Implications of the first cycle irreversible capacity on cell balancing for Li2MnO3-LiMO2 (M = Ni, Mn, Co) Li-ion cathodes

Much of the research on lithium-ion cathodes consisting of layered solid solutions of Li₂MnO₃-LiMO₂ (M = Mn, Co, Ni) has focused on identifying the causes of the irreversible capacity loss on the first cycle. However, a key issue that must be addressed is whether the high irreversible capacity observed seen on the first cycle is associated with intercalated lithium at the anode, or if it is associated with irretrievable capacity (i.e., film formation, and/or decomposition reactions). To this end, we have quantified the amount of utilizable lithium that is made available for the anodes when employing Li₂MnO₃-LiMO₂ as cathodes. Using a MoS₂ anode lithiation plateau transition as a reference point to the amount of lithium transferred to the anode during charge, it has been shown that almost none of the cathode irreversible charge capacity resulted in lithiation of the anode. Further, by reacting charged graphitic anodes that were retrieved from C anode-Li_1.2Ni_0.175Co_0.1Mn_0.52O₂ cathode cells with water to generate H₂ gas to measure the active amount of lithium in the anode, we confirmed the results with the MoS₂ titration experiments, demonstrating that lithium released from the cathode during the first charge is not proportionate to the cathode charge capacity.