Research On Preparation And Electrochemical Performance Of Biomass Carbon Anode Materials For Sodium-ion Batteries

In order to cope with environmental pollution and energy shortages,the demand for energy storage are growing quickly.Currently,the lithium ion batteries have been widely used in commercial applications for energy storage devices.However,lithium resource reserves are scarce and costly,thus more and more researchers turn to the new generation sodium ion batteries（SIBs）.In particular,it has been a key issue on the successful commercialization road of SIBs to look for safe,stable,low-cost,simple-prepared and environmentally friendly anode materials.Biomass carbon materials are the most commercially available materials due to the wide selection of precursors,simple preparation methods,high yield and good cycle stability.Here,coir and mangosteen shells are chosen as precursors to prepare biomass carbon anode materials with different morphologies.In this dissertation,the effects of morphologies on the electrochemical properties of the biomass carbon are investigated.Furthermore,the preparation methods of the material obtained by coir are explored to optimize the microstructure and electrochemical performance.The main results obtained are listed as follows:（1）Two kinds of biomass carbon anode materials with different morphologies are prepared by direct carbonization using coir and mangosteen shell as precursors.The coir carbon is consist of 3D side-by-side through holes,just as micro-honeycomb.On the opposite,the mangosteen shell carbon has irregular block structure.The micro-morphology of the two electrode materials is identical to that of the corresponding natural biomass materials,indicating that the biomass carbon has an inheritance property in terms of the morphology.The electrochemical performance of the two electrode materials are characterized using a sodium ion half-cell.The coir carbon and mangosteen shell carbon exhibit reversible capacity of 116 m A h g^-1 and 102 m A h g^-1 at a current density of 0.02A g^-1,respectively.Even when increasing the current density to 0.5 A g^-1,a specific capacity of 53 m A h g^-1 still can be achieved,with a capacity retention of 99%after 500cycles.However,the mangosteen shell carbon hardly obtain capacity at current density of 0.5 A g^-1.Moreover,the capacity decreases lightly after a small increase after 100cycles at a current density of 0.1 A g^-1.Coir carbon has excellent cycle stability and rate performance due to its 3D channel structure.（2）In order to further optimize the state of graphite domain inside the material,the carbonization temperature is explored.Three kinds of electrode materials are prepared by carbonization at 800℃,1000℃ and 1200℃ after the conventional ion activation pretreatment with coir as the precursor.The effect of carbonization temperature on the microstructure and its relationship with electrochemical performance are investigated.The graphite domain structure of the biomass carbon obtained by carbonization at1000℃ is most suitable for sodium ion storage and exhibits the best electrochemical performance.The reversible capacity of electrode is approximately 250 m A h g^-1 at the current density of 0.02 A g^-1.When increasing the current density to 0.5 A g^-1,a specific capacity of 110 m A h g^-1 still can be achieved.At the current density of 0.02 A g^-1,the capacity retention of 99%after 500 cycles was retained.（3）To further increase the reversible capacity of coir carbon,the different activation methods are studied.Three kinds of coir carbon anode materials are prepared by direct carbonization,ion activation pretreatment and air secondary activation at 1000℃ optimal carbonization temperature,respectively.The spacing of average graphene interlayer is expanded by ion activation,and the coir carbon further produces abundant nanopores by the secondary air activation.The electrode obtained by secondary air activation exhibits the most excellent electrochemical performance.The electrode demonstrates a high reversible specific capacity of 408 m A h g^-1 at a current density of 0.02 A g^-1.Even at a high current capacity density of 0.5 A g^-1,a capacity of 168 m A h g^-1 is achieved,and about 99%of the capacity is maintained over 500 cycles.After modified by activation,the electrode possess a higher theoretical capacity in addition to excellent cycle stability.