Surface Modifications of Li-Ion Battery Electrodes with Ultrathin Amphoteric Oxide Coatings for Enhanced Elevated-Temperature Cycleability

Abstract

ABSTRACTTo enhance cycleability of LiMn2O4 at elevated-temperature we use atomic layer deposition (ALD) method to deposit a variety of ultrathin and highly conformal amphoteric oxide (ZnO, ZrO2, Al2O3) coatings for surface modification of LiMn2O4 electrodes. High-resolution transmission electron microscopic (HRTEM) images of ZnO, ZrO2 and Al2O3 ALD coated LiMn2O4 particles demonstrate the high qualities of ALD coatings with respect to remarkable conformity, homogeneity and uniformity. Two types of ALD-modified LiMn2O4 electrodes are fabricated: one is ALD-coated LiMn2O4 composite electrode, the other is electrode composed of ALD-coated LiMn2O4 particles and uncoated carbon/poly-vinylidenefluoride (PVDF) network. All LiMn2O4 electrodes modified with 6 oxide ALD layers (as thin as ∼1 nm) reveal significantly enhanced electrochemical performances than bare electrodes at both 25°C and 55°C. After 100 electrochemical cycles at 1 C at 55°C, the electrode consisting of LiMn2O4 particles coated with 6 ZnO ALD layers remains the highest capacity of 56.1 mAh/g, higher than 51.1 mAh/g of ZrO2 coated LiMn2O4 particles, 45.8 mAh/g of Al2O3 coated LiMn2O4 particles and 27.0 mAh/g of the bare composite electrode as well as 44.5 mAh/g of the composite electrode coated with 6 ZnO ALD layers. These results indicate that ZnO ALD coating is the most effective protective film for improved cycling stability, followed by ZrO2 and Al2O3. It is also found that amphoteric oxide coating on LiMn2O4 particles is more effective to enhance the cycleability of LiMn2O4 than coating on composite electrode. Furthermore, for coating either on composite electrode or on LiMn2O4 particles, the effect of ALD coating on improving capacity retention and increasing specific capacity of LiMn2O4 is more phenomenal at elevated temperature than at room temperature.