Analysis of control strategies in alternating current preheating of lithium-ion cell

Among various methods of preheating lithium-ion cells at low temperatures, alternating current preheating (ACP) has the advantage of high efficiency. However, the risk of lithium deposition exists when using the ACP method. To prevent lithium deposition, terminal voltage control strategy (TVCS), negative electrode potential control strategy (NEPCS) and full cell impedance control strategy (FCICS) are proposed. However, each of the three control strategies has limitations. In this paper, the applicability boundaries of the three control strategies (TVCS, NEPCS, FCICS) are analyzed by measuring the electrochemical impedance spectrum (EIS) of a three-electrode model cell at different temperatures and state-of-charge (SOC). The results show that TVCS leads to lithium deposition when the frequency is lower than boundary frequency, while NEPCS leads to the terminal voltage exceeding the cut-off voltage when the frequency is higher than boundary frequency. As for FCICS, when the SOC is 100 %, 75 %, 50 % and 25 %, the heat generation is decreased by 8.61 % -34.5 %, 9.18 -51.7 %, 6.49 -40.7 % and 8.61 -61.4 %, respectively, compared with NEPCS. Moreover, the applicability boundary obtained by FCICS also leads to the terminal voltage exceeding the cut-off voltage. Based on the above analysis, this paper proposes a strategy to control the terminal voltage without lithium deposition. When the frequency is lower than the boundary frequency, NEPCS is employed, and when the frequency is higher than the boundary frequency, TVCS is employed.