Microwave-assisted hydrothermal synthesis of a high-voltage microcube LiMn1.5Ni0.5O4−δ spinel cathode material

•High-quality LiMn1.5Ni0.5O4−δ was synthesized by microwave-assisted hydrothermal method.•Microwave-treated LiMn1.5Ni0.5O4−δ offers higher battery performance than LiMn2O4.•Microwave irradiation modulates content of Mn3+ and O vacancy improving performance.•Material with longer irradiation shows higher discharge capacity but less stability.•Improving intrinsic stability is required before practical use in Li-ion batteries.