Acta Phys. -Chim. Sin. ›› 2002, Vol. 18 ›› Issue (08): 705-709.doi: 10.3866/PKU.WHXB20020807

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

Tang Xin-Cun;He Li-Ping;Chen Zong-Zhang;Xia Xi   

  1. College of Chemistry and Chemical Engineering, Hunan University, Changsha 410082;Institute of Applied Chemistry, Xinjiang University, Wulumuqi 820046
  • Received:2001-12-05 Revised:2002-03-28 Published:2002-08-15
  • Contact: Chen Zong-Zhang

Abstract: 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.

Key words: Ratio of potentio-charge capacity to galvano-charge capacity,   Diffusion coefficient, Graphite, Lithium-ion batteries