Synthesis And Investigation Of Prussian Blue Cathode Materials For Potassium-ion Batteries

With the advantages of high energy density,long cycle life,Lithium-ion batteries?LIBs?have been regarded as one of the most predominant devices,widely used in energy storage systems,portable electronics,and electric vehicles.However,rising prices and limited storage of lithium salts would restrict its large-scale application.Thus,exploring new batteries based on other alkaline metals like potassium or sodium is of great importance.On account of its cheap cost,abundant storage,and similar standard potential compared to Li⁺/Li couple?K⁺/K,-2.93 V;Li⁺/Li,-3.04 V?,Potassium-ion batteries?PIBs?have aroused enormous attention and been considered as a promising competitor in the future large-scale EESs.However,due to the large radius of potassium ions?K⁺,1.38?;Li⁺,0.76??,current PIBs are still impeded by low K-storage capacity,poor rate performance and so on,that is primarily limited by the electrochemical performance of cathodes.Hence,the development and investigation of the new cathodes with excellent performance has become an important research topic in PIBs.Due to their 3D open framework with available diffusion channels of K ions,Prussian blue?PB?and its analogues have gained extensive attention.Nevertheless,those materials also have problems such as low capacity,poor cycling stability.In this work,we attempt to synthesize the ternary-metal Prussian blue materials via a co-precipitation method,and systematically investigate the cause of the improved electrochemical property of ternary-metal materials.In this research basis,the Fe-based Prussian blue materials are researched by doping various amount of Ni,and Ni-doping is investigated to the effect of capacity performance and voltage plateau.Furthermore,we have prepared the Prussian blue materials with regular structure and morphology via a hydrothermal method,and studied the effect of particle size on potassium storage performance.The main investigation findings are as follows:?1?By adjusting the Ni,Co ratio,Our optimal ternary-metal sample K₂Ni_0.36Co_0.64Fe?CN?₆?PBNC?is investigated,which could effectively improve the initial capacity and cycle stability of materials.its reversible capacity is 85.7 mAh g^-1,and still has 83.3 mAh g^-1 after 50 cycles,which is 47% and 325% higher than the values of K_1.49Ni[Fe?CN?₆]_0.91?PBN? and K_1.49Co[Fe?CN?₆]_0.91?PBC?,respectively.According to the mechanism analysis,the suitable Ni substitution could balance the 3D open framework structure during large K ions intercalation/deintercalation contributed by the electrochemical inactive state of Ni.?2?The post-optimized Prussian blue NiFePB-5 represents superior electrochemical performance via suitable Ni doping,it shows enhanced initial capacity of 134.89 mAh g^-1 and excellent cycle performance,just declining 0.0059% per cycle from 150th cycle to 300th cycle.According to the investigation,Ni ions could motivate the C-coordinated Fe²⁺C₆/Fe³⁺C₆ redox by changing the electronic state of Fe ions,so the corresponding high-voltage plateau capacity is improved from⁴0 mAh g^-1 up to 53 mAh g^-1.That would obviously improve the energy density of batteries.?3?The Prussian blue materials with regular structure and morphology are prepared via the hydrothermal method.It is found that the small-sized PB-S's initial discharge capacity is up to 124 mAh g^-1,which is significantly improved compared to large-sized PB-L.We suppose that small-sized particles shorten the migration path of K ions compared to large-sized particles,and are more conducive to the rapid diffusion of potassium ions.