Lithium charge capacity

The cycling improvement for the Cu-metallized graphite over the pristine graphite was also observed by K. Guo et al. [15] in their study of electroless Cu deposited on graphite cycled in a lithium cell with a 20% PC blend electrolyte. Also, they recorded a rate capability improvement in their Cu graphite material as well. At a current density of 1.4 mA/cm2, the cell achieved about 60% ( 200 mAh/g) of the charge capacity measured at 0.14 mA/cm2, compared to about 30% ( 100 mAh/g) for the non-treated pristine natural graphite cell [15]. 

Kanno et al. studied less crystalline carbons like pyrolyzed polymers and commercial carbon fibers. They reported an irreversible charge capacity in the first cycle related to the carbon surface. However, the reversible charge capacity which they could observe over several cycles was independent of the surface reaction.106 Mohri et al.107 demonstrated only 20% capacity fading over 500 cycles with a lithium-ion cell containing a lithium metal oxide and low crystallinity pyrolytic carbon electrode. 

They showed that the reversible charge capacity of heat-treated cokes as a function of their degree of graphitization is in remarkable agreement with the expression (Equation 7.6) if xaa = 0.75, xaP = 0.20, and Xpp = 1. The lower value of xap was qualitatively confirmed by STM observations on pyrocarbons heat-treated at 2000°C.172 In the ap state, interstitial clusters of carbon atoms which commensurate with the graphite lattice hindered the intercalation of lithium and, thus, decreased the stoichiometric coefficient x with respect to a random distribution of interstitials. 

High-crystallinity natural graphite materials are attractive active materials in the negative electrode of lithium-ion batteries due to their high theoretical reversible charge capacity of 372 mAh g 1 as well as the low and flat potential profile below 0.2 V vs. Li/Li+, which are important features which are needed to improve the energy density of portable lithium-ion batteries. The drawbacks for the... 

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