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Temperature-dependent lithium diffusion in phographene: Insights from molecular dynamics simulation
Siby Thomas,Saibal Jana,Byeongsun Jun,이치호,Sang Uck Lee 한국공업화학회 2020 Journal of Industrial and Engineering Chemistry Vol.81 No.-
It is noteworthy to elucidate the underlying atomistic insights of next-generation battery electrodematerials to overcome the existing constraints associated with its rapid progress. By employing classicalmolecular dynamics (MD) simulations, we have studied the temperature dependent structural, thermomechanical,and Lithium diffusion properties of α- and β-phographene (PhoG) for Lithium-ion battery(LIB) anode applications. Our results show that at 300 K both the PhoGs possess negative thermalexpansion coefficient and is expounded as proof of anharmonicity present in it due to the existence ofpliable bending modes in the out-of-plane direction. The computed ultrahigh stiffness of PhoG helps toprevent the acute lattice expansion issue upon Li intercalation. The study also brings out that Li atomcould freely diffuse on the surface of the PhoGs, and thus a fast Li diffusivity and superior conductivity isobserved. The calculated Li diffusion activation energies (<0.20 eV) of these membranes are lower thanmany of the typical for Li-based graphitic anode with a Li diffusion coefficient of 10 10–10 12cm2 s 1. Inthis regard, the excellent structural and thermo-mechanical stability, and low activation energy barrier inPhoGs assures its application as an anode material in high-performance LIBs.
Thomas, Siby,Nam, Eun Bi,Lee, Sang Uck American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.42
<P>A fundamental understanding of the thermomechanical properties of electrode materials and Li-ion diffusion kinetics is indispensable for designing high-performance Li-ion batteries (LIBs) with high structural stability and safety. Herein, we performed both molecular dynamics (MD) simulations and density functional theory (DFT) calculations to investigate the thermomechanical properties and Li diffusion kinetics in a two-dimensional (2D) defect-filled graphene-like membrane consisting of 5-, 6-, and 7-membered rings, called psi (ψ)-graphene. Our results reveal that ψ-graphene has a negative linear thermal expansion coefficient, a high specific heat capacity, and high elastic constants that satisfy the Born’s criterion for mechanical stability, which can be elucidated as the evidence of strong anharmonicity in ψ-graphene because of the soft out-of-plane bending modes. These characteristics can help prevent the thermal runaway that can occur during overheating and prevent structural damage because of the severe volume expansion of the LIBs. In addition, the Li diffusion coefficient was estimated to be 10<SUP>-9</SUP> cm<SUP>2</SUP>/s at 300 K with a low Li migration activation energy (<0.16 eV), which suggests favorable electrode kinetics with fast Li conduction. Our DFT calculations also show that ψ-graphene can possess a fairly good theoretical capacity (339 mA h g<SUP>-1</SUP>) and a lower Li diffusion barrier (<0.21 eV). Our results suggest that the new fundamental insights presented here will help to stimulate further experimental work on ψ-graphene for promising future applications as a superior electrode material for LIBs.</P> [FIG OMISSION]</BR>
Thomas, Siby,Lee, Chi Ho,Jana, Saibal,Jun, Byeongsun,Lee, Sang Uck American Chemical Society 2019 The Journal of Physical Chemistry Part C Vol.123 No.35
<P>The progress of ecofriendly, clean, and sustainable energy resources always demands suitable anode materials for batteries with high structural stability and superior storage capacity. Herein, we use density functional theory predictions to examine the potential features of newly proposed planar membranes consist of 5-, 6- and 8- membered carbon rings, named as α- and β-phographene (PhoG). Our calculations disclose that both α- and β-PhoG structures possess high structural, thermal, and mechanical stability with intrinsic metallic characteristics. We have further extended our calculations of PhoG as a suitable anode material for use in Lithium-ion batteries. Our results reveal the Li adsorption in PhoG is exothermic and the α-PhoG show a higher theoretical specific capacity of Li<SUB>2.4</SUB>C<SUB>6</SUB> for Li atoms (892 mAh g<SUP>-1</SUP>) compared to the LiC<SUB>6</SUB> of graphite. We also found that both the α- and β-PhoG structures show fast Li mobility with a low diffusion barrier for Li atoms (<0.30 eV) as well as low average open circuit voltage (∼0.26 V). Our findings show that both the PhoG structures, especially α-PhoG, are suitable anode candidates for use in future Li-ion batteries owing to the metallic characteristic combined with the low open circuit voltage, low diffusion barrier, high Li storage capacity, and high thermo-mechanical stability. Our results would supply guidelines to develop better high-capacity anode materials for future Li-ion batteries.</P> [FIG OMISSION]</BR>
Thomas, Siby,Jung, Hoejoong,Kim, Suyeon,Jun, Byeongsun,Lee, Chi Ho,Lee, Sang Uck Elsevier 2019 Carbon Vol.148 No.-
<P><B>Abstract</B></P> <P>There is great interest in finding suitable electrode materials for metal-ion batteries with good performance, low diffusion barriers and high capacity. Using the art of density functional theory (DFT), we systematically evaluated the possibility of planar carbon haeckelite structures (h567, r57, and o567) for a suitable anode in Lithium-ion batteries (LIBs). Our results show that haeckelites possess significant structural, mechanical, and electronic stability with high metallicity for LIB anode applications. Especially, the haeckelite h567 shows improved specific capacity (Li<SUB>1<I>.</I>875</SUB>C<SUB>6</SUB> ∼ 697 mAhg<SUP> <I>−</I>1</SUP>) compared to LiC<SUB>6</SUB> graphite due to the negative Li binding energy without clustering of Li atoms. In addition, it is worth noticing that the low open-circuit voltage (<0.30 V) and Li diffusion energy barrier (E<SUB> <I>a</I> </SUB> < 0.35 eV) of the haeckelite h567comparable to that of the graphite is beneficial to the overall performance of the LIBs. Based on the excellent electronic structure, superior Li mobility, extremely high in-plane stiffness, low open-circuit voltage, and high specific capacity, haeckelite h567 can be a promising anode material for the low-cost and high-performance LIBs.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Blends of Natural Rubber and Butadiene Rubber-Distribution Quantification of Carbon Black Filler
Vaishak Nambiathodi,Siby Varghese,Neethu Varghese 한국고분자학회 2021 폴리머 Vol.45 No.6
The present study deals with the distribution of N330 carbon black in cured 50/50 blend of natural rubber (NR) and butadiene rubber (BR). The results were reported in terms of tan δ and glass transition temperature (Tg). The reduced tan δ peaks in the BR phase with the increased filler loading and the corresponding shift in Tg of BR towards the positive side have shown that there was a preferential migration of carbon black towards the BR phase. Carbon black dispergrader was used to determine the dispersion of the filler on a series of blends with varying BR content. A theoretical evaluation on determining the preference of N330 has also been performed using Wu’s equation. The evaluation was well correlated with the result obtained from analytical data. It has been inferred that the N330 has migrated more towards the BR phase.
Vaishak Nambiathodi,Siby Varghese,Neethu Varghese 한국고분자학회 2021 폴리머 Vol.45 No.5
Combinations of natural rubber (NR), butadiene rubber (BR), and reclaim rubber (RR) were prepared with a view to producing low-cost re-treading materials. It was found that cure time and scorch time decreased with the increase in the reclaim content. Only a small reduction in the properties was observed in almost all systems upon the addition of 30 phr of reclaim rubber. Systems with good abrasion resistance and tensile strength were obtained. High tensile values of 22.8 and 20.1 MPa were able to obtain for the NR-rich system. Tear strength can be enhanced by the addition of reclaim rubber. Elongation at break was higher for all the systems even after adding 30 phr of RR. Modulus and compression set values were increased with RR loading. The thermal behavior and activation energy of NR/BR/RR blends were improved by the addition of RR. The phase morphology of the blends was studied using a scanning electron microscope.