Preparation Of Biomass Porous Carbon And Elect-Rochemcal Performance Of Modified Sulfur Cathode

Preparation of large-capacity batteries is an inevitable demand for the development of the information age.Sulfur can transfer multiple electrons,generating the specific capacity of lithium-sulfur batteries which is more than six times that of conventional Li+ batteries.Therefore,lithium-sulfur batteries have broad application prospects.Due to poor conductivity of sulfur,how to prepare a cathode with high conductivity and large sulfur loading is the key to a lithium-sulfur battery.Eggs are able to produce pores during the simple frying process,and retain the polar N,O and other elements originated from the amino acid after carbonization.The as-prepared biomass porous carbon can improve the conductivity of sulfur,provide a rich sulfur-bearing space for the modified sulfur cathode,and adsorb the intermediate polysulfide,thereby improving the electrochemical performance of the battery.In this paper,egg white,egg yolk and egg were used as raw materials to prepare porous carbon materials with rich pore structure and natural O and N polar elements through a simple and reproducible process.The corresponding carbons were labeled as AC.YC and EC,respectively.The effects of carbon source,carbonization temperature and pore former concentration on the porous carbon pore structure and battery performance were studied to determine the optimal preparation process.It not only provides reference for the preparation of porous carbon materials,but also provides the basis for the modification of the cathode materials of lithium-sulfur batteries.The research results are as follows:Egg white source porous carbon(AC)has the most abundant hierarchical pore morphology with natural polar element doping(O and N).Its BET specific surface area and mesoporous pore size distribution are 693 m2·g-1 and 3.1 nm.AC.shows strong adsorbability(0.0012 g liththium polysulfide/g adsorbent)of polysulfides,which is suitable for the modification of sulfur cathode;The electrochemical performance.The AC/S cathode displays a discharge specific capacity as high as 1115 mAh·g-1 at 0.05 C.The reversible rate capacity at 2 C(437 mAh·g-1)was 15%and 25%higher than egg source carbon/sulfur(EC/S)and egg yolk source carbon/sulfur(YC/S),respectively.The capacity retention rate of AC/S was 77%after 50 cycles at 0.2 C,which is 15%and 11%higher than EC/S and YC/S,respectively.Pore structure and morphology modification experiments show that the carbon material(AC-0.5M)prepared with 0.5 moL.L-1 NaOH has the most abundant pore structure;As used to modifiy the cathode of lithium-sulfur battery,it exhibits minimal charge transfer resistance and the smallest lithium ion diffusion coefficient compared to cathodes(AC-0.4M/S and AC-0.7M/S)prepared with 0.4 moL·L-1 and 0.7 moL·L-1 NaOH solution.The rate specific capacity of AC-0.5M is 31%and 19%higher than that of the cathode AC-0.4M/S and AC-0.7m/S,respectively.And the average capacity decay rate of 0.21%is delivers in 150 cycles at 0.2 C.The modified sulfur cathode based on 800 ? carbon material(AC-800/S)shows a minimum charge transfer resistance(62 ?)and a minimum lithium ion diffusion coefficient.The initial discharge specific capacity of AC-800/S at 0.2 C rate is 16%and 11%higher than AC-700/S and AC-900/S cathode(prepared based on AC-700 and AC-900),respectively;After 160 cycles,the capacity retention rate is 120%and 11%higher than that of AC-700/S and AC-900/S cathode,respectively.The sulfur cathode modified by AC porous carbon with 30 min ball milling(AC-30min/S)displays the best rate stability,and the rate capacity at 2 C rate is 8%and 27%higher than that of the cathodes modified by AC porous carbon with 60 min ball milling and the pristine AC porous carbon,respectively.The optimum condition for the preparation of AC porous carbon is 0.5 moL·L-1 pore former at 800? carbonization temperature with 30min ball milling.The optiimun porous carbon-modified lithium-sulfur cathode can work stably within 160 cycles at 0.5 C;Under high sulfur load(4.5 mg·cm-2)condition,the cathode displays an high areal capacity of 4.4 mAh·cm-2,higher than the currently used lithium ion battery.Moreover,the cantode can be stably cycled for 40 times,revealing highly potential for practical application.