Vfe Prussian Blue And Its Derivatives Nanostructures:Preparation And Applications In Aqueous Ion Battery Electrode Materials

At present,due to the shortage of fossil energy and pollution problems,the development of renewable energy based on solar,wind and tidal energy has become an inevitable choice to solve the human energy crisis.However,these renewable energy sources still have problems such as uneven distribution in space and time,so in order to realize their application and popularization,the development of new energy storage technologies that are economical,safe and efficient is still the focus of current research.Among them,aqueous ion batteries have attracted wide attention of researchers because of their advantages such as safety,reliability,low cost and fast ion conduction.Due to their three-dimensional frame structure which can accommodate for ion fast transporting and storing,and multiple redox processes(V3+?V4?V5+,Fe(CN)63-?Fe(CN)64-),VFe Prussian blue framework materials are expected to become the next generation of commercial aqueous ion battery cathode materials.There fore,this paper focuses on the VFe-based Prussian blue framework cathode material in aqueous ion batteries,and deeply investigates its energy storage mechanism in ammonium ion batteries,combining nanosizing,phase conversion,doping and other modifications to optimize its performance in aqueous ion batteries.The main research results and innovations are as follows:By using first principle calculations,it was confirmed that the ammonium ions are adsorbed at the Ax sites in the Prussian blue framework material(AxMa[Mb(CN)6])by van der Waals interaction forces and the charge transfer is realized mainly through the interaction between hydrogen atom in ammonium ion and nitrogen atom in Prussian blue frame.On this basis,theoretical screening of ammonium ion battery performance was performed for iron-based Prussian blue analogs with different Ma site elements(Ma=Co,Cu,Fe,Mg,Mn,Ni,V,Zn).Taking into account the structural stability and nominal battery voltage range of the materials,the VFe Prussian blue framework material is selected as the aqueous ammonium ion battery cathode material that is expected to exhibit excellent electrochemical energy storage performance.In order to synthesize VFe Prussian blue framework materials with controlled raw material cost and regulated nanomorphology.KVFe Prussian blue analogues nanocubes(KVFe PBAs NCs)with regular morphology and homogeneous particle size were successfully prepared with hydrothermal method by introducing oxalic acid as complexing agent,using cheap ammonium metavanadate as vanadium source and potassium ferricyanide to provide ferricyanide ions.Because of the high electrochemical activity of vanadyl ion,the capacity of the aqueous ammonium ion battery can reach 92.85 mAh·g-1 at a high current density of 2 A·g-1.Meanwhile,due to the unique three-dimensional ion diffusion channels and good structural stability of the Prussian blue framework material,a capacity retention of 91.44%(84.9 mAh·g-1)after 2000 cycles can be achieved.To further improve the electrochemical energy storage performance of aqueous ammonium ion batteries,KVFe PBAs NCs were used as precursors and transformed into VSe2/FeSe2 composites with nanocubic morphology by a simple heat treatment selenization process.Thanks to the low reaction potential and high electrochemical activity of selenide,VSe2/FeSe2 NCs can effectively broaden the working voltage window(1.7→2.1 V)and significantly increase the specific capacity(227.1 mAh·g-1 at 1 A·g-1)based on the precursor.At the same time,due to the laminar ion diffusion channel introduced by vanadium selenide,excellent rate performance at ultra-high current densities(109.7 mAh·g-1 at 5 A·g-1)and good cycling stability(139.7 mAh·g-1 after 2000 cycles)can be achieved,which has excellent application prospects for aqueous ammonium ion batteries.In view of the excellent performance of aqueous ammonium ion batteries of VFe Prussian frame materials and its derived selenide composites,selenium doping in KVFe PBAs nanocubes was successfully achieved by microwave assisted heat treatment.The performance of SeKVFe PBAs NCs in different carriers(Li+,Na+,K+,Mg2+,Zn2+,Al3+,NH4+,OH-)was tested.Among them,the wide operating voltage window(2.0 V),fast ion diffusion rate and high specific capacity(207.9 mAh·g-1 under 0.5 A·g-1)are displayed in the aqueous magnesium ion battery,which further expands the application of VFe Prussian blue framework materials in the field of aqueous ion battery.