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 degrees C and elevated temperature of 55 degrees 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 TiOxFy layers can inhibit Mn dissolution and electrolyte decomposition.