The Recycling Of Lithiated Graphite Anode Of Spent Lithium-ion Batteries And Its High Value Applications

The recycling of spent lithium-ion batteries（LIBs）in the battery industry has become an important challenge.At present,the recycling of spent LIBs from the market is extremely limited when they are mainly treated by traditional methods（e.g.,landfill,incineration and compost）.These treatment methods not only threaten public safety and cause irreversible environmental pollution,but also waste valuable metal resources.This is due to the spent LIBs containing valuable metals（e.g.,cobalt,nickel,lithium,and manganese）,as well as inorganic and organic compounds.Therefore,the efficient recycling of spent LIBs is critically urgent.Current recycling methods mainly focus on cathodes and current collectors,which contain high-value metal elements.In contrast,the recycling of graphite anode was tending to be neglected.The graphite anode contains incompletely extracted lithium and residual lithium in the solid electrolyte interfaces（SEI）film.As expected,recovery of graphite from spent LIBs can achieve both graphite reused and lithium resource regeneration.This is because it not only reduces the environmental problems caused by the excessive-exploitation and high purification of graphite and lithium ores,but also ensures the supply chain of graphite and lithium-based products.In addition,the recycled graphite and its derivatives can also be extended to use in other emerging electrochemical energy storage applications,such as sodium（potassium）ion batteries and air batteries.These emerging applications could further drive the recycling of the electrode materials from the spent LIBs.Based on the necessity and importance of the recovery of graphite and lithium elements,this thesis reports a method based on the water vapor oxidizing the lithium-containing graphite anode of spent LIBs（lithiated spent graphite）for the recovery of high-purity lithium and the formation of porous graphite.This is realized with the help of the developed mechanism of lithium-containing active sites activating carbon.Moreover,a series of heteroatom-doped porous carbon materials as high-performance electrode materials for LIBs,sodium-ion batteries（SIBs）and lithium-oxygen Batteries（LOBs）,were also prepared through the Hummer’s and ball-milling methods using the porous graphite as the raw materials.The main contents and conclusions of this thesis are summarized as follows:（1）A cheap and environmentally friendly water vapor oxidation method was developed to realize the recovery of high-purity lithium element and the formation of porous graphite.Porous graphite（c-Li-h SG-800）was obtained by annealing lithiated spent graphite at 800 ^oC under the regulated flow of Ar/H₂O gas mixture.After that,the c-Li-h SG-800 was ultra-sonicated with deionized water to leach lithium so that the purity of lithium product（lithium carbonate）can be recovered as high as 97.2%.The c-Li-h SG-800 after Li leaching（c-h SG-800）contains abundant and uniformly distributed defects,which is induced by the H₂O and Li OH activation.Based on the c-h SG-800 as raw material,a hierarchical porous graphene material（c-h Sr G-900）with micro/medium/macropores was also prepared.As a result,the c-h SG-800 and c-h Sr G-900 as LIBs anode and LOBs cathode,respectively,display good lithium storage performance.（2）The holey graphene（h G）was prepared by the water vapor oxidizing the reduced graphene oxide.Benefiting from the abundant holey structures and edge sites of h G,both B（3.0 at.%）and N（2.1 at.%）were co-doped in h G to form B,N-h G.The in-plane pores of B,N-h G not only increase the specific surface area of the electrode,but also enhance the mass transfer of Li⁺/O₂.In addition,the synergistic effect induced by the co-doping of B and N also enable the B,N-h G as LOBs cathode achieving a maximum discharge specific capacity of 15340m Ah g^-1 and a cycle life over 117 cycles.（3）The lithiated spent graphite（Li-SG）was treated by water vapor oxidation to produce porous graphite（Li-h SG）.Graphene based materials（e.g.,Nr Eh SG@H₂O）with"worm-like"and hierarchical pore structures were prepared by thermal expansion,H₂O/CO₂ re-oxidation and N doping of the Li-h SG generating derivatives.Benefiting from the increased the specific surface area and pore volume of Nr Eh SG@H₂O due to the re-oxidation so that it can strengthen the mass transfer process of Li⁺/O₂,as well as the enhanced structural stability and catalytic activity of Nr Eh SG@H₂O due to the N doping,the Nr Eh SG@H₂O as cathode for LOBs displays a maximum discharge specific capacity of 11816 m Ah g^-1 and long cycling life over1600 h and 800 cycles at a high current density of 1000 m A g^-1.（4）To prepare targeted edge-modified graphene nanosheets,the ball milling method was developed.Based on Li-h SG after leaching lithium（h SG）as raw materials,the edges of holey graphene nanosheets decorated with ultra-high oxygen-containing functional groups（～37.8at.%,h SGn Ps）were obtained.Due to the high specific surface area,abundant oxygen-containing functional groups at the edges as additional active sites,and enlarged interlayer distance between graphite layers,the h SGn Ps as anodes for SIBs exhibit excellent sodium ion storage properties with a high initial Coulombic efficiency of 82.4%,a high reversible specific capacity of 375.7 m Ah g^-1 at a low current density of 30 m A g^-1,and a high reversible specific capacity of 153.3 m Ah g^-1 at a high current density of 2 A g^-1,a reversible specific capacity of137.5 m Ah g^-1 after 500 cycles at 1.5 A g^-1.