Electrochemical Hydrogen Storage Behavior Of Hydrogen Storage Alloy And Amorphous Silicon In Proton Ionic Liquid Electrolyte

Ni-MH batteries have excellent power characteristics,energy density and safety,but its open circuit voltage is often limited by the narrow electrochemical stability window of water-based electrolyte?theoretical voltage of water decomposition 1.23V?,making its energy density lower than LIB.At the same time,the hydrogen storage alloy electrode has poor cycle stability in the KOH electrolyte.Therefore,finding a new type of electrolyte with wide electrochemical window and low corrosivity and high-capacity electrode material matched the electrolyte is an effective way to solve the problem,which has great significance for the development of high energy density Ni-MH batteries.In this paper,1-ethyl-3-methylimidazolium acetate?EMIMAc?and acetic acid were mixed as the protic ionic liquid electrolyte instead of alkaline solution.The electrochemical hydrogen storage behavior of A₂B₇ hydrogen storage alloy,palladium modified alloy and amorphous silicon as negative electrode materials in protic ionic liquid electrolyte were investigated.The research results were as follows:?1?The protic ionic liquid electrolyte had good thermal stability and its initial thermal decomposition temperature was 210?.The viscosity of ionic liquid could be reduced and the conductivity could be increased by adding acetic acid.With the temperature increased,the viscosity decreased rapidly and the conductivity increased significantly.?2?A₂B₇ alloy electrode in 4M mixed electrolyte showed the maximum discharge capacity reached 26.6mAh/g.There were several holes on the electrode surface for the electrode after reaction and mass linear matter appeared in the holes.Palladium plating alloy electrode had the maximum discharge capacity 23.2mAh/g.The alloy electrode prepared by wet method possessed slower activation process which showed the maximum discharge capacity 21.5mAh/g.Plating Palladium and changing the electrode preparation method had little effect on improving the electrochemical performance of the alloy electrode.?3?The amorphous silicon?a-Si?powder with layered structure was prepared by chemical delithiation from Li₁₃Si₄ compounds and the ball milling modification of a-Si was carried out subsequently.The hydrogenation behavior of the a-Si before and after modification in H₂ and the effect of hydrogenation treatment on the electrochemical hydrogen storage performance of the a-Si electrode in proton conducting ionic liquid were investigated.The results showed that ball milling could obviously reduce the particle size of a-Si,but it introduced Fe,Cr impurities and leaded to the formation of Fe₂Si and CrSi₂.Crystallization of a-Si occurred gradually during hydrogenation and a-Si was completely crystallized when the hydrogenation time was more than 8h.Ball milling contributed to increase the initial hydrogen absorption of a-Si and the hydrogen absorption increased gradually with the hydrogenation time prolonged,while the hydrogen absorption of a-Si for 2h,5h,8h and 58h were 0.38wt.%,0.76wt.%,0.91wt.%and 3.8wt.%,respectively,but the rate of hydrogen absorption in later stage were relatively slow.There were electrochemical hydrogen absorption and desorption activity for a-Si electrode in proton conducting ionic liquid,but its discharge capacity were relatively low?42¹63mAh/g?,which the a-Si with ball milling and hydrogenation for 8h had the maximum discharge capacity 163mAh/g after 20 cycles.Ball milling modification and proper hydrogenation dealing?8h?were favorable to improve the discharge capacity of a-Si electrode.