Mechanically and Thermally Stable Cathode Electrolyte Interphase Enables High‐temperature, High‐voltage Li||LiCoO2 Batteries

The development of high-energy-density Li||LiCoO₂ batteries is severely limited by the instability of cathode electrolyte interphase (CEI) at high voltage and high temperature. Here we propose a mechanically and thermally stable CEI by electrolyte designing for achieving the exceptional performance of Li||LiCoO₂ batteries at 4.6 V and 70 °C. 2,4,6-tris(3,4,5-trifluorophenyl)boroxin (TTFPB) as the additive could preferentially enter into the first shell structure of PF₆ ^- solvation and be decomposed on LiCoO₂ surface at low oxidation potential to generate a LiB_x O_y -rich/LiF-rich CEI. The LiB_x O_y surface layer effectively maintained the integrity of CEI and provided excellent mechanical and thermal stability while abundant LiF in CEI further improved the thermal stability and homogeneity of CEI. Such CEI drastically alleviated the crack and regeneration of CEI and irreversible phase transformation of the cathode. As expected, the Li||LiCoO₂ batteries with the tailored CEI achieved 91.9 % and 74.0 % capacity retention after 200 and 150 cycles at 4.6 and 4.7 V, respectively. Moreover, such batteries also delivered an unprecedented high-temperature performance with 73.6 % capacity retention after 100 cycles at 70 °C and 4.6 V.