Degradation mechanism of LiNi0.8Co0.1Mn0.1O2 cathode after ambient storage and self-repairing strategy by electrolyte additive

Abstract

As a next-generation cathode material for lithium-ion batteries, the LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode undergoes significant performance degradation after ambient storage, hindering its commercial development. Herein, the failure mechanism of the stored NCM811 material was elaborately investigated from the perspective of electrolyte/electrode interfaces. The result manifests that the impurities generated on the NCM811 surface during the storage are mainly LiOH and Li2CO3, accompanied by a few transition metals-based hydroxides and carbonates. These substances can readily catalyze the oxidative decomposition of electrolytes through electrochemical pathways, which should be the main culprit for the fast capacity fading. The adverse effects of surface impurities can be effectively eliminated after introducing a Lewis acid additive into traditional liquid electrolytes. The multifunctional electrolyte additive in the electrolyte firstly serves as an anion receptor to induce the dissolution of contaminants. Then it constructs a stable electrode/electrolyte interphase film to isolate these detrimental substances from electrodes. The NCM811 cathode, after 1-day storage at an 80% RH environment, is almost completely recovered in the additive-containing electrolyte, maintaining a capacity retention rate of 80% after 100 cycles (44% for the baseline electrolyte). The practicability of this strategy is verified by graphite||NCM811 pouch cells, which exhibit superior cyclability than the pristine cell without storage. This work not only reveals a novel insight into the mechanism underlying the degradation of nickel-rich materials following ambient storage but also offers a viable strategy for self-repairing moderately degraded materials, which is of profound commercial significance.