ALD-Coated Graphite Anode Materials for Improved Cycle Life, Calendar Life, and Safety of Li-Ion Cells

Abstract

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 cycle life of full cells. However, ALD coatings on graphite anode materials have received relatively little attention, despite the role of the negative electrode in predominant energy loss mechanisms in graphite-based full cells. In this work we studied the effects of ALD coatings of Al2O3 and other chemistries on graphite active material powders, in full 95mm x 64mm pouch cells considering cycle life, calendar life, and thermal stability via ARC. We further studied the effects of different voltage windows including “high voltage” 4.4V charge limit. We found that the chemistry of the negative electrode was fundamentally altered, including SEI chemistry, growth, and resistance; and capacity slippage electrode misalignment. FTIR spectroscopy and depth-profiling XPS confirmed changes in graphite surface and SEI chemistry with ALD coatings. The result in full cells was a more stable SEI that gave significantly longer cell lifetimes and enhanced safety under conditions of high-temperature cycling, high-temperature storage, and high-voltage cycling. Moreover, we found the effects of ALD coatings on cathodes were enhanced in “Dual ALD” cells combining ALD-coated cathode materials and ALD-coated anode materials.