The Evolution of LiNi0.5 Mn0.3 Co0.2 O2 Particle Damage from Fast Charging in Optimized, Full Li-Ion Cells

Molleigh B. Preefer, Tanvir R. Tanim, Samuel S. Welborn, David N. Agyeman-Budu, Alison R. Dunlop, Stephen E. Trask, Eric J. Dufek, Andrew N. Jansen, and Johanna Nelson Weker

December 2022 - Fast charging batteries are critical to the widespread adoption of electric vehicles to compete with refueling times of combustion-based vehicles. In the near term, adapting current commercial battery technologies to perform better under fast charging conditions through engineering optimizations will greatly expedite the process while exploratory fast-charging electrode materials are being pursued. To do so, the degradation modes in optimized Li-ion batteries need to be completely explored to understand fast charging limits while maintaining a high energy density and a long cycle life. While lithium plating on graphite still remains a challenge, cathode degradation also plays a key role in battery performance. We used nano- and micro-X-ray computed tomography to characterize the mechanical degradation of LiNi0.5Mn0.3Co0.2O2 (NMC532) in optimized Li-ion batteries cycled at three rates, 1C, 6C, and 9C, and at different stages of cycle life, 225 and 600 cycles. Despite using a conservative upper voltage cutoff limit aimed to minimize extensive cathode degradation, higher charging rates and increased cycling caused the polycrystalline NMC532 particles to fracture and pulverize, which likely drives cathode capacity fade and contributes to the decrease in overall cell performance.

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