In this study, a kind of novel double phase change energy storage materials (DPCESM) based on two kinds of phase change nanocapsules and bentonite was reported. The nanocapsules (n-ODE@CLPS and n-ESE@CLPS) were synthesized with n-octadecane (n-ODE) and n-eicosane (n-ESE) as phase change material (PCM), respectively, crosslinked polystyrene (CLPS) as shell, and DNS-86 as polymerizable emulsifier via soap-free miniemulsion polymerization method. The morphology, thermal energy storage capacity, and structure of nanocapsules and DPCESM were characterized and analyzed, respectively. Besides, the effects of DNS-86 on the thermal storage performance of nanocapsules were investigated. The results showed that the encapsulation efficiency of nanocapsules was the highest along with the excellent chemical stability and heat storage capacity when the percentage of polymerizable emulsifier was 2 wt%. The average diameter of n-ODE@CLPS was 136 nm, and the latent heat of phase change and encapsulation efficiency were 140.39 J/g and 91.28%, respectively. Meanwhile, the average diameter of n-ESE@CLPS was 134 nm, the latent heat of phase change and encapsulation efficiency were 148.32 jig and 91.77%, respectively. Besides, the melting points of DPCESM were 26.25 degrees C and 34.58 degrees C, and the heat storage capacity was 90.17 J/g. Moreover, because of the doping of bentonite, the thermal conductivity of DPCESM can reach to 0.45 W/(m.K), which is 104.5% and 150% larger than pure n-ODE and n-ESE, respectively. The DPCESM can be used to adjust the indoor temperature and would be widely used as a promising composite phase change material. (C) 2019 Elsevier Ltd. All rights reserved.