Study On Properties Of Net-? And H_4,4,4-graphyne As Anode Material Of Na-ion Batteries

With the continuous progress of human science and technology in the 21st century,batteries have become an indispensable part of all kinds of new energy vehicles and mobile electronic devices.Lithium-ion batteries,which have high storage capacity,fast charge-discharge capacity and long cycle life in practical commercial applications,dominate the market.However,the crustal abundance of lithium is relatively low.With the increasing demand of global lithium market,the proven reserves of lithium can only last for a few more decades.Therefore,we urgently need to find alternative metal elements with similar properties to lithium.We found that sodium elements in the same main group as lithium meet the requirements very well.The crustal abundance of sodium reaches 2.83%,while the crustal abundance of lithium is only 0.0065%,and sodium is 435 times that of lithium.Moreover,sodium resources are widely distributed worldwide,with low cost and mature extraction and preparation technology.In addition,in terms of safety,sodium ion batteries have good thermal stability,which is very suitable for large-scale use.However,the current problems of sodium ion batteries are low storage capacity and slow charge and discharge rate.Based on first principles and density functional theory,two novel two-dimensional carbon nanoporous materials,net-?and H4,4,4-graphyne,were investigated for their performance as anode materials for sodium ion batteries.The main research contents and conclusions are as follows:(1)22 possible stable adsorption sites were tested in the original net-?cell.The results show that there are 6 sites which can adsorb sodium atoms stably.The maximum adsorption energy is-1.88 e V,and the average distance from the nearest carbon atom is 2.72(?)just above the center of the 10-member carbon ring.There are five possible diffusion paths,and the best path has a diffusion barrier of 0.50 e V.Up to 24 sodium can be adsorbed,the theoretical specific capacity is 2680 m Ah/g,the average open circuit voltage is 0.42 V.(2)19 possible stable adsorption sites were tested in the original crystal cells of H_4,4,4-graphyne.The results show that there are four sites that can truly stably adsorb sodium atoms.The maximum adsorption energy is-2.54e V,located just above the center of the 12-binary carbon ring.The average distance to the nearest carbon atom is 2.87(?).The metallic properties of H4,4,4-graphyne structure are good.There are two possible diffusion paths,and the best path has a diffusion barrier of 0.63e V.The theoretical specific capacity is 1675 m Ah/g,and the average open circuit voltage is 0.67 V.