富锂锰基正极材料的协同稳压结构设计及性能研究

The capacities of cathode materials are generally low, which have blocked from the further improvement in properties of lithium ion batteries. Lithium-rich manganese-based cathode materials can effectively increase the height of short board with low capacities for lithium ion batteries. However, some bottleneck challenges, such as a rapid voltage decay, and a low rate capability, have to be overcome prior to the practical application for these materials. Herein, lithium-rich manganese-based cathode materials are selected as our research object. We intend that the increasing of the order, the stability and the electrochemical reactivity for the grain structures is realized by the coordinated controls of the structures of the domain, the surface and the crystallographic orientation from multiple aspects of the processes, and the enhancing of the energy density, the rate capability and the cycle stability for the batteries is achieved by the synergized inhibition of the voltage decay of the cathodes from multiple aspects of the grain structures. In details, the effect laws of the processes parameters and the conditions on the grain structures are revealed by the coprecipitation-solvothermal synthesis process, the doping process and the dipping-heat treatment surface modification process. The mechanism for the grain structure control is elucidated. The corresponding results are expected to achieve controllable fabrication of the grain structures of lithium-rich manganese-based cathodes, which can provide the reference for optimization in the grain structures of electrodes. Furthermore, the influence rules of the grain structures on the discharge voltages, the rate capabilities and the cycle stabilities are demonstrated by the electrochemical performance tests. The mechanism for the synergized inhibition of the voltage decay from multiple aspects of the grain structures is elucidated. The obtained results are hoped to effectively prevent voltage decay and significantly enhance the electrochemical properties for lithium-rich manganese-based cathodes, which may afford the support for high-performance lithium ion batteries.

锂离子电池正极材料的容量普遍偏低，这制约着其性能进一步提高。富锂锰基正极材料能够有效提升锂电低容量的短板高度，但该材料的推广却面临着电压易衰减、倍率性能差等瓶颈难题。为此，本项目以富锂锰基材料为研究对象，拟多角度联动地调控晶粒的晶畴结构、表面结构及结晶取向结构，增强结构的有序性、稳定性及电化学反应活性；多结构协同地抑制富锂锰基材料的压降，提高电池的能量密度、倍率性能及循环稳定性能。具体地，通过共沉淀-溶剂热制备工艺、掺杂工艺及浸渍-热处理表面修饰工艺的研究，揭示工艺参数及条件对晶粒结构的影响规律，阐明结构调控的机制，实现富锂锰基材料晶粒结构的可控制备，为电极材料结构的优化提供参考；通过电化学性能测试，揭示晶粒结构对电池放电电压、倍率性能及循环稳定性能的影响规律，阐明多结构协同稳压的作用机理，实现富锂锰基电池的压降有效抑制及其性能显著提高，为高性能锂电的开发提供参考。

当前商用锂离子正极材料的容量普遍较负极材料偏低，这正制约着电池性能的提高。富锂锰基正极材料的容量高达250 mAh g-1以上，能有效提升低容量短板的高度。但它却有电压易衰减、倍率性能差等性能瓶颈难题。因此，开发具有高储锂性能的富锂锰基正极材料至关重要。本项目主要通过调整共沉淀-溶剂热工艺参数，调控富锂锰基正极材料的零维、一维、二维与三维形貌与结构，来优化富锂锰基正极材料的储锂性能，并阐明结构优化性能的作用机理。本项目取得的重要进展如下：①实现了Li1.2Mn0.54Ni0.13Co0.13O2正极材料形貌与结构的精确调控。具体地，当在前驱体制备时添加氨水时得到长约2μm的一维短棒样品，未添加氨水则得到长4-10μm的一维长棒样品；当在前驱体制备时添加5ml一缩二乙二醇时得到二维纳米片样品，添加量小于5ml时则得到一维棒与二维片混合形貌的样品；当在前驱体制备时添加10ml一缩二乙二醇时得到三维球状结构样品，添加量大于10ml时则得到微球与无规则块状混合形貌的样品。②获得了Li1.2Mn0.54Ni0.13Co0.13O2正极材料优异的储锂性能，并阐明了结构优化性能的作用机理。例如，对于三维球状结构样品：在0.1、0.2、0.5、1、2、5C充放电倍率下分别获得了252、243、228、203、161、102 mA h g−1的放电容量，表现出了较高的容量与倍率性能；在0.5C、2.0-4.8V截至电压内充放电经100圈循环后容量保持率可达87%，表现出了稳定的循环性能；相对二维纳米片样品，表现出了良好的放电电压；我们把三维球状结构样品表现出的优异储锂性能归因于其具有三维组装形貌和多尺度分级多孔结构上的特殊优势。本项目的实施为高性能富锂锰基Li1.2Mn0.54Ni0.13Co0.13O2正极材料的可控合成提供了新方法，同时为其它高性能锂离子电池材料的设计开发提供了新思路。