Study On The Carbonization Behavior Of Prussian Blue And Its Use As A Negative Electrode Material For Lithium-ion Batteries

The derivatives of metal-organic frameworks（MOFs）after pyrolysis and carbonization can usually inherit the multi-dimensional structure of MOFs materials and are considered as a kind of lithium-ion battery anode materials with great development potential.Among them,the cheap MOFs material Prussian blue（PB）,because of its skeleton structure contains elements such as iron,carbon and nitrogen,and its pyrolysis-derived nanomaterials have received extensive attention.Based on this,this article uses commercial PB as the precursor,and uses atmospheric pressure,hydrothermal,and static high pressure pyrolysis methods,conducted related research around the pyrolysis and carbonization behavior of PB under normal pressure and high pressure,such as structure,morphology,and electrochemical lithium storage performance.The specific research content and results are as follows:（1）The effects of temperature,atmosphere and hydrothermal coating on the carbonization behavior of PB and the performance of lithium storage were systematically studied in a normal pressure environment.In the air environment,two crystalline Fe₂O₃ are formed after PB pyrolysis,and the temperature has a great influence on the crystalline quality and microscopic morphology of Fe₂O₃.In addition,electrochemical tests show that the three samples prepared in this environment have poor electrochemical performance and cannot be used as negative electrode materials for batteries.In an argon atmosphere,PB gradually transforms into Fe₃C as the pyrolysis temperature increases,and its microscopic morphology also transforms from cubes to nanospheres.In addition,the 400℃sample has a higher reversible specific capacity,but the rate performance is poor;the 650℃and 900℃samples have better rate performance,but the reversible capacity is lower.Based on the above research,the Fe₃C@C composite material was prepared by pyrolyzing PB after carbon coating by hydrothermal method.Fe₃C@C has a uniform cubic structure with a BET specific surface area of 144.26 m²/g.In addition,the generated pseudocapacitance improves the electrochemical performance of Fe₃C@C.Among them,when the current density is 1000 m Ag^-1,the reversible specific capacity can still be stabilized at 428.9 m Ahg^-1 after 200 cycles.（2）The effects of temperature and pressure on PB carbonization behavior and lithium storage performance were studied under high pressure environment.Different from pyrolysis under normal pressure environment,high pressure has a greater influence on the morphology of the product,especially the cubic morphology of PB is difficult to retain.In addition,the 1.5 GPa,650℃sample showed excellent electrochemical performance.After 60 cycles at different current densities,the discharge specific capacity can still recover to 707.2 m Ahg^-1when it returns to 50 m Ag^-1.（3）On the basis of the previous two chapters,porous carbon was prepared by hydrochloric acid etching,and its morphology,structure and lithium storage performance were studied.The porous carbon AP-650 derived from the sample at 650℃under atmospheric argon atmosphere showed a"honeycomb"porous structure,while the porous carbon HP-650 derived from the sample at 650℃at 1.5 GPa showed a uniform porous structure.The BET specific surface areas of AP-650 and HP-650 are 355.13 m²/g and 166.93 m²/g,respectively.In addition,AP-650 still has a high reversible specific capacity of 515.1m Ahg^-1 after being cycled for 100 cycles at a current density of 100 m Ag^-1.The excellent electrochemical performance is attributed to the large-area contact between the electrode and the electrolyte brought about by the"honeycomb"porous structure,which provides more active sites for the insertion of lithium ions.