锌负极材料的制备与性质及密封锌镍二次电池的产业化研究博士论文

I摘 要锌镍二次电池是最有希望成为未来电动汽车驱动电源的电化学体系之一，具有能量密度高，功率密度高，工作电压高，原材料便宜，生产和使用过程均无环境污染等优点。然而，由于锌电极存在变形，枝晶，自放电和钝化等问题，严重阻碍了其大规模的运用和市场化。研究表明锌电极变形和锌枝晶生长是氧化锌在碱性电解液中的溶解和反复充放电过程中锌的电沉积所导致的结果。本论文针对影响电极变形和枝晶的最关键因素锌负极活性物质在电解液中的溶解度展开研究，采用锡酸钙添加剂对传统的锌负极进行改进、对锌负极活性物质的材料进行重新设计以及材料的表面包覆来降低其在高浓度电解液中的溶解性，制备并首次将锡酸钙引入到锌镍二次电池领域，成功地对氧化锌进行了铟和硅化合物的表面包覆，系统研究了锌酸钙的各种制备方法并首次采用水热法成功制备出锌酸钙，首次对锌酸钙进行了铟和锡化合物表面包覆，此外，本论文还针对密封锌镍二次电池在产业化过程中遇到的各种技术难题进行了重点研究。采用共沉淀法成功合成 CaSn(OH)6，并首次将其作为锌镍二次电池的添加剂使用，研究发现 CaSn(OH)6 在充电过程中能游离出金属锡和 Ca(OH)2，并能在充放电循环过程中进一步生成锌酸钙。添加 CaSn(OH)6 样品的模拟锌镍二次电池具有较高的放电平台和更好的循环性能，锌酸钙的生成可以降低锌电极活性物质在电解液中的溶解度，从而在一定程度上缓解锌负极的形变、枝晶等问题，改善了锌电极的循环性能。为了改善氧化锌在高浓度电解液中的稳定性问题，对氧化锌进行了表面改性实验，重点研究了铟和硅的化合物的包覆对氧化锌性能的影响。氧化锌的表面包覆均能有效改善锌负极的电化学性能。采用表面包覆氧化铟的氧化锌的锌负极的腐蚀电位相对于采用了掺杂氧化铟的氧化锌的锌负极的腐蚀电位发生了正移，锌负极的抗腐蚀能力增强。采用表面包覆二氧化硅的氧化锌作为负极活性物质的电池经过 269 次循环后，电池放电容量为设计容量的 80.33%，达到了实用化的水平。对锌酸钙的各种制备方法进行了研究，重点研究了 KOH 介质II的浓度对球磨法制备锌酸钙的影响，并首次采用水热法制备出了锌酸钙。在 10%、20% 、30% 、40%(wt)KOH 溶液中，通过球磨法能够制备得到锌酸钙晶体，且均为不规则形貌。不同浓度 KOH 溶液中制备的锌酸钙实际比容量仅能达到理论值的 56%左右。通过对水热法制的锌酸钙材料的检测，发现水热法制备的锌酸钙具有较小的粒径、其晶形不规则，晶体内含结晶水较少，其化学组成是 Ca(OH)22Zn(OH)21.2H2O。以该锌酸钙为负极活性物质的模拟锌镍二次电池具有较低的充电电压、较高的放电平台和优良的循环性能，所以水热法制备的锌酸钙比较适合作为锌镍二次电池的电极活性材料。在低倍率充放电时，锌酸钙的形貌对锌负极充放电以及循环寿命影响较小，但随着充放电倍率增大，影响也逐渐变大。添加结晶完整的四边形和六变形锌酸钙要优于添加不规则形貌的锌酸钙，其中以六边形锌酸钙最佳，其电极反应速度快，放电平台高，循环寿命最长，而添加不规则形貌锌酸钙的负极在大倍率充放电时容量损失最快。为了解决锌酸钙在高浓度电解液中的不稳定性问题，率先对锌酸钙进行了表面包覆改性实验，重点研究了铟和锡的化合物的包覆对锌酸钙性能的影响。XRD分析结果表明铟和锡的包覆物分别为In(OH)3和Ca(Sn(OH) 6)，锌酸钙的主体结构变化不大；扫描电子显微镜分析结果显示包覆物晶体均匀地分散在锌酸钙晶体的表面和间隙中。交流阻抗和Tafel曲线的测试结果显示，包覆后的锌酸钙具有更大的电荷转移电阻和更正的腐蚀电位，在一定程度上抑制了锌酸钙与电解液之间的电荷转移，然而这并没有减弱锌酸钙的循环性能。包覆在锌酸钙的表面的金属锡不但能减少锌酸钙和电解液的直接接触，抑制了锌酸钙在电解液中的溶解，而且提高了锌电极的析氢过电位，增强了锌酸钙的耐腐蚀性能和循环性能。针对密封锌镍二次电池在产业化过程遇到的难题，重点研究了密封锌镍二次电池的自放电、浆料分散剂、负极粘合剂和电池充电方式等问题。研究发现锌负极集流体和钢壳镀层材料的析氢过电位对抑制密封锌镍二次电池的自放电具有重要作用。在电池钢壳表面镀有较高析氢过电位金属Cu和Sn能有效抑制锌负极的析氢腐蚀行为，是减小锌镍二次电池自放电的有效途径之一。使用5.0M KOH+2.0M NaOH的混合电解液的自放电性能远好于使用 7.0 M KOH；磺化聚丙烯隔膜因其在碱液及高温环境中稳定性好，具有不分解、不氧化等III优点，对锌镍二次电池自放电的抑制效果明显优于维纶隔膜。采用六偏磷酸钠能显著改善锌负极配料和拉浆过程中的结团问题，促使负极活性物质和各种添加剂在搅拌配浆过程中得到非常有效地分散，制得的锌负极片表面光滑平整。通过对实验电池的充放电测试发现，采用六偏磷酸钠作为分散剂能抑制锌负极在循环过程中的形变和内阻在循环过程中的不断增长问题，降低充电电压，从而明显延长了实验电池的循环寿命。采用0.4%HPMC +1.5%SBR+0.1%PVA作为锌负极的粘合剂浆料具有良好的流动性，极片强度改善，卷绕时脱粉的问题也得到了解决。具有较低的内阻和充电电压，较高的放电平台，循环寿命显著延长，高温储存能力也有所提高。采用二段式充电方式能有效避免过充电现象的发生，缓解了析氧反应对密封锌镍二次电池危害，实验电池放电容量在80次循环后趋于稳定，经过300次充放电后，其容量保持率在75%左右。关键词 锌镍二次电池，锌酸钙，水热法，耐腐蚀性，表面包覆IIABSTRACTZinc-nickel battery is a promising electrochemical system for electric vehicle force power, due to its attractive advantages of high energy density, high power density, high working voltage, low-cost raw materials, and free of environment pollution in produce and application. However, the cycle life of Zn-Ni battery remains relatively low because of the technical difficulties of the Zn electrode shape change, Zn dendrite formation, Zn passivation and self-discharging that occur with the increasing number of charge/discharge cycles. Thereby, the development of Zn-Ni battery is geatly limited and the massive production and utilization are currently impossible. A mong the aforementioned problems, the most critical problems are shape change and dendrite formation. The mechanism of Zn-Ni battery shows that the shape change and dendrite formation are ascribed to the solution of ZnO in the alkaline electrolyte and Zn electrodeposition during the repeatedly charge/discharge, of which the most important factor causing shape change and dendrite formation is considered to be the solution of ZnO in the alkaline electrolyte. In order to solve the problem, the research work was focused on redesign of the active materials for zinc electrode, improvement of the traditional material and surface modification of raw material for zinc electrode. In this dissertation, CaSn(OH)6 was prepared by coprecipitation method, and was introduced into Zn-Ni battery for the first time, zinc oxides coated with indium and silicon compounds were successfully prepared, various methods of synthesizing calcium zincate were studied systematically, and calcium zincate was surface modified with indium and tin compounds for the firsr time, respectively. In addition, the technical difficulties encountered during massive production were also investigated thoroughly.CaSn(OH)6 was prepared by coprecipitation method, was used as the additive in Zn-Ni batteries for the first time. The results revealled that some favorable substances of Ca(OH)2 and Sn could dissociate from CaSn(OH)6 during charging process, and continue to react with ZnO to IIIproduce calcium zincate. The simulated Ni/Zn battery using CaSn(OH)6 as the additive had a high discharge plateau and an excellent cycling ability. The improvement could be sumed up to that the appearance of calcium zincate, which could highly reduce the dissolvability of anode active materials, greatly alleviate the shape change and dendrite formation problems, and further improve the cycle performance of zinc electrode. In order to improve the stability of zinc oxide in high-concentration electrolyte, zinc oxides coated with indium and silicon compounds were successfully prepared, and their influences on the performances of zinc anodes were studied. The results showed that both the coating could remarkably improve electrochemical properties of the zinc anodes. The steady-state potential of indium-coating zinc oxide anode shifted in the more positive direction, compared to indium-mixed zinc oxide anode, enhancing the alkali-tolerant performance of zinc anode. The simulated Ni/Zn battery using silicon-coating zinc oxide as the active material of zinc electrode had an excellent cycling ability, it could retain about 80.33% of initial discharge capacity after 269 charge-discharge cycles, exhibit a very practically performance.Various methods of synthesizing calcium zincate were studied, of which the effects of KOH concentration on the calcium zincate prepared by high energy ballmilled method were investigated emphatically, and the hydrothermal method was firstly achieved in synthesizing calcium zincate. Irregular calcium zincate were prepared by high energy ballmilled method using 10%, 20%, 30%, 40% (wt) as the medium, but the practical specific capacities of the samples could only approached about 56% the theoretical value. The calcium zincate prepared by hydrothermal method were irregular crystals with smaller diameter and less crystal water than the calcium zincate prepared by other methods with a chemical component of Ca(OH)22Zn(OH)21.2H2O. The simulated Zn-Ni battery had a low charge voltage, a very high discharge plateau and a good cyclic performance, testifying that the material was conformable for the zinc electrode material of Zn-Ni secondary batteries. The charge-discharge performances of calcium zincate electrodes showed little difference among samples with various morphologies in low-rate testing. However, IVthe distinctness seemed to be more and more evident with the increasing testing rate. The results showed that the calcium zincate with tetragonal and hexangular crystal phases had better high-rate abilities than and the irregular one, of which the calcium zincate with hexangular microstructure showed the best performances with quick electrochemical reaction ability, high discharge plateau, long cycle life, while the irregular calcium zincate exhibited a much poorer high-rate cyclic ability.With the aim of enhancing the stability of calcium zincate in high-concentration electrolyte, calcium zincates coated with indium and tin compounds were firstly prepared, and their influences as active materials in zinc anode on the performances of Zn/Ni batteries were studied. The chemical composition of coating materials, In(OH)3 and Ca(Sn(OH)6) was verified by X-ray powder diffraction pattern, and no obvious change occurred in the crystalline phase of the monoclinic calcium zincate after coating. The SEM pictures revealled that the small particles of coating materials distributed uniformly on the surface and in the interspace of calcium zincate crystalls. The impedance diagrams and the Tafel plots indicated that the surface modified calcium zincate had larger charge-transfer resistances and more positive steady-state potentials, suppressing the charge transfer between core calcium zincate and the electrolyte to some extent, but the improvement did not worsen the cyclic ability. The coating materials was reduced into metal at charging, and the metal on the surface of calcium zincate particles could prohibit the direct contact of the active core material with the alkaline electrolyte, suppress the dissolution of calcium zincate in the electrolyte, increase the hydrogen evolution overpotential, and further strengthen the alkali-tolerant ability as well as the cyclic performance.In order to solve the technical difficulties encountered during massive production, the self-dischargement of sealed Zn-Ni secondary battery, the dispersibility of zinc slurry, the binders of zinc electrode, as well as the charging mode were systematically studied. The results revealled that the hydrogen evolution overpotentials of metal electroplated anode current collectors and shells played a very important role in suppress the self-dischargement of sealed Zn-Ni secondary battery. VElectroplating the shells with high hydrogen evolution overpotential metals, such as copper and tin, could markedly decrease the hydrogen evolution reaction and reduce the self-discharge rate. The self-dischargement of sealed Zn-Ni secondary battery using 5.0M KOH+2.0M NaOH as the electrolyte was much better than that of using 7.0M KOH, and self-dischargement of sealed Zn-Ni secondary battery using sulfonic polypropylene membrane was much better than that of using polyvinyl alcohol membrane, due to sulfonic polypropylene membrane characteristics of the good stability in high alkaline and high temperature, hard to decompose and be oxidated. Employing hexametaphosphate as the dispersant could obviously improve agglomeration problem, facilitate the good dispersal of the active materials and additives during stirring to get glazed zinc electrodes. The charge-discharge test showed that using hexametaphosphate as the dispersant could markedly suppress the shape change and the accretion of internal resistance during cycling, reduce the charging voltage, and prolong the cycle life of Zn-Ni secondary battery. The mixed binder of 0.4%HPMC +1.5%SBR+0.1%PVA could enable the zinc slurry with good fluidity, and nice binding force, which could alleviate the disjoint problem during winding. The sealed Zn-Ni secondary battery using mixed binder had a low internal resistance and charging voltage, high discharge plateau, good cyclic ability and storable performance at high temperature. Two-step charging method (constant-current/constant-voltage) could effectively avoid the occurrence of overcharge and relax the side effect of oxygen evolution. The sealed Zn-Ni secondary battery charging with the two segments method could retain about 75% of initial discharge capacity after 300 charge-discharge cycles.KEY WORDS Zn-Ni secondary battery, calcium zincate, hydrothermal method, alkali-tolerant ability, surface coating i目 录摘 要 .IABSTRACT .II目 录 .i第一章 绪 论 .11.1 引言 .11.2 锌镍二次电池简介 .31.2.1 锌镍二次电池的工作原理 .31.2.2 锌镍二次电池的组成 .41.2.2.1 镍正极 .41.2.2.2 锌负极 .61.2.2.3 隔膜 .71.2.2.4 负极集流体 .81.2.2.5 电解液 .81.2.3 锌镍二次电池的分类 .91.3 锌镍二次电池的历史与研究现状 .111.3.1 锌镍二次电池的历史 .111.3.2 国内锌镍二次电池的发展现状 .111.3.3 国外锌镍二次电池的发展现状 .121.3.3.1 美国 .121.3.3.2 日本与韩国 .141.3.3.3 欧洲 .151.4 锌镍二次电池产业化面临的主要问题简析 .151.4.1 锌镍二次电池存在的主要问题 .151.4.2 锌镍二次电池性能的主要影响因素 .161.4.2.1 锌镍二次电池锌负极的变形问题 .161.4.2.2 锌镍二次电池锌负极的枝晶问题 .171.4.2.3 锌镍二次电池锌负极的钝化问题 .181.4.2.4 锌镍二次电池锌负极的自腐蚀问题 .191.4.2.5 锌镍二次电池镍正极的毒化问题 .201.4.2.6 锌镍二次电池镍正极的不可逆化问题 .201.4.3 锌镍二次电池的循环性能 .201.4.4 锌镍二次电池的气密封性能 .211.4.5 锌镍二次电池的自放电 .211.4.6 锌镍二次电池的产品一致性 .221.4.7 锌镍二次电池的成本 .221.4.8 锌镍二次电池的改进途径 .231.4.8.1 镍正