Exploring the origin of electrochemical performance of Cr-doped LiNi0.5Mn1.5O4

Discorded LiNi0.5Mn1.5O4 has become a promising candidate for Li ion battery due to its high specific energy. However, its poor structural stability restricts practical applications. After extensive exploration, Cr-doped disordered LiNi0.5Mn1.5O4 demonstrates enhanced structural stability and electrochemical performance. Thus far, its origin at electronic structure level remains elusive, which is important to further performance improvement. First-principle calculations disclose that Cr atom prefers to substitute Ni rather than Mn atom. The transferred charge from Cr to Mn causes the reduction of Mn ion and lengthens the distance of Li-O bond, which are mainly responsible for the lower Li ion diffusion energy barrier and Li vacancy formation energy. The heavy oxidation of O ion is a main factor to induce the structural degeneration. In this case, the reduced Mn ion delays the oxidation of O ion, enhancing the structural stability. In addition, Cr doping increases the thermodynamic stability of intermediate phases during delithiation, decreasing the structural strain in delithiation process. Ordered and disordered LiNi0.5Mn1.5O4 are also included for comparison. Our work provides an opportunity to fully understand Cr-doped LiNi0.5Mn1.5O4 at the atomic scale.