Learning from electrochemical data: Evaluation and classification of LiMO2 type based positive electrodes for Li ion batteries by using a novel electrochemical analysis methodology

Kasnatscheew J, Evertz M, Kloepsch R, Streipert B, Wagner R, Cekic-Laskovic I, Winter M

Abstract

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