강병우 교수

The Na superionic conductor (aka Nasicon, Na 1+ x Zr 2 Si x P 3– x O 12, where 0 ≤ x ≤ 3) is one of the promising solid electrolyte materials used in advanced molten Na-based secondary batteries that typically operate at high temperature (over ∼270 °C). Nasicon provides a 3D diffusion network allowing the transport of the active Na-ion species (i.e., ionic conductor) while blocking the conduction of electrons (i.e., electronic insulator) between the anode and cathode compartments of cells. In th

Chemical reactions at the solid electrolyte (SE) and Li metal interface form an interphase before electrochemical reactions occur. This study investigates the effects of the chemically formed interphase between Li metal and Li 1.5 Al 0.5 Ge 1.5 (PO 4 ) 3 (LAGP) on cell failures under various experimental conditions. LAGP forms a black interphase by chemically reacting with Li metal. The interphase comprises a stoichiometrically changed LAGP and Li-related oxides and behaves as a mixed ionic and

All-Solid-State Batteries (ASSBs) that use oxide-based solid electrolytes (SEs) have been considered as a promising energy-storage platform to meet an increasing demand for Li-ion batteries (LIBs) with improved energy density and superior safety. However, high interfacial resistance between particles in the composite electrode and between electrodes and the use of Li metal in the ASBS hinder their practical utilization. Here, we review recent research progress on oxide-based SEs for the ASSBs wi

LiMnPO 4 was synthesized from an off-stoichiometric mix of starting materials with nominal composition LiMn 0.9 P 0.95 O 4- . Stoichiometric LiMnPO 4 with particle size 50 nm was found with X-ray diffraction even with the large overall deviation from stoichiometry in the sample, indicating that other noncrystalline compounds are present. The off-stoichiometric sample had a discharge capacity of 145 mAh/g at C/10 and 100 mAh/g at 2C after a constant current constant voltage charge. Capacity reten

Use of compounds that contain fluorine (F) as electrode materials in lithium ion batteries has been considered, but synthesizing single‐phase samples of these compounds is a difficult task. Here, it is demonstrated that a simple scalable single‐step solid‐state process with additional fluorine source can obtain highly pure LiVPO 4 F. The resulting material with submicron particles achieves very high rate capability ≈100 mAh g −1 at 60 C‐rate (1‐min discharge) and even at 200 C‐rate (18 s dischar

We tried to understand the reversible capacity of SiO during the first cycle and its effect on the poor initial Coulombic efficiency (ICE). Several SiO samples that have slightly different microstructures were prepared by a solid-state reaction. They have similar irreversible capacities but have different reversible capacities during the first cycle. As a result, the ICEs of the samples increase as their reversible capacities increase. The limited reversible capacity in SiO originates from the d

Co-free Mn-based Li-rich layered materials have been attracting a lot of attention due to their high capacity via the additional oxygen redox reaction and their low cost. However, their poor capacity retention and voltage fade upon cycling remains a problem for practical applications. Herein, we report on long-term cyclability of a Co-free Mn-based Li-rich layered material with superior voltage retention for 490 cycles. The developed one-step solid-state reaction, which comprises a thorough mixi

In this study, electrochemical behaviors of Li2S such as a large potential barrier at the beginning of the 1st charging process and a continuous increase in potential to ∼4 V during the rest of this process were understood through X-ray photoelectron spectroscopy measurements and electrochemical evaluations for a full utilization of Li2S. The large potential barrier to the 1st charge in Li2S can be caused by the presence of insulating oxidized products (Li2SO3 or Li2SO4-like structures) on the s

Electrochemical activity in high-voltage spinel LiNi0.5Mn1.5O4 (LNMO) is strongly affected by the disordering of Ni/Mn and the presence of Mn3+ ions. However, understanding the effect of the Ni/Mn disordering or the presence of Mn3+ ions on electrochemical properties is not trivial because disordering is typically coupled with the presence of Mn3+ ions. Here, we demonstrate for the first time that the doping of Li instead of Ni increases Ni/Mn disordering, which is decoupled from the presence of

We report a new triplite-type iron fluoro-sulfate compound, a cation-disordered NaFeSO4F that has redox potential of ∼3.7 V versus Na+/Na0 and can have 138 mA·h/g of theoretical capacity. This compound shows practical energy density (∼430 W·h/kg) comparable to that of several Li-ion battery positive electrode materials such as LiMn2O4 (430 W·h/kg). Therefore, triplite NaFeSO4F is a candidate positive electrode material which can meet the requirements for high energy density Na-ion batteries. Fur