Abstract:

A spinel lithium manganese oxide doped with nickel (LiNi0.05Mn1.95O4) was prepared by a sol-gel method using acetic lithium, nickel and manganese as rawmaterials. The lithiumion-sieve (denoted as LiNiMn-H) was obtained by acidification of the obtained LiNi0.05Mn1.95O4 with 0.5 mol·L-1 (NH4)2S2O8. After testing, we found that the dissolution ratio of Mn2+ fromLiNi0.05Mn1.95O4 during the acid-modification process was only 0.31% (w, mass fraction) and the saturation ion-exchange capacity of LiNiMn-Hfor Li+ was 5.29 mmol (36.72 mg) Li+/g ion-sieve. The exchange isothermal curves of LiNiMn-H in the H+-Li+ system were measured at 15, 25, 35 and 45 ℃ and the average activity coefficients of the electrolyte were calculated using Pitzer electrolyte solution theory. Other thermodynamic constants, such as the equilibrium constants Ka, △Gm, △Hm, and △Sm, were calculated during the exchange process. We conclude that the equilibrium constants reduce with the increase in temperature and that the selectivity of LiNiMn-H for Li+ is higher than the original ionH+. The exchange process is exothermic and the adsorption process occurs spontaneously (△Gm<0).

Key words: LiNi0.05Mn1.95O4, Lithiumion-sieve, Thermodynamics, Pitzer electrolyte solution theory