锂离子电池正极材料磷酸钒锂的改性研究

Based on the key problems of the Li3V2(PO4)3 cathode materials for lithium ion batteries, Such as the actual low specific capacity, materials circulation and performance ratio difference under high voltage and low electronic conductivity and ionic mobility The project plans to carry out the preparation, doping modification and composite electrode materials of Li3V2(PO4)3 and It’s effect of the electrochemical properties and mechanism.Through the design and preparation of the carbon dots (CDs) as the kernel of CDs@Li3V2(PO4)3/C and the research to improve the conductivity of the material, Proven the electrochemical behavior and interface features of the new core-shell structure materials CDs@Li3V2(PO4)3/C.Based on the doping modification of the material CDs@Li3V2(PO4)3/C,Proven the action of the doping ion type, shape and number for Li3V2(PO4)3 crystal structure, Especially to improve the performance of the ion migration rate of the materials and conductive effect and mechanism .Through the design and preparation of the two or three composite electrode materials (1-x-y)Li3V2(PO4)3•xLiMnPO4•yLiFePO4 as well as to the research of the intercalated lithium features for composite electrode materials and energy storage .Proven the relationship between chemical structure and electrochemical properties of materials, and reveal the composite electrode materials of electrochemical behavior together.By constructing and optimizing the new multi-electron reaction electrode materials (1-x)Li3V2(PO4)3•xLi3PO4, expounds the new lithium storage mechanism and tries to analyze and solve the key problems of high energy density batteries.The reseach is a beneficial support for the electronic design and deepen the related basic theories, improve the multi-electron reaction theory and constructing the system of new type of the chemical power source and pushing forward the innovation of new energy power battery technology .

针对磷酸钒锂材料的实际比容量低以及电子导电率和离子迁移率低的关键问题。项目拟开展制备工艺、掺杂改性和电极材料复合对材料电化学性能的影响及作用机制研究。通过设计和制备出以碳点为内核的CDs@Li3V2(PO4)3/C材料以及对提高材料导电性的研究，探明新型核壳结构材料的电化学行为和界面特征。通过对材料掺杂改性研究，探明掺杂离子种类、形态和数量对磷酸钒锂晶体结构，特别是对提高材料的离子迁移率及导电性能的影响及作用机制。通过设计并制备以及对复合电极材料嵌锂特性和储能规律研究，探明材料的化学结构与电化学性能之间关系，揭示出复合电极材料的电化学协同行为。通过构建和优选出新型多电子反应电极材料(1-x)Li3V2(PO4)3•xLi3PO4，阐明新的储锂机制并试图分析和解决高能量密度电池的关键问题。项目研究为多电子反应电极材料设计以及和构筑新型化学电源体系及推动新能源动力电池创新技术应用提供支持。

Li3V2(PO4)3拥有合成原料丰富、生产成本低廉、较高的电位、良好的循环性能等，是具有潜力的锂离子电池正极材料。材料的主要缺陷是实际功率较低、高充放电压下材料结构不稳定导致衰减快以及电子和离子导电率低。该项目研究的总体思路如下：在锂离子电池正极材料Li3V2(PO4)3研究基础上，针对影响Li3V2(PO4)3实际应用中的关键问题开展了材料合成新工艺、掺杂改性、电极材料复合等技术提高材料电化学性能和基于多电子反应的电极材料设计以及材料电化学行为和相关机制的基础研究。采用微波辅助-机械活化法，得到了制备 Li3V2(PO4)3的最佳工艺条件为：微波辐射功率为750W，微波辐射时间为10min，最佳蔗糖加入量为30%，样品放电容量132.9 mAh/g，具有较好的电化学循环性能。掺杂Ni2+能够有效改善LVP/C材料的电化学性能，掺入2% Ni2+的样品具有最高的电化学性能。掺杂Cr3+对改善LVP/C材料的电化学性能具有较好的改善。掺杂Mo6+对改善LVP/C材料的电化学性能具有较好的改善。Al3+-BO33-掺杂后的材料，当充放电倍率为0.2C和5C时，材料的首周放电比容量是142mAh·g-1和109.1mAh·g-1，结果表明，协同掺杂能有效改善Li3V2(PO4)3/C材料的电化学性能。采用溶胶凝胶法成功制备0.75Li3V2(PO4)3∙0.25Li3PO4/C复合材料，800 ℃条件下烧结15 h得到的材料具有较好的电化学性能。采用溶胶凝胶法成功制备0.875Li3V2(PO4)3∙0.125VPO4/C材料，850 ℃条件下烧结15 h得到的材料具有较好的电化学性能。研究表明，VPO4材料的加入对本体材料的结构和形貌未造成影响，但能放有效底提高材料的电化学性能，这归于VPO4材料有较高的比表面积，有利于电解液的充分湿润，因此在充放电的过程中有利于锂离子在其内部的传递。