Ni‐rich layered oxides have been considered one of the most promising cathode materials for lithium‐ion batteries on account of their high reversible capacity. However, their chemical sensitivity to moisture and carbon dioxide results in the formation and growth of residual lithium compounds, leading to a deterioration in electrochemical performance and difficulty in cathode electrode preparation. In this work, a passivation coating of polydimethylsiloxane with 5 molecular layers is successfully coated on LiNi0.8Co0.1Mn0.1O2 particles. To examine the hydrophobicity of polydimethylsiloxane, bare and coated NCM811 are exposed to a hot and humid chamber for dozens of hours, even exposure to damp air over 120 h. The results indicate that the hydrophobic coating can inhibit the formation and growth of residual lithium compounds on the surface of LiNi0.8Co0.1Mn0.1O2, resulting in slightly less degradation in electrochemical performance. Herein, a rapid, low‐cost, and easily employed method to generate an even hydrophobic/passivation surface is developed, which provides a generic approach to treat various electrode materials, especially nanosized and water‐sensitive ones, to improve their tolerance to extreme environments.

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