Non-Uniformity Behaviors of Commercial Large-Format Batteries: Performance and Durability

Coin cells and small pouch cells are commonly fabricated in laboratory to study performance and degradation mechanisms of battery materials. However, for real world applications such as hybrid electric vehicles large-format Li-ion based batteries are used currently. Performance, durability, and safety are more complex in these large-format batteries than in small ones. For example, temperature spatial profile can be significantly varied in large-format batteries during high-rate charging and discharging periods. In addition, non-uniform battery material distribution, small local defects, and inappropriate cell assembly designs may magnify the non-homogeneous behaviors in large-format batteries. Better understanding of large-format commercial batteries is essential to ensure safety and performance reliability.

Both in-situ and ex-situ techniques utilizing synchrotron X-ray diffraction and Neutron diffraction are being developed at Argonne National Laboratory and Oak Ridge National Laboratory, respectively. Under various operating conditions, 3-D profiles of temperature, internal stress, and electrode SOC% can be collected on large-format Li-ion based prismatic cells. Both techniques, complementary to each other, will be briefly described. We will focus on discussing non-uniformity behaviors of local battery performance and changes of local material structure and chemistry before and after storage tests and charge-discharge cycles. These results will be correlated to the diffraction data, to understand the effects of non-uniform profiles of temperature, internal stress, and electrode SOC% on battery life-time durability. Important implications on battery quality, safety, and controls will also be mentioned.

Acknowledgement

This project is partially funded by US-CHINA Clean Energy Research Center (CERC)-Clean Vehicles Consortium.