镁二次电池用正极材料研究

Developing high-efficiency rechargeable batteries is critical to alleviate energy and environmental problems. Rechargeable magnesium batteries are one potential candidate for 'heavy load' applications, such as stationary energy storage, owing to the unique characteristics of magnesium metal, such as high-energy density, low cost, environmental benign, and safe to handle. However, rechargeable magnesium batteries are still plagued with two electron redox reaction of Mg2+ and the sluggish kinetics during the insertion/desertion of Mg2+, which leads to the low capacity and poor cycle life. Inspired by the great advantages of nanosized electrode materials in rechargeable lithium ion batteries, this project will come up with the concept of the improvement of kinetics upon Mg2+ insertion/desertion process via nanoscale intercalation materiales with two-dimensional layered or three-dimensional network structure and radical polymer with two-electron redox reaction as alternative cathode materials for rechargeable magnesium batteries. The three-dimensional mixed conductivity network will be constructed with the aid of carbon nanomaterials. Herein we will synthesize cathode materials for rechargeable magnesium batteries by facile chemical or physical methods, and then intend to utilize in-situ investigations in combination with quasi-in situ technologies to clarify the energy storage mechanism in rechargeable magnesium batteries, and further optimize the electrochemical performances of the nanocomposites by tuning the synthesis parameters. Through the development of high-efficiency cathode materials, we can obtain the rechargeable magnesium batteries prototype, which may underlies for the next generation rechargeable battery with sustainable energy storage.

发展高效稳定的二次电池储能技术是缓解能源问题及环境问题的关键支撑技术。由于金属镁具有能量密度高、价格低廉、对环境友好且操作安全等优点，使得镁二次电池在大负荷储能方面具有良好的应用前景。目前困扰镁二次电池发展的主要瓶颈问题包括正极材料的镁离子双电子反应及嵌入动力学过程非常缓慢，造成容量低下、循环性差等问题。借鉴纳米材料作为锂二次电池电极材料展现的新奇纳米效应与动力学优势，本项目面向具有潜在应用前景的镁二次电池关键电极材料的研究，拟设计合成二维层状/三维网状结构的嵌入式纳米材料，以及非嵌入式有机自由基聚合物，并构筑具有三维混合导电网络的正极材料；利用先进的原位、准原位表征技术研究影响电极反应动力学的重要因素，探索并调控限制镁二次电池电化学过程的方法。通过构筑高活性正极材料，获得高能量密度的原型镁二次电池，为下一代高能量密度、长寿命、安全、廉价、环境友好的二次电池发展奠定良好的科学基础。

在项目执行的三年时间里，紧密围绕镁离子双电子反应及嵌入动力学过程非常缓慢，造成容量低下、循环性差等问题，开发了可实现镁电池用镁离子可逆脱嵌的Li4Ti5O12纳米颗粒和锡纳米颗粒/石墨烯纳米片复合电极材料。在研究中，我们首次成功实现了Mg2+在尖晶石Li4Ti5O12中的可逆嵌脱，通过球差校正透射电子显微镜等先进表征手段并结合理论计算，提出了Li4Ti5O12储镁的电化学反应机理，并发现其储镁过程中的低应变特性和强烈的尺寸依赖性。进一步提出利用混合离子共嵌/脱的思想改善大尺寸材料的动力学及电化学性能的新思想，为开发新型的镁二次电池电极材料提供了新的设计思路。