Study of the lithium/nickel ions exchange in the layered LiNi _0.42Mn_0.42Co_0.16O₂ cathode material for lithium ion batteries: Experimental and first-principles calculations

Mix transition metal layered oxide materials are much attractive for cathode materials in lithium ion batteries. However, the disordered arrangement between lithium and transition metal ions in local regions of these materials always occurs, and seriously affects their electrochemical performance. Here we report experimental and first-principles calculations of Li⁺/Ni ²⁺ ion exchange in the LiNi_0.42Mn_0.42Co _0.16O₂ materials prepared by solid state reaction and co-precipitation methods. The impact of Li⁺/Ni²⁺ ions exchange on the crystal/electronic structure, electrochemical performance and stress are investigated in detail. The results show that there are obvious anisotropic stress and smaller inter-slab space of the unit cell associated with greater Li⁺/Ni²⁺ ion exchange. During the delithiation process, the distortion force in the unit cell of the material with large Li⁺/Ni²⁺ ion exchange increases sharply and presents strong spin-flip transition of Ni ions (magnetic moment direction change). These issues are closely associated with the electrochemical performance of these layered oxide materials and definitely affect their reversible capacity, cycle stability and rate performance.