【作者】 张昭；

【导师】 左春柽；

【作者基本信息】 吉林大学 ， 机械设计及理论， 2014， 博士

【摘要】 电子设备的快速发展对电池提出了更高的性能要求，提高电池的容量及能量密度是电池领域最主要的研究方向。金属空气燃料电池以空气中的氧为氧化剂，将金属燃料中的化学能直接转化为电能，具有很高的能量密度及利用效率，是高性能电池的理想解决方案。与传统的氢燃料电池相比，金属空气燃料电池的优势在于制备成本低、燃料储运安全以及便于维护等。Li, Ca, Mg, Al, Fe及Zn等活性金属均可被用作金属空气燃料电池的阳极材料，其中铝的理论容量密度高达2.98Ah g-1-Al，理论能量密度8.195Wh g-1-Al。同时铝还具有储量丰富、便于获取、价格低廉且无毒环保等优点，是金属空气燃料电池的理想阳极材料。本文以铝作为阳极，在碱性聚合物凝胶电解质环境中与氧气反应放电，得到一种高容量密度的全固态聚合物铝空气电池方案。在此过程中，对阳极金属腐蚀防护、电解质电导率提高及电池结构优化等问题进行了深入研究。最后，制备了柔性薄膜铝空气电池及固态凝胶超级电容，扩展了本文研究内容的应用领域。典型的铝空气电池系统由铝阳极、电解质以及多孔空气阴极构成。传统液态电解质流动性很强，易渗透多孔空气电极从而造成泄漏。本文引入交联聚丙烯酸合成碱性聚合物凝胶电解质，并基于此制备全固态聚合物铝空气电池，从根本上解决了电解质的渗漏问题。丙烯酸单体（AA）聚合得到聚丙烯酸高分子链（PAA），进而交联形成三维网络结构，将氢氧化钾（KOH）溶液固定在其中，形成固态凝胶状。电导率是电池电解质最重要的性能参数之一。碱性电解质溶液中，电导率随KOH浓度的增加，呈现先升后降的规律，在KOH质量分数36wt%时达到峰值。本文最终选定KOH36wt%，AA6wt%的电解质成分，配合1wt%的交联剂和0.6wt%的聚合引发剂，得到固态碱性聚合物凝胶电解质，电导率达到460mS cm-1，优于现有技术。铝金属在碱性电解质环境中的析氢腐蚀是铝电池面临的另一重要问题。实验证明，铝在碱性环境中的腐蚀速率受限于氧化反应速率及离子扩散速率中较低者，在KOH质量分数30wt%时达到峰值。碱性聚合物凝胶电解质中，PAA分子附着在铝表面，具有非常明显的缓蚀作用，适用于铝空气电池领域。针对实验中观察到的电解质溶液电导率的变化规律，采用分子动力学方法研究其内在机制。建立不同浓度KOH水溶液体系的全原子模型，根据带电离子的运动轨迹计算其均方位移MSD及扩散系数。由Nernst-Einstein关系可知，电导率与带电离子浓度和扩散系数的乘积成正比。随着KOH质量分数的增加，带电离子浓度上升，扩散率下降，因此电导率表现出先升后降的规律；电导率峰值出现在KOH36wt%处，与实验结果一致。电解质体系中各粒子的分布规律表现为径向分布函数RDF。将两种粒子的RDF曲线积分至第一个波谷，即得到该粒子对之间的配位数。K+离子与OH-离子间存在很强的静电引力，因此能够形成较为紧密的结合体。KOH含量的增加可以提高阴阳离子间的配位数，即在更高浓度的KOH溶液中，每个离子受到更多相反电荷的吸引作用，限制其移动。离子的扩散系数随配位数的升高线性下降，证明阴阳离子间的结合和阻滞是抑制扩散系数及电导率的主要原因，从而在分子尺度揭示了电导率的变化机制。采用碱性聚合物凝胶电解质，制备全固态聚合物铝空气电池样机。电池阳极采用铝网与镍质集流体结合的结构，铝网孔洞用作氢气逸出通道。将导电材料、催化剂、粘接剂和有机溶剂组成的阴极材料涂布在泡沫镍上，干燥冷压得到多孔空气阴极。铝网阳极、聚合物凝胶电解质和空气阴极层叠布置，得到全固态聚合物铝空气电池，在恒流放电测试中表现出持续稳定的放电特性。电流密度由0.3mAcm-2上升至43.3mAcm-2，放电峰值电压和平均有效电压有所下降，输出功率随之升高，功率密度最高可达34.0mW cm-2。电流密度在8~20mAcm-2范围内，电池容量密度及能量密度分别取到峰值1166mAh g-1-Al和1230mWh g-1-Al。电流密度过大会加剧电池极化，降低电池可用容量；电流过小会延长放电时间，析氢腐蚀中消耗的铝金属随之增加。为降低铝金属的腐蚀损耗，本文提出一种可分离式全固态铝空气电池方案，电池搁置时将铝网与聚合物凝胶电解质分离，从而避免了自放电腐蚀，提高了阳极金属的利用效率。本文还开发了一种柔性薄膜铝空气电池，以满足微小电子设备及可穿戴电子产品的需求。文中提出了铝箔金属阳极以及超薄碳膜空气电极方案并给出了详细的制备过程。采用宣纸作为电池的机械支撑及隔离层，与碱性聚合物凝胶电解质相结合，得到纸基凝胶电解质。薄膜铝空气电池的整体厚度为0.32mm，面积密度为0.1g cm-2，具有良好的可弯折性及柔韧性。柔性薄膜铝空气电池放电时的最大电流密度为3.9mAcm-2，功率密度3.7mW cm-2。电池容量密度和能量密度的峰值出现在电流密度3.1mAcm-2时，分别达到2.33mAh cm-2及2.48mWh cm-2，对应的阳极金属铝的质量容量密度为932mAh g-1-Al，质量能量密度为992mWh g-1-Al。超级电容具有很高的充放电速度及电荷效率，常与电池组成复合电源共同使用。本文研究的碱性聚合物凝胶电解质同样适用于超级电容领域。基于凝胶电解质与多孔电极制备固态凝胶超级电容，并测试其循环伏安特性及充放电性能。固态凝胶超级电容额定工作电压设定在1.0V，允许20%过载。循环伏安测试中，电流密度随电压扫描速度的增加而明显升高，电容密度有所下降；在0.01V s-1的电压扫描速度下，电容密度达到0.343F cm-2。电容充放电实验中，大电流密度下的快速充放电会减小可用的电容密度，但电荷效率提高至接近100%（5mA cm-2），可忽略电荷损失。固态凝胶超级电容在循环充放电实验中性能稳定，具有良好的应用前景。综上所述，本文使用铝作为金属空气燃料电池的阳极材料，得到了很高的容量密度和能量密度。将聚合物凝胶电解质应用在铝空气电池领域，有效解决了渗漏及腐蚀问题。采用分子动力学方法对电解质进行研究，解释了电导率变化规律的内在机制。最后，将上述研究成果应用在柔性薄膜电池及超级电容上，扩展了其应用领域。更多还原

【Abstract】 The rapidly developing electric equipments require energy storage devices with highcapacity and energy densities. Metal-air fuel batteries can convert the chemical energy inmetals into electrical power directly with relatively high capacity density and energyefficiency. Compared with traditional hydrogen fuel cells, metal-air batteries have lowerprices and maintenance costs. Furthermore, the preparation, storage and transport of metalare more convenient than hydrogen. Aluminum (Al) is an ideal candidate because of tistrivalence and atomic weight of26.98. The theoretical capacity density of Al is up to2.98Ah g-1-Al. Al also exhibits a high energy density of8.195Wh g-1-Al. Besides, Al hasattracted extended attention due to its abundance, low price, non-toxicity, andenvironmental friendliness. In this paper, an all-solid-state polymer Al-air battery with Alanode and polymer alkaline gel electrolyte is proposed to show an excellent capacityperformance. Research on the anodic corrosion, the electrolyte conductivity and thestructural optimization of the battery has also been carried out during this work. Finally, aflexible thin-film Al-air battery and an all-solid-state ultracapacitor are presented to extendthe application field of this work.A typical Al-air battery is consisted of an Al anode, an electrolyte and a porous aircathode. The fluidity of popular aqueous electrolytes may lead to the penetrations andleakages through the capillaries in the porous air cathode. In this paper, cross-linkedpoly-acrylic acid (PAA) based alkaline gel electrolyte is prepared to solve this problem.Acrylic acid (AA) monomers can be polymerized into PAA chains and then cross-linked tobe3-dimensional matrix, in which the aqueous electrolyte can be stored to form a gel. Theconductivity, which is one of the most important characteristics of the electrolyte, firstlyrises and then decreases as the KOH fraction increases. The final polymer gel electrolyte iscomposed of36wt%KOH,6wt%AA,1wt%cross-linker and0.6wt%polymerizationinitiator. The conductivity of the gel electrolyte is460mS cm-1. In addition to the leakage,the anodic corrosion is another problem of Al-air batteries. The corrosion rate reaches thepeak with the KOH fraction of30wt%. It is indicated that PAA is a good corrosion inhibitor for Al.A molecular dynamic method is used to find the mechanism behind the electrolyteconductivity. All atom models of aqueous alkaline solutions with different KOH fractionsare built to calculate the dynamic and structural performances. According to theNernst-Einstein relationship, the conductivity is proportional to the product of the iondensity and the diffusion coefficient. A higher KOH fraction can raise the ion density butreduce the ion diffusion coefficient. As a result, the peak conductivity is obtained with theKOH fraction of36wt%, which is consistent with the experimental result. In moreconcentrated solutions, the coordination number between ion pairs is enhanced and restrictsthe mobility of ions.An all-solid-state Al-air battery has been fabricated with polymer alkaline gelelectrolyte. An Al mesh with a Ni current collector is used as the anode. The cathodic pasteconsisting of conductive carbon, catalyst, polymer binder and organic solvent is casted ontoa Ni foam. The porous air cathode is obtained after evaporation and cold press. The Almesh anode, the polymer alkaline gel electrolyte membrane and the porous air cathode arelaminated sequentially to form an all-solid-state Al-air battery, which presents an excellentperformance during discharging measurements. As the discharging current density risesfrom0.3to43.3mA cm-2, the peak and average voltage drop together, while the powerdensity is promoted up to34.0mW cm-2. The maximum capacity and energy densities canreach1166mAh g-1-Al and1230mWh g-1-Al, respectively. Besides, a separable Al-airbattery is proposed in this work to inhibit the Al corrosion during rest in order to maintainthe available capacity of the battery.Base on the all-solid-state polymer Al-air battery, we present a flexible thin-film Al-airbattery using an Al foil anode and an ultra-thin carbon air cathode. A paper based gelelectrolyte is prepared by the combination of polymer gel electrolyte and double rice papers.The total thickness of the whole battery is only0.32mm, and the area density is0.1g cm-2.The maximum power density of the battery can reach3.7mW cm-2with the current densityof3.9mA cm-2. The peak area capacity and energy density are2.33mAh cm-2and2.48mWh cm-2, respectively, when the battery is discharging at3.1mA cm-2. The capacity and energy densities corresponding to anodic Al are932mAh g-1-Al and992mWh g-1-Al,respectively.What’s more, the gel electrolyte can also be applied to fabricate solid gelultracapacitors. The ultracapacitor prototype is composed of a gel electrolyte membraneand two porous carbon electrodes. During the cyclic voltammetry testing, the voltagewindow is set as1.0V, and an overload of20%is permitted. The promoted voltagescanning rate can enhance the current density, but the capacitance is limited. Thecapacitance density of0.343F cm-2is obtained with the scanning rate of0.01V s-1. In thecontinuous charging and discharging tests, the capacitance is restricted by large currentdensity, while the coulomb efficiency is promoted to approximate to100%over5mA cm-2.The possible of the combination of all-solid-state batteries and solid gel ultracapacitors isconfirmed in this work.As mentioned above, Al has been employed as the anode material in metal-air batteriesto achieve high capacity and energy densities. A PAA based alkaline gel electrolyte is usedto fabricate the all-solid-state polymer Al-air battery to avoid leakage and corrosion. Themechanism of the electrolyte conductivity is investigated using a molecular dynamicmethod. Finally, the results of this work have been extended to flexible thin-film batteriesand solid gel ultracapacitors.更多还原