SCHEDULED MAINTENANCE
Reconstruction of LiF-rich interphases through an anti-freezing electrolyte for ultralow-temperature LiCoO2 batteries†
Abstract
The lowest operational temperature of commercial graphite‖LiCoO2 (LCO) batteries is limited to ∼−20 °C due to the high reaction energy barrier of Li+ in the interlayers of the graphite anode and the unstable solid electrolyte interphase (SEI) forming at low temperatures. Lithium (Li) metal with ideally host-less nature is expected to support the low-temperature operation of the LCO cathode, but low-temperature applications of Li‖LCO batteries are severely challenged with disastrous issues of conventional electrolytes including the high solvation structure of Li+, low desolvation energy, low Li+ saturation concentration, and LiF-barren SEI and cathode electrolyte interphase (CEI) (below 7%) with a small Li+ conductivity and diffusion coefficient. Here, using iso-butyl formate (IF) as an anti-freezing agent with an ultralow melting point of −132 °C and an ultralow viscosity of 0.30 Pa s, a fluorine–sulfur electrolyte is designed to achieve a low-coordination number (0.07), high desolvation energy (−27.97 eV) and high Li+ saturation concentration (1.40 × 10−10 mol s−1) electrolyte, which enables efficient reversible transport of Li+ and formation of abundant F radicals to construct stable LiF-rich SEI (10.48%) and CEI (17.91%) layers with large Li+ conductivities (1.00 × 10−5 mS cm−1 and 6.65 × 10−5 mS cm−1) and large diffusion coefficients (1.10 × 10−21 m2 s−1 and 2.07 × 10−20 m2 s−1). With the electrolyte, Li‖LCO batteries deliver unprecedented cyclic performances at −70 °C including a stable capacity of 110 mA h g−1 over 170 cycles. The work provides an opportunity for developing ultralow-temperature LCO batteries.
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