Preparation of pitch-based hard carbon by bi-functional activation strategy for sodium-ion batteries
As the most promising anode material for sodium-ion batteries(SIBs),hard carbon has been widely studied and focused on its controllable adjustment of morphology and structural optimization.Herein,a novel bifunctional activation strategy was developed to prepare the hard carbon materials with highly disordered structures as anode for SIBs by using coal tar pitch as precursors with the help of potassium citrate monohydrate(C6 H5 K3 O7·H2 O).It is believed that the C6 H5 K3 O7·H2 O has a dual role:(1)its gas decomposition products can consume excessive hydrogen and further realize solid pyrolysis of pitch precursors,preventing the formation of ordered microcrystals;(2)the solid decomposition products(potassium salt)act as activating agents to introduce rich closed nanopores into the carbon matrix during high-temperature carbonization.Interestingly,the microstructure of pitch-based hard carbon can be optimized by tuning the amount of activating agents.Furthermore,the electrochemical performance investigations revealed that the as-optimized hard carbon(HC-2-1300)delivers a reversible specific capacity of 214.2 mAh·g-1 at 0.1 A·g-1 with an initial coulombic efficiency of as high as 81.5%,which is superior to that of directly carbonized samples(DC-1300).In addition,there is still a high reversible specific capacity of 116.7 mAh·g-1 at 5 A·g-1 and good cycling stability with a capacity retention rate of 75.1%over 2000 cycles,highlighting the great potential of pitch-based hard carbon anodes for SIBs.
sodium-ion batteriespitch-based hard carbonbi-functional activating agentelectrochemical performance
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