The Study Of The Method And Mechanism Their Formation Of Calcium Zincate And Zinc Dendrites

In this paper, it gives us a brief introduction to the energy crisis in today's world and the urgency of new energy research. It also gives us an overview of cell structure, principles, purpose, advantages and disadvantages of the clean, environmental friendly zinc-based batteries, as well as the current development. It highlights the reasons for the dendrite and deformation problems of zinc negative electrode in the zinc-based batteries especially Ni/Zn battery, and summarizes the solution to the problems. On this basis, it has a further discussion over Calcium Zincate negative material which replace activated ZnO to solve the dendrite and deformation problems, in addition, some innovative research has been done based on the predecessors'research.In the study of the synthesis of Calcium Zincate, this paper summarizes the preparation techniques, synthesis conditions, advantages and disadvantages of various methods such as solid-phase synthesis method, ball milling synthesis, co-precipitation synthesis, low-temperature solid-phase method, hydrothermal synthesis method, and so on. We boldly combined the electrolytic synthesis with the chemical synthesis of calcium Zincate and successfully synthesized calcium Zincate crystals in the electrolytic cell, whose trough voltage is between 2V and 5V and the trough current is 1A to 3A.The samples have been confirmed as Calcium Zincate and having a good electrochemical performance by the tests about surface morphology, chemical structure, electrochemical properties, etc. In order to facilitate commercial batch production of calcium Zincate in the future, we explored systematically of electrolytic preparation of calcium Zincate, including:the type of electrolyte, the concentration of electrolyte, the current density, the cell voltage, the temperature in electrolyzer, the length of time and many other factors that may affect the synthesis. Based on the above, we analyzed and summarized the optimal conditions for electrolytic synthesis, that is, the anode chamber electrolyte we selected is the 0.5M CaCl2 or the 20 wt% KOH solution as the electrolyte,125mA/cm2 as electrolytic current density,6h as appropriate length of time, we get the good quadrilateral crystal.we have a study in the electrolyte additives too,and get a conclusion that the the most appropriate anode electrolyte additives and the cathode electrolyte additives are 0.05M KC1 and 0.05M KNO3.while the temperature makes little difference.The as-synthesized calcium zincate was examined by X-ray powder diffraction pattern, scanning electron microscope, energy dispersive X-ray, and thermogravimetric test. The electrochemical performance of this material was measured by cyclic voltammetry and galvanistatic charge-discharge test showing a good reversibility, a high specific capacity and a good cycling durability.the redox potential difference is about 90mV, the specific capacity can reach 243.2mAhg-1.After the 32th cycle,the specific capcity can retain above 90% of the maximum discharge specific capacity.The Influence of CO2 during the reaction that the preparation of the zincate calcium was analyzed and studyed.we succeed synthesize the zincate calcium with ZnO and CaCO3 in 5 wt %～35 wt % KOH solution.and in the weak alkaline solution the crystal is trend to hexagon crystal,in the strong alkaline solution the production is quadrilateral crystal. We take a lot of tests with this kind of solid powders,and find this powder has good morphology and well electrochemical performance. We take an experiment with ZnO and Ca(OH)2 as reactants in a solution which contain different concentration of CO3-,and succeed synthesis the zincate calcium below the 1M CO3-. The Ksp of zincate calcium also be tested by titration method. Base on the previous research,we propose a new reaction mechanism of zincate calcium.which is expressed as: Ca2++2Zn(OH)3-+2H2O(?)Ca(Zn(OH)3)2·2H2O. In the end,we get the conclusion that the presence of the CO2 and CO3- in certain concentration can't obstruct the target product.In this paper, an innovation has been carried out in the measurement of solubility of ZnO and Calcium Zincate samples in alkaline solution and electrical gravimetric has been used as method of measurement. After the feasibility of the electric gravimetric method can be proved, the author tested and compared ZnO and Calcium Zincate and the solubility of Calcium zinc samples with different morphologies and preparation methods were compared at the same temperature,the result shows the fact that the solubility of calcium zincate is smaller than ZnO, the solubility of Hexagon calcium zincate is smaller than quadrilateral one.At this late stage of the experiment, the author have studied the factors that have influence on zinc dendrite, such as the concentration of metal solution, the current size and types of solution anions,at the same time recorded experimental photos with digital microscope, and analyzed the results,then obtained a few simple rules.