Study On Anodic Corrosion Inhibition To Improve Discharge Performance Of Alkaline Aluminum-air Batteries

Metal-air batteries have the characteristics of high theoretical energy density,low cost,good safety,and environmental friendliness,which are regarded as one of the most promising energy supplements to lithium batteries.Among them,the aluminum-air（Al-air）battery has received extra attention because of its high theoretical energy density(8100 Wh kg^-1),negative electrode potential（-2.34 V vs SHE）,abundant reserves of aluminum and low price.Al-air batteries usually operate in alkaline electrolytes,because the alkaline electrolyte can remove the oxide film on the surface of Al anodes and effectively activate the Al anodes to achieve high discharge voltage and power density.However,serious self-corrosion reaction of Al anodes also occurs in alkaline electrolytes,resulting in a great difference between the actual energy density and the theoretical value.Hydrogen release from the self-corrosion process also increases security risks of the Al-air battery.Therefore,slowing down the self-corrosion of Al anodes to improve the utilization rate and energy density of Al anodes are crucial for realizing the commercialization of Al-air batteries.To solve the above problems,Al anode alloying,deformation and heat treatment and electrolyte additives are applied to inhibit the self-corrosion of Al anodes at present.However,Al anode alloying lacks sufficient theoretical basis and is limited by high preparation cost.It is difficult to obtain large-scale Al anodes through deformation processing.Meanwhile,the use of conventional electrolyte additives aggravates environmental pollution.To solve these key problems,a series of research work has been carried out in the aspects of composition design of Al anodes,new preparation process and electrolyte additives of aluminum anode materials to inhibit the self-corrosion of Al anodes,improve the utilization rate of Al anodes and the battery performance in this dissertation.It provides theoretical support and technical practice for the commercialization of high-performance Al-air batteries.The main contents and conclusions of the dissertation are as follows:1.Three kinds of Al alloy anodes（Al-Sn,Al-Mg,Al-Mg-Sn）were designed.The effects of the addition of Mg and Sn on the microstructure,electrochemical performance,corrosion resistance and battery performance of Al anodes in alkaline solutions were studied through experiments and DFT（Density functional theory）calculation.The results show that the addition of Mg and Sn can effectively improve the corrosion resistance,electrochemical performance and battery performance of Al anodes.Addition of Magnesium can inhibit the corrosion of Al anodes more effectively.Al-Mg displays the smallest self-corrosion rate and the largest specific electrode capacity compared with Al-Sn and Al-Mg-Sn Al anodes.Magnesium and tin elements have a synergistic effect on improving the electrochemical activity of Al anodes.The Al-Mg-Sn anode displays the highest electrochemical activity,the highest voltage and energy density.The calculated results of the surface energy of pure Al and Al alloy anodes are highly consistent with the experimental results.The calculation of the surface energy can provide reference for the design of Al anodes.2.Commercial 7050 Al alloys prepared by conventional casting and spray forming processes were studied as anodes for alkaline Al-air batteries.The effects of microstructural and precipitation changes caused by spray forming process,deformation and heat treatment on corrosion resistance,electrochemical behavior and battery performance of 7050 Al anodes were evaluated.The spray forming process can effectively refine the grains and reduce the microsegregation of Al alloy anodes;deformation and heat treatment can further eliminate the coarseηphase in the Al alloy anode,leading to a more uniform and dense microstructure.Spray-formed Al anodes and spray-formed Al anodes after deformation and heattreatment show better corrosion resistance and higher electrochemical activity,which is mainly attributed to the increased content of active elements such as Mg and Zn in Al matrix and the more uniform and compact microstructure of Al anodes due to the reduction of precipitated phases.The discharge capacity,energy density and utilization rate of the spray-formed Al anodes after deformation and heat treatment are 2655.2 m Ah g^-1,3159.7 m Wh g^-1 and 89.1%,respectively.It is proved that spray forming process makes it possible for commercial aluminum alloy to be used as anodes of Al-air batteries.3.High pressure die casting commercial pure Al was used as anodes for alkaline and neutral Al-air batteries for the first time.The effects of high-pressure die casting on the microstructure,electrochemical behavior and battery performance of Al andoes were studied.The research results show that high pressure die casting can effectively improve the microstructure of Al anodes,leading to the fragmentation and reduction of precipitated phase in Al matrix and can effectively refine the grains.High pressure die casting Al anodes show higher corrosion resistance and electrochemical activity in alkaline electrolytes than conventional casting Al andoes.The improved microstructure of high pressure die casting Al anodes can lead to more uniform anodic dissolution process,slighter self-corrosion and less discharge product accumulation,and the increase of grain boundary density also contributes to the improvement of Al anode activity.High pressure die casting Al andoes show higher anode utilization,discharge voltage and power density at all current densities in alkaline electrolytes.High pressure die casting Al anodes show better discharge stability in neutral electrolytes,but its effect on improving discharge voltage and power density is limited.4.Guar gum was used as the electrolyte additive for alkaline Al-air batteries.The results show that guar gum can effectively inhibit the self-corrosion process of Al anodes and hydrogen evolution reaction.The highest corrosion inhibition efficiency of guar gum is79.56%when its addition is 0.4 g L^-1.The 4N6 Al anodes show higher open circuit voltage and higher constant current discharge voltage in Na OH solution with 0.4 g L^-1 guar gum.The utilization rate and discharge specific capacity of the Al anodes also increases after adding guar gum.The adsorption of guar gum on the surface of Al anodes reduces the hydrogen evolution reaction sites.Guar gum reconstructs the hydrogen bond network and reduce the proportion of free water in the electrolyte,which is helpful to inhibit the self-corrosion of Al anodes and hydrogen evolution.Meanwhile,the addition of guar gum can reduce the accumulation of discharge products and self-corrosion products on Al anodes.Guar gum is an effective electrolyte additive for Al-air batteries.