Improved SiGr/NCM523 Cycling via Triethyl Phosphate-Solubilized Lithium Nitrate Electrolyte

The performance of silicon-graphite (SiGr)/Li and SiGr/LiNi0.5Co0.2Mn0.3O2 (NCM523) cells was investigated in electrolytes containing lithium difluoro(oxalato)borate (LiDFOB) and lithium nitrate (LiNO3) in ethylene carbonate (EC), ethylmethyl carbonate (EMC), and different proportions of triethyl phosphate (TEP). While the LiDFOB and LiNO3- containing electrolytes both showed improved cycling stability over industry standards, the 10% TEP electrolyte demonstrated the best capacity retention in SiGr/Li cells and the best overall cycling performance in SiGr/NCM523 cells. Ex-situ surface analysis reveals that the LiDFOB and LiNO3 preferentially decompose on both the anode and cathode surface during the first cycle to generate films consisting of oxalates, fluoroborates, and nitrate reduction products. Therefore, incorporation of two different film-forming additives into the electrolyte is significantly more beneficial in formation of a robust SEI and improved cycle life in silicon-containing anodes.