Composite coating agent and high-voltage lithium cobalt oxide, and preparation methods thereof

The invention discloses a composite coating agent and high-voltage lithium cobalt oxide, and preparation methods thereof. The composite coating agent comprises a first coating agent and a second coating agent, wherein the first coating agent is alpha-zirconium phosphate adsorbing lithium ions while the second coating agent is ammonia-substituted alpha-zirconium phosphate adsorbing rare earth ions. In the first coating agent, a mol ratio of the lithium ions to alpha-zirconium phosphate is 1: 1 to 1: 3; and in the second coating agent, a mol ratio of the rare earth ions to ammonia-substituted alpha-zirconium phosphate is 1: 1 to 1: 3. According to the composite coating agent, alpha-zirconium phosphate is subjected to lithium adsorption so as to form zirconium phosphate loaded with a great number of lithium ions, so the conductivity of zirconium phosphate is improved on one hand and a layered lithium-intercalated compound is formed on the other hand, which enables the diffusion rate of lithium ions to be increased; moreover, a part of alpha-zirconium phosphate is subjected to loading of rare earth, so a carrier is provided for uniform coating of rare earth metal. The composite coating agent can uniformly coat the surface of lithium cobalt oxide and had good conductivity.