磷酸铁锂锂离子电池容量衰减机理分析

Analysis of capacity fading mechanism of LiFePO_(4)Li-ion battery

分析容量衰减机理,对优化电池体系十分重要。研究23 Ah方形铝壳磷酸铁锂(LiFePO_(4))锂离子电池高温(55℃)循环容量衰减的机理。通过SEM、X射线能量色散谱(EDS)、XRD、电感耦合等离子体发射光谱(ICP)及傅立叶变换红外光谱(FTIR),分析材料的表面形貌、晶体结构及界面组分。利用电化学微分电压曲线(DVA)及扣式半电池测试,对高温循环后的电池容量衰减机理进行量化分析。失效电池的电极活性材料,整体结构没有被破坏,正极活性物质颗粒表面出现裂纹,负极固体电解质相界面(SEI)膜增厚,有机锂化合物占比增大。DVA结果表明,可循环锂损失(LLI)和活性物质结构损失(LAM)分别占全电池容量衰减的74.82%和25.18%。扣式半电池测试结果表明,负极SEI膜和死锂、正极电解质相界面(CEI)膜、正极结构损失分别占全电池容量衰减的77.13%、1.83%和21.04%。

It was very important to analyze the mechanism of capacity fading for optimizing the battery system.The capacity fading mechanism of 23 Ah square aluminum shell lithium iron phosphate(LiFePO_(4))Li-ion battery cycled at elevated temperature(55℃)was studied.The surface morphology,crystal structure and interface composition of materials was analyzed by SEM,energy dispersive X-ray spectroscopy(EDS),XRD,inductive coupled plasma emission spectrometer(ICP)and Fourier transform infrared spectroscopy(FTIR).The quantitative analysis capacity fading mechanism of cycled battery at elevated temperature based on differential voltage analysis(DVA)and half button cell analysis was carried out.The overall structure of the electrode active material of the failed battery was not destroyed,cracks appeared on the surface of the cathode active material particles,the solid electrolyte interface(SEI)film of the anode thickened,the proportion of organic lithium compounds increased.DVA results showed that loss lithium inventory(LLI)and loss active material(LAM)accounted for 74.82%and 25.18%of the capacity fade of full battery,respectively.The coin-type half cell tests showed that anode SEI and dead lithium,cathode electrolyte interface(CEI)and cathode structure loss accounted for 77.13%,1.83%and 21.04%of the capacity fade of full battery,respectively.