锂离子电池铜集流体表面功能结构设计、加工及性能分析

发布时间：2018-07-31 05:27

【摘要】：作为移动电子设备、电动工具、电动汽车等的电源以及在工业储能方面的巨大潜力，，锂离子电池引人注目。锂离子电池的广泛应用，对其性能提出了更高的要求，推动了高容量负极材料的发展。但是，高容量负极材料在实际应用中受到诸多限制，因为在与锂离子的合金化和脱合金过程中，其体积发生严重变化，致使电极材料粉化、与铜集流体之间发生脱离，电极结构被破坏，锂离子电池容量快速衰减。针对这个问题，本文提出具有表面功能结构的高性能新型铜集流体，围绕结构的设计、成形、作用机理及对锂离子电池循环性能的影响展开系统研究，主要研究工作如下： 1.高容量负极材料粉化失效的数学模型基于线弹性材料的基本假定，根据锂离子电池中锂离子在负极材料中的扩散规律，分析电极材料中应力的产生机理。将锂离子在负极材料中扩散引起的膨胀等效成热膨胀，通过对电极材料膨胀时的力学分析，得出了电极材料中应力的函数。根据线弹性材料脆性断裂的K准则，讨论了电极材料的断裂失效，得出了决定材料失效的关键函数，即高容量负极材料粉化失效的数学模型。 2.铜集流体表面结构设计及数学模型根据材料粉化失效模型，当锂离子在电极材料中扩散时会有内应力产生。为了避免内应力导致的电极材料失效，提出铜集流体表面微盲孔结构及微球结构。结构对电极材料的体积变化有较好的约束，即可以提供良好的力学环境来抑制电极材料的膨胀。根据结构应满足的约束条件，建立了表面微盲孔结构及微球结构的数学模型。分析表明：同种孔形，深宽比越大，材料受到孔的约束就越大，限制膨胀的效果就越好；不同孔形，相同深宽比的情况下，锥形孔、圆柱形孔及球形孔的功能依次增强。微球结构的数学模型与球形孔的模型相同，理论上两种结构在抑制电极材料膨胀上的作用相同。 3.微盲孔结构激光加工成形、微球结构烧结成形采用激光技术制备具有微盲孔结构的铜集流体。针对激光光束移动的特点，本文提出光束同心圆扫描——光束定点的加工方案，在一定程度上提高了打孔的质量。实验结果表明：当激光输出功率、激光扫描速度、激光脉冲重复频率及激光光束离焦量分别取20W、500mm/s、20kHz、10μm时，可以得到较好的孔形。采用固相烧结技术制备表面微球结构铜集流体，制定了球形铜粉颗粒与板状铜集流体的烧结工艺。结果表明：在烧结时间及铜粉粒径不变的情况下，烧结温度与烧结颈的大小成正比，即烧结温度越高烧结颈越大，烧结强度就越高；在铜粉颗粒粒径及烧结温度不变时，烧结时间越长，烧结颈就越大，烧结强度就越高。得出：烧结温度为1000℃，烧结时间为3h时，各粒径铜粉与铜集流体之间的烧结强度最大，为最佳的烧结工艺。 4.铜集流体性能测试、高容量硅负极锂离子电池性能测试通过循环伏安实验、接触角测试及拉伸实验分别研究了铜集流体的电化学性能、表面润湿性及力学性能。结果表明：表面具有结构的铜集流体在电解液中性质稳定，作为负极集流体时负极电压不得高于3.5V vs. Li+/Li；表面结构对铜集流体的亲水性影响不大；表面微盲孔结构铜集流体的抗拉强度可以满足要求，表面微球结构铜集流体的抗拉强度偏低。通过充放电循环实验，测试表面微盲孔结构及微球结构铜集流体制备的高容量硅负极锂离子电池的性能。结果表明这两种结构可以提供高效的约束力来抑制电极材料的膨胀，改善锂离子电池的性能。微盲孔的结构参数对锂离子电池的性能有一定的影响：同一孔径下，孔越深性能越好；同一深度下，孔径小的表现出的性能好。对于微球结构铜集流体，随着微球粒径的增大，锂离子电池的性能表现逐渐变好，即大粒径微球结构更具优势。
[Abstract]:Lithium ion batteries are attractive as power sources for mobile electronic equipment, electric tools, electric vehicles, and in industrial energy storage. Lithium-ion batteries are attracting more and more attention. The wide application of lithium ion batteries has put forward higher requirements for its performance and promoted the development of high capacity negative electrode materials. However, high capacity negative electrode has been widely used in practical applications. Restriction, because in the process of alloying and dealloying with lithium ion, the volume of the electrode is changed seriously, the electrode material is pulverized, the electrode structure is broken, the electrode structure is destroyed and the capacity of lithium ion battery is fast attenuated. Structural design, forming, mechanism of action and its effect on cycle performance of lithium-ion batteries are systematically studied. The main research work is as follows:
A mathematical model for the pulverization failure of 1. high capacity negative electrode materials
Based on the basic assumption of linear elastic material, according to the diffusion law of lithium ion in the anode material of lithium ion battery, the mechanism of the stress in the electrode material is analyzed. The expansion of the lithium ion in the negative material is equivalent to the thermal expansion. The stress in the electrode material is obtained by the mechanical analysis of the expansion of the electrode material. According to the K criterion of brittle fracture of linear elastic material, the fracture failure of electrode material is discussed, and the key function of material failure is obtained, that is, the mathematical model of high capacity negative material pulverization failure.
Surface structure design and mathematical model of 2. copper collecting fluid
According to the failure model of material powder, the internal stress is produced when the lithium ion diffusion in the electrode material. In order to avoid the failure of the electrode material caused by the internal stress, the micro blind hole structure and the microsphere structure of the copper collector surface are put forward. The structure has a good constraint on the volume change of the electrode material, that is, a good mechanical environment can be provided to suppress the electricity. The expansion of polar materials. Based on the constraint conditions that the structure should satisfy, a mathematical model for the structure of the micro blind hole and the structure of the microsphere is established. The analysis shows that the larger the ratio of the depth to width, the greater the ratio of the hole to the material, the better the effect of the expansion is, the conical hole, the cylindrical hole and the ball in the case of the same hole shape, the same depth and width ratio. The mathematical model of the microsphere structure is the same as that of the spherical pore, and the effect of the two structures on restraining the expansion of electrode material is the same in theory.
3. micro blind hole structure laser forming, microsphere structure sintering forming
Laser technology is used to prepare copper collector with micro blind hole structure. Aiming at the characteristics of laser beam movement, this paper proposes a beam concentric circle scanning, the processing scheme of the beam fixed point, to a certain extent the quality of the perforation is improved. The experimental results show that the laser output power, the laser scanning speed, the laser pulse repetition frequency and the excitation are shown. When the light beam defocus is 20W, 500mm/s, 20kHz, and 10 m, good aperture shape can be obtained.
The solid phase sintering technology was used to prepare the surface microsphere copper collector, and the sintering process of spherical copper powder particles and plate shaped copper collector was made. The results show that the sintering temperature is proportional to the size of the sintered neck, that is, the higher the sintering temperature, the higher the sintering neck and the higher the sintering strength. When the particle size and sintering temperature are constant, the longer the sintering time, the larger the sintering neck and the higher the sintering strength. It is concluded that the sintering temperature is 1000, and the sintering time is 3h, the sintering strength between the copper powder and the copper collector is the best, which is the best sintering process.
4. copper collector performance test, high capacity silicon negative electrode lithium ion battery performance test
The electrochemical properties, surface wettability and mechanical properties of copper collector fluid are studied by cyclic voltammetry, contact angle test and tensile test. The results show that the properties of the copper collector on the surface are stable in the electrolyte, and the negative electrode voltage is not higher than 3.5V vs. Li+/Li when the negative electrode is used as a negative collector; the surface structure is to the copper collector. The hydrophilicity of the copper collector has little effect, the tensile strength of the copper collector with the surface micro-blind hole structure can meet the requirements, and the tensile strength of the copper collector with the surface micro-sphere structure is low.
The performance of the high capacity silicon negative lithium ion battery prepared by the micro blind hole structure and the microsphere structure copper collector is tested by the charge discharge cycle experiment. The results show that the two structures can provide effective binding to suppress the expansion of the electrode materials and improve the energy of the lithium ion batteries. The performance has a certain influence: the deeper the hole is, the better the performance of the hole, the better the performance of the small aperture at the same depth. For the microsphere structure copper collector, the performance of the lithium ion battery becomes better with the increase of the particle size, that is, the structure of the large particle size microsphere is more advantageous.
【学位授予单位】：华南理工大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TM912

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