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With the degradation of lithium-ion batteries, the battery safety performance changes, which further influences the safe working window. In this paper, the pouch ternary lithium-ion battery whose rated capacity is 4.2 Ah is used as the research object to investigate the impact of the high-temperature calendar and cyclic aging on tolerance performance. The overcharge-to-thermal-runaway test is performed on the fresh cell and aged cell (90% SOH). The inflection point of voltage for aged cells appears earlier than that of the fresh cell, while the voltage corresponding to the inflection point is the same for them, which means that the voltage at which lithium plating occurs is the same. However, the voltage plateau and the crest voltage before thermal runaway of aged cell are significantly higher than that of the fresh cell. Besides, ohmic heat, reversible heat, and side reaction heat make contribution to the thermal runaway triggering.

Lithium-ion battery charging strategy affects charging time of electric vehicles, energy efficiency of entire vehicle, service life and safety. This paper focuses on the lithium iron phosphate (LiFePO4) battery, based on the battery internal mechanism and the working conditions, taking charging time, effective full-charge capacity and charge energy efficiency as the evaluation indexes. Firstly, through a series of comparative experiments of the constant-current constant-voltage and the constant current charging strategy, the evaluation indexes variations in different temperatures and charging currents have been studied in the paper. By analyzing the respective characteristics of constant current charging phase and constant voltage charging phase in the whole charging process and their own contributions, we have found out the superiority of the constant current charging strategy.