从电解液看磷酸铁锂动力锂离子电池失效

Failure of lithium iron phosphate power Li-ion battery seen from electrolyte

为进一步研究磷酸铁锂(LiFePO_(4))动力锂离子电池失效原因,从电解液角度出发,以电动汽车退役的方形LiFePO_(4)/石墨动力电池为研究对象,研究4种容量保持率(100%、80%、70%和60%)的LiFePO_(4)电池的衰退特性,采用SEM、电化学阻抗(EIS)、气相色谱(GC)和电感耦合等离子(ICP)等技术分析电池极片厚度、极片形貌、阻抗、电解液剩余量及组分特性。随着电池容量保持率的降低,电池极片增厚、电极活性物质脱落、正极活性物质LiFePO_(4)分解、铁溶解沉积、电解液与电极发生副反应在界面形成高阻抗正极固体电解质相界面(CEI)或负极固体电解质相界面(SEI)膜、电解液分解消耗、电解液组分及电解液体系的改变、电解液副反应产物的生成,这些因素的协同作用,使得电池正负极电极界面间阻抗增大,活性Li^(+)含量降低,造成电池正负极片和电解液失效,最终导致电池循环寿命衰减和失效。

In order to further study the failure cause of lithium iron phosphate(LiFePO_(4))power Li-ion battery,from the perspective of electrolyte,the capacity fading characteristics of LiFePO_(4)Li-ion batteries with four kinds of capacity retention rates(100%,80%,70%and 60%)were studied by taking retired square LiFePO_(4)/graphite power batteries for electric vehicles.The electrode thickness,electrode morphology,impedance,residual amount and composition of electrolyte were analyzed by SEM,electrochemical impedance spectroscopy(EIS),gas chromatography(GC)and inductively coupled plasma(ICP).With the reduction of capacity retention rates,the thickness of battery electrode increased,electrode active material fell off,the cathode active material LiFePO_(4)decomposed,Fe dissolved and deposited,high impedance cathode electrolyte interface(CEI)or anode solid electrolyte interface(SEI)film formed at the interface by side reaction between electrolyte and electrode,the electrolyte in the battery gradually decomposed and consumed,electrolyte components and electrolyte system changed,side reaction products produced by electrolyte.The synergy effect of these factors led to the increase of the impedance between the cathode and anode of battery,the decrease of content of active Li^(+),the cathode and anode of battery and the electrolyte failed.Eventually,the cycle life of battery decreased and failed.