Preparation And Properties Of Manganese Dioxide For Aqueous Zinc-Ion Batteries

With the rapid development of portable electronic devices and new energy vehicles,the demand for high energy density batteries is increasing.Under continuous development,lithium ion batteries are close to their theoretical limitation of capacity.Moreover,the safety of the lithium-ion batteries is a currently urgent issue.Therfore,it becomes critically important to develop the next generation of battery systems with both high energy density and safety.Zinc is considered to be an ideal anode material for aqueous batteries because of its high capacity（820 mAh g^-1）,low potential（-0.762 V Vs.the standard hydrogen electrode）,high abundance,low toxicity and intrinsically safe.Aqueous zinc-ion batteries have attracted more and more attention because of their low cost,high safety and high energy density.Among these cathode materials,MnO₂ attracts much attention used as cathode materials in aqueous zinc-ion battery because of their low cost,safety and non-toxicity and good cycle performance.However,the MnO₂ hosts suffer serious the dissolution of Mn²+ from Mn³+ disproportionation and structural transformation during cycling processes result in poor reversible of aqueous Zn-MnO₂ battery.In this dissertation,to develope aqueous zinc-ion batteries with good rate performance and cycle performance,we designed and developed t-MnO₂ with large tunnel structure and layered MnO₂ with expanding the layer spacing.The main research results are summarized as follows:（1）We studied the performance of manganese dioxide with large tunnel structure.The t-MnO₂ with 3×3 tunnel structure is prepared.It is confirmed that manganese dioxide with large tunnel structure has the advantage of storing zinc ions.The effect of concentration of MnSO₄ to performance of t-MnO₂.t-MnO₂ battery with 0.5 M MnSO₄ dilivers a high discharge capacity of 284 mAh g^-1（92%of the theoretical capacity）.Considering the low first discharge specific capacity of t-MnO₂,t-MnO₂ doped with metal elements as cathode materials for Zn-ion batteries.the t-MnO₂ doped with metal elements were prepared by hydrothermal method.The results show that the doping of iron can improve the first discharge specific capacity of t-MnO₂.The first discharge capacity of Fe doped t-MnO₂ cathode is 12%higher than that of pristine t-MnO₂.The charge and discharge mechanism of t-MnO₂ is also studied.（2）The expansion of manganese dioxide layer spacing of layered structure is beneficial to the insertion of zinc ions.In this paper,two kinds of macromolecular organic molecules,tetramethyl ammonium hydroxide and tetrabutylammonium hydroxide,were inserted into the layered MnO₂ structure step by step.The layer spacing of layered MnO₂ was successfully increased from 0.71 nm to 0.92 nm.The electrochemical results show that the cycle performance of the battery is improved with the expansion of the layer spacing.When the concentration of Mn²+ in the electrolyte is 0.5 M,the battery can provide discharge specific capacity of 185 mAh g^-1 at 2 C after 100 cycles（100%capacity retention）.