Study On Lithium Extraction From Brine By LMO/MXene Composite Electrode Controlled By Pulsed Electric Field

With the extensive application of lithium ion battery in various fields,the supply and demand of lithium resource presents a serious imbalance.Extracting lithium from brine with low cost and high efficiency is the key to solve energy and environmental problems.Compared with other lithium extraction methods in brine,electrochemical lithium extraction has the advantages of high selectivity,low energy consumption and environmental protection.Spinel LiMn₂O₄（LMO）is considered as one of the most suitable anode materials for lithium extraction from brine.However,manganese dissolution and Jahn-Teller effect destroy the crystal structure of LMO,resulting in rapid capacity decline.In addition,the direct electrochemical extraction of lithium from brine will face the problem of lithium and sodium separation.In order to solve the above problems,two innovations are proposed in this paper:firstly,layered MXene material is used as the protective layer of lithium manganese oxide electrode material,and sandwich structure composite electrode material is used as embedded lithium electrode.Secondly,in the solution with low li-na ratio,the pulse electric field control mode is adopted to increase the kinetic advantage of lithium ion embedding and improve the selectivity of lithium extraction in the low li-Na ratio solution.Specific contents include:LMO,MXene and composite LMO/MXene were successfully synthesized by high temperature solid-phase method,solvothermal method and electrostatic self-assembly method.The sandwich composite structure was successfully prepared by structural characterization such as X-ray diffraction,scanning electron microscopy,transmission electron microscopy,X-ray photoelectron spectroscopy and other characterization methods.In stream solution,its high capacity,good cyclic stability and low charge transfer impedance were verified by electrochemical tests.After 30 cycles,the specific discharge capacity of LMO/MXene sample is 129.44 m Ah/g,and the capacity retention rate is 94.27%,both of which are better than that of unmodified lithium manganate material（108.71 m Ah/g,capacity retention rate is 91.18%）.Lithium extraction parameters were optimized for different current ratio,different electric field operation mode and different feed concentration.The effects of the new pulsed electric field mode and the traditional constant-current electric field mode on the cyclic stability were investigated in solutions with different initial ratios of lithium to sodium.The pulsed electric field provides a period of rest for the electrode,ensuring a more uniform concentration of lithium and sodium in the electrode.The addition of reverse pulse provides a more uniform concentration for ion diffusion and effectively eliminates concentration polarization.Finally,cyclic lithium extraction experiments were carried out in Atamuca simulated brine.The lithium extraction capacity and purity of LMO/MXene//AC system were improved under the pulse electric field mode.The energy efficiency of lithium extraction was 2.16Wh/mol Li at a time,and the purity of lithium ion in receiving liquid was 97.16%.After 15cycles,the purity is 93.81%,the retention rate is 96.55%,and the separation coefficient of lithium sodium is 1020.In conclusion,the LMO/MXene electrode in the pulse electric field control mode has an obvious advantage in the long-acting and stable lithium extraction with low lithium sodium than with high selectivity in the solution.