【作者】 汤兴贤；

【导师】 叶邦彦； 汤勇；

【作者基本信息】 华南理工大学 ， 机械制造及其自动化， 2014， 博士

【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。更多还原

【Abstract】 Lithium ion battery (LIB) is regarded as an attractive power source, which can be usedfor portable electronic devices, power tools, electric vehicles, and industrial energy storage.The critical requirements of LIB’s performance promote the development of anode materialswith high capacity. The anode materials are limited in practice, because of severe volumechanges during insertion and extraction of Lithium ion, which leads to capacity fading andthe breakage of anode materials. To this end, a novel copper current collector with surfacestructures of micro-blind holes and micro-balls were proposed in this thesis. The design,fabrication, mechanism and effects on LIB of the surface structure were symmetricallystudied, The main contents in this thesis were as follows:1. Pulverization model of anode materials with high capacityThe stress in electrode materials was analyzed based on difusion law of lithium ions inanode materials which were supposed as linear elastic material. The expansion caused bydifusion of lithium ions was equivalent as thermal expansion. The stress functionwasobtained by mechanical analysis of anode materials. The fracture failure was discussed basedon the K criterion of linear elastic material brittle fracture, and the key function of materialfailure was obtained.2. The design and mathematical model of surface structuresThe stress growed when difusion. A novel copper current collector with surfacestructures of micro-blind holes and micro-balls were proposed to avoid electrode failure. Thestructures could providedbinding force. Therefore, structure models were built. The modelsindicated that: the bigger the ratio of depth to width, the bigger the binding force, and thebetter the effect of restricted expansion at the same holes. Cone holes, cylinder holes andspherical holeshad the better function in turn. The model of micro-balls was same as themodel of spherical holes, they had the same function theoretically.3. Fabrication of micro-blind holes by laser processing and micro-balls by sinteringThe copper current collector with micro-blind holes was fabricated by laser system. Inthis thesis, the processing programme of concentric circles scanning-fixed beam wasproposed to increase processing quality. The experimental results show that: the values of laser out power, laser scanning speed,pulse frequency of laser and laser focuses should be20W,500mm/s,20kHz and10μm for better structures.The copper current collector with micro-balls was fabricated by solid phase sinterprocessing, sintering process was formulated. The experimental results show that: thesintering temperature is proportional to thesintering neckat the under of the condition ofconstant of sintering time and the copper powder diameter. The higher sintering temperature,the bigger thesintering neck andsintering strength. At the under of the condition of constant ofsintering time and the copper powder diameter, the longer sintering time, the biggerthesintering neck andsintering strength. Sintering temperature1000℃and sintering time3hwas the best sintering process.4. Performance test of copper current collector, Performance test of LIB withcopper current collectorElectrochemical performance, surface wettability and tensile performance of coppercurrent collector were investigated by cyclic voltammetry test, contact angle test and tensiletest. The results indicated: the copper current collector with surface structures were stable inthe electrolyte, and the anode potential should be under3.5V vs. Li+/Li. The surfacestructures effected on surface wettability slightly. The tensile strength of copper currentcollector with micro-blind holes was to meet the requirements of industry, but the tensilestrength of copper current collector with micro-balls was lower.LIBs fabricated by copper current collector with micro-balls and copper current collectorwith micro-blind holes were test by Charge-Discharge cycling. The results show that: thesurface structures could provide reasonable binding force to increase cycle performance ofLIB. The increasing depth of micro-blind hole help to increase cycle performance of LIB atthe same diameter. The smaller the diameter, the better performance the LIB at the samedepth. The bigger diameter of copper powders was advantageous to performance of LIB.更多还原