锂离子电池高活性磷酸锰锂基正极材料可控制备研究

LiMnPO4 based material is one of the most promising cathodes utilized in lithium ion batteries to power the electric vehicles due to its advantages of stable structure and relatively high energy density. However, its intrinsic kinetics is very poor and the improvement of its electrochemical activity was the most important topic since it was proposed. In recent efforts, we developed a novel synthetic route, DMSO-assisted co-precipitation method, via which LiMnPO4 crystals with a size of ~ 100 nm were directly obtained under 1 atm and 130 ºC. The synthetic materials presented the much better activities than the samples obtained from other ways. Based on these accumulations, we shall further investigate the mechanism to improve the intrinsic kinetics and develop the controllable synthesis of high-performance LiMnPO4 based materials. Firstly, the crystal growth will be optimized by introduction of additives and other solvents into the system to exert the disturbing effects. Then, the influence on carriers’ transportation will be studied for the samples with bulk substitution and gradient structure. Also the corresponding relationship of the electrochemical performance will be established to the surface structures modified with cation doping or reduction. Finally, the controllable synthesis of LiMnPO4 with the expected performance would be explored after thoroughly understanding the relation between the crystal’s characteristics, modification strategies and performance. In a word, the implementation of this project would provide the technical support and theoretical direction on the mass production of LiMnPO4 based materials.

由于结构稳定、能量密度较高等优势，磷酸锰锂基正极材料在动力锂离子电池领域拥有巨大的发展潜力。但是，它的本征动力学极差，高活性制备始终是其最重要的发展方向。前期工作中，申请人开发出二甲基亚砜辅助共沉淀制备磷酸锰锂的新方法，在常压、130 ºC下能够得到~100 nm磷酸盐晶体，活性优于其他方法合成的样品。在此基础之上，本申请拟深入研究磷酸锰锂电子、离子输运能力的改善机制，探索性能可控的制备技术。首先研究添加剂、其它有机溶剂对晶体生长的扰动作用，建立反应环境与晶粒尺寸、晶面取向的对应关系，开发晶体可控生长技术；然后研究体相取代、梯度材料对载流子输运行为的影响，通过离子注入、还原等方式修饰表面，研究表面微结构与电化学行为的关系，理解载流子高效输运的体表特征；最后尝试建立晶体特性、改性措施与材料动力学之间的关系，开发性能可设计的电极材料制备技术，为磷酸锰锂的产业化提供技术支持和理论指导。

随着动力电池的高速发展和燃烧事故的持续发生，大家开始重新关注磷酸盐正极材料在动力电池中的价值。磷酸锰锂具有更高的能量密度，且热稳定性与磷酸铁锂相近，是最具应用前景的正极材料之一。按照计划，本项目研究了磷酸锰锂基正极材料的制备技术和改性技术，取得了较大研究进展。以自主开发的DMSO辅助共沉淀方法为基础，在优化制备工艺后，研究了LiMn1-xFexPO4/C(x=0.7~0.95)固熔体电化学特性，其中LiMn0.7Fe0.3PO4/C在所有测试倍率容量最高，但LiMn0.8Fe0.2PO4/C具有更高的能量密度；随后，我们开发了LiMnPO4-LiFePO4核壳结构材料，可逆容量显著高于均相样品，表明磷酸锰锂动力学缓慢的主要源自表面，为未来材料开发提供了新的思路；我们还开发出磷酸锰铁锂材料的表面成膜添加剂，发现HDI能够显著改善磷酸盐材料的循环稳定性和倍率特性；同时，我们还研究了磷酸锰铁锂材料作为添加剂对NCA8893的影响，发现1%、2%添加能够提高NCA8893的循环寿命从77%提升至86%、88%，且没有降低材料的可逆容量。在进行磷酸盐研发的同时，受核壳结构思路的启发，我们开发了LiNi0.8Co0.1Mn0.1O2¬-LZO核壳材料，这一策略显著提高材料的循环寿命和抗水蚀特性；随后，我们研究了层状材料的力学特性，确认材料力学劣化遵守断裂损伤模型，并重新认识了体相掺杂对材料力学的影响规律。通过本项目的执行，揭示了磷酸锰锂基材料的关键问题在于调控表面，发展核壳结构是一个有效解决方案，同时这一策略也适合于高镍正极材料，这些进展为这些材料的产业化应用奠定了基础。本项目共发表文章9篇、正在审稿1篇，申请专利5项，有一项技术转移，培养学生6人，参加学术会议10余次。