Since firstly commercialized by Sony, lithium batteries are becoming ubiquitous in 3C electronic products, electric vehicles (EVs), and large-scale energy storage (ES) devices, [1][2][3][4][5] while the applications of EVs and ES still call for batteries with higher energy density. The combination of high voltage (≥4.3 V) nickel-rich cathode (LiNi x Mn y Co (1-x-y) O 2 , NCM) and lithium metal anode is no doubt an ideal choice to fulfill the energy demand, while the poor cycle stability and safety concern brought about by inferior interfacial stability between lithium and electrolyte are seriously hindering its development. Electrolyte is no doubt the most convenient way to enhance the stability of high energy density batteries; therefore, tremendous efforts have been devoted to novel electrolyte design. [6][7][8] Stable cathode/anode electrolyte interface (CEI/SEI) is the key to enable long life of Li|| NCM batteries, and in terms of electrolyte design, several strategies have been trialed and proved to be effective. The first and most commonly used one is using special additives that could promote the formation of SEI/CEI, typical ones including lithium difluoro(oxalato)borate (LiDFOB), [9,10] Lithium bis(fluorosulfonyl)imide (LiFSI), [11] lithium nitrate (LiNO 3 ), [12] to name but a few. With 1.5 wt% LiDFOB as additive, graphite|| LiNi 0.83 Mn 0.05 Co 0.12 O 2 cell kept 83.1% of its initial capacity after 200 cycles at C/3 rate, while capacity retention of the one without LiDFOB is only 59.9% under the same condition. [10] However, this strategy suffers from additive loss, as the additives usually need to be self-sacrificed to form the protection layer on the electrode. [13] When the additives are used up, cell is approaching the end of its life. The second strategy is introducing solvents with better electrochemical stability, such as fluorinated carbonate, [14] sulfones, [15] and phosphates, [16] to prohibit the electrolyte from being oxidized on the cathode surface. Chen et al. [17] introduced an all-fluorinated electrolyte, 1 M LiPF 6 in methyl 3,3,3trifluoropionate (MTFP)/fluoroethylene carbonate (FEC) (9:1, by vol.), which significantly enhanced the high voltage performance of Li|| NMC811 cell. Attributed to the fluorine-rich interface formed by the electrolyte, it demonstrated a capacity retention of 80% after 250 cycles even under a high cutoff voltage of 4.5 V, whereas capacity retention of the one with 1 M LiPF 6 in ethylene carbonate (EC)/diethyl carbonate (DEC) (1:1, by vol.) is only 53%. The third strategy is to adjust the Li + solvation structure by preparing (localized) high-concentration

Lithium metal battery (LMB) is one of the most attractive candidates for next generation high energy density devices owing to the high specific capacity (3860 mAh/g) and low electrochemical potential...

Increasing energy demand throughout the world produces great environmental issues. Therefore, renewable and clean energy sources, such as tidal energy, wind energy, solar energy and geothermal energy, are greatly desired. Developing a new critical energy storage technology to balance the instantaneous energy supply and demand is urgent. Rechargeable flow batteries are solutions for storing electricity in the form of chemical energy, containing positive and negative electrodes reserved in two separate containers, which have the advantages of low self-discharge and independent scaling of power, making them promising energy storage technologies. Ionic liquids have been widely studied and used in energy storage devices, such as lithium ion batteries, for their unique prospective properties. Herein, the key role of ILs and their applications in supporting electrolytes, separators, and additives in flow batteries are highlighted. The approaches and challenges in developing ILs supported flow batteries are discussed, and a significative overview of the opportunities of ILs promote flow batteries is provided to help achieve further improvements in flow batteries.