The Investigation On Preparation And Performance Of Enhanced Electrochemical Assisted Electrodes For Lithium Ion Extraction

It is very urgent to develop lithium extraction technology since lithium is a widely used metal element.In China,the brine/seawater is the main source for providing lithium because of the low extraction cost.However,it suffers from the issues that the concentration of Li+is relatively low which is only 0.17 mg/L.Therefore,the extraction of lithium is still challanging.The capacitive deionization(CDI)which is emerges as an efficient,low cost and environmental-friendliness seawater desalination technology.Due to this fact,this thesis designed and prepared a sandwich structure of reduced graphene oxide(rGO)/lithium vanadate(Li3VO4,LVO)and carbon-coated staghorn coral-like lithium vanadium phosphate(Li3V2(PO4)3 LVPO)Nano composite electrode to extact Li+from the seawater by constituting CDI device with activated carbon(AC).The content can be classified as below:A facile in situ sintering method was used to prepare the LVO/rGO nanocomposite electrode.Electrochemical tests show that when the rGO doping amount is 20(LVO/rGO-20),it has the highest specific capacity at a scan rate of 100 mV/s,which is 318.70 F/g.This is higher than pure LVO(208.31 F/g).Lithium ion extraction experiment(LIE)results illuminate that the Li+extraction capacity of LVO/rGO-20 ? AC is as high as 39.53 mg/g,which is highly improved by compared with LVO ? AC system(29.35 mg/g).In addition,the LVO/rGO-20 ? AC system has been demonstrated the promintent cycling performance.After 20 cycles,the Li+extraction capacity is 30.84 mg/g,Moreover,experimental results show that the addition of rGO increases the active sites and the transport kinetics of Li+.After 20 cycles,the capacity retention rate is 78.02%.The freeze-drying and post annealing approach was employed to prepare LVPO/C composite electrode by using citric acid(CA)as the reducing agent.The X-ray diffraction(XRD)results show that the prerequisite for the synthesis of LVPO is to introduce the CA which promotes the transformation of V5+to V3+.The electrochemical measurement shows that the LVPO/C-1.00 which implies that the molar ratio of CA to NH4VO3 is 1:1 possesses the best capacity.When the scan rate at 100 mV/s,the specific capacity of LVPO/C-1.00 is 316.68 F/g.The LIE results confirm that the Li+extraction capacity of the LVPO/C-1.00 ? AC device reaches 9.60 mg/g under the constant voltage mode while it is 35.20 mg/g under the constant current mode.Further,the Li+extraction capacity of the device dropped from 25.89 to 14.07 mg/g after 20 cycles.Beyond that,the X-ray photoelectron spectroscopy and in situ XRD demonstrate that the Li+can be facily inserted/de-inserted from/out of LVPO/C without dertoreating the structure.Meanwhile,the CA is benefical to improve the Li+diffusion kinetics.