Exploration Of The Technology Of Lithium Extraction From Seawater By Electrolysis Based On Hybrid Electrolyte

In the past decade,lithium battery has been developed rapidly because of its high theoretical energy density,long service life,low self-discharge rate and environmental protection.It has been widely used in consumer electronics products such as electric vehicles,mobile phones and computers.However,with the continuous popularity of lithium batteries,the consumption of lithium resources is also increasing,which leads to the price increase of the lithium resources.The shortage of lithium resources caused by the continuous consumption of lithium resources will become an important factor restricting the development of lithium-ion batteries.Compared with the limited land lithium reserves of 1.4×10⁷ t,sea water resources with lithium reserves of 2.3×10¹¹ t are expected to become a new type of lithium resource reserve,providing almost inexhaustible lithium resources for the development of lithium batteries.Researchers have developed various methods of lithium extraction from seawater,such as evaporation crystallization,precipitation,extraction,adsorption,dialysis and electrochemical method.However,due to a small amount of lithium of 0.17 mg·L^-1 and a large number of other metal cations in seawater,the existing technology has been greatly limited with low lithium productive rate and purity.In this manuscript,a technology of lithium extraction from seawater by electrolysis based on hybrid electrolyte is proposed and studied in depth.This technology can selectively extract metallic lithium from seawater by electrolytic cell using Ru base catalyst as anode,seawater as anode electrolyte,copper as cathode,propylene carbonate solution of 0.5 M Li Cl O₄ as cathode electrolyte and LAGP as the separation layer of anode electrolyte and cathode electrolyte.With the electric energy powered by solar energy,the anode underwent oxidation reaction with the separation of oxygen and chlorine;lithium ions reduced as metallic lithium on the cathode;the lithium ions passed through LAGP to replenish the consumed lithium ions in cathode electrolyte while other cations were blocked in seawater by LAGP.Under the current density of 240?A·cm^-2,the technology showed the highest lithium productive rate of 60?g·h^-1 and the energy utilization efficiency of 50 mg·Wh^-1.However,this technology is still not mature enough with the high cost caused by Ru based catalyst and the instability of LAGP.The cost could be reduced without sacrificing the electrochemical performance by replacing the cheaper transition metal oxide as anodic catalyst.Ni O@SP,Co O@SP and Mn O₂@SP all showed excellent electrocatalytic activity with the electrolytic potential lower than 4.7 V and the energy utilization efficiency beyond 50 mg·Wh^-1.Ni O@SP showed best electrocatalytic performance no less than noble metals with the electrolysis potential of 4.54 V and the energy utilization efficiency of 57 mg·Wh^-1.The stability and service life of the technology could be improved by in-situ photopolymerization of a PMMA seawater protective layer on the sea water side of LAGP.PMMA/LAGP the Li-ion conductivity of 1.58×10^-5 S·cm^-1 an order of magnitude lower than LAGP due to the inferior Li-ion conductivity of PMMA and the interface impedance.Therefore,PMMA/LAGP showed the higher potential of 4.7 V compared with the pristine of 4.4 V.However,PMMA/LAGP shows much better stability and service life than LAGP.