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.

Electrochemical flow capacitors (EFCs) are highly promising for grid-scale energy storage since they benefit from having advantages of both electrochemical capacitors and flow batteries, including their high power density, long cycle lifetime, and scalable energy capacity. Here, we demonstrate a high-performance flow capacitor using redox-active hydroquinone (HQ)-based pseudocapacitive slurry electrodes. The maximum capacitance value of 513 F g⁻¹ is attainable for a slurry with a 0.38 M HQ redox mediator. Considering both the rate performance and capacitance of slurry electrodes, the optimum HQ concentration is 0.3 M of HQ. The as-prepared slurry electrodes show the highest capacitance and energy density (∼14 W h kg⁻¹) among the previously reported slurry electrodes for aqueous flow capacitors. Furthermore, we performed first-principles calculations to understand the effect of HQ grafting on the activated carbon pore texture and the origin of increased capacitance by HQ mediators at the electrolyte and electrode interface.

Flow-electrode-based capacitive deionization (FCDI) is a desalination process that uses electrostatic adsorption and desorption of ions onto electrode materials. It provides a continuous desalination flow with high salt removal performance and low energy consumption. Since lithium has been regarded as an essential element for the last few decades, the efficient production of lithium from the natural environment has been intensively investigated. In this study, we have extracted lithium ions from aqueous solution by using FCDI desalination. We confirmed that lithium and chloride ions could be continuously collected and that the salt removal rate depends on various parameters, including feed-flow rate and a feed saline concentration. We found that the salt removal rate increases as the feed-flow rate decreases and the feed salt concentration increases. Furthermore, the salt removal rate depends on the circulation mode of the feed solution (continuous feed stream vs. batch feed stream), which allows control of the desalination performance (higher capacity vs. higher efficiency) depending on the purpose of the application. The salt removal rate was highest, at 215.06 μmol/m⁻²s⁻¹, at the feed rate of 3 mL/min and the feed concentration of 100 mg/L. We believe that such efficient and continuous extraction of lithium chloride using FCDI desalination can open a new door for the current lithium-production industry, which typically uses natural water evaporation.

A facile mussel-inspired surface modification of interconnected porous carbon nanosheet (IPCN) electrodes is demonstrated through the formation of a polydopamine coating and the subsequent layer-by-layer deposition of ferric ions (Fe³⁺) and tannic acid, with the aim of developing high-performance electrochemical capacitors. After the deposition of the polydopamine coating, the specific capacitance increases by ∼40% as compared to that of an unmodified IPCN electrode. This increase in the capacitance can be explained based on the pseudocapacitance induced by the catechol groups of polydopamine. Furthermore, the electrodes coated with both polydopamine and layers of Fe³⁺ and tannic acid exhibit an additional increase in the capacitance to ∼244 F g⁻¹ at 5 mV s⁻¹, which is ∼83% higher than that of the unmodified IPCN electrode. This is attributable to the presence of many redox moieties, which are introduced by polydopamine and tannic acid. Furthermore, the strong interactions between the Fe³⁺ ions and the catechol groups result in improved capacitance retention even after 1000 cycles. The mussel-inspired surface modification of IPCN electrodes demonstrated in this work can potentially be exploited for developing novel pseudocapacitive electrode materials with excellent performances.

For practical utilization of proton-conducting ceramic fuel cells and electrolyzers, it is essential to lower the sintering temperature and processing time of BaZrO₃-based proton conductors. We investigated the effect of sintering temperature and time on the structural and electrochemical properties of dense BaZr_0.8Y_0.2O_3−δ (BZY) prepared by a solid-state reactive sintering process, using NiO as a sintering aid. The sintered BZY prepared from the micronized precursor powder exhibited a density higher than 93%, and an average grain size in the range of 0.6 to 1.4 μm. The orthorhombic BaY₂NiO₅ phase was also observed in the sintered BZY from the combined conventional and synchrotron X-ray diffraction measurements. Electrochemical impedance spectroscopy showed that the total proton conductivities of BZY can be modulated by sintering temperature in a wet reducing atmosphere. The maximum total ion transport number achieved was 0.89 at 600 °C, and the maximum power density of the symmetric BZY electrolyte supported cell with Pt electrodes was 5.24 mW·cm⁻² at 900 °C.