Electrochemical Energy Storage Mechanism Of Magnesium Ions In FeOOH Electrode Material And Its Application In Microcapacitors

Micro supercapacitors are one of the most important micro energy storage devices.Because of their advantages that micro batteries do not have,such as their high power density,long cycle life,and fast charge and discharge rates,they are used in The application of miniaturized,portable devices has the prospect of complementing or even replacing microbatteries.However,low energy density is still the key to limit the application of micro-supercapacitors.In this paper,aiming at the low energy density of micro-supercapacitors,the research mainly focuses on electrode materials and electrolytes.FeOOH,a material with high specific capacity,is used as the Basic,constructing a three-dimensional conductive network,designing asymmetric micro-supercapacitors,and proposing a conductive polymer coating solution for the instability of FeOOH,introducing high-valent ionic aqueous electrolyte,and studying the reaction of FeOOH with magnesium ions in detail The final designed micro-supercapacitor showed excellent electrochemical performance.The research contents of this paper are as follows:（1）Construct a three-dimensional conductive network of indium oxide nanowires（ITO NWs）,improve the loading and conductivity of FeOOH electrode materials,construct an asymmetric device structure,introduce high-valent magnesium ion aqueous electrolyte,and enhance the energy storage performance of micro supercapacitors.The conductive network of indium oxide nanowires was prepared by chemical vapor deposition（CVD）method,and then FeOOH electrode material was electrochemically deposited on ITO NWs.In addition,the performance test of FeOOH in different ionic solutions(Mg²⁺,Na⁺,Li⁺,K⁺)found that it has higher redox activity in Mg²⁺aqueous electrolyte;under the same experimental conditions,it has the highest areal capacitance(108 m F cm^-2).At the same time,this work also studied the appropriate electrochemical deposition parameters of cathode Mn₃O₄,and found that electrochemical deposition at-1.4 V can maximize the loading of Mn₃O₄（0.56 mg,time300 s）.Afterwards,an asymmetric micro-supercapacitor was constructed by laser etching ITO NWs interdigitated electrodes,and electrochemical selective deposition of negative FeOOH and positive Mn₃O₄ electrode materials.Due to the introduction of Mg²⁺aqueous electrolyte,the device showed a wide voltage window（1.6 V）.and higher areal capacitance(26.31 m F cm^-2),larger areal energy density and power density(9.36μwh cm^-2,0.4 m Wh cm^-2 at a current density of 0.5 m Acm^-2).After 2000 cycles,the capacitance retention rate is 51.76%.（2）FeOOH was coated with conductive polymer Ppy to improve its stability,and in-situ XRD and quasi-in-situ XPS techniques were used to explore the energy storage mechanism of FeOOH.FeOOH was coated by electrochemical deposition of Ppy,and it was found that the stability and capacity were greatly improved.After 3000 cycles,the capacitance retention rate was 94.33%,and the capacity contribution rate of Ppy was 46%.In situ XRD and quasi-in situ XPS were used to determine the phase transition of magnesium ions during the reaction with FeOOH,that is,the formation of Mg O and Mg（OH）₂,and the intercalation reaction accompanied by Mg²⁺ions was the main energy storage mechanism.The assembled negative Ppy@FeOOH@ITO NWs//positive Mn₃O₄@ITO NWs asymmetric micro-supercapacitors exhibited a voltage window as high as 2.2 V,areal capacitance of 105.89 m F cm^-2,and energy density of 0.22 m Wh cm^-2.After 5000 cycles,its capacitance retention rate was 85%,showing excellent cycling stability.