锂离子电池放电过程能量损失分析

Analysis of energy conversion losses of lithium-ion battery in discharging cycles

对锂离子电池循环寿命实验数据包括不同倍率下电池的电压、电流和温度等进行分析,计算了能量损失率和不可逆热量等随着电池循环次数的变化。分析结果显示:在0.5 C和1 C倍率循环条件下放电,电池的过电压在放电深度为0~10%阶段缓慢上升,10%~60%阶段缓慢下降,60%~100%阶段快速上升。在3 C倍率循环条件下放电,过电压在放电深度为0~10%阶段缓慢上升,10%~60%阶段快速下降,60%~100%阶段缓慢上升。在0.5 C、1 C和3 C倍率循环条件下,能量损失率在放电过程中随着充放电循环次数增加呈现先缓慢下降,然后持续上升的变化,并且在电池容量衰减到额定容量80%~60%的阶段,快速上升。在所有3个放电倍率循环条件下,不可逆热占能量损失比例随循环次数逐渐增加,可作为电池健康状态的一个评测指标。

The experimental data of the cycle life test of lithium-ion battery,including the voltages,currents and temperatures,were analyzed;the energy loss rate and irreversible heat with cycle numbers were calculated.The analysis shows that:at 0.5 C and 1 C discharging rates,the over-voltage of the battery rises slowly in the 0-10%depth of discharge(DOD),then falls slowly at 10%-60%DOD,and rises rapidly at 60%-100%DOD.At 3 C discharging rate,the over-voltage of the battery rises slowly at 0-10%DOD,then falls rapidly at 10%-60%DOD,and rises slowly at 60%-100%DOD.The energy loss rates fall firstly and then rise continuously with the increase of cycle numbers,and show sharp rise while the battery fades to 80%-60%of its initial capacity.The ratio of irreversible heat to energy loss,which is increasing with the cycle numbers at all three discharging rates cycles,can be used as one of the features to determine the state of health of the lithium ion batteries.