新型钠镁双盐二次电池的构建及电化学储能机理研究

In recent years, the Li-Mg dual-salt rechargeable battery has attracted intensive attention in electrochemical energy storage. This kind of battery combines the advantages of the metallic Mg anode (such as large columbic efficiency, dendrite-free Mg deposition etc.) and the Li-intercalation cathode (such as high structural stability, good electrochemical kinetic properties etc.), resulting in excellent cycle stability and high rate capability. However, the Li-Mg dual-salt battery is not suitable for large-scale energy storage because of the serious issue of Li shortage in the earth crust which causes high price of the battery. In order to develop resourceful, environment-friendly and low-cost Mg-based rechargeable batteries, we aim to study new Na-Mg dual-salt batteries under the support of this NSFC project. We will first develop compatible dual-salt electrolytes with wide electrochemical window, high ionic conductivity and high stability, then construct three types of Na-Mg dual-salt batteries using state-of-the-art Na+ storage materials including high-voltage Na+ intercalation cathodes, high-capacity conversion type cathodes, and high-capacity sulfur cathode, respectively. We will study the electrochemical reaction mechanisms of the Mg anode and Na+ storage cathodes in the dual-salt electrolyte, and reveal the key factors those affecting the electrochemical performance of Na-Mg dual-salt batteries. Based on this, we will develop some new Na-Mg dual-salt batteries that could afford high specific energy and then study their problems in practical applications. The outcomes of this project will provide fruitful basic knowledge and technical supports for the practical applications of Mg-based dual-salt batteries in electrochemical energy storage.

锂镁双盐电池是近年来倍受关注的新体系二次电池。它结合了金属镁负极充放电效率高、不形成枝晶，以及嵌锂正极结构稳定、动力学性质好的优点，表现出优良的倍率性能和循环稳定性。但是，理论上锂镁双盐电池并不能解决大规模储能电池面临的锂资源短缺、低成本制造问题。为了开发资源丰富、环境友好、成本低廉的镁基储能电池，本项目提出构建新型钠镁双盐电池，通过开发新的宽电化学窗口、高电导率、高稳定性的钠镁双盐电解液，分别基于高电压型嵌钠反应正极材料、高容量型转换反应正极材料，和高容量型钠硫反应正极材料构建三类典型的钠镁双盐电池体系；研究镁负极和储钠正极在钠镁双盐电解液中的电化学反应机理，系统地阐明钠镁双盐电池电化学反应的特殊性；在此基础上，构建具有较高比能量的示范性钠镁双盐电池体系，并探索有关应用基础问题，为发展先进的电化学储能体系提供基础数据和知识支持，促进我国新能源领域的技术创新和应用发展。

镁离子电池是资源丰富、环境友好、成本低廉的新型储能二次电池，但是当前其技术发展距离实际应用还有很大差距。主要原因在于Mg2+离子与主体材料晶格之间存在强烈的静电相互作用，导致Mg2+在晶格中扩散困难，使得材料的电化学利用率和倍率性能很差，并且容易造成晶体结构坍塌，致使材料的循环稳定性变差。此外，当前常用的镁离子电解液对集流体的腐蚀较大，在镁负极上容易形成表面钝化层，阻碍镁离子的扩散，并且电解液的电化学稳定窗口较窄，限制了储镁正极材料的选择范围。本项目围绕上述问题，开展了新型镁离子电解液和储镁正极材料的研究，设计了钠镁双盐电解液1.0M NaBH4 + 0.1M Mg(BH4)2/DGM、锂镁双盐电解液0.4M APC + 0.4M LiCl/THF、和离子液体添加镁离子电解液APC-PP14Cl/THF，以及VS2、Ni3Se4、(NH4)2V6O16·1.5H2O等新型镁离子电池正极材料。通过研究金属镁负极和上述新型储镁正极材料在三类电解液中的电化学反应机理，发现双盐电解液和离子液体添加剂对层状硫化物正极材料的电化学原位扩层作用可以极大地提升材料的离子迁移动力学，揭示了层状氧化物正极材料中预嵌入水分子可以有效屏蔽Mg2+与主体晶格间的静电相互作用。最后，利用本项目设计的新型电解液和正极材料构建了高比能量、高比功率、以及长循环寿命的示范性镁基二次电池，并探索其应用基础问题。基于本项目支持，在Advanced Functional Materials、Energy Storage Materials、ACS Nano等杂志发表多篇高质量学术论文，培养博士研究生4人，硕士研究生1人，为我国先进电化学储能技术的发展提供了必要的理论基础和高层次人才储备。