skip to main content


Title: Exploring Thermal Transport in Electrochemical Energy Storage Systems Utilizing Two-Dimensional Materials: Prospects and Hurdles
Two-dimensional materials (e.g., graphene and transition metal dichalcogenides) and their heterostructures have enormous applications in electrochemical energy storage systems such as batteries. A comprehensive and solid understanding of these materials’ thermal transport and mechanism is essential for practical device design. Several advanced experimental techniques have been developed to measure the intrinsic thermal conductivity of materials. However, experiments have challenges in providing improved control and characterization of complex structures, especially for low-dimensional materials. Theoretical and simulation tools, such as first-principles calculations, Boltzmann transport equations, molecular dynamics simulations, lattice dynamics simulation, and nonequilibrium Green’s function, provide reliable predictions of thermal conductivity and physical insights to understand the underlying thermal transport mechanism in materials. However, doing these calculations requires high computational resources. The development of new materials synthesis technology and fast-growing demand for rapid and accurate prediction of physical properties requires novel computational approaches. The machine learning method provides a promising solution to address such needs. This review details the recent development in atomistic/molecular studies and machine learning of thermal transport in two-dimensional materials. The paper also addresses the latest significant experimental advances. However, designing the best two-dimensional materials-based heterostructures is like a multivariate optimization problem. For example, a particular heterostructure may be suitable for thermal transport but can have lower mechanical strength/stability. For bilayer and multilayer structures, the interlayer distance may influence the thermal transport properties and interlayer strength. Therefore, the last part of this review addresses the future research direction in two-dimensional materials-based heterostructure design for thermal transport in energy storage systems.  more » « less
Award ID(s):
2237990
NSF-PAR ID:
10472637
Author(s) / Creator(s):
;
Editor(s):
Chu, Wilson
Publisher / Repository:
Annual Review of Heat Transfer
Date Published:
Journal Name:
Annual Review of Heat Transfer
ISSN:
1049-0787
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Abstract

    The successful discovery and isolation of graphene in 2004, and the subsequent synthesis of layered semiconductors and heterostructures beyond graphene have led to the exploding field of two-dimensional (2D) materials that explore their growth, new atomic-scale physics, and potential device applications. This review aims to provide an overview of theoretical, computational, and machine learning methods and tools at multiple length and time scales, and discuss how they can be utilized to assist/guide the design and synthesis of 2D materials beyond graphene. We focus on three methods at different length and time scales as follows: (i) nanoscale atomistic simulations including density functional theory (DFT) calculations and molecular dynamics simulations employing empirical and reactive interatomic potentials; (ii) mesoscale methods such as phase-field method; and (iii) macroscale continuum approaches by coupling thermal and chemical transport equations. We discuss how machine learning can be combined with computation and experiments to understand the correlations between structures and properties of 2D materials, and to guide the discovery of new 2D materials. We will also provide an outlook for the applications of computational approaches to 2D materials synthesis and growth in general.

     
    more » « less
  2. Abstract The densification of integrated circuits requires thermal management strategies and high thermal conductivity materials 1–3 . Recent innovations include the development of materials with thermal conduction anisotropy, which can remove hotspots along the fast-axis direction and provide thermal insulation along the slow axis 4,5 . However, most artificially engineered thermal conductors have anisotropy ratios much smaller than those seen in naturally anisotropic materials. Here we report extremely anisotropic thermal conductors based on large-area van der Waals thin films with random interlayer rotations, which produce a room-temperature thermal anisotropy ratio close to 900 in MoS 2 , one of the highest ever reported. This is enabled by the interlayer rotations that impede the through-plane thermal transport, while the long-range intralayer crystallinity maintains high in-plane thermal conductivity. We measure ultralow thermal conductivities in the through-plane direction for MoS 2 (57 ± 3 mW m −1  K −1 ) and WS 2 (41 ± 3 mW m −1  K −1 ) films, and we quantitatively explain these values using molecular dynamics simulations that reveal one-dimensional glass-like thermal transport. Conversely, the in-plane thermal conductivity in these MoS 2 films is close to the single-crystal value. Covering nanofabricated gold electrodes with our anisotropic films prevents overheating of the electrodes and blocks heat from reaching the device surface. Our work establishes interlayer rotation in crystalline layered materials as a new degree of freedom for engineering-directed heat transport in solid-state systems. 
    more » « less
  3. Abstract Designing a new heterostructure electrode has many challenges associated with interface engineering. Demanding simulation resources and lack of heterostructure databases continue to be a barrier to understanding the chemistry and mechanics of complex interfaces using simulations. Mixed-dimensional heterostructures composed of two-dimensional (2D) and three-dimensional (3D) materials are undisputed next-generation materials for engineered devices due to their changeable properties. The present work computationally investigates the interface between 2D graphene and 3D tin (Sn) systems with density functional theory (DFT) method. This computationally demanding simulation data is further used to develop machine learning (ML)-based potential energy surfaces (PES). The approach to developing PES for complex interface systems in the light of limited data and the transferability of such models has been discussed. To develop PES for graphene-tin interface systems, high-dimensional neural networks (HDNN) are used that rely on atom-centered symmetry function to represent structural information. HDNN are modified to train on the total energies of the interface system rather than atomic energies. The performance of modified HDNN trained on 5789 interface structures of graphene|Sn is tested on new interfaces of the same material pair with varying levels of structural deviations from the training dataset. Root-mean-squared error (RMSE) for test interfaces fall in the range of 0.01–0.45 eV/atom, depending on the structural deviations from the reference training dataset. By avoiding incorrect decomposition of total energy into atomic energies, modified HDNN model is shown to obtain higher accuracy and transferability despite a limited dataset. Improved accuracy in the ML-based modeling approach promises cost-effective means of designing interfaces in heterostructure energy storage systems with higher cycle life and stability. 
    more » « less
  4. null (Ed.)
    Achieving a molecular-level understanding of how the structures and compositions of metal–organic frameworks (MOFs) influence their charge carrier concentration and charge transport mechanism—the two key parameters of electrical conductivity—is essential for the successful development of electrically conducting MOFs, which have recently emerged as one of the most coveted functional materials due to their diverse potential applications in advanced electronics and energy technologies. Herein, we have constructed four new alkali metal (Na, K, Rb, and Cs) frameworks based on an electron-rich tetrathiafulvalene tetracarboxylate (TTFTC) ligand, which formed continuous π-stacks, albeit with different π–π-stacking and S⋯S distances ( d π–π and d S⋯S ). These MOFs also contained different amounts of aerobically oxidized TTFTC˙ + radical cations that were quantified by electron spin resonance (ESR) spectroscopy. Density functional theory calculations and diffuse reflectance spectroscopy demonstrated that depending on the π–π-interaction and TTFTC˙ + population, these MOFs enjoyed varying degrees of TTFTC/TTFTC˙ + intervalence charge transfer (IVCT) interactions, which commensurately affected their electronic and optical band gaps and electrical conductivity. Having the shortest d π–π (3.39 Å) and the largest initial TTFTC˙ + population (∼23%), the oxidized Na-MOF 1-ox displayed the narrowest band gap (1.33 eV) and the highest room temperature electrical conductivity (3.6 × 10 −5 S cm −1 ), whereas owing to its longest d π–π (3.68 Å) and a negligible TTFTC˙ + population, neutral Cs-MOF 4 exhibited the widest band gap (2.15 eV) and the lowest electrical conductivity (1.8 × 10 −7 S cm −1 ). The freshly prepared but not optimally oxidized K-MOF 2 and Rb-MOF 3 initially displayed intermediate band gaps and conductivity, however, upon prolonged aerobic oxidation, which raised the TTFTC˙ + population to saturation levels (∼25 and 10%, respectively), the resulting 2-ox and 3-ox displayed much narrower band gaps (∼1.35 eV) and higher electrical conductivity (6.6 × 10 −5 and 4.7 × 10 −5 S cm −1 , respectively). The computational studies indicated that charge movement in these MOFs occurred predominantly through the π-stacked ligands, while the experimental results displayed the combined effects of π–π-interactions, TTFTC˙ + population, and TTFTC/TTFTC˙ + IVCT interaction on their electronic and optical properties, demonstrating that IVCT interactions between the mixed-valent ligands could be exploited as an effective design strategy to develop electrically conducting MOFs. 
    more » « less
  5. The success of graphene created a new era in materials science, especially for two-dimensional (2D) materials. 2D single-crystal carbon nitride (C 3 N) is the first and only crystalline, hole-free, single-layer carbon nitride and its controlled large-scale synthesis has recently attracted tremendous interest in thermal transport. Here, we performed a comparative study of thermal transport between monolayer C 3 N and the parent graphene, and focused on the effect of temperature and strain on the thermal conductivity ( κ ) of C 3 N, by solving the phonon Boltzmann transport equation (BTE) based on first-principles calculations. The κ of C 3 N shows an anomalous temperature dependence, and the κ of C 3 N at high temperatures is larger than the expected value following the common trend of κ ∼ 1/ T . Moreover, the κ of C 3 N is found to be increased by applying a bilateral tensile strain, despite its similar planar honeycomb structure to graphene. The underlying mechanism is revealed by providing direct evidence for the interaction between lone-pair N-s electrons and bonding electrons from C atoms in C 3 N based on the analysis of orbital-projected electronic structures and electron localization function (ELF). Our research not only conduct a comprehensive study on the thermal transport in graphene-like C 3 N, but also reveal the physical origin of its anomalous properties, which would have significant implications on the future studies of nanoscale thermal transport. 
    more » « less