Preparation And Investigation Of High Performance Prussian Blue Analogues Cathode Materials For Potassium-ion Batteries

As one of the most important storage batteries,lithium-ion batteries(LIBs)have been widely used in portable devices,electric vehicles and so on.However,the overuse of lithium resources leads to rising prices and limited resources,which will constrict the development of LIBs.Thus,it is meaningful to explore new energy storage devices/batteries as the substitution of LIBs.Potassium and lithium have similar physicochemical properties and potassium resources are abundant and cheap,thus,potassium-ion batteries(KIBs)are regarded as a kind of promising large-scale storage device/battery.However,due to the large radius of K⁺,it is difficult for K⁺to intercalate/deintercalate the traditional cathode materials.Hence,developing new types of cathode materials with larger ions channel and excellent performance becomes an important and urgent issue for KIBs.As a kind of 3D open-framwork materials,Prussian blue analogues(PBAs)have spacious channels for intercalation/deintercalation of K⁺,which have gained comprehensive attention in recent years.Nevertheless,KIBs with PBAs materials as cathode still suffer the bad rate performance and poor cycling stability problems.In this thesis,we foucus on the Fe-based Prussian blue(FeHCF),and investigated the influence of the coating of Ni-based Prussian blue materials(NiHCF)and polydopamine(PDA)on the electrochemical perforemance of Fe-based Prussian blue(FeHCF).Futhermore,we also investigated the effect of the addition of Na Cl in the synthesis process on the structure and electrochemical perforemance of FeHCF.The main research contents and achievements are as follows:(1)The core-shell FeHCF@NiHCF composites were prepared by an in-situ growing method.It is found that NiHCF coating improves the electronic conductivity,stabilizes the structure and activates more C-Fe²⁺/Fe³⁺couples to participate in the redox reaction.The capacitiy of FeHCF@NiHCF at 500 mA g^-1 is 79.24 mAh g^-1,which is 465%higher than the value of FeHCF.And the capacity of this sample remains 80.38%after 250 cycles at 200 mA g^-1.(2)The FeHCF@NiHCF@PDA composites were prepared by an in-situ polymerization method.FeHCF@NiHCF with PDA coating further improves the electrochemical performance of FeHCF@NiHCF.Compared to FeHCF@NiHCF,the capacity of FeHCF@NiHCF@PDA is improved from 104.79 mAh g^-1to 115.06 mAh g^-1 at 50 mA g^-1 and from 79.24 mAh g^-1to 94.72mAh g^-1 at 500 mA g^-1.And the capacity of the sample remains 86.16%after 250 cycles at 200mA g^-1.(3)The NI-FeHCF composites were prepared by adding Na Cl into the synthesis process.Due to less coordinated water and Fe(CN)₆vacancies,the sample has excellent electrochemical performance.The composite exhibits a high capacity of 125.89 mAh g^-1 at 50 mA g^-1,82.00mAh g^-1 at a high current density of 500 mA g^-1,and 79.71%capacity retention after 250 cycles at 200 mA g^-1.Futhermore,less Fe(CN)₆vacancies increase the number of C-Fe²⁺/Fe³participating in the redox reaction.The corresponding high-voltage plateau capacity is improved from 39.41 mAh g^-1 to 54.65 mAh g^-1,which increases the energy density of batteries.