Preparation And Performance Study Of Wheat Straw Carbon As Anode Material For Lithium/Sodium Ion Batteries

The efficient use of agricultural waste in energy materials can solve the environmental pollution problem and is fully in line with the sustainable development strategy.Biomass-derived carbon prepared from agricultural waste as carbon precursors has been studied in the field of anode materials for lithium-ion and sodium-ion batteries.Biomass-derived carbon materials have superior properties such as high surface area,good electronic conductivity and excellent mechanical stability.However,the complex composition and microstructure morphology of biomass limit the further improvement of electrochemical properties.Therefore,it is of great significance to optimize the biomass-derived carbon and improve the preparation method for the efficient application of biomass and the research of high performance lithium-sodium ion battery anode materials.The main elements of this paper are:（1）We used a highly concentrated sodium hydroxide solution to saponify the pectin on the straw surface and dissolve hemicellulose and lignin,while crystalline cellulose was not dissolved.In the subsequent carbonization process,separation between the cellulose layers occurs,and finally porous flake biomass carbon（PFBC）derived from wheat straw is obtained.Test results show that the obtained porous flake biomass carbon has the best overall performance at 700°C.In LIBs,the capacity can reach 923 m A h g^-1at 0.2 C.When PFBC-700 is used as the electrode material for SIBs,the high capacity of 322 m A h g^-1is still maintained after 300 cycles at 0.2 C.（2）The wheat will absorb a lot of nitrogen-containing elements as well as phosphorus-containing nutrients from the soil during the growth process,and then there will be a relatively abundant amount of nitrogen and phosphorus elements remaining in the straw.Therefore,nitrogen and phosphorus doped wheat straw carbon（NPWSC）can be obtained by simple treatment of wheat straw with an alcohol solution.The specific capacity of NPWSC-700 was 1059 m A h g^-1after 120 tests at0.5 C in LIBs.In SIBs,the capacity was 350 m A h g^-1after 150 cycles.350 m A h g^-1.In addition,the ion diffusion rate in NPWSC-700 was found to be further improved by the GITT test.（3）We performed the density functional theory（DFT）calculations using Material Studio software based on the tests in experiment（2）,and simulated the spin density,Mulliken charge,HOMO and LUMO orbitals,adsorption energy,differential charge density（DCD）,and density of states（DOS）of nitrogen-phosphorus doped carbon materials.The results of simulation calculations reveal that the doping of nitrogen and phosphorus elements can significantly improve the physical and chemical properties（such as energy level and charge density）of the pristine carbonaceous material,which in turn improves the storage capacity of lithium and sodium ions.