Asymmetric pathways for lithium extraction and recovery based on the two-phase equilibrium of layered oxides

Electrochemical intercalation offers a promising platform for Li⁺ extraction. However, only limited types of electrode materials have been investigated. The challenge to broaden and tailor materials for electrochemical intercalation-based Li⁺ extraction lies in the lack of understanding of material's response upon co-intercalation of multiple ions, therefore, paired process design to enable reversible Li⁺ extraction and recovery. Here, we showcase the design of asymmetric ion pathways for Li⁺ extraction and recovery for host material with complex Li⁺ and Na⁺ interaction using layered cobalt oxide as a model material. The two-phase equilibrium of Na_0.48CoO₂ and Li_0.94CoO₂ governs Li⁺ selectivity when a high depth of intercalation is achieved (low vacancy level). We show that the relative rate between ion exchange and intercalation is critical to determine the ion pathways. The relationship can be quantitatively compared using the average pseudo ion exchange rate (C_pseudoIX) and the intercalation rate (C_inter). The ion pathways at the three regimes with C_pseudoIX > C_inter, C_pseudoIX ~ C_inter, and C_pseudoIX inter are constructed. By selecting the optimized ion pathway and particle size, we demonstrate 9.7×10⁴ Li⁺ selectivity with 99% purity Li⁺ recovery from an initial 1:1000 Li: Na molar ratio solution using 115 mAh/g specific capacity.