Modification And Electrochemical Performance Of LaFeO₃ Materials

The perovskite oxide LaFeO₃ matreials used as the novel negative matieral for metal hydride-nickel?MH-Ni?batteries has many advantages,such as wide range of sources,easily prepared and high discharge capacity at high temperature.However,several inherent drawbacks,such as the particles easy aggregation,intrinsical poor conductivity and electrochemical kinetic properties,deteriorate its performance seriously.Aiming at this problem,nickel-treatments,carbon-treatments and carbon/nickel combined treatments are applied.The LaFeO₃ materials were synthesized by solid-state method.And we studied the influences on the morphology characterization and electrochemical properties which were caused by the nickel-treatments.After nickel treatments,the crystal and phase structure remained,the grain size decreased and the aggregation reduced.The sample which was treated by 10wt%nickel had the best electrochemical properties.The maximum discharge capacity(C_max)of the LaFeO₃ electrodes increased from 266.8 mAh g^-1 to 346 mAh g^-1,and the high rate dischargeability at a discharge current density of 1500 mA g^-1(HRD₁₅₀₀)increased from 23.8%to 41.8%.The electrochemical kinetic test showed that the electrocatalytic activity and hydrogen diffusion rate of LaFeO₃ particles were increased,and the hydrogen diffusion coefficient was increased from 0.53×10^-16 cm² s^-1 to 2.32×10^-16 cm² s^-1.After nickel treatment,the charge transfer resistance on the surface of LaFeO₃ electrode was decreased,thus the electrochemical reaction rate increased.The modifications of carbon-treatment and carbon/nickel combined treatments were realized by mechanical ball milling method.After either of the above two methods,the surface of the material became rough,and the aggregation was reduced.A translucent carbon coating layer appeared.After carbon/nickel combined treatments,the maximum discharge capacity,high rate dischargeability and cycle stability of LaFeO₃ electrode were improved,C_max improved from 266.8 mAh g^-1 to 345.1 mAh g^-1,HRD₁₅₀₀ enhanced from37.5%to 50.1%,and S₁₀₀ increased from 52.9%to 60.9%.Electrochemical kinetic tests showed that the exchange current density and hydrogen diffusion coefficient were increased.