新型阳离子无序富锂岩盐结构复合正极材料的制备及电化学性能研究

The new lithium rich cation-disordered rock salt cathode materials Li-Ni-Ti-Mo-O have been recognized as promising material under the direction of percolating network theory. However, lower electronic/ionic conductivity and depredation of percolating network because of the O2 lose and lower Ni2+ discharge capacity because of the larger lattice parameters and Ni 3d and O 2p band overlap should be improved. In this project, the double coating layer Li1.3Al0.3Ti1.7(PO4)3/C with high electronic and ionic conductivity will be used to enhance the electronic and ionic conductivity of composite material. The O2- lose will be restrained by the double coating layer and Al-O band formed by mutual doping between coating layer and inner core, which results in stable 0-TM percolating network. The lattice parameters and Ni 3d and O 2p band overlap will be reduced and Ni2+ charge/discharge capacity will be delivered fully after Mo6+ replaced by smaller radius Cr6+ and Al3+ doping. This study will shows the mechanism how the Li1.3Al0.3Ti1.7(PO4)3/C double coating layer effect the Li+ diffuse rute and enhance diffuse dynamics between the coating and inter layer, Cr6+ (Al3+) effect the Ni2+ charge/discharge capacity. These all can provide new ideas and theoretical evidence for development and application of new cathode materials for lithium ion battery.

随着逾渗网络理论的提出，新型阳离子无序富锂岩盐结构正极材料Li-Ni-Ti-Mo-O被认为是极具潜力的正极材料之一。但是氧脱出导致0-TM逾渗网络结构破坏及较低的表面离子和电子电导；较大的晶胞参数及Ni3d和O2p能带重叠抑制Ni2+的容量发挥是亟待解决的问题。本项目拟利用具有较高离子和电子电导率的磷酸钛铝锂/碳双重修饰层提高复合材料表面的电子/离子电导率；结合表面双重修饰和核壳互掺杂在内核形成的Al-O键，抑制氧脱出，稳定0-TM逾渗网络结；利用半径较小的Cr6+取代Mo6+以及Al3+掺杂，降低内核材料晶胞参数以及Ni3d和O2p能带重叠，充分释放Ni2+充放电容量。通过研究，重点揭示磷酸钛铝锂/碳的双重修饰对Li+在复合材料内核层和包覆层中的扩散路径和动力学以及Cr6+(Al3+)掺杂对Ni2+充放电机制和容量的影响规律和作用机理，为新型正极材料的开发提供研理论依据和思路。

新型阳离子无序富锂岩盐结构正极材料被认为是极具潜力的正极材料之一。但是氧脱出导致0-TM逾渗网络结构破坏及较低的表面离子和电子电导；较大的晶胞参数及Ni3d和O2p能带重叠抑制Ni2+的容量发挥是亟待解决的问题。本项目首先采用溶胶凝胶法制备了纳米级的Nb掺杂的富锂无序岩盐结构正极材料Li1+x/100Ni1/2-x/100Ti1/2-x/100Nbx/100O2，电化学测试结果表明，掺杂可以改善材料的循环和倍率性能。在20 mAg-1的电流密度下，Li1.2Ni0.3Ti0.3Nb0.2O2的首次放电比容量为210 mAhg-1。然后通过液相法结合不同温度的烧结在LNTNO表面包覆不同含量的碳，最后通过溶胶凝胶法结合固相烧结在LNTNO表面包覆不同含量的Al2O3。具有较高离子和电子电导率的Al2O3/碳双重修饰层提高复合材料表面的电子/离子电导率；结合表面双重修饰和核壳互掺杂在内核形成的Al-O键，抑制氧脱出，稳定0-TM逾渗网络结；XPS结果表明Al2O3层生成过程时部分半径较小的Al3+会进入晶格提高Ni2+/Ni4+活性，提升中值电压。另外Al2O3层减少副反应，降低界面及电荷转移阻抗，提升材料循环寿命。双层包覆后样品 LNTNO@C-Al2O3的锂离子扩散系数为1.74×10−12cm2s−1，较原始材料LNTNO高一个数量级；且其首次放电比容量为 224.9 mAhg−1，在40 mAg−1下循环100次后容量达161.2mAhg−1，保持率为81.5%。XPS、XAS与DFT结果表明双层包覆后材料中氧空位增多且 Ni 3d 能带与O2p能带重叠降低，表明材料同时具有更高的O−/O2−与Ni2+/Ni4+活性，碳包覆层提升容量及高倍率性能，而Al2O3包覆层降低阻抗并提高循环寿命。通过本项目的研究，为富锂无序岩盐结构正极材料的开发提供研理论依据和思路。