二氧化锰基超级电容器的研究进展

Research Progress on Manganese Dioxide Based Supercapacitors

在能源日益紧张的今天,超级电容器作为一种新型的储能装置,以其寿命长、功率高、绿色环保等特点而备受关注。其中二氧化锰基超级电容器不仅具有高功率密度、长循环寿命、快速充放电等特点,还具有价格低廉、来源广泛、环境友好的优势,在各个领域都拥有非常广阔的应用前景和经济价值。然而因受到二氧化锰材料自身导电性和比表面积的限制,二氧化锰基超级电容器的比电容与理论值相差较大;同时其结构不稳定也造成循环稳定性较低。针对上述问题,目前对于二氧化锰超级电容器的研究主要集中于寻找简单可控的电极制备方法以提高电极的导电性、比电容、循环稳定性等电化学性能,以及设法综合利用各种电极材料的优点发挥其协同效应等方面。探究简单可控的电极制备方法是获得高质量二氧化锰基超级电容器的研究的首要任务,常见的方法有溶胶-凝胶法、水热合成法、化学沉淀法、低温固相法和电化学沉积法。溶胶-凝胶法制备的样品纯度高,但是受干燥条件的影响较大,易团聚。化学沉淀法可直接得到化学成分均一、分布均匀的粉体材料,但是对合成温度要求较高,也易发生团聚。低温固相法制备电极粉末改善了高温时产物粒子易快速生长、团聚的问题,但是存在接触不均匀、反应不充分的缺点。水热法简单、成本低,是目前制备粉末电极较为常用的方法。这些制备方法各有千秋,但是这类先制备出粉末再合成电极的方式不仅延长了工艺,而且不符合节能环保的原则,相比之下电沉积法可直接将二氧化锰沉积到基底上,操作简单且参数灵活可控。二氧化锰电极材料的改性问题一直颇受关注,目前掺杂和复合仍是改性方面较为常用的方法。例如向二氧化锰中掺杂少量的金属元素可以提高电极的导电性,而与某些导电聚合物复合则可以有效地解决二氧化锰因结构不稳定而易在电解液中溶解的问题。掺杂物质与复合材料的选择、掺杂和复合方式以及与二氧化锰材料的配比是获得高质量电极的关键。当前二氧化锰基超级电容器电极材料不仅仅只有二氧化锰这一种,而是结合了各种炭材料、复合材料或者金属及其氧化物等物质,组合形成多元复合材料以利用各组分的特点,这对优化电容器性能有很大的帮助。此外,学者们还发现电解液的选择对扩大超级电容器的电化学窗口、提高电容器能量密度和功率密度有很大的影响。本文简单介绍了二氧化锰基超级电容器的储能机理,综述了电容器电解液与电极的制备和改性研究现状,此外还介绍了二氧化锰基超级电容器的组装方式,并对未来的研究趋势提出了展望。

Nowadays,the energy issue has increasingly become a hot spot of social attention,and the supercapacitor as a new type of energy storage device attracts much attention due to its long service life,high power and environmental friendliness.MnO2 based supercapacitors not only assume the characteristics of high power density,long cycle life,fast charge and discharge,but also have the advantages of low cost,broad source and environmental friendliness.Thus they have displayed a very broad application prospects and economic value in various fields.However,the specific capacitance of the MnO2 based supercapacitor is considerably lower than the theoretical value due to its poor conductivity and limited specific surface area.Moreover,its unstable structure also results in poor cycling stability.To resolve the above mentioned problems,the current researches about the MnO2 based supercapacitor mainly focus on finding facile and controllable preparation methods to improve the electrochemical properties like conductivity,specific capacitance,cycling stability,etc.,and trying to magnify the advantages and realize synergistic effect of various electrode materials.Searching a simple and controllable electrode preparation method has become a primary task for high quality MnO2 based supercapacitors.The common methods include sol-gel method,hydrothermal synthesis method,chemical precipitation method,low temperature solid phase method and electrochemical deposition method.The resultant powders prepared by sol-gel method have high purity,agglomerate easily due to the drying conditions.Through the chemical precipitation method can obtain uniformly distributed powders with even chemical compositions,and still,ease of agglomerat owing to high synthesis temperature.The low temperature solid phase method can efficiently overcome the shortcomings mentioned above involving the rapid growth and agglomeration of particles at high temperature,but nevertheless suffers low reaction conversion rate which is attributed to the inadequate contact among the reactants.The hydrothermal synthesis is a simple and low cost method which has been applied to prepare the powder widely at present.The powders prepared by the above methods need certain pre-treatment for the fabrication of electrode,which extends the process and is detrimental to energy saving and environmental protection.On the contrary,the electrodeposition method can directly deposit manganese dioxide on different substrates with flexible operation and controllable operating parameters.The modification of manganese dioxide electrode material has converged intensive research endeavors,the doping and composing methods are still used commonly at present,for example,a small amount of metal elements doped in manganese dioxide can improve the conductivity of the electrode,and some conductive polymers added into manganese dioxide can effectively solve the unstable structure of manganese dioxide which results in its easy dissolution in the electrolyte.In order to obtain the high-quality electrode,it is very essential to select the species of the doped materials and composited materials,their proportions,and the doping and composing methods.Now,the MnO2 based supercapacitor is not barely composed of MnO2,but a combination of MnO2 and other substances,such as a variety of carbon materials,composite materials or metal oxides.The combination of multiple composite materials can adequately make use of the characteristics of each component,which contributes to optimizing the performance of the capacitor.In addition,some scholars also found that the selection of electrolyte has great influence on expanding the electrochemical window of supercapacitors,improving the energy density and power density of capacitors.This paper briefly introduces the energy storage mechanism and summarizes the research status of capacitor electrolyte,electrode preparation and modification method.The fabrication and performance characteristics of MnO2 based supercapacitors device are introduced,and the future research trends are also presented.