Study On Anodic Materials For Nickel-zinc Secondary Batteries

With the continuous development of human society,the demand for energy is increasing rapidly.In addition,coal,oil and other non-renewable energy is on the verge of depletion,so the development of clean,environmentally friendly and sustainable new energy is very crucial.According to the current development,researchers mainly focus on the solar cells,rechargeable batteries,fuel cells and super capacitors and strive to make greater progress in these fields.Among these new energy sources,nickel-zinc rechargeable batteries become one of the representatives of the high-energy green power and cause more and more attention of researchers due to their high working voltage,high energy density,high power density,low cost and environmental friend.According to the current development status,short circle life and bad discharge performance restrict the practical application of nickel-zinc rechargeable batteries,leading to weak competitiveness compared with lithium ion battery and nickel-hydrogen,nickel-cadmium rechargeable batteries.ZnO is the active substance of negative electrode materials in nickel-zinc rechargeable batteries,as an amphoteric oxide,which has good solubility in alkaline electrolyte.In the discharge process,zinc dendrites are easy formed,thus cause deformation of negative electrode and internal short.Therefore,many researchers make efforts on this problem and modify the zinc negative electrodes to improve their electrochemical performances.Tamped density is another important factor restricting the practical application of nickel-zinc rechargeable batteries.In nickel-zinc rechargeable batteries we often use two or three times as much ZnO to match nickel-zinc rechargeable batteries,so the tamped density of negative electrode substances can determine the cost of the battery production.In this paper,we fabricated some active negative electrode substances with high tamped density and their formation mechanism and usage in zinc negative electrodes have been studied.The electrochemical performance and practical application of nickel-zinc rechargeable batteries were highly improved.The main research contents are as follows:(1)Negative electrode active materials,high tap-density ZnO microspheres,with enhanced volumetric capacity and improved cycling performance of nickel-zinc rechargeable batteries have been synthesized via a novel complexing co-precipitation method.The physical and electrochemical properties of the obtainedZn O microspheres are investigated.Notably,tap-density of the resultant ZnO microspheres can reach 3.00g·cm-3,three times higher than that of commercial conventional ZnO.Compared with the conventional ZnO,the obtained Zn O microspheres have demonstrated superior electrochemical properties,including higher volume speci?c capacity,better high-rate ability and better cyclic stability.At rates of 0.2C and 2C,the obtained ZnO microspheres deliver volumetric capacities of 1450 and 1110 mAh·cm-3,respectively,which are about three times higher than those of the conventional ZnO.These performance improvements are attributed to its unique highly dense spherical microstructure,thus leading to better reaction reversibility,more excellent anti-corrosion ability,smaller charge transfer resistance and better inhibiting effect on shape change of the material.Owing to its facile synthesis and outstanding electrochemical properties,this high-density spherical Zn O sample is a promising negative electrodes material for fabricating high performance Ni-Zn secondary batteries.(2)Use the high tap-density ZnO microspheres as precursor and glucose as carbon source to synthesize carbon-coated ZnO microspheres taking example by carbon-coated anode materials in lithium ion battery.This is the first time that we have put forward the concept of in-situ carbon-coated and double-carbon-film modification.After studying the physical and electrochemical properties of four as-prepared samples including high tap-density ZnO microspheres,as-calcined ZnO microspheres,as-calcined Zn O microspheres under protection of N2 and carbon-coated Zn O microspheres under protection of N2,we can find that the tap-density of double-carbon-film coated ZnO microspheres reaches 2.56 g·cm-3.At rate of 1 C,after 200 cycles the discharge capacity of double-carbon-film coated Zn O microspheres is 418 mAh·g-1,about 88% of its maximum discharge capacity,which is far more big than that of the other three samples.The morphology and other electrochemical properties have been studied,according to the result we can find that these properties have been improved mainly due to the modification of double-carbon-film,which can improve the conductivity of the material,reduce the polarization in the process of electrode reaction,reduce the internal resistance and decrease the solubility of ZnO in alkaline electrolyte.(3)According to the research idea of high tap-density ZnO microspheres,we investigate the influence of different morphology of ZnO precursors on the formation of calcium zincate.Calcium zincate crystals with high tap-density and good crystallinity have been fabricated via a simple chemical precipitation method using high tap-density ZnO microspheres as precursor.Another calcium zincate crystal is fabricatedusing commercial Zn O as precursor.We use scanning electron microscope and X-ray diffractometer to study the morphology and structure of these two calcium zincate crystals.We also study the tamped density and electrochemical properties of these samples.According to the results,we can find the formation of calcium zincate crystal is through a dissolved restructuring process and the morphology of the products has little to do with the morphology of the precursor.Although the test does not reach our expected purpose,I do learn the formation mechanism of calcium zincate.This work can lay a good foundation for later to modify calcium zincate and improve the material performance.