Dual functional MgHPO4 surface modifier used to repair deteriorated Ni-Rich LiNi0.8Co0.15Al0.05O2 cathode material

Abstract The layered LiNi0.8Co0.15Al0.05O2 (NCA) material, especially after being stored in air for a long time, encounters a practical challenge caused by irreversible phase transfer and large amounts of surface lithium impurities. To overcome these drawbacks, an effective strategy was implemented by mixing the deteriorated NCA with MgHPO4 precursor, followed by annealing at 750 °C (MP-DNCA). This process successfully achieved Mg2+ surface doping and Li3PO4 coating, thereby decreasing the degree of Li/Ni cation-mixing, and reducing the amount of surface residual lithium species such as LiOH and Li2CO3. Both aspects synergistically suppress the increase in polarization and restore the cycle performance of deteriorated NCA materials. Specifically, the revived MP-DNCA maintain 84.6% capacity retention after 200 cycles at room temperature, and 83.6% of initial capacity after 100 cycles at elevated temperature, which is significantly better than that of deteriorated NCA. These improvements are mainly owing to the enhanced structure and chemical stability. And this facile strategy could promote the recycling of severely degraded NCA materials in practical applications.