Modification Design And Electrochemical Performance Of Electrode Materials For Aqueous Zinc-ion Batteries

With the advancement and development of social science and technology,people's demand for energy is urgently increasing.As an energy storage device,secondary batteries play an important role in industrial production and daily life.Aqueous zinc-ion batteries have the characteristics of high conductivity,low cost,safety and environmental friendliness,and have garnered extensive attention from researchers in recent years.Electrode materials play a key role in the electrochemical performance of aqueous zinc-ion batteries.Manganese-based materials possess the advantages of high energy density,easy preparation,and non-toxicity,and are considered to be an ideal cathode material for aqueous zinc-ion batteries.However,manganese-based oxides still address the following problems in practical applications:1)Low electrical conductivity and slow ion diffusivity;2)The dissolution of Mn²⁺during discharge leads to the reduction of active species;3)The structure undergoes phase transition and collapse due to repeated intercalation/deintercalation of ions.In addition,aqueous zinc-ion batteries use metallic zinc as the anode,which can achieve higher energy density thanks to the low redox potential and high specific capacity of zinc.However,the zinc anode also faces serious problems:1)the growth of zinc dendrites leads to short circuit of the battery;2)the coulombic efficiency decreases due to side reactions such as hydrogen evolution and corrosion.The positive and negative materials faced with these problems seriously hinder the further development of aqueous zinc-ion batteries.Therefore,it is of great significance to develop high-performance positive and negative electrode materials for aqueous zinc-ion batteries.Based on the crystal structure and working principle of energy storage materials,this topic proposes modification strategies for positive and negative electrodes,aiming to develop high-performance aqueous zinc-ion battery materials.1.We prepared a cation-defective manganese tetroxide(D-AMO)by a hydrothermal-etching method.Specifically,an aluminum source(Al)was introduced during the synthesis of Mn₃O₄ to prepare Al-substituted Mn₃O₄(AMO),and then AMO was etched in an alkaline environment to obtain Mn₃O₄(D-AMO)with cationic defects.As a cathode material,D-AMO has the following advantages:1)The mesoporous structure increases the specific surface of the material and improves the ion diffusion rate;2)Benefiting from the synergistic regulation of aluminum and cations,the material exhibits good electrical conductivity;3)The cationic defects can weaken the electrostatic interaction between the intercalated ions and the lattice framework and increase the diffusion kinetics of the ions.The D-AMO was assembled into a coin cell battery for testing.When the current density was 100 m A g^-1,D-AMO exhibited a reversible capacity of 302 m Ah g^-1,and it remained stable after 1000 cycles at a current density of 1500 m A g^-1.Maintaining a stable capacity of 147 m Ah g^-1,it was assembled as a pouch battery for testing,and still showed excellent electrochemical performance.2.We prepared a kind of manganese dioxide(KMO)with a super-large interlayer distance of 7.4?by the method of"hydrothermal potassium intercalation".The"hydrothermal insertion of potassium"strategy can promote more K⁺and crystal water to enter the interlayer and act as"pillars"to widen the sterically stable structure.Experimental and theoretical calculations prove that the larger interlayer distance of KMO is beneficial to the fast migration of intercalated ions.In addition,this process is a form of ion exchange,which can resurrect more active sites.Using KMO as the cathode material for aqueous zinc-ion batteries,it can exhibit a reversible capacity of 300 m Ah g^-1 at a current density of 200 m A g^-1,and at a current density of 2000 m A g^-1,it can still be used after 12,000 ultra-long cycles.A stable capacity of 158 m A g^-1 is maintained.In addition,the KMO electrode material also showed excellent rate and cycle performance in the pouch battery test.3.Based on the previous optimization of the electrochemical performance of the two manganese-based modified materials,in order to further improve the electrochemical performance of the zinc-ion battery,it is necessary to design and modify the negative electrode.We fabricated a 3D carbon nanotube current collector(g-Ag@CNT)with a gradient concentration of silver nanoparticles(Ag NPs)to suppress Zn dendrite growth by a multi-stage coating process.The good zincophilicity of Ag NPs can reduce the nucleation overpotential of Zn to regulate uniform deposition.In addition,the gradient distribution of Ag NPs can accelerate the deposition of Zn inside the 3D electrode to suppress dendrites.It was tested as a working electrode in half-cells and showed good deposition/stripping ability.The g-Ag@CNT//D-AMO full battery composed of g-Ag@CNT//D-AMO after pre-zincification and the cation-deficient manganese tetroxide(D-AMO)prepared in chapter three was tested at a current density of 100 m A g^-1,the capacity can reach305 m Ah g^-1,and under the current density of 1500 m A g^-1,the stable capacity of161 m Ah g^-1 can still be maintained after 1000 cycles.This strategy of developing a3D current collector with a gradient distribution of zinc-philic sites provides a new designing idea for suppressing the growth of zinc dendrites and improving the overall performance of the battery.