| As one of the important raw materials for preparing lithium batteries,the development and utilization of lithium resources has become a global concern.Compared to lithium-bearing ores,the low content of lithium and the abundant stotage in bine make the researchers look forward to find a highly efficient liquid-phase lithium extraction technology.?-MnO2 has a selective adsorption capability for lithium ions and is called a "lithium ion sieve".Ion exchange method based on lithium ion sieve material is one of the methods for recoverying lithium from brine with complex ion exists.However,if the lithium enrichment process is carried out by a conventional diffusion method,the equilibrium time required is as long as 10 hours or more.At the same time,the recycling performance of X-MnO2 is poor due to dissociation reaction of manganese ions,and these problems limit the ?-MnO2 Lithium ion sieves are applied to the extraction of lithium from salt lakes.In order to solve the above-mentioned problems,a polypyrrole-coated?-MnO2 lithium ion-sieve electrode(PPy/?-MnO2)was prepared in this paper.Mn?/Mn? was transformed by the electric field to increase the adsorption rate of lithium ions,and at the meantime the recycling performance was promoted by the PPy cladding.In this paper,our main work can be included in 2 parts.First,a PPy/?-MnO2 powder electrode was prepared.Hydrothermal synthesis of ?-MnO2 powder,and pyrrole polymerization initiated by Fe3+oxidation to form PPy/?-MnO2 powder material,and finally the powder material was loaded on the graphite plate substrate electrode with a binder to make PPy/?-MnO2 powder electrode.The electrochemical behavior of the electrode in a lithium-containing supporting electrolyte solution indicates that the electrochemical conversion of Mn?/Mn? on the electrode is affected by the diffusion rate of lithium ions.The charge-discharge test in a two-electrode system composed of Ag/AgCl electrode shows that the cycle stability of the PPy/?-MnO2 powder electrode is significantly improved,and in 50 cycles of charging and discharging test at a current density of 150 mA·g-1,the discharge capacity is only degraded by 5%while ?-MnO2 powder electrode has decreased by almost 30%,therefore,the stability is improved after PPy introduced.The AC impedance test also showed that the Introduction of PPy can significantly improve the conductivity of the electrode.Lithium recovery test in simulated brine,reveals that the lithium extraction efficiency was 17.10 mg·g-1·h-1 which in another word means that the extraction of 1 mol of lithium ions only consumed 4.92 Wh of electrical energy.Secondly,a self-supporting LiMn2O4 film electrode with no binder was prepared on the surface of a base electrode by a series of steps including cathode deposition-air oxidation-lithium intercalation.and then it followed by a electropolymerization of pyrrole step and delithiation to obtain PPy/?-MnO2 film electrode.In this-film electrode,because of binder-free property and porous honeycomb structure,the contact area between the electrode active material and the solution is effectively improved.Therefore,the efficiency of lithium extraction by the-film electrode was up to 21.97 mg·g-1·h-1,while the extraction of 1 mol of lithium ions only consumed 3.70 Wh of electric energy.The discharge capacity of the film electrode degraded by about 12%during the 100 charge/discharge tests,therefore it was obviously better than the film electrode coated with PPy(capacity decreased by about 50%).In summary,the results of the present study show that the ?-MnO2 electrode can be used to induce the Mn?/Mn? conversion in ?-MnO2 by the electric field,which can effectively improve the adsorption rate of lithium ions in the solution.However,Polypyrrole coating will not affect the lithium ion adsorption performance while effectively solving the Mn loss problem,thus significantly improve the electrode's recycling performance. |
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