Significant Improvement on Electrochemical Performance of LiMn₂O₄ at Elevated Temperature by Atomic Layer Deposition of TiO₂ Nanocoating

The spinel LiMn₂O₄ cathode is considered a promising cathode material for lithium ion batteries. Unfortunately, the poor capacity stability, especially at elevated temperature, hinders its practical utilization. In this study, the atomic layer deposition (ALD) technique is employed to deposit a TiO₂ nanocoating on a LiMn₂O₄ electrode. To maintain electrical conductivity, this amorphous coating layer with high uniformity, conformity, and completeness is directly coated on cathode electrodes instead of LiMn₂O₄ particles. Among all the samples studied, the TiO₂-coated sample with 15 ALD cycles exhibits the best cyclability at both room temperature of 25 °C and elevated temperature of 55 °C and has the higher specific capacity of 136.4 mAh g^–1 at 0.1 C that is nearly close to the theoretical capacity of LiMn₂O₄. Meanwhile, this sample realizes lower polarization and less self-discharge. The improved electrochemical performance is ascribed to the high conformal and ultrathin TiO₂ coating, which enhances the kinetics of Li⁺ diffusion and stabilizes the electrode/electrolyte interface. Also, the deconvolution of Ti 2p X-ray photoelectron spectroscopy shows a weaker peak of Ti–O–F after cycling, which indicates that the coexistence of TiO₂ and TiO_<i>x</i>F_<i>y</i> layers can inhibit Mn dissolution and electrolyte decomposition