The high density of heat generated in power electronics and optoelectronic devices is a critical bottleneck in their application. New materials with high thermal conductivity are needed to ...effectively dissipate heat and thereby enable enhanced performance of power controls, solid-state lighting, communication, and security systems. We report the experimental discovery of high thermal conductivity at room temperature in cubic boron arsenide (BAs) grown through a modified chemical vapor transport technique. The thermal conductivity of BAs, 1000 ± 90 watts per meter per kelvin meter-kelvin, is higher than that of silicon carbide by a factor of 3 and is surpassed only by diamond and the basal-plane value of graphite. This work shows that BAs represents a class of ultrahigh-thermal conductivity materials predicted by a recent theory, and that it may constitute a useful thermal management material for high-power density electronic devices.
Thermal conductivity of two-dimensional (2D) materials is of interest for energy storage, nanoelectronics and optoelectronics. Here, we report that the thermal conductivity of molybdenum disulfide ...can be modified by electrochemical intercalation. We observe distinct behaviour for thin films with vertically aligned basal planes and natural bulk crystals with basal planes aligned parallel to the surface. The thermal conductivity is measured as a function of the degree of lithiation, using time-domain thermoreflectance. The change of thermal conductivity correlates with the lithiation-induced structural and compositional disorder. We further show that the ratio of the in-plane to through-plane thermal conductivity of bulk crystal is enhanced by the disorder. These results suggest that stacking disorder and mixture of phases is an effective mechanism to modify the anisotropic thermal conductivity of 2D materials.
Formation of thick, high energy density, flexible solid supercapacitors is challenging because of difficulties infilling gel electrolytes into porous electrodes. Incomplete infilling results in a low ...capacitance and poor mechanical properties. Here we report a bottom-up infilling method to overcome these challenges. Electrodes up to 500 μm thick, formed from multi-walled carbon nanotubes and a composite of poly(3,4-ethylenedioxythiophene), polystyrene sulfonate and multi-walled carbon nanotubes are successfully infilled with a polyvinyl alcohol/phosphoric acid gel electrolyte. The exceptional mechanical properties of the multi-walled carbon nanotube-based electrode enable it to be rolled into a radius of curvature as small as 0.5 mm without cracking and retain 95% of its initial capacitance after 5000 bending cycles. The areal capacitance of our 500 μm thick poly(3,4-ethylenedioxythiophene), polystyrene sulfonate, multi-walled carbon nanotube-based flexible solid supercapacitor is 2662 mF cm
at 2 mV s
, at least five times greater than current flexible supercapacitors.
Zinc blende boron arsenide (BAs), boron phosphide (BP), and boron nitride (BN) have attracted significant interest in recent years due to their high thermal conductivity (Λ) predicted by ...first‐principles calculations. This research reports the study of the temperature dependence of Λ (120 K < T < 600 K) for natural isotope‐abundance BP and isotopically enriched 11BP crystals grown from modified flux reactions. Time‐domain thermoreflectance is used to measure Λ of sub‐millimeter‐sized crystals. At room temperature, Λ for BP and 11BP is 490 and 540 W m−1 K−1, respectively, surpassing the values of conventional high Λ materials such as Ag, Cu, BeO, and SiC. The Λ of BP is smaller than only cubic BN, diamond, graphite, and BAs among single‐phase materials. The measured Λ for BP and 11BP is in good agreement with the first‐principles calculations above 250 K. The quality of the crystals is verified by Raman spectroscopy, X‐ray diffraction, and scanning transmission electron microscopy. By combining the first‐principles calculations and Raman measurements, a previously misinterpreted Raman mode is reassigned. Thus, BP is a promising material not only for heat spreader applications in high‐power microelectronic devices but also as an electronic material for use in harsh environments.
Thermal conductivities of high quality natural‐abundance BP and isotopically‐enriched 11BP single crystals measured between 120–600 K using time‐domain thermoreflectance show good agreement with theoretical calculation, surpassing many conventional high‐thermal‐conductivity materials at above 300 K. Such high intrinsic thermal conductivities, combined with their outstanding chemical inertness and high mechanical hardness, suggest their potential applications for heat dissipation in high‐power electronics.
Graphdiyne is a newly discovered 2D carbon allotrope with many special features. Using density functional theory plus van der Waals (vdW) density functional, we investigate the structural, ...electronic, and optical properties of several possible graphdiyne bulk structures. We find that bulk graphdiyne can be either a semiconductor or a metal, depending on its stacking configuration. The interlayer vdW force red shifts the optical absorption peaks of bulk graphdiyne relative to those of the monolayer, and spectra of different stackings display notable differences in the energy range below 1 eV. Finally, combining with previous electrical and optical experiments, we identify the structure of the recently synthesized graphdiyne film.
The mass adoption of electric vehicles is hindered by the inadequate extreme fast charging (XFC) performance (i.e., less than 15 min charging time to reach 80% state of charge) of commercial ...high-specific-energy (i.e., >200 Wh/kg) lithium-ion batteries (LIBs). Here, to enable the XFC of commercial LIBs, we propose the regulation of the battery's self-generated heat via active thermal switching. We demonstrate that retaining the heat during XFC with the switch OFF boosts the cell's kinetics while dissipating the heat after XFC with the switch ON reduces detrimental reactions in the battery. Without modifying cell materials or structures, the proposed XFC approach enables reliable battery operation by applying <15 min of charge and 1 h of discharge. These results are almost identical regarding operativity for the same battery type tested applying a 1 h of charge and 1 h of discharge, thus, meeting the XFC targets set by the United States Department of Energy. Finally, we also demonstrate the feasibility of integrating the XFC approach in a commercial battery thermal management system.
Materials with an abrupt transition between a low and a high thermal conductance state at a critical temperature would be useful for thermal regulation applications. Here, the authors report a high ...contrast reversible thermal conductivity change through the thermally‐induced martensitic transition (MT) in Ni–Mn–In alloys. The authors measure the thermal conductivity of a wide temperature range 130 < T < 530 K using time‐domain thermoreflectance (TDTR). The thermal conductivity of these alloys increases from ≈7.0–8.5 W m−1 K−1 to ≈11.5–13.0 W m−1 K−1 through the MT near 300 K as temperature rises, with a rate of change among the highest yet reported in solid‐state materials with thermally‐induced phase transitions. Based on Hall resistivity measurements, the authors further show that the change of thermal conductivity is dominated by the electronic contribution, which results from a unique carrier mobility change through the MT. Their findings highlight the interplay between the structural disorders and the thermal transport in alloys through solid‐state phase transitions and open a new avenue in the search of high‐performance materials for thermal regulation.
The thermal conductivity (Λ) of Ni–Mn–In Heusler alloys increases by up to 75% across the martensitic transition near 300 K as temperature rises, with a rate of change among the highest yet reported in solid‐state materials with thermally‐induced phase transitions. The change of Λ is dominated by the electronic contribution resulting from a unique carrier mobility change through the transition.
High volumetric energy density secondary batteries are important for many applications, which has led to considerable efforts to replace the low volumetric capacity graphite-based anode common to ...most Li-ion batteries with a higher energy density anode. Because most high capacity anode materials expand significantly during charging, such anodes must contain sufficient porosity in the discharged state to enable the expansion, yet not excess porosity, which lowers the overall energy density. Here, we present a high volumetric capacity anode consisting of a three-dimensional (3D) nanocomposite formed in only a few steps which includes both a 3D structured Sn scaffold and a hollow Sn sphere within each cavity where all the free Sn surfaces are coated with carbon. The anode exhibits a high volumetric capacity of ∼1700 mA h cm–3 over 200 cycles at 0.5C, and a capacity greater than 1200 mA h cm–3 at 10C. Importantly, the anode can even be formed into a commercially relevant ∼100 μm thick form. When assembled into a full cell the anode shows a good compatibility with a commercial LiMn2O4 cathode. In situ TEM observations confirm the electrode design accommodates the necessary volume expansion during lithiation.
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