碳纳米管增强锡铜合金负极的一体化结构设计及储锂性能研究

发布时间：2018-06-18 07:15

本文选题：锂离子电池 + 负极材料　；参考：《湘潭大学》2014年博士论文

【摘要】：我国对锂离子电池材料及其关键技术的发展尤为重视，将其列入到《2006~2020年的国家中长期科技发展规划纲要》中。与此同时，电动汽车、混合动力汽车等大型交通工具以及其它大型用电设备的高速发展也对锂离子电池在容量方面提出了更高的要求。负极材料是影响锂离子电池容量的关键材料之一。作为新型负极材料的杰出代表之一，锡基合金负极材料的理论质量比容量(993mAh/g)是石墨负极的近三倍。但该材料在充放电过程中伴随着巨大的体积变形(260%)，导致材料在充放电过程中粉化脱落，降低材料的电化学循环性能，该现象是阻碍锡基合金负极材料的市场化应用的关键所在。提升锡基合金负极材料的循环性能的方法众多，与碳材料复合是有效方式之一，其中与碳纳米管复合的报道逐渐增多。一体化电极材料能减少传统电极在集成过程中的冗余连接成分(导电剂与粘结剂)，从而提高空间与材料的利用率，因而该类型电极也被广泛地应用于锡基负极材料当中。本论文以锡基合金负极的商业化应用为目标，针对锡基合金负极存在的以上不足，借鉴集流体与活性材料一体化的思想，采用生产成本低廉，工艺简单的电沉积，结合热处理的工艺方法，制备了不同结构类型的电极，并对其微观结构与储锂性能进行了研究。本论文获得的创新性研究成果如下： (1)为了提高锡铜合金负极的循环性能，我们基于锡/铜交替的多层结构，在低温短时热扩散处理条件下形成了一体化Cu6Sn5合金负极。我们采用电镀的方法，以铜带基底成功制备了特定厚度比的锡/铜多层膜结构材料。再对多层结构材料进行热处理，从而得到一体化锡铜合金负极。并研究了热处理温度等参数对电极材料结构与循环性能的影响。结果表明，由于不同温度下原子活性不同，多层结构材料热处理形成的合金成分存在差异。多层结构材料在200℃，热处理30min时，其电化学循环性能最优，且该电极材料比传统方法制备的电极容量更高，循环更为稳定，在经过40次循环后，容量高出传统锡铜合金负极26.9%。该电极性能优越的原因在于电极活性材料主要为Cu6Sn5相，且材料晶粒细小，在热处理前后变化不大。 (2)为了缓解锡基负极材料在充放电过程中材料粉化的问题，我们基于高强度，高导电的碳纳米管，将其与锡金属负极复合制备了Sn-CNTs一体化电极材料。我们采用复合电沉积的方式，制备了Sn-CNTs复合电极，并对制备复合电极的工艺参数以及CNTs直径对电极循环性能的影响进行了研究。结果表明，CNTs的含量随电流密度不同而改变；采用直径范围为(10~20nm)的CNTs对电极的循环性能提升最为明显。该电极循环性能最好的原因在于：电极内CNTs含量最高，内阻最小。 (3)为了增强集流体与活性材料之间的结合，进一步减缓锡铜合金负极材料在充放电过程中材料粉化的问题，我们在Sn-CNTs复合电极基础上，基于Cu-CNTs复合镀层，设计了Sn/Cu-CNTs双层结构电极，增强了活性材料(锡铜合金)与集流体(铜)之间的电连接，并最终热处理得到Sn-Cu-CNTs一体化电极材料。我们采用电沉积的方式，首先在铜箔基底上制备Cu-CNTs复合镀层，再电沉积了一定厚度的锡镀层，最后热处理得到Sn-Cu-CNTs一体化电极。我们首先研究了电流密度对复合镀层表面形貌与碳纳米管含量的影响，然后研究了热处理温度对电极电化学循环性能的影响。结果表明，Cu-CNTs复合镀层形貌与碳含量均随电流密度改变而改变，电极在200℃热处理6h后循环性能最优。该电极循环性能最优的原因在于：电极活性材料晶粒细小，与集流体之间结合良好；CNTs与活性材料连接紧密，能起到骨架材料与导电连接的作用。 (4)为了提高了活性材料内碳纳米管的含量，达到改善锡基合金循环性能的目的，我们以Cu-CNTs连接层为基础，将Sn-CNTs活性材料与Cu-CNTs连接层结合，设计了Sn-CNTs/Cu-CNTs复合电极。我们采用复合电沉积的方式，以铜箔为基底先电沉积Cu-CNTs复合镀层，然后在电沉积Sn-CNTs复合镀层制备了Sn-CNTs/Cu-CNTs复合电极材料，并对热处理时间对电极循环性能的影响进行了研究。结果表明，，经过200℃，6h热处理后，电极的循环性能最优，在1C倍率下，充放电100次循环后容量仍可达到584.4mAh/g；且电极倍率性能良好，在20C倍率下充放电时，其容量仍可达到434.6mAh/g。电极循环性能最优的原因在于：电极活性材料内部分布有大量的CNTs，内阻相对较小，离子传导性好；电极内部存在一定的孔隙结构，能为锡铜合金在嵌脱锂过程中的体积变化提供缓冲空间；电极相结构以Cu6Sn5为主，且Sn与Cu3Sn的含量相对较少。本文通过设计不同结构类型的一体化锡基合金负极材料，采用廉价低成本的方法，极大地提升了锡铜合金负极材料的循环性能。由于本文采用的是一体化电极材料，减少了冗余的连接成分，因而能提升全电池的体积容量，为该材料的商业化应用奠定了坚实的基础。
[Abstract]:China attaches great importance to the development of lithium ion battery materials and its key technologies, and puts it into the national medium and long term development plan of science and technology in <2006~2020. At the same time, the rapid development of large traffic tools, such as electric vehicles, hybrid electric vehicles and other large electric equipment, also puts forward the capacity of lithium ion batteries in terms of capacity. Higher requirements. Negative electrode material is one of the key materials affecting the capacity of lithium ion batteries. As one of the outstanding representative of the new anode material, the theoretical mass ratio (993mAh/g) of the tin based alloy negative electrode is nearly three times that of the graphite negative electrode. However, the material is accompanied by a huge volume deformation (260%) during the charge discharge process, which leads to the material. This phenomenon is the key to the market application of tin based alloy negative electrode during charge discharge, which is the key to the market application of tin based alloy negative electrode material. There are many ways to improve the cycle performance of tin based alloy negative electrode material, and the composite of carbon materials is one of the effective ways, and the report of composite with carbon nanotubes is increasing gradually. The integrated electrode material can reduce the redundant connection components (conductive agent and binder) of the traditional electrode in the integration process, thus improving the utilization of space and materials, so the type electrode is also widely used in tin based negative electrode materials.
In this paper, aiming at the commercialization of tin based alloy negative electrode, in view of the above shortcomings of tin based alloy negative electrode, using the idea of integration of fluid collection and active material, using low production cost, simple process electrodeposition and heat treatment process, the electrode of different structure types was prepared, and its microstructure and storage were also made. Lithium properties have been studied. The innovative research results obtained in this paper are as follows:
(1) in order to improve the cyclic performance of the tin copper alloy negative electrode, we formed an integrated Cu6Sn5 alloy negative electrode under the condition of low temperature and short-time heat diffusion treatment based on the multilayer structure of tin / copper alternately. The effects of heat treatment temperature and other parameters on the structure and cyclic properties of the electrode materials were investigated by heat treatment. The results showed that the alloy components formed by the heat treatment of multilayer structure materials were different because of the different atomic activity at different temperatures. The multilayer structure material was treated at 200 degrees C and heat treated for 30min. The optimal electrochemical performance, electrode capacity and the electrode material than the traditional preparation method of the higher cycle is more stable, after 40 cycles, the capacity is higher because of the advantages of traditional tin copper alloy anode electrode is 26.9%. the electrode active material is mainly Cu6Sn5 phase, and the material grains in heat treatment after a little change.
(2) in order to alleviate the material pulverization of tin based anode materials during charging and discharging, based on the high strength and high conductivity carbon nanotubes, we prepared the Sn-CNTs integrated electrode material with the tin metal anode. We prepared the Sn-CNTs composite electrode by composite electrodeposition, and the process parameters for the preparation of the composite electrode were made. The effect of the diameter of CNTs on the performance of the electrode cycle was studied. The results showed that the content of CNTs changed with the current density, and the cycle performance of the electrode with the diameter range of (10~20nm) was the most obvious. The best cycle performance of the electrode was that the CNTs content in the electrode was the highest and the internal resistance was the least.
(3) in order to enhance the combination of fluid collector and active material to further slow the material pulverization of Sn Cu alloy negative material during charge discharge process, based on the Sn-CNTs composite electrode, based on the Cu-CNTs composite coating, the Sn/Cu-CNTs double layer structure electrode was designed to enhance the active material (tin copper alloy) and the fluid collector (copper). Sn-Cu-CNTs integrated electrode materials were obtained by electric connection and final heat treatment. We first prepared Cu-CNTs composite coating on copper foil substrate by electrodeposition, and then electrodeposited a certain thickness of tin coating. Finally, the Sn-Cu-CNTs integrated electrode was obtained by heat treatment. The surface morphology of the composite coating was first studied. The influence of the content of carbon nanotubes was studied. The effect of heat treatment temperature on the electrochemical performance of electrode was studied. The results showed that the morphology and carbon content of the Cu-CNTs composite coating changed with the current density, and the performance of the electrode was the best after heat treatment at 200 c for 6h. The optimal cycle performance of the electrode was the electrode active material crystal. Fine particles are well integrated with the collector. CNTs is tightly linked with active materials, and can play a role in the connection between framework materials and conductive materials.
(4) in order to improve the content of carbon nanotubes in active materials and to improve the cycling performance of tin based alloys, we designed the Sn-CNTs/Cu-CNTs composite electrode by combining the Sn-CNTs active material with the Cu-CNTs connection layer on the basis of the Cu-CNTs connection layer. We used the composite electrodeposition to deposit the Cu-CNTs complex with copper foil as the base. Sn-CNTs/Cu-CNTs composite electrode was prepared by electrodeposition of Sn-CNTs composite coating, and the effect of heat treatment time on the performance of electrode cycle was studied. The results showed that after 6h heat treatment, the cycle performance of the electrode was the best, and the capacity of 100 cycles after charge discharge was 584.4mAh/g at 1C ratio. The performance of the electrode has a good performance. When charging and discharging at the 20C ratio, the capacity of the electrode can still reach the optimal cycle performance of the 434.6mAh/g. electrode. The internal distribution of the electrode has a large number of CNTs, the internal resistance is relatively small, the ionic conductivity is good, and the inner pore structure exists in the electrode, which can be the body of the tin and copper alloy in the process of lithium-ion removal. Product variation provides buffer space; the electrode structure is mainly Cu6Sn5, and the content of Sn and Cu3Sn is relatively small.
In this paper, the cyclic properties of tin copper alloy negative materials are greatly improved by the design of integrated tin based alloy negative materials with different structural types and low cost and low cost. Since this paper uses an integrated electrode material, it reduces the redundant connection components and thus improves the volume capacity of the whole battery as a Merchant of the material. The industrial application laid a solid foundation.
【学位授予单位】：湘潭大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TM912

【共引文献】