Effect Of Heteropolyacid Treatment And Electrolyte Solution Composition On The Electrochemical Properties Of Hydrogen Storage Alloys

In the past,the research on enhancing and improving the performance of conventional Ni-MH batteries was mostly focused on electrode materials,especially hydrogen storage alloy electrodes,but with the continuous development of hydrogen storage alloy research,it is difficult to effectively improve the electrochemical performance of hydrogen storage alloy electrodes by conventional alloying and tissue modulation methods,and the cost is high.In this paper,the electrochemical properties of hydrogen storage alloy electrodes were studied by XRD,SEM/EDS,XPS and electrochemical tests using La-Y-Ni series A₂B₇-type La_0.33Y_0.67Ni_3.23Mn_0.17Al_0.1 hydrogen storage alloy as the electrode material,and on the other hand,the laws and characteristics of the electrolyte composition and additives of alkaline aqueous solution on the electrochemical properties of hydrogen storage alloy electrodes were investigated.On the other hand,the effect of surface heteropolyacid treatment on the electrochemical properties of hydrogen storage alloy was explored.On this basis,the synergistic effect of alloy surface treatment and electrolyte modification on the electrochemical performance of hydrogen storage alloy was investigated,and the discharge capacity and cycling stability of hydrogen storage alloy electrode were obviously improved by the above-mentioned comprehensive modification treatment.The main research results are as follows:（1）Using Al（OH）₃ as an ion activator precursor,the effect of adding it to the traditional6MKOH electrolyte on the electrochemical performance of the alloy electrode was studied.It was found that adding a small amount of Al（OH）₃ to the traditional 6MKOH electrolyte improved the activation performance and cyclic stability of the alloy electrode to varying degrees.Specifically,when the alloy electrode was cycled in 6MKOH+1MAl（OH）₃,the cycle life S₁₀₀ was increased to 93.55%,which was nearly 10%higher than the S₁₀₀ of 82.79%in6MKOH alone.However,the addition of Al（OH）₃ had a negative impact on the high-rate discharge performance of the alloy electrode.（2）Using 6MKOH as a reference,different concentrations of K₂SO₄ were added to a mixed alkaline electrolyte of 6M Na OH+0.8MLi OH to investigate their effect on the electrochemical performance of the alloy electrode.It was found that compared to the single electrolyte of6MKOH,the high-rate performance,discharge capacity,and cycle life of the alloy electrode in the mixed electrolyte 6M Na OH+0.8MLi OH+x MK₂SO₄ were improved to some extent without significant improvement in high-rate performance.Specifically,the maximum discharge capacity C_max increased from 370.1m Ah/g in 6MKOH to 378.7m Ah/g in 6M Na OH+0.8MLi OH+0.1MK₂SO₄,and the capacity retention rate after 100 charge-discharge cycles improved from S₁₀₀=79.54%in 6MKOH to S₁₀₀=86.72%in6MNa OH+0.8MLi OH+0.05MK₂SO₄.（3）The effect of treating the alloy with different concentrations of phosphotungstic acid（TPA）as an acid treatment agent on the electrochemical performance of the alloy in 6MKOH electrolyte was studied.The morphology of the alloy surface after acid treatment showed an increase in the number of pits or corrosion holes,which increased its specific surface area.Effective improvement of the cyclic stability and high-rate discharge performance of the alloy electrode was achieved after treatment with TPA,with the capacity retention rate increasing from S₁₀₀=88.92%before treatment to S₁₀₀=92.44%after treatment with 0.05M phosphotungstic acid,and the high-rate discharge performance increasing from HRD₉₀₀=76.05%before treatment to HRD₉₀₀=81.84%after treatment with 0.05M phosphotungstic acid.Compared to other concentrations of TPA,the alloy electrode treated with 0.1M phosphotungstic acid showed relatively better electrochemical performance,with a minimal decrease in C_max from371.8m Ah/g to 370.7m Ah/g,and capacity retention rate of S₁₀₀=91.68%and HRD₉₀₀=81.24%.（4）Based on the previous results,it was found that the alloy electrode treated with 0.1 M TPA exhibited relatively good electrochemical performance.The electrochemical performance of the alloy electrode combined with different component electrolytes under this treatment condition was studied.It was found that the maximum discharge capacity of the acid-treated alloy electrode in 6M Na OH+0.8MLi OH+0.05MK₂SO₄ could reach 385.1 m Ah/g,and the capacity retention rate of the alloy electrode treated with heteropoly acid in 6M Na OH+0.8MLi OH+1M K₂SO₄ was S₁₀₀=94.6%,which was 13.3%higher than that of the untreated alloy electrode in 6MKOH.The cycle stability was also improved,which further demonstrated the synergistic effect of surface modification of hydrogen storage alloys and electrolyte modification on the electrochemical performance of the alloy electrode.