Cobalt disulfide (CoS2) is a promising thermal battery electrode material for its superior thermal stability and discharge performance. However, the low natural resource and poor air stability restrict its application in thermal battery fabrication. In this work, carbon coated CoS2 composite was prepared by a facile one-pot hydrothermal method with glucose as carbon source. During the growth of CoS2, the glucose molecules were in situ adsorbed and carbonized on the surface of the as-synthesized CoS2, and the resultant carbon coating provided improved electrical conductivity and discharge performances to the composite. The thermal battery cell, which was fabricated with such a composite cathode and with a Li-Si anode, can output a capacity of 235.8mAhg−1 and an energy density of 416.9Whkg−1 at a cut-off voltage of 1.7V. This carbon coated CoS2 composite also presented enhanced air stability. After being stored in dry air for 3 months, the composite can still provide a capacity of 232.4mAhg−1 to 1.7V, whereas the capacity of bare CoS2 stored with the same condition dropped from 202.4mAhg−1 to 189.7mAhg−1.