Study On Construction And Properties Of Lignocellulosic Biomass-based Energy Storage Materials

As the most abundant natural renewable resource on the earth,lignocellulosic biomass could be used for the production of pulp and paper,and also has a widely applications in the field of energy storage due to its rich carbon content and natural porous structure.Therefore,how to achieve the fully utilization of the carbon skeleton of lignocellulosic biomass to prepare energy storage materials has become a hot topic.In this work,poplar wood chips and bleached softwood kraft pulp were used as the raw materials,the construction methods for the production of energy storage materials based on these two lignocellulosic biomass were explored,and their properties were analyzed.The first part of this work is to prepare wood-based porous carbon materials using poplar wood chips as raw materials.Firstly,poplar wood chips were subjected autohydrolysis pretreatment to dissolve most of the hemicellulose in the wood chips.The changes of lignin structure and pore structure in wood chips after autohydrolysis pretreatment were revealed.The effects of these changes on the structure and electrochemical performance of wood-based porous carbon materials were also discussed.The results showed that the cleavage of ?-O-4 linkages in lignin structure occurred during the autohydrolysis pretreatment,and the degradation reaction was further increased with increase of the combined hydrolysis factor.The dissolution of chemical components results in the increase of specific surface area,average pore size and total pore volume in wood chips.The autohydrolysis pretreatment had no significant effect on the crystalline structure of carbon,but the degree of disorder of carbon increased.Secondly,the cellulose in the poplar wood chips was partially dissolved by the molten salt hydrate pretreatment,and the influence of this method on the structure and electrochemical performance of the wood-based porous carbon material was investigated.Metal ions could be remained in the wood chips after the pretreatment using the inorganic molten salt hydrate,resulting in the change in the crystalline structure of the carbon.Among the two kinds of inorganic molten salt hydrates used in this work,the ZnCl2 played more important influence on the degree of disorder on wood-based porous carbon materials than CaCl2.Finally,a combination of autohydrolysis pretreatment and molten salt hydrate pretreatment was used to dissolve more chemical components in poplar wood chips,and the pretreated wood chips were carbonized to prepare porous carbon materials.The structure and electrochemical performance of such carbon materials were analyzed.The effects of auto-hydrolysis pretreatment,molten hydrate treatment,and the combination of these two treatment methods on the electrochemical performance of wood-based porous carbon materials were compared.Both autohydrolysis pretreatment and inorganic molten salt hydrate pretreatment were beneficial to improve the electrochemical performance of wood-based porous carbon materials,but the effects of the two pretreatments were independent.The porous carbon materials prepared by using HCl-treated autohydrolyzed poplar wood chips had an excellent capacity of 280.5 F g-1 at a current density of 1 A g-1.In the second part of this work,bleached softwood kraft pulp was used as the scaffold and carbon source.The spacing of micro fibrils in the cell wall of the fiber increased after the alkali pretreatment,which could improve the accessibility of the fibers.The physical and chemical characteristics were investigated after pretreatment in different alkali concentrations,and the effects of the alkali concentration on the surface morphology,structural characteristics and electrochemical properties of wood pulp fiber-based SiO2/C composite materials were also revealed.In addition,we also analyzed the effects of precursor concentration and carbonization temperature on the morphology,structural characteristics,and electrochemical performance of the composite materials.The results showed that the alkali pretreatment could reduce the crystallinity of wood pulp fiber.It also increased water absorption and water retention values,as well as the absorption capability of the wood pulp fibers for the precursor silicon liquid.The charge-discharge specific capacity and the first cycle efficiency of the SiO2/C composite materials derived from alkali swollen wood pulp fibers were significantly improved.The SiO2/C composite materials could keep the original shape of wood pulp fiber no matter whether the pulp fiber was pretreated with alkali or not,and the carbon scaffolds derived from the wood pulp fiber could provide a reliable buffer layer and a good mechanical support for silicon dioxide,which offered the excellent cycle stability of SiO2/C composite materials.Both the increase of precursor concentration and carbonization temperature could lead to the increase of the silicon content in SiO2/C composites,but the presence of silicon could affect the formation of carbon lattice.At a carbonization temperature of 600?,the higher silicon content,the higher graphitization of carbon.The higher carbonization temperature,the lower t graphitization of carbon at the same precursor concentration.Increasing the concentration of the silicon precursor liquid could effectively increase the specific capacity of the SiO2/C composite materials,and the increase of the carbonization temperature improved the rate performance of the SiO2/C composite materials.After 15 wt%NaOH solution pretreatment,impregnation with 0.4 M silicon precursor and carbonization at 800?,the first charge-discharge specific capacity of SiO2/composite materials derived from wood pulp fiber was 1446/1954 mAh g-1 at a current density of 0.1 A g-1,the first cycle efficiency was 73.99%,and the discharge specific capacity was 1325 mAh g-1 when the cycle is stable.