Sang-Gil Woo

Characterizations of a new lithium ion conducting Li2O–SeO2–B2O3 glass electrolyte

Abstract A new lithium-ion conducting glass electrolyte, x Li 2 O–(1− x )(ySeO 2 –(1− y )B 2 O 3 ) was prepared by melt quenching technique and characterized using various analytical techniques. 0.5Li 2 O–0.5(ySeO 2 –(1− y )B 2 O 3 ) glass shows typical mixed-former behavior and the conductivity increased significantly compared with binary Li 2 O–B 2 O 3 glass with a maximum conductivity close to 10 −6 S/cm at y =0.5. Based on FT-IR and DSC analyses, SeO 2 acts either glass modifier or glass former as the composition of SeO 2 changes. The glass transition temperature is found to be about 300 °C, and the glass is electrochemically stable without any significant decomposition reaction between 0 and 5 V (vs. Li/Li + ).

Electrochemical Characteristics of Ti–P Composites Prepared by Mechanochemical Synthesis

Titanium phosphide composites with various Ti/P molar ratios (1:1, 1:2, and 1:4) were synthesized by a mechanochemical method and their potential use as an alternative anode material for Li secondary batteries was investigated. The titanium phosphide composites with Ti/P molar ratios of 1:1 and 1:2 did not show any electrochemical reactivity with Li, while both the TiP 2 and P in the composite with a Ti/P molar ratio of 1:4 reacted with Li, yielding a reversible capacity of 1422 mAh/g. Ex situ X-ray diffraction analyses and X-ray absorption spectroscopy showed that the TiP 2 -P composite transformed into cubic Li 10.5 TiP 4 phase without decomposing into Ti and Li 3 P during the initial Li insertion. Subsequent cycling showed a highly reversible insertion/ extraction process of Li to/from Li 10.5 TiP 4 phase, accompanied by the loss/recovery of the long-range cubic order. The cubic Li 10.5 TiP 4 phase showed excellent cycling performance with a large capacity of 625 mAh/g for 80 cycles when the amount of lithium reacted was suitably controlled.

Self-Extinguishing Lithium Ion Batteries Based on Internally Embedded Fire-Extinguishing Microcapsules with Temperature-Responsiveness

User safety is one of the most critical issues for the successful implementation of lithium ion batteries (LIBs) in electric vehicles and their further expansion in large-scale energy storage systems. Herein, we propose a novel approach to realize self-extinguishing capability of LIBs for effective safety improvement by integrating temperature-responsive microcapsules containing a fire-extinguishing agent. The microcapsules are designed to release an extinguisher agent upon increased internal temperature of an LIB, resulting in rapid heat absorption through an in situ endothermic reaction and suppression of further temperature rise and undesirable thermal runaway. In a standard nail penetration test, the temperature rise is reduced by 74% without compromising electrochemical performances. It is anticipated that on the strengths of excellent scalability, simplicity, and cost-effectiveness, this novel strategy can be extensively applied to various high energy-density devices to ensure human safety.

5V-class high-voltage batteries with over-lithiated oxide and a multi-functional additive

Over-lithiated oxides are promising cathode materials for 5V-class high-voltage batteries, however, their widespread adoption has been seriously restricted owing to their complicated chemical and electrochemical limitations. To resolve both of these issues at once, we suggest a multi-functional additive, tris(trimethylsilyl)phosphite (TMSP), with a comprehensive working mechanism that is demonstrated by systematic spectroscopic analyses combined with first-principles calculations. First, TMSP remarkably reduces the internal pressure because trivalent phosphorus effectively scavenges the oxygen gas in the cell. Second, TMSP greatly enhances the overall chemical stability of electrolytes because electrophilic phosphorus and silicon readily remove nucleophilic lithium oxide species by means of a chemical scavenging reaction. Third, TMSP affords a phosphite component in the protection layer on the electrode surface, inhibiting additional electrolyte decomposition under a high working potential. Finally, TMSP provides a silyl ether component in the protection layer, which is responsible for preventing transition metal dissolution through a fluoride scavenging reaction. Based on these verified effects, TMSP-controlled cells offer remarkable cycle performance with 90.2% capacity retention for 100 cycles.

Copper incorporated CuxMo6S8 (x ≥ 1) Chevrel-phase cathode materials synthesized by chemical intercalation process for rechargeable magnesium batteries

An effective method to control the composition of CuxMo6S8 Chevrel-phase is introduced to incorporate more than 1 mol of Cu in the Mo6S8 Chevrel cathode material for rechargeable Mg batteries. By adopting a chemical intercalation process, CuxMo6S8 (x ≥ 1) ternary Chevrel phases can be successfully synthesized up to x = 1.7. Through a combination of various structural and electrochemical analyses, it is confirmed that our synthesized products have a homogeneous size and single phase, in contrast with the product made by the conventional method controlling the chemical leaching time, which leads to a high reversible capacity close to the theoretical value at the Cu1.3Mo6S8 electrode. Furthermore, the electrode exhibits excellent discharge rate capability and cycling performance at room temperature. As x in CuxMo6S8 increases further, while the specific capacity decreases, capacity retention is well maintained during cycles. The information obtained from this study would contribute for the utilization of ternary Chevrel phases as cathode materials for rechargeable Mg batteries.

1,3-Propanesultone as an effective functional additive to enhance the electrochemical performance of over-lithiated layered oxides

Over-lithiated layered oxides (OLOs) are one of the promising positive electrode (PE) materials, however, the poor cycle-life of OLOs has to be resolved in order to make OLO cells available. In this work, several kind of additives are investigated to enhance the interfacial stability and the most efficient additive is 1,3-propanesultone (PS). According to spectroscopic analysis, it is found that the surface film derived from PS is effective in suppressing both metal dissolution and undesired reactions of the electrolyte on the PE, which results in remarkably enhanced cycle performance of the OLO electrode.

Effect of acid scavengers on electrochemical performance of lithium–sulfur batteries: Functional additives for utilization of LiPF6

We investigated a novel approach for utilizing LiPF6 as the lithium salt for Li–S batteries and verifying its chemical reactivity with the main solvent. It is found that the main obstacle for the adoption of LiPF6 is the undesired acid-catalyzed, cascade-type polymerization reaction between cyclic ether components in the solvent and LiPF6. Therefore, several kinds of acid scavengers are proposed to enhance the chemical stability between the main solvent and LiPF6. Simple storage tests indicate that polymerization occurred as acid residue is removed from the electrolyte. Consequently, the cell with a modified electrolyte shows excellent discharge capacity and moderate retention based on its improved chemical stability. These results indicate that assuring the chemical stability is the most important factor to utilizing LiPF6 as the main lithium salt for a Li–S cell. Additionally, it is believed that an understanding of the nature of chemical reactivity will be beneficial to constructing more efficient electrolyte systems owing to enhanced electrochemical performance of many kinds of energy storage systems including Li–S, Li–air, and metal–air batteries.

Effect of Electrolytes on Electrochemical Properties of Magnesium Electrodes

ABSTRACT: Magnesium (Mg) deposition and dissolution behaviors of 0.2 M MgBu 2 -(AlCl 2 Et) 2 , 0.5 MMg(ClO 4 ) 2 , and 0.4 M (PhMgCl) 2 -AlCl 3 -based electrolytes with and without tris(pentafluorophe-nyl) borane (TPFPB) are investigated by ex situ scanning electron microscopy (SEM) and gal-vanostatic cycling of Mg/copper (Cu) cells. To ascertain the factors responsible for the anodicstability of the electrolytes, linear sweep voltammogrametry (LSV) experiments for various elec-trolytes and solvents are conducted. The effects of TPFPB as an additive on the anodic stability of0.4 M (PhMgCl) 2 -AlCl 3 /THF electrolyte are also discussed.Keywords : Anodic limit, Electrolyte, Magnesium deposition, Magnesium dissolution, Scanningelectron microscopy Received November 14, 2012 : Accepted December 4, 2012 1. Introduction Rechargeable magnesium (Mg) batteries are one ofthe most promising energy storage devices because theMg anode offers potential advantages such as high spe-cific capacities (3832 mAh cm