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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1.5V(vsLi/Li+)的锂离子固相扩散系数值均在1.060×10-10cm2·s-1左右.采用RPG法对石墨电极在1.0～2.5V(vsLi/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1.0～2.5V的高电压区,随着电压的升高,D值从4.292×10-10cm2·s-1减小到1.219×10-11cm2·s-1.
Based on the spherical diffusion model, the relationship between constant voltage and constant current charge capacity ratio (RPG) and lithium ion solid phase diffusion coefficient in graphite electrode was deduced. A new method for measuring solid phase diffusion coefficient of lithium ion in graphite negative electrode was given Namely RPG method.The theoretical results show that the solid-phase diffusion coefficient D is related to the RPG value q, the particle radius R and the constant-current charging time tG.When q≤0.5, the relationship can be fitted by the minimum variance linearization to D = R2 / (15.36qtG) (q≤0.5) .Experimental results show that the RPG method has a very good reproducibility. The values of lithium ion solid-state diffusion coefficient at 1.5V (vsLi / Li +) at different constant current charging current and time (1.060 × 10-10cm2 · s-1) .The lithium ion solid-state diffusion coefficient of graphite electrode in the high voltage region of 1.0 ~ 2.5V (vsLi / Li +) was tested by RPG method.The results showed that at 1.0 ~ 2.5V With the increase of voltage, the value of D decreases from 4.292 × 10-10cm2 · s-1 to 1.219 × 10-11cm2 · s-1 in high voltage region.