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Although poly(l-lactic acid) (PLLA) is the widely used material for bioresorbable stents, publications on PLLA braided stents are still lacking. In this paper, the PLLA monofilaments were prepared via melt spinning and solid-state drawing. The total draw ratios are from 2.8 to 30.8. The properties of the monofilaments, such as crystallinity, elastic modulus, elongation at break, were characterized. Due to the relatively good mechanical properties, PLLA monofilaments with draw ratio of 16.8 were used to braid carotid stents. The curve of the radial force of the braided PLLA stent almost overlaps with that of a Carotid Wallstent with similar parameters, which indicates that the braided PLLA stent can provide adequate support to the carotid lesion.

Memory is an essential element for a computer to process information, which is integrated by logical circuits. Like electronic computing, thermal information can also be stored and read out by a thermal memory. Here, we show that a phase-changing polymer with hysteretic thermal transport properties can be experimentally processed into thermal memories at room temperature. We used a temperature-responsive and reversible polymer synthesized with melamine (M) and 6,7-dimethoxy-2,4[1H,3H]-quinazolinedione (Q) as a model system to demonstrate the manipulation of thermal transport at a molecular level. Fourier transform infrared spectroscopy and differential scanning calorimetry measurements indicate that this hysteretic behavior is based on the interaction of hydrogen bonds at high (317 K) and low (297 K) temperatures. This work demonstrates a controllable phonon transport process through the manipulation of hydrogen bonds, and thus it has potential applications in thermal memories.

Several theoretical models have been developed so far to predict the thermal conductivities of carbon nanotube (CNT) networks. However, these models overestimated the thermal conductivity significantly. In this paper, we claimed that a CNT network can be considered as a contact thermal resistance network. In the contact thermal resistance network, the temperature of an individual CNT is nonuniform and the intrinsic thermal resistance of CNTs can be ignored. Compared with the previous models, the model we proposed agrees well with the experimental results of single-walled CNT networks.

Optimizing the efficiency of heat dissipation across an interface is a great challenge with the continuously increasing integration of microelectronic devices. In this work, an effective method in tuning the heat conduction across the Al/graphene/SiO2 interface is reported. It was found that the interfacial thermal conductance of Al/irradiated graphene/SiO2 can be increased by a factor of 3, as compared with that of Al/pristine graphene/SiO2. The X-ray photoelectron spectroscopy (XPS) analysis indicates that ion irradiation may promote the formation of CO bonds on the irradiated graphene surface, which is beneficial to the enhancement of interfacial thermal conductance. The density functional theory (DFT) calculations reveal that in addition to the formed bonds between O atoms and Al atoms, the adsorption strength between Al and irradiated graphene is intensified, which plays a dominant role in enhancing the interfacial thermal conductance of Al/graphene/SiO2.

Unlike the wide range control of electrical conductivity, the tuning of thermal conductivity is difficult especially for the increase or bidirectional tuning. Traditional methods typically only dec...

In an isothermal process, applying an electric field E to a ferroelectric material can change its entropy S through two distinct mechanisms: namely, through changing the dipole alignment or configurational entropy (ΔSconf), and the vibrational entropy due to the intrinsic structure response (ΔSvib). Previous numerical investigations yield only the total entropy change ΔS but cannot separate these two contributions. Here we develop a full first-principles method to extract ΔSvib and the corresponding induced adiabatic temperature change ΔTvib under E, i.e., the electrocaloric effect (ECE), and compare them to the total ΔS and ΔT from molecular dynamics simulation based on a first-principles effective Hamiltonian model. For both single crystal PbTiO3 (PTO) and PbZr0.5Ti0.5O3 (50/50 PZT), the calculation results show that for T far from the phase transition temperature Tpt, ΔSvib plays an important and even dominant role in the ECE. On the other hand, for T close to Tpt, ΔSconf dominates the ECE. Moreover, for PTO, we find that positive E can cause positive ECE, while negative E cause negative ECE. Therefore, by combining both positive and negative ECE in a “bipolar” Ericsson cycle, the cooling energy density can significantly increase as compared to that of a unipolar cycle.

Optimizing the efficiency of heat dissipation across an interface is a great challenge with the continuously increasing integration of microelectronic devices. In this work, an effective method in tuning the heat conduction across the Al/graphene/SiO

For a long time, the validity and accuracy of Maxwell model are not clear when the model is applied to predict the thermal conductivities of semi-crystalline polymers. In this paper, based on the two-phase model of semi-crystalline polymers, Maxwell model is derived according to the theory of heat transfer. With the help of Maxwell model, the effective thermal conductivities of crystalline and amorphous phases are determined for isotropic high-density polyethylene (HDPE) and ultra-high molecular weight polyethylene (UHMWPE) at 300 K. The predicted values of Maxwell model are compared with the results reported in the existing literatures and that of other models. The result shows that Maxwell model can accurately predict the thermal conductivity of HDPE even when the degree of crystallinity is close to 90 %. Maxwell model is also compared with Lord Rayleigh’s model when predicting the thermal conductivity of UHMWPE. It is found that there is little difference between these two models. This implies that the influence of the interaction among nearby discrete phases can be ignored when Maxwell model is used to predict the thermal conductivity of isotropic polyethylene. This work indicates that the thermal conductivity of isotropic polyethylene can be accurately predicted by Maxwell model no matter what degree of crystallinity is.

Kinks in nanowires have recently been shown to be able to effectively tune the nanowire thermal conductivities; however, the underlying mechanisms have not been fully understood yet. To further disclose the details of phonon transport in kinked nanowires, here we report on non-equilibrium molecular dynamics studies of thermal transport through kinked and straight silicon nanowires. Results show that kinks can induce additional resistance and lead to lower thermal conductivity for kinked nanowires than that of corresponding straight wires. Detailed analysis indicates that kinks produce additional resistance through reflecting phonons back into their incoming arms. Moreover, through introducing heavier isotope atoms in the kink region, the simulation replicates the experimental observation that defects in the kink regime, instead of posing additional resistance, can actually facilitate thermal transport through deflecting phonons into the opposite arm.

The effects of interatomic bonding strengths of graphite itself, in the in-plane (IP) and cross-plane (CP) direction, on the interfacial thermal conductance between graphite and substrate copper (Cu), are investigated by molecular dynamics simulations. It is found that the interfacial thermal conductance at the graphite/Cu interface monotonically decreases with respect to the increase of the IP bonding strength of graphite. However, the interfacial thermal conductance has a maximum with respect to the increase of the CP bonding strength of graphite. By extracting the acoustic iso-energy surfaces and phonon density of states of graphite under various bonding strength parameters, it is found that increasing the IP bonding strength decreases both the incident phonon group velocity component and average interfacial transmission coefficient. Increasing the CP bonding strength also decreases the incident phonon transmission coefficient. However, increasing the CP bonding strength increases the phonon group velocity component. To provide a practical method to enhance the interfacial thermal conductance, we compared the interfacial thermal conductance of porous graphite/Cu interface, which is higher than the graphite/Cu interface mainly due to the large reduction of the in-plane elasticity. This study provides important guidance in the active regulation of the interfacial thermal conductance between anisotropic materials and substrate.

Heat conduction has been shown to be greatly suppressed in Si nanomeshes, which has attracted extensive attention for potential thermoelectric applications, yet the precise suppression mechanism remains to be fully understood. Attempting to further disclose the underlying mechanisms, we report on the thermal conductivity of the building block for nanomeshes, i.e., Si nanoribbons with fins attached to the two opposite sides. By expanding only the fin width while keeping both the period length and the backbone size constant, we observed an unexpected non-monotonic trend of the effective thermal conductivity normalized with the backbone cross-section. Further analysis showed that the corrected thermal conductivity extracted with appropriate consideration of the geometrical effect on diffusion followed a monotonically decreasing trend, reaching a maximum thermal conductivity reduction of 18% at 300 K for a ribbon with the maximum explored fin width of 430 nm, as compared to that of the straight ribbon of 66 nm backbone width. We attribute the thermal conductivity reduction to the thermal constriction resistance induced by the cross-section reduction between the fin and backbone sections. For ribbons with a larger fin width, the effective phonon mean free path is longer for phonons arriving at the constriction, which boosts the ballistic constriction resistance, i.e., Sharvin resistance, and leads to a lower thermal conductivity.

It is generally accepted that the low-energy electron beam (e-beam) irradiation has a negligible effect on the physical properties of metallic nanostructures during the in-situ imaging and welding inside the scanning electron microscope. Here, a pronounced decrease in the electrical conductivity of Ag nanowires is obtained after contacting the ends by using the e-beam induced deposition nanolithography. A vivid crystal defect migration inside nanowire is observed under the transmission electron microscope, revealing that the e-beam induced internal stress provides an explanation for the remarkable conductivity decrease. These observations indicate that e-beam exposure can cause anomalous morphology change inside Ag nanowire. In addition, the electrical conductivity provides an effective strategy to monitor the related nanostructure change.

This work experimentally investigated quantum transport characteristics of heavily doped bismuth selenide topological insulator nanoribbons to understand their physical origins. Transport properties of nanoribbons were measured via a suspended micro-device for eliminating the substrate effect. A series of quantum transport behaviors such as weak antilocalization, Shubnikov-de Haas oscillations, universal conductance fluctuation, and linear perpendicular-field magnetoresistance have been systematically studied to achieve a coherent understanding on their origins in topologically protected surface states, band bending, or bulk states. The parallel-field magnetoresistance, however, is found to be diverse, which can exhibit negative or positive values for the whole measurement range of the magnetic field strength or change from positive to negative values with the increase of the magnetic field strength. The tunable behavior of the parallel-field magnetoresistance is suggested to be the collective effects of the positive magnetoresistance from surface transport and the negative magnetoresistance possibly owing to the axial anomaly, resulting from long-range ionic impurity-scattering processes in bulk carriers. The transport properties of nanoribbons of heavily doped bismuth selenide, a topological insulator, have been systematically studied in suspended devices. Hao Tang, Juekuan Yang, Minghui Lu, Dongyan Xu and colleagues from several Chinese institutions characterized nanoribbons with different carrier densities and surface-area-to-volume ratios; they observed quantum signatures such as weak antilocalization, Shubnikov-de Haas oscillations, universal conductance fluctuations, and linear magnetoresistance, discussing whether they originate from the surface states, band bending, or bulk states. In particular, the magnetoresistance is anisotropic, and whereas the perpendicular-field magnetoresistance displays the same behavior for all samples, the parallel-field magnetoresistance varies from sample to sample and can be tuned from positive to negative values. The authors thus identify it as a collective effect, with contributions from both the topologically protected surface states and scattering processes in the bulk.

Friction represents a major energy dissipation mode, yet the atomistic mechanism of how friction converts mechanical motion into heat remains elusive. It has been suggested that excess phonons are mainly excited at the washboard frequency, the fundamental frequency at which relative motion excites the interface atoms, and the subsequent thermalization of these nonequilibrium phonons completes the energy dissipation process. Through combined atomic force microscopy measurements and atomistic modeling, here we show that the nonlinear interactions between a sliding tip and the substrate can generate excess phonons at not only the washboard frequency but also its harmonics. These nonequilibrium phonons can induce resonant vibration of the tip and lead to multiple peaks in the friction force as the tip sliding velocity ramps up. These observations disclose previously unrecognized energy dissipation channels associated with tip vibration and provide insights into engineering friction force through adjusting the resonant frequency of the tip-substrate system.

At the nanometer scale, heat (phonon) transport is sensitive to the contact details at the interface due to the phonon wave property. However, the effects of contact atom distribution are ignored. In this work, the atomic Green's function (AGF) method and molecular dynamics (MD) simulation are applied to explore those effects. A parameter named as the average distance d[combining macron] is raised here to measure the distribution of contacted atoms at the interface. Based on the AGF method, phonon transmission profiles at different d[combining macron] (distribution) with the same number of contacted atoms have a coincident point, the reverse frequency fr. If the phonon frequency f is smaller (larger) than fr, smaller d[combining macron] has smaller (larger) phonon transmission. The overlap of the vibrational density of states from the MD simulation and the local density of states from the AGF method indicate that the reverse frequency is caused by the match degree of vibration modes across the interface. The existence of reverse frequency leads to the reverse temperature Tr. Increasing the contact area or the interfacial coupling strength can cause the blue shift of fr and the increase of Tr. The MD simulations observe a larger temperature jump at the interface for larger d[combining macron], similar to that from the AGF method at temperatures higher than Tr due to the high-temperature limit property in MD. The results are independent of the choice of cutoff distance in potential and interfacial coupling strength, indicating that the conclusion here is applicable for the general interface.

Thermal bridge method is widely used in thermal conductance measurements of one-dimensional nanostructures. The studies used by thermal bridge method advances our understanding of one-dimensional nanoscale thermal transport. And many efforts have been made to boost the reliability of the thermal bridge method and improve the measurement sensitivity. In this paper, uncertainty analysis is performed on the thermal bridge measurements of a CNT and a CdSe nanowire. Both the Taylor series method and the Monte Carlo method are used to figure out the propagation of the errors in the direct measurements. Our results show that the uncertainty of the thermal conductance decreases as the thermal conductance of the measured sample decreases, which can be attributed to the increase in the temperature drop on the measured sample. This finding indicates that we can reduce the measurement uncertainty by increasing the measured length of the sample or increasing the Joule heating generated on the heat source.

In this paper, both transient and steady state heat transfer in graphite are investigated with molecular dynamics (MD) simulations. The simulation results demonstrate that elastic anisotropy controls heat transfer in the transient state, which makes the outermost isothermal surface of temperature distribution similar to the phonon group velocity surface that has a shape of very flat ellipse in layered materials. In steady state, with the help of phonons engaging in sufficient scattering, the basal plane phonon modes determine the thermal conductivity along all directions except those very close to the cross plane. Our simulation results confirm that the classical theoretical model can accurately predict the thermal conductivity along arbitrary directions in layered materials.

The electrochemical intercalation of metal ions into layered materials is a useful strategy to reversibly tune thermal-transport properties, but the fundamental mechanisms are not well understood. In this study, we systematically investigated the effects of lithium-ion concentrations on the anisotropic thermal conductivity of intercalated graphite by molecular-dynamics simulations and a continuum-mechanics method. It was found that the in-plane thermal conductivity rapidly decreased to 34.3% of that of graphite in the same direction when the lithium-ion concentration increases to 0.1667. However, the cross-plane thermal conductivity first decreased to 23.7% of that of the graphite. Then, it surprisingly recovered to a thermal conductivity even higher than that of graphite when the lithium-ion concentration increased further. These two different trends and thermal-conductivity anisotropies were explained by extracting the phonon lifetimes and elastic constants of intercalated graphites with various lithium...

Interfacial thermal conductance as an accumulation function of the phonon mean free path is rigorously derived from the thermal conductivity accumulation function. Based on our theoretical model, the interfacial thermal conductance accumulation function between Si/Ge is calculated. The results show that the range of mean free paths (MFPs) for phonons contributing to the interfacial thermal conductance is far narrower than that for phonons contributing to the thermal conductivity. The interfacial thermal conductance is mainly contributed by phonons with shorter MFPs, and the size effects can be observed only for an interface constructed by nanostructures with film thicknesses smaller than the MFPs of those phonons mainly contributing to the interfacial thermal conductance. This is why most experimental measurements cannot detect size effects on interfacial thermal conductance. A molecular dynamics simulation is employed to verify our proposed model.

Nanowires of complex morphologies, such as kinked wires, have been recently synthesized and demonstrated for novel devices and applications. However, the effects of these morphologies on thermal transport have not been well studied. Through systematic experimental measurements, we show that single-crystalline, defect-free kinks in boron carbide nanowires can pose a thermal resistance up to ∼30 times larger than that of a straight wire segment of equivalent length. Analysis suggests that this pronounced resistance can be attributed to the combined effects of backscattering of highly focused phonons and required mode conversion at the kink. Interestingly, it is also found that instead of posing resistance, structural defects in the kink can actually assist phonon transport through the kink and reduce its resistance. Given the common kink-like wire morphology in nanoelectronic devices and required low thermal conductivity for thermoelectric devices, these findings have important implications in precise thermal management of electronic devices and thermoelectrics.

The thermal conductance across Au/graphene/Au and Au/hydrogenated graphene(H-graphene)/Au interfaces are measured using the time domain thermoreflectance (TDTR) technique. It is found that the thermal conductance decreases from 30 ± 5 MWm−2 K−1 to 14 ± 3 MWm−2K−1 when the graphene is hydrogenated. However, nonequilibrium molecular dynamics (NEMD) simulation results show that the thermal conductance can be decreased by no more than 30% as the graphene is hydrogenated if only phonons are considered as the heat energy carriers. Considering the difference between the experimental and simulated results, we infer that electrons are involved in heat conduction across the Au/Graphene/Au interface. Once the graphene is hydrogenated, the electron contribution channel is closed. It is estimated that the contribution from electrons accounts for approximately 53% of the total interfacial thermal conductance for the metal/graphene/metal interfaces.

The thermal conductivities of the newly synthesized all- sp 2 three-dimensional graphene are investigated by equilibrium molecular dynamics simulations in this work. It is found that the thermal conductivity parallel to the honeycomb axis direction ( k z ) is one order magnitude higher than that perpendicular direction ( k xy ). This anisotropy is explained by the direction-dependent effective elastic constants. For the size effects, the k xy is found to be independent of the hexagon size, while k z increases with it. Both k xy and k z are also validated by the nonequilibrium method. For the pressure effects, this study also reveals an unexpected k z reduction with increasing pressure. A critical pressure is found to be 0.65 GPa. Beyond this critical pressure, the three-dimensional graphene breaks its crystal symmetry, leading to the in-plane k xy becomes anisotropic and lower comparing to the three-dimensional graphene with no pressure. These investigations provide important guidance to develop all- sp 2 three-dimensional graphene for energy storage, catalysis, and sensor applications.

It is usually very difficult to measure the intrinsic thermal conductivity of fibers using direct electrical heating method, due to the presence of lateral heat loss. In this study, we demonstrate that the intrinsic thermal conductivity and lateral heat transfer coefficient of fibers can be extracted simultaneously via multiple measurements on the same fiber. In our experiments, three samples of various lengths were prepared from an individual polyacrylonitrile-based carbon fiber of 5.6 µm in diameter and measured with the direct electrical heating method. From each sample, we can get a curve of thermal conductivity vs lateral heat transfer coefficient. We showed that the intrinsic thermal conductivity and lateral heat transfer coefficient can be extracted from the intersection of these curves. Our results also showed that ignoring the lateral heat loss can result in an overestimation in thermal conductivity of carbon fibers by more than 3 times.

In an isothermal process, applying an electric field E to a ferroelectric material can change its entropy S through two distinct mechanisms: namely, through changing the dipole alignment or configurational entropy (ΔSconf), and the vibrational entropy due to the intrinsic structure response (ΔSvib). Previous numerical investigations yield only the total entropy change ΔS but cannot separate these two contributions. Here we develop a full first-principles method to extract ΔSvib and the corresponding induced adiabatic temperature change ΔTvib under E, i.e. the electrocaloric effect (ECE), and compare them to the total ΔS and ΔT from molecular dynamics simulation based on a first-principles effective Hamiltonian model. For both single crystal PbTiO3 (PTO) and PbZr0.5Ti0.5O3 (50/50 PZT), the calculation results show that for T far from the phase transition temperature Tpt, ΔSvib plays an important and even dominant role in the ECE. On the other hand, for T close to Tpt, ΔSconf dominates the ECE. Moreover, for PTO, we find that positive E can cause positive ECE, while negative E cause negative ECE. Therefore, by combining both positive and negative ECE in a "bipolar" Ericsson cycle, the cooling energy density can significantly increase as compared to that of a unipolar cycle.

Severe stress concentration and bad sealing performance are encountered in a non-metallic engineering part during an interference fit assembly process. Both numerical calculation and experimental test are employed to analyze the causes resulting in the assembly failure. Based on the finite element method (FEM), commercial computational software, ANSYS, is first used to simulate the whole assembly process with different boundary conditions. By comparing simulation results of the assembly process with various boundary conditions, it is found that deformation energy and friction force contribute differently to the reaction force at varying assembly depths. In virtue of these simulation results, an improved engineering part is designed and fabricated. Experimental test results show that stress concentration and sealing performance problems are basically solved compared to those in the original model. Moreover, reaction forces calculated from numerical simulation and measured from experimental tests agree reasonably with each other during the interference fit progress. This work is beneficial to the understanding of the interference fit process in engineering application and the avoiding of part failure resulting from inappropriate design.

In this paper, we report a high power density cross-plane micro-thermoelectric generator (TEG) fabricated by integrating pulsed electroplating with micro-fabrication processes. The TEG consists of a total of 127 pairs of n-type Bi2Te3 and p-type Sb2Te3 thermoelectric pillars embedded in a SU-8 matrix in order to enhance the overall mechanical strength of the device. Both bottom and top electrical connections are formed by electroplating, which is advantageous because of facile and low cost fabrication and low parasitic electrical resistances. The device demonstrates a maximum power of 2990 $\mu \text{W}$ at a temperature difference of 52.5 K, corresponding to a power density as high as 9.2 mW $\cdot $ cm $^{-2}$ . The power density of our device is more than two times the highest value reported for the electroplated micro-TEGs in the literature, which can be attributed to the low internal resistance and high packing density of thermoelectric pillars. [2015-0348]

The non-equilibrium Green's function method was employed to investigate the pressure effects on the interfacial thermal resistance of few-layer graphene. It is found that a compressive pressure of 10 GPa along the cross-plane direction can reduce the interfacial resistance by approximately 4 times, when compared with no applied pressure. As pressure is applied along both in-plane and cross-plane directions, the effects of the in-plane direction pressure on the cross-plane thermal transport are much weaker than those of the cross-plane pressure. Our results indicate that the interlayer interfacial thermal resistance of graphite can be modulated to a large extent by external pressure.

This work reports a thermal transport study in quasi-one-dimensional organic nanostructures self-assembled from conjugated planar molecules via π-π interactions. Thermal resistances of single crystalline copper phthalocyanine (CuPc) and perylenetetracarboxylic diimide (PTCDI) nanoribbons are measured via a suspended thermal bridge method. We experimentally observed the deviation from the linear length dependence for the thermal resistance of single crystalline β-phase CuPc nanoribbons, indicating possible subdiffusion thermal transport. Interestingly, a gradual transition to the linear length dependence is observed with the increase of the lateral dimensions of CuPc nanoribbons. The measured thermal resistance of single crystalline CuPc nanoribbons shows an increasing trend with temperature. However, the trend of temperature dependence of thermal resistance is reversed after electron irradiation, i.e., decreasing with temperature, indicating that the single crystalline CuPc nanoribbons become 'amorphous'. Similar behavior is also observed for PTCDI nanoribbons after electron irradiation, proving that the electron beam can induce amorphization of single crystalline self-assembled nanostructures of planar π-conjugated molecules. The measured thermal resistance of the 'amorphous' CuPc nanoribbon demonstrates a roughly linear dependence on the nanoribbon length, suggesting that normal diffusion dominates thermal transport.

In this work, fullerene (C60) nanorods were prepared by a surfactant-assisted self-assembly method. Although the orientation of molecular alignment remains unchanged from one end to the other end in these C60 nanorods, they cannot be rigorously treated as single crystals because of the existence of amorphous-like regions formed by a high density of defects such as stacking faults and vacancy clusters. The partially crystalline and partially amorphous structure results in unusual thermal transport behavior in C60 nanorods, which cannot be classified into either typical crystalline-like or typical glass-like behavior. The thermal resistances of the C60 nanorods decrease with increasing temperature and reach a plateau around 100 K, which can be attributed to the combined effect of Einstein localized vibration in C60 molecules, intracluster vibration, and phonon-defect scattering. Accompanied with depositing Pt/C composites at two ends of a C60 nanorod to improve thermal contact between Pt electrodes and the C60 nanorod, tensile strain may be introduced in the C60 nanorod due to contraction, which enhances thermal resistance, especially in the low temperature range. Ultralow thermal conductivity (less than 0.06 W m−1 K−1) is observed for self-assembled C60 nanorods at room temperature, which is significantly lower than the thermal conductivity of bulk C60 single crystals and polycrystalline C60/C70 compacts but on the same order of magnitude as the lower limit of thermal conductivity of amorphous carbon.

The electrochemical intercalation of metal ions into layered materials is an innovative approach to actively and reversely regulate the thermal transport properties of layered materials. In this work, the molecular dynamics (MD) simulation and lattice dynamics calculation are performed to investigate the thermal boundary conductance (TBC) between metal aluminum (Al) and intercalated graphite with various lithium-ion (Li-ion) concentrations. Both the thermal relaxation simulation and the non-equilibrium MD simulation show that the TBC in the intercalated graphene/Al interface is significantly high as compared to that in pristine graphite/Al interface, by a factor of 5.5. Besides, the TBC presents a slightly increasing trend with increasing Li-ion concentration. This is because increasing the Li-ion concentration increases the out-of-plane phonon group velocity of the intercalated graphite, leading to a sharp increase of phonon irradiation heat flux. By calculating the phonon interfacial transmission coefficient that includes the inelastic scattering effects, it is found that the transmission from the intercalated graphite to Al significantly decreases with increasing Li-ion concentration. The competition between the increased phonon irradiation heat flux and the decreased phonon interfacial transmission coefficient results in the slight increase of the TBC at high Li-ion concentration. This study provides important guidance to develop novel electrode materials and structures for thermal management in Li-ion batteries.

In this work, the time-domain thermoreflectance (TDTR) method is used to measure the thermal conductivity of graphite along different crystallographic planes at room temperature for the first time and the thermal conductivities along the non-principal axes of graphite are obtained. A focused ion beam is used to cut graphite samples along different crystallographic planes for the TDTR measurement. Then, a thermal model is developed to extract the thermal conductivity of graphite along different crystallographic planes from the measured signals of the TDTR method. The measured thermal conductivities along different crystallographic planes in graphite agree well with the anisotropy model, revealing that the traditional TDTR method can be used to measure the non-principal axis thermal conductivity of anisotropic layered materials. Moreover, the experimental results demonstrate that once the crystallographic plane deviates from the cross-plane direction, the in-plane phonon modes will dominate the heat transfer in graphite.