RESUMEN
Highly thermally conductive graphitic film (GF) materials have become a competitive solution for the thermal management of high-power electronic devices. However, their catastrophic structural failure under extreme alternating thermal/cold shock poses a significant challenge to reliability and safety. Here, we present the first investigation into the structural failure mechanism of GF during cyclic liquid nitrogen shocks (LNS), which reveals a bubbling process characterized by "permeation-diffusion-deformation" phenomenon. To overcome this long-standing structural weakness, a novel metal-nanoarmor strategy is proposed to construct a Cu-modified graphitic film (GF@Cu) with seamless heterointerface. This well-designed interface ensures superior structural stability for GF@Cu after hundreds of LNS cycles from 77 to 300 K. Moreover, GF@Cu maintains high thermal conductivity up to 1088 W m-1 K-1 with degradation of less than 5% even after 150 LNS cycles, superior to that of pure GF (50% degradation). Our work not only offers an opportunity to improve the robustness of graphitic films by the rational structural design but also facilitates the applications of thermally conductive carbon-based materials for future extreme thermal management in complex aerospace electronics.
RESUMEN
Excellent through-plane thermally conductive composites are highly demanded for efficient heat dissipation. Giant sheets have large crystalline domain and significantly reduce interface phonon scattering, making them promising to build highly thermally conductive composites. However, realizing vertical orientation of giant sheets remains challenging due to their enormous mass and huge hydrodynamic drag force. Here, we achieve highly vertically ordered liquid crystals of giant graphite oxide (more than 100 µm in lateral dimension) by microwire shearing, which endows the composite with a recorded through-plane thermal conductivity of 94 W m-1 K-1 . Microscale shearing fields induced by vertical motion of microwires conquer huge hydrodynamic energy barrier and vertically reorient giant sheets. The resulting liquid crystals exhibit extremely retarded relaxation and impart large-scale vertical array with bidirectional ordering degree as high as 0.82. The graphite array-based composites demonstrate an ultrahigh thermal enhancement efficiency of over 35 times per unit volume. Furthermore, the composites improve cooling efficiency by 93% for thermal management tests compared to commercial thermal interface materials. This work offers a novel methodology to precisely manipulate the orientation of giant particles and promote large-scale fabrication of vertical array with advanced functionalities.
RESUMEN
Aqueous rechargeable batteries are highly safe, low-cost, and environmentally friendly, but restricted by low energy density. One of the most efficient solutions is to improve the concentration of the aqueous electrolytes. However, each salt is limited by its physical solubility, generally below 21-32 mol kg-1 (m). Here, a ZnCl2 /ZnBr2 /Zn(OAc)2 aqueous electrolyte with a record super-solubility up to 75 m is reported, which breaks through the physical solubility limit. This is attributed to the formation of acetate-capped water-salt oligomers bridged by Br- /Cl- -H and Br- /Cl- /O-Zn2+ interactions. Mass spectrometry indicates that acetate anions containing nonpolarized protons prohibit the overgrowth and precipitation of ionic oligomers. The polymer-like glass transition temperature of such inorganic electrolytes is found at ≈-70 to -60 °C, without the observation of peaks for salt-crystallization and water-freezing from 40 to -80 °C. This supersoluble electrolyte enables high-performance aqueous dual-ion batteries that exhibit a reversible capacity of 605.7 mAh g-1 , corresponding to an energy density of 908.5 Wh kg-1 , with a coulombic efficiency of 98.07%. In situ X-ray diffraction and Raman technologies reveal that such high ionic concentrations of the supersoluble electrolyte enable a stage-1 intercalation of bromine into macroscopically assembled graphene cathode.
RESUMEN
Aqueous electrolytes, which possess the advantages of nonflammability and high ionic conductivity for safe and sustainable energy storage systems, are restricted by their narrow potential windows due to water electrolysis. The recent study of high-voltage aqueous electrolytes has mainly focused on the molecular-level hydration structure of electrolyte salts, while the influence from subatomic-scale neutrons of the water solvent has never been considered. Here, for the first time, we report an electrochemical isotope effect in which the numerically increased neutrons in the water solvent extend the potential window of aqueous electrolytes. This effect is caused by the following factors: the lower zero-point energy of the deuterium compound, the smaller ion product, and the larger dehydration energy of heavy water. It is affected by ion species, electrolyte concentrations, and the ratio of deuterium to protium. Our finding provides the new insight into aqueous electrochemistry that the isotope in molecular water improves the performance of aqueous electrolytes.
