In this work, using model layered cobalt oxide, we investigated the co-intercalation ion pathways and unveiled the importance of the relative kinetics of intercalation and ion exchange to Li + extraction capacity, selectivity, and reversibility. The two-phase equilibrium between Li0.94CoO2 and Na0.48CoO2 divided the materials space into Li-rich and Na-rich regions when outof-equilibrium with v between 0.06 and 0.52 (Fig. ). To quantitatively compare the kinetics, we define an average ion exchange rate as CpseudoIX and divided the different intercalation behaviors into three regimes. Using both in situ and ex situ composition and structural characterization, we constructed the three different ion pathways that depends on the relationship between CpseudoIX and intercalation rate (Cinter). This relationship is predictive of the behavior when intercalating from Li0.48CoO2 as the extraction starting material. At CpseudoIX < Cinter, the intercalation quickly brings the structure into the Na-rich out-of-equilibrium region with following intercalation resembling the Na + intercalation features. In this case, ion exchange is needed after intercalation to bring the structure back to equilibrium to restore the Li + content and if ion exchange cannot be completed, both Li + selectivity and recovered Li + purity will decrease. We also show that particle morphology is important and smaller particles can promote faster and more reversible ion exchange. At CpseudoIX > Cinter, the intercalation will not push the structure out of the Li-rich region; therefore, a high depth of intercalation and high Li + selectivity can be achieved in a single step of intercalation without additional ion exchange. When CpseudoIX is close to Cinter, the ion pathway is a combination of the previous two with longer period of intercalation maintained in the Li-rich region; however, the structure still enters the Na-rich region at the end. Enabled by the understanding of the ion pathway, we designed the Li + extraction and recovery process and achieved 9.7×10 Li + selectivity during extraction from an initial 1:1000 Li: Na molar ratio solution and ~ 99% purity during Li + recovery with 115 mAh/g capacity. A good reversibility was also demonstrated with the optimized Li + extraction and recovery path. The possible paths for Li + extraction and recovery using model layered cobalt oxide are illustrated in Fig. . Fig. shows the phase diagram of CoO2-LiCoO2-NaCoO2 with the phase equilibrium between Na0.48CoO2 and Li0.94CoO2 shown as the purple line. Regions out of equilibrium are shown in blue and red triangles as Li-rich and Na-rich regions for Li + and Na + dominated structures, respectively . When the host composition is within either the blue or the red region, the host prefers to ion exchange with solution Na + (blue) or Li + (red), to reestablish the phase equilibrium. The composition is electrochemically controlled by modulating the vacancy and therefore the phase volume of the two phases that coexist in host material (Fig. ). Fig. shows different hypothetical paths of Li + extraction and recovery considering the Faradaic Efficiency (FE) and purity of Li + . FE describes the amount of Li + intercalated per e -added. Based on the two-phase equilibrium between Na0.48CoO2 and Li0.94CoO2, optimizing Li + extraction requires pushing the host to as close as Li0.94CoO2 at the end of the intercalation to minimize the content of Na + in the structure. If high depth of intercalation (1-v = 0.94) is not achieved, both the FE and purity of Li + will be sacrificed. Therefore, the kinetics of concurrent intercalation and ion exchange are critical to ensure that the depth of intercalation can be maximized, and two-phase equilibrium can be achieved. Moreover, there exist two extreme cases that needs to be understood in determining the extraction and recovery paths. The first case starts from Na0.48CoO2 and ends at Li0.94CoO2 which are both the equilibrium composition of the host at the given vacancy level. For this path, the FE can reach ~200% (46% charge capacity for 0.94 Li + composition), which is attractive from the energy perspective. The second one is for Li recovery to maximize Li + purity. This pathway requires the recovery to be done as delithiation in Li + solution from Li0.94CoO2 to Li0.48CoO2. To prioritize Li + selectivity and purity, it is ideal to use Li + solution for recovery which results in Li0.48CoO2 at the end of the recovery. However, Li0.48CoO2 could automatically convert to Na0.48CoO2 in the extraction condition (1:1000 Li: Na) by ion exchange. Therefore, it is unknown when starting from Li0.48CoO2, how the host structure will transform responding to the competitive intercalation and ion exchange and how to design the pathway of Li + extraction to enable a reversible loop to Li0.94CoO2. Li: Na acetonitrile solution at C/10 rate with two different voltage cutoffs for (NaLi)0.67CoO2 formed by ion exchange with the different parent materials a, Li0.67CoO2 with insert SEM of LiCoO2 and 10 µm scale bar, b, smaller Li0.67CoO2 with insert SEM of smaller LiCoO2 and 500 nm scale bar, and c, Na0.67CoO2 with insert STEM of Na0.67CoO2 and 50 nm scale bar. The blue lines are for the -0.2 V cutoff and the red lines are for the 0.1 V cutoff (blue and red curves are different electrodes). The darker lines and arrows indicate intercalation, and the lighter lines and arrows indicate OCP. d, XRD spectra for parent Na0.67CoO2 (black), after ion exchange completion (blue), and after the pulse/ion exchange sequence (red, sequence in f). The black, blue, and red dashes indicate the peaks for Na0.67CoO2, Na0.48CoO2, and Li0.94CoO2, respectively. The * labels comes from the carbon cloth substrate. e, The OCP curves for Na1-vCoO2 with v = 0.50, 0.45, 0.33, and 0.28 while soaking in 1:1000 solution. f, The ion exchange (light red) and intercalation (dark red, at C/10) curves for the conversion of Na0.67CoO2 (parent material) to Na0.08Li0.86CoO2 in Li: Na 1:1000 solution.