A study on the irreversible capacity of initial doping/undoping of lithium into carbon

The initial irreversible capacity, Qi, is one of the parameters to express the material balancing of the cathode to anode in lithium-ion cells. In this work, a new terms are introduced, namely, the initial intercalation Ah efficiency (IIE) and the initial irreversible specific capacity at the surface (Qis), to express precisely the irreversibility of an electrode/electrolyte system. The terms depend on the active-materials and composition of the electrode, but do not change with charging state. Mesophase carbon microbeads (MPCF) have the highest value of IIE and the lowest value of Qis in 1 M LipF6/ethylene carbonate (EC)+diethyl carbonate (DEC) (1:1 volume ratio) electrolyte. The IIE value of a LiCoO2 electrode is 97–98%, although the preparation conditions of the material and the electrolyte are different. The Qis value of LiCoO2 is 0–1 mAh g−1. The MPCF-LiCoO2 cell system has the lowest latent capacity. The Qis value increases slightly on adding conductive material. The IIE and Qis values vary with the electrolyte. By introducing propylene carbonate to the EC+DEC mixed solvent, the IIE values are retained, but Qis is increased. With the addition of methyl propionate, the IIE value is increased, and the Qis value is also increased slightly.