In Situ Reconstruction Of Spent Lithium Cobalt Oxide Cathode Material And Its Electrocatalytic Oxygen Evolution Performance

The recycling of spent Li-ion battery materials is developing towards the direction of in-situ reconstruction and synthesis of new functional materials.However,most of the researches in this field are focused on the directional deintercalation of Li⁺in organic electrolyte,while the researches on the selective directional embedding of other metal elements are very scarce.In this paper,taking the spent lithium cobalt oxide（LiCoO₂）materials as object,the number of active sites in LiCoO₂ and the exposure of active sites were increased by the deintercalation and intercalation of ion in the aqueous two-electode system and hydrogen reduction methods.Through these methods,catalysts with good performance in OER and Li-O₂ batteries were obtained.The main research works were as follows:（1）To verify the feasibility of deintercalation and intercalation of Li⁺in the aqueous two-electrode system.Taking the nano LiCoO₂ as the research object,the feasibility of deintercalation and intercalation of Li⁺in the aqueous two-electrode system was proved.The nano LiCoO₂ was prepared as an electrode to realize the repeated deintercalation and intercalation of Li⁺in the aqueous system.At the same time,the effect of cycling times on the catalytic performance of LiCoO₂ was discussed.During the process,the lattice of LiCoO₂ expands,the crystal is broken resulting in the size reduction,while the content of Co⁴⁺and oxygen vacancy increase.The overpotential of nano LiCoO₂ with five cycles in aqueous OER is?₁₀=365 m V,and the Tafel slope is 55 m V dec^-1.At the same time,as the cathode of Li-O₂ batteries,the OER overpotential of the material is 1.01 V.And under the limited capacity of 500 m Ah g^-1,the battery realized lifetime of 60 cycles,which is improved by 25%compared with the nano LiCoO₂（48 cycles）.（2）The recycling and function reuse of spent LiCoO₂ was realized by the intercalation of Fe³⁺.Based on the experimental result in the previous chapter,that the deintercalation and intercalation of ions in the LiCoO₂ can be realized in aqueous two-electrode system.In this chapter,the spent LiCoO₂ was used to prepare electrodes,the deintercalation of Li⁺and the intercalation of Fe³⁺were realized in the aqueous system.The deintercalation of Li⁺breaks the interlayer of LiCoO₂ and form the porous layered structure.The intercalation of Fe³⁺increases the OER active sites such as Fe³⁺while promoting the conductivity of LiCoO₂.The material with intercalation time of 0.5 h exhibits better OER performance in 1 mol L^-1 KOH,the OER overpotential decreases from 456 m V to 325 m V,and Tafel slope decreases to 55 m V dec^-1.In the Li-O₂ batteries,the charge overpotential is reduced from 1.16 V to 0.94 V,and the lifetime of 47 cycles is achieved under the limited capacity of 500 m Ah g^-1,which is nearly double that of the original material（25 cycles）.（3）Porous layered LiCoO₂ rich in oxygen vacancies was synthesized by hydrogen reduction.In view of the large size and few active sites of LiCoO₂ particles,the spent LiCoO₂ was reconstructed by chemical delithiation and hydrogen thermal reduction,and finally the three-dimensional porous layered LiCoO₂ rich in oxygen vacancies was obtained.Chemical delithiation results in partial fragmentation of the layered structure of LiCoO₂ to form the three-dimensional porous structure.Subsequently,by controlling the reduction temperature,more oxygen vacancies are formed as well as maintaining the three-dimensional porous layered structure of LiCoO₂.The results show that the catalytic activity of the sample obtained with the hydrogen reduction temperature of 300°C is better.The overpotential in the aqueous OER decreases to 361 m V with the current density of 10 m A cm^-2,while the Tafel slope was 67 m V dec^-1.And the current density remains at 85%of the original value after continuous oxygen evolution for 16 h.As the cathode for Li-O₂ batteries,the OER overpotential is reduced to 0.93 V,which is 0.23 V lower than that of the original LiCoO₂（1.16 V）.And the lifetime increases to 82 cycles,which is3.3 times that of the original LiCoO₂（25 cycles）.