Stabilizing the LiNi_0.8Mn_0.1Co_0.1O₂ Interface with an In Situ Constructed Composite Film for a Lithium Metal Battery under High Voltage

Cathodes containing Ni, Co, and Mn frequently undergo side reactions with the electrolyte during the long cycles of the battery in traditional electrolytes under high voltage. In this work, an efficient composite cathode–electrolyte interface (CEI) film is constructed in situ with two additives; that is, 2-[(trimethylsilyl)ethynyl]thiophene (TET) is oxidized and polymerized in advance to form a film attached to the cathode surface, while oxidation products of bis(pinacolato)diboron (BDB) as a high ion conductor are doped into the TET polymer film. The combination of the oxidation products of the two additives not only effectively isolates solvent molecules and hydrofluoric acid erosion, preventing the occurrence of side reactions, but also does not affect the transfer of lithium ions. The crystal structure stability of LiNi0.8Mn0.1Co0.1O2 (NCM811) could be effectively regulated by the composite CEI film through in situ X-ray diffraction characterization during the charge–discharge process. The dynamic performance of the battery has also been improved by comparing the discrepancy of pseudocapacitance across the battery with different electrolytes. Furthermore, the solid–electrolyte interface film formed by TET and BDB could provide effective protection for lithium metal from electrolyte corrosion and inhibit the formation of lithium dendrites. Therefore, the battery capacity retention rate could reach 91.12% after 300 cycles. In addition, the battery with a high-load cathode (2.52 mAh cm–2) has a capacity retention rate of up to 90.19% after 50 cycles, which may make the future application of pouch batteries more feasible.