Keywords

Deformation, degradation, electrochemical cells, electrodes, nanoparticles

Abstract

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.

How Our Software Was Used

All of the reconstructed data sets were visualized and segmented using Dragonfly. The nanoCT data sets were cropped to remove much of the background, and the intensities were normalized between 0 and 1.

Author Affiliation

(1) Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, California94025, United States
(2) Idaho National Laboratory, 2525 North Fremont, Idaho Falls, Idaho83415, United States
(3) Department of Materials Science & Engineering, University of Pennsylvania, Philadelphia, Pennsylvania19104, United States
(4) Argonne National Laboratory, 9700 South Cass Avenue, Lemont, Illinois60439, United States