Boosting Fast-Charging Capability of High-Voltage Li Metal Batteries with Ionic Liquid Modified Ethereal Electrolyte

Given the high compatibility with Li metal anodes, ethereal electrolytes have found widespread use in Li metal batteries. Unfortunately, their applications in high-voltage Li metal batteries are hampered by a limited electrochemical window. In this study, a diluted ethereal electrolyte (with Li salt concentration < 1.5 m) is developed containing 1 m lithium bis(fluorosulfonyl) imide (FSI) and 0.3 m LiNO3 in a N-methyl-N-propylpiperidinium bis(trifluoromethanesulfonyl)imide (PP13TFSI):dimethyl ether (DME) (v:v = 1:4) mixture for Li metal batteries with an aggressive high-voltage cathode via the formation of an anion-enriched solvation sheath. In contrast to high-concentration electrolytes, the formation of the anion-enriched solvation sheath in this design is facilitated by the addition of ionic liquids. Further theoretical calculations indicate that the presence of FSI- and NO3- anions in the first solvation sheath weakens the desolvation energy of the DME solvent, suggesting a faster desolvation process at the electrode interphase. Consequently, the designed electrolyte enables long-term cycling of Li || LiNi0.8Co0.1Mn0.1O2 (NCM811) full cells over 1000 cycles at a high rate of 10 C. More notably, it also allows for a long cycle life of 100 cycles under a high rate of 5 C, even with limited negative capacity to positive capacity (N/P) ratio of 1.