L. Kong, Y. Yu, K. Hu, X. Liu
George Washington University,
United States
Keywords: electrochemical intercalation, direct lithium extraction, geothermal brines
Summary:
As Li-ion batteries are increasingly being deployed in electric vehicles and grid-level energy storage, the demand for Li is growing rapidly. Extracting lithium from alternative aqueous sources such as geothermal brines plays an important role in meeting this demand. Electrochemical intercalation emerges as a promising Li extraction technology due to its ability to offer high selectivity for Li and its avoidance of harsh chemical regenerants. In this talk, I will discuss the prospects and challenges of using electrochemical intercalation for direct lithium extraction from geothermal brines. First, we design an economically feasible electrochemical process that achieves selective lithium extraction from Salton Sea geothermal brine and purification of lithium chloride using LiFePO4 as the intercalation material, and conversion to battery grade (>99.5% purity) lithium hydroxide by bipolar membrane electrodialysis. We conduct techno-economic assessments using a parametric model and estimated the levelized cost of LiOH•H2O as 4.6 USD/kg at an electrode lifespan of 0.5 years. The results demonstrate the potential of our technology for electro-driven, chemical-free lithium extraction from alternative sources. One of the key challenges for electrochemical intercalation is electrode durability in complex water environments. While geothermal brines contain abundant Li, they also have high concentrations of co-existing constituents, including Fe(II), Mn(II), and silica, which can form scaling layers on the electrode surface, presenting substantial challenges for Li+ extraction from LFP. We further investigate the influence of Fe(II), Mn(II), and silica on Li+ extraction by LFP and the underlying mechanisms involved. The performance and stability of LFP electrodes are compared after cycling experiments in solutions containing different impurities. Experimental results reveal that the presence of Fe(II) markedly reduces the capacity, energy efficiency, and Li+ selectivity over Na+ in LFP electrodes. The primary mechanism identified is the formation of a scaling layer by Fe(II) on the electrode surface, which impedes Li+ diffusion and disrupts the crystal structure of LFP. Mn(II) and silica can also contribute to the scaling issue but have minimal impact on the electrode. Finally, we propose a simple and cost-effective pre-treatment method for removing Fe(II) from geothermal brine to extend the lifespan of LFP electrodes.