Prussian Blue Derived Iron-Carbon Composite As The Cathode Of Lithium Ion Battery

In recent years,Prussian blue（PB）has been widely studied because of its low price,simple preparation process and hollow structural skeleton.In particular,the nanomaterials prepared by pyrolysis of Prussian blue can often inherit some of its structural characteristics,such as large specific surface area,interconnected pore structure and hierarchical pore size,which makes Prussian blue have unique application advantages in many aspects.Among them,its structural characteristics will play a huge role in energy storage and conversion systems.For example,by adjusting the temperature or atmosphere in the synthesis conditions,nanoelectrode materials with ideal structure and properties can be prepared,especially as the anode of lithium-ion batteries.At present,the pyrolysis behavior and pyrolysis products of Prussian blue under normal pressure have been extensively studied,but the pyrolysis reaction of Prussian blue under high pressure has been rarely involved.Based on this,pyrolysis and carbon coating behavior of Prussian blue were studied under high pressure conditions.On this basis,the relationship between morphology,structure and electrochemical properties of the product was studied.The results are as follows:1.To study the effects of different pressures and reaction times on the carbonization behavior of Prussian blue and the electrochemical properties of its products.Under the conditions of 600℃ and 30 min,Prussian blue carbonized at 1.0 GPa to form a mixture of FeO and Fe₃C.Carbonization at 1.5,2.0 and 2.5 GPa to generate a mixture of FeO and Fe₃O₄;Carbonization at 3.0,3.5 and 4.0 GPa produces a mixture of Fe₃O₄ and Fe₃N.In addition,with the increase of pressure,the morphology of the product changed from a aggregated state to a granular structure of tens of nanometers,and the specific surface area also increased,among which the PB-3.5 sample could reach 163.919 m²g^-1.The electrochemical performance of Prussian blue products under these different conditions is different.Among them,the reversible specific capacity of PB-3.5 at a small current density of 100 m Ag^-1 was 869.63 m Ahg^-1,and PB-2.5 had the best performance under high current charge and discharge;in addition,the reversible specific capacity increased with the increase of charge and discharge times at a current density of 1000 m Ag^-1,and finally stabilized at 799.03 m Ahg^-1.In addition,while the pressure and temperature remained constant only extended the reaction time to 2 h,it was found that Prussian blue mainly produced a mixture of FeO and Fe₃N.The morphology of the product changed from granular to aggregated,and the specific surface area decreased accordingly.Electrochemical tests have shown that the electrochemical performance of the product after extended reaction time is reduced.Among them,the reversible specific capacity of PB-2.5 2 h cycling 100 times at a small current density of 100m Ag^-1 reaches 395.66 m Ahg^-1.2.To study the carbonation behavior of urea coated Prussian blue and its effect on electrochemical performance.At 600℃,3.0 GPa and 30 min,the carbon-coated products of urea and Prussian blue with mass ratios of 12.5%and 25%,respectively,were mixtures of FeO and Fe₃N.The carbon coating products with mass ratios of 50%,100%and 200%were Fe₃O₄.In addition,the product is microscopicly aggregated when the urea content is small,and when the urea content reaches 50%,it shows a uniform granular structure with a size between 20-30 nm.When the urea content increases further,the nanoparticles become larger in size and begin to connect with each other.The samples with a mass ratio of 50%in this series have a large specific surface area(246.460 m²g^-1).XPS photoelectron spectroscopy analysis of the sample showed that the product contained four elements,Fe,O,C and N,and a clear amorphous carbon structure around Fe₃O₄ was observed by HR-TEM test.This shows that the Fe₃O₄@CN composite material is successfully prepared when the mass ratio of urea and Prussian blue is 50%.Electrochemical tests on urea-coated Prussian blue products with different contents showed that the performance of the coating was improved after carbonization of Prussian blue.Among them,the reversible specific capacity of 100 cycles Fe₃O₄@CN at a current density of 100 m Ag^-1 reaches 1198.70 m Ahg^-1,and its rate performance is optimal.In addition,the specific capacity increases during 500 cycles at a high current density of 1000m Ag^-1,and finally stabilizes at 843.69 m Ahg^-1,and the good performance is attributed to the contribution of its pseudocapacitance.In addition,samples with a mass ratio of 50%at 2.5 and 3.5 GPa showed that the product was a mixture of FeO and Fe₃O₄ under the two pressures,and the morphology gradually agglomerated by nanoparticles and the specific surface area was also reduced.Electrochemical tests showed a decrease in electrochemical performance compared to samples at 3.0 GPa.This result may be related to the reduced specific surface area of both samples.3.Study the carbonation behavior and electrochemical performance of urea-formaldehyde resin（UF）coated with Prussian blue.We synthesized four urea-formaldehyde resins with different levels of formic acid.At 600℃,3.0 GPa and 30 min,four urea-formaldehyde resins were used to coat Prussian blue.The results showed that the Prussian blue products coated with urea-formaldehyde resin were all mixtures of Fe₃N and FeO.In addition,with the increase of formic acid content,the morphology of the product is transformed from nanoparticles into a network structure and finally aggregates into a block.Electrochemical tests show that the electrochemical performance of the sample with the network structure is superior.