Recovery And Reuse Of Graphite Anode Of Discarded Lithium-ion Batteries

Lithium-ion batteries（LIBs）have been extensively applied in portable devices and electric vehicles due to their superior energy density and low self-discharge rate.However,the LIBs have a limited lifespan,in which means a large number of LIBs is facing recycling.Due to the organic matter and valuable metals contained in waste graphite,if not handled properly,it will cause resources waste and environmental pollution.But the current recycling methods mainly face the separation difficulty of graphite and impurities and single recycled product with low added value.Given above-mentioned condition,this thesis takes waste graphite as raw material and adopts the process of combining hydrometallurgy and pyrometallurgy to achieve the recycling and regenerate various products as anode materials for LIBs The specific research contents are as following:Aiming at the separation difficulty and structural damage of waste graphite,this thesis uses（NH₄）₂S₂O₈ to treat waste graphite,which realizes the removal of impurities and the repair of lithium-ion transmission channels.And the mechanisms of impurities separation and structure repairment are deeply analyzed.The regenerated graphite material shows excellent electrochemical performance.In half-cell test,the reversible capacity of regenerated graphite after 500 cycles at 0.3 A g^-1 was 330.2m Ah g^-1.In full-cell test,the reversible capacity of regenerated graphite after 50 cycles at 0.085 A g^-1 was 95.6 m Ah g^-1.To improve the value of recovered graphite,this thesis adopts oxidation-intercalation method.Through multiple sets of single-factor experiments,expanded graphite（EG）with best performance can be prepared when the reactants are 4 m L of concentrated phosphoric acid,12m L of concentrate sulfuric acid,1 g of potassium permanganate,and 1 g of waste graphite.It is shown that the prepared EG has a worm-like long-range ordered structure and exhibits excellent lithium storage performance.Its reversible capacity reaches 347.7 m Ah g^-1 after 1000 cycles at a current density of 0.3 A g^-1.To deal with the problem of single recycled product,the composite materials EG@10%Si@C as anode material for LIBs is prepared with EG and Si through wet ball milling and thermal cracking.It shows that single-crystal nano Si particles are evenly dispersed in EG.The carbon coating layer strengthens the connection between Si particles and EG,which can enhance the conductivity for the whole electrode,and makes it have high capacity,good cycle stability and excellent rate doubling ability.The cycle stability of the EG@10%Si@C is significantly higher than that of EG at0.37 A g^-1,the specific capacity reaches 413.2 m Ah g^-1 after 500 cycles.There are 48 figures,9 tables and 150 references in this thesis.