Research On The Recycling Of Graphite Cathode Materials For Waste Lithium-ion Batteries

Lithium-ion batteries are considered to be the most successful source of power for electronic devices due to their high power density,portability,and environmental friendliness.Since 2018,lithium-ion batteries have captured more than 86%of the market,including mobile devices,personal computers,and electric vehicles（electric and hybrid electric vehicles）.With the renewal of electronic devices and the popularity of electric vehicles,the disposal of used lithium-ion batteries has become a very important issue in recent years.Graphite occupies almost the entire market of anode materials for Li-ion batteries because of its good electrical conductivity,ordered layered crystal structure,reversible lithium storage capacity,low charge/discharge potential and good stability.The insertion of lithium ions into graphite forms a LiC₆compound,giving it a theoretical capacity value of 372 m Ah g^-1.As the main anode material for lithium-ion batteries,83.41%of the anodes are made up of waste graphite every year.According to statistics,the output of natural graphite in China reaches650,000 tons in 2020,of which nearly 35～40%is used in batteries,electrode materials,etc.It can be seen that waste graphite recycling has a huge market,and the total amount of natural graphite,which is a mineral resource,is limited.According to reports in recent years,the lithium-ion battery production market will grow at a compound annual growth rate of about11%and is expected to reach$47 billion by 2023.This also represents that,with the gradual development of cell phones and the field of new energy vehicles industry,graphite resources will face an oversupply situation,so the exploration of the recycling process of used lithium-ion battery graphite is the situation is also the trend.The study uses microwave water treatment method to directly recover the anode graphite on waste lithium-ion batteries,and the graphite obtained by microwave method has a good crystal structure.The optimal process conditions for recovering graphite are explored by adjusting the energy density and reaction time of microwaves.By this method,not only the graphite can be recovered and reused in the battery,but also the complete copper foil collector can be recovered to achieve the overall recovery and reuse of lithium-ion battery anodes.The recovered graphite was characterized by XRD and found to retain the complete graphite crystal structure.The SEM and TEM characterization results showed that the recycled graphite did not agglomerate,instead,a portion of the recycled graphite was exfoliated into a graphene-like lamellar structure after microwave treatment,providing more active sites for lithium ion embedding and exfoliation.After assembled into a lithium-ion battery,the cycle specific capacity can reach 361.52 m Ah g^-1at 1C,which is close to the theoretical specific capacity value of commercial graphite(372 m Ah g^-1).The microwave reaction was used to modify the recycled graphite by the combined effect of nitric acid and microwave reaction,which led to the redox reaction to graphite and potassium permanganate.The redoxed manganese dioxide grows stably on the surface of the graphite,forming a dense layer of manganese oxide.By using graphite as the carrier,a graphite-manganese dioxide composite material is built with graphite as the substrate and manganese dioxide growing on it.This material has a high cyclic capacity density,and the optimal reaction ratio is selected by adjusting the ratio of nitric acid,potassium permanganate and graphite.In the case of nitric acid,potassium permanganate and graphite with a mass ratio of 1:1:1,a capacity density of 565.15 m Ah g^-1was obtained at a current density of 0.4 A g^-1.Two characteristic peaks of the newly produced manganese dioxide can be observed by XRD.In contrast,the manganese dioxide alone without a carrier only has a capacity density of 30 m Ah g^-1at 0.4A g^-1.It indicates that graphite plus Mn O₂produces a 1+1 greater than 2effect by the correct loading.The study utilized recycled graphite as a raw material to prepare graphene using the Hummers method and compared it with graphene prepared for commercial graphite.XRD showed that the graphene oxide prepared from the three different raw materials all had the same characteristic peaks.After SEM,TEM images characterization a clear lamellar structure can be seen.Good capacity density and cycling stability were obtained at 1A g^-1,and the specific capacity could reach 550 m Ah g^-1.The capacity enhancement of microwave graphite are particularly outstanding,which proves that the graphite recovered by microwave method has the possibility of reuse.