traditional Li-ion batteries. [1][2][3] Although extensive worldwide efforts have already been devoted to fabricate an ideal Li-O 2 battery system to realize its practical application, there are still several challenges regarding both air electrodes and electrolytes in rechargeable Li-O 2 batteries, especially electrolyte instability against reduced oxygen species. [4] In a typical nonaqueous Li-O 2 battery, the oxygen reduction process results in the formation of the superoxide radical anion (O 2 •− ), lithium superoxide (LiO 2 ), lithium peroxide (Li 2 O 2 ), and others. The O 2 •− , LiO 2 , and Li 2 O 2 have very high reactivity towards most of the components inside the Li-O 2 battery such as carbon-based air electrodes, polymer binders, and organic electrolytes, [5,6] especially the nonaqueous electrolytes, [7][8][9][10][11][12][13][14][15][16] including solvents [6,17] (such as the organic carbonate solvents widely used in Li-ion batteries, [9,12] ether-based solvents, [13,14] and ionic liquids [15,16] ) and salt anions. [10] It is known that most organic solvent systems are not stable against reduced oxygen species, especially O 2 •− . Although some ether-based solvents are relatively stable and have been widely used in Li-O 2 battery studies, further improvement of their stability during Li-O 2 reactions still remains a major challenge for Li-O 2 batteries. It is worth noting that using superconcentrated electrolytes (including ether-based, [18] dimethyl sulfoxide (DMSO)-based, [19] or acetonitrile-based [20] ) can enable enhancement of electrolyte stability for fast-charging Li-ion batteries, which presents a promising superconcentrated-salt strategy. Besides the use of aforementioned electrolytes in Li-ion batteries, use of highly concentrated electrolytes (i.e., lithium bis(trifluoromethanesulfonyl) imide (LiTFSI)-anhydrous 1,2-dimethoxyethane (DME), [13] LiTFSI-tetraethylene glycol dimethyl ether (TEGDME), [21] and lithium bis(fluorosulfonyl)imide (LiFSI)-DME [22] ) also brought new insights into electrolyte selection in Li-O 2 and Li metal batteries.Recently, the organic solvent DMSO has been used in Li-O 2 batteries to enhance the performance of Li-O 2 batteries due to the relative stability of DMSO against LiO 2 as well as its enhanced oxygen diffusion coefficient and high Li + conductivity compared to other solvents. [23][24][25][26][27][28] Bruce and co-workersThe conventional electrolyte of 1 m lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in dimethyl sulfoxide (DMSO) is unstable against the Li metal anode and therefore cannot be used directly in practical Li-O 2 batteries. Here, we demonstrate that a highly concentrated electrolyte based on LiTFSI in DMSO (with a molar ratio of 1:3) can greatly improve the stability of the Li metal anode against DMSO and significantly improve the cycling stability of Li-O 2 batteries. This highly concentrated electrolyte contains no free DMSO solvent molecules, but only complexes of (TFSI − ) a Li +  (DMSO) b (where a + b = 4), and thus enhances their st...

The electrolyte generally dictates the working temperature range of lithium-ion batteries (LIBs), thus developing a new class of electrolytes (primarily functional additives) in LIBs for wide temperature applications will be quite essential for further development of LIBs for the electric vehicle market. In this study, we develop new functional electrolytes containing multiple additives to enable the LIBs to perform well in a wide temperature range from −40 to 60 °C. Importantly, those cells based on the above optimized electrolytes have been proven to behave significantly enhanced discharging performance at −40 °C, the long-term cycling stability at 25 °C (more than 85% of capacity retention after 1000 cycles at 1C/1C rates in 1 Ah pouch cells), as well as the obviously improved cycling stability at 60 °C. These remarkable cell performances originate from the highly conductive, uniform, and compact passivating films formed on both anode and cathode surfaces by the synergistic effects of the multiple additives. Our finding on the synergistic benefits originating from a certain additive combination in the optimized electrolytes would favorably widen the working temperature range of future highperformance LIBs.

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In this work, for the first time an in situ electrochemical pretreatment approach to fabricate a highly reversible oxygen electrode with redistributed ultrafine RuO2 catalysts on a carbon nanotube (CNT) matrix is reported. The optimally pretreated RuO2/CNT oxygen electrodes demonstrate an extremely stable cycling life, 800 times with non‐Li metal anode, under a capacity‐limited protocol of 800 mAh g−1 in an ether‐based electrolyte in an O2 environment. The highly stable activity of ultrafine RuO2 catalysts in oxygen reduction and evolution processes originates from the synergetic effect of greatly reduced size of catalyst (<2 nm) and uniform redistribution of catalyst particles after the in situ electrochemical pretreatment process. The pretreatment method discovered in this work can not only significantly enhance the activity/efficiency of the catalysts used for air electrodes but can also be widely applied to other electro‐catalysis systems.

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