Preparation And Sodium Storage Performance Study Of High-quality Prussian Blue Analogues

Because of their long life and high specific energy,LIBs are widely used in portable electronic devices and electric vehicles.However,safety hazards and limited lithium resources hinder using LIBs for large-scale ESSs.In this context,low-cost,long-life SIBs offer a more attractive alternative to LIBs for EESs.Therefore,it is imperative to develop sustainable electrode materials for SIBs.PBAs,a new material allowing reversible insertion/extraction of Na ions in their structural frameworks,are extensively studied as cathode materials for SIBs,following NASICON,polyanion-type compounds,and layered oxides.Usually,the chemical formula of PBAs can be denoted as A_xM[Fe?CN?₆]_1-y??_y?z H₂O,?where A is an alkali-metal ion,M is transition-metal ion,?represents vacancies,and the values of x,y,and z depend upon the stoichiometry?.Theoretically,PBAs can store two Na ions per formula;however,most PBAs suffer from poor cyclability and low Coulombic efficiency due to large lattice distortion during cycling and high vacancies of Fe?CN?₆ in crystal frameworks,respectively.1.In summary,a series of HQ-Ni_xCo_1-x[Fe?CN?₆]PBAs with a tunable Ni-Co ratio,few[Fe?CN?₆]vacancies,and low crystal water content were synthesized by a facile chelating agent/surfactant co-assisted method.It was found that,benefitting from limited charge/discharge depth,the Ni-introduced PBA framework undergoes minor lattice variation during cycling,which significantly impacts PBAs'electrochemical performance as cathode materials for SIBs.In addition,there are fewer Fe?CN?₆ vacancies and water molecules in HQ-PBAs frameworks.As a result,HQ-NiCoFe exhibits a high specific capacity of 145 mAh g^-1 by performing a 1.68-electron transfer,an impressive cycling stability with a⁹0%capacity retention over 600 cycles at 5C,and a high Coulombic efficiency of 100%.Meanwhile,the full cell using HQ-NiCoFe as cathode delivers a reversible capacity of 125.6 mAh g^-1 at current rate of 0.1 C and still retains a reversible capacity of 109.6 mAh g^-1 without noticeable capacity fading at a current rate of 1 C after300 cycles.The application of HQ-NiCoFe might give new insight into the design of high-capacity and high-stability cathode materials for room-temperature SIBs.2.a novel“zero-strain”insertion cathode materials,cerium hexacyanoferrate?CeHCF?,were successfully synthesized by a facile co-precipitation method for the application in Li⁺,Na⁺batteries.Owing to its open 3D framework and highly stable crystal structure,CeHCF shows impressive Li/Na storage properties.When applied as cathode material for LiBs and SIBs,they delivered specific capacity of 58 mAh g^-1@0.25C and 77%capacity retention@8.3C;55 mAh g^-1@0.25C and 54%capacity retention@8.3C,respectively.Through multiple characterization techniques combined with ex situ XRD and ex situ Raman,alkali ion intercalation of CeHCF is unveiled.Our studies not only enrich the family of Prussian blue analogues,but also offer a new promising candidate as a universal host for alkali ion batteries.3.Prussian blue?PB?and its analogues?PBAs?are considered as promising cathode materials for Na-ion batteries because of its rigid open framework with large interstitial sites and high theoretical specific capacity(170 mAh g^-1).Nevertheless,the reported specific capacity of PB still falls far behind the theoretical value.Meanwhile,PB suffers from low Coulombic efficiency and poor cycling stability.According to research,PB prepared through the conventional synthetic method always exhibits large amounts of vacancies and defects in the crystal framework.In this work,we discussed a method to improve the crystallization process to prepare more perfect crystals.PBAs?FeFe,CoFe,NiFe?were synthesized at room temperature through a facile coprecipitation method,then I transferred the solution into reactors.The solution was maintained at 120?for 24hours.This step continues the growth of PBAs and the high temperature provides energy to the crystals to overcome the already generated defects,which makes the crystals more prefect and less vacancies and achieving the theoretic capacity when acted as cathode material for sodium ion batteries.