| The negative electrode materials of traditional Ni-MH batteries are mostly hydrogen storage alloys,which have high capacity,but they are easily oxidized and corroded by alkaline electrolyte under high temperature conditions,as well as high material costs and poor cycle life,which make them unable to be widely used.Perovskite-type oxide(ABO3)has a unique crystal structure,which makes the material have good electrochemical properties.After the substitution of metal cations at A and B sites,the crystal composition and structure will be changed,the concentration of lattice vacancy defects and the number of valence states will be changed.The formed composite oxides have rich adjustable physical and chemical properties,especially with the increase of test temperature.With the increase of the discharge platform of the sample electrode,the octahedral gap and oxygen vacancy that hydrogen atoms can enter increase,and the discharge capacity of the sample will be greatly increased.Therefore,it is of great potential and important application value and research significance to use it as a new type of Ni-MH battery anode material.In this paper,a series of ABO3 type oxide La MO3(M=Co,Cr,Fe)sample materials were prepared.The structure and microstructure of the samples were characterized by XRD,SEM,TEM and Raman.The energy gap and oxygen vacancy concentration of the samples were analyzed by UV and fluorescence spectra.Combined with the kinetic properties of the samples,the electrochemical properties of the samples at different test temperatures were studied systematically.The main research work is as follows:The LaCoO3 series samples(LaCoO3,LaCo0.9Fe0.1O3,La Co0.9Mn0.1O3,La Co0.9Zn0.1O3,La Co0.9Cr0.1O3,La0.9Li0.1Co O3)prepared by sol-gel method have excellent activation properties,uniform element distribution,high crystallinity,different concentrations of vacancy defects in oxide lattice and reduced band gap.The charge transfer ability and hydrogen absorption and desorption reaction ability of the composite sample electrode surface are obviously improved,and the limit current density of La Co0.9Zn0.1O3 and La Co0.9Cr0.1O3 and the hydrogen diffusion coefficient inside the electrode are better.When the test temperature is 303K,the Cmax of La Co0.9Cr0.1O3sample is the highest,which is 89.8m Ah·g-1.When the test temperature is 333K,the electrochemical performance of La0.9Li0.1Co O3 sample is the best,the capacity retention rate is 64.2%after 30 charge-discharge cycles with a Cmax of 153 m Ah·g-1.The LaCrO3 series samples(LaCrO3,LaCr0.9Co0.1O3,La0.9Li0.1Cr O3,La Cr0.9Mn0.1O3,La Cr0.9Fe0.1O3)prepared by combustion method have small grain size and uniform element distribution.After doping,the band gap decreases and the oxygen vacancy defect increases,which is helpful to improve the electrochemical capacity and electron transfer rate.The charge transfer rate and hydrogen absorption and desorption reaction on the surface of the electrode are enhanced,and the limit current density and hydrogen diffusion coefficient inside the electrode are increased.At 303K,the electrochemical performance of La Cr0.9Mn0.1O3 is the best,and the maximum discharge capacity is 18.8m Ah·g-1.The capacity retention rate is 88%after 30 charge-discharge cycles.When the test temperature is 333K,the electrochemical performance of La Cr0.9Co0.1O3 sample is the best,and the maximum discharge capacity is 94.3 m Ah·g-1.The capacity retention rate is 77%after 150 charge-discharge cycles.And with the increase of the number of charge-discharge cycles,the discharge capacity and capacity retention of lanthanum chromate series samples continue to increase.The La Fe O3 series samples(La Fe O3,La Fe0.9Co0.1O3,La Fe0.9Cr0.1O3,La0.9Li0.1Fe O3,La Fe0.9Mn0.1O3)prepared by sol-gel method have small grain size and uniform element distribution.The band gap of the composite sample decreases and the oxygen vacancy defect increases,which promotes the increase of electrochemical capacity and electron transfer rate.The doping and recombination of lanthanum ferrite samples not only did not enhance the surface activity of oxide samples,but also reduced the reversibility of hydrogen absorption and desorption electrochemical reaction on the electrode surface.However,the limiting current density and hydrogen diffusion coefficient of some composite sample electrodes have been improved.When the test temperature is 303K,the electrochemical performance of La Fe0.9Mn0.1O3 sample is the best,and the maximum discharge capacity is 38.8 m Ah·g-1.The capacity retention rate is 83.5%after 100 charge-discharge cycles.When the test temperature is 333K,the electrochemical performance of La0.9Li0.1Fe O3 sample is the best,and the Cmax is161.6m Ah·g-1.And with the increase of the number of charge-discharge cycles,the discharge capacity and capacity retention of lanthanum ferrite series samples continue to increase. |
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