恒压-恒流充电容量比值法测定石墨电极中的锂离子扩散系数

通过球形扩散模型推导了恒压-恒流充电容量比(简称RPG)与石墨电极中锂离子固相扩散系数的关系,给出了一种测量锂离子在石墨负极中固相扩散系数的新方法即RPG法.理论结果表明固相扩散系数D与RPG值q,颗粒半径R和恒流充电时间tG有关.当q ≤ 0.5时,其关系式可通过最小方差线性化拟合为D=R2/(15.36qtG) (q ≤ 0.5).实验结果表明,RPG法具有非常好的重现性,不同恒流充电电流和时间下测得1.5 V(vs Li/Li＋)的锂离子固相扩散系数值均在1.060×10－10 cm2•s－1左右.采用RPG法对石墨电极在1.0～2.5 V(vs Li/Li＋)高电压区的锂离子固相扩散系数进行了测试,结果表明在1.0～2.5 V的高电压区,随着电压的升高,D值从4.292×10－10 cm2•s－1减小到1.219×10－11 cm2•s－1.

Determination of the Li+ Diffusion Coefficient in Graphite By the Method of the Ratio of Potentio-charge Capacity to Galvano-charge Capacity

A novel electrochemical method (RPG method) has been theoretically and experimentally developed to determine the diffusion coefficient of intercalary species within insertion-host materials on the basis of the spherical diffusion model. Theoretical results show that the diffusion coefficient D is dependent to the ratio (q) of the potentio-charge capacity to the galvano-charge capacity (abridged as RPG), the radius of insertion-host particle R, and the galvano-charge time tG. The RPG equation obtained is as D=R2/(15.36qtG)(q ≤ 0.5).Using this method, the values of the Li＋ diffusion coefficient determined at different galvano-charge currents with 1.5 V cutoff voltage are all around the value of 1.060×10－10 cm2•s－1.This result indicates that the RPG method has a good reliability for determination of the diffusion coefficient. The Li＋ diffusion coefficient in graphite has been reduced from 4.292×10－10 to 1.219×10－11 cm2•s－1 among the voltage range of 1.0～2.5 V (vs Li/Li＋),respectively.