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 Li2Co1-xNixO2 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 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 (Fd (3) over barm) vs trigonal-layered HT-LiCoO2 (R (3) over barm), respectively) can be explained by a small difference in the free energy between these 20 30 40 50 60 70 80 26 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 Fd (3) over barm LT-Li1-xCoO2, has been calculated to help understand the complex electrochemical charge/discharge processes. A search of LiCoxM1-xO2 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, LiNi0.8125Co0.1875O2 (Fd (3) over barm), with a composition close to that of commercial, layered LiNi0.8Co0.05Al0.05O2, which may have the potential for exploitation in structurally integrated, layered spinel cathodes for next generation lithium-ion batteries.