Ultrathin Surface Coatings for Improved Electrochemical Performance of Lithium Ion Battery Electrodes at Elevated Temperature

To enhance the cycling stability of LiMn2O4 especially at elevated temperature, we use the atomic layer deposition (ALD) method to deposit ultrathin and highly conformal ZnO coatings (as thin as 0.34-1.7 nm) onto LiMn2O4 cathodes with precise thickness-control at atomic scale. We prepare two types of ALD-modified electrodes: one is an electrode composed of ALD-coated LiMn2O4 particles and uncoated carbon/polyvinylidenefluoride (PVDF) network; the other is ALD-coated LiMn2O4 composite electrode. All ALD-modified LiMn2O4 electrodes demonstrate significantly enhanced cycling performances than bare electrodes at both 25 and 55 degrees C. In particular, the electrode coated with 6 ZnO ALD layers (1.02 nm thick) shows the best cycling performances among electrodes coated with ALD films of different thicknesses at both 25 and 55 degrees C, indicating cycling performances of coated electrodes can be easily optimized by accurately tuning coating thickness via varying ALD growth cycles. Furthermore, an electrode consisting of LiMn2O4 particles coated with 6 ZnO ALD layers and uncoated carbon/PVDF network shows even better electrochemical performances than an electrode coated with 6 ZnO ALD layers at both 25 and 55 degrees C. The enhanced electrochemical performances of ALD-coated cathodes are ascribed to the high-quality ALD coatings that are highly conformal, dense, complete, and thus effectively protect active material from Mn dissolution especially at elevated temperature.