Graphite is used as a state-of-the-art anode in commercial lithium-ion batteries (LIBs) due to its highly reversible lithium-ion storage capability and low electrode potential. However, graphite anodes exhibit sluggish diffusion kinetics for lithium-ion intercalation/deintercalation, thus limiting the rate capability of commercial LIBs. In order to determine the lithium-ion diffusion coefficient of commercial graphite anodes, we employed a galvanostatic intermittent titration technique (GITT) to quantify the quasi-equilibrium open circuit potential and diffusion coefficient as a function of lithium-ion concentration and potential for a commercial graphite electrode. Three plateaus are observed in the quasi-equilibrium open circuit potential curves, which are indicative of a mixed phase upon lithium-ion intercalation/deintercalation. The obtained diffusion coefficients tend to increase with increasing lithium concentration and exhibit an insignificant difference between charge and discharge conditions. This study reveals that the diffusion coefficient of graphite obtained with the GITT (1 × 10⁻¹¹ cm²/s to 4 × 10⁻¹⁰ cm²/s) is in reasonable agreement with literature values obtained from electrochemical impedance spectroscopy. The GITT is comparatively simple and direct and therefore enables systematic measurements of ion intercalation/deintercalation diffusion coefficients for secondary ion battery materials.

The structure and oxygen permeability of SrCo_0.9-xNb_0.1Sn_xO_3–δ (x = 0, 0.03, and 0.05) perovskite membranes were systematically investigated by co-doping the B-site of SrCoO_3–δ oxide with Nb and Sn. Combined X-ray and neutron diffraction experiments showed that all materials crystallized in the tetragonal P4/mmm space group and that the crystal structures approached the ideal cubic perovskite structure with increasing Sn concentration. In addition, X-ray photoelectron spectra confirmed that Sn-doping increases the (Co, Nb, Sn)-O bond strengths. The impact of Sn-doping on the oxygen transport of dense SrCo_0.9-xNb_0.1Sn_xO_3–δ membranes was also investigated, under air/He gradient, as a function of both temperature and membrane thickness. The results showed that the oxygen transport of SrCo_0.9Nb_0.1O_3–δ is governed by oxygen ion diffusion, while the oxygen surface exchange reaction is the limiting process for the Sn-doped membranes, SrCo_0.87Nb_0.1Sn_0.03O_3–δ and SrCo_0.85Nb_0.1Sn_0.05O_3–δ.