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Dive into the research topics where Aishui Yu is active.

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Featured researches published by Aishui Yu.


Journal of Power Sources | 1999

Synthesis and characterization of LiNi1−x−yCoxMnyO2 as the cathode materials of secondary lithium batteries

Zhaolin Liu; Aishui Yu; Jim Yang Lee

Abstract LiNi1−x−yCoxMnyO2 (0≤x≤0.5, 0≤y≤0.3) were prepared by heating Ni1−x−yCoxMny(OH)2 and LiNO3 in flowing oxygen for 10 h at 550°C, followed by another heating at 750°C. The XRD patterns of LiNi1−x−yCoxMnyO2 (0≤x≤0.5, 0≤y≤0.3) samples with different x and y values show a pure phase of layered hexagonal structure. The lattice parameters a, c and the unit cell volume are found to decrease with increasing x in LiNi1−xCoxO2. The partial substitution of Ni by Co and Mn as in LiNi1−xCoxO2 and LiNi1−yCo0.2MnyO2 has a positive effect on lithium stoichiometry. However, lithium deficiency is still found after a prolonged thermal treatments (24 h). Among the doped materials synthesized, LiNi0.8Co0.2O2 and LiNi0.7Co0.2Mn0.1O2 have shown the best characteristics in terms of initial capacity and cycle life.


Journal of The Electrochemical Society | 1997

Ultrasonically Treated LiV[sub 3]O[sub 8] as a Cathode Material for Secondary Lithium Batteries

Naoaki Kumagai; Aishui Yu

A new treatment of LiV{sub 3}O{sub 6} has been proposed for improving its electrochemical behavior as a cathode material for secondary lithium batteries. The ultrasonically treated products in water were characterized by x-ray diffractometry, thermogravimetric analysis, scanning electron microscopy, and specific surface area measurements. These measurements showed that the ultrasonic treatment process of crystalline LiV{sub 3}O{sub 8} causes a decrease in crystallinity and considerable increases in specific surface area and interlayer spacing. The product, ultrasonically treated in water for 3 h and then heat-treated at 250 C for 6 h, showed a high initial discharge capacity of 283 mAh/g active material, which was 62% higher than that of the starting material, and was charge-discharge cycled without a large capacity loss during 40 cycles. The ultrasonic treatment of LiV{sub 3}O{sub 8} can improve not only the specific capacity but also the cycling behavior.


Journal of Power Sources | 1998

Cycle life improvement of LiMn2O4 cathode in rechargeable lithium batteries

Zhaolin Liu; Aishui Yu; Jim Yang Lee

Abstract Spinel LiMn 2 O 4 and LiCo 0.1 Mn 1.9 O 4 were synthesized by solid state reactions and were used as the positive electrode in liquid cells with Li as the negative electrode. Through extensive ball milling of the spinel with carbon black during the preparation of the cathodic mix, significant decrease in contact resistance between the oxide phase and carbon particles was achieved. The spinel LiCo 0.1 Mn 1.9 O 4 cathode so prepared showed good cyclability and rate capability.


Journal of Power Sources | 1998

A new method for preparing lithiated vanadium oxides and their electrochemical performance in secondary lithium batteries

Aishui Yu; Naoaki Kumagai; Zhaolin Liu; Jim Yang Lee

Abstract This paper describes a new method for preparing lithiated vanadium oxides which are suitable as the cathode material for secondary lithium batteries. Characterization by powder X-ray diffraction (XRD), infrared spectroscopy (IR), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA) shows that these oxides are somewhat structurally different from LiV 3 O 8 prepared by the solid-state reaction route, although the starting materials are identical in both cases. The discharge capacity of the oxide is much higher than that of crystalline LiV 3 O 8 , and can attain 250 mAh g −1 at the current density of 0.2 mA cm −2 . The specific capacity and the cycling behaviour of these lithiated vanadium oxides are closely related to post-synthesis heat treatment. This suggests that the amount of water bound to the structure determines electrochemical performance of the oxide in secondary lithium batteries.


Solid State Ionics | 2000

Synthesis and properties of LiGaxMgyNi1-x-yO2 as cathode material for lithium ion batteries

Aishui Yu; G. V. Subba Rao; B. V. R. Chowdari

Abstract Simultaneous doping of magnesium (Mg) and gallium (Ga) at the Ni-site in LiNiO 2 has been tried to improve the cathode performance, in view of the recent reports that Ga or Mg dopants can suppress the crystallographic phase transitions and decrease the irreversible capacity. The results show that co-doping (2 atom% Ga and 3 atom% Mg) definitely has a large beneficial effect in increasing the capacity (150 mAh/g) and cycling behavior. Comparison of the differential capacity vs. voltage curves for pristine and co-doped LiNiO 2 show suppression of the phase transitions and stabilization of the hexagonal (H1) phase. Differential scanning colorimetry (DSC) data indeed confirm the above by way of increased thermal stability of the charged cathode.


Solid State Ionics | 1998

Preparation of sodium molybdenum oxides by a solution technique and their electrochemical performance in lithium intercalation

Aishui Yu; Naoaki Kumagai; Zhaolin Liu; Jim Yang Lee

Abstract Several sodium molybdenum oxides with different structures were prepared by acidification of Na 2 MoO 4 solutions with 1–3.5 N of strong acids (HCl, HNO 3 ) at 100°C followed by heat treatment. Structural and compositional analyses of the oxides show that their structures were determined by preparation conditions such as acid type and concentration, and heat-treatment temperature. The electrochemical intercalation of lithium into these oxides was attempted using them as the positive electrode materials for secondary lithium batteries. The results show reversible lithium intercalation and electrochemical performance that greatly depends on the oxide structure and composition.


Journal of Power Sources | 1999

Modifications of synthetic graphite for secondary lithium-ion battery applications

Zhaolin Liu; Aishui Yu; Jim Yang Lee

Abstract Experimentally, three types of synthetic graphite from TimRex (SFG44, SFG15 and KS6) were plated with copper electrolessly. The specific capacities of untreated TimRex samples are typically in the range of 140–280 mA h/g, with low coulombic efficiencies in the first few cycles of charge and discharge. Electroless copper plating on these graphites could substantially improve the material performance in discharge capacity and coulombic efficiency. Some improvement in high rate dischargeability was also observed.


Journal of The Electrochemical Society | 1999

Electrochemical performance of amorphous and crystalline Sn{sub 2}P{sub 2}O{sub 7} anodes in secondary lithium batteries

Y. W. Xiao; Jim Yang Lee; Aishui Yu; Zhaolin Liu


Journal of Solid State Electrochemistry | 1998

Electrochemical lithium intercalation into WO 3 and lithium tungstates Li x WO 3+ x /2 of various structures

Aishui Yu; Naoaki Kumagai; Zhaolin Liu; Jim Yang Lee


Solid State Ionics | 2000

Synthesis and properties of LiGa x Mg y Ni 1− x− y O 2 as cathode material for lithium ion batteries

Aishui Yu; G. V. Subba Rao; B. V. R. Chowdari

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Jim Yang Lee

National University of Singapore

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Zhaolin Liu

National University of Singapore

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B. V. R. Chowdari

National University of Singapore

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G. V. Subba Rao

National University of Singapore

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Yaowu Xiao

National University of Singapore

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