The charge and discharge characteristics of lithium batteries with sulfur composite cathodes have been investigated. The sulfur composites showed novel electrochemical characteristics. The analysis of the differential capacity indicated that the discharge process showed two voltage plateaus of 2.10V and 1.88V, and the charge process also presented two voltage plateaus of 2.22V and 2.36V. The overcharge test showed that the composite cannot be charged over 4.0V, the voltage always stopped at about 3.9V during charging, indicating that the composite presented the intrinsic safety for the overcharge of lithium batteries. The overcharge can cause serious safety problem for the conventional Li-ion batteries. The overcharge test also showed that the batteries with sulfur composite were destroyed when the upper cut-off voltage was over 3.6V. However, the composite presented good reversible capacity after it was deep discharged even to 0V. It showed stable cycleability and high cycling capacity of 1000mAhg−1 when cycling between 0.1V and 3.0V, indicative of the different characteristic from the conventional oxide cathode materials. The prototype polymer battery with the composite cathode material presented the energy density of 246Whkg−1 and 401WhL−1.