Smart design and construction of nanoflake-like MnO2/SiO2 hierarchical microcapsules containing phase change material for in-situ thermal management of supercapacitors

Abstract

Phase change materials (PCMs) have been widely applied for thermal energy storage and thermoregulation. This paper reported a smart design and construction of nanoflake-like MnO2/SiO2 hierarchical microcapsules containing n-docosane PCM for in-situ thermal management of supercapacitors. The microcapsules based on an n-docosane core and SiO2 shell were first synthesized through interfacial polycondensation, and then a mesoporous nanoflake-like MnO2 layer was fabricated onto the surface of SiO2 shell through template-directed self-assembly. The chemical compositions of the resultant microcapsules were confirmed by energy dispersive X-ray, X-ray photoelectron and Fourier-transform infrared spectroscopy, and their nanoflake-like hierarchical morphology and well-defined core–shell structure were identified by scanning and transmission electron microscopy. The mesoporous architecture of nanoflake-like MnO2 outer layer was determined by nitrogen adsorption–desorption isotherm. The obtained microcapsules exhibited high phase-change enthalpies, high encapsulation efficiency, good phase-change and anti-osmosis performance and an effective thermoregulation capability. Most of all, these microcapsules demonstrated a higher specific capacitance than traditional MnO2/SiO2 solid particles at operation temperatures higher than 45 °C due to in-situ thermal management by the n-docosane core. They not only achieved a high specific capacitance of 312.2F/g at 45 °C with a current density of 1.0 A/g due to the mesoporous architecture of MnO2 layer, but also presented a superior long-term cycling stability with high capacitance retention of 94.7% after 1000 charging/discharging cycles. With the above-mentioned superiorities, the microcapsules developed by this work will be a good candidate as an electrode material for supercapacitors. This study opens a new pathway for the development and applications of microencapsulated PCMs in the thermoregulatory electrode system of supercapacitors and Li-ions battery cells.