基于“水盐”电解质的高电压高能量密度混合型超级电容器关键材料的优化

Hybrid supercapacitors are expected to meet the requirements of long-life, fast-charging and safety for mobile devices by integrating the high energy density of lithium ion battery and high power density of electrochemical double layer capacitors. In this proposal, we will conduct a new type of hybrid supercapacitor with both high voltage and high energy density, consisting by two-dimensional MnO2/graphene-like structure intercalation material as positive electrode, "protected lithium electrode" as the negative electrode and "water-in-salt" electrolyte. The hybrid supercapacitor has the following advantages: 1) The positive electrode takes into account of both the high pseudocapacitance of the two-dimensional MnO2 material and the high electronic conductivity of the graphene-like structure material; 2) The high-concentration "water-in-salt" electrolyte is able to provide a safe aqueous environment and break the limitation of the low electrochemical stability window of traditional "salt-in-water" electrode, which is usually less than 2 V for normal aqueous electrolyte; 3) the multi-layer water-stable "protected lithium electrode" makes it possible to use metallic lithium as the negative electrode for the aqueous hybrid supercapacitor, thus can provide a cell voltage higher than 4 V for hybrid supercapacitor with aqueous electrolyte. In this research, we will focus on solving two scientific issues including the interface compatibility of multi-layer "protected lithium electrode" and the preparation process of MnO2/graphene-like structural material. The research achievements of this project are expected to provide theoretical supports for the development, application and stable operation of the aqueous hybrid supercapacitors with both high voltage and high energy density.

混合型超级电容器兼具双电层电容器的高功率密度与锂离子电池的高能量密度特性，有望满足可移动式设备对长续航、快充及安全等方面的需求。本立项拟设计一种新型的高电压高能量密度混合型超级电容器，采用二维MnO2/类石墨烯互插层材料为正极、宽电化学稳定窗口“水盐”电解质及“保护锂电极”为负极。其具有以下特点：1）正极兼顾二维层状MnO2材料的高赝电容属性以及类石墨烯材料的高电子电导率；2）“水盐”电解质不仅提供安全的水系环境，同时也解决了常规“盐水”体系电化学稳定窗口小于2V的限制；3）采用多层水稳定“保护锂电极”，使锂作为水系混合型超级电容器的负极成为可能，同时可将其工作电压提高到4V以上。本项目中我们将集中解决多层“保护锂电极”中各界面之间的相容性及MnO2/类石墨烯互插层材料的新型制备工艺等科学难题。研究结果有望为高电压高能量密度水系混合型超级电容器的开发应用及稳定运行提供科学依据。

相比于电池，超级电容器的短板在于其能量密度受限，这主要归因于较窄的电压窗口和较低的比容量。基于多层“保护锂金属电极”的混合型超级电容器由于使用金属锂作为负极，其工作电压可以高达4V以上，目前限制4V级高电压混合型锂离子电容器发展的主要因素在于正极活性材料比电容不高以及多层“保护锂金属电极”界面相容性不佳等问题，导致电容器界面阻抗过大及充放电过程中电容器的极化明显。因此，本项目基于高性能混合型超级电容器开发了一系列高比电容正极材料，如多孔活性炭材料及二维层状金属氧化物/类石墨烯互插层复合材料等。以小分子为原材料，利用苯胺类有机物小分子能够自聚合的特点，采用一步法制备了一系列具有较高比表面积的氮掺杂的多孔炭材料，该制备工艺较常规商业化制备活性炭材料更加简单，所得炭材料的比表面积可高达3709m2/g。同时，通过进一步调控多孔炭的微观结构，利用对苯二胺和二氯甲烷之间的溶剂热反应制备多孔前体材料来制备多孔炭材料的产率可高达13.0%。其在水性电解液中能够实现331.5 F/g（1M H2SO4）、392.3 F/g（6 M KOH）和246.1 F/g（1M Li2SO4）的高比电容。另外，基于多层“保护锂电极”结构，我们设计开发了石榴石型固态电解质隔膜将金属锂与水性电解液隔离开来，通过添加高质量含量和低熔点硼酸锂作为烧结助剂来进一步提高石榴石型固态电解质隔膜的锂离子电导率及致密度，其中，硼酸锂作为无定型相存在于电解质的晶界处可以优化电解质晶粒阻抗，通过优化多层“保护锂电极” 负极结构、结合使用高浓度“水盐”电解质和高比电容活性炭材料等设计组装的4V级高电压混合型超级电容的能量密度高达228.9Wh/kg。