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Highly porous coral-like silicon particles synthesized by an ultra-simple thermal-reduction method
Ngo, Duc Tung,Le, Hang T. T.,Pham, Xuan-Manh,Jung, Ji-Won,Vu, Ngoc Hung,Fisher, John G.,Im, Won-Bin,Kim, Il-Doo,Park, Chan-Jin The Royal Society of Chemistry 2018 Journal of materials chemistry. A, Materials for e Vol.6 No.6
<P>Porous Si is considered a potential anode material for next-generation Li-ion batteries (LIBs) because of its high specific capacity, low lithiation/delithiation potential, low cost, and environmental friendliness. In this work, we introduce a simplified Mg-thermal-reduction method for the production of mass-scalable coral-like bulk-Si powder with a high surface area (38 m<SUP>2</SUP> g<SUP>−1</SUP>), broad pore-size distribution (2-200 nm), and 3-dimensionally (3D) interconnected Si structure for application in LIBs. The porous, coral-like Si electrode delivered a high reversible capacity of 2451 mA h g<SUP>−1</SUP>, corresponding to ∼70% of the theoretical capacity of Si, at a rate of C/10. After 100 cycles, the porous, coral-like Si electrode maintained a capacity of 1956 mA h g<SUP>−1</SUP>, corresponding to 79.8% of the initial reversible capacity. Importantly, a reasonably high reversible capacity of 614 mA h g<SUP>−1</SUP> was achieved even at a high rate of 10C. These outstanding results demonstrate that the 3D-networked, porous, coral-like Si powder, synthesized <I>via</I> a NaCl-assisted Mg-thermal-reduction process on a stainless-steel plate over a period of one minute, can be employed as a promising anode material for the next generation of high-energy LIBs.</P>
Facile Synthesis of Si@SiC Composite as an Anode Material for Lithium-Ion Batteries
Ngo, Duc Tung,Le, Hang T. T.,Pham, Xuan-Manh,Park, Choong-Nyeon,Park, Chan-Jin American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.38
<P>Here, we propose a simple method for direct synthesis of a Si@SiC composite derived from a SiO2@C precursor via a Mg thermal reduction method as an anode material for Li-ion batteries. Owing to the extremely high exothermic reaction between SiO2 and Mg, along with the presence of carbon, SiC can be spontaneously produced with the formation of Si. The synthesized Si@SiC was composed of well-mixed SiC and Si nanocrystallites. The SiC content of the Si@SiC was adjusted by tuning the carbon content of the precursor. Among the resultant Si@SiC materials, the Si@SiC-0.5 sample, which was produced from a precursor containing 4.37 wt % of carbon, exhibits excellent electrochemical characteristics, such as a high first discharge capacity of 1642 mAh g(-1) and 53.9% capacity retention following 200 cycles at a rate of 0.1C. Even at a high rate of 10C, a high reversible capacity of 454 mAh g-1 was obtained. Surprisingly, at a fixed discharge rate of C/20, the Si@SiC-0.5 electrode delivered a high capacity of 989 mAh g(-1) at a charge rate of 20C. In addition, a full cell fabricated by coupling a lithiated Si@SiC-0.5 anode and a LiCoO2 cathode exhibits excellent cyclability over 50 cycles. This outstanding electrochemical performance of Si@SiC-0.5 is attributed to the SiC phase, which acts as a buffer layer that stabilizes the nanostructure of the Si active phase and enhances the electrical conductivity of the electrode.</P>
Object Connection Hypergraphs-an Approach for Nested Object Query Optimization
Hung Hoang Bao,Phuong Ngo Viet,Thanh Le Manh 보안공학연구지원센터 2016 International Journal of Software Engineering and Vol.10 No.5
In Object-Oriented Databases (OODB), nested object queries are used regularly. Nested structures are put in conditional expressions of the queries in two forms: nested sub-queries or path expression containing hidden joins – nested predicates in WHERE clauses. For nested queries, when analyzing the estimated cost of the nested algebraic expression, the expression evaluation result gives out an ineffective cost. Therefore, our method proposed in this paper will resolve the problems by leveling nested sub-queries in the nested queries. This method will increase the effectiveness of the query processing cost – We use object connection hypergraphs to present nested queries.
Manh Dung TRAN,Thi Tuyet Mai NGO,To Uyen PHAN,Duc Tai DO,Thi Thuy Hang PHAM 한국유통과학회 2020 The Journal of Asian Finance, Economics and Busine Vol.7 No.3
The research aims to investigate the impact levels of determinants on the conversion of financial statements from Vietnamese accounting standards (VAS) to International financial reporting standards (IFRS) in the multinational firms in Vietnam. The method of data collection was done through the survey and subjects are accountants in Multinational Firms doing business in Hanoi and ten neighboring provinces. After checking the information on the votes, there are 170 questionnaires with full information for data entry and analysis. We use Cronbach‟s Alpha, EFA analysis and run regression model to investigate the impact levels of each independent variable on dependent variable of the conversion of VAS financial statements to IFRS. The results show that five determinants including Economic, Politics, Law, Culture, and Conditions for implementation have positive relationships with the conversion of VAS financial statements to IFRS. In particular, Economic determinant is the most strongest. Based on the findings, some recommendations are given for improving the conversion of VAS financial statements to IFRS of multinational firms doing business in the context of Vietnam. The results are considered a useful reference for firms when making financial statements to transparently change the financial statement information and improve the quality of financial statement information.
A self-encapsulated porous Sb-C nanocomposite anode with excellent Na-ion storage performance
Pham, Xuan-Manh,Ngo, Duc Tung,Le, Hang T. T.,Didwal, Pravin N.,Verma, Rakesh,Min, Chan-Woo,Park, Choong-Nyeon,Park, Chan-Jin The Royal Society of Chemistry 2018 Nanoscale Vol.10 No.41
<P>In this study, a self-encapsulated Sb-C nanocomposite as an anode material for sodium-ion batteries (SIBs) was successfully synthesised using an SbCl3-citrate complex precursor, followed by a drying and calcination process under an inert N2 atmosphere. When the molar ratio of SbCl3 to citric acid was varied from 1 : 1 to 1 : 4, the Sb-C nanocomposite with a molar ratio of 1 : 3 (Sb-C3) exhibited the highest specific surface area (265.97 m<SUP>2</SUP> g<SUP>−1</SUP>) and pore volume (0.158 cm<SUP>3</SUP> g<SUP>−1</SUP>). Furthermore, the Sb-C3 electrode showed a high reversible capacity of 559 mA h g<SUP>−1</SUP> at a rate of C/10 and maintained a high reversible capacity of 430 mA h g<SUP>−1</SUP> even after 195 cycles at a rate of 1C. The Sb-C3 electrode exhibited an excellent rate capability of 603, 445, and 357 mA h g<SUP>−1</SUP> at the rates of C/20, 5C, and 10C, respectively. Furthermore, a full cell composed of an Sb-C3 anode and a Na3V2(PO4)3 cathode exhibited good specific capacity and cyclability, making the Sb-C composite a promising anode material for high-performance SIBs.</P>