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A new super-concentrated aqueous electrolyte is proposed by introducing a second lithium salt. The resultant ultra-high concentration of 28 m led to more effective formation of a protective interphase on the anode along with further suppression of water activities at both anode and cathode surfaces. The improved electrochemical stability allows the use of TiO2 as the anode material, and a 2.5 V aqueous Li-ion cell based on LiMn2 O4 and carbon-coated TiO2 delivered the unprecedented energy density of 100 Wh kg(-1) for rechargeable aqueous Li-ion cells, along with excellent cycling stability and high coulombic efficiency. It has been demonstrated that the introduction of a second salts into the "water-in-salt" electrolyte further pushed the energy densities of aqueous Li-ion cells closer to those of the state-of-the-art Li-ion batteries.

Recent advances, fundamental mechanisms and design strategies of high-voltage liquid electrolytes are comprehensively summarized in this review.

With the highest energy density ever among all sorts of commercialized rechargeable batteries, Li‐ion batteries (LIBs) have stimulated an upsurge utilization in 3C devices, electric vehicles, and stationary energy‐storage systems. However, a high performance of commercial LIBs based on ethylene carbonate electrolytes and graphite anodes can only be achieved at above −20 °C, which restricts their applications in harsh environments. Here, a comprehensive research progress and in‐depth understanding of the critical factors leading to the poor low‐temperature performance of LIBs is provided; the distinctive challenges on the anodes, electrolytes, cathodes, and electrolyte–electrodes interphases are sorted out, with a special focus on Li‐ion transport mechanism therein. Finally, promising strategies and solutions for improving low‐temperature performance are highlighted to maximize the working‐temperature range of the next‐generation high‐energy Li‐ion/metal batteries.

An ew super-concentrated aqueous electrolyte is proposed by introducing as econd lithium salt. The resultant ultra-high concentration of 28 ml ed to more effective formation of aprotective interphase on the anode along with further suppression of water activities at both anode and cathode surfaces.The improved electrochemical stability allows the use of TiO 2 as the anode material, and a2.5 Vaqueous Li-ion cell based on LiMn 2 O 4 and carbon-coated TiO 2 delivered the unprecedented energy density of 100 Wh kg À1 for rechargeable aqueous Li-ion cells,along with excellent cycling stability and high coulombic efficiency.I th as been demonstrated that the introduction of as econd salts into the "water-in-salt" electrolyte further pushed the energy densities of aqueous Li-ion cells closer to those of the state-of-the-art Li-ion batteries.Lithium-ion batteries (LIB) overwhelmingly dominate the portable electronics market (ca. 50 Wh) with their superior energy densities. [1] To withstand the high voltages (> 3.0 V) generated by the highly energetic electrochemical couples, flammable and toxic non-aqueous electrolytes have to be used, causing safety and environmental concerns that will worsen by orders of magnitude in large-scale applications, such as automotive (ca. 10 3 Wh) and grid-storage (ca. 10 6 Wh). Aqueous electrolytes that are intrinsically nonflammable and green would have provided ideal solutions. However,t heir narrow electrochemical stability window (1.23 V), imposed by hydrogen and oxygen evolution, [2] restricted the voltage output of such aqueous LIB under 1.50 Vand resulted in severely compromised energy densities. Thus,e xpanding the electrochemical stability window of aqueous electrolytes becomes an issue of fundamental importance that would not only determine the practicality of aqueous LIB,b ut in ab roader context, general aqueous electrochemistry.U nfortunately,n os uch effort has been reported given the significant difficulty of suppressing water decomposition reactions,inparticular the reduction of water leading to hydrogen evolution, until recently when we successfully demonstrated a3 .0 Vs tability window when an ew class of "water-in-salt" electrolyte was formulated. In such as uper-concentrated electrolyte,t he decomposition of salt anion occurs preferentially on the anode before hydrogen evolution occurs,l eading to the formation of ad ense solid electrolyte interphase (SEI) primarily consisting of LiF. [3] A 2.3 Vaqueous Li-ion cell based on the electrochemical couple of LiMn 2 O 4 and Mo 6 S 8 was supported by such an electrolyte to provide an unprecedented energy density of 84 Wh kg À1 based on total electrode weight, which should be over 100 Wh kg À1 if the irreversible loss associated with SEI formation could be eliminated. [3a] Apparently,t he efficiency of forming aS EI in aqueous electrolytes depends on the salt concentration, whose increase indicates ad ecrease in water molecules in the solvation sphere of Li + and areduction in the electrochemical activity of water. However, th...

The lithium metal anode is considered as the ultimate choice for high-energy-density batteries. However, the organic-dominated solid electrolyte interphase (SEI) formed in carbonate electrolytes has a low interface energy against metallic Li as well as a high resistance, resulting in a low Li plating/stripping Coulombic efficiency (CE) of less than 99.0% and severe Li dendrite growth. Herein, inorganic-enhanced LiF-Li3N SEI is designed in commercial 1 M LiPF6/EC-DMC electrolytes by introducing lithium nitrate (LiNO3) and fluoroethylene carbonate (FEC) through a small amount of sulfolane (SL) as a carrier solvent owing to the high solubility of SL for both carbonate solvents and LiNO3. The comprehensive characterizations and simulations demonstrate that the synergistic interaction of LiNO3 and FEC additives alters the solvation structure of 1 M LiPF6/EC-DMC electrolytes and forms additive-derived LiF-Li3N SEI, which increases the average Li CE up to 99.6% in 100 cycles. The designed carbonate electrolyte enables the Li/LiNi0.80Co0.15Al0.05O2 (NCA) cell with a lean lithium metal anode (∼50 μm) to achieve an average CE of 99.7% and a high capacity retention of 90.8% after 150 cycles. This work offers a simple and economical strategy to realize high-performance lithium metal batteries in commercial carbonate electrolytes.

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Li-rich layered-oxide cathodes have the highest theoretical energy density among all the intercalated cathodes, which have attracted intense interests for high-energy Li-ion batteries. However, O3-structured layered-oxide cathodes suffer from a low initial Coulombic efficiency (CE), severe voltage fade, and poor cycling stability because of the continuous oxygen release, structural rearrangements due to irreversible transition-metal migration, and serious side reactions between the delithiated cathode and electrolyte. Herein, we report that these challenges are migrated by using a stable O2-structured Li1.2­Ni0.13­Co0.13­Mn0.54­O2 (O2-LR-NCM) and all-fluorinated electrolyte. The O2-LR-NCM can restrict the transition metals migrating into the Li layer, and the in situ formed fluorinated cathode–electrolyte interphase (CEI) on the surface of the O2-LR-NCM from the decomposition of all-fluorinated electrolyte during initial cycles effectively restrains the structure transition, suppresses the O2 release, and thereby safeguards the transition metal redox couples, enabling a highly reversible and stable oxygen redox reaction. O2-LR-NCM in all fluorinated electrolytes achieves a high initial CE of 99.82%, a cycling CE of >99.9%, a high reversible capacity of 278 mAh/g, and high capacity retention of 83.3% after 100 cycles. The synergic design of electrolyte and cathode structure represents a promising direction to stabilize high-energy cathodes.