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Optimizing Structural Properties of Non-Structural Components: Multifunctional Battery System in Electric Vehicle

Abstract

To reduce greenhouse gas emission, to increase energy efficiency, and to enhance vehicle performance, electric vehicle (EV) has been extensively investigated. Currently, the major hurdles include the limited drive range, the heavy weight, the high cost, and the fire safety concerns, all of which are associated with the battery system.

In this study, we developed a multifunctional lithium-ion battery (LIB) system that, upon mechanical abuse, did not undergo thermal runaway. In an EV, such LIB modules would drastically enhance the system robustness and safety. Moreover, they not only do not need excessive protection, but also can be employed as energy-absorbing components in the autoframe, so as to significantly save weight and cost at the system level. The structural and energy storage functionalities of the LIB modules are achieved by separated elements.

The thermal-runaway mitigation (TRM) mechanism was incorporated into the LIB cells, particularly the current collectors. Our experiments on LIB coin cells indicated that appropriate surface grooves could alter the fracture mode of current collector as the LIB cell was impacted. If the damaged areas could be completely separated from the rest of electrode, only the relatively small portion of electric energy stored by the active materials immediately adjacent to the internal shorting spots could be released. Hence, the heat generation rate of the damaged LIB cell could be reduced by more than an order of magnitude. Shorting resistance was identified as the governing factor of the heat generate rate of the damaged LIB cell.

A set of comprehensive parameterized studies was carried out to understand the effects of surface-groove depth, width, and contour. Scalable processing techniques were developed to precisely control the surface-groove configurations on large current collector sheets. Large-sized LIB pouch cell testing confirmed that the modified current collectors could prevent thermal runaway as the battery cell was severely damaged by metal impact penetration. Selected current collectors were also tested with high-energy active materials, and the experimental results were encouraging.

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