Binary eutectic chloride (NaCl-CaCl2)/expanded graphite (EG) composite phase change materials (PCMs), used as high-temperature thermal energy storage materials, were prepared by an impregnating method, and the effects of EG additives on thermal properties of compound salts were investigated by TEM, DSC and Hotdisk techniques. The results revealed that both the specific heat capacity and phase change latent heat of composite PCMs decreased with the increase of EG content, the variation of phase change temperature was negligible, and the thermal conductivities of composite PCMs increased linearly with the addition of EG content and density. In particular, the thermal conductivity of the composite PCM with 20 wt% of EG and 2 g/cm(3) of density was 4.937 W/(m K), which showed 701.1% higher than binary eutectic chloride. The heating and cooling rate of composite PCMs were higher than binary eutectic chloride, and the melting and freezing platform time also reduced with the addition of EG content. (C) 2016 Elsevier B.V. All rights reserved.