| Aqueous zinc-ion batteries（AZIBs）are characterized by low cost,high specific capacity(820 mAh g-1)and green environmental protection.In the future,it will show the great possibilities of large-scale energy storage.The aqueous electrolytes used at the same time have high ionic conductivity and safety.However,Zn2+has a large size（0.074 nm）,resulting in strong charge pulsion during charging and discharging.This also means there are higher requirements for the cathode materials of Aqueous zinc-ion batteries.At present,the main cathode materials for Aqueous zinc-ion batteries are manganese oxide,vanadium oxide and Prussian blue analogues.Among these cathode materials,manganese oxide has been widely studied for its advantages of low cost,environmental friendly and high operating voltage.However,the main problems of this kind of materials are:poor conductivity,easy collapse of structure in the cycle process,irreversible phase transformation,etc.As a result,its specific capacity decreases rapidly and its cycle performance and rate performance are poor.This paper adopts the strategies of Na+and water molecules co-embedding and metal ion doping,that could improve the conductivity of manganese dioxide and the diffusion rate of Zn2+during charging and discharging,thereby achieving high performance cathode material for aqueous zinc ion battery,and probes into its electrochemical performance and zinc storage mechanism.The main research contents and conclusions are as follows:1.A layered Na0.55Mn2O4·1.5H2O cathode material co-embedded with Na+ and H2O water molecules was successfully constructed by salt template-assisted solid-phase sintering.Compared to the conventional solid-phase sintering system,NaCl crystals are used as templates,and the two-dimensional lamellar material manganese oxide is grown on its surface,and the two phases are in close contact,which reduces the spatial ion obstruction.The results show that compared with pure MnO2,the Na0.55Mn2MO4·1.5H2O material with layered structure provides a smooth transport channel for electron transport,and the Na+and H2O molecules between the layers play the role of "pillars",which can not only expand the layer spacing,but also firm the structure of the material.In addition,the "shielding" effect of water molecules reduces the effective charge of Zn2+,thereby improving the transport efficiency of Zn2+and enhancing the diffusion kinetics of ions.Benefitting for the unique structural advantages,it still has a reversible specific capacity of 155.7 mAh g-1 after 900 cycles when current density of 500 mA g-1,when it was tested as the cathode of aqueous zinc-ion battery,demonstrating excellent cycle stability.2.In order to improve the zinc storage kinetics,the Co-doped Na0.55Mn2O4·1.5H2O twodimensional lamellar materials were further prepared under the guidance of first-principles calculation.The doping of an appropriate amount of Co is beneficial to improve the conductivity of the material,stabilize the internal structure of the material system,improve the charge distribution of the system,and improve system band structure and electron distribution.The two strategies work together to improve the electrochemical performance of manganese dioxide in an overall way.The battery system at the current density of 500 mA g-1,after 550 cycles,discharge capacity is still 243.48 mAh g-1,at the same current density,discharge capacity of the undoped electrode is only 137.72 mAh g-1.At 1000 and 2000 mA g-1 current density,after 1000 cycles,there is only a slight decrease in capacity,demonstrating excellent cycle stability.In addition,the zinc storage mechanism of electrode was studied in depth by ex situ XRD and XPS.Moreover,the quasi-solid electrolyte has good self-healing and mechanical properties.When it is assembled into a quasi-solid state flexible battery at a current density of 100 mA g-1,the capacity retention rate is 50%after 50 cycles,and there is still very great room for improvement. |
