Study On Preparation And Electrochemical Performance Of Biomass-Based Hard Carbon Anode Materials For Potassium Ion Batteries

Potassium has the advantages of abundant reserves and low cost,so that potassium ion batteries（PIBs）have attracted much attention as an energy storage system that is expected to replace lithium ion batteries（LIBs）.Anode materials are one of the important factors affecting the performance of PIBs,among which carbon based materials have become an important research part of PIBs anode electrodes due to their low cost,environmental friendliness,and high safety.However,larger sized potassium ions are prone to significantly cause electrode structure expansion during charging and discharging,leading to poor cycling performance and reversible capacity.Based on this,developing hard carbon anode materials with large interlayer spacing and good electrochemical performance is an important research direction for PIBs.This work uses biomass hard carbon as the research object and conducts the following research work around the theme of preparing low-cost,high capacity,and high cycle stability anode electrodes for PIBs:1.The carbonization temperature,carbonization time and heating rate in the preparation process were studied with the hydrothermal wutong fruit as the precursor,and the process conditions for the best electrochemical performance were obtained,under which nitrogen doping was carried out.The results showed that the introduction of nitrogen not only increased the specific surface area of the material(109.6 m²·g^-1),but also enhanced the adsorption capacity of K by the presence of pyridine nitrogen and pyrrole nitrogen,thereby improving the capacity and rate performance of the electrode.Therefore,it can achieve a reversible capacity of 290.2 m Ah·g^-1 at a current density of 200 m A·g^-1.2.In order to further improve the cycling stability of electrode materials,porous layered hard carbon was prepared by nitrogen sulfur co-doping precursor,and its morphology,structure,and electrochemical behavior were studied.The results showed that nitrogen sulfur co-doping was beneficial for expanding the interlayer spacing（0.376 nm）and increasing the degree of disorder(I_D·I_G^-1=1.45).At the same time,the formation of C-S bonds effectively reduced the attenuation of capacity during the cycling process,allowing the material to stably provide 195.64 m Ah·g^-1 capacity after 5000 cycles at a current density of 2000 m A·g^-1,greatly improving the cycling stability.3.To verify the feasibility of nitrogen sulfur co doped biomass carbon anode electrode materials in practical applications,they were assembled into a full battery and subjected to electrochemical testing.First,Prussian blue was prepared by coprecipitation method as the cathode material of all cell,and its physical characterization and electrochemical test were carried out.Then,the obtained cathode and anode electrode materials were assembled into a full battery and the process of the full battery was explored.It was found that the ratio of anode electrode to cathode electrode material capacity（NP ratio）was 1.1 when the electrochemical performance was optimal,and the optimal electrolyte was 0.8 M KPF₆dissolved in EC and DEC solvents with a volume ratio of 1:1.Its energy density at 25 m A·g^-1 was 306.18 Wh·kg^-1,which can easily light up light-emitting diodes（LED）with a working voltage of 3 V,highlighting the feasibility of its practical application.