Isolating membrane and preparation method thereof, secondary battery and electric device

The invention relates to an isolating membrane and a preparation method thereof, a secondary battery and an electric device. The isolating membrane comprises a base material and a protective layer. The protective layer is disposed on at least one surface of the substrate. Wherein the protective layer contains microcapsule particles; each microcapsule particle comprises a core material and a shell coating the surface of the core material, and the core material comprises hydrated metal salt; the shell is broken under the condition of 100 DEG C to 200 DEG C. A protective layer containing the microcapsule particles is arranged on the surface of an isolating membrane base material, when the temperature of the secondary battery reaches 100-200 DEG C, shells of the microcapsule particles are broken to release hydrated metal salt in a core material, and the hydrated metal salt can absorb heat and dehydrate, so that the temperature of the secondary battery is reduced, and the service life of the secondary battery is p