Study On The Structure And Properties Of Rare Earth Ni-based Multicomponent Alloys As Electrode Materials For Ni/MH Batteries

In this paper,the rare-earth Ni-based multi-component alloy is used as the negative electrode material for Ni/MH batteries.The purpose is to study the phase structure and electrochemical performance of the rare-earth Ni-based multi-component alloy.The thesis uses the hydrogen storage alloy La_0.8Mg_0.2Ni_3.1Al_0.3Mn_0.1 as the alloy benchmark to explore the effect of element substitution and annealing on the phase structure and electrochemical performance of the benchmark alloy.The research content mainly includes two modules:the effect of Co element substitution of Ni on the electrochemical performance of the benchmark hydrogen storage alloy,and the optimal ratio of the alloy is selected by comparison;on the basis of the optimal ratio,the Mo element substitution and annealing treatment for hydrogen storage The influence of alloy phase structure and electrochemical performance.The XRD diffraction pattern shows that the element substitution and annealing treatment did not change the phase structure of the hydrogen storage alloy.The phase structure of the alloy contains three phases,respectively LaNi₅ phase,La₂Ni₇ phase,La₇Ni₃ phase.Although the composition of the phase structure has not changed,the unit cell volume and unit cell parameters in the phase structure have changed;the SEM image of the alloy shows that the alloy has a multi-phase structure,and each phase structure is distributed regionally;Consistent with XRD.Electrochemical test results show that after the base alloy is replaced with Co element（the ratio is 0,0.1,0.3,0.5,0.7）,the cycle stability and the maximum discharge capacity of the battery are significantly increased.When the Co element substitution ratio is 0.5 The highest discharge capacity of the alloy is 307.2 mAh/g,and the stability is 79.5%at 50cycles.The addition of Co element improves the cycle stability.At 50 cycles,the cycle stability of Co0.5 is increased by 13%compared to the benchmark,In summary,the optimal ratio of Co element substitution is 0.5.On the basis of the optimal ratio,Mo element substitution（the ratio is 0,0.1,0.15,0.2）and annealing treatment were performed respectively,and it was found that the high rate discharge performance and cycle life of the battery were generally improved.When the Mo element ratio is 0.1,the cycle life is up to 83.67%at 100 cycles;after annealing,the maximum discharge capacity increases to 325 mAh/g,especially when the temperature is-20℃,the discharge capacity is 291.3mAh/g,low Electrochemical studies have shown that as the temperature decreases,the discharge capacity decreases.Annealing treatment reduced the electrochemical impedance.The HRD600（%）of the annealed alloy was62.54%,which was 8%higher than the as-cast alloy.