Improving the Calendar Life of Silicon Anodes with Inorganic Solid–Electrolyte Interphases

Silicon anodes unlock higher energy density in Li-ion batteries but suffer from poor calendar life due to inadequately passivating solid–electrolyte interphases (SEIs). Here, we contrast the calendar aging behaviors of single- and mixed-salt locally superconcentrated electrolytes (LSCEs) against carbonate electrolytes. Mixed-salt LSCE cells retained 96% and 44% of precalendar capacity after one month and then after five months, while carbonate electrolyte cells retained 77% and 1%, respectively. The mixed-salt LSCE advantage is tied to the formation of a predominantly inorganic SEI, evidenced by nanoscale Fourier transform infrared spectromicroscopy, X-ray photoelectron spectroscopy, and 3D time-of-flight secondary ion mass spectrometry. After 5 months, however, perturbations to SEIs were evident in all cells, accelerating voltage decay and capacity loss by lithium inventory loss associated with SEI growth. These findings suggest that future electrolytes may benefit from strategies that continuously reinforce the SEI through controlled anion and solvent redox in LSCEs.