Electrochemical Activation Inducing Rocksalt-to-Spinel Transformation for Prolonged Service Life of LiMn2O4 Cathodes.

Abstract

LiMn2O4 spinel is emerging as a promising cathode material for lithium-ion batteries, largely due to its open framework that facilitates Li+ diffusion and excellent rate performance. However, the charge-discharge cycling of the LiMn2O4 cathode leads to severe structural degradation and rapid capacity decay. Here, an electrochemical activation strategy is introduced, employing a facile galvano-potentiostatic charging operation, to restore the lost capacity of LiMn2O4 cathode without damaging the battery configuration. With an electrochemical activation strategy, the cycle life of the LiMn2O4 cathode is extended from an initial 1500 to an impressive 14 000 cycles at a 5C rate with Li metal as the anode, while increasing the total discharge energy by ten times. Remarkably, the electrochemical activation enhances the diffusion kinetics of Li+, with the diffusion coefficient experiencing a 37.2% increase. Further investigation reveals that this improvement in capacity and diffusion kinetics results from a transformation of the redox-inert LiMnO2 rocksalt layer on the surface of degraded cathodes back into active spinel. This transformation is confirmed through electron microscopy and corroborated by density functional theory simulations. Moreover, the viability of this electrochemical activation strategy has been demonstrated in pouch cell configurations with Li metal as the anode, underscoring its potential for broader application.