restrained through the suppressed water activity and formation of a protective inorganic solid electrolyte interphase. The unique redox chemistry of the multivalent–ion system is also demonstrated for aqueous magnesium–ion/sulfur||metal oxide and aluminum–ion/sulfur||metal oxide full cells. Rechargeable multivalent-ion batteries are promising candidates for future energy storage technologies. Here, the authors develop various aqueous multivalent-ion cells using concentrated aqueous gel electrolytes, sulfur-containing anodes, and high-voltage metal oxide cathodes. [ABSTRACT FROM AUTHOR]

Aqueous Zn batteries are promising energy‐storage devices. However, their lifespan is limited by irreversible Zn anodes owing to water decomposition and Zn dendrite growth. Here, we separate aqueous electrolyte from Zn anode by coating a thin MOF layer on anode and filling the pores of MOF with hydrophobic Zn(TFSI)2‐tris(2,2,2‐trifluoroethyl)phosphate (TFEP) organic electrolyte that is immiscible with aqueous Zn(TFSI)2–H2O bulk electrolyte. The MOF encapsulated Zn(TFSI)2‐TFEP forms a ZnF2‐Zn3(PO4)2 solid electrolyte interphase (SEI) preventing Zn dendrite and water decomposition. The Zn(TFSI)2‐TFEP@MOF electrolyte protected Zn anode enables a Zn||Ti cell to achieve a high average Coulombic efficiency of 99.1 % for 350 cycles. The highly reversible Zn anode brings a high energy density of 210 Wh kg−1 (of cathode and anode mass) and a low capacity decay rate of 0.0047 % per cycle over 600 cycles in a Zn||MnO2 full cell with a low capacity ratio of Zn:MnO2 at 2:1. [ABSTRACT FROM AUTHOR]

Zn metal has been regarded as the most promising anode for aqueous batteries due to its high capacity, low cost, and environmental benignity. Zn anode still suffers, however, from low Coulombic efficiency due to the side reactions and dendrite growth in slightly acidic electrolytes. Here, the Zn plating/stripping mechanism is thoroughly investigated in 1 m ZnSO4 electrolyte, demonstrating that the poor performance of Zn metal in mild electrolyte should be ascribed to the formation of a porous by‐product (Zn4SO4(OH)6·xH2O) layer and serious dendrite growth. To suppress the side reactions and dendrite growth, a highly viscoelastic polyvinyl butyral film, functioning as an artificial solid/electrolyte interphase (SEI), is homogeneously deposited on the Zn surface via a simple spin‐coating strategy. This dense artificial SEI film not only effectively blocks water from the Zn surface but also guides the uniform stripping/plating of Zn ions underneath the film due to its good adhesion, hydrophilicity, ionic conductivity, and mechanical strength. Consequently, this side‐reaction‐free and dendrite‐free Zn electrode exhibits high cycling stability and enhanced Coulombic efficiency, which also contributes to enhancement of the full‐cell performance when it is coupled with MnO2 and LiFePO4 cathodes. [ABSTRACT FROM AUTHOR]

Narrow electrochemical stability window (1.23 V) of aqueous electrolytes is always considered the key obstacle preventing aqueous sodium-ion chemistry of practical energy density and cycle life. The sodium-ion water-in-salt electrolyte (NaWiSE) eliminates this barrier by offering a 2.5 V window through suppressing hydrogen evolution on anode with the formation of a Na+-conducting solid-electrolyte interphase (SEI) and reducing the overall electrochemical activity of water on cathode. A full aqueous Na-ion battery constructed on Na0.66[Mn0.66Ti0.34]O2 as cathode and NaTi2(PO4)3 as anode exhibits superior performance at both low and high rates, as exemplified by extraordinarily high Coulombic efficiency (>99.2%) at a low rate (0.2 C) for >350 cycles, and excellent cycling stability with negligible capacity losses (0.006% per cycle) at a high rate (1 C) for >1200 cycles. Molecular modeling reveals some key differences between Li-ion and Na-ion WiSE, and identifies a more pronounced ion aggregation with frequent contacts between the sodium cation and fluorine of anion in the latter as one main factor responsible for the formation of a dense SEI at lower salt concentration than its Li cousin. [ABSTRACT FROM AUTHOR]

Bipolar materials, which work as both the cathode and anode material in aqueous sodium-ion batteries, have advantages over aqueous electrolytes such as the low cost of sodium and high convenience of the material processing. However, the available materials are greatly limited. Herein, Prussian blue FeFe(CN)6 nanocubes were successfully synthesized by using a modified co-precipitation method. Owing to the well-separated redox reactions, fair cycling stability and rate capability of FeFe(CN)6, it could be developed as a bipolar material in an aqueous sodium-ion battery. The as-obtained full battery exhibits good cycling stability and rate capability. It was able to deliver a capacity of 32 mAhg-1 at 20 C, 76% of the capacity at 2 C. After 200 cycles at 2 C, 97% of the initial capacity was maintained for this battery, which suggests good cycling stability. [ABSTRACT FROM AUTHOR]

Rechargeable alkaline zinc-air batteries promise high energy density and safety but suffer from the sluggish 4 electron (e−)/oxygen (O2) chemistry that requires participation of water and from the electrochemical irreversibility originating from parasitic reactions caused by caustic electrolytes and atmospheric carbon dioxide. Here, we report a zinc-O2/zinc peroxide (ZnO2) chemistry that proceeds through a 2e−/O2 process in nonalkaline aqueous electrolytes, which enables highly reversible redox reactions in zinc-air batteries. This ZnO2 chemistry was made possible by a water-poor and zinc ion (Zn2+)–rich inner Helmholtz layer on the air cathode caused by the hydrophobic trifluoromethanesulfonate anions. The nonalkaline zinc-air battery thus constructed not only tolerates stable operations in ambient air but also exhibits substantially better reversibility than its alkaline counterpart. [ABSTRACT FROM AUTHOR]

The rapid growth in demand for lithium-ion batteries that can deliver more energy and power has generated concerns over safety. Aqueous electrolytes are a strong candidate to alleviate this apprehension, however their ability to overcome the "cathodic challenge" is limited due to anion-dominated passivation at the anode. In this work, the recently developed "hybrid aqueous/nonaqueous" electrolyte (HANE) strategy was employed to tune the degree of passivation at the anode in solid polymer electrolytes (SPEs) by using various ionic liquids as the nonaqueous component. Whereas common HANE systems sacrifice ionic conductivity to create a more robust passivation layer at the cathodic limit, the "hybrid aqueous/ionic liquid" SPEs (HAILSPEs) investigated in this work do not. Two HAILSPE systems (H1, H2.5) were fabricated from a blend of polyacrylonitrile (PAN), water, lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), and either triethylsulfonium-TFSI (S 2,2,2) or N -methyl- N -propylpyrrolidinium-TFSI (Pyr 1,3). These HAILSPE systems demonstrated a remarkable improvement in transport properties compared to their predecessors, achieving room temperature ionic conductivities of up to 5.39 mS/cm. A reduction in apparent activation energy and nearly complete decoupling of ionic transport from polymer chain mobility were found to contribute to this increase. Stable and complete growth of a passivating layer at 2 V vs. Li/Li+ was also observed, which was tuned by changing the ionic liquid. The work presented here provides a potential route for overcoming the "cathodic challenge" in aqueous SPEs. [Display omitted] [ABSTRACT FROM AUTHOR]

High electrochemical reversibility of the TiS 2 anode in “Water-in-Salt” electrolyte (21 m LiTFSI in H 2 O) is demonstrated for the first time. The wide electrochemical window and low chemical activity of H 2 O in the “Water-in-Salt” electrolyte not only significantly enhanced the electrochemical reversibility of TiS 2 but also effectively suppressed the hydrolysis side reaction in the aqueous electrolyte. Paired with a LiMn 2 O 4 cathode, the LiMn 2 O 4 /TiS 2 full cell delivers a relatively high discharge voltage of 1.7 V and an energy density of 78 Wh kg − 1 as well as a satisfactory rate performance. [ABSTRACT FROM AUTHOR]

A system of electrolytes using water as a solvent was successfully used to support a typical lithium-ion battery chemistry that operates at 3.7V–4.2 V using standard ultraviolet-cured acrylic-based polymers as hydrophobic barriers. The aqueous electrolyte is contained in a system of poly(ethylene glycol) acrylate polymers crosslinked to produce an electrolyte gel that has electrochemical properties similar to that of the liquid phase component. The electrolyte gels have elastic moduli in the kPa range, making them soft enough to tolerant flexing, cutting, and blunt force impacts while keeping the electrodes covered and safe from shorting. While batteries based on water-in-salt electrolyte provides intrinsic safety that is otherwise unavailable from typical non-aqueous electrolytes, acrylate-based aqueous gel electrolytes offer the potential of large-scale manufacturing owing to the relatively low volatility of the electrolyte components and the low complexity of the proposed manufacturing process. • UV-cured gel electrolytes were used to construct a 4 V lithium ion battery. • The main gel electrolyte was water-based, making the battery safe. • Gel electrolytes had conductivity ≥0.3 mS/cm. • Gel electrolytes exhibited favorable impedance characteristics. • Battery cells used graphite anodes and LiCoO 2 cathodes. [ABSTRACT FROM AUTHOR]