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Aqueous sodium-ion batteries are practically promising for large-scale energy storage, however energy density and lifespan are limited by water decomposition. Current methods to boost water stability include, expensive fluorine-containing salts to create a solid electrolyte interface and addition of potentially-flammable co-solvents to the electrolyte to reduce water activity. However, these methods significantly increase costs and safety risks. Shifting electrolytes from near neutrality to alkalinity can suppress hydrogen evolution while also initiating oxygen evolution and cathode dissolution. Here, we present an alkaline-type aqueous sodium-ion batteries with Mn-based Prussian blue analogue cathode that exhibits a lifespan of 13,000 cycles at 10 C and high energy density of 88.9 Wh kg−1 at 0.5 C. This is achieved by building a nickel/carbon layer to induce a H3O+-rich local environment near the cathode surface, thereby suppressing oxygen evolution. Concurrently Ni atoms are in-situ embedded into the cathode to boost the durability of batteries. Aqueous sodium-ion batteries show promise for large-scale energy storage, yet face challenges due to water decomposition, limiting their energy density and lifespan. Here, the authors report a cathode surface coating strategy in an alkaline electrolyte to enhance the stability of both electrolyte and battery. [ABSTRACT FROM AUTHOR]

The formation of lithiophobic inorganic solid electrolyte interphase (SEI) on Li anode and cathode electrolyte interphase (CEI) on the cathode is beneficial for high‐voltage Li metal batteries. However, in most liquid electrolytes, the decomposition of organic solvents inevitably forms organic components in the SEI and CEI. In addition, organic solvents often pose substantial safety risks due to their high volatility and flammability. Herein, an organic‐solvent‐free eutectic electrolyte based on low‐melting alkali perfluorinated‐sulfonimide salts is reported. The exclusive anion reduction on Li anode surface results in an inorganic, LiF‐rich SEI with high capability to suppress Li dendrite, as evidenced by the high Li plating/stripping CE of 99.4% at 0.5 mA cm−2 and 1.0 mAh cm−2, and 200‐cycle lifespan of full LiNi0.8Co0.15Al0.05O2 (2.0 mAh cm−2) || Li (20 µm) cells at 80 °C. The proposed eutectic electrolyte is promising for ultrasafe and high‐energy Li metal batteries. [ABSTRACT FROM AUTHOR]

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]

The performance of all-solid-state lithium metal batteries (SSLMBs) is affected by the presence of electrochemically inactive (i.e., electronically and/or ionically disconnected) lithium metal and solid electrolyte interphase (SEI), which are jointly termed inactive lithium. However, the differentiation and quantification of inactive lithium during cycling are challenging, and their lack limits the fundamental understanding of SSLMBs failure mechanisms. To shed some light on these crucial aspects, here, we propose operando nuclear magnetic resonance (NMR) spectroscopy measurements for real-time quantification and evolution-tracking of inactive lithium formed in SSLMBs. In particular, we examine four different sulfide-based solid electrolytes, namely, Li10GeP2S12, Li9.54Si1.74P1.44S11.7Cl0.3, Li6PS5Cl and Li7P3S11. We found that the chemistry of the solid electrolyte influences the activity of lithium. Furthermore, we demonstrate that electronically disconnected lithium metal is mainly found in the interior of solid electrolytes, and ionically disconnected lithium metal is found at the negative electrode surface. Moreover, by monitoring the Li NMR signal during cell calendar ageing, we prove the faster corrosion rate of mossy/dendritic lithium than flat/homogeneous lithium in SSLMBs. All-solid-state lithium batteries performance is affected by the solid electrolyte interphase (SEI) and electrically disconnected ("dead") Li metal. Here, via operando NMR measurements, the authors quantify the Li metal in the SEI and "dead" regions using various inorganic solid-state electrolytes. [ABSTRACT FROM AUTHOR]

Solid electrolyte interphase (SEI) formation and H2O activity reduction in Water‐in‐Salt electrolytes (WiSE) with an enlarged stability window of 3.0 V have provided the feasibility of the high‐energy‐density aqueous Li‐ion batteries. Here, we extend the cathodic potential of WiSE by rationally controlling intermolecular interaction and interphase chemistry with the introduction of trimethyl phosphate (TMP) into WiSE. The TMP not merely limits the H2O activity via the strong interaction between TMP and H2O but also contributes to the formation of reinforced SEI involving phosphate and LiF by manipulating the Li+ solvation structure. Thus, water‐tolerance LiMn2O4 (LMO)||Li4Ti5O12 (LTO) full cell with a P/N ratio of 1.14 can be assembled and achieve a long cycling life of 1000 times with high coulombic efficiency of >99.9 %. This work provides a promising insight into the cost‐effective practical manufacture of LMO||LTO cells without rigorous moisture‐free requirements. [ABSTRACT FROM AUTHOR]

The instability of carbonate electrolyte with metallic Li greatly limits its application in high‐voltage Li metal batteries. Here, a "salt‐in‐salt" strategy is applied to boost the LiNO3 solubility in the carbonate electrolyte with Mg(TFSI)2 carrier, which enables the inorganic‐rich solid electrolyte interphase (SEI) for excellent Li metal anode performance and also maintains the cathode stability. In the designed electrolyte, both NO3− and PF6− anions participate in the Li+‐solvent complexes, thus promoting the formation of inorganic‐rich SEI. Our designed electrolyte has achieved a superior Li CE of 99.7 %, enabling the high‐loading NCM811||Li (4.5 mAh cm−2) full cell with N/P ratio of 1.92 to achieve 84.6 % capacity retention after 200 cycles. The enhancement of LiNO3 solubility by divalent salts is universal, which will also inspire the electrolyte design for other metal batteries. [ABSTRACT FROM AUTHOR]

The instability of sulfide solid electrolytes to Li anode and high‐voltage LiNi0.8Mn0.1Co0.1O2 (NMC811) cathodes limits the cyclic performance of all‐solid‐state lithium battery (ASSLB). Herein, the stability of Li6PS5Cl against Li anode is enhanced by mixing a small amount (0.32 wt%) of CuF2‐LiNO3 (CL) into Li6PS5Cl electrolyte layer to in‐situ form a mixed‐conductive‐lithiophobic and self‐healing LiF‐Li3N‐Cu solid electrolyte interphase (SEI) at Li6PS5Cl‐CL/Li interface. The critical current density (CCD) of Li6PS5Cl‐CuF2‐LiNO3 increases to 1.4 mA cm–2/1.4 mAh cm–2 at room temperature, which is much higher than that of pristine Li6PS5Cl (0.4 mA cm–2/0.4 mAh cm–2) even though mixing 0.32 wt% CL into Li6PS5Cl slightly reduces the ionic conductivity from 2.9 × 10–3 to 1.5 × 10–3 S cm–1. The compatibility of Li6PS5Cl‐CL electrolyte to single‐crystalline NMC811 (S‐NMC811) is further enhanced by adding a small amount (0.02 wt%) of AlF3 into Li6PS5Cl‐CL forming Li6PS5Cl‐CuF2‐LiNO3‐AlF3 (Li6PS5Cl‐CLA) as a cathode electrolyte and by doing Cl– on S‐NMC811 (Cl@S‐NMC811) surface. The Cl@S‐NMC811‐Li6PS5Cl‐CLA|Li6PS5Cl‐CL|Li cells with areal capacity of 2.55 mAh cm‐2 achieve a capacity retention of 69.4% after 100 cycles at 1C (1C = 200 mAh g‐1). Adding a small amount of SEI and cathode/electrolyte interphase (CEI) former into the sulfide electrolytes with minimal reduction (48.3%) of ionic conductivity is an effective method to enhance the performance of ASSLB. [ABSTRACT FROM AUTHOR]

Since the advent of the Li ion batteries (LIBs), the energy density has been tripled, mainly attributed to the increase of the electrode capacities. Now, the capacity of transition metal oxide cathodes is approaching the limit due to the stability limitation of the electrolytes. To further promote the energy density of LIBs, the most promising strategies are to enhance the cut-off voltage of the prevailing cathodes or explore novel high-capacity and high-voltage cathode materials, and also replacing the graphite anode with Si/Si–C or Li metal. However, the commercial ethylene carbonate (EC)-based electrolytes with relatively low anodic stability of ∼4.3 V vs. Li+/Li cannot sustain high-voltage cathodes. The bottleneck restricting the electrochemical performance in Li batteries has veered towards new electrolyte compositions catering for aggressive next-generation cathodes and Si/Si–C or Li metal anodes, since the oxidation-resistance of the electrolytes and the in situ formed cathode electrolyte interphase (CEI) layers at the high-voltage cathodes and solid electrolyte interphase (SEI) layers on anodes critically control the electrochemical performance of these high-voltage Li batteries. In this review, we present a comprehensive and in-depth overview on the recent advances, fundamental mechanisms, scientific challenges, and design strategies for the novel high-voltage electrolyte systems, especially focused on stability issues of the electrolytes, the compatibility and interactions between the electrolytes and the electrodes, and reaction mechanisms. Finally, novel insights, promising directions and potential solutions for high voltage electrolytes associated with effective SEI/CEI layers are proposed to motivate revolutionary next-generation high-voltage Li battery chemistries. [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]

[Display omitted] Pre-lithiation is critical for improving the energy density of lithium-ion batteries (LIBs) in practical applications. The pre-lithiation of the high-capacity anode with a large surface area enhances the initial coulombic efficiency (ICE) by compensating the lithium loss from the formation of solid electrolyte interphase (SEI). However, pre-lithiation also affects cycle life, which has been paid little attention to. Here, we first discuss the impact of pre-lithiation on the cycling stability of the full cells, which is closely related to anode material, the degree of pre-lithiation, and the stability of SEI. Then we provide suggestions on how to achieve both high energy density and long cycle life by pre-lithiation. The understanding of the correlation between pre-lithiation and cycling stability sheds light on achieving the optimal performance of lithium-ion batteries from pre-lithiation technology. [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]