Effect Of In Situ Synthesized Transition Metal Sulfides On The Electrochemical Properties Of La-Y-Ni-based A₅B₁₉ Hydrogen Storage Alloys

La-Y-Ni superlattice hydrogen storage alloys have become one of the research hotspots of new high-performance Ni-MH battery anode materials due to their excellent electrochemical properties and controllable preparation.Improving the dynamic performance and cycle life of hydrogen storage alloys is of great significance for the application of Ni-MH batteries in the field of new energy vehicles.A transition metal sulfide active layer with high electrocatalytic activity,good electrical conductivity and strong bonding force is prepared on the alloy surface by hydrothermal synthesis,which is expected to improve the high rate discharge performance of the alloy electrode.This research mainly in La-Y-Ni system A₅B₁₉-type La_0.25 Nd_0.2Y_0.55Ni_3.22Co_0.3Mn_0.18Al_0.1 alloy as the research object,and as a source of Ni in the alloy elements,using one step hydrothermal method in the alloy surface in situ growth Ni₃S₂ and Ni₃S₂/MoS₂.By means of XRD,SEM,EDS,TEM,XPS and electrochemical analysis characterization(at25?),the influence of hydrothermal synthesis process on the growth of active substances and the electrochemical properties of the alloy was systematically explored.The research results of this paper are as follows:(1)Using sodium sulfide(Na₂S)as the precursor solution,the effect of hydrothermal treatment time on the growth of Ni₃S₂and the electrochemical performance of the electrode was studied.The results show that the Ni₃S₂film is formed on the rough surface of the alloy.With the increase of time,the Ni₃S₂production increases and the coating area gradually expands.At the same time,the cycle life and high-rate discharge ability of the alloy electrode are increased firstly and then decreased with the prolonging of treatment time.After 100 cycles,the capacity retention rate(S₁₀₀)of the alloy electrode hydrotreated for 4 h reached 89.2%,which was 3.3%higher than that of the untreated alloy electrode(S₁₀₀=85.9%).When the discharge current density of the alloy electrode hydrothermal for 7 h was 1800 m A/g,the high rate discharge performance of the alloy electrode HRD₁₈₀₀=45%is 7.7%higher than that of untreated alloy(HRD₁₈₀₀=37.3%),the 7 h treated alloy electrode has the best high rate discharge performance in this series.(2)Subsequently,in order to further improve the high-rate discharge ability,the effects of hydrothermal treatment temperature on the growth of Ni₃S₂ and the electrochemical performance of the electrode need to be further explored based on the above 7 h treatment process.The results show that with the increase of preparation temperature,a large area of disordered growth of Ni₃S₂ occurs,so that the selective nucleation is no longer possible.With the increase of hydrothermal treatment temperature,the high-rate discharge ability and cycle life of the alloy electrode both increased firstly and then decreased.The result of S₁₀₀=90.7%after 160?hydrothermal treatment is 4.8%higher than that of the untreated alloy(S₁₀₀=85.9%).The HRD₁₈₀₀ of the alloy after 140?hydrothermal treatment is 55.3%,which is 18%higher than that of the untreated alloy(37.3%).(3)The electrochemical performance of Ni₃S₂ modified alloy electrode is limited,Ni₃S₂/MoS₂ was synthesized in situ by hydrothermal method using ammonium tetrasulfide molybdate((NH₄)₂MoS₄)as the precursor solution.The influence of solute content of precursor on the growth of Ni₃S₂/MoS₂ and electrochemical properties of alloys was investigated.The results show that with the increase of solute content,the cycle life increases first and then decreases,and the high-rate discharge ability increases monotonically.When the solute content is less than 12 mg,MoS₂ and NiO are formed on the surface of the alloy.When the solute content reaches 12 mg,a small amount of Ni₃S₂/MoS₂was synthesized on the alloy surface.After hydrothermal treatment with 10 mg of solute precursor solution,the result of the alloy S₁₀₀=88.9%is improved by 3%compared with that of the untreated alloy(S₁₀₀=85.9%),and the HRD₁₈₀₀ of the alloy treated with 12 mg of solute precursor solution is improved by 9.4%compared with that of the untreated alloy(37.3%).(4)A small amount of Ni₃S₂/MoS₂ was synthesized on the surface of the alloy,and the improvement of electrochemical performance of the alloy electrode was limited.It was found that the production of active substances increased with the increase of hydrothermal time.In order to increase the yield of Ni₃S₂/MoS₂,it is necessary to explore the influence of different temperatures on the growth of Ni₃S₂/MoS₂ and the electrochemical properties of the alloy on the basis of prolonging the hydrothermal time.The results show that the Ni₃S₂/MoS₂composite products can be successfully prepared on the surface of the alloy by hydrothermal treatment at different temperatures.After treatment,the cycle life and high-rate discharge ability of the alloy electrode are significantly improved.After the hydrothermal treatment at 120?,the S₁₀₀=92%of the alloy electrode is increased by 6.1%compared with that of the untreated alloy(S₁₀₀=85.9%).The HRD₁₈₀₀ of the alloy electrode after the hydrothermal treatment at 160?is65.8%,while that of the untreated alloy(37.3%)is increased by 28.5%.