Design Of Manganese And Tungsten Oxide Electrode Materials And Study Of Aqueous Ion Storage Mechanism

Unlike ion batteries,aqueous batteries are gradually applied to energy storage owing to their high safety and energy density.Transition metal oxide electrode materials such as MnO₂,WO,etc.are the main research objects in aqueous battery electrode materials owing to their simple preparation,high specific capacity and various crystalline structures.However,due to the poor structural stability of transition metal oxide electrode materials,the appearance of negative"dendrites"and low electrical conductivity,transition metal oxide electrode materials are still facing the problems of poor cycling stability and multiplicity performance.In order to solve these problems and develop aqueous batteries with excellent structural stability and multiplicative performance,metal Pre-intercalation and vacancy modulation are carried out for MnO₂ and W₁₈O₄₉ electrode materials respectively to enhance their electrochemical performance as follows:（1）Firstly,Al-O bonds were constructed in the 2 x 2 tunneled[MnO₆]cell unit ofα-MnO₂ using Al（NO₃）₃?6H₂O as a dopant,and AMO cathode materials were synthesized and investigated as cathode materials for aqueous Zinc ion batteries.TEM and XPS tests demonstrated that Al was successfully intercalated into the MnO₂ lattice and improved the crystal plane spacing of AMO.DFT calculations demonstrate that Al-O is a triple coordination structure,and the band gap of AMO is reduced to 0.85 e V owing to the intercalation of Al,while the spin-down state of Mn 3d orbitals is increased due to the intercalation of Al,indicating that the AMO cathode has superior electrochemical activity.The electrochemical test results show that the AMO cathode has a capacity of 401.7 m Ah g^-1 at a current density of 0.5 A g^-1,which is almost twice that of pristine MnO₂,and has excellent multiplicative performance.In addition,the reversible phase transition of the AMO cathode during Zn²⁺insertion/extraction was investigated using In-situ Raman,and the cycle retention of the AMO cathode after 2000 cycles was above 95%owing to the stabilizing effect of the Al-O bond on the[MnO₆]cell.（2）W₁₈O₄₉-O_V anode were prepared and applied to aqueous aluminum ion batteries by introducing oxygen vacancies in W₁₈O₄₉ with a reducing gas containing hydrogen.The successful introduction of oxygen vacancies in W₁₈O₄₉-O_V was demonstrated by XPS and EPR investigation.DFT calculations demonstrate that the W₁₈O₄₉-O_V anode has lower Al³⁺ion migration energy barriers and insertion energy,indicating that the vacancies improve the electrochemical kinetic performance of the W₁₈O₄₉-O_V anode.The maximum specific capacity of the W₁₈O₄₉-O_V anode in aqueous aluminum ion batteries is 251.3 m Ah g^-1 with a capacity retention of 96.5%after 5000 cycles.In addition,the reversible phase transition of W₁₈O₄₉-O_V anode during the insertion/extraction of Al³⁺ions were investigated by In-situ Raman.Finally,the storage behavior of Al³⁺ions in W₁₈O₄₉-O_V was further investigated by Ex-situ XRD measurement,which demonstrates the reversible phase transition from W₁₈O₄₉-OV to Alx W18O49-OV.（3）Finally,the prepared AMO and W₁₈O₄₉-O_V were used as the cathode of the aqueous zinc ion battery and the anode of the aqueous aluminum ion battery to construct the soft pack cell,respectively.Benefit from the excellent flexibility of Zn@Carbon cloth,the assembled flexible aqueous zinc ion battery can be connected to sensors,enhancing the application of wearable energy storage devices.Cu Fe-PBA//W₁₈O₄₉-O_V soft pack aqueous aluminum ion battery was constructed by using W₁₈O₄₉-O_V as the anode.The prepared battery has superior cycling stability compared with making non-aluminum foil anodes and aluminum foil anodes.The maximum energy density of the prepared soft pack battery is 55.3 Wh kg^-1 owing to the1.8 V electrochemical window of the soft pack battery,which will further expand the application of aqueous aluminum ion batteries in energy storage devices.