First-Principles Study of Lithium Cobalt Spinel Oxides: Correlating Structure and Electrochemistry

Embedding a lithiated cobalt oxide spinel (Li₂Co₂O₄, or LiCoO₂) component or a nickel-substituted LiCo_{1- x}Ni _xO₂ analogue in structurally integrated cathodes such as xLi₂MnO₃·(1- x)LiM'O₂ (M' = Ni/Co/Mn) has been recently proposed as an approach to advance the performance of lithium-ion batteries. Here, we first revisit the phase stability and electrochemical performance of LiCoO₂ synthesized at different temperatures using density functional theory calculations. Consistent with previous studies, we find that the occurrence of low- and high-temperature structures (i.e., cubic lithiated spinel LT-LiCoO₂; or Li₂Co₂O₄ ( Fd3̅ m) vs trigonal-layered HT-LiCoO₂ ( R3̅ m), respectively) can be explained by a small difference in the free energy between these two compounds. Additionally, the observed voltage profile of a Li/LiCoO₂ cell for both cubic and trigonal phases of LiCoO₂, as well as the migration barrier for lithium diffusion from an octahedral (O_h) site to a tetrahedral site (T_d) in Fd3̅ m LT-Li_{1- x}CoO₂, has been calculated to help understand the complex electrochemical charge/discharge processes. A search of LiCo _xM_{1- x}O₂ lithiated spinel (M = Ni or Mn) structures and compositions is conducted to extend the exploration of the chemical space of Li-Co-Mn-Ni-O electrode materials. We predict a new lithiated spinel material, LiNi_0.8125Co_0.1875O₂ ( Fd3̅ m), with a composition close to that of commercial, layered LiNi_0.8Co_0.15Al_0.05O₂, which may have the potential for exploitation in structurally integrated, layered spinel cathodes for next-generation lithium-ion batteries.