Synthesis of Co-Free Ni-Rich Single Crystal Positive Electrode Materials for Lithium Ion Batteries: Part II. One-Step Lithiation Method of Mg-Doped LiNiO2

Abstract

This second study in a two part series investigates the synthesis of Co-free single crystalline Mg-doped LNO via the one-step lithiation method. The synthesized materials were characterized by scanning electron microscopy, X-ray diffraction and particle size analysis to understand the impact of synthesis conditions. Higher heating temperatures promoted grain growth but also increased the Ni content in the Li layer. Increasing the Li/TM ratio does not seem to have an effect on grain growth at lower temperatures but influences the formation of Li2O impurity. The separation of particle aggregates is required to improve the cycling performance of the material. The utilization of a lower temperature step after the calcination step can reduce the Ni content in the Li layer below what would be expected at the calcination temperature, and this can be used to grow larger grains while keeping an acceptable amount of Ni in the Li layer. However, all single crystalline materials are still not yet electrochemically competitive with polycrystalline materials and have lower capacities, higher irreversible capacities and similar cycling fade. The lower capacities of single crystalline materials stem from increased kinetic hindrances to Li diffusion. Cycling single crystalline materials at 55 °C can recover ∼20 mAh g−1 of discharge capacity and yield similar irreversible capacity compared with polycrystalline cells cycled at 30 °C.