【作者】 吴建波；

【导师】 涂江平；

【作者基本信息】 浙江大学 ， 材料加工工程， 2007， 博士

【摘要】 金属氢化物镍（MH／Ni）电池是现今应用最广泛的二次电池之一，提高MH／Ni电池的功率特性是MH／Ni电池在电动汽车等领域推广应用的重要任务。但正极活性材料β-Ni（OH）₂导电性差的特点影响了MH／Ni电池高倍率性能的提高。本论文合成了纳米CoO、多壁碳纳米管、球形纳米α-Ni（OH）₂和表面非晶态纳米碳，并将这些纳米材料作为MH／Ni电池Ni（OH）₂电极的添加剂，通过XRD、SEM和TEM等方法对纳米添加剂进行了微观组织结构分析；利用循环伏安、交流阻抗和恒电流充放电等方法，对含纳米添加剂的Ni（OH）₂电极和密封MH／Ni电池进行了电化学性能测试，分析了各种纳米添加剂对MH／Ni电池综合电化学性能的影响，尤其是对高倍率性能的影响。采用液相沉淀法合成纳米棒状CoCO₃前驱体，真空分解前驱体制备了直径约80 nm、均匀分散的短棒状纳米CoO粉末。研究发现：同添加普通亚微米级CoO的电极相比，添加纳米CoO有效地减小了Ni（OH）₂电极电化学反应的欧姆阻抗和反应阻抗，减小电化学反应氧化还原峰值电位间距，提高电化学反应的反应电位。当纳米CoO含量为8 wt．％时，放电比容量达到283 mAh／g，与β-Ni（OH）₂的理论比容量接近。正极添加纳米CoO的密封MH／Ni电池具有放电比容量高、放电电压高、内阻小、循环寿命长和高倍率放电性能优异等特性。正极添加8 wt．％CoO的MH／Ni电池在10 C放电倍率下放电容量仍保有设计容量的90％，电池寿命为165次，相比较添加普通亚微米CoO的MH／Ni电池的115次，提高了近43％。利用化学气相沉积法（CVD）催化分解乙炔制备了结晶性良好的多壁碳纳米管（CNTs），管径约10 nm。研究结果表明，将纯化、分散处理后的多壁CNTs添加到MH／Ni电池的正极，形成以CNTs为骨架的复合导电网络，同时又由于CNTs的高强度和高韧性而维护了网络的完整性。电化学交流阻抗和线性极化曲线测试证实了添加CNTs电极内部欧姆阻抗和电化学反应阻抗减小，电极交换电流密度提高。正极添加CNTs的密封碱性MH／Ni二次电池，具有放电比容量高、容量衰减慢、循环寿命长、内阻小及内阻增长速率慢，放电中值电压高等特性。在高倍率放电条件下正极添加CNTs的作用更为明显。0.5 wt．％是比较合适的添加比例，其在10 C放电条件下当循环次数达到120次时容量保持率仍有85％。添加过多的CNTs，对电池性能的提高无益。采用合适的反应温度和葡萄糖溶液浓度，通过水热反应实现了对球形β-Ni（OH）₂表面非晶态纳米碳修饰。电化学测试表明，在0.2 C和1 C的低中倍率下，虽然表面碳修饰的β-Ni（OH）₂电极电化学循环性能更稳定，但电极活性物质球形β-Ni（OH）₂的利用率约为87％，比普通Ni（OH）₂电极减少约10％。但在3 C倍率放电条件下，表面碳修饰的β-Ni（OH）₂电极在循环30周期后放电容量基本没有变化，且放电电压高出普通Ni（OH）₂电极约30 mV。此外，为了更好的实现碳修饰β-Ni（OH）₂电极的高倍率性能，应适当添加约6 wt．％CoO。采用湿化学沉淀法在醇-水体系中制备了结晶良好、粒度约20-30 nm、振实密度为1.7 g／ml的球形α-Ni（OH）₂，并研究讨论了络合剂与陈化时间对α-Ni（OH）₂组织结构的影响。含10 wt．％α-Ni（OH）₂的复相β／α-Ni（OH）₂粉体，振实密度高达2.41g／ml。对β／α-Ni（OH）₂复相电极材料电化学性能的研究发现，纳米α-Ni（OH）₂的电化学活性高于β-Ni（OH）₂。纳米球形α-Ni（OH）₂的添加提高了电极的放电比容量、放电电压和循环寿命。纳米α-Ni（OH）₂的最佳含量为10 wt．％，添加过多的纳米α-Ni（OH）₂会恶化电极的电化学性能。更多还原

【Abstract】 As one of the most widely used rechargeable batteries, nickel-metal hydride （MH/Ni） batteries are required to improve the high power characteristics considering application for electric vehicles. The high power performance of MH/Ni battery is affected strongly by the positive electrode because of the poor conductivity of the active material β-Ni（OH）₂. In this work, nanosized additives such as nanoscale CoO, multiwalled carbon nanotubes （CNTs）, nanoscale α-Ni（OH）₂ and surface-modified amorphous nanosized carbon were synthesized as additives for the Ni（OH）₂ electrodes. The morphologies and structures of the nanoscale additives were charactered by XRD, SEM and TEM. The influences of these nanosized additives on the overall performance of Ni/MH batteries, especially the high-rate capability, were evaluated by the means of electrochemical measurements, including electrochemical impedance spectrum, cyclic voltammetry and charge-discharge cycling.CoCO₃ nanorods as precursor were synthesized by precipitation method and short rod-like nanoscale CoO was prepared by decomposing CoCO₃ in vacuum. Compared with the electrodes with usual sub-micron CoO, the electrochemical measurements indicate that the electrodes with nanoscale CoO exhibit lower Ohm impedance and the lower electrochemical reaction impedance, narrower redox potential space and high reaction potential. The specific capacity of the electrodes with nanoscale CoO is up to 283 mAh/g, which is close to the theoretical specific capacity of β-Ni（OH）₂. The sealed MH/Ni batteries with nanoscale CoO present better high-rate performance. At 10 C discharge rate the capacity of the batteries with 8 wt.% CoO in the positive electrodes still remains 90% of original capacity, and the lifespan is 165 cycles, which is 43% longer than the usual batteries with 115 cycles.Well crystallized multi-walled carbon nanotubes （CNTs） with diameter about 10 nm were synthesized by chemical vapor decomposition （CVD） method. After purification and ball-milling, the as-prepared CNTs were added to the positive electrodes of MH/Ni batteries as additives. During the process of transformation from CoO to CoOOH, a complex conductive network was created with CNTs as the frame. Because of the high conductivity and intension characteristics of CNTs. thecharge-transfer capability was improved and the integrality of the complex condutive network was enhanced. The electrochemical measurements show that the impedance of the electrodes was lessened and the exchange current density was increased by addition of CNTs. Further researches on sealed batteries show that the batteries with CNTs in the positive electrodes exhibit improved capacity, modified discharge stability, restrained internal resistance and prolonged lifespan. The advantages of CNTs are more obvious when discharged at high current rates. 0.5 wt.% was proved a desired amount for CNTs and the capacity of the batteries with 0.5 wt.% CNTs maintained 85% after discharging at 10 C rate even for 120 cycles.Surface modified β-Ni（OH）₂ by amorphous nanoscale carbon was prepared by the decomposition of glucose in hydrothermal condition. Electrochemical measurements show that though the carbon modification will enhance the discharging stability, the utility of β-Ni（OH）₂ dimished to 87%, which is 10% lower than the electrode without carbon modification at 0.2 C and 1 C. However, at a high discharge rate of 3 C, the carbon-modified β-Ni（OH）₂ electrodes can be discharged stably for 30 cycles without any specific capacity loss and the discharge voltage is 30 mV higher than the electrode without carbon modification. In addition, a proper mount of 6 wt.% CoO was nesessary to the carbon modified β-Ni（OH）₂ electrodes for the high-rate performance.Well-crystallized nanoscale α-Ni（OH）₂ with diameter of 20-30 nm and the tap density of 1.7 g/ml was synthesized through co-precipitation in alcohol-water system. Influnce of the complexing agent and the ageing procedure on the microscopic morphologies of α-Ni（OH）₂ were studied. The tap density of β/α-Ni（OH）₂ biphase powder with 10 wt.% nanoscale α-Ni（OH）₂ could get to 2.41 g/ml. Electrochemical investigation shows that the nanoscale α-Ni（OH）₂ exhibits better electrochemical activities than β-Ni（OH）₂. The discharge capacity increases and the cyclic stability is enhanced for the biphase electrodes with proper mount of α-Ni（OH）₂. The biphase electrode with 10 wt.% nanoscale α-Ni（OH）₂ has a best overall electrochemical performances. Excessive addition of nanoscale α-Ni（OH）₂ does no good to improve the performances of the biphase electrode material.更多还原