Flame-retardant electrolyte with boosted interfacial stability for practical Li metal batteries

Developing Li metal batteries (LMBs) with high-voltage cathodes is crucial for realizing high energy storage systems. Thus, advanced electrolytes that can derive stable interphases for both Li anode and high-voltage cathodes are highly desired. LiNO3 has been widely used as an efficient additive for solid electrolyte interphases in ether-based electrolytes, but its poor solubility in carbonate-based electrolytes limits its application in high-voltage LMBs. Herein, trimethyl phosphate was proposed as co-solvent in ethyl methyl carbonate/fluoroethylene carbonate electrolyte to endow the electrolyte with high LiNO3 solubility and flame-retardant properties. Additionally, lithium bis(oxalato) borate was added to improve the interfacial stability at both the anode and the cathode sides. As a result, the obtained electrolyte exhibited high compatibility towards both Li metal anode and high-voltage layered cathodes. After cycled between 2.8–4.3 V at a current density of 1.2 mA cm−2 for 300 times, Li∣LiCoO2 and Li∣LiNi0.8Co0.1Mn0.1O2 (NCM811) full cells delivered high capacity retention of 80.2% and 84.2%, respectively. More amazingly, the Li∥NCM811 cell with a negative-to-positive capacity ratio of 3.33 still remained a capacity retention of ∼80% after 150 cycles under the same charge/discharge conditions. The understanding of this fire-retardant, high-voltage electrolyte enriched with LiNO3 inspires the development of safe and high energy LMBs through interphases regulation.