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

Embedding a lithiated cobalt oxide spinel (Li2 Co2 O4 , or LiCoO2 ) component or a nickel-substituted LiCo1- x Ni x O2 analogue in structurally integrated cathodes such as xLi2 MnO3 ·(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 Li2 Co2 O4 ( 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 (Oh ) site to a tetrahedral site (Td ) in Fd3̅ m LT-Li1- x CoO2 , has been calculated to help understand the complex electrochemical charge/discharge processes. A search of LiCo x M1- 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, LiNi0.8125 Co0.1875 O2 ( Fd3̅ m), with a composition close to that of commercial, layered LiNi0.8 Co0.15 Al0.05 O2 , which may have the potential for exploitation in structurally integrated, layered spinel cathodes for next-generation lithium-ion batteries.