Ultrafast kinetics in a phase separating electrode material by forming an intermediate phase without reducing the particle size

Abstract

A fast charging/discharging capability in electrode materials is one of the essential properties of Li-ion batteries. A well-known approach for improving the kinetics of electrode materials is minimization of the particle size to the nanoscale, especially for phase separating materials such as LiFePO₄ and Li₄Ti₅O₁₂. Here, we report on ultrafast kinetics in a phase separating material with submicron particles enabled by the formation of an intermediate phase during discharge even without minimizing the particle size. The intermediate phase during (dis)charging acts as a structural buffer between the Li-rich and Li-poor phases, leading to reduced mechanical stress/strain on the interface in a particle, which can suppress structural defects, and a substantial reduction in the phase transformation barrier, which can make the electrochemical reaction of particles in the electrode homogenous. As a result, the resulting phase separating material can deliver ∼70 mA h g⁻¹ at a 200C discharge rate (18 s for full discharge) with a 1C charge rate, and prolonged cycling stability for 1000 cycles even though it has a wide particle size distribution from 50 nm to 600 nm with an average of ∼300 nm. This finding will provide a new avenue for achieving fast electrochemical kinetics with a high volumetric energy density in electrode materials for high performance Li-ion batteries.