Fast discharging mitigates cathode-electrolyte interface degradation of LiNi0.6Mn0.2Co0.2O2 in rechargeable lithium batteries

Abstract

The rapid deterioration of lithium-ion batteries in fast-charging and discharging conditions poses a major challenge for future mobility technologies. Accelerated failure is attributed to the non-equilibrium de/lithiation reaction at inter- and intra-particle levels in electrodes induced by high current densities. However, the correlation between the reaction heterogeneity and degradation rate remains elusive. Here, we unambiguously decouple the effects of fast charging and discharging on battery degradation by applying asymmetric charging-discharging protocols. Our findings reveal that fast charging stimulates the electrolyte decomposition and surface reconstruction and, surprisingly, fast discharging mitigates these detrimental effects. The improved cyclability originates from the kinetically lowered depth of discharge (DOD) upon fast discharging, enabling a homogeneous electrochemical reaction by evading the slow-kinetics state-of-charge regime. Proving the beneficial effect of limiting DOD, we demonstrate a protocol that effectively suppresses degradation under fast charging conditions, resulting in negligible capacity decay while delivering an accumulated capacity of 30 Ah g-1. In contrast, conventional protocols show drastic capacity decay (13.8% retention). This study establishes a causal coupling between cathode degradation, reaction heterogeneity, and current density and direction at multiple length scales, providing valuable guidance for designing advanced battery cycling protocols that promote stable long-term battery operation, particularly under fast-charging conditions.