高倍率锂离子电池正极材料LiNi1/3Co1/3Mn1/3O2的设计、制备及电化学性能研究

The LiNi1/3Co1/3Mn1/3O2 cathode material has demonstrated the potential as an good candidate material replacing the LiFePO4 for positive electrode used in lithium ion power batteries because its higher specific capacity, high voltage platform, favourable structural stability and low-temperature characteristics. Furthermore, it has become the main cathode material for lithium ion batteries used in telephones, laptops and other mobile information products at present. However, the LiNi1/3Co1/3Mn1/3 has poor rate capability, which becomes a main obstacle for the large scale application. In this proposal, Zr and Cl co-doped in the LiNi1/3Co1/3Mn1/3O2 material was adopted to surpress the cation mixing, graphited carbon membrane coating on the surface of the LiNi1/3Co1/3Mn1/3O2 was adopted to surpress the dissolution of the surface ions, compositing with graphene and carbon nanotubes was adopted to improve the electron conductivity, furthermore, a rheological phase reaction route in combination with a spray drying technology was adopted to design and make the final composite has high rate capability and high tap density. Adopting experimental research and theory analysis, it is hoped to clarify the relationship between the Zr,Cl co-doping,coating graphited carbon membrane, compositing with graphene/carbon nanotubes and the improvement of the rate capability of the LiNi1/3Co1/3Mn1/3O2. Based on the above studying working, this proposal will discover the key factors that might affect the rate capability of LiNi1/3Co1/3Mn1/3O2. It is expected to obtain theoretical basis for designing and preparation of LiNi1/3Co1/3Mn1/3 with excellent high rate capability through the above research.

三元正极材料LiNi1/3Co1/3Mn1/3O2(NCM)因具有高比容量、高电压平台、良好的结构稳定性以及低温特性，在手机、笔记本电脑等便携式电子产品用锂离子电池中已逐渐成为主导正极材料，另外，代替磷酸亚铁锂作为动力锂离子电池正极材料也已经越来越被看好。然而，NCM大电流充放电性能差（倍率性能差）的问题成为制约其规模化应用的主要瓶颈之一。本项目拟通过Zr及Cl元素共掺杂抑制NCM阳离子混排、表面包覆石墨化碳膜抑制NCM表面离子溶解、与石墨烯和碳纳米管共复合提高电子导电性能的方法，采用流变相结合喷雾干燥技术，设计并制备出具有高倍率性能的NCM。结合实验研究和理论分析，阐明Zr、Cl元素共掺杂，包覆石墨化碳膜、共复合石墨烯及碳纳米管与NCM倍率性能提高之间的关联，发现影响NCM倍率性能的关键因素，为设计和制备具有大电流充放电能力的NCM提供理论依据。

三元正极材料LiNixMn1-x-yCoyO2（0 < x < 1, 0 < y < 1）相对于传统LiCoO2，LiNiO2、LiMn2O4等具有较为显著的优势，已逐渐成为锂离子电池的主流正极材料。三元正极材料主要包括LiNi1/3Co1/3Mn1/3O2、LiNi0.4Co0.2Mn0.4O2、LiNi0.5Co0.2Mn0.3O2、LiNi0.6Co0.2Mn0.2O2、LiNi0.8Co0.1Mn0.1O2等，（1:1:1、4:2:4、5:2:3）体系相对成熟，已得到较为广泛的应用。而随着正极材料对高容量的不断需求，（6:2:2、8:1:1）体系也将很快得到市场化应用。当前，三元正极材料在实际应用中仍然面临不少问题，如导电性差、阳离子混排严重、受电解液腐蚀发生有害表面晶体结构转变等，性能需要进一步提升。本项目以LiNi1/3Co1/3Mn1/3O2为主，围绕三元正极材料面临的上述问题，开展了系列研究。主要包括，通过与导电材料复合提升其电子导电性，通过表面掺杂、包覆抑制阳离子混排及表面有害相转变等。研究结果表明：①通过三元正极材料与碳纳米管（MCNT）和还原氧化石墨烯（rGO）共复合，MCNT和rGO可以发挥协同效益，能够在电极中形成三维导电网络，更好的与三元正极材料活性物质接触，从而极大的提升了表面电子导电性能，使三元材料的倍率性能得到了显著提升；②通过锆（Zr）等元素掺杂，发现Zr元素能够进入到三元正极材料的表面晶体结构中，抑制阳离子混排，优化晶体结构，此外，未进入晶体结构的Zr元素还能够在三元正极材料表面形成一层锆酸锂包覆层（Li2ZrO3），抑制电解液腐蚀，从而使三元正极材料的循环性能得到了显著提升；③通过表面包覆，如包覆Li3VO3，Li2O-BPO4等快离子导体，不仅可以隔绝三元正极材料与电解液的直接接触，抑制电解液对电极活性物质的侵蚀，还有助于三元正极材料表面离子电导率的提升，因此，三元正极材料的循环性能和倍率性能等均得到较明显的改善。此外，利用基金资助，进一步从原子尺寸考察了富锂锰等高容量正极材料的容量衰减与循环次数之间的关联机制，并利用元素掺杂、表面包覆等措施，对富锂锰正极材料进行修饰改性，并从原子尺寸的角度深入剖析了性能提升的机理。上述工作开展，对于揭示三元正极材料的电化学性能衰减机制及解决其在实际应用中面临的问题具有重要的理论和实际意义。