铜修饰多孔硅电极的制备及其结构、性能的研究

论文总字数：49339字

摘 要

镁热还原法广泛应用于锂电池负极材料纳米多孔硅的制备过程中，但此前由镁热反应引起的过热效应一直被认为会使得材料性能劣化。本文介绍了一种利用镁热反应的过热效应来制备多孔硅的简易制备技术，即先通过压片处理将混合反应物压成片体，使得反应热能在片体积累，导致二氧化硅前驱体介孔结构的崩塌、合并，从而形成均一的大孔硅结构。与未压片制得的介孔硅相比，预压片制备的大孔硅首次库伦效率更高（86.5%），循环稳定性也更好（60次循环之后放电比容量为1260mAh·g^-1）。XRD分析显示预压片之后，镁热还原反应的温度大幅下降至430-435^oC（基于管式炉设定温度），远低于未压片时的反应温度（开始温度在500-550^oC之间，结束温度在600-650^oC之间），显著降低了加热过程的能耗。同时，压片后反应对升温速率的敏感性降低，提高了工业化生产的适应性。此外，产物的大孔结构对于前驱体的依赖性降低，使得多种二氧化硅前驱体，如生物质二氧化硅等，均可用于大孔硅的制备之中。预压片法能有效降低反应温度、降低样品温升敏感度和对前驱体依赖性，所制备的大孔硅作为锂电池负极材料具有较高的首次库伦效率和良好的循环稳定性。

利用金属铜电子导电率高、延展性好等特点，创新性地使用了“浸渍-氢还原法”在介孔硅/大孔硅表面修饰铜颗粒。铜颗粒在多孔硅表面、孔道内分布均匀。铜颗粒主要为硅在锂离子脱出的过程中（充电过程）提供了结构支撑，阻碍了孔道的塌缩、崩裂；同时，在锂离子的嵌入过程中（放电过程），铜颗粒与硅相互挤嵌，限制了硅的过度膨胀变形，从而延缓了硅的粉化的发生，使得材料的循环稳定性得到提升。同时，添加Cu颗粒之后提高了硅表面的导电性，为电子从集流体到每个硅颗粒颗粒表面的传导提供了渗流路径，使得Si-Cu复合物的电子迁移阻抗显著降低、高倍率放电能力显著提升。随着CuCl₂浸渍液浓度的提升，两类Si-Cu复合物的循环稳定性和高倍率放电能力都得到了明显提升。

本文所使用的“改良镁热还原法”、“浸渍-氢还原法”具有简便、适应性强等优点，可推广应用于硅电极规模化生产。此外，作为石墨碳素电极的替代材料，本文所制备的大孔硅、硅-铜复合物具有比容量高、循环性能好、倍率性能好等优势，因而具有广阔的市场前景。

关键词：多孔硅-铜复合物 大孔硅 硅负极材料 锂离子电池

Abstract

Magnesiothermic reduction is an extensively used synthesis method for preparation of nano-porous silicon as anode materials for Li-ion batteries. Overheating caused by exothermic nature of magnesiothermic reduction reaction is generally considered as a drawback in preparing porous silicon. A facile preparation strategy taking advantage of thermal effect was developed in the present work by tabletting pretreatment. The released heat in reaction became easier to accumulate on the tablet with high density, leading to the collapse of the mesoporous structure of the precursor and formation of uniform macroporous silicon. Such macroporous silicon show a higher initial Coulomb efficiency (86.5%) and enhenced cycling stability (reversible capacity of 1260mAh·g^-1 after 60 cycles) compared to mesoporous silicon prepared without tabletting treatment. XRD analysis informs that the reaction temperature decreased to 430-435^oC (based on set temperature), much lower than starting temprature (500-550℃) and ending temperature (600-650 ℃) of the reaction without pretreatment, which is significant for reducing energy consumption. And this process is less sensitive to the heating rate, uniform macroporous structure can also be obtained at a lifted heating rate of 3℃·min^-1 or 5℃·min^-1, which is of great significance for industrial production. Moreover, the structure of product less depends on precursor, so that a wide variety of precursors can be used to synthesize macroporous silicon, such as low cost biosilica. With the advantages of low reaction temperature, heating rate insensitivity, less dependency on precursor, good cycling performance and high initial Coulomb efficiency of the Si products.

Taking advantage of high conductivity and ductility of copper, a facile preparation strategy was developed by impregnation-hydrogen reduction method to assembly copper nano particles into mesoporous/macroporous silicon particles surface. Homogeneously distributed nano copper particles were observed on the surface of porous silicon. The copper particles provide structural support for porous silicon during the lithium intercalation process (discharging process) and effectively inhibit the collapse of pores. Meanwhile, copper particles and silicon squeeze each other during the lithium deintercalation process (charging process), which limits the excessive expansion of silicon, slows down the silicon anode pulverization and promotes the cyclic stability. At the same time, deposited copper particles improved the electrical conductivity of Si-Cu composite surface and provide an electron transferring paths from the current collector to the whole surface area of individual active particles (porous silicon particles), which significantly reduced material’s electron migration impedance and increased the rate capability. With the increase of the concentration of CuCl₂ solution, both capacity retention and rate capability were remarkably improved.

The revised magnesiothermic reduction method and immersion-hydrogen reduction method developed in this paper exhibit the advantages of simplicity and adaptability, which can be applied to the commercial large scale production of silicon electrodes. In addition, as an alternative material for graphite carbon electrode, the porous silicon and porous Si-Cu composites prepared in this paper

shows a remarkably improved lithium-storage performance, good cyclic stability and rate capability, which displays a promising application prospect.

Key words porous silicon-copper composite, macroporous silicon, silicon anode material,lithium ion battery

目 录

摘 要......................................................................................................................................................I

Abstract............................................................................................................................................... Ⅱ

第一章 绪论........................................................................................................................................ 1

1.1 引言................................................................................................................................. 1

1.2 锂离子电池硅负极材料研究进展................................................................................. 1

1.2.1 硅-碳复合体系的研究.......................................................................................... 2

1.2.2 硅-铜复合体系的研究.......................................................................................... 6

1.2.3 其他复合体系的研究........................................................................................... 9

1.3 本论文的研究目的及主要内容....................................................................................10

第二章 实验方法与仪器.................................................................................................................. 11

2.1 实验药品与材料........................................................................................................... 11

2.2 实验用仪器与设备....................................................................................................... 11

2.3 电极材料制备与处理方法........................................................................................... 12

2.3.1 二氧化硅SBA-15............................................................................................... 12

2.3.2 镁热还原法制备介孔硅 ....................................................................................13

2.3.3 预压片-镁热还原法制备大孔硅.........................................................................13

2.3.4 “浸渍-氢还原法”制备Si-Cu复合......................................................................13

2.4 电极制备与实验电池装配............................................................................................14

2.4.1 电极的制备..........................................................................................................14

2.4.2 实验电池装配......................................................................................................14

2.5 电化学性能测试............................................................................................................15

2.5.1 电池充放电循环实验..........................................................................................15

2.5.2 电池倍率放电实验..............................................................................................16

2.5.3 循环伏安曲线和交流阻抗曲线..........................................................................17

2.6 材料的形貌与组成表征................................................................................................18

2.6.1 X射线衍射分析....................................................................................................18

2.6.2 BET氮吸附孔径分析...........................................................................................18

2.6.3 扫描电子显微镜..................................................................................................18

2.6.4 透射电子显微镜..................................................................................................18

第三章 介孔硅、大孔硅的制备及电化学研究.................................................................................19

3.1 引言................................................................................................................................19

3.2 介孔硅和大孔硅的制备与结构分析............................................................................19

3.3 制备介孔硅和大孔硅的反应过程分析........................................................................22

3.4 介孔硅和大孔硅电极的电化学性能............................................................................28

3.4.1 充放电循环性能..................................................................................................28

3.4.2 倍率放电能力......................................................................................................29

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