富锂锰基正极材料表面改性、结构稳定性及电化学行为的研究

As the structural instability and low surface electron-ion conductivity during charging-discharging process are key factors that controls the electrochemical performance of lithium-rich manganese based cathode materials, this project proposes innovatively combining the gradient ions layer of vanadium, which has a stronger M-O bonding energy than manganese, and composite coating layer with high electron-ion mixed conductivity, with the formation of vanadium ion gradient doping layer and Li3V2(PO4)3/C composite layer on the particle surface of the lithium-rich manganese substrate by sol-gel coating and heat treatment process, to improve the material structural stability and surface physicochemical properties, leading the enhanced electrochemical performance. In order to construct the relation between the preparative process, coated layer morphology, element distribution in the coated-layer and interface structure, it is necessary to study the effect of coating and heat treatment process on lithium-rich manganese substrate,coating layer and interface structure. With combination of the experimental results and theoretical computation, this work can understand the microscale mechanism for improving the material structural stability during the charging-discharging process by investigation of effects of vanadium ions gradient doping on the lattice oxygen oxidation and cations transport in the material.Through the analysis of the materials surface structure and physicochemical properties, the relation will be obtained between the surface modification and surface physicochemical properties.Based on the above investigations, the rational relation will be constructed of material design, preparation, structural stability/surface physicochemical property and electrochemical behavior. These fundamental studies are significant for the development of lithium-ion-battery with high energy density, high power density, long life and low cost.

因充放电过程中结构失稳和表面理化状态差是制约富锂锰基材料电化学性能的关键因素，本项目创新性提出综合利用元素钒（比Mn具有更强M-O结合能）渐变掺杂和高电子-离子混合导电网络层，通过溶胶凝胶-热处理方法一次性地在富锂锰颗粒表面包覆形成钒离子渐变掺杂层和Li3V2(PO4)3/C复合层，改善材料结构稳定性和表面理化特性，提高其电化学性能。研究改性过程对富锂锰基体、包覆层及界面结构的影响，建立制备过程与包覆层形貌、元素分布及界面结构的关系；结合实验研究和理论计算，认识钒离子渐变掺杂层对晶格氧氧化和阳离子迁移的影响规律，揭示其改善材料结构稳定性的微观机制；通过对表面结构和化学态的分析，阐明复合包覆层对材料表面理化特性的影响规律；基于上述研究，建立"材料设计-制备过程-结构稳定性/表面理化特性-电化学行为"之间的关系，为该类材料在高能量及功率密度、长寿命、低成本锂离子电池技术中的应用奠定基础。

富锂锰基金属氧化物由于兼具放电比容量高，工作电压范围宽，成本低廉等优势被普遍认为是新一代锂离子电池正极材料。电子-锂离子电导率低和工作过程中结构失稳是制约其实用化的关键因素。针对上述问题，本项目首次探讨了Li3V2(PO4)3/C复合包覆层制备过程对Li1.2Mn0.54Ni0.13Co0.13O2理化特性的影响规律，发现聚丙烯腈和柠檬酸在氮气环境中的热解过程会导致材料的过度还原，破坏其结构；系统研究了LiAlO2/C和AlF3/C复合包覆层制备过程对Li1.2Mn0.54Ni0.13Co0.13O2理化特性和电化学行为的影响规律，发现在蔗糖在空气环境下的原位热解过程能够引起富锂锰基正极材料Li2MnO3相的活化，增加材料表面的电子和锂离子电导率，进而显著提高正极材料的电化学性能；开展了基于抗坏血酸的化学处理过程对Li1.2Mn0.54Ni0.13Co0.13O2和Li1.2Mn0.6Ni0.2O2理化特性和电化学行为影响规律的研究，证实了该过程能够在富锂锰基正极材料表面原位形成高电子-锂离子电导的尖晶石包覆层，优化材料体相微结构，进而调控富锂锰基正极材料在工作过程中的相结构演变行为；首次系统研究了基于聚多巴胺的表面尖晶石相/C复合包覆层制备过程对Li1.2Mn0.54Ni0.13Co0.13O2理化特性和电化学行为的影响规律，发现该过程能够显著提高富锂锰基正极材料表面的电子-锂离子的电导率，抑制电解液对正极材料的腐蚀，进而提高改性材料的放电比容量和工作稳定性。系统开展了基于锂离子电池正极材料制备过程的AlF3掺杂改性，发现该过程能够同时实现Li1.2Mn0.54Ni0.13Co0.13O2的表面LiF包覆和体相Al掺杂，进而增加其表面和体相结构稳定性，提高改性材料的电化学性能。项目执行期间共发表学术论文33篇，授权国家发明专利14件，培养硕士研究生7人。该项目开发出了多种针对富锂锰基正极材料的改性方法，建立了“材料设计-制备过程-结构稳定性/表面理化特性-电化学行为”之间的关系，为该类材料在高能量及功率密度、长寿命、低成本锂离子电池技术中的应用奠定了基础。