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

Embedding a lithiated cobalt oxide spinel (Li ₂ Co ₂ O ₄ , or LiCoO ₂ ) component or a nickel-substituted LiCo _{1- x} Ni _x O ₂ analogue in structurally integrated cathodes such as xLi ₂ MnO ₃ ·(1- x)LiM'O ₂ (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 LiCoO ₂ 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-LiCoO ₂ ; or Li ₂ Co ₂ O ₄ ( Fd3̅ m) vs trigonal-layered HT-LiCoO ₂ ( 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/LiCoO ₂ cell for both cubic and trigonal phases of LiCoO ₂ , 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} CoO ₂ , has been calculated to help understand the complex electrochemical charge/discharge processes. A search of LiCo _x M _{1- x} O ₂ 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 _0.8125 Co _0.1875 O ₂ ( Fd3̅ m), with a composition close to that of commercial, layered LiNi _0.8 Co _0.15 Al _0.05 O ₂ , which may have the potential for exploitation in structurally integrated, layered spinel cathodes for next-generation lithium-ion batteries.