Engineered Ionic Diffusion Layers to Increase Rate Capability of NCA Cathode with Larger Particle Sizes in Lithium-Ion Cells

Abstract

Low cost, high energy and long cycle life Lithium-ion batteries are the technology of choice widespread implementation of high-performance electric vehicles (EVs). In spite of the strides technology has made, current high energy density solutions suffer from well understood and catastrophic degradation mechanisms that have prevented the full fruition of NCA cathode materials. There is growing evidence that the cathode surface is the initiation site of all the above mechanisms, motivating the use of larger particle sizes to minimize surface area and mitigate degradation. However, larger particle sizes decrease the overall rate of diffusion of lithium ions, causing a loss of activation of Li-rich phases and an increased loss of capacity at higher rates. Here we show that Al2O3 and TiO2 ALD coatings applied to NCA powder, completely covering active material particle surfaces, create a cathode artificial SEI layer which facilitates an improved Li-ion diffusion pathway, increasing the rate capability of NCA cathodes even with larger particle sizes. Electrochemical analyses showed increased rate capability in 95x64 mm pouch cells (~2.5Ah) with coated NCA compared to uncoated, and XRD and TEM were used to characterize the underlying favorable interactions of coatings with the cathode surface. XALT Energy’s integrated cell design and manufacturing makes 95x64 mm cell performance representative of large format (216x216 mm) production EV cells, demonstrating the validity and scalability of this approach.