Formation of a Continuous Solid‐Solution Particle and its Application to Rechargeable Lithium Batteries

High‐energy electrode materials are under worldwide development for rechargeable lithium batteries to be used in electric vehicles and other energy storage applications. High capacity and energy density are readily achievable using Ni‐rich Li[Ni1‐xMx]O2 (x = 0.1–0.2, M = Ni, Co, Mn, and Al) cathodes. Unfortunately, their structural instability is associated with severe capacity fading on cycling, which hinders practical applications. Here, a method is presented for producing a continuous compositional change between Li[Ni0.8Co0.2]O2 (center) and Li[Ni0.8Co0.01Mn0.19]O2 (surface) in a spherical particle, resulting in an average composition of Li[Ni0.8Co0.06Mn0.14]O2. The chemical composition in the particle is gradually altered by decreasing the Co concentration while adding Mn content. The Ni content remains fixed. Coin cells with the solid‐solution cathode deliver a specific capacity over 210 mAh g−1 in the voltage range of 2.7–4.3 V vs. Li/Li+ with capacity retention of 85% over 100 cycles at 25 and 55 °C. The main exothermic temperature upon heating appears at around 250 °C with relatively low heat generation (810 J g−1). The presence of the tetravalent Mn at the particle surface is mainly responsible for the high capacity upon cycling and excellent thermal properties.