The equilibrium state of the lithium-ion battery refers to a state where concentration of lithium ions within the solid and the liquid becomes uniformly distributed, and as a result, no potential difference is present. This steady state is particularly required for measurements of cell properties such as open circuit voltage (OCV), entropy coefficient (dOCV/dT) and impedances by electrochemical impedance spectroscopy (EIS). Currently, it takes hours or even days of relaxation to reach the equilibrium state at a given state of charge (SOC) after charging or discharging, which prolongs the entire preparation time prior to actual measurements. In this work, a new equilibration method is developed using optimal time control based on an electrochemical model. The optimal time control is numerically solved by employing a direct solution approach to obtain an optimal current profile. Experimental results have shown that equilibration can be accelerated, so measurement time can be significantly reduced. For large format pouch type lithium-ion cells, the measurement time is reduced up to 58.3% compared with that by the current pulse-relaxation method at three different SOCs at 25 °C. In addition, the method is applied and experimentally tested at 40 °C and 10 °C and the effectiveness is verified.

锂离子电池的平衡状态是指固体和液体中锂离子的浓度均匀分布的状态，因此不存在电位差。通过电化学阻抗谱（EIS）测量电池特性（例如开路电压（OCV），熵系数（dOCV / dT）和阻抗）时，特别需要这种稳态。当前，在充电或放电后，在给定的充电状态（SOC）下需要数小时甚至数天的松弛时间才能达到平衡状态，这会延长实际测量之前的整个准备时间。在这项工作中，使用基于电化学模型的最佳时间控制开发了一种新的平衡方法。最佳时间控制通过采用直接求解方法来获得最佳电流曲线，从而在数值上得到解决。实验结果表明，平衡可以加速，因此测量时间可以大大减少。对于大型袋式锂离子电池，在25°C的三种不同SOC下，与当前脉冲松弛方法相比，测量时间最多可减少58.3％。此外，该方法在40°C和10°C的条件下进行了应用和实验测试，并验证了有效性。与在25°C下三种不同SOC的电流脉冲松弛方法相比，降低了3％。此外，该方法在40°C和10°C下应用并进行了实验测试，并验证了有效性。与在25°C下三种不同SOC的电流脉冲松弛方法相比，降低了3％。此外，该方法在40°C和10°C下应用并进行了实验测试，并验证了有效性。