Study On The Preparation And Recovery Of Carbon-based Anode Materials For Sodium Storage

Due to a series of environmental problems caused by the large consumption of fossil energy,renewable energy such as solar,wind,water and biomass energy has attracted much attention.And various energy storage devices play a vital role in utilizing these new clean energies effectively.For example,to eliminate the difference between peak and valley loads in the power system during the day and night,reduce electrical energy supply costs,and improve the reliability of the electrical energy supply for the grid.Among them,sodium ion battery has the characteristic of abundant resources,low cost and environmental friendliness,which is one of the most promising candidates in the next generation of large-scale energy storage systems.However,the practical application of sodium ion battery is greatly limited to low energy density and short cycle life.Therefore,it is necessary to find electrode materials with high energy density,high voltage window and stable structure.Carbon materials have the advantages of low potential,abundant reserves,low price and environmental friendliness,which have been widely applied in the field of anode materials for sodium ion battery.However,carbon materials have different sodium storage mechanisms due to different structures and surface chemical properties,which makes the electrodes exhibit big different performances.At the same time,how to simplify the preparation conditions and preparation processes are also an urgent challenge in the practical application of the material.In this work,biomass derived hard carbon with the hierarchically porous loose sponge-like structure,heteroatom-doped carbon materials and graphitized carbon fibers are prepared in a simple method by using carbon materials（or precursors）from different sources,and the reaction mechanism is studied.The main contents are as follows:（1）Sycamore bark is used to prepare porous waste biomass derived hard carbon by the pretreatment with concentrated sulfuric and low temperature pyrolysis to improve its rate performance and cycle stability in ester-based electrolyte.After acid treatment,the material has a hierarchically porous structure,which provides abundant ion transmission channels and shortens the ion transmission distance effectively.The obvious increase of the carbon layer spacing is beneficial to the insertion and extraction of sodium ions with larger radius.Surface defects are reduced and the degree of graphitization is increased,which promote the rapid formation of the electrolyte interface,and improve the electrochemical performance of the biomass hard carbon material.In the ester-based electrolyte,the reversible charge specific capacity of the material at a high current density of 1 A·g^-1 reaches 165 m Ah·g^-1,and the capacity retention rate after 2000 cycles is 71.5%.XPS research results show that the hierarchically porous loose sponge-like structure can accelerate the formation of the solid-electrolyte interface（SEI）between electrode and electrolyte,and they are beneficial to the diffusion and transmission of sodium ions in the SEI film,enhancing the cycle stability.（2）A S-doped biomass hard carbon material based on the precursor of biomass-derived hard carbon material with hierarchically porous structure is prepared through the introduction of sulfur active sites,which improves the sodium storage performance of the material effectively.The precursor has a large specific surface area and porosity,and a defect structure.S-doped hard carbon material is prepared by introducing sulfur elements into biomass-derived hard carbon at 450°C to form C-S bonds.The introduction of S is beneficial to increase the reactive sites,reduce the surface defects of the carbon layer,and improve the rate performance.Therefore,an excellent rate performance is demonstrated with cycle life(～222 m Ah·g^-1 and 72.1%capacity retention after 100 cycles at 1 A·g^-1),and an initial coulombic efficiency of 65.2%.（3）Using recycling commercial waste carbon fiber as the raw material,through high temperature and grinding treatment methods,a self-supporting electrode and coating electrode is prepared.Commercialized carbon fiber with a good degree of graphitization has a high-temperature treatment process at about 3000°C,and exhibits good electrochemical performance after secondary 900°C treatment.At a current density of 20 m A·g^-1,the coulomb efficiency of the current collector-free electrode in the ether-based electrolyte is 77.4%in the initial cycle,and the reversible charge specific capacity is 132 m Ah·g^-1.The electrode after grinding has a coulomb efficiency of 64.5%in the initial cycle and a reversible charge specific capacity of 195 m Ah·g^-1,which shows good electrochemical performance in the ester-based electrolyte.