【作者】 王海波；

【导师】 陈立泉； 黄可龙； Ulrich.Stimming；

【作者基本信息】 中南大学 ， 应用化学， 2008， 博士

【摘要】 本论文主要由两部分构成,第一部分是关于水溶液锂离子电池的电化学性能、循环容量衰减机理及其稳定方法的研究;第二部分是关于中温燃料电池用聚磷酸铵基质子导体电解质制备、表征和电化学性能的研究。水溶液锂离子二次电池结合了非水电解液锂离子电池和传统水溶液电池的优点,消除了使用有机电解液而存在的燃烧、爆炸等安全隐患,其在低电压电池如铅酸电池、碱锰电池等领域存在很大的竞争潜力。但是水溶液锂离子电池循环寿命太短,此前对于其循环容量衰减机理还不是很清楚,对于循环寿命提高的方法也没有报道。同时,由于受到水溶液锂离子电池电化学窗口的限制,具有明显电池充放电特性的阳极材料选择十分困难。中温燃料电池结合了高温燃料电池和低温燃料电池的优点,避免了低温条件下催化剂CO中毒和高温条件下电池制作材料的高要求,是一种很有发展潜力的燃料电池。聚磷酸铵基复合物由于其较高的质子电导性而成为中温燃料电池电解质备选材料。虽然目前聚磷酸铵基复合物的电导率已经可以达到实用化的要求,但是对于该类复合物的电导率稳定性和材料结构的变化研究还不够,研究开发高电导率、高稳定性的聚磷酸铵基复合物质子导体对于推进中温燃料电池的发展至关重要。本论文针对上述两个体系存在的不足,开展了如下工作:首次提出了采用导电聚合物对阳极材料进行表面包覆以稳定其在水溶液中的电化学性能的方法,实现了对水溶液锂离子电池循环寿命的提高。首先对水溶液锂离子电池体系的集流体、电极材料以及电解液的pH值进行了考察和筛选,建立了水溶液锂离子二次电池组合LiNi_1/3Mn_1/3Co_1/3O₂/5 M LiNO₃（pH 11）/Li_xV₂O₅。研究了该体系电池的循环性能下降的原因。XRD和ICP的检测结果表明阳极对电池容量衰减的影响远大于阴极。通过采用聚苯胺对阳极的表面包覆,明显地提高了电池的循环寿命。同时还对聚苯胺包覆阳极提高电池循环寿命的机理进行了研究,为水溶液锂离子电池循环寿命提高提供理论依据。对电池组合LiMn₂O₄/5 M LiNO₃/Li_xV₂O₅的容量衰减原因进行进一步考察。研究了阴阳极材料以及过渡金属溶解量随循环次增加的演变过程。采用原位聚合法,在阳极表面进行聚吡咯包覆以提高水溶液锂离子电池循环寿命。通过阳极表面包覆,电池的循环寿命由20次左右增加到60次以上（容量保持80%以上）,为此前文献报道中的最高值。比较了包覆前后电解液中过渡金属离子溶解度的变化情况以及包覆聚吡咯对活性材料和集流体之间粘结力的影响。此外,还考察了阳极表面聚吡咯不同包覆量对电池循环稳定性的影响。采用具有3D结构的TiP₂O₇和LiTi₂（PO₄）₃等聚阴离子化合物作为水溶液锂离子二次电池的阳极。以LiMn₂O₄为阴极分别与上述两种材料组成电池TiP₂O₇/5 M LiNO₃/LiMn₂O₄和LiTi₂（PO₄）₃/5M LiNO₃/LiMn₂O₄,基于电极活性物质重量,前者放电容量为42mAh g^-1,平均电压为1.40 V;后者放电比容量为45 mAhg^-1,平均电压为1.50 V。LiTi₂（PO₄）₃是一种很好的快离子导体,采用循环伏安法研究了锂离子在LiTi₂（PO₄）₃中的扩散系数,结果表明锂离子在该材料中具有很高的扩散系数,充电和放电过程为别为6.08×10^-5,2.24×10^-5cm² s^-1。考察了不同嵌锂量时LiTi₂（PO₄）₃晶胞参数的变化情况。当嵌锂量为1.8时,晶胞体积变化最大,为1.28%。该部分内容的研究为水溶液锂离子电池的进一步发展提供新的平台。考察了（NH₄）₂SnP₄O₁₃复合物作为中温燃料电池用电解质在分别在干燥氢气、氮气、空气以及潮湿氢气、氮气、空气中的电导率情况。干燥气氛中,当采用氢气,温度为275℃时,该材料得到最高电导率为13.8 mScm^-1;潮湿气氛中,在氢气中得到最高电导率,其值为35.5 mScm^-1。（NH₄）₂SnP₄O₁₃复合物电导率的研究丰富了中温燃料电池电解质备选材料。采用固相法制备了系列（NH₄）₂Si_1-xTi_xP₄O₁₃复合物,系统考察了该系列复合物在不同气氛中的电导率以及不同Ti含量对复合物电导率的影响。在干燥气氛和潮湿气氛下,分别得到最高电导率为0.68mS cm^-1和30.8 mS cm^-1。其中复合物（NH₄）₂Si₅₀Ti₅₀P₄O₁₃在干燥和潮湿气氛中表现出较好的综合性能。因此,实验对（NH₄）₂Si₅₀Ti₅₀P₄O₁₃的电导率稳定性、热稳定性以及结构变化情况进行了一步考察,对其在中温燃料电池中的实际应用具有十分重要的价值。更多还原

【Abstract】 This thesis is composed of two parts. The first part is study on electrochemical properties, capacity fading mechanism and improving cycle life method of aqueous lithium ion batteries. The second part is study on preparation, characterization and electrochemical properties of ammonium polyphosphate based composites for intermediate temperature fuel cells.Aqueous lithium ion batteries have the advantages of non-aqueous lithium ion battery and traditional secondary batteries with aqueous electrolyte, which will eliminate burning, explosive crisis resulted from organic electrolyte. It has competitive potential compared with lead-acid, nickel-cadmium and some other low voltage batteries. However, the cycle life is short and the reasons on capacity fading are still not very clear at present. Moreover, the candidate with flat charge/discharge curve for the anode is very limited.Intermediate temperature fuel cells are very attractive because they combine the advantages of high- and low-temperature fuel cells. This kind of fuel cells avoids the catalyst poisoning at low temperature and high requirement on assembling materials at high temperature. Ammonium polyphosphate based composites are promising electrolyte for this kind of fuel cells. However, the studies on conductive stability and structure transformation during measuring process are very little. Research and development on ammonium polyphosphate based composites with high conductivity and high stability will be significant to the application of intermediate temperature fuel cells.In this paper, the following contents are included:First, selection and investigation on current collector, active materials, and the pH value of the electrolyte were conducted. Reasons of capacity fading of LiNi_1/3Mn_1/3Co_1/3O₂/5 M LiNO₃ （pH 11） / Li_xV₂O₅ lithium ion cell based on structure and dissolution of transition metals were investigated preliminarily. XRD and ICP results showed that the properties of the anode have more impact on the cycle life of the cell. In order to stabilize the cycling capacity of the anode, thus improve the cycle life of the cell, coating with an ionic conductive polyaniline （PAn） on the surface of the anode was proposed. Cycle tests revealed that the stability of the lithium ion cell with surface coated anode has greatly improved. The improving mechanism of surface coating by PAn was also investigated.More details on capacity fading during cycling process of LiMn₂O₄/ Li_xV₂O₅ lithium ion cell with 5 M LiNO₃ aqueous solution as electrolyte was investigated. In order to improve the cycle performance of the as-assembled cell, coating with an ionic conductive polypyrrole （PPy） on the surface of the anode was proposed via in-situ polymerization method. Cycling tests revealed that the stability of the lithium ion cell with surface coated anode was greatly improved. Moreover, the effect of different coating amount of polypyrrole on the cyclability of the lithium ion cell was investigated. The force between electrode and current collector affected by PPy coating was also investigated.Some polyanionic compounds, e.g. TiP₂O₇ and LiTi₂（PO₄）₃ with 3D framework structure were proposed to be used as anodes of lithium ion battery with aqueous electrolyte. The TiP₂O₇ and LiTi₂（PO₄）₃ give capacities of about 80 mAh g^-1 between potentials of -0.50 V and 0 V （vs. SHE） and 90 mAh g^-1 between -0.65 V and -0.10 V （vs. SHE） , respectively. A test cell consisting of TiP₂O₇/5M LiNO₃/ LiMn₂O₄ delivers approximately 42 mAh g^-1 （weight of cathode and anode） at average voltage of 1.40 V, and LiTi₂（PO₄）₃/ 5M LiNO₃/ LiMn₂O₄ delivers approximately 45 mAh g^-1 at average voltage of 1.50 V. Lithium ion diffusion coefficient in LiTi₂（PO₄）₃ was investigated by Cyclic Voltammogram （CV） method, and the results are 6.08×10^-5,2.24×10^-5cm² s^-1 respectively during charge and discharge process. The lattice parameter change with x of Li_1+xTi₂（PO₄）₃ was investigated. The capacity fading maybe related to deterioration of anode material.A proton-conductive composite of （NH₄）₂SnP₄O₁₃ was synthesized by solid-state method. X-ray diffraction （XRD）, scanning electronic microscopy （SEM） and thermal gravimetric analysis （TGA） investigation were performed on this composite. The conductivity of （NH₄）₂SnP₄O₁₃ measured by impendence spectroscopy with the temperature range of 125 - 275℃under different atmosphere. Maximum conductivities of 13.8 mS cm^-1 at 275℃under dry H₂ and 35.5 mS cm^-1 at 225℃under wet H₂ respectively were obtained.We prepared （NH₄）₂Si_1-xTi_xP₄O₁₃ composites, which have potential application in intermediate temperature fuel cells as electrolyte. The effect of Ti content on the conductivity of the composite was investigated systematically. Maximum conductivities of 0.68 mS cm^-1 under dry atmosphere and 30.8 mS cm^-1 under wet atmosphere respectively were obtained. Among them, （NH₄）₂Si₅₀Ti₅₀P₄O₁₃ gave good conductivity both in dry and humid atmosphere. The （NH₄）₂Si₅₀Ti₅₀P₄O₁₃ composite also showed good conductivity stability when changing the atmosphere between dry and humid gas. Moreover, the XRD results showed that the structure of （NH₄）₂Si₅₀Ti₅₀P₄O₁₃ changed after measuring in dry gas and humid gas.更多还原