Modification of Ni Rich FCG NMC and NCA Cathodes by Atomic Layer Deposition: Preventing Surface Phase Transitions for High Voltage Lithium Ion Batteries
The energy density of current lithium ion batteries (LIBs) based on layered LiMO2 cathodes (M Ni, Mn, Co: NMC; M Ni, Co, Al: NCA) needs to be improved significantly in order to compete with internal combustion engines and allow for widespread implementation of electric vehicles (EVs) In this report, we show that atomic layer deposition (ALD) of titania (TiO2) and alumina (Al2O3) on Ni rich FCG NMC and NCA active material particles could substantially improve LIB performance and allow for increased upper cutoff voltage (UCV) during charging, which delivers significantly increased specific energy utilization. Our results show that Al2O3 coating improved the NMC cycling performance by 40% and the NCA cycling performance by 34% at 1 C/ 1 C with respectively 4.35 V and 4.4 V UCV in 2 Ah pouch cells. High resolution TEM/SAED structural characterization revealed that Al2O3 coatings prevented surface initiated layered to spinel phase transitions in coated materials which were prevalent in uncoated materials. EIS confirmed that Al2O3 coated materials had significantly lower increase in the charge transfer component of impedance during cycling. The ability to mitigate degradation mechanisms for Ni rich NMC and NCA illustrated in this report provides insight into a method to enable the performance of high voltage LIBs.
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