Polyvinylpyrrolidone-Induced Uniform Surface-Conductive Polymer Coating Endows Ni-Rich LiNi_0.8Co_0.1Mn_0.1O₂ with Enhanced Cyclability for Lithium-Ion Batteries

The Ni-rich LiNi_0.8Co_0.1Mn_0.1O₂ (NCM₈₁₁) cathode has attracted great interest owing to its low cost, high capacity, and energy density. Nevertheless, rapid capacity fading is a critical problem because of direct contact of NCM₈₁₁ with electrolytes and hence restrains its wide applications. To prevent the direct contact, the surface inert layer coating becomes a feasible strategy to tackle this problem. However, to achieve a homogeneous surface coating is very challenging. Considering the bonding effect between NCM₈₁₁, polyvinylpyrrolidone (PVP), and polyaniline (PANI), in this work, we use PVP as an inductive agent to controllably coat a uniform conductive PANI layer on NCM₈₁₁ (NCM₈₁₁@PANI-PVP). The coated PANI layer not only serves as a rapid channel for electron conduction, but also prohibits direct contact of the electrode with the electrolyte to effectively hinder side reaction. NCM₈₁₁@PANI-PVP thus exhibits excellent cyclability (88.7% after 100 cycles at 200 mA g^-1) and great rate performance (152 mA h g^-1 at 1000 mA g^-1). In situ X-ray diffraction and in situ Raman are performed to investigate the charge-discharge mechanism and the cyclability of NCM₈₁₁@PANI-PVP upon electrochemical reaction. This surfactant-modulated surface uniform coating strategy offers a new modification approach to stabilize Ni-rich cathode materials for lithium-ion batteries.