Study On Effect Of Rare Earth And Annealing Treatment On Hydrogen Storage And Electrochemical Properties Of Super Lattice Structure La-Y-Ni A₅B₁₉ Alloy

The research results of La-Mg-Ni hydrogen storage alloys with super lattice structure are abundant and some commercial applications of the alloys have been realized currently.There are larger security risks during the preparation due to the low melting points and high saturated vapor pressure of the key element Mg,meanwhile,the difficulty of accurately controlling the Mg content in the preparation process also be increased.Studies have shown that the new La-Y-Ni hydrogen storage alloys with super lattice structure has high electrochemical discharge capacity,easy activation,low hydrogen-induced amorphization tendency as well as good reversible hydrogen absorption and discharge performance,which possess high research value and development prospects as a anode material for Ni-MH battery in the future.At present,there are many reports on the La-Y-Ni series A₂B₇ hydrogen storage alloy show that the A₂B₇ alloys have higher electrochemical discharge capacity,its charge-discharge cycle stability needs to be improved.In addition,due to A₅B₁₉ type has more[CaCu₅]substructure unit stacking than A₂B₇ type structure,theoretically it should have better structure and cycle stability when charging and discharging?absorbing hydrogen?.On the basis of the above research background,in this paper,the La-Y-Ni A₅B₁₉ type La_1-xY_xNi_3.52Mn_0.18Al_0.1?x=0-1?hydrogen storage alloy was selected as the research object,which systematically studied the influence of Y element on the phase structure,gaseous hydrogen storage performance and electrochemical performance of A₅B₁₉ hydrogen storage alloy,and determined the best Y element by XRD,SEM,EDS,Sievelts type PCT device and electrochemical test methods.Furthermore,the effects of heat treatment and substitution of rare earth elements?R=Yb?Er?Nd?Pr?Ce?La?Sm?Gd?on the microstructure and electrochemical properties of A₅B₁₉ alloy were analyzed.The main conclusions of this article are as follows.?1?When the content of Y element is less than 0.3,the phenomenon of hydrogen-induced amorphization is serious,which generate unobvious hydrogen absorption and desorption platform of A₅B₁₉ type La_1-xY_xNi_3.52Mn_0.18Al_0.1?x=0-1?hydrogen storage alloy,reversible hydrogen absorption and desorption performance and low electrochemical capacity;while the Y element content is between 0.5 and 0.7,the alloy has a more suitable hydrogen absorption and desorption plateau pressure and a higher electrochemical discharge capacity?324.3³85.8 mA·h/g?,when the Y element content is 0.6,alloy electrodes have the highest electrochemical discharge capacity(C_max=385.8 mA·h/g)and better cycle stability(S₁₀₀=84.06%);if the Y element content is higher than 0.85,the discharge capacity of alloy electrode is lower due to the high pressure of hydrogen absorption and discharge platform.?2?Taking the alloy in the A₅B₁₉ type with better comprehensive performance as the research object,the effect of heat treatment on the phase structure and electrochemical cycling performance of La_0.4Y_0.6Ni_3.52Mn_0.18Al_0.1 alloy was systematically studied.The results show that when the annealing temperature of La_0.4Y_0.6Ni_3.52Mn_0.18Al_0.1?x=0.6?alloy is 1273 K,the abundance of A₅B₁₉ type phase accounts for 92.92%.After annealing for 48 hours at 1273 K,the alloy electrode has the best electrochemical cycling performance(S₁₀₀=89.84%),and after annealing for 48 hours at 1298 K,the alloy electrode has the highest electrochemical discharge capacity(C_max=386.6 mA·h/g).It shows that heat treatment has a greater influence on the electrochemical performance of A₅B₁₉ type La_0.4Y_0.6Ni_3.52Mn_0.18Al_0.1 alloy.?3?An investigation on microstructure and electrochemic properties of?R=Yb,Er,Nd,Pr,Ce,La,Sm,Gd?R_0.4Y_0.6Ni_3.52Mn_0.18Al_0.1 alloys were developed.The results showed that the cycling stability of the A₅B₁₉ alloy electrode was the best if the replacement element is Nd,Capacity retention S₁₀₀ increased from 82.87%to 93.38%.?4?This section systematically investigated the effect of Nd content on the microstructure,gas hydrogen storage performance of La_0.4-xNd_xY_0.6Ni_3.52Mn_0.18Al_0.1.1 alloys.The results show that with the increase of Nd content,the hydrogen absorption and desorption platform pressure of the alloy is below 0.1 MPa;the activation performance and maximum discharge capacity of the alloy electrode are reduced with the increase of Nd content,but the cycle stability is gradually improved.The capacity retention rate(S₁₀₀)gradually increased from82.87%?x=0?to 93.7%?x=0.4?after 100 charge and discharge.The HRD₉₀₀ also gradually increased to 87.79%.