Modification And Investigation Of Electrochemical Performance Of Graphite Flakes And Prussian Blue Analogous Cathode Materials

The development of new cathode materials with high specific capacity and long cycle life is the key to improve the energy density of electrochemical energy storage devices.In view of the disadvantages of serious electrolyte decomposition and poor cyclicability of graphite cathode material for dual-ion batteries,and the disadvantages of low cycle life of Prussian Blue Analogues cathode material for sodium-ion batteries caused by high interstitial water content and various lattice defects,herein light-weight g-C₃N₄ and amorphous carbon-modified graphite flakes（CN+C）/GF were prepared by liquid-solid phase separation method as cathode materials for dual-ion batteries.In addition,Na-enriched Na_1.71Mn[Fe（CN）₆]_0.90·1.06H₂O（NMF）was prepared by direct precipitation method using trisodium citrate dihydrate（TSC）as the complexing agent.The structure,composition and electrochemical performance of the two cathode materials were systematically studied,and the following conclusions were obtained:（1）In the（CN+C）/GF samples prepared by liquid-solid phase separation method,g-C₃N₄ particles with sizes of 4～5 nm are homogeneously embedded in the amorphous carbon matrix covering the GF surface.g-C₃N₄ can suppress the decomposition of electrolyte and induce the formation of cathode-electrolyte interphase（CEI）layer,while the presence of amorphous carbon improves the binding strength between the modification layer and graphite flakes.The reversible capacity retention of（CN+C）/GF-2 reaches 87%after 1500 charge/discharge cycles at 5 C with a capacity fading rate of as low as 0.0087%,exhibiting excellent cyclicability.Compared with Ti O₂/carbon modified GF,the capacity of（CN+C）/GF-2 is increased by～11%and～3%at 1 C and 10 C,respectively.（2）The sodium content of NMF can be increased by increasing the content of TSC complexing agent in the raw material.Meanwhile,the addition of TSC can also decrease the rate of reaction;reduce the content of interstitial water,vacancy and other defects in NMF.NMF-2 has the highest content of sodium atoms and the lowest content of interstitial water in lattice,exhibiting the excellent electrochemical performance.At the current density of 50 m A g^-1,the initial specific discharge capacity of NMF-2 reaches 119.2 m Ah g^-1,and the initial Coulombic efficiency reaches 91.1%.After 150 cycles,the specific discharge capacity of NMF-2 reaches102.2 m Ah g^-1,and the capacity retention reaches 85.8%with a capacity fading rate of as low as 0.095%.