Preparation And Energy Storage Mechanism Of Amino-rich Nitrogen-doped Porous Hard Carbon Nanosheets

Renewable energy has been widely used in life scenarios,and more efficient and low-cost green energy storage systems need to be developed.Lithium-ion batteries（LIBs）have been maturely used in daily life scenarios.Sodium-ion batteries（SIBs）and potassium-ion batteries（PIBs）are"post-LIBs".Their working principles and battery devices are similar to those of lithium-ion batteries,and they can also be used as a high energy density energy storage system.However,the ionic radii of alkali metals vary,and conventional graphite anodes for LIBs are not suitable for SIBs and PIBs.Therefore,how to develop advanced anode materials with good electrochemical performance is very important for the further application of alkali metal-ion batteries.Biomass-based hard carbon has the characteristics of abundant resources,low cost and environmental protection,and is considered to be the most potential anode material substitute for alkali metal ion batteries.In this project,the waste resource waste cooking oil is used as the precursor,and the derived biomass carbon material is rationally designed.By combining morphology engineering,interlayer spacing engineering,defect engineering and interface engineering,the structure and performance of carbon-based nanosheets can be regulated,and they can be used as anode materials for alkali metal ion batteries.After optimizing the synthesis conditions,the close relationship between structure and performance was found out,and the energy storage mechanism and amino nitrogen enhanced capacitance were also explored and analyzed.The following are the main findings of the study:1.In this experiment,the collected waste cooking oil（WCO）was first purified and removed by activated clay,and then converted into higher fatty acid potassium salt through ester decomposition reaction,and then mixed with melamine and calcined to synthesize three-dimensional nitrogen-doped porous carbon nanosheets NWCOC（undoped hard carbon is WCOC）.At the same time,the ratio of strong base KOH and waste cooking oil in the ester decomposition reaction was optimized.The anode material was applied to LIBs,and a charge specific capacity of 1331.8 m Ah g^-1 was obtained in the electrochemical performance test,and a stable long-cycle charge-discharge was achieved.The analysis of properties and structure shows that the storage of Li⁺by hard carbon derived from waste cooking oil is mainly a pseudocapacitive behavior.2.Based on the electrochemical behavior of NWCOC650 in lithium-ion batteries,the experimental preparation process was optimized,and the electrochemical performance of NWCOC as a negative electrode material for SIBs and PIBs was studied.It was found that amino functional groups have a synergistic effect on the adsorption of Na⁺/K⁺on graphene,leading to an effective increase in the storage capacity of NWCOC.The experimental results and DFT calculations also show that after the surface charge of NWCOC is adjusted,Na⁺/K⁺is mainly stored in the form of adsorption and coexists in a mixed intercalation/filling mechanism.At the same time,different doping sites have different adsorption effects,which generally show as Pores>Basal plane>Edge.In particular,NWCOC650 exhibited high capacities of 489.4 and388.3 m Ah g^-1 at a current density of 100 m A g^-1,respectively,and excellent cycling stability as the anode for SIBs and PIBs.In addition,NWCOC650 also exhibits excellent performance(107.84 m Ah g^-1)in Na₃V₂（PO₄）₃/NWCOC650 full cells.