聚苯胺在LiFePO_4/C正极中的双重功能

Dual Function of Polyaniline in the Positive Electrode LiFePO_4/C

锂离子电池(LIB)中正极活性材料的导电率σ都很低,要减小正极的极化程度,增大活性材料的比充、放电容量和充、放电电流密度,最有效方法之一是选用高导电率的导电剂,与粘结剂混合在一起在正极中组成良好的导电网络.测试结果表明:聚苯胺(PAn)的导电率(σPAn=18.39 S/cm)大于正极中常用导电剂乙炔黑(AB)的导电率(σAB=7.77 S/cm).以PAn作为正极活性材料,不添加其他导电剂,对其进行恒电流充、放电试验(电流密度I=15 mA/g)时,其第3循环的比放电容量D3=60.8 mAh/g,充、放电效率η3=94.56%,试验结果表明:PAn在正极中兼有导电剂和活性材料的功能.以LiFePO4/C含碳复合材料作为正极活性材料,以PAn替代AB作为导电剂进行了恒电流充、放电试验,在电流密度为15 mA/g,30 mA/g,45 mA/g,60 mA/g,75 mA/g,90 mA/g和120 mA/g时,LiFePO4/C的比充、放电容量都增加了,表明正极的极化程度减小了.正极在经过较大电流密度(120 mA/g)充、放电后,再以小电流密度(15 mA/g)进行充、放电时,比充、放电容量几乎没有变化,表明经大电流(120 mA/g)充、放电后LiFePO4/C的贮锂结构没有变化.

The electronic conductivities of all the positive electrode active materials for lithium ion batteries（LIB） are very low.One of the most effective methods to decrease the polarization extent of positive electrode,to increase the specific charge-discharge capacities of active materials and to increase the charge-discharge current densities is to select one kind of electronic conductive reagent with high electronic conductivity and mix it with binder to build up a good electronic conductive network.The results of measurements have shown that the electronic conductivity of polyaniline（PAn）（σPAn=18.39 S/cm） is greater than that of acetylene black（AB）（σAB=7.77 S/cm）.The galvanostatic experiment（current density I=15 mA/g） of the above PAn was done,and no other conductive reagent was used.In the third cycle,the specific discharge capacity D3 was 60.8 mAh/g and the charge and discharge efficiency η3 was 94.56%.The experiment results have shown that PAn in the positive electrodes has both the function of electronic conductive reagents and that of active materials.Galvanostatic experiments were conducted with the LiFePO4/C as the positive electrode active materials and PAn as the electronic conductive reagent to take the place of AB.When the current density was 15 mA/g,30 mA/g,45 mA/g,60 mA/g,75 mA/g,90 mA/g and 120 mA/g,respectively,all the specific charge and discharge capacities increased.After charging and discharging with large current density（120 mA/g）,the positive electrode charged and discharged with the original small current density（15 mA/g）.The specific charge and discharge capacities were almost unchanged.It was shown that the storing lithium ions structure of LiFePO4/C did not change.