Wednesday, 4 October 2017: 11:40
National Harbor 1 (Gaylord National Resort and Convention Center)
Lithium-ion battery-based energy storage is widely regarded as the best technology to realize affordable electrification of automobiles (hybrids and EVs), buses, and ships. However, strategies to realize higher energy density and lower cost come at the expense of cell lifetime and safety. Extensive effort has been devoted to studying the effects of ALD coatings on cathode materials, with varying reports of the impact on full cell cycle life. The changes in surface chemistry of ALD-coated cathode particles and their specific effects on electrochemical performance have not been studied in detail. Unmodified particle surfaces contain active oxygen, LiOH, and Li2CO3 species. The chemistry of these species during delithiation and interaction with the electrolyte can introduce components of impedance that can limit the capacity and rate capability of the material. Moisture adsorption can occur over time which can interact with and generate more of these species, causing a further deterioration of capacity. We have shown that important functions of ALD are to “clean” the particle surfaces, decreasing the content of LiOH and moisture, and forming a barrier to water adsorption and further generation of these species. Thus an important mechanism of ALD enhancement of cathode materials in full cells is demonstrated. This understanding should be applied to past and future studies, and represents a powerful new strategy to mitigate the effects of moisture.