A positive electrode for lithium-ion secondary batteries, comprising a positive electrode active material and at least one polymer electrolyte being polyether polymer, said positive electrode active material comprising at least elements selected from Li, M′, and oxygen, wherein the metal M′ has a formula: Ni1-x-y-zMnxCoyAz with 0.00≤x≤0.70, 0.00≤y≤0.40, and 0.00≤z≤0.10, wherein A, when present, is different than Ni, Mn, Co and Li, and is preferably at least one of: B, Mg, Al, Nb, Ti, Y, W, S, Ba, Sr, and Zr.