高镍三元/硅氧碳软包电池在不同温度下的日历老化机制

Calendar aging mechanism of NCM811/graphite-SiOx pouch cells at different temperatures

由于电动汽车在大多数时间处于非工作状态,因此电池搁置期间的日历老化会对电池的寿命产生显著影响。高温加速实验是快速评价电池日历寿命的常用方法,为了获得可靠的高温加速老化实验结果,需要对不同温度条件下的电池衰减机理进行研究。以高镍三元/硅氧碳软包电池为研究对象,基于无损的电化学微分曲线分析和电池拆解验证,研究不同搁置温度对高镍/硅氧碳电池日历老化性能及老化机制的影响。结果表明:随着搁置温度的升高,电池老化速度逐渐加快,表现为容量加速衰减和直流内阻大幅增加。无损分析结果表明:活性锂损失和正极活性物质损失是电池日历老化的主要影响因素,随着温度升高,电池的活性锂损失程度和正极活性物质损失程度都有所增加,负极老化情况基本保持不变;进一步结合拆解验证结果表明:55℃下的高温搁置加速了正极材料性能的衰退,高温下正极NCM811材料颗粒出现内部裂纹和粉化,不宜作为电池搁置期间加速老化实验的加速因子。

Considering that a personal car spends about 95%of its life in parking mode,calendar aging can have a significant impact on battery life.High temperature storage is a common method for rapid evaluation of battery calendar life.In order to obtain reliable results of high temperature accelerated aging test,it is necessary to study the aging mechanism of battery stored at different temperature conditions.In this paper,the calendar aging experiment of graphite-SiOx/NCM811 pouch cells were carried out within the temperature range of 25-55℃.The differential curve analysis and post-mortem analysis were used to explore the aging mechanism.The results show that the calendar aging of pouch cells is mainly caused by the loss of lithium inventory and the loss of cathode active materials.When cells store at higher temperature,the loss of lithium inventory and the loss of cathode active materials increase,while the loss of anode active materials remains relatively unchanged.Based on various test results,it can be inferred that the parasitic reactions on the surface of electrode lead to the loss of lithium inventory and the increase of SEI.With the increase of storage temperature,this side reaction continues and consumes more lithium inventory.It is worth mentioning that when storage at 55℃,the microcracking develops and even breaks some of the secondary particles of cathode materials.Therefore,the pouch cells suffer severe loss of cathode active materials,which makes it inappropriate to accelerate the aging of batteries at such high temperature.