Study On Doping Modification Of Manganese Based Ionic Sieve And Lithium Adsorption Performance

In recent years,due to the wide application of lithium batteries in new energy fields,the demand and consumption of lithium are increasing,and it is of great practical importance to extract lithium efficiently from liquid resources rich in lithium reserves.Li_1.6Mn_1.6O₄ type lithium ion sieve（LIS）has good theoretical lithium adsorption capacity and excellent adsorption selectivity,and is considered as a potential Li⁺ion recovery from brine adsorbent.However,in practical applications,the easy dissolution loss of manganese leads to the decrease of LIS adsorption capacity and poor cycling stability,which limits its industrial application.In this work,a series of aluminum-chromium bimetallic doped manganese Li-ion sieves and aluminum,chromium and fluorine triple doped Li-ion sieves were prepared to improve the adsorption performance of Li-ion sieves by reducing the manganese dissolution loss.The details of the study and the results are as follows:A series of Al-Cr bimetal doped Mn-based LIS with different doping amounts were prepared by a facile hydrothermal synthesis method.The characterization results show that Al and Cr ions are uniformly doped into the spinel crystal structure of LIS,and the introduction of Al and Cr ions could shrink the crystal,reduce the Mn³⁺content,increase the average valence of Mn in the co-doped samples,and effectively improve their structural stability.Compared with the undoped ion sieve H_1.6Mn_1.6O₄,the 2%Al and 4%Cr co-doped ion sieve H_1.6Mn_1.54Al_0.02Cr_0.04O₄ exhibited higher lithium adsorption capacity,lower Mn dissolution loss,and good cycling stability.In addition,H_1.6Mn_1.54Al_0.02Cr_0.04O₄ has a higher adsorption selectivity for Li⁺compared to Mg²⁺,Ca²⁺,K⁺and Na⁺.The adsorption of lithium on the prepared LIS was determined as a chemical and monolayer adsorption process by fitting kinetic and isothermal models to the adsorption process.Combining the experimental and characterization results,the adsorption mechanism of lithium on Al,Cr co-doped Mn-based LIS was investigated.To further improve the structural stability and adsorption capacity of LIS,a series of aluminum,chromium and fluorine triple-doped manganese-based lithium ion sieves were prepared by hydrothermal synthesis method.The characterization results showed that Al,Cr and F were uniformly introduced into the LIS,and the insertion of F did not change the spinel structure of the LIS;however,the introduction of F caused the formation of a fluoride cladding layer of about 5.0 nm on the surface of the LIS,which had an important role in stabilizing the LIS structure.The highly electronegative F^-replaces part of the O^2-on the surface,forming a more stable metal-fluorine bond.The combined effect of Al,Cr and F enhances the structural stability of LIS,while the doping of F provides more carriers for adsorption/desorption.Compared with the double-doped ion sieve H_1.6Mn_1.54Al_0.02Cr_0.04O₄,the triple-doped ion sieve H_1.6Mn_1.54Al_0.02Cr_0.04F_0.1O_3.9 with 10%F doping exhibited higher lithium adsorption capacity,lower Mn dissolution loss and better cycling stability.