【作者】 瞿佰华；

【导师】 王太宏；

【作者基本信息】 湖南大学 ， 材料科学与工程， 2014， 博士

【摘要】 “能源危机”和“环境污染”是人类在21世纪必须面对的两个严峻问题,电动汽车和大规模绿色储能电网的发展是解决此问题的主要途径。锂(钠)离子电池、超级电容器等电化学储能器件凭借高能量密度、大功率特性、长使用寿命、价格廉价和绿色环保的优势,已逐渐成为电动汽车(减少对化石燃料的依赖和二氧化碳排放)最有竞争力的动力电源和绿色电网储能(加快发展可再生清洁能源)最有潜力的储能电池,特别是锂离子电池和钠离子电池对发展电动汽车和大规模绿色储能电网有重要意义。目前,锂离子电池和钠离子电池负极材料主要是石墨和其他碳材料,而碳负极的储锂和储钠容量有限,极大地限制了目前的锂离子电池和钠离子电池的能量密度进一步的提高,单纯通过改进制备工艺来提高性能已难以取得突破性进展。因此,开发具有高比容量、高倍率、长寿命的锂离子电池和钠离子电池电极材料急剧迫切性。最近的研究进展证明硫化物具有比较好的储锂和储钠性能,主要是由于其具有独特的物理和化学性能。本论文中,我们合成了SnS2-RGO复合材料,三元Cu2SnS3和CuFeS2等硫化物复合材料,并对材料的储锂和储钠性能进行系统研究,主要内容和创新点如下：(1)在第2章中,我们设计了一种二维(2D)层状SnS2-RGO复合材料具有非常高的可逆储锂性能,极好储锂性能主要表现在,第一：具有非常高的储锂比容量和极好的循环性能(电流密度为0.2A g-1时100次循环之后比容量高达1063mAh g-1,并且在电流密度为1A g-1时500次循环之后比容量仍然有918mAh g-1)；第二,2D层状SnS2-RGO复合材料具有极好的可逆嵌锂和脱锂,首次的库伦效率高达89.7%,第三,2D层状SnS2-RGO复合材料也展现出极好的倍率性能,当电流密度为5A g-1时,储锂比容量高达712mAh g-1,显著的电化学储锂性能主要是由于其独特的二维层状结构。(2)钠离子电池相比于锂离子电池具有成本上的优势将有可能大规模应用到绿色储能电网领域,最近几年,钠离子电池电极材料的进展引起了广大电池研究者的研究兴趣。在第3章中,我们首次以层状SnS2-RGO复合材料应用到钠离子电池负极材料,复合材料展现出非常高的嵌钠和脱钠比容量(电流密度为0.2A g-1时,首次充电容量为630mAh g-1)；极好的倍率性能(电流密度为2A g-1时,储钠容量高达544mAh g-1);和稳定的循环性能(经过恒流充放电400次,钠存储容量稳定在500mAh g-1),是到目前为止报道的最好的钠离子电池负极材料。如此好的储钠性能主要是由于层状SnS2具有比较大的层空间,该结构有利于钠离子的快速嵌入和脱出,并且能缓冲在钠锡合金形成过程中大的体积变化；并且石墨烯和SnS2之间的强相互作用和高导电率的石墨烯使复合材料在充放电过程中有较快的电子传导速率和收集效率。(3)在第4章中,我们采用简单的溶剂热法合成了三元Cu2SnS3介孔纳米球和卷心菜状纳米花,我们研究了硫源和表面活性剂对不同形貌的Cu2SnS3硫化物材料的形成机理和过程的影响,并且通过循环伏安测试和充放电过程中的XRD测试研究了Cu2SnS3纳米材料的电化学反应机理。通过储锂(锂离子电池)性能测试比较,发现卷心菜状Cu2SnS3纳米花比介孔纳米球有更好的储锂性能,首次可逆脱锂比容量高达842mAh g-1,并且50次充放电之后仍然有621mAh g-1,而介孔纳米球50次循环之后比容量仅有436mAh g-1。(4)在第5章中,我们采用简单的溶剂热法合成了一种新颖的三元CuFeS2微米结构,三元CuFeS2微米电极材料具有较好的储锂性能,具体表现为：在电流密度为0.2A g-1充放电时,其首次放和充电容量分别为767mAh g’1和614mAh g-1,首次库伦效率高达80%；当电流密度为2A g-1时,放电比容量仍有-400mAh g-1;值得一提的是其循环性能,经过400次大电流(0.5A g-1)充放电测试后,比容量始终维持在-600mAh g-1。并且我们也研究了其储钠性能,首次放电比电容量(嵌钠)为628mAh g-1、充电(脱钠)比容量为511mAh g-1,相应的首次不可逆比容量损失率为18.6%。我们所合成的三元CuFeS2微米材料制备方法简单并且原材料价格便宜,特别是表现出优异的储锂性能,并且初步探索了其材料的储钠性能,为研究其他硫族化合物作为锂离子电池和钠离子电池负极材料提供宝贵的经验和广阔的思路。更多还原

【Abstract】 "Energy crisis" and "environmental pollution" is the two serious problems, which have received considerable attention since2000s. The development of electric vehicles (could be decrease dependence on fossil fuels and reduced carbon emissions) and large-scale green energy storage system (deployment of renewable energy resources) is the main way to solve this problem. Lithium (sodium) ion battery and supercapacitor et al, with the many advantages, such as:high energy density, high power density, long life, cheaper and environmental protection, have become the most promising electrical energy storage. Now, the commercialized graphite and other carbon for lithium (sodium) ion batteries are very difficult to break through performance it only from the battery assembly technological. Especially, the lithium ion battery and sodium ion battery has important significance for the development of electric vehicle and large-scale green energy storage. Therefore, the development high performance lithium ion battery and sodium ion battery electrode material is more and more importance. Recent progress has demonstrated that sulphide composites are very promising candidates of electrode material for lithium (sodium) ion battery based on their unique physical and chemical properties, such as conductivity, mechanical and thermal stability and cyclability. In this paper, we have fabricated SnS2-Graphene composite, ternary Cu2SnS3and CuFeS2, which were researched their lithium (sodium) storage properties. The main results and new findings in this work are summarized as follows:(1) In chapter2, we design a novel2D layer SnS2/graphene nanosheet composite with highly reversible lithium ion storage. The high lithium storage performance exhibit in three aspects:first, the specific capacity of this composite is high and good cycle life (it could deliver a charge capacity of1063mAh g-1for at least100cycles at0.2A g-1and918mAh g-1even after500cycles at1A g-1); second, the first cycle columbic is as high as89.7%; third, this composite electrode still could deliver a reversible capacity of712mAh g-1at5A g-1. The outstanding electrochemical performance of this composite is due to the unique2D layer structure of this composite.(2) The idea of sodium-ion batteries as a substitute of lithium-ion batteries for grid-scale energy storage was initially driven by cost considerations. Hence there is a strong current interest in research high-performance sodium-ion batteries electrode marterials. In chapter3, we have firstly developed a SnS2-RGO composite with excellent electrochemical performance as the anode of sodium-ion batteries. The SnS2-RGO electrode demonstrated a high charge specific capacity (630mAh g-1at0.2A g-1), good rate performance (544mAh g-1at2A g-1) and long cycle-life (500mAh g-1at1A g-1for400cycles). The performance surpasses any other NIB anode reported in the literature to date. The excellent electrochemical performance could be attributed to the SnS2layered structure where the increased interlayer spacing could better accommodate the volume change in Na-Sn insertion and de-insertions; and fast collection and conduction of electrons through a highly conductive RGO network.(3) In chapter4, ternary Cu2SnS3mesoporous nanospheres and cabbage-like nanostructures are synthesized by a simple solvothermal route. A different structures formation mechanism was controled by the reactant and surfactant. Besides, a possible electrochemical reaction mechanism was proposed based on cyclic voltammetry testing results and confirmed by subsequent ex situ XRD studies. By comparison, the Cu2SnS3nanostructures electrodes deliver a better lithium storage and cycle life performance, which is the first reversible capacity as high as842mAh g"1and remain at621mAh g"1after50cycles (only436mAh g-1after50cycles of mesoporous nanospheres).(4) In chapter5, we report a novel ternary CuFeS2microstructure by a simple solvothermal route. The CuFeS2microstructures have been shown an admirable lithium storage property. The first discharge and charge specific capacity of767and614mAh g-1at0.2A g-1, respectively. The first coulombic efficiency is80%. A good rate performance up to4A g"1, the discharge specific capacity is-400mAh g-1. The electrode was also very stable to cycling; providing a nearly unvarying capacity of-600mAh g-1at0.5A g-1even after400charge-discharge cycles. We have also studied the sodium storage property of the CuFeS2microstructures. The first discharge specific capacity628mAh g-1is and charge specific capacity of511mAh g-1, which is the the initial irreversible capacity loss of18.6%. The ternary CuFeS2microstructure is showing excellent lithium storage performance, and the synthesis approach is very simple and inexpensive. This is providing valuable experience for studing other sulphide materials as lithium (sodium) ion battery.更多还原