A lithium niobate with high lithium ion conductivity. Disclosed is a method for producing a lithium niobate for use in a covering layer covering at least part of a surface of cathode active material particles, the method comprising: preparing a solution containing niobium ions and lithium ions, drying the solution to obtain a lithium niobate precursor, and heating the lithium niobate precursor at a temperature of from 250° C. to 300° C. for a heating time of more than 0 minute and 10 minutes or less.