Research on safe charging strategy of lithium-ion battery based on three-electrode equivalent circuit model

Under extreme conditions of low temperature or fast charging, the side reaction of lithium (Li) plating can occur on the anode surface of lithium-ion batteries (LIBs), which may cause causing capacity fade. Alarmingly, in severe cases, dendrites will grow and pierce the separator. As a result, thermal runaway will be induced, which seriously affects the safety performance of LIBs. Along these lines, to avoid Li plating during the charging process, the safe charging strategy was thoroughly investigated in this work based on the implementation of the three-electrode equivalent circuit model (ECM). More specifically, for the three-electrode LIB implanted with a reference electrode (RE), its ECM was improved based on the traditional ECM. The cathode and anode of the LIB were decoupled through the RE, whereas combined with the heat generation, transfer, and aging characteristics, a first-order RC electro-thermal coupled model of three-electrode was established, and the semi-empirical aging model of the LIB was combined to analyse the coupling characteristics between the parameters of each model. According to the acquired experimental data, the key parameters of modelling were identified and the accuracy of the model was verified. In addition, aiming at the contradiction between the fast charging and aging speed, and combined with the NSGA-II optimization algorithm, the self-adaptive multi-stage constant current constant voltage (SMCCCV) charging strategy was also proposed to avoid Li plating on the anode surface. An optimization model was thus established with the charging time and aging loss as the objective functions, resulting in three charging strategies, namely minimum charging time, minimum aging, and balanced charging. From the simulated outcomes, it was demonstrated that the anode potential was strictly maintained above the safety threshold for these three strategies. On top of that, the balanced charging strategy reduced the aging loss by 11.5 %, while the relatively equivalent charging speed compared with the traditional constant current constant voltage (CCCV) strategy was maintained. The proposed safe charging strategy based on multi-objective optimization provides some valuable insights for next-generation fast charging techniques.