A lithium manganate positive electrode active material, comprising a lithium manganate matrix and a cladding layer as a “barrier layer” and a “functional layer” are described. The cladding layer can not only “prevent” the transition metal ions which have been produced by the lithium manganate matrix from directly “running” into the electrolyte solution, but also “prevent” the hydrofluoric acid in the electrolyte solution from directly contacting with the lithium manganate substrate, and then prevent the lithium manganate matrix from dissolving out more transition metal manganese ions; as a “functional layer”, the cladding layer contains various effective ingredients inside, which can reduce the transition metal manganese ions already present inside the battery through chemical reactions or adsorption effects, thus slowing down the generation of transition metal manganese and the decomposition of the SEI film (solid electrolyte interphase film) catalyzed by the transition metal manganese.