In this work, the electrical and thermal conductivities of open-cell porous aluminium materials produced by replication casting method are investigated and the correlations between them studied. The ...four-point probe method was used to measure the electrical conductivity of the samples, while the C-therm analyser was used to experimentally determine the thermal conductivity of the cellular materials. The results show that both electrical and thermal conductivities of the porous samples increase as their relative density is increased. Comparison of the measured data with theoretical models shows that the scaling function with a dynamic exponent equal to 1.55 fits the experimental data for electrical conductivity. In addition, an empirical relationship was found to exist between measured electrical and thermal conductivities, while a modified Wiedemann-Franz law was also deduced to correlate the electrical and thermal conductivities of the porous aluminium materials.
The properties of the electrolyte are the dominant factors for the overall performance and safety of electrical energy storage devices. Highly concentrated “water in salt” (WIS) electrolytes are ...inherently non-flammable, moisture-tolerant, and exhibit wide electrochemical stability windows, making them promising electrolytes for high-performance energy storage devices. However, WIS electrolytes possess intrinsically low conductivity and high viscosity, which usually impair the high-rate performance of many energy storage devices, especially supercapacitors (SCs). Additionally, the inevitable salt precipitation at low temperature for WIS electrolytes narrows down their applicable temperature range. Here, we introduce acetonitrile as a co-solvent to a typical “water in salt” electrolyte to formulate an “acetonitrile/water in salt” (AWIS) hybrid electrolyte that provides significantly improved conductivity, reduced viscosity and an expanded applicable temperature range while maintaining the aforementioned important physicochemical properties of WIS electrolytes. Using the AWIS electrolyte for a model SC remarkably enhances the high-rate performance, accompanied by a 2.4 times capacitance increase at 10 A g −1 with respect to the original WIS electrolyte. This AWIS electrolyte also enables a stable long-term cycling capability of the model SC for over 14 000 cycles at a high operation voltage of 2.2 V.
Li+‐conducting oxides are considered better ceramic fillers than Li+‐insulating oxides for improving Li+ conductivity in composite polymer electrolytes owing to their ability to conduct Li+ through ...the ceramic oxide as well as across the oxide/polymer interface. Here we use two Li+‐insulating oxides (fluorite Gd0.1Ce0.9O1.95 and perovskite La0.8Sr0.2Ga0.8Mg0.2O2.55) with a high concentration of oxygen vacancies to demonstrate two oxide/poly(ethylene oxide) (PEO)‐based polymer composite electrolytes, each with a Li+ conductivity above 10−4 S cm−1 at 30 °C. Li solid‐state NMR results show an increase in Li+ ions (>10 %) occupying the more mobile A2 environment in the composite electrolytes. This increase in A2‐site occupancy originates from the strong interaction between the O2− of Li‐salt anion and the surface oxygen vacancies of each oxide and contributes to the more facile Li+ transport. All‐solid‐state Li‐metal cells with these composite electrolytes demonstrate a small interfacial resistance with good cycling performance at 35 °C.
The strong interaction between the surface oxygen vacancies of GDC/LSGM and the TFSI− anions in the composite polymer electrolyte changes Li+ distribution in two local environments, and the population increase of mobile Li+ ions in A2 significantly enhances the Li+ conductivity of the composite electrolyte.
No single polymer or liquid electrolyte has a large enough energy gap between the empty and occupied electronic states for both dendrite‐free plating of a lithium‐metal anode and a Li+ extraction ...from an oxide host cathode without electrolyte oxidation in a high‐voltage cell during the charge process. Therefore, a double‐layer polymer electrolyte is investigated, in which one polymer provides dendrite‐free plating of a Li‐metal anode and the other allows a Li+ extraction from an oxide host cathode without oxidation of the electrolyte in a 4 V cell over a stable charge/discharge cycling at 65 °C; a poly(ethylene oxide) polymer contacts the lithium‐metal anode and a poly(N‐methyl‐malonic amide) contacts the cathode. All interfaces of the flexible, plastic electrolyte remain stable with no visible reduction of the Li+ conductivity on crossing the polymer/polymer interface.
A double‐layer polymer electrolyte is prepared for all‐solid‐state high‐voltage batteries, in which one polymer provides dendrite‐free lithium plating and the other allows Li+ extraction from a high‐voltage cathode without oxidation of the electrolyte, which exhibits good cycling stability in all‐solid‐state Li/LiCoO2 cells.
Due to their unique properties, polymers - typically thermal insulators - can open up opportunities for advanced thermal management when they are transformed into thermal conductors. Recent studies ...have shown polymers can achieve high thermal conductivity, but the transport mechanisms have yet to be elucidated. Here we report polyethylene films with a high thermal conductivity of 62 Wm
K
, over two orders-of-magnitude greater than that of typical polymers (~0.1 Wm
K
) and exceeding that of many metals and ceramics. Structural studies and thermal modeling reveal that the film consists of nanofibers with crystalline and amorphous regions, and the amorphous region has a remarkably high thermal conductivity, over ~16 Wm
K
. This work lays the foundation for rational design and synthesis of thermally conductive polymers for thermal management, particularly when flexible, lightweight, chemically inert, and electrically insulating thermal conductors are required.
GeTe is a promising thermoelectric material at medium temperature, but its carrier concentration tends to go beyond the optimal range for thermoelectrics. This work realized a significant ZT ...enhancement from 1.0 to 2.0 by suppressing the formation of Ge vacancies and band convergence. By simply optimizing the amount of excessive Ge, the hole carrier concentration is greatly reduced. It is demonstrated that the suppression of Ge vacancies can not only optimize the carrier concentration but also recover the mobility to a high value of 90 cm 2 V −1 s −1 , which well exceeds the previously reported data and guarantees superior electrical transport properties, leading to a ZT of 1.6. Further Bi doping facilitates band convergence as featured by the increased band effective mass and high mobility, which in turn yields large power factors and low electronic thermal conductivity. Bi doping induced mass and strain fluctuation also favors the reduction of the lattice thermal conductivity. Consequently, a maximum ZT of ∼ 2.0 at 650 K with an average ZT of over 1.2 is achieved in the nominal composition Bi 0.05 Ge 0.99 Te, which is one of the best thermoelectric materials for medium temperature applications.
•PCM insertion lowers the base temperature.•Low melting point PCMs are suitable for low heating loads.•Lower porosity foam has better heat transfer performance both for charging and discharging.
In ...this paper, experimental investigations are carried out to study the thermal performance of metallic foams impregnated with phase change material (PCM) based heat sinks for thermal management of electronics. Herein, RT-35HC with melting point 34–36 °C is chosen as PCM and copper foam1 (95% porosity), copper foam2 (97% porosity) and Iron-Nickel foam (97% porosity) are used as thermal conductivity enhancer. Various configurations of the heat sink are investigated for 5400 s each for charging and discharging processes under heat flux 0.8–2.4 kW/m2 for PCM volume fractions 0.0, 0.6, 0.7 and 0.8. Results revealed that copper foam-based heat sink showed 5–6 °C less base temperature as compared to that of Iron-Nickel foam. While investigating the effect of foam porosity, copper foam with lower porosity (95%) has shown 11% less base temperature at the end of the charging cycle. It was also noticed that the maximum thermal conductivity enhancement of PCM was found to be 34 times for 95% porosity copper foam with the latent heat reduction of 37%. Copper foam1-PCM composite posed the maximum enhancement in operation time of heat sink 7.9 times more as compared to that of the empty aluminum heat sink. Copper foam -PCM composite with 95% porosity of foam with 0.8 vol fraction of PCM is best recommended configuration for the present experimental study.
Though controversially discussed, understanding of the electronic properties of B4.3C, carbon-rich limit of the homogeneity range has meanwhile reached an advanced degree. In contrast, the knowledge ...on more boron-rich boron carbides has remained small. As a contribution for closing this gap, we present a study of the electrical conductivity from ∼5 to ∼2100 K. Numerous samples covering the whole homogeneity range came from various sources and were differently prepared, thus allowing to separate intrinsic effects from those of impurities, density and preparation method. We show that at low temperature, the electrical conductivity meets formally Mott's law of variable-range hopping. However, its parameters are incompatible with experimental results and need redefinition. At high temperatures, the electrical conductivity is thermally activated. The activation energies yield the energetical position of gap states above the valence band, which are related to intrinsic defects in the structure depending on the actual chemical composition.
Electrical conductivity of B4.3C boron carbide. Display omitted
•The electrical conductivity of boron carbide is studied between 5 and 2100 K in the whole homogeneity range.•Effects of various structural defects are recognized.•Specific gaps states are identified acting at high and low T in different function, each.•At high T the electrical conductivity is thermally activated, while at low T Mott's law of variable range hopping is formally met.•In the case of boron carbide, the parameter σ0 of Mott's law require redefinition.
Abstract
Two-dimensional (2D) materials and their corresponding van der Waals heterostructures have drawn tremendous interest due to their extraordinary electrical and optoelectronic properties. ...Insulating 2D hexagonal boron nitride (
h
-BN) with an atomically smooth surface has been widely used as a passivation layer to improve carrier transport for other 2D materials, especially for Transition Metal Dichalcogenides (TMDCs). However, heat flow at the interface between TMDCs and
h
-BN, which will play an important role in thermal management of various electronic and optoelectronic devices, is not yet understood. In this paper, for the first time, the interface thermal conductance (G) at the MoS
2
/
h
-BN interface is measured by Raman spectroscopy, and the room-temperature value is (17.0 ± 0.4) MW · m
−2
K
−1
. For comparison, G between graphene and
h
-BN is also measured, with a value of (52.2 ± 2.1) MW · m
−2
K
−1
. Non-equilibrium Green’s function (NEGF) calculations, from which the phonon transmission spectrum can be obtained, show that the lower G at the MoS
2
/
h
-BN interface is due to the weaker cross-plane transmission of phonon modes compared to graphene/
h
-BN. T
h
is study demonstrates that the MoS
2
/
h
-BN interface limits cross-plane heat dissipation, and thereby could impact the design and applications of 2D devices while considering critical thermal management.
PDF
