薄膜型锰基LiMnxFe1-xPO4正极材料的有序化构筑及高效嵌脱锂机制研究

All-solid-state thin film lithium-ion battery is considered to be an inevitable development trend for microbattery research. Among them, thin-film cathode is the basis of its energy density. As a common manganese-based cathode material, LiMnPO4 has an ideal redox potential and a high theoretical energy density. However, due to the low electronic/ionic conductivities, the inherent metastability of the delithiated phase and the lithium deficiency of the lithiated phase, it is difficult for this cathode material to achieve the desired energy density. This project uses physical vapor deposition technology to construct an ordered film structure, which means optimized of crystal orientation, intrinsic defects, iron doping, carbon coating, nitriding and lithium supplement/conduction to prepare manganese-based LiMnxFe1-xPO4 thin-film cathode materials with highly efficient lithiation/delithiation performance. By studying of the ordered growth mechanism of thin-film, the coupling mechanism of multiple films and the coordination mechanism of lithium supplement/conduction, the energy storage level and conversion efficiency of battery can be improved, the structural stability of film can be promoted and a transport model of lithium-ion will be established, which contribute to obtain high energy density and high stability film-type cathode materials.

全固态薄膜锂离子电池被认为是微电池发展的必然方向，其中薄膜正极是电池能量密度的基础。LiMnPO4作为通常的锰基正极材料，拥有理想的充放电平台和较高的理论能量密度，但由于其存在着低电子/离子传导率、脱锂相稳定性差以及嵌锂相锂缺失等问题，导致该材料难以达到理想的能量密度。本项目采用物理气相沉积技术构筑有序化的薄膜结构，拟通过优化晶格取向、本征缺陷、铁/碳/氮掺杂以及补锂导锂途径等制备具有高效嵌脱锂性能的薄膜型锰基LiMnxFe1-xPO4正极材料。通过研究薄膜的有序化生长机制、多重膜的耦合机制以及协调补锂导锂机制，提升电池的能量存储水平和转换效率，提升薄膜的结构稳定性，建立锂离子的输运模型，以获取高能量密度、高稳定性的薄膜型正极材料。

电源系统的微型化和集成化是解决超大规模集成电路和微机电系统等片上系统（SOC）元器件能源匹配的最理想方案。全固态薄膜锂离子电池不仅很容易加工成微米级电池并集成在SOC芯片内，而且能够有效解决固固界面的微观缺陷，实现固固界面的致密结合，被认为是微电池研究必然的发展方向。为了研发出高性能全固态薄膜锂离子电池，本项目结合磁控溅射沉积、脉冲激光溅射沉积和电沉积等薄膜制备技术，研究了磷酸锰铁锂、Na2/3Ni1/4Mn3/4O2、聚吡咯以及复合材料等正极薄膜的择优生长机制、多层膜耦合机制以及补锂导锂机制。. 首先，针对锰基LiMPO4/C正极材料，结果证明：当乙二醇和去离子水比值接近12:1时，拥有较小的颗粒尺寸以及较大的晶粒和晶格尺寸；循环稳定性和极化效应主要依赖于材料尺寸大小；规则的表面形貌有助于提升材料比容量；还原性石墨烯进一步提升了倍率性能和热稳定性。. 针对聚吡咯修饰的LiFePO4/C正极材料，结果显示聚吡咯在磷酸铁锂颗粒间形成了互通的导电网络，提升了复合材料的导电性，同时贡献了自身的容量，制备的复合电极具有更稳定的结构和更佳的电化学性能，这为导电聚合物材料进入未来储能市场，特别是柔性全固态锂离子电池领域提供了基础。. 在物理气相沉积过程中，通过调节衬底温度、工作压强、电压电流以及激光频率、能量等对薄膜性能进行优化，实现了薄膜的可重复制备，使得薄膜的结晶性、择优取向性得到大幅度改善，进而提升了磷酸锰铁锂和P2-Na2/3Ni1/4Mn3/4O2正极薄膜电化学性能。. 采用恒电势一步电沉积法制备无添加剂的聚吡咯薄膜电极过程中，通过在聚吡咯链上成功的掺杂对甲苯磺酸离子，来提升薄膜的导电性，增加活性位点，所制备的薄膜电极具有高放电比容量，优异的倍率性能和长循环稳定性。. 以上关键研究成果的突破，为接下来制备高能量、大功率、长寿命全固态锂离子动力储能电池提供了科学指导和理论参考依据。