2,6-Dihalogen atom substituted-9,10-anthraquinones are used as organic cathode materials for rechargeable lithium ion batteries. The differences in the cyclic voltammetry curves, voltage profiles and cycling performance of these compounds are analyzed. An important regularity is strikingly found: the lighter the density of a material, the easier is the achievement of the material’s theoretical capacity at the first scanning cycle. This finding gives an understanding to improve the practical specific capacity of lithium battery and a very clear direction to design new compounds in future so as to make full use of the theoretical capacities.