Tak Kang

The Insertion Mechanism of Lithium into Mg2Si Anode Material for Li‐Ion Batteries

The reaction mechanism of lithium insertion into Mg{sub 2}Si was studied using various analytic techniques including electrochemical measurements, X-ray diffraction (XRD), and Auger electron spectroscopy (AES). Electrochemical tests demonstrated that 1 mol Mg{sub 2}Si reacted with 3.9 mol Li from which the initial capacity obtained was approximately 1,370 mAh/g. Ex situ XRD and AES data showed that lithium intercalated into the Mg{sub 2}Si lattice first followed by alloying with Si and Mg. The degradation mechanism of Mg{sub 2}Si during cycling was investigated because the Mg{sub 2}Si materials degraded rapidly within ten cycles. The electrode material disintegrated and Li remained within the active material after ten cycles. The XRD and scanning electron microscope data suggested that the degradation mechanism of Mg{sub 2}Si was due to the volume change during the alloying/dealloying reaction, and the volume expansion/contraction made the Mg{sub 2}Si electrode materials electrically isolated.

Reaction Mechanism of Tin Phosphide Anode by Mechanochemical Method for Lithium Secondary Batteries

Nanosized Sn 4 P 3 with a layered structure was synthesized by a mechanochemical method, and electrochemical and local structural characteristics of tin phosphide during charge/discharge were studied for its use as an anode material for lithium secondary batteries. As the amount of lithium insertion increased, tin phosphide was converted into lithium phosphides followed by lithiumtin alloy formation, which was confirmed by differential capacity plots and X-ray absorption spectroscopic (XAS) analysis. Based on X-ray diffraction, XAS, and electrochemical data, a three-step reaction mechanism of Sn 4 P 3 with lithium was suggested. Tin phosphide showed a good cyclability and retained a fairly large capacity of 370 mAh/g up to 50 cycles when cycled within a limited voltage window.

Nanosized Sn–Cu–B alloy anode prepared by chemical reduction for secondary lithium batteries

Nanosized Sn–Cu–B alloy powder is synthesized by chemical reduction to be used as an alternative anode material for secondary lithium batteries. The alloy powder consists of two phases, i.e. mainly η′-Cu6Sn5 and a small amount of e-Cu3Sn. The reaction of Cu6Sn5 with lithium proceeds in two steps. Lithium is inserted into the Cu6Sn5 lattice first as LixCu6Sn5, which is isostructural with Li2CuSn, followed by alloying with tin, reversibly even after long cycling. The cycle performance of the nanosized Cu6Sn5 electrode is significantly enhanced in comparison with that of the same material prepared by sintering or mechanical alloying.

Mechanochemical synthesis and electrochemical characteristics of Mg2Sn as an anode material for Li-ion batteries

Abstract Mg 2 Sn prepared by mechanochemical process was examined as an alternative anode material for Li-ion batteries. Electrochemical tests demonstrated that the initial charge and discharge capacity of Mg 2 Sn was 556 and 460 mAh/g, respectively. Ex-situ XRD and differential capacity plots showed that lithium inserted into the Mg 2 Sn lattice first followed by alloying with Sn. Contrary to the isostructural Mg-based intermetallic compound, Mg 2 Si, alloying reaction between Li and Mg was not observed during lithiation of Mg 2 Sn. Mg 2 Sn showed better capacity retention characteristic than that of Mg 2 Si. It is thought that this may be attributed to that Mg formed at Mg 2 Sn electrode did not react with lithium, and also active materials of Mg 2 Sn electrode changed from Mg 2 Sn to Sn with the increase of cycles. Also Mg 2 Sn showed improved cycle performance under restricted voltage range due to prevention Sn from aggregation into larger clusters.

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 + ).

Microbiologically Influenced Corrosion of Carbon Steel Exposed to Anaerobic Soil

Abstract Microbiologically influenced corrosion (MIC) of plain carbon steel in anaerobic soil was investigated using field survey, the electrochemical polarization technique, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM) coupled with energy-dispersive spectroscopy (EDS), a thin-film electrical resistance (ER) probe, and galvanic current measurement. The field survey revealed that the risk of MIC could be predicted by the analysis of environmental parameters such as soil resistivity, water content, the content of total organic carbon, reduction-oxidation potential, and the content of sulfate with the consideration of the effectiveness of cathodic protection (CP). From the results of conventional electrochemical experiments, it is evident that the presence and therefore the activity of sulfate-reducing bacteria (SRB) alter the corrosion mechanism of steel by the production of hydrogen sulfide (H2S) and iron sulfide (FeS) film on the steel surface, which reduces the polariz...

Electrochemical characteristics of Mg–Ni alloys as anode materials for secondary Li batteries

Abstract The electrochemical characteristics of Mg and several Mg–Ni alloys were studied as alternatives to anode materials for secondary Li batteries. Li was alloyed and dealloyed reversibly with Mg at very low voltage region (below 100 mV vs. Li/Li+), and the initial capacity obtained was approximately 3070 mA h/g. Alloys of Mg50Ni50, Mg67Ni33 and Mg75Ni25 were prepared by mechanical alloying and characterized using X-ray diffraction (XRD) and Auger electron spectroscopy (AES). Mg50Ni50 and Mg67Ni33 were found amorphous and crystalline, respectively, while Mg75Ni25 was a mixture of Mg and Mg2Ni phases. Electrochemical tests with these Mg–Ni alloys demonstrated that only Mg75Ni25 reacted significantly with Li at room temperature while Mg67Ni33 reacted with Li at high temperature. Mg75Ni25 showed enhanced cycle performance compared to that of pure Mg.

In situ surface enhanced Raman spectroscopic study on the effect of dissolved oxygen on the corrosion film on low carbon steel in 0.01 M NaCl solution

Abstract In situ surface enhanced Raman spectroscopy was employed to study the effect of dissolved oxygen (DO) on the composition of the corrosion film formed on a low carbon steel surface in 0.01 M NaCl solution. Raman spectra were taken during cyclic voltammetric and potential step experiments. The spectra taken during cyclic voltammetry were similar to those previously obtained for passive iron. It showed a peak for a trivalent species at 670 cm −1 in the passive potential range, which was usually assigned to FeOOH rather than to γ-Fe 2 O 3 . However, in the spectra taken during potential step experiments, it was apparent that the main trivalent species in the corrosion film was γ-Fe 2 O 3 at 640, 670, 715 cm −1 , and DO behaved as an oxidizer to convert iron from the divalent state in Fe 3 O 4 to the trivalent state (γ-Fe 2 O 3 ). The presence of γ-Fe 2 O 3 in the corrosion film on iron was detected for the first time by taking SER spectra during potential step experiments. Though this film showed a weak protective property, and had corrosion products due to pitting induced by chloride ions, the detection of γ-Fe 2 O 3 supports the previous ex situ and in situ findings that the trivalent oxide in iron passivity is γ-Fe 2 O 3 .

Particulate-reinforced Al-based composite material for anode in lithium secondary batteries

Particulate-reinforced Al/SiC composite materials are prepared by ball-milling technique to be used as an anode material for lithium secondary battery. The microstructure of the composite powders show that the SiC particles are embedded homogeneously in the Al matrix. This feature is distinctively different from any other active/inactive composite anode materials reported recently. The cycle performance of these composite electrodes is superior to that of an unreinforced aluminium electrode. This improved cycelability may be due to an enhanced mechanical stability of the electrode.

Microstructural change upon annealing FeZrB alloys with different boron contents

To clarify the reason for the change in effective permeability with increasing boron content before and after crystallization, we investigated the microstructure of Fe93−xZr7Bx (x = 2, 4, 6, 8) alloys annealed for 1 h in the temperature range 350–600 °C, using transmission electron microscope. In low boron alloys (x = 2, 4), the amorphous phase showed indications of a typical interconnected pattern, exhibiting a spinodal-type decomposition. After crystallization, it changed to a mainly single b.c.c. structure with a homogeneous grain size distribution of about 20 nm, and the effective permeability had a high value of around 19000. In high boron alloys (x = 6, 8), the microstructure after crystallization showed an inhomogeneous grain size distribution, and a low effective permeability. These results may be the result of the different phase separation pattern in the amorphous state.