燃烧合成制备高倍率锰酸锂正极材料及性能研究

As a likely successor to LiCoO2, lithium manganate cathode materials have become an attractive cathode for high-rate lithium ion batteries. But this material is fast capacity fading during cycle charge, especially at elevated temperatures, which are currently preventing the use of these promising materials in practical applications. It has been considered that the main methods to restrain the capacity attenuation are doping and coating the cathode materials, and modifying electrolyte. In this project, a new low-temperature combustion synthesis method will be used to prepare doping and/or coating lithium manganate with high-rate and high-cycling performances, and its synthesis mechanism will be proposed. The effects of crystallinity, particle size and morphology on electrochemical performances are the most importance content. The relationship between microstructures and electrochemical performances will be discovered and the capacity attenuation mechanism will be also revealed. Thermodynamics and dynamics of lithium manganate during discharge/charge cycles and preparation by the above method are studying, and the mechanisms will be further illuminated in this project. Hence, this project will provide a direction to mass-produce lithium manganate cathode materials with high-rate and high-cycling performances.

以锰为基础的锰酸锂是最有可能替代LiCoO2的正极材料之一，锰酸锂材料被认为是高倍率锂离子电池中极具吸引力的正极材料，但,锰酸锂正极材料的循环性能较差,尤其是在较高温度下容量衰减很快。研究表明，解决锰酸锂容量衰减的主要方法是掺杂和包覆及电解质修饰。本研究主要是探索低温燃烧合成制备具有高倍率、高循环性能的掺杂和包覆型锰酸锂正极材料的理论和工艺，重点是研究掺杂和包覆时材料结晶度、粒径大小、形貌等对电化学性能，尤其是与材料的高倍率和高循环性能的关联，研究制备正极材料和充放电过程中的热、动力学过程的反应机理等。为提高材料的可逆比容量、循环性能、高倍率性能，以及产业化制备锰酸锂正极材料提供科学依据。

尖晶石型LiMn2O4正极材料因其高电压、低成本、高安全性等优点被广泛研究和应用，但Jahn-Teller效应、锰的溶解等问题，使得LiMn2O4的循环性能较差，尤其是在较高温度下容量衰减很快，解决其容量衰减的主要方法是金属离子掺杂和表面包覆及电解质修饰。. 本研究探索了低温燃烧合成制备具有高倍率、高循环性能的掺杂型和包覆型锰酸锂正极材料的新工艺，系统地研究了材料结晶度、粒径大小和形貌等对掺杂和包覆改性LiMn2O4电化学性能的影响，尤其是对高倍率和高循环性能的影响规律。重点研究了Zn、Cu、Al、B掺杂和Ag包覆尖晶石型LiMn2O4正极材料的制备及其电性能。. 结果表明，在1 C的放电倍率条件下，产物Li1.05Cu0.05Mn1.90O4的首次放电比容量为106.9 mAh•g-1，500次循环后，容量保持率为89.2%。甚至在5 C的较高倍率条件下，产物Li1.05Cu0.05Mn1.90O4的首次放电比容量为88.3 mAh•g-1，1500次循环后，容量保持率为63.5%；LiAl0.1Mn1.9O4材料在25 ℃、5 C和10 C倍率条件下，其首次放电比容量分别为112.2 和99.5 mAh•g-1，2000次循环之后的容量保持率分别为57.3% 和57.0%。在55 ℃、1 C倍率条件下，其首次放电比容量为112.0 mAh•g-1，500次循环之后的放电比容量为91.3 mAh•g-1，容量保持率为81.5%。在25 ℃、5 C倍率条件下，Li1.05Al0.05Mn1.90O4在1000次循环后容量保持率为82.4%。CV和EIS测试表明，Li1.05Al0.05Mn1.90O4具有更好的电极动力学过程，其表观活化能Ea值(19.10 kJ•mol-1)低于未掺杂LiMn2O4的Ea值(32.5 kJ•mol-1)。. 本项目的研究结果为进一步提高LiMn2O4正极材料的可逆比容量、循环性能、高倍率性能及其产业化提供了科学依据。.