First-Principles Predictions of Lithium Adsorption in Doped Titanium Oxide Ion Sieves

Hydrogen titanium oxide (HTO) is a promising material to efficiently extract lithium ions from oil, gas, or geothermal brines. Tremendous experimental efforts, including doping selective foreign elements into HTO materials, have been performed to improve their performances; however, a clear mechanistic understanding is still missing. Here, ab initio molecular dynamics (AIMD) simulations are carried out to investigate the effects of a wide range of possible dopants (Pb, Zr, Sn, Mo, Fe, Mn, Ni, and Si) on HTO lithium adsorption, which, to the best of my knowledge, have never been studied in the literature. Simulation results show that, for dopant sizes larger than Ti in HTO (Pb, Zr, Sn, and Mo), the maximum Li adsorption capacity is limited by a characteristic Li-poor/Li-rich phase transition; for dopant sizes smaller than Ti in HTO (Fe, Mn, Ni, and Si), the maximum Li adsorption capacity decreases due to early crystal volume shrinkages that result in a free energy minimum. These results are helpful in guiding future research directions for more efficient lithium-ion sieve materials.