Learning from Electrochemical Data: Simple Evaluation and Classification of LiMO2-type-based Positive Electrodes for Li-Ion Batteries

The required boost in the specific energy of lithium-ion battery (LIB) cells can only be achieved by increasing the cell voltage and/or the specific capacities of the electrodes. In the latter regard, the positive electrode constitutes the specific energy bottleneck. Lithium transition-metal oxides (LiMO2) such as LiNixMnzCo1-x-zO2 (NMC) are regarded as the most suitable positive electrode materials for next-generation high-specific-energy LIBs. In this work, the electrochemically induced structural stability limits as well as the associated reversible specific energies and specific energy efficiencies were assessed by means of constant current charge/discharge experiments for the most popular and promising LiMO2 compositions. The electrochemically induced structural stability of the positive host material was not determined by the applied charge cut-off potential, but rather by the amount of extracted Li+ ions. In this regard, the electrochemically induced structural stability order of selected LiMO2 compositions was modified by assessing the structural stability as a function of the Li+-ion extraction ratio. With respect to application, relevant requirements (e.g., specific energy, specific energy efficiency, temperature-dependent structural stability, kinetics) revealed that NMC532 and NMC622 showed the best compromise among the various LiMO2 compositions, revealing significant insight into the structure-property relationship.