Unexpected Improved Performance of ALD Coated LiCoO2/Graphite Li-Ion Batteries

The performance of Al2O3 atomic layer deposition (ALD) coatings for LiCoO2/natural graphite (LCO/NG) batteries is investigated, where various permutations of the electrodes are coated in a full battery. Coating both electrodes with ∼1 nm of alumina as well as coating only the LCO (positive electrode) enables improved performance when cycling at high voltage, where the LCO is known to degrade. However, we found that coating only the NG (negative electrode) also improves the performance of the whole battery when cycling at high voltage. Under these conditions, the uncoated LCO (positive electrode) should degrade quickly, and the NG should be unaffected. A variety of characterization techniques show the surface reactions that occur on the negative electrode and positive electrode are related, resulting in the enhanced performance of the uncoated LCO. Coating the negative electrode (graphite) only in LiCoO2/graphite full cell improves the performance of the positive electrode (LiCoO2) when cycling at a high voltage where the LiCoO2 degrades quickly. The underlying mechanism for the improvement is explained by closely related side reactions between the negative electrode and positive electrode.