Implications of the first cycle irreversible capacity on cell balancing for Li_2MnO_3-LiMO_2 (M = Ni, Mn, Co) Li-ion cathodes

摘要

Much of the research on lithium-ion cathodes consisting of layered solid solutions of Li_2MnO_3-LiMO_2 (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 Li_2MnO_3-LiMO_2 as cathodes. Using a M0S2 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_(1.2)Ni_(0.175)Co_(0.1)Mn_(0.52)O_2 cathode cells with water to generate H_2 gas to measure the active amount of lithium in the anode, we confirmed the results with the M0S2 titration experiments, demonstrating that lithium released from the cathode during the first charge is not proportionate to the cathode charge capacity.