Layered-to-Spinel Phase Transformations Inhibited By ALD Coatings on NMC Cathodes to Mitigate Voltage Fade 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 to full fruition of lithium- and manganese-rich NMC cathode materials. Capacity, power, and voltage fade, excessive SEI growth, electrolyte oxidation, cathode dissolution, structural degradation, and phase transformations are only few of the mechanisms that have been identified. Layered-to-spinel phase transformations at high voltages (~4.8 V), are a main contributor to voltage fade in LMR-NMC-based batteries. Here we show that TiO2 and Al2O3 atomic layer deposition (ALD) coatings applied to NMC powder, conformally coating active material particle surfaces, create a cathode artificial SEI layer which alters and slows the chemical pathways for nucleation and propagation of layered-to-spinel phase transformations at high voltages. XRD, TEM, and magnetic susceptibility characterization of active materials before cycling and at end of cycle life in 95x64 mm pouch cells (~2.5Ah) showed decreased extent of phase transformation with coated NMC compared to uncoated. 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.