钾离子电池电极新材料的合成、电化学反应机理与性能研究

Potassium-ion batteries would be very promising for applications in the large-scale electrochemical energy storage system because of the abundant potassium resources and low cost. However, the existing electrode materials typically exhibit low capacities of storing potassium ions, serious polarizations, and short cycle life which make them difficult to meet the demands of fast charging/discharging and desirable cyclability. The key to developing potassium-ion batteries lies in the exploration of new electrode materials with excellent electrochemical performances, low cost, and high safety. Therefore, in this project, we will focus on the design, synthesis and electrochemical behaviors of new inorganic materials. Specifically, we will synthesize a serial of new inorganic materials which are made up of abundant elements on the earth, and then tune their material structures through ion-doping, lattice vacancy, and nanostructure construction. At the same time, we will investigate their electrochemical reaction mechanisms and the structure-activity relationships between material structures and electrochemical performances. We will also examine the growth mechanism and chemical compositions of the solid electrolyte interphase forming on the electrode surface. The effects of electrolyte additives to the formation of solid electrolyte interphase and the electrochemical performances of potassium-ion batteries will be explored as well. The strategies and universal laws uncovered in the process of project implementation could provide new insights into the developments of new electrode materials for potassium-ion batteries.

钾离子电池具有成本低廉的优势，非常有希望应用于智能电网等大规模电能存储技术。然而，现有钾离子电池电极材料普遍存在比容量低、极化严重、循环寿命短等问题，难以满足高倍率应用下长循环寿命的要求。因此，探索性能优异、价格低廉且安全性高的电极新材料成为钾离子电池研发的关键。本项目拟以无机新材料探索为切入点，设计合成由地壳含量丰富元素构筑的无机钾盐新材料；通过离子掺杂、晶格缺位引入及纳米结构构筑等策略进行材料结构调控；研究新材料的电化学反应机理、材料结构与电化学性能之间的构效关系；揭示材料表面固体电解质界面层的形成机制、化学组成以及电解液添加剂的作用规律；本项目实施过程中揭示的策略和普遍规律可为研发综合性能优异的钾离子电池体系提供科学依据。

钾离子电池因钾资源丰富和成本低的优势有望应用于大规模储电领域。然而，大尺寸的钾离子的嵌入与脱出反应动力学缓慢，且易引起材料结构变化，造成材料可逆性差、倍率性能差、循环寿命短等问题。本项目针对上述关键科学问题，围绕电极新材料的设计合成、电化学性能及机理进行了一系列探索。取得的研究结果如下：（1）探究了金属铋负极材料的钾离子存储性能与机制，并揭示了电解液浓度对铋负极表面固体电解质界面层的形成和铋负极材料电化学性能的作用规律。（2）首次研究了层状结构二硫化钨的电化学钾离子存储行为，并揭示了二硫化钨的钾离子插层反应机理以及长循环寿命的内在原因。（3）合成了无机开放框架材料KTiOPO4并首次将其作为钾电池负极材料，获得了平稳安全的电压平台、长循环寿命和快速的钾离子运输动力学；实验结果和第一性原理计算揭示了双相和固溶体反应共存的电荷存储机制、9.5%的低体积变化、一维螺旋钾离子扩散路径和低至0.15 eV的扩散能垒；我们进一步通过异价离子取代策略设计了一种无机开放框架化合物K0.76V0.55Nb0.45OPO4。该化合物可同时作为钾电池的正/负极材料，其在嵌脱钾离子过程中晶格体积变化低至3.1%/7.1%；优异的低应变特性使得材料表现出优异的结构稳定性和18个月的超长循环寿命。（4）系统研究了硫属（S/Se/Te）正极材料：利用高浓度盐电解液策略抑制了钾硫电池反应中间产物的溶解和穿梭问题，研究了电解液浓度对电池性能的影响并揭示了钾硫电池反应机理；利用高浓度电解液提升了钾硒电池能量密度，结合第一性原理计算与实验结果探索了钾硒电池的中间产物及其电子电导性，揭示了其多步可逆相变反应机制；此外，我们首次提出一种新型钾碲电池，该电池新体系表现出快速的反应动力学和倍率性能，有望应用于储能领域。本项目中揭示的策略和普遍规律可为探索高性能和低成本钾离子电池提供新思路。