高比能水系钠离子电容器结构-电解质协同设计、储钠机理与功能化

水系钠离子电容器安全、成本低、功率高，但正负极精准匹配难、电压低是长期制约其发展的关键问题。本项目提出协同引入赝电容材料和廉价高浓度电解质，将赝电容MnO2和MoO2与电池型NaTi2(PO4)3和氟磷酸钒钠配对，构建两类全新水系钠离子电容器。不同于常规双电层电极，赝电容同时在容量和反应动力学上与电池型电极良好匹配，最大程度提升器件容量；而高浓度电解质中几乎所有水分子均与Na+强烈配位，电活性低，可实现~2.8 V器件高电压，使比能量翻倍。进一步设计刚柔兼备的高浓度双网络水凝胶聚合物电解质，赋予器件良好柔性和机械强度；利用聚合物链极性基团对有限水分子的限域与氢键结构调制，极大促进器件的环境适应性。项目还重点研究电极储能机理、负极SEI成因以及高浓水凝胶电解质组分间相互作用与Na+传导机制，构筑高能量、长循环和一定功能化（柔性、环境稳定）的混合电容器，为水系钠离子储能器件的发展提供科学参考。

Aqueous sodium ion capacitors (ASICs) are safe, inexpensive and with high power density. However, the difficulty in the charge and kinetics balance between cathode and anode as well as the low voltage has been hindering the development of ASICs. In this proposal, with the simultaneously introduction of pseudocapacitive materials and low-cost high-concentration electrolytes, we construct two kinds of novel ASICs using pseudocapacitive MnO2 and MoO2 to pair with battery-type NaTi2(PO4)3 and sodium vanadyl fluoride phosphate. In our design, firstly, different from electric-double-layer capacitive materials, pseudocapacitive electrode in ASICs can easily achieve both the charge balance and reaction kinetics balance with battery-type electrode, greatly increasing the specific capacity of the device; secondly, nearly all the water molecules are coordinated with Na+ and have low electroactivity in the highly concentrated electrolytes, leading to high device working voltage of ~2.8 V and thus making the energy density doubled. In addition, by designing high-concentration double-network structured hydrogel polymer electrolyte with both rigid and flexible microstructures, good flexibility and high mechanical robustness of the device can be attained. Taking use of the confinement effect and hydrogen-bond structure modulation endowed by polar groups on the polymer chains towards limited water in the electrolyte, the environmental suitability of the device will also be promoted. Our proposal will also focus on the energy storage mechanisms of electrodes, anode SEI formation process and reasons and the interactions between components within the hydrogel polymer electrolyte as well as the Na+ conducting pathways & mechanism. With fully understanding these fundamentals, our purpose is to design ASICs with high energy density, long cycling stability and good functionality (flexibility, environmental stability, etc.). Our research will pave a new avenue to the development of high-performance aqueous sodium ion storage devices.