Preparation And Study Of Manganese-Based Cathode Materials For Aqueous Zinc-Ion Batteries

With the continuous increase of energy demand in human society,the development and utilization of clean and renewable energy has become the main way for countries in the world to overcome the energy crisis.However,most renewable clean energy sources are intermittent energy sources,which cannot achieve continuous energy supply.Therefore,it is imperative to create cheap and safe large-scale energy storage systems.Among a series of energy storage systems,aqueous Zn-ion batteries have the potential to realize large-scale energy storage applications.However,there is still no cathode material that can meet its commercial application in aqueous Zn-ion batteries,and the most promising manganese-based cathode materials still have problems such as poor conductivity,unstable crystal structure,loss of Mnelements,and poor kinetic properties.Therefore,this thesis studied the modification of MnO₂ through the method of composite structure design and ion pre-intercalation,and obtained a manganese-based cathode material with high discharge specific capacity and good cycle stability.The specific research contents are as follows:（1）Using CNT as the conductive substrate and reaction template,CNT@MnO₂composites with a three-dimensional conductive network structure was successfully prepared through in-situ chemical reactions.Based on the high conductivity and high specific surface area of CNT,the conductivity and kinetic properties of CNT@MnO₂ are significantly improved.The ion diffusion coefficient of CNT@MnO₂ is as high as3.72×10^-13 cm²/s,which is two orders of magnitude higher than that of commercial MnO₂.At the same time,the obtained CNT@MnO₂ effectively suppresses the loss of Mnelement in MnO₂ due to the Jahn-Teller effect,and stabilizes the crystal structure of the material.The discharge specific capacity of the obtained CNT@MnO₂ can reach 275.54m Ah/g,and the capacity retention rate can reach 86.50%after 1200 cycles at a current density of 500 m A/g.（2）Starting from the overall structure of the cathode,a three-dimensional layered carbon-based conductive substrate LGP with abundant active sites and a self-supporting integrated manganese-based cathode（LGP@K_xMnO₂）without binders and conductive agents were successfully prepared by electrochemical treatment and in situ hydrothermal reaction.In addition,the amount of K⁺intercalation in LGP@K_xMnO₂ can be adjusted by adjusting the p H value of the reaction environment.It is found that the pre-intercalation of an appropriate amount of K⁺can broaden the interplanar spacing of the material and stabilize the crystal structure of the material.Meanwhile,the energy storage mechanism of LGP@K_0.15MnO₂ was explored in detail,and the results found that in addition to the reversible deintercalation of H⁺and Zn²⁺in the crystal structure of the material,there are also reversible side reactions and chemical conversion processes during the charge and discharge process.The discharge specific capacity of the obtained LGP@K_0.15MnO₂ is as high as 358.9 m Ah/g,and the capacity retention rate can reach 92.5%.（3）Using LGP as a conductive substrate,the pre-intercalation of different metal cations(Na⁺,Ca²⁺,K⁺)in the crystal structure of MnO₂ was successfully achieved by electrochemical deposition reaction.It is found that the pre-intercalation of metal cations can not only widen the interplanar spacing of the material,stabilize the crystal structure of the material,but also improve the microscopic morphology of the material and improve the conductivity of the material.The capacity retention of the obtained Na_0.017MnO₂,Ca_0.036MnO₂ and K_0.039MnO₂ after 100 cycles at a current density of 200 m A/g is as high as 126.91%,119.12%and 111.21%,respectively.At the same time,a flexible wearable energy storage device with practical application prospects was assembled with Ca_0.036MnO₂ as the cathode and LGP@Zn as the anode.The discharge specific capacity of the obtained energy storage device is as high as 386.40 m Ah/g,and the capacity retention rate can reach 85.52%.