Study On High Capacity Carbon Based Anode Materials For Lithium Ion Batteries

Graphite anode material,as the most commercial anode material,has the advantages of wide source,low price,stable structure and high capacity.But at the same time,the layered structure of graphite makes lithium ions intercalated from the edge into the interlayer,resulting in a single lithium ion diffusion path,resulting in a low lithium ion diffusion kinetics between graphite layers,which seriously reduces its rate performance.The volume expansion and stress concentration caused by the formation of lithium graphite intercalation compound?Li-GIC?during charging and discharging process lead to graphite exfoliation and pulverization,resulting in electrode failure and poor stability.In addition,the low theoretical specific capacity(372 mAh g^-1)of graphite is difficult to meet the requirements of high-power energy storage equipment.In this report,the specific capacity,rate performance and cycle performance of graphite are improved through the structural modification and doping modification of graphite.?1?In this report,ammonium bicarbonate was used to doped graphite with nitrogen.It was found that a small amount of nitrogen was doped in the form of pyridine nitrogen,pyrrolidine nitrogen,graphitized nitrogen and nitro nitrogen,which increased the amount of lithium storage sites,improved the lithium ion activity and improved the cycling stability of graphite.The modified graphite has a specific capacity of 370 mAh g^-1 at 0.5 C.The capacity retention rate is 99.4%after 100 cycles and 97.27%at 1 C for 200 cycles.Ammonia thiocyanate was used as modifier to co-doped graphite with sulfur and nitrogen.The synergism of sulfur and nitrogen not only increased the specific capacity of graphite,but also improved the cycle stability of graphite.The specific capacity of modified graphite is 410 mAh g^-1,407 mAh g^-1,378 mAh g^-1 and 370 mAh g^-1 at the rate of 0.1 C,0.25 C,0.5 C and 1 C,respectively.The capacity retention rate of modified graphite is 100%after 250 cycles at 1 C,which is much higher than that of pure graphite.?2?In this report,graphite was activated by KOH with microwave heating.Compared with the pure graphite,the modified graphite has microcrack structure and a trace of potassium doping,which increases the interlayer spacing,graphitization degree,specific surface area,mass specific capacity,cycle stability and rate capacity of graphite anode.When KOH concentration was 20%,microwave power was 500 W and heating time was 15 min,the specific capacity was 449 mAh g^-1?0.1 C?,380mAh g^-1?0.25 C?,356 mAh g^-1?0.5 C?,320 mAh g^-1?1 C?,respectively.?3?In this report,the microwave and KOH activated graphite was modified by nitrogen doping with ammonium bicarbonate.The specific capacity and cycle performance of graphite were improved by combining microcrack structure and nitrogen doping.The specific capacity of graphite was 403 mAh g^-1 at 0.1 C.In this report,ammonium thiocyanate was used to modify the microwave and KOH modified graphite by sulfur and nitrogen co-doping.The specific capacity and rate performance of graphite was improved because of the microcrack structure,sulfur doping and nitrogen doping.The modified graphite has a specific capacity of 397 mAh g^-1 at 0.5C.The capacity retention rate was 100%after 100 cycles at 0.5 C and 1 C.