| Supercapacitors,also known as electrochemical capacitors,are typical high-capacity capacitors.Recently,some research indicates that a great amount of heat is continuously produced and then accumulated inside the supercapacitors during the charging and discharging processes.If this heat cannot be treated in time,it will evidently result in a sharp increase in temperature,a significant decrease in capacitance,a decrease in lifespan,and even serious safety problems(such as fires and explosions).In this case,a high efficient and low-cost thermal management system is necessary for supercapacitors or battery systems to preserve an optimum working temperature range.Phase change materials(PCMs)are a class of thermal energy-storage materials,which can store huge amounts of latent heat through physical phase transitions and controllably release them afterwards with a very small variation in temperature on the basis of thermal energy demand.Based on above all,we pitched an innovative idea to establish a thermoregulatory electrode system with the functions of electrical energy storage and thermal management by combination of a PCM and metal oxide electrode.In this study,a novel type.of microcapsules based on an n-docosane core and nanoflake-like MnO2/SiO2 hierarchical shell as a thermoregulatory electrode material for in-situ thermal management of supercapacitors has been developed.The microcapsules based on an n-docosane core and amorphous SiO2 shell were first synthesized through interfacial polycondensation using tetraethyl orthosilicate(TEOS)as a silica source.Based on the optimum synthetic conditions,the amounts of n-docosane and TEOS should be loaded for the emulsion at a weight ratio of 50:50 so that the microcapsules obtained in this work could achieve a good balance between the core loading and necessary shell thickness.SEM and TEM confirmed that these microcapsules not only exhibit a distinct core-shell structure,but also have a compact and smooth surface,as well as a uniform particle size.FTIR determined that there are an abundance of hydroxyl groups on the SiO2 shell,which may favor the establishment of surfactant-directed templating system for further construction of nanoflake-like MnO2 layer.Secondly,a mesoporous nanoflake-like MnO2 layer was fabricated on the surface of SiO2 microcapsules through an amphiphilic triblock copolymer(P104)surfactant template-assisted redox method.Therefore,the microcapsules consisting of a nanoflake-like MnO2/SiO2 hierarchical shell and n-docosane core were successfully constructed as a thermoregulatory electrode system.These resultant microcapsules show an interesting hierarchical morphology with a large number of irregular nanoflakes with a high density and uniformity distributed on the microcapsule surface in terms of SEM and TEM observations.Nitrogen adsorption-desorption isotherm was used to determine the mesoporous architecture of nanoflake-like MnO2 outer layer.An effective thermal management capability was confirmed by infrared thermography and thermoregulation behaviors observed in the simultaneous charging and discharging processes of latent heat.In addition,in order to further identify the in-situ thermal management effectiveness of thermoregulatory electrode system,the electrochemical properties of the microcapsules with a nanoflake-like MnO2/SiO2 hierarchical shell were also investigated.The results showed that these microcapsules demonstrated a higher specific capacitance and a superior long-term cycling stability than traditional MnO2 SiO2 solid particles at operation temperatures higher than 45? due to in-situ thermal management by the n-docosane core.As a result,the microcapsules designed by this work exhibit a greater potential as an electrode material than the conventional MnO2-based ones.This study also opens a new pathway for the development and applications of microencapsulated PCMs as thermoregulatory electrode materials in supercapacitors. |
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