5V尖晶石结构锂镍锰氧化物的全电池研究和放电过程热电耦合模拟

LiNi0.5Mn1.5O4 (abbr. LNMO) cathode material for lithium-ion batteries has a high voltage of near 5V, relatively high energy density and excellent cycling performance in half cells, so LNMO is a very hot topic. However, the performance of the LNMO in full cells is still poor and studies on this are rather insufficient. Some improvement methods such as doping and coting are rarely studied in full cells. This problem has affected the application of this material. In this project, Cr, Ti doped LNMO with big particle size, low specific surface area and excellent electrochemical performance will be synthesized via PVP gel combustion method, then the doped LNMO will be tested in full cell with graphite or Li4Ti5O12 anode and the effect of doping on full-cell performance will be studied. Based on improving LNMO full-cell performance by doping, Al2O3 will be coated on the surface of doped LNMO and the performance of coated LNMO will be studied in full cells. The valence state change of Mn on the surface of doped and coated LNMO during cycling will be studied by soft X-ray absorption to understand the mechanism of improving cycling performance by doping and coating, cooperating with Advanced Light Source in Lawrence Berkeley National Laboratory, USA. At last, parameters in modelling will be measured to build model of LNMO full cell with graphite and Li4Ti5O12, then thermoelectric-coupled modelling will be conducted.

锂离子电池正极材料LiNi0.5Mn1.5O4（缩写为LNMO）具有接近5V的高工作电压，具有较高的能量密度和优异的半电池循环性能，一直是人们研究的热点。但该材料在全电池中的性能仍然较差，研究十分薄弱，掺杂、包覆等改进材料性能手段也很少能够结合全电池进行研究，阻碍了材料的实用化进程。本项目拟通过PVP-凝胶燃烧法合成低比表面积，大颗粒，性能优异的Cr、Ti掺杂LNMO材料，对掺杂后的材料搭配石墨和钛酸锂负极进行全电池测试，研究掺杂对全电池性能的影响。在掺杂提高LNMO全电池性能的基础上，进行ALD法包覆Al2O3，研究包覆后的全电池性能。与美国劳伦斯伯克利国家实验室先进光源合作，对掺杂、包覆后的LNMO在充放电循环过程中表面Mn价态的变化进行软X射线吸收研究，理解掺杂和包覆改善循环性能的机理。最后，测定LNMO的模拟相关参数，建立LNMO与石墨、钛酸锂全电池的模拟模型，进行热电耦合模拟。

项目以申请书和计划书为指导，结合国内外研究最新进展，以提高LiNi0.5Mn1.5O4材料在全电池中的循环性能为核心目标，研究了Cr、Co、Nb等掺杂对材料性能的改进，对结构和形貌的影响，充放电过程中表面元素电子状态的演变。制备了以石墨和硬碳为负极的全电池，研究了其电化学性能。进行了正极热力学参数的测定和全电池放电的热电耦合模拟。研究取得以下主要进展和结果：1. Cr和少量Nb掺杂可以提高材料的扩散系数从而提高倍率性能，材料的循环性能也有所改善。Co掺杂提高了材料的倍率性能，大幅提高了材料的循环性能。2. 利用资源丰富的松果通过高温碳化和清洗工艺制备硬碳并用作于全电池负极材料，展现出良好的电化学性能。3. 以石墨为负极的全电池，虽然掺杂后的样品对石墨负极的循环性能有所改善，但衰减仍然非常快。以硬碳为负极的全电池，掺杂的样品显示了大幅改善的循环性能。4. Co掺杂可以抑制全电池中Mn2+的产生，在负极表面未检测到Mn的沉积。5. 测定了开路电压、dU/dT和扩散系数随SOC变化的拟合表达式，建立了模拟程序，进行了热电耦合模拟，得到了不同散热条件下恒阻放电电流和温度随时间变化和和生热速率随时间变化的关系。项目的研究成果对于LiNi0.5Mn1.5O4材料走向实用化、进一步开发基于该材料的快速充电电池具有重要意义，项目的热电耦合模拟成果对于研究相应的温度控制技术和产热预测技术具有重要意义。