Polyalcohol is one of the important medium temperature phase change materials (PCMs) for thermal energy storage, in which liquid-free solid-solid PCMs are more promising although sublimation can hardly be avoided when crystals transform to the "plastic phase". We reported here the preparation of encapsulated Tris(hydroxymethyl)methyl aminomethane (Tris) with the SiO2 shell by sol-gel process. Through the hydrolysis and polycondensation of the bicomponent silicon precursors mixed with tetraethoxysilane (TEOS) and 3-aminopropyl triethoxysilane (APTS) of proper ratio, Tris@SiO2 microcapsules with excellent sealing property can be obtained, which prevent the leakage of Tris outside the capsules. Besides, silica encapsulation doubles the thermal conductivity of the PCMs to 0.478 W/(m K). The DSC measurement shows that the Tris@SiO2 capsule owns a reversible phase change in the range of 110-155 degrees C, which will stabilize at about 146 J/g during 70 times of thermal cycling. The Tris@SiO2 capsules have good potential for medium temperature thermal energy storage applications. (C) 2015 Elsevier Ltd. All rights reserved.