| Due to the advantages of abundant sodium resources,low cost and superior overall performance,sodium ion batteries can meet the requirements of low cost,long life and high safety performance in the new energy field,and to a certain extent alleviate the shortage of lithium resources,making them a useful supplement to lithium ion batteries and potentially playing an important role in new energy storage applications.In the research of electrode materials for sodium ion batteries,pitch has the advantages of high carbon yield,friendly to the environment and lower cost,which is an ideal carbon source for the preparation of anode materials for sodium ion batteries,but its specific capacity is low,about 90m Ah g-1.If its sodium storage performance is improved,pitch will be an excellent anode material for sodium ion batteries.The low sodium storage capacity of pitch is due to the ordered rearrangement of molecules during the high temperature pyrolytic carbonization of pitch to form a graphite-like layer structure,which is not conducive to the storage of sodium ions.To realize the application of pitch-based soft carbon in sodium ion battery anode,limiting the graphitization of pitch during high-temperature carbonization becomes an effective idea,and three methods are used in this paper to inhibit the graphitization of pitch:（1）Pitch-based soft carbon was prepared by pre-oxidation and low-temperature carbonization to explore the effects of carbonization temperature and pre-oxidation treatment on the surface structure and electrochemical properties of asphalt.The experimental results show that the pitch has the maximum layer spacing and the highest disorder at the carbonization temperature of 800°C.After the pre-oxidation treatment of pitch OP800,the layer spacing becomes larger,the material has larger specific surface area and more micropores,and the reversible specific capacity is 315m Ah g-1on the first charge at 20m A g-1.After 170 charge-discharge cycles at 100m A g-1 current density,the capacity retention is 72.9%,and the reversible capacity of the cell decays to 199.7m Ah g-1.It showed good cycle stability.（2）On the basis of the above work,peanut powder,rice husk powder and cellulose are used as hard carbon precursors,and pitch and different proportions of hard carbon are ball-milled together respectively to prepare soft and hard carbon composites with high sodium storage capacity and high first coulomb efficiency,and to investigate the relationship between different proportions and types of hard carbon composites and electrochemical properties.Pitch will adhere to the surface of hard carbon and make some open pores to form closed pores,reducing the number of open pores can reduce the initial capacity loss and increasing the number of closed pores can enhance the platform capacity.Among them,LQA73 with a pitch-to-cellulose mass ratio of 7:3presents the best sodium storage performance.LQA73 exhibits a first-cycle charging specific capacity of 331.9m Ah g-1 at a current density of 20m A g-1,with a first coulomb efficiency of 74.26%,and a remaining reversible specific capacity of 175m Ah g-1 after250 cycles of charging and discharging at 50m A g-1.（3）Combined with the above studies,it is known that the unique structure of disordered and randomly oriented hard carbon is more favorable for sodium ion storage,but the first coulomb efficiency of hard carbon materials is generally low,so the structural disorder is regulated by cracking pitch with different concentrations of KOH and Na OH activators,so that it has the characteristics of hard carbon and has a high first coulomb efficiency.The effects of different concentrations and types of activators on the disorder and first coulomb efficiency of pitch materials were investigated.The experimental results showed that the pitch LQ10KOH treated with 1.0mol L-1 KOH solution had the most disordered structure and the highest first coulomb efficiency.The first charge specific capacity was 294m Ah g-1 at 20m A g-1 current density,and the capacity retention was 81%after 50 cycles,respectively... |
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