Facet dependent ion channel of iron phosphate for electrochemical lithium extraction

Lithium resources can be extracted from liquid by electrochemical intercalation processes. However, the response of material structure to ion transport channels in aqueous environments is not fully understood, which limits the effective design of materials. In this study, we present LiFePO4 samples with exposed (1 0 0) and (0 1 0) crystal facets (named LFP (1 0 0) and LFP (0 1 0)) as a model host to explore ion transport behavior and demonstrate the effect of exposed facet on surface adsorption and bulk phase diffusion of ions. Batch experimental results demonstrated that LFP (0 1 0), despite having a significantly smaller surface area, exhibits superior adsorption performance, with an adsorption capacity of 11.13 mg/g in a 50 ppm Li+ solution. Computational investigation reveals that due to the different exposed facets, the adsorption energy of Li(H2O)4+ on the LFP (0 1 0) is higher, but the immigration energies of Li+ in LFP (0 1 0) bulk phase are significantly lower (0.12 eV), leading to different adsorption rates at different time intervals. All these findings suggest that the adsorption process of Li+ is significantly crystal facet dependent, influenced by the adsorption energy and migration pathway, reflected in two stages of Li+ surface adsorption and bulk phase migration. These findings contribute to a better understanding of the interface interaction between Li+ and the adsorbent at the microscopic level and facilitate the design of more efficient adsorbents.