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We present a novel concept to achieve high performance and high safety simultaneously by passivating a Li-ion cell and then self-heating before use. By adding a small amount of triallyl phosphate in conventional electrolytes, we show that resistances of the passivated cells can increase by ~5×, thereby ensuring high safety and thermal stability. High power before battery operation is delivered by self-heating to an elevated temperature such as 60°C within tens of seconds. The present approach of building a resistive cell with highly stable materials and then delivering high power on demand through rapid thermal stimulation leads to a revolutionary route to high safety when batteries are not in use and high battery performance upon operation.

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Li metal batteries (LMBs) employing high voltage cathodes are necessary to attain high energy density. Although highly concentrated ether-based electrolytes (e.g. 4 M LiFSI/DME) can yield stable cycling of Li metal anodes, their high voltage instability fosters incompatibility with high voltage cathodes. In this work, the temperature dependence of fresh cell performance, Li Coulombic efficiency (CE), and cycling stability of LMBs in highly concentrated LiFSI/DME electrolytes was explored. Elevated temperature operation was deemed essential for highly concentrated electrolytes to achieve practical rate capability. Moreover, at 60 °C, the cycling stability of Li metal anodes with a Li CE as high as 99.2% was demonstrated in a highly concentrated LiFSI-1.2DME electrolyte (LiFSI: DME = 1: 1.2 mol.). At room temperature, the LiFSI-1.2DME electrolyte enabled stable LMBs with NMC622 cathodes. However, due to the high temperature and high voltage instability of the LiFSI-1.2DME electrolyte in contact with NCM622, a small amount of TAP (∼1 wt.%) was added, significantly enhancing the cycling stability at 60 °C. This newly developed LiFSI-1.2DME electrolyte with 1 wt.% TAP ultimately enabled LMBs with NMC622 cathodes and minimal excess Li metal anode to be cycled stably for 200-300 cycles at 60 °C.

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