【作者】 余丹梅；

【导师】 周上祺； 陈昌国；

【作者基本信息】 重庆大学 ， 材料学， 2004， 博士

【摘要】 比能量高，性能优良的金属氢化物镍电池（MH-Ni）在电子、通讯、计算机等行业的应用相当广泛，在电动汽车领域也将得到广泛应用。作为正极活性物质，氢氧化镍的性能是决定MH-Ni电池整体性能的关键。本文从以下四方面对纳米氢氧化镍进行了全面的研究： 第一，分别采用手工、球磨机对微米级氢氧化镍进行研磨，以制备纳米氢氧化镍，并利用X射线衍射仪，扫描电镜，透射电子显微镜和循环伏安曲线测试装置研究研磨对氢氧化镍结构和性质的影响。研究表明：在研磨过程中，氢氧化镍晶体在切应力的作用下沿（0001）：<1120>滑移系滑移而破碎，使其沿c轴方向的晶粒尺寸不断减小。当机械研磨强度不大时，随着时间的延长，氢氧化镍晶胞的晶格常数c值逐渐减小，而在高强度的机械研磨下，不但氢氧化镍的晶格常数c值随时间发生改变，而且，a值也随之减小。高强度的机械研磨导致晶格产生畸变，增加Ni（OH）₂材料的电化学活性。随着研磨的进行，样品的晶粒尺寸和颗粒尺寸减小，材料的比表面积增大，质子H⁺的扩散路径缩短，改善了电极的导电性能和降低了电极的反应阻抗，促进了质子H⁺在Ni（OH）₂中的嵌入和脱出，从而提高了电极的可逆性。但是，当机械研磨的强度和时间增至一定程度时，随着氢氧化镍晶粒尺寸的不断减小，会使电极反应中质子传递过程的晶界阻力增大，材料的电化学性能随之变差。电极导电性的增强也促进了电极的析氧反应，使析氧峰电位与氧化峰电位之差值减小，氢氧化镍电极的充电效率和活性物质的利用率降低。机械研磨不会使锌、铜添加剂与氢氧化镍之间发生反应，研磨后，样品中各组分都保持自己的独立结构，但它们的晶粒尺寸和颗粒尺寸均随研磨时间和强度的增加而减小。添加适量的锌粉、铜粉，能抑制氢氧化镍电极的析氧反应，提高电极的充电效率和活性物质的利用率。同时，金属铜还能增进电极反应的可逆性，改善氢氧化镍的电化学活性。 第二，采用微乳液法制备纳米氢氧化镍，用X射线衍射法，透射电子显微技术和循环伏安实验，研究合成条件对氢氧化镍结构和性质的影响，并用正交实验优化合成条件。实验结果证实：微乳液法可合成颗粒尺寸为3～15nm的β型氢氧化镍，其颗粒呈椭球形结构。合成时的pH、温度、反应物浓度、合成搅拌时间、搅拌强度等条件的改变，将引起氢氧化镍的晶粒尺寸发生变化。晶粒尺寸减小，质子H⁺在传递过程中的晶界阻力增大，氢氧化镍电极反应的可逆性降低；反之，可逆性提高，氢氧化镍的电化学性质得到改善。正交实验给出制备纳米β型氢氧化镍的最佳工艺条件是：pH为10，温度60℃，氢氧化钠浓度4mol／dm³，硫酸镍浓重庆大学博士学位论文度lmoFdm3，合成搅拌时间30min，合成搅拌强度为中强。采用机械研磨和微乳液法都能制备晶粒尺寸、颗粒尺寸相近的纳米氢氧化镍，但微乳液法合成的纳米氢氧化镍具有严重的晶格畸变，有利于质子H+在电极材料中的传递，促进了电极反应，从而改善了氢氧化镍的电化学活性。因此，微乳液法是一种具有发展优势的合成电池用纳米氢氧化镍的方法。 第三，采用X射线衍射法，透射电子显微技术，循环伏安和恒电流充放电实验，研究锌系、钙系添加剂对纳米氢氧化镍结构和性能的影响。结果说明:机械混合添加的锌以金属单质的形式与氢氧化镍共存，不影响氢氧化镍的结构。由于金属锌是良导体，所以添加锌改善了氢氧化镍的导电性，使其电化学性能提高，放电比容量也随之提高。包覆、共沉淀添加锌时，z矛+取代了部分Niz+进入氢氧化镍结构，形成p一Ni，-x Znx（oH）2，锌加入使晶体结构产生畸变，促进了质子H+在电极材料中的传递，改善了氢氧化镍电极反应的可逆性，提高了放电比容量。随着锌添加量的增加，氢氧化镍晶体的缺陷增加，更有利于质子H十的传递，氢氧化镍的电化学性质不断改善，电极的放电比容量也随之提高。但锌量增至一定限度后，会因氢氧化镍中镍的有效成分减少过多而使其性能变差，放电比容量降低。共沉淀添加锌的最佳量为2.5%。以“前沉淀”，“后沉淀”方式添加CaO、CaCO3，不影响氢氧化镍的结构，但混杂在氢氧化镍中的Cao、CaCO3会使晶体内产生缺陷，促进了质子H+在电极材料中的传递，改善了氢氧化镍电极反应的可逆性，提高了放电比容量。当Cao、CaCO3的添加量大于1%时，因为镍的有效成分减少使氢氧化镍的性能变坏，放电比容量降低。机械混合CaO、CaCO3会使合成物的晶粒尺寸增大，降低了质子H十传递过程中的晶界阻力，改善了氢氧化镍的电化学性能，放电比容量也随之增大。 第四，通过量子化学DV一Xa法，研究氢氧化镍和掺杂氢氧化镍的电子结构，以便从理论上认识氢氧化镍的结构特征和掺杂元素对其结构和性质的影响。研究发现:氢氧化镍中镍、氧、氢原子都只带部分电荷，表明氢氧化镍并不是典型的离子晶体，其结构中的化学键具有较强的共价性。氢氧化镍主要以镍原子和氧原子间的强烈相互作用结合形成，氢原子与体系的结合不紧密，所以能自由地脱出和嵌入。氢的脱出不会引起氢氧化镍的结构改变，仍然能保持原来的层状六方晶系结构，镍原子的净电荷数升高。但过度脱氢会造成结构转变，使氢氧化镍?更多还原

【Abstract】 Metal hydride nickel (MH-Ni) batteries with high energy density and excellent properties, was widely used in many fields such as electronic industry, communication, computer and electric vehicles. As a positive active material, the performance of nickel hydroxide was the key deciding entire property of MH-Ni batteries. In this paper, nano-scale nickel hydroxide was studied comprehensively from the following four aspects.Firstly, nano-scale nickel hydroxide was prepared with grinding micro Ni(0H)2 byhandwork and ball mill respectively, the effect of grinding on its structure andelectrochemical properties was measured and investigated through X-ray diffraction,TEM, SEM and cyclic voltammetry. Results showed that during grinding nickelhydroxide crystal slipped and broke along (0001) <1120> slip system under shearingstress. Meanwhile the size of crystalline grain decreased along c axis direction. It wasfound that under gentle mechanical grinding, only the crystal lattice constant c value ofnickel hydroxide decreased gradually with time prolonging, under strong mechanicalgrinding, both the crystal lattice constant c value and a value of nickel hydroxidechanged with time. Strong mechanical grinding caused the distortion of crystal latticeand thus increased the electrochemical properties of nickel hydroxide material. Stronggrinding also increased the surface area of synthesis samples, shortened diffuse distanceof protons H+, improved the electric conductivity of electrode material, reduced theimpedance of electrode reaction, and enhanced the reversibility of electrode with theaccelerated intercalation and de-intercalation of protons H+ in nickel hydroxide.However, if the strength and performing time of mechanical grinding were increased tosome degree, the resistance of crystal interface of protons H+ transfer process inelectrode reaction was increased and electrochemical performance of the materialdeclined. The high electric conductivity of electrode caused by grinding accelerated theoxygen evolution reaction and thus reduced the difference between the evolutionoxygen potential and the oxidation potential. As a result, the charge efficiency ofelectrode decreased and the utilization of active material were suffered. Although zincand copper additives did not react with nickel hydroxide during mechanical grindingand each ingredient of samples maintained its own independent structure, the size ofcrystalline grains and grains decreased along with the increase of strength and time ofmechanical grinding. By adding appropriate amount of zinc and copper powder, the oxygen evolution reaction could be inhibited and the charge efficiency of electrode and utilization of active material could be improved. At the same time, the reversibility of electrode reaction was enhanced and the electrochemical performance was improved by doping metal copper powder.Secondly, nano-scale nickel hydroxide was synthesized with micro-emulsion method. By the aid of X-ray diffraction, TEM, SEM, cyclic voltammetry, the effect of the preparation condition of micro-emulsion method on the structure and properties of nickel hydroxide was investigated and the preparation process was optimized by orthogonal test. The result of test showed that Ni(0H)2 of elliptical spheroid form, with the size of grain within 3-15nm, could be gained through micro-emulsion method. The size of crystalline grain could be altered with changing pH value, the consistency of reacting substance, stirring time and stirring degree. The decrease of the crystalline grain size increased the resistance of crystal interface of protons H+ transfer process and reduced the reversibility of electrode reaction of nickel hydroxide, whereas the increase of the crystalline grain size improved the reversibility and the electrochemical performance of nickel hydroxide. The optimal preparation condition of nano-scale -Ni(0H)2 obtained by orthogonal test was that pH value was 10, temperature was 60, the consistency of NaOH was 4mol/dm3, the consistency of NiSO4 was lmol/dm3, preparative stirring time was 30m更多还原