Abstract:
On the 26th, the reporter learned from the Dalian Institute of Chemical Physics, Chinese Academy of Sciences, that the team of researcher Chen Zhongwei from the Power Battery and System Research Department of the National Key Laboratory of Energy Catalytic Conversion, together with the team of Professor Zou Changfu of Chalmers University of Technology in Sweden, Beijing Institute of Technology and related research teams of Jikrypton Technology Europe, have made new progress in the research on the actual operating degradation and resource utilization of electric vehicle power batteries.
Based on long-term actual vehicle operation data, the research team established a fleet-scale battery cell aging diagnosis and whole-package performance evaluation framework. The system quantitatively revealed the impact of cell inconsistency on the battery pack's health status, available power, life, power capability and full-life energy resource utilization. Relevant research results were recently published in "Nature·Energy".
Single degradation limits the performance of the entire power battery pack. Photo provided by the interviewed unit
Electric vehicle power battery packs are usually integrated with multiple single cells. Even if they are located in the same battery pack, different cells may gradually show different aging rates due to differences in raw materials, manufacturing processes, group matching, local temperature distribution and actual operating conditions. This will cause the battery pack to exhibit a typical "barrel effect." When charging, the cells with smaller capacity are the first to reach the upper voltage limit; during discharging and high-power operation, the cells with larger internal resistance are the first to touch the safety boundary; when the cells with the fastest aging reach the retirement threshold, the entire battery pack often needs to be withdrawn from use early.
In response to this problem, the research team conducted research on long-term actual vehicle operation data covering electric passenger cars equipped with ternary lithium batteries and electric buses equipped with lithium iron phosphate batteries. The relevant vehicles have been in operation for more than three years, and the cumulative mileage of the vehicles is up to 300,000 kilometers.
The research results show that in the passenger fleet studied, the health differences between units in the lower mileage stage are generally smaller; when the cumulative mileage exceeds about 170,000 kilometers, individual units in many vehicles begin to enter the accelerated aging stage, and the differences between units significantly expand. Further calculations show that, taking into account the impact of early retirement and inconsistent state of charge, the full-life energy resource utilization rates of electric passenger car and bus battery packs are only 80.7% and 72.9% respectively. In other words, when the weakest cell forces the entire battery pack to reach retirement conditions, approximately 19.3% and 27.1% of the potential energy resources are still not fully utilized.
"Research shows that the performance and life of electric vehicle battery packs are not only determined by the average aging level of the cells, but may be significantly restricted by a small number of accelerated aging cells. By quantifying this 'weakest cell' effect under real operating conditions, it can provide a basis for improving battery utilization, optimizing life management and system-level design." Chen Zhongwei said.
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