Formation Mechanism and New Function of Cathode Electrolyte Interphase/Solid Electrolyte Interphase in Lithium-Ion Battery with LiPF6 + LATP Composite Electrolyte

The inorganic components of the cathode electrolyte interphase (CEI) and solid electrolyte interphase (SEI) play an important role in the cycle stability of lithium batteries. The electrolyte additive can modify CEI and SEI simultaneously. In this work, Li_1.3Al_0.3Ti_1.7(PO₄)₃(LATP) is used as an electrolyte additive to form CEI and SEI layers with abundant LiF and Li₃PO₄. LTAP not only modulates the embedding/de-embedding process of Li⁺ by lowering the oxidation potential and forming CEI during the battery charge/discharge cycling process but also enhances the thermal stability and self-discharge. More importantly, during the charging and discharging processes, LATP participates in the electrochemical reaction, resulting in an enrichment of Li⁺ on the CEI surface, which increases the concentration difference of lithium ions in the electrolyte and enhances their migration speed during charging and discharging. When assembling the LiFePO₄/Li coin cells, the experimental results indicate that the cell with LiPF₆ + LATP composite electrolyte can discharge 119.12 mA h g^-1 (2 C, 500 cycle), approximately 2 times that with pure LiPF₆ electrolyte. Meanwhile, it can discharge 128.9 mA h g^-1 (0.1 C) after being stored for 400 h, which is about 4 times higher than that with pure LiPF₆, indicating that LATP improves the self-discharge and discharge capacity of LFP. Furthermore, the formation mechanism and function of CEI/SEI in lithium-ion batteries with LiPF₆ + LATP composite electrolyte are discussed, which offers a new perspective for constructing composite electrolytes with superior energy density, high-rate capability, safety, and support for fast charging and discharging in the future.