二维限域储能的高效氧化铁柱撑层状钛酸协同复合负极及其水系锂/钠离子电池

Aqueous rechargeable Li and Na ion batteries have great advantages of high safety, low cost and high power density. Nevertheless, challenges still remain in obtaining highly-stable and high-capacity negative (anode) materials. In this project, sub-nano (hydroxyl) iron oxide-pillared layered titanate is proposed as a new type of hybrid anode for aqueous Li and Na ion batteries. By utilizing the interlayer Fe(III)/Fe(0) conversion reaction, the capacity is expected to be improved to the level more than 3 times that of the traditional anode materials; during the conversion process, the charge in the interlayer changes, thus Li+ or Na+ in the electrolytes may simultaneously enter or exit the interlayer to balance the charge with the Ti-O slab, which makes the hybrid anode behaviors like intercalation/de-intercalation of Li/Na. In addition, with the two-dimensional confinement within the interlayer, the conversion reaction is almost not diffusion-controlled, greatly reducing the polarization and H2 evolution; this confinement effect can also restrict the volume expansion and dissolution of the iron oxide. Therefore, it is possible to realize high cycling stability (>5000 times). In this project, we will choose layered titanates with different charge density in the Ti-O slab and fabricate the hybrid anode by using two methods: exfoliation-reassembly and stepwise ion exchange. By controlling the Fe:Ti molar ratio, interlayer spacing/water content, the degree of stacking order and the pore structure, the “structure-property” relationship, charge transport behaviors as well as the energy storage mechanism will be uncovered. Eventually, C/LiMn2O4 and C/λ-MnO2 cathodes will be controllably synthesized, and matched with the hybrid anode, respectively, for the construction of high-energy density, long-lifetime aqueous Li and Na ion battery devices. Our project will provide new avenue for the development of new types of electrode materials and aqueous rechargeable batteries.

水系锂/钠离子电池具有安全性高、成本低、功率高等优势，如何获得高稳定、高容量的负极材料是当前的关键挑战。本项目提出新型亚纳米（羟基）氧化铁柱撑层状钛酸复合负极，利用层间Fe(III)到Fe(0)转换反应可望获得通常水系负极材料3倍以上的高容量，同时电解液中Li+或Na+可进出层间来弥补层间电荷的改变，维持与层板的静电平衡，表现出协同嵌脱锂/钠行为。二维层间限域下，电极过程几乎不受扩散控制，极大减小极化和析氢干扰；亦能抑制体积膨胀和电极溶解等负效应，实现优异的循环寿命（>5000次）。项目拟选择层板电荷密度不同的钛酸，通过剥离-重组和分步交换两种方法制备电极，重点调控Fe:Ti比例、层间距/含水量、层叠有序度、孔结构等，比较研究储能构效关系，揭示离子输运行为和储能机制，并分别可控合成C/LiMn2O4和C/λ-MnO2正极进行搭配，实现高比能、长寿命水系锂/钠电，为水系电池发展提供崭新思路。

相比于有机电解液的锂/钠离子电池，水系锂/钠离子电池具有安全性高、成本低、功率高等优势，获得高稳定、高容量的负极材料是当前该领域的研究热点。本项目将铁基负极材料的高比容量特点和层状钛酸的高稳定性优势巧妙结合，设计制备了新型亚纳米（羟基）氧化铁柱撑层状钛酸复合负极，系统地研究了复合负极在水溶液锂盐和钠盐电解液中的电化学性能与储能构效关系，揭示了离子输运行为和储能机制，并与成熟的LiMn2O4等正极进行搭配，构建了2类高性能水系（水凝胶）锂/钠离子储能器件。依据扩展X射线吸收精细结构谱（EXAFS）分析和球差电镜等表征，证实了层间三价铁化合物的柱撑特征以及铁与氧的配位结构。电化学研究结果表明，柱撑的层状钛酸利用层间Fe(III)到Fe(0)转换反应以及Li+或Na+协调进出层间补偿电荷变化来储存能量，并且，碱金属离子的水合半径直接影响电极的比容量和反应动力学快慢。二维层间限域下，电极过程几乎不受扩散控制，极大减小了极化和析氢干扰，亦有效抑制了体积膨胀和电极溶解等负效应。组装的水系电池器件不仅具有高的容量和优异的倍率性能（可5 A g-1及以上电流密度下充放电），而且可实现高达8000余圈的循环稳定性，综合性能优于许多基于铁基负极的水系电池体系。本项目的实施为其它“转换反应材料-层状结构”协同复合新负极的设计提供了新的思路，对高性能水系二次电池的发展具有十分重要的科学意义。