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

The initial irreversible capacity, Q(i), is one of the parameters to expres s the material balancing of the cathode to anode in lithium-ion cells. In t his work, a new terms are introduced, namely, the initial intercalation Ah efficiency (IIE) and the initial irreversible specific capacity at the surf ace (Q(is)), to express precisely the irreversibility of an electrode/elect rolyte system. The terms depend on the active-materials and composition of the electrode, but do not change with charging state. Mesophase carbon micr obeads (MPCF) have the highest value of IIE and the lowest value of Q(is) i n 1 M LipF(6)/ethylene carbonate (EC) + diethyl carbonate (DEC) (1:1 volume ratio) electrolyte. The IIE value of a LiCoO2 electrode is 97-98%, althoug h the preparation conditions of the material and the electrolyte are differ ent. The Q(is) value of LiCoO2 is 0-1 mAh g(-1). The MPCF-LiCoO2 cell syste m has the lowest latent capacity. The Q(is) value increases slightly on add ing conductive material. The IIE and Q(is) values vary with the electrolyte . By introducing propylene carbonate to the EC + DEC mixed solvent, the IIE values are retained, but Q(is) is increased. With the addition of methyl p ropionate, the IIE value is increased, and the Q(is) value is also increase d slightly. (C) 2001 Elsevier Science B.V. All rights reserved.