| Graphitic cathode materials of dual-ion batteries（DIBs）play a key role in determing energy density and cyclic lifetime of DIBs.The working potential of graphite is high,inducing electrolyte decomposition and fading of the cyclic performance.In this thesis,graphite flakes with thickness of 30～50 nm,artificial graphite powders and SiO2/carbon coated flake graphite were selected as cathode candidates for DIBs.A variety of structural and electrochemical methods were employed to analyze their microstructure and electrochemical PF6─-storage performance.The following conclusions were obtained:（1）In both Li-ion-based and Na-ion-based DIBs,graphite flakes exhibit superior cyclic stability and rate capability to those of the artificial graphite powders.In Li-ion-based DIBs,the reversible capacity of the graphite flakes remains 68.2 m Ah g-1after3000 discharge/charge cycles.The capacity fading rate is only 0.0059%.In addition,the graphite flakes display higher reversible capacity than that of the graphite powders at high current density,indicating that the graphite flakes have a great potential in application of high-charging-rate DIBs.（2）The graphite flakes exhibits good electrochemical performance at high working voltage.The capacity retention is 93%after 600 discharge/charge cycles at a voltage window of 3.5-5.2 V.（3）The cyclic stability and rate capability are enhanced after the flake graphites are modified with SiO2 nanoparticles and carbon.The capacity fading rate is only 0.004%after 450 cycles.The cyclic capacity of G/SiO2 is much higher than that of graphite at high current density.（4）G/SiO2 exhibits good electrochemical performance at high working voltage.The capacity retention is still 98.5 m Ah g-1 after 300 cycles at a voltage window of3.5-5.2 V,and there is no decay trend.It is a efficient strategy to enhance cyclic stability of graphite cathode and suppress electrolyte decomposion by co-coating of SiO2 nanoparticles and carbon. |
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