【作者】 马萍；

【导师】 张宝宏；

【作者基本信息】 哈尔滨工程大学 ， 材料学， 2007， 博士

【摘要】 单质硫的理论比容量高，是新一代高能二次锂电池中有应用潜力的正极材料。但由于其电子和离子的绝缘性以及溶剂可溶性，锂／硫电池的活性物质利用率低，容量衰减快。因此硫单质硫正极材料必须和导电剂有很好地接触。本论文设计并制备了活性炭一硫，导电聚合物-硫，氧化物-硫三类复合材料作为锂电池正极用电化学活性物质，借助X-射线衍射和扫描电镜对样品的结构形貌进行表征，通过恒电流充放电、循环伏安、电化学交流阻抗等电化学测试研究了复合材料的电化学性能。通过热处理方法制备单质硫-活性炭复合材料，当单质硫含量为78.2％时，首次放电比容量高达1057.8mAh·g^-1，30次循环后仍可保持在400mAh·g^-1左右。氧化物-硫复合材料包括二氧化钛-硫，五氧化二矾-硫和二氧化铈-硫三种材料：采用五氧化二钒改性的硫材料，首次放电比容量达844.68mAh·g^-1，样品循环容量衰减明显改善，30次后比容量保持在696.71 mAh·g^-1；而物理混合法制备的二氧化钛-单质硫复合材料，初始放电比容量为600.83mAh·g^-1，30次循环后比容量为419.34mAh·g^-1；化学沉积法二氧化铈-单质硫复合材料中CeO₂在硫颗粒表面形成了一层膜，复合材料在电流密度为0.2 mA·cm^-2的条件下充放电，首次放电容量达到731.25mAh·g^-1，经过30次充放电循环后，容量保持在468.39 mAh·g^-1，电化学阻抗谱表明，CeO₂的包覆使得电化学反应阻抗减小了。导电聚合物-硫复合材料包括聚苯胺-硫和聚氧化乙烯-硫两种材料。原位聚合法制备的聚苯胺包覆硫复合材料，以0.2mA·cm^-2电流密度充放电，含聚苯胺为15％的聚苯胺／硫复合材料的首次放电容量为1134.01mAh·g^-1，比未改性硫电极增加了82.42％；充放电循环30次后放电电容量为526.89 mAh·g^-1，容量衰减仅为明显减少。当充放电电流密度提高到0.3mA·cm^-2，0.4mA·cm^-2时，聚苯胺-硫复合材料的放电容量分别为704.81mAh·g^-1，194.77mAh·g^-1。改性后的聚苯胺-硫复合材料的电化学性能得到了较大的改善。聚氧化乙烯-单质硫复合材料是通过热处理的方法制备的，PEO与单质硫质量比为1：3时，首次放电比容量为843.45mAh·g^-1，到第30次放电时，比容量为438.64 mAh·g^-1，大于已经商业化的锂离子正极材料LiMn₂O₄和LiCoO₂的理论比容量。结果表明，PEO不仅能够起到导电剂的作用，而且其网络结构对再生硫的团聚起到抑制的作用。锂离子蓄电池负极材料锂钛复合氧化物Li₄Ti₅O₁₂是一种“零应变”材料。具有应用在电动汽车、储能电池等方面的优良前景。本文选用Li₂CO₃作为锂源，与活性较高的无定型TiO₂固相法合成了锂钛复合氧化物Li₄Ti₅O₁₂，研究了考察温度，时间，比例关系等合成条件对其结构及电化学性能的影响。Li₂CO₃过量8％，在800℃的煅烧温度下保温24h制备的Li₄Ti₅O₁₂首次放电比容量163mAh·g^-1，60次充放电循环后为156.0mAh·g^-1，容量保持为95.6％。固相法制备了C改性的Li₄Ti₅O₁₂，以LiCoO₂为正极组装为全电池，当电流密度为0.1mA·cm^-2，电池的初始放电比容量为122.9mAh·g^-1，100次后比容量衰减仅为3.43％。当电流密度增大时，容量呈下降趋势，但是容量衰减率逐渐减小了。物理混合法和化学沉积法制备SnO₂改性Li₄Ti₅O₁₂复合材料，并将这两中方法与未改性的Li₄Ti₅O₁₂进行了对比，物理混合法能有效地抑止Sn体积的膨胀，表现出更好的循环性能，15次循环后，比容量为207.7mAh·g^-1。Sb₂O₃掺杂改性Li₄Ti₅O₁₂得到复合材料Li₄Ti_5-xSb_xO₁₂进行测试，提出了可能的反应机理。结果显示，掺杂后x=1材料的首次放电容量高达595·84mAh·g^-1，首次充放电效率为45.7％，存在首次不可逆容量损失，经过20次充放电循环后，比容量保持在249.57 mAh·g^-1，具有较好的循环性能，是一种较好的锂离子电池负极材料。更多还原

【Abstract】 Elemental sulfur has been proposed as promising cathode materials for the next generation of high-performance rechargeable lithium batteries due to their high theoretical capacity. However, they exhibit low utilization and fast capacity fades in lithium batteries due to their electrically and ionically insulated nature as well as solvent-solubility. Therefore, the cathode material must be well combined with a conductive agent when prepared as an electrode.In this study, three types of sulfur composite materials were prepared, that is: active carbon-sulfur composites, conductive polymer-sulfur composites and oxide-sulfur composites, which can be used as advanced cathode materials for rechargeable lithium batteries. The structure of the prepared cathode material was characterized by XRD.The electrochemical performance of sulfur composite electrodes was investigated by galvanostatic charge/discharge, cycling voltammetry methods and AC impedance.Sulfur-carbon composites were prepared by thermal treatment. The composites with favorable sulfur contents exhibited high specific capacity up to 1057.8 mAh/g in the initial cycle and a stable reversible capacity approximately 400 mAh/g.Oxide-sulfur cathode materials have been synthesized by mechanical milling or chemical aggradation, using mixture of oxides （V₂O₅, TiO₂, and CeO₂） and elemental sulfur. Combined with gel polymer electrolyte, the V₂O₅-S composites exhibited high specific capacity up to 844.68 mAh·g!（-1） in the initial cycle and a stable reversible capacity approximately 696.71 mAh·g^-1 after 30 cycle numbers. The discharge capacity of TiO₂-S is 600.83 mAh·g^-1 in the first cycle and 419.34 mAh·g^-1 in the 30th cycle. CeO₂-sulfur composites were prepared by depositing CeO₂ on the surface of sulfur power. The results indicated that the appending of CeO₂ formed a thin layer over sulfur particles. The initial capacity of CeO₂-sulfur composite was as high as 731.25 mAh·g^-1. The capacity was still 468.39 mAh·g^-1 after 30 charge-discharge cycles. EIS results showed that CeO₂-coating could suppress the electrochemical reaction resistant.Conductive polymer-sulfur composites were containing polyaniline-sulfur composites and poly ethylene oxide-sulfur composites.A novel conducting sulfur-polyaniline composite material was prepared by the chemical polymerization method .When the cathode materials are cycled at 0.2mA·cm^-2, the polyaniline/sulfur composites containing 15% polyaniline can delivered 1134.01mAh·g^-1 at the first discharge which is 82.42% higher than that of bare sulfur, the capacity was still 526.89 mAh·g^-1 after 30 charge-discharge cycles. When the discharge current density reaches up to 0.3mA·cm^-2, 0.4mA·cm^-2, the capacity of polyaniline/sulfur composites are 704.81mAh·g^-1,194.77mAh·g^-1 respectively. Poly （ethylene oxide） -sulfur composite was prepared by the thermal treatment method. The cathode with poly （ethylene oxide）-sulfur composite material shows the improvement of not only the charge-discharge capacity but also cycle durability.When the ratio of poly （ethylene oxide） and sulfur is 1:3, the cmposites can delivered 843.45mAh·g^-1 at the first discharge,after 30 cycles, the discharge capacity was 438.64 mAh·g^-1.The lithium titanium oxide Li₄Ti₅O₁₂ as anode material for lithium ion battery is regarded as a"zero strain"material. The lithium ion battery using Li₄Ti₅O₁₂ material as anode material is suitable for electric vehicle （EV） and power storage battery.In this paper, Li₄Ti₅O₁₂ was synthesized by amorphous titanium dioxide TiO₂ and Li₂CO₃ as lithium sources. Influential factors such as temperature, materials, time and proportion of reactants were researched. Pure spinel Li₄Ti₅O₁₂ can be synthesized by solid phase reaction at 800℃for about 24h, with excessive 8% Li₂CO₃. investigated. The results showed that the initial discharge capacity was 163mAh·g^-1, after 60 cycles, the specific capacity was 156.0mAh·g^-1, Its cycle retention rate after 60 cycles was 95.6%.Li₄Ti₅O₁₂ modified by C was obtained by solid state reaction. The system used LiCoO₂ as cathode was characterized. The results showed that, the battery’s initial discharge specific energy was 122.9mAh·g^-1 with the current density 0. 1 mA·cm^-2, and decreased only by 3.43% after 100 cycles. The capacity was decreased as current density increased. But the rate of decrease was declined.Spinel Li₄Ti₅O₁₂ was modified by SnO₂ by physical and chemical procedures respectively. Both of the two procedures were compared with pure Li₄Ti₅O₁₂ to find the favorable way that could improve the performance.The experiments demonstrate that the physical procedure could restrain the bulk swell of Sn effectively and delivered promising electrochemical performance. After 15 cycles, its capacity is 207.7 mAh·g^-1。Li₄Ti₅O₁₂ was modified by doped Sb₂O₃. The composites materials Li₄Ti_5-xSb_xO₁₂ were characterized by constant current charge-discharge, cyclic voltammetry and electrochemical impedance spectrum. And the possible principle of reaction was proposed. The results showed that, when x=1, the initial discharge specific energy was 595.84mAh·g^-1 and the initial charge-discharge efficiency was only 45.7%.. After 20 cycles, the specific energy was still 249.57mAh·g^-1 which showed better cyclicity and can be a kind of preferable lithium ion battery.更多还原