Anion-π Interaction and Solvent Dehydrogenation Control Enable High-Voltage Lithium-ion Batteries

Abstract

Extending the charging cutoff voltage of lithium cobalt oxide (LCO) cathode is an effective strategy to enhance energy density of lithium-ion batteries (LIBs), while the formation of poor cathode electrolyte interphase (CEI) has limited its widespread application. Various electrolyte additives, particularly nitrile compounds, have shown promise in addressing these interfacial issues, though the fundamental design principles remain unclear. Herein, we introduce an interfacial leverage mechanism utilizing nitriles adsorbed on LCO surface to fine-tune the CEI composition. A nitrile additive's suitability for high-voltage LCO is determined by the repulsive interaction with the solvent (E_sol) and the attractive interaction with the anion (E_anion). The former inhibits solvent decomposition, while the latter facilitates the anion decomposition during CEI construction. These interactions can be tailored through the functional design of nitrile compounds, as demonstrated using 3,5-bis(trifluoromethyl)benzonitrile (BFBN) in a commercial carbonate electrolyte. The BFBN molecules adsorb onto the LCO surface through coordination between cyano groups (-CN) and cobalt (Co) atoms. Exhibiting repulsive interactions with the solvent and attractive interactions with the anion through anion-π interaction, BFBN suppresses carbonate solvent dehydrogenation while promoting PF₆^- anions decomposition to form an inorganic-rich CEI. A 1 wt.% addition of BFBN enables 4.55 V-graphite||LCO pouch cells to achieve over 550 cycles at 25 °C and more than 145 cycles at 45 °C, significantly surpassing the lifespan of around 110 and 50 cycles observed in the baseline electrolyte. This work provides new insights into the design of high-voltage electrolyte additives for high-energy-density LIBs.