高价掺杂金属在镍基水滑石正极材料中的作用机制研究

Rechargeable aqueous batteries have attracted intensive interest in the field of wearable and implantable electronic devices due to their safety, environmental friendliness and low cost. NiM-layered double hydroxides (NiM-LDHs) are promising cathode materials for the secondary aqueous batteries owing to their high specific capacity and long cycle life. However, the critical role of the doped metal M with high valence for the electrochemical performance has not been clearly revealed, which restricts further development of Ni-based cathode materials. In this proposal, a concise and reasonable model system will be developed based on atomic-thin LDH monolayers, in which the electrochemical process can be optimized and accurately evaluated. By a combined study of in situ techniques and simulation calculations, fine （electronic and crystalline）structures and the structural transitions of NiM-LDHs could be examined and analyzed on an atomic scale. The variations of the oxidation states, local structures and charge transfer during electrochemical cycling will be explored. The energy storage mechanism and synergistic effects between Ni and M will be further demonstrated. An in-depth understanding of the correlations between the type, proportion and distribution of M as well as the energy storage behaviors will be achieved, which hence builds up effective strategies to manipulate the capacity and stability of NiM-LDHs electrodes. This project will provide the theoretical foundation to design and fabricate high-performance Ni-based cathode materials for aqueous batteries.

鉴于安全、绿色及价格低廉的特点，水系二次电池在可穿戴式和植入式电子器件中已展现出重要价值。镍基水滑石（NiM-LDHs）是一类有望能兼顾高比容量及长循环寿命的水系电池正极材料，但是高价掺杂金属M对于电化学行为的作用机制及科学规律不清晰成为了进一步发展的瓶颈。本项目拟以原子级厚LDHs单片层为研究主体，构建简洁合理的模型电极体系，实现电极反应过程的优化及准确评价。在此基础上，结合仿真模拟计算及原位表征技术，从原子尺度深入解析NiM-LDHs材料的精细（电子和晶体）结构特征及其在充放电过程中的演化过程，分析局域结构、价态及电子转移等关键信息的变化趋势，阐明层板金属之间的协同作用及储能机理，进而揭示M的种类、比例及分布对体系储能性能的调节规律，建立以NiM-LDHs为掺杂载体的材料比容量及稳定性调控策略。本项目的实施无疑为发展新型高性能Ni基水系电池正极材料提供科学依据。

穿戴式智能设备和植入式电子器件的飞速发展对相应的小型、轻便二次电池系统提出了更高的要求。Ni基氧化物及氢氧化物是最为典型的正极材料，在碱性环境中通过质子脱嵌可发生快速可逆的氧化还原反应。特别地，利用高价金属阳离子对Ni进行同晶取代形成的Ni基层状双金属氢氧化物材料（NiM-LDHs）有望兼顾高比容量和长循环寿命。但是，高价金属种类和取代量对Ni放电平台及比容量的影响显著，其调控机制的揭示尚未能形成共识，对兼顾高能量密度和结构稳定体系的认知还存在争议。本申请项目拟设计NiM-LDHs单片层为研究主体，构建结构和尺度合理的模型体系，旨在研究NiM-LDHs结构及储能性能的之间的内在联系，明确高价掺杂金属M对NiM-LDHs电化学行为的调控。本项目主要取得了如下重要进展：（1）结合理论模拟，我们筛选了可与Ni在LDHs主体层板中稳定共存的高价金属元素，主要为Al、Co、Fe、Mn和Ti。根据价态平衡原则以及金属离子半径，同时通过调整制备参数（反应时间、温度、原料种类、配比、浓度、pH值等），已经成功制备了不同掺杂组成和比例的NiM-LDHs前体材料，进而通过不同的合成手段得到了NiAl-LDH、NiCo-LDH、NiFe-LDH、NiMn-LDH和NiTi-LDH的单片层结构。发现并归纳了不同高价金属的掺杂对于Ni的氧化还原反应储能反应过程的影响规律和机制。（2）通过多种多价金属的共掺杂进一步对NiM-LDHs的电化学行为进行探讨。结合仿真模拟和多种表征技术，从分子尺度研究了精细电子/晶体结构及储能性能的构效规律，揭示了电化学可逆容量有利的NiM-LDHs体系的掺杂规律和作用机制。本项目为开发兼顾高能量密度和结构稳定的NiM-LDHs正极材料提供了新见解和新策略。