POSITIVE ELECTRODE AND LITHIUM ION SECONDARY BATTERY THAT INCLUDE UNDERCOAT LAYER CONTAINING MICROCAPSULE

A positive electrode for a lithium ion secondary battery, including a positive electrode current collector; and a positive electrode mixture layer that is provided on at least one side of the positive electrode current collector, the positive electrode mixture layer including a positive electrode active material layer, and an undercoat layer formed between the positive electrode current collector and the positive electrode active material layer, the undercoat layer containing a conductive auxiliary, a binder, and a thermally expandable microcapsule having a maximum volume expansion temperature of from 70° C. to 180° C.