【作者】 孙艳芝；

【导师】 许淳淳；

【作者基本信息】 北京化工大学 ， 材料物理与化学， 2007， 博士

【摘要】 在目前锂离子电池正极材料中，市售的主要是LiCoO₂材料，但是由于钴资源稀缺且有毒性，不完全符合当今全球可持续发展战略和绿色经济的要求。LiNiO₂及其衍生物系列由于具有放电容量高、对环境友好和资源丰富等优点，逐渐成为下一代锂离子电池最有希望的候选正极材料之一。采用二价镍盐或者氢氧化镍为原料，在氧气氛中合成LiNiO₂的传统高温固相氧化法，其工艺条件要求苛刻，难以得到大批量符合化学计量比的LiNiO₂，限制了它的工业化生产。因此，寻找新型温和可控的LiNiO₂制备工艺是发展LiNiO₂正极材料的关键所在。本论文的主要研究目的是在电解合成高纯度羟基氧化镍（NiOOH）的基础上，直接采用这种层状的三价镍为原料，在空气氛中制备锂离子正极材料LiNiO₂。另外，本文还研究了电解制备高纯度前驱体NiOOH的各种技术参数，为其在合成LiNiO₂和碱性锌镍电池的应用提供了研究支撑。本论文主要取得了以下几方面的研究成果：本文针对现有化学法制备NiOOH需要消耗大量试剂和反应步骤多的缺点，通过压合式电解法一步得到球形NiOOH，研究了碱液的浓度、电解温度和电流密度等因素对电解制备NiOOH的影响。研究结果表明，以含有5.5％钴的氢氧化镍为原料，在35％（wt.）KOH电解液中，控制1.73V—1.85V（Vs.Zn／ZnO）阳极电位和30℃的电解温度，以60mAg^-1的电流密度电解360min为最佳。该电解法得到的NiOOH具有96％以上的纯度和很高的电化学活性，在30mAg^-1的电流密度下给出了高达273.7mAhg^-1的比容量。在直接电解过程中，我们发现阳极和球形氢氧化镍之间的有效电接触是提高NiOOH纯度和电解效率的关键。本文首次提出了以KMnO₄为代表的高锰酸盐作为电解过程电子传递的媒介，通过锰盐自身氧化还原反应的参与，在阳极和溶液中的球形Ni（OH）₂之间建立起高效的电子转移过程，使球形Ni（OH）₂和阳极之间单一的固体之间的点点接触放电，转变为点点接触放电和球镍与溶液全方位包围接触放电过程，大大提高了电解过程的效率。通过实验，我们提出了KMnO₄的催化电解原理，并研究了电解催化剂的种类和浓度、电解温度和电解时间等因素对制备NiOOH的影响。实验结果表明该法可得到电化学性能良好的NiOOH，在120mAg^-1的电流密度下给出了267mAhg^-1的比容量。基于前面成功合成NiOOH的研究基础，本论文研究了以NiOOH和氢氧化锂为原料在三种不同的反应体系中，通过离子交换反应来制备镍酸锂的新工艺。（1）研究了采用高纯度的NiOOH代替原有的二价镍的高温固相法合成LiNiO₂的工艺条件，该法避免了氧气的消耗和持续稳定氧气氛的苛刻条件，具有生产工艺简单，易于工业化的优点。实验结果表明，采用锂镍摩尔比为1.05：1，在650℃下空气氛中焙烧反应10h，所得到的LiNiO₂具有典型的层状结构，晶形较好，基本保留了前躯体NiOOH的球形形貌。充放电实验结果表明该样品具有较好的电化学性能，首次放电比容量达到175.9mAhg^-1，充放电效率为85.3％。循环20次后，其容量保持率为81.3％。（2）利用NiOOH自身的质子特性和LiOH水溶液所具有的Li⁺和OH^-，通过低温水热离子交换法得到镍酸锂材料的最佳工艺条件是210℃下反应72h。充放电实验结果表明，该材料虽然具有一定的电化学性能，但首次放电容量只有129.9mAhg^-1，距离镍酸锂的理论容量还有一定的差距。（3）利用NiOOH和熔融的LiOH进行离子交换法来制备镍酸锂，发现其最佳合成工艺是550℃下反应20h，该材料层状结构完整，晶形良好，粒度均匀适中。熔融离子交换法制备的镍酸锂材料的电化学性能优良，首次放电容量为169.1 mAhg^-1，充放电效率为90.96％；具有良好的循环性能，循环20次后，容量保持率为91.6％。最后，本论文研究了LiNiO₂电极材料在空气中尤其是潮湿环境中贮存后发生明显的增重现象和电化学性能的衰减问题。研究表明，这与镍酸锂易发生水解在表面生成LiOH，进而吸附H₂O和CO₂，生成Li₂CO₃覆盖层，导致电化学性能变差有关。因而单纯的LiNiO₂电极材料在潮湿的空气中具有比LiCoO₂更差的贮存稳定性，为了保证LiNiO₂的电化学性能，必须隔绝水分和二氧化碳，采用干燥密封条件。更多还原

【Abstract】 Among the cathode materials of rechargeable lithium batteries, LiCoO has been commercially used as positive active material for lithium-ion cells, but it has some disadvantages such as low effective specific capacity, toxicity and expensiveness. LiNiO has been regarded as the most potential cathode material for lithium-ion batteries because of its high discharge capacity, low cost and environmentally benign. However, it is difficult to obtain large batch stoichiometric LiNiO by conventional solid-phase reaction with Ni(OH) or Ni(Ⅱ) salts at high temperature. That restricts its industrialized production. Therefore, the key to the development of LiNiO cathode material is to develop a mild and controllable new synthesis technology. Based on the studies on highly pure nickel oxyhydroxides (NiOOH), the aim of this dissertation is to prepare layered LiNiO material by ion-exchange reaction in air atmosphere. In addition, we also studied various technology conditions of electro-synthesis NiOOH to provide fundamental support for its application in the synthesis of LiNiO and the manufacture of alkaline Zn/NiOOH batteries.In order to get rid of consuming too much reagent and reduce reaction steps in chemical synthesis, we report a new method to obtain highly pure NiOOH by one-step electrolysis of sphere Ni(OH) in alkali solution. The influence of various parameters (e.g. electrolyte concentration, temperature, electrolysis duration, and current density) on electrolysis was investigated. The experimental results indicate that the optimum conditions are a temperature of 30℃, a current density of 60 mA g, an anodic potential of 1．73 V-1．85 V (vs. Zn/ZnO) and an electrolysis duration of 360 min. The electrolysis-generated NiOOH has high purity of 96% and high electrochemical activity, providing a discharge capacity of over 273．7 mAh g at current density of 30 mA g.In the study of one-step electrolysis, we found that the effective electronic contact between the anode and Ni(OH) was beneficial to the improvement of the purity of NiOOH and the electrolytic efficiency. In the dissertation we firstly propose KMnO, a representative of permanganates, as the medium of electron transfer during the electrolytic process. In this process, the discharge process of single point to point contact is transformed to the process of both point to point contact and the overall surrounding contact of sphere Ni(OH) through the self redox reaction, thus making a highly efficient electron transfer process. In this dissertation, the catalytic electrolysis mechanism is discussed. The influence of various parameters (e.g. kind and concentration of catalyst, reaction temperature and electrolysis duration) on electrolysis were investigated. The results show that the NiOOH prepared by catalytic electrolysis has good electrochemical performance and displays a discharge capacity of 267 mAh g at current density of 120mA g.Based on the study of NiOOH, we developeded the new technologies for preparing LiNiO by ion exchange reaction of NiOOH to LiOH·HO with three different methods.(1) The synthesis process of LiNiO by solid phase reaction using NiOOH as raw materials instead of Ni(Ⅱ) was studied. The advantage of this method is simple in technology process and easy in industrialization. The LiNiO cathode material, which is synthesized at 650℃for 10h in air atmosphere at Li/Ni molar ratio of 1．05, has typical layered structure and almost keeps homogenous sphere shape like the raw material NiOOH. The charge/ discharge test indicates that the sample has a high initial discharge capacity of 175．9 mAh g, an initial charge-discharge efficiency of 85．3% and capacity retention of 81．3% after 20 cycles.(2) The influence of various technological conditions on the preparation of LiNiO material by hydrothermal reaction at low temperature was studied. The optimum synthesis condition is at 210℃for 72h. Charge/discharge experiment results show that the discharge capacity of the LiNiO sample is only 129．9 mAh g, much lower than the theoretical capacity of LiNiO.(3) The LiNiO sample was synthesized by ion exchange reaction using NiOOH and melted LiOH as raw materials. The LiNiO compound synthesized at 550℃for 20h was found to be the optimum preparation condition in this study. The XRD and SEM analysis results indicate that the prepared LiNiO has a layered structure and sphere shape. Charge and discharge tests show that the LiNiO cathode exhibits good electrochemical performance. The first discharge capacity of the sample is 169．1mA h g and the initial coulombic efficiency is 90．96%. Galvanostatic charge/discharge and cyclic voltammetry tests show that LiNiO electrode exhibits good cycling reversibility and the capacity retention is 91．6% after 20 cycles.Finally, the storage performance of LiNiO cathode in air atmosphere was investigated. The results show that LiNiO material can generate LiOH on the surface through hydrolytic reaction and further form a LiCO cover with the adsorption of CO. That leads to the deterioration of its electrochemical performance. Therefore, the storage stability of LiNiO is worse than LiCoO material in wet air atmosphere. It is necessary to store in sealed package to isolate the LiNiO product from HO and CO for keeping its storage performance.更多还原