| Lithium-sulfur batteries?LSBs?have received great attention from researchers due to its extremely high energy density(2,600 Wh kg-1)and low cost.However,this new and efficient battery system still faces some urgent problems:the low conductivity of sulfur,and there is a serious volume expansion during the reaction;In addition,the lithium polysulfide generated during the electrochemical reaction migrates back and forth in the electrolyte,resulting in a severe shuttle effect.These problems lead to a series of troubles such as low actual capacity of lithium-sulfur batteries,poor cycle stability,and rapid decline in battery capacity.The high specific surface biochar material obtained through special treatment is often used in lithium-sulfur batteries because of its good conductivity and good adsorption performance for polysulfides.This paper explores the preparation of high specific surface area biomass charcoal with optimal porosity and its derived high specific surface biochar-transition metal nickel composite materials through reasonable processes,as the main skeleton material of sulfur,and then explores its electrochemical performance.The research content of the thesis is as follows:?1?Determine the optimal activated carbonization process for iron leaf biomass carbon.We use the common biomass waste iron leaves as a carbon source,use KOH as a pore-forming activator,the main process parameters affecting the pore structure are adjusted by adjusting the alkali-carbon ratio and activation temperature,and use BET test to analyze the pore structure changes of porous carbon.Then,we explored the best process suitable for preparing iron leaf biomass carbon.?2?Based on the suitable process,the structure of biomass charcoal was further refined and graded,and the application of the material in lithium-sulfur batteries after regulation was explored.The weakly acidic HAc was used to dredge the cavities and pores blocked during the pore-making process to improve the porosity and permeability of the carbon material.The results prove that the specific surface area and pore volume of the obtained biomass carbon have been greatly improved.Its large specific surface area ensures uniform contact between sulfur and the inner wall of carbon and improves the conductivity of sulfur;at the same time,the large pore volume can be used as an efficient carrier of sulfur(the sulfur load of the cathode is0.8 g cm-2)and provides Efficient adsorption of polysulfides.The high porosity biomass carbon/sulfur composite positive electrode?HPBC/S?has a specific discharge capacity of up to 1317 m Ah g-1 for the first time.After the first 5 cycles of charge and discharge cycles are stable,the capacity is stable at 910 m Ah g-1,and after200 cycles,the capacity can also be maintained at 790 m Ah g-1,showing good cycle stability.?3?In response to the problem of low efficiency of physically adsorbing polysulfides,we designed a carbon-based nickel metal sulfur-containing composite material?HPBC/Ni/S?based on high specific surface biomass carbon using surface electroless plating technology and molten sulfur injection method.Here,HPBC retains the advantages of high specific surface carbon-based materials,enhances the conductivity of sulfur,and at the same time serves as an efficient sulfur storage material(sulfur load of the composite positive electrode is 1.6 g cm-2);Ni is used to catalyze the reaction to enhance the reaction power At the same time,the two materials cooperate in"physical+chemical"adsorption of lithium polysulfide.The prepared HPBC/Ni/S composite positive electrode,while ensuring a significant increase in sulfur loading,at the rate of 0.5 C for the first discharge specific capacity up to 907.3 m Ah g-1,after 200 cycles,it can still maintain 610.6 m Ah g-1,the single-turn capacity attenuation rate is only 0.16%. |
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