Stabilizing the LiNi<sub>0.8</sub>Mn<sub>0.1</sub>Co<sub>0.1</sub>O<sub>2</sub> Interface\nwith an In Situ Constructed\nComposite Film for a Lithium Metal Battery under High Voltage

Cathodes containing Ni, Co, and Mn frequently undergo\nside reactions\nwith the electrolyte during the long cycles of the battery in traditional\nelectrolytes under high voltage. In this work, an efficient composite\ncathode–electrolyte interface (CEI) film is constructed in\nsitu with two additives; that is, 2-[(trimethylsilyl)ethynyl]thiophene\n(TET) is oxidized and polymerized in advance to form a film attached\nto the cathode surface, while oxidation products of bis(pinacolato)diboron\n(BDB) as a high ion conductor are doped into the TET polymer film.\nThe combination of the oxidation products of the two additives not\nonly effectively isolates solvent molecules and hydrofluoric acid\nerosion, preventing the occurrence of side reactions, but also does\nnot affect the transfer of lithium ions. The crystal structure stability\nof LiNi<sub>0.8</sub>Mn<sub>0.1</sub>Co<sub>0.1</sub>O<sub>2</sub> (NCM811) could be effectively regulated by the composite CEI film\nthrough in situ X-ray diffraction characterization during the charge–discharge\nprocess. The dynamic performance of the battery has also been improved\nby comparing the discrepancy of pseudocapacitance across the battery\nwith different electrolytes. Furthermore, the solid–electrolyte\ninterface film formed by TET and BDB could provide effective protection\nfor lithium metal from electrolyte corrosion and inhibit the formation\nof lithium dendrites. Therefore, the battery capacity retention rate\ncould reach 91.12% after 300 cycles. In addition, the battery with\na high-load cathode (2.52 mAh cm<sup>–2</sup>) has a capacity\nretention rate of up to 90.19% after 50 cycles, which may make the\nfuture application of pouch batteries more feasible.