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배터리 전극 설계를 위한 응력-확산 완전연계 멀티스케일 해석기법
장성민,문장혁,조경재,조맹효,Chang, Seongmin,Moon, Janghyuk,Cho, Kyeongjae,Cho, Maenghyo 한국전산구조공학회 2013 한국전산구조공학회논문집 Vol.26 No.6
In this paper, we device stress-diffusion full coupling multiscale analysis method for battery electrode simulation. In proposed method, the diffusive and mechanical properties of electrode material depend on Li concentration are estimated using density function theory(DFT) simulation. Then, stress-diffusion full coupling continuum formulation based on finite element method(FEM) is constructed with the diffusive and mechanical properties calculated from DFT simulation. Finally, silicon nanowire anode charge and discharge simulations are performed using the proposed method. Through numerical examples, the stress-diffusion full coupling method shows more resonable results than previous one way continuum analysis. 본 논문에서는 배터리 전극 해석을 위한 응력-확산 완전 연계 멀티스케일 해석기법을 고안하였다. 제안된 방법에서는 먼저 리튬농도에 따른 확산계수 및 기계적 물성을 계산하였다. 이를 고려하여 확산에 의한 응력뿐만 아니라 응력에 의한 확산 거동 변화까지 모두 고려한 응력-확산 완전연계 연속체 모델을 유한요소 기반으로 구성하였다. 이를 통해 실리콘 나노와이어 음극의 충/방전 전산 모사를 수행하였다. 이러한 해석결과를 통하여 기존의 확산에 의한 응력 연속체 모델보다 더 실제와 가까운 해석결과를 제안된 방법이 보여줌을 확인할 수 있었다.
제일원리 계산법을 이용한 비정질 실리콘 내에서의 리튬 이온 확산 예측
문장혁(Janghyuk Moon),조경재(Kyeongjae Cho),조맹효(Maenghyo Cho) 대한기계학회 2012 대한기계학회 춘추학술대회 Vol.2012 No.11
We have studied the lithium absorption in crystalline silicon with the strain effects on unit cell using density functional theory calculation. We have concluded that the dependences of the lithium diffusion were on the local volume and environmental. In the various strained cells, the effect of the lattice deformation about migration barriers for the motion of the lithium atom has been fit on the linear regression equation based on the volume of silicon surrounding lithium impurity and the migration distance of lithium atom. This result has applied to the calculation of diffusion coefficient in amorphous silicon which was generated by annealing from crystalline structure at 3000K. The migration barriers and attempt frequency, by Arrhenius formula, of lithium in the amorphous silicon structures has been determined by local environment using the linear regression equation. Then, the statistical method, kinetic Monte Carlo method, has been demonstrated for the diffusion coefficient of lithium. Finally, we have parameterized in terms of the amorphous effects into Arrhenius diffusion formula. This study have supported that the diffusion of lithium in amorphous silicon is faster than that in crystalline silicon.
제일원리 계산법을 이용한 실리콘 음극 소재의 그래핀 코팅 효과 분석
문장혁(Janghyuk Moon),조경재(Kyeongjae Cho),조맹효(Maenghyo Cho) 대한기계학회 2013 대한기계학회 춘추학술대회 Vol.2013 No.12
Computational study on the effect of graphene coating to Si anode material is performed by using density functional theory calculations. We construct the atomic model to examine interactions between amorphous silicon and graphene during lithiation. The lithiation of Si anode increases the mechanical contact force between outer graphene layer and amorphous silicon and the shear resistance is also increased. To explain the interaction between graphene and silicon we examine the charge distribution of silicon and graphene considering lithiation insertion. The number of density, electro field distribution and electric potential are also calculated. Charge-non polar interaction between Li-ion and graphene increase the contact energy between graphene-silicon. To calculate the contact force, we simplified interaction atomic force model. In this theoretical study, potential improvement of cyclability and improved mechanical properties of graphene coating for Si anode have been investigated.
제일 원리법을 이용한 리튬 이온베터리 음극 물질의 물성치 예측
문장혁(Janghyuk Moon),조경재(Kyeongjae Cho),조맹효(Maenghyo Cho) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.11
An investigation of Li-M (M:Si, Sn) alloys using density functional theory is presented. DFT calculation methods performed total energy calculations, structural optimizations, bulk modulus and elastic constant with Li-Sn, Li-Si. To simulate the lithiation of amorphous Si at room temperature, we simply make up amorphous Si cell with additional Li atom at the center of the largest void. The cells optimize was used in conjunction with DFT methods. These cell volume changes agree with experiment data and Li-Si crystalline.
제일원리 계산을 통한 두께 변화에 따른 산화 아연 나노 박막의 압전 효과 해석 및 유한요소법으로의 응용
임진명(Jin-Myoung Lim),조경재(Kyeongjae Cho),조맹효(Maenghyo Cho) 대한기계학회 2011 대한기계학회 춘추학술대회 Vol.2011 No.10
Nano-structured piezoelectric materials, with their unique electromechanical coupled properties, have enabled the successful design and operation of a wide range of nano-sensors and -actuators. The size dependent piezoelectricity of ZnO nanofilms is investigated through First-principles calculations. Piezoelectric tensor is calculated, whose calculation scheme is based on Berry phase theory. Nanofilms ranging from 0.27 to 1.8 nm in thickness are modeled quantum mechanically. A three-dimensional finite element model is developed to accurately predict the complete electromechanical properties in piezoelectric nanofilms with thickness changes. The effective piezoelectric constant of ZnO nanofilms has inclination to converge monotonically that of bulk ZnO, and the thickness effect of piezoelectric nanofilms is represented.
제일원리 계산법을 이용한 리튬 이차 전지의 음극 물질의 비교 및 예측
문장혁(Janghyuk Moon),조경재(Kyeongjae Cho),조맹효(Maenghyo Cho) 대한기계학회 2011 대한기계학회 춘추학술대회 Vol.2011 No.10
An investigation of Li-M (M:Si, Ge, Sn) alloys using ab initio calculation is presented. Ab initio calculation methods performed for total energy calculations, structural optimizations, electric and mechanical properties with Li-Sn, Li-Ge, Li-Si. To achieve anode materials design, specific characteristics, such as large volume change and elastic softening, are compared in Group 14 chemistry.
다양한 전이 금속의 조합을 가진 규산염들의 기계적 물성 비교 해석
이상관(Yi Sang Koan),조맹효(Cho Maenghyo),조경재(Cho Kyeongjae) 대한기계학회 2014 대한기계학회 춘추학술대회 Vol.2014 No.11
Silicate is an electrode material of Li ion battery that has been found recently. This material has higher theoretical capacity and energy density. But silicate has voltage drop problem when second Li ion is extracted. Previous research showed that multicomponent silicate can solve this problem of voltage drop. Mechanical properties of electrode materials are very important because mechanical properties are relate to various structural properties. Also, at Li ion batteries, these properties are changed during the charge and discharge processes. In the previous studies, the battery electrode material was assumed isotropic. However the cathode material of battery is anisotropic. Until now, mechanical properties of multicomponent silicate have not been calculated. In this study, we investigate these mechanical properties and anisotropy of multicomponent silicates by first principles calculation.