Preparation Of Sunflower Seed Shell-based Carbon Anode Materials And Their Potassium Storage Performance

With the advantages of good power performance,long service life and high energy density,lithium-ion batteries have been used on a large scale in new energy vehicles,portable electronic devices and other fields.However,the limited reserves and uneven distribution of lithium resources have seriously affected the sustainable application of lithium-ion batteries in the future.Given that the same main group of alkali metals have similar physical and chemical properties,researchers have begun to focus on postlithium-ion batteries,such as potassium-ion batteries.Potassium-ion batteries have a similar redox potential to lithium ion batteries(K/K+=-2.93 V vs Li/Li+=-3.04 V),so K+ can also be electrochemically embedded in the graphite anode to give KC8,which exhibits a theoretical specific capacity of 279 mAh g-1.Unfortunately,the size radius of K+(1.38 ?)is larger than that of Li+(0.76 ?),resulting in a dramatic volume expansion of the anode during the deembedding process of K+,which in turn affects the reversible capacity and decreases the multiplicative performance.Compared with conventional commercial carbon materials,biomassderived carbon is not only environmentally friendly and inexpensive,but also inherits the native pore structure of biomass after pyrolysis and possesses an ultra-high specific surface area with a large number of defects,which can provide a high ion diffusion coefficient and can effectively alleviate the volume expansion of the electrode and exhibit high potassium storage performance when used as a potassium ion battery anode.In this paper,using sunflower seed hulls as raw material,honeycomb hard carbon and porous carbon spheres were prepared by impregnation-pyrolysis-carbonization method and soft template method respectively,which were applied to potassium ion battery anode materials,and the prepared biomass carbon was subjected to physical characterization and electrochemical performance analysis as follows.(1)Sunflower seed hull powder was used as the precursor and K2CO3 as the activator.Firstly,the sunflower seed hull powder was impregnated with K2CO3 in a water bath to mix the two thoroughly,followed by pyrolysis in a muffle furnace and carbonisation in a tube furnace,and finally acid washing and water washing to obtain porous carbon materials with a honeycomb structure.The effect of K2CO3 dosage and carbonisation temperature on the structure and properties of the honeycomb hard carbon was compared and analysed.The test results showed that when the activation temperature was 700℃ and the sunflower seed shell:K2CO3 was 1:2.5,the sample had uniform pore size,abundant pores,high self-doped N content and obvious honeycomb structure;after 100 cycles at 0.2 C multiplicity,the capacity was stable at 313.8 mAh g-1,showing high capacity and long cycle stability with the best electrochemical performance.(2)Sunflower seed hull cellulose was extracted by KOH alkaline cooking and acid treatment,and porous carbon spheres with adjustable mesoporous structure and high specific surface area were prepared by high temperature and high pressure hydrothermal treatment using sunflower seed hull cellulose as the carbon source and F127,SDS and SDBS as the soft template.After physical characterization and electrochemical tests,it was concluded that the best results were obtained when F127 was used as the soft template,with smooth surface,uniform size and high number of spheres.The effect of F127 dosage and hydrothermal time on the morphological structure and potassium storage performance of the porous carbon spheres was investigated.The results showed that when the cellulose:F127 was 1:0.5 and the hydrothermal time was 12 h,the porous carbon spheres had the most regular morphology and the most abundant mesoporous structure.It has excellent long cycle stability.