Kyu-Nam Jung

Carbon-free cobalt oxide cathodes with tunable nanoarchitectures for rechargeable lithium–oxygen batteries

Carbon-free cobalt oxide cathodes for lithium-oxygen batteries are fabricated via an electrodeposition-conversion process. The Co3O4-only cathodes show a remarkably reduced voltage gap (by ca. 550 mV compared to the carbon-only cathode) as well as excellent long-term cyclability.

Doped Lanthanum Nickelates with a Layered Perovskite Structure as Bifunctional Cathode Catalysts for Rechargeable Metal–Air Batteries

Rechargeable metal-air batteries have attracted a great interest in recent years because of their high energy density. The critical challenges facing these technologies include the sluggish kinetics of the oxygen reduction-evolution reactions on a cathode (air electrode). Here, we report doped lanthanum nickelates (La2NiO4) with a layered perovskite structure that serve as efficient bifunctional electrocatalysts for oxygen reduction and evolution in an aqueous alkaline electrolyte. Rechargeable lithium-air and zinc-air batteries assembled with these catalysts exhibit remarkably reduced discharge-charge voltage gaps (improved round-trip efficiency) as well as high stability during cycling.

One-dimensional manganese-cobalt oxide nanofibres as bi-functional cathode catalysts for rechargeable metal-air batteries

Rechargeable metal-air batteries are considered a promising energy storage solution owing to their high theoretical energy density. The major obstacles to realising this technology include the slow kinetics of oxygen reduction and evolution on the cathode (air electrode) upon battery discharging and charging, respectively. Here, we report non-precious metal oxide catalysts based on spinel-type manganese-cobalt oxide nanofibres fabricated by an electrospinning technique. The spinel oxide nanofibres exhibit high catalytic activity towards both oxygen reduction and evolution in an alkaline electrolyte. When incorporated as cathode catalysts in Zn-air batteries, the fibrous spinel oxides considerably reduce the discharge-charge voltage gaps (improve the round-trip efficiency) in comparison to the catalyst-free cathode. Moreover, the nanofibre catalysts remain stable over the course of repeated discharge-charge cycling; however, carbon corrosion in the catalyst/carbon composite cathode degrades the cycling performance of the batteries.

Promoting Li2O2 oxidation by an La1.7Ca0.3Ni0.75Cu0.25O4 layered perovskite in lithium–oxygen batteries

We demonstrate for the first time that La(1.7)Ca(0.3)Ni(0.75)Cu(0.25)O(4) with a layered perovskite structure promotes electrochemical oxidation of Li(2)O(2) in lithium-oxygen batteries with a non-aqueous aprotic electrolyte.

Rechargeable lithium–air batteries: a perspective on the development of oxygen electrodes

Lithium–air battery (LAB) technology is currently being considered as a future technology for resolving energy and environmental issues. During the last decade, much effort has been devoted to realizing state-of-the-art LABs, and remarkable scientific advances have been made in this research field. Although LABs possess great potential for efficient energy storage applications, there are still various technical limitations to be overcome before the full transition. It has been well recognized that the battery performance of LABs is mainly governed by the electrochemical reactions that occur on the surface of the cathode. Thus, the rational design of highly reliable cathodes is essential for building high-performance LABs. In this respect, we introduce recent advances in the development of LABs, particularly focusing on the cathodes based on a fundamental understanding of Li–O2 electrochemistry. Furthermore, we review the remaining technical challenges in order to formulate a strategy for future research and consolidate Li–O2 electrochemistry for successful implementation of LABs in the near future.

Thermodynamic and kinetic approaches to lithium intercalation into Li[Ti5/3Li1/3]O4 film electrode

Lithium intercalation into Li[Ti5/3Li1/3]O4 film electrode in the two-phase coexistence was investigated from the thermodynamic and kinetic viewpoints. The electrode potential versus lithium content curve of the film electrode was theoretically calculated in consideration of the interactions between lithium ions based upon a lattice gas model with the Monte Carlo simulation. According to the model, it was proposed that a wide potential plateau indicating the coexistence of a Li-poor phase α and a Li-rich phase β is due to the repulsive interactions between lithium ions. From the analysis of the ac-impedance spectra in the coexistence of two phases α and β, it was confirmed that the fraction of α phase at the electrode surface and that fraction of β phase continuously decreases and increases, respectively, with increasing lithium content. The analysis of the current transient led to the conclusion that transport of lithium ions subjected to the repulsive interactions within the electrode is governed by the cell-impedance-controlled constraint at the electrode surface during the phase transformation between α and β phases.

Manganese oxide/carbon composite nanofibers: electrospinning preparation and application as a bi-functional cathode for rechargeable lithium–oxygen batteries

Manganese oxide/carbon composite nanofibers are fabricated via an electrospinning technique. The electrospun composite nanofibers show an excellent catalytic performance for oxygen reduction and evolution, leading to reduced discharge–charge overpotentials and improved cycling properties of a Li–O2 battery with a hybrid electrolyte.

Carbon-, binder-, and precious metal-free cathodes for non-aqueous lithium-oxygen batteries: nanoflake-decorated nanoneedle oxide arrays.

Rechargeable lithium-oxygen (Li-O2) batteries have higher theoretical energy densities than todays lithium-ion batteries and are consequently considered to be an attractive energy storage technology to enable long-range electric vehicles. The main constituents comprising a cathode of a lithium-oxygen (Li-O2) battery, such as carbon and binders, suffer from irreversible decomposition, leading to significant performance degradation. Here, carbon- and binder-free cathodes based on nonprecious metal oxides are designed and fabricated for Li-O2 batteries. A novel structure of the oxide-only cathode having a high porosity and a large surface area is proposed that consists of numerous one-dimensional nanoneedle arrays decorated with thin nanoflakes. These oxide-only cathodes with the tailored architecture show high specific capacities and remarkably reduced charge potentials (in comparison with a carbon-only cathode) as well as excellent cyclability (250 cycles).

Tin phosphide-based anodes for sodium-ion batteries: synthesis via solvothermal transformation of Sn metal and phase-dependent Na storage performance.

There is a great deal of current interest in the development of rechargeable sodium (Na)-ion batteries (SIBs) for low-cost, large-scale stationary energy storage systems. For the commercial success of this technology, significant progress should be made in developing robust anode (negative electrode) materials with high capacity and long cycle life. Sn-P compounds are considered promising anode materials that have considerable potential to meet the required performance of SIBs, and they have been typically prepared by high-energy mechanical milling. Here, we report Sn-P-based anodes synthesised through solvothermal transformation of Sn metal and their electrochemical Na storage properties. The temperature and time period used for solvothermal treatment play a crucial role in determining the phase, microstructure, and composition of the Sn-P compound and thus its electrochemical performance. The Sn-P compound prepared under an optimised solvothermal condition shows excellent electrochemical performance as an SIB anode, as evidenced by a high reversible capacity of ~560 mAh g−1 at a current density of 100 mA g−1 and cycling stability for 100 cycles. The solvothermal route provides an effective approach to synthesising Sn-P anodes with controlled phases and compositions, thus tailoring their Na storage behaviour.

Nanostructured doped ceria for catalytic oxygen reduction and Li2O2 oxidation in non-aqueous electrolytes

Herein, we report the catalytic activities of porous nano-crystalline oxides with surface active sites synthesized by a wet chemical route. Zr doped ceria (ZDC) has been tested as active oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalysts in air electrodes for Li–O2 batteries. A ZDC-based air electrode exhibits a higher discharge capacity than that of a bare carbon-based air electrode. ZDC loaded in carbon air electrodes delivers a discharge capacity of 8435 mA h g−1. The higher discharge voltages of Li–O2 cells with ZDC, instead of bare carbon, could have originated from the higher oxygen reduction activity of ZDC. These oxides show a lower potential for Li2O2 oxidation than pure carbon. A significant increase in the kinetics for Li2O2 oxidation indicates the influence of the ZDC catalyst on the oxygen evolution reaction. The ORR and OER properties of the catalyst are explained in terms of the high fraction of active defect sites on its surface.