The Structure Regulation Of Biomass-based Materials And Their Electrochemical Performances

Biomasses possess wide sources,renewable and unique structure and so on.It is an important raw material for the preparation of porous carbon with high specific surface,hierarchical pore structure and excellent electron conductivity.Algae is a kind of marine plants,can cause red tide and other water pollution.The porous carbon was prepared and applied in the field of energy storage materials to realize high value utilization.In this paper,porous carbon materials were prepared by carbonization method and H₂O-steam activation method with porphyra as carbon source and Ni as catalyst.Meanwhile,this paper aimed to study the electrochemical properties as LIBs anode material and as the dispersive carrier of active sulfur in Li-S battery to enhance the conductivity,the loading of sulfur and improve the"shuttle effect".The main research contents are as follows:（1）Porous carbon materials were prepared by carbonation-activation method with porphyra as carbon source and Ni as catalyst.The graphitization degree of carbon materials were controlled by changing the carbonization temperature.With the increase of carbonization temperature（700-1000℃）,the contents of graphited carbon and amorphous carbon’s ratio increased from 1:1 to4:1.With the increase of graphited carbon content,the rate capacities of porous carbon were improved.The porous carbons were prepared at the carbonization temperature of 1000℃and its reversible capacity of 420.9 mAhg^-1 at the current density of 5.0 A g^-1.（2）Ni metal can not only act as a catalyst,but also play a role in pore formation.Therefore,this chapter explored the regulation rule of Ni content on the pore structure of biomass materials.The pore size of Ni particles formed was30-90 nm and the pore size formed by H₂O-activation was 3-5 nm.The hierarchical structure can facilitate lithium storage and charge transfer,thus improving the electrochemical properties.The porous carbon was prepared by the content of Ni（NO₃）₂ was 10 g,the pore volume formed by Ni particles accounted for 23.2%of the total pore volume.Its reversible capacity was maintained at 1288.1 mAhg^-1 with 200 cycles at 0.1 A g^-1.（3）Porous carbons were prepared by carbonation-steam activation method and used as a carbon carrier to load sulfur powder to obtain C-S composite materials.In order to enhance the poor conductivity of sulfur powder and improve shuttle effect in Li-S battery,the porous C-S composite materials’s graphitization degree（I_D/I_G=1.28）and the loading of sulfur（5.34%）were higher than that of the Acetylene black-S composite and the Super P-S composite.Three composite materials,at the current density of 0.1 C A g^-1,had the initial charging capacity were 501.5,524.5 and 660.1 mAhg^-1,the discharge capacity were 357.5,466.8 and 606.1 mAhg^-1,respectively.The use of flow Ar atmosphere protection caused the low loading of sulfur,resulting in low battery capacity.The subsequent experiments were carried out in a vacuum environment,which greatly increased the loading of sulfur（10-20 times）.When the loading of sulfur was 45%,the porous C-S composite materials had the capacity of 1226.2 mAhg^-1 at 0.1C A g^-1 and the capacity retention rate of 84.7%after 100 cycles.At the current density of 5C A g^-1,the capacity was 316.3 mAhg^-1.