Delithiation Of Cathode Materials Of Lithium-ion Batteries And Relative Applications

Development of delithiation methods with cost-efficiency and highly kinetic effectivity using secondary lithium-ion battery cathode materials as raw materials are of great importance for the preparation of diverse intercalation materials,mechanistic study,and lithium extraction from spent lithium-ion batteries.Electrochemical delithiation in aqueous electrolytes is low-cost,straightforward,and fast,but has been plagued by incomplete delithiation.To address this issue,it is necessary to explore the electrochemical delithiation parameters settings and the choice of electrolytes.Herein,this thesis selected Li Fe PO₄ as a model cathode material,and mainly studied the influence of the electrochemical delithiation parameters of Li Fe PO₄ in the aqueous Na₂SO₄electrolyte on the performance of the delithiation materials,the kinetic improvement method and promotion mechanism of the electrochemical delithiation in the aqueous electrolyte,and the application of delithiation materials,with the main research content as follows.Firstly,in order to enhance the degree of delithiation of cathode materials for Li-ion batteries,the effects of voltage and discharge specific capacity were investigated and the optimum delithiation conditions were determined.The introduction of Na₂S₂O₈ into the mixed electrolyte was also found to have a facilitating effect on the delithiation,and the optimum ratio of the mixed electrolyte for electrochemical delithiation was explored here.Secondly,the mechanism of electrochemical delithiation in a single electrolyte Na₂SO₄ and an optimally proportioned mixed salt electrolyte Na₂SO₄+Na₂S₂O₈ was compared at the optimum voltage and discharge specific capacity,and the promotion mechanism of Na₂S₂O₈ on delithiation was explored.The obtained olivine Fe PO₄ in Na₂SO₄+Na₂S₂O₈ electrolyte exhibited integrity in terms of structure and electrochemical properties,with discharge specific capacity of 157.1 m Ah/g at 0.1 C,constant voltage plateau of 3.37 V,and 98.8%capacity retention after 100 cycles.Mechanistic studies showed that Na₂S₂O₈ promoted the electrochemical delithiation by providing acidic conditions and chemically oxidation.Finally,the obtained FePO₄ material was electrochemically intercalated with sodium to prepare Na Fe PO₄ material,which realized the system conversion between lithium-ion battery and sodium-ion battery.The prepared Na Fe PO₄ material had a discharge specific capacity of 120.3 m Ah/g at 0.1 C,and the retention rate was 91.6%after 100 cycles.It also revealed the two-phase change of Na Fe PO₄ in the extraction/intercalation of sodium ions.Through the above study,the goal of complete delithiation for Li Fe PO₄material was basically achieved,and the setting of delithiation parameters was completed.The delithiation mechanism of Li Fe PO₄ material in aqueous electrolyte was explained,thus helping other cathode materials to carry out further related delithiation studies.The replacement of Li-ion intercalation materials by Na ions in intercalation chemistry was realized for application in sodium-ion batteries.