Interface stabilization via lithium bis(fluorosulfonyl)imide additive as a key for promoted performance of graphite$‖$LiCoO₂ pouch cell under $−20○$C

The effects of lithium bis(fluorosulfonyl)imide, Li[N(SO₂F)₂] (LiFSI), as an additive on the low-temperature performance of graphite$‖$LiCoO₂ pouch cells are investigated. The cell, which includes 0.2M LiFSI salt additive in the 1M lithium hexafluorophosphate (LiPF₆)-based conventional electrolyte, outperforms the one without additive under −20 °C and high charge cutoff voltage of 4.3 V, delivering higher discharge capacity and promoted rate performance and cycling stability with the reduced change in interfacial resistance. Surface analysis results on the cycled LiCoO₂ cathodes and cycled graphite anodes extracted from the cells provide evidence that a LiFSI-induced improvement of high-voltage cycling stability at low temperature originates from the formation of a less resistive solid electrolyte interphase layer, which contains plenty of LiFSI-derived organic compounds mixed with inorganics that passivate and protect the surface of the cathode and anode from further electrolyte decomposition and promotes Li⁺ ion-transport kinetics despite the low temperature, inhibiting Li metal-plating at the anode. The results demonstrate the beneficial effects of the LiFSI additive on the performance of a lithium-ion battery for use in battery-powered electric vehicles and energy storage systems in cold climates and regions.