The Study Of Prussian Blue And Electrolyte For High Voltage Aqueous Secondary Battery

Aqueous metal ion batteries（RAMB）have the advantage of high safety,high rate capability,low cost and environmentally-friendly,which make it a significant potential to be applied in the large scale energy storage and portable equipment field.But they possess a low working voltage,poor energy density and cycling performance,hence it is very important to develop novel concept and theory of building high voltage aqueous batteries.In this work,the target is designing new RAMB by selecting appropriate electrodes materials,hoping to improve the working potential and energy density of the batteries.Meanwhile,the battery should also exhibit a good cycling performance.Firstly,Prussian blue crystals were prepared by coprecipitation method,and three-electrode system was used to test the electrochemical performance of the Fe₄[Fe（CN）₆]₃（FeHCF）in aqueous electrolyte containing the same concentration of Li⁺、Na⁺、K⁺、Ca²⁺.The results proves that the ion selectivity of FeHCF in aqueous solutions follow the order:K⁺>Na⁺>>Li⁺>Ca²⁺.And FeHCF shows better shows better electrochemical stability in the electrolyte containing Na and Li.But in the electrolyte of K⁺and Ca²⁺,it has a lower working voltage and more serious hydrogen evolution and oxygen evolution reaction.Because of the limitation of negative electrode,Li-Na mixed electrolyte is used to realize the secondary battery with high specific energy and high stability.It lays a foundation for the further application of FeHCF in aqueous batteries filed.Secondly,by controlling the concentration of sodium ferrocyanide,the amount of pH value of the solution and the dose of polyvinylpyrrolidone（PVP）,the well-defined FeHCF particles with cubic phase are obtained.Combining FeHCF as cathode,TiP₂O₇ as anode,the aqueous Li⁺/Na⁺nixed-ion battery were manufactured,in which the ion-selectivity mechanism are studied by Ex-XRD test.The battery of FeHCF//TiP₂O₇ possesses a potential of 1.92V,and its capacity retention was 95.6%after 400 cycles,which shows a good cycle stability.It is also found that the volume change of FeHCF crystal cell from 1.1%to 4.0 with the increase of Na ratio in electr olyte,which exhibit a small volume straiFinally,TiNb（PO₄）₃（TNPO）anode material with NASICON structure is synthesized by high temperature solid state method,and it was verified that TNPO has electrochemical activity for lithuium and sodium.Meanwhile,the TNPO anode exhibits the best electrochemical performance in 3M LiClO4 electrolyte.Utilizing TNPO as anode,LiMn₂O₄（LMO）as cathode and 3M LiClO₄ aqueous solution as electrolyte,the aqueous LMO//TNPO lithium ion battery is manufactured,which delivers an voltage of 2.1V with a high energy density of 180Wh Kg^-1.Meanwhile,the battery shows an excellent cycling performance,which indicated that TNPO was suitable for aqueous electrolyte system.This not only expands the selection range of anode materials,but also indicates that there is room to improve the voltage of battery in aqueous system.