Porous LiNi0.5Mn1.5O4 sphere as 5 V cathode material for lithium ion batteries

Abstract

A new type of microsized porous spherical LiNi_0.5Mn_1.5O₄ (LNMO-Air) cathode material for a lithium ion secondary battery has been synthesized by an impregnation method using highly reactive nanocupule MnO₂ spheres as the manganese source. These LNMO-Air spheres are aggregates of nanosized polyhedron particles with well-defined cubic spinel structure. They showed excellent rate capability and cycle stability, compared with other microspheres of LNMO. We also investigated the effect of the trace amounts of Mn³⁺ in the crystal structure on its specific capacity and cycle stability. Compared with the sample (LNMO-O₂) calcined in an oxygen atmosphere, which is considered to be Mn³⁺ free, LNMO-Air exhibits superior specific capacity, cycling ability and rate capability. Because of the presence of trace amounts of Mn³⁺, the LNMO-Air sample presents a discharge specific capacity of 108 mA h g⁻¹ at 5 C rate at 55 °C after 80 cycles without significant reduction. These improvements can be explained by better ion conductivity as the metal oxide layer spacing is enlarged to facilitate faster ion transfer and significantly improved electrical conductivity; both are attributed to the presence of Mn³⁺.