Introducing electrolytic electrochemical polymerization for constructing protective layers on Ni-rich cathodes of Li-ion batteries

LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) is the most promising cathode for high-energy Li-ion batteries, despite its poor cycling stability that originates from the reactions that occur with the electrolyte. Herein, to solve this interfacial issue, a facile electrolytic electrochemical polymerization process was introduced in this paper, and a uniform conductive electrolyte interface (polyaniline) was successfully constructed on the surface of the NCM811 porous electrode (PANI-NCM), which facilitated the charge transfer during charge/discharge. The side reactions at the interface between the cathode and the electrolyte are suppressed, and thereby, the cycling performance and rate capability are considerably improved. PANI-NCM delivers an initial capacity of 157.2 mAh·g⁻¹ as well as excellent cyclability (capacity retention of 88% after 500 cycles at 2C), whereas the capacity of the bare NCM811 has dropped to 31.3 mAh·g⁻¹. In addition, polypyrrole and polythiophene also can be formed through electrolytic electrochemical polymerization process, which provides a practicable tactic to modify the interfacial stability of cathodes for high-energy Li-ion batteries.