富锂锰基正极中高导电骨架结构粘结剂的构建及其作用机制研究

High-capacity lithium-rich manganese-based cathode materials have broad application prospects in lithium-ion batteries. However, a great challenge lies in its structural transformation and voltage fading during cycling. In this project, based on the quantitative calculation of the interfacial adhesion energy and the dynamic stability of polymer, a binder with high conductive skeleton structure will be constructed on the surface of lithium-rich materials by in-situ polymerization and cross-linking technology to achieve the organic combination of three modification strategies including surface coating, ion doping and binder. The binder with high conductive skeleton structure can effectively inhibit the voltage fading of lithium-rich materials, improve the electrochemical performance of electrodes. The function mechanism of the binder on structural stabilization will also be revealed. Ionic conductive polymer (NaPAA or LiPAA) coating layer can stabilize the interface between electrode and electrolyte, maintain the layered structure of lithium-rich materials and improve the conductivity of electrodes. Na+ in NaPAA can enlarge the spacing of lithium layers and play a pillar role in stabilizing the crystal structure of lithium-rich materials. The mechanical stability of electrodes can be improved by crosslinking coatings layer with high elastic polymers (PVA, TPU, etc.). The research contents include preparation and performance optimization of lithium-rich materials, regulation and construction of high conductive skeleton structure and formation mechanism, and the electrochemical performance evaluation and structure stabilization mechanism of electrodes. It is expected that this project will become the basis of the development and industrialization of lithium-ion batteries with high energy density, and promote the rapid development of electric vehicles.

高容量富锂锰基正极材料在锂离子电池中具有广阔的应用前景，其亟待解决的问题是缓解循环中结构转变和压降现象。本项目基于界面粘附能与聚合物动力学稳定性量化计算，通过原位聚合和交联技术在富锂材料表面构建高导电骨架结构粘结剂，实现表面包覆、离子掺杂、粘结剂三种改性措施的有机结合，有效抑制富锂材料压降现象，提高电极电化学性能，并揭示粘结剂对电极结构及性能的作用机制。离子导电聚合物(NaPAA或LiPAA)包覆层可稳定电极/电解液界面，维持材料层状结构，提高电极电导率；NaPAA中Na+可扩大层间距，并发挥稳定晶体结构的支柱作用；聚合物包覆层与高弹性聚合物(PVA、TPU)交联，可提高电极机械稳定性。研究内容包括：富锂材料的制备与性能优化；高导电骨架结构的调控构建及形成机制研究；电极电化学性能评价及结构稳定化机制研究。期望本研究为高能量密度型锂离子电池的研发与产业化奠定基础，促进电动汽车领域快速发展。

开发高容量型正极材料是提高锂离子电池能量密度的关键。富锂锰基正极材料的应用前景广阔，其亟待解决的问题是缓解循环中结构转变和压降现象。本项目采用溶胶凝胶法、氢氧化物/草酸盐共沉淀法等方法优化制备出具有不同颗粒尺寸的富锂锰基正极材料(如Li[Li0.2Ni0.2Mn0.6]O2、Li[Li0.2Co0.13Ni0.13Mn0.54]O2、Li1.2Fe0.16Ni0.24Mn0.4O2)，结果发现沉淀剂种类、煅烧温度等工艺参数对产物晶体结构、微观形貌、元素构成、比表面积等性质具有重要影响。本项目还将多类高分子聚合物通过原位聚合和交联技术构建了多种高导电骨架结构的复合粘结剂，通过对比不同粘结剂所构建电极的电化学性能，探明了高导电骨架结构粘结剂的形成机制及其改性富锂锰基正极的相关机理。结果表明，高导电骨架结构的粘结剂可以维持富锂正极材料的结构稳定性并抑制其在循环中的电压降现象，从而有效改善富锂锰基正极的比容量、循环稳定性和倍率性能，这主要归因于表面包覆、离子掺杂和粘结剂改性这三个措施的优势结合。高导电骨架结构的粘结剂紧密覆盖在富锂活性颗粒表面，充当保护活性颗粒的表面包覆层，抑制副反应的发生和来自电解液的侵蚀；粘结剂中含有的Li+或Na+可以通过脱嵌反应掺杂到富锂材料的层状结构内部，来补偿活性锂在电池充放电过程中的损耗，发挥稳定晶体结构的支柱作用；粘结剂还可以通过结构中的各种基团与活性富锂颗粒的氧原子形成强烈的氢键，为富锂活性材料、导电剂和集流体之间提供大量的活性键合位点，在电极内部形成高导电网络；某些粘结剂的双螺旋结构还可以发挥机械互锁效应，易于与电极组分结合形成稳定结构，抑制活性颗粒从电极上脱落。这项粘结剂改性富锂锰基正极性能的工作为后续富锂锰基正极材料的优化制备及其改性研究打下了坚实的基础，为改善电化学电池系统的性能提供了一种简单而环保的方法。