Improving the energy output of batteries at sub-zero temperatures is crucial to the long-term application of advanced electronics in extreme environments. This can generally be accomplished by employing high-voltage cathodes, applying Li metal anodes, and improving the electrolyte chemistry to provide facile kinetics at ultralow temperature. However, systems capable of all three of these have seldom been studied. Herein, we demonstrate the design of such a system through solvent fluorination, applying a 1 M LiPF6 in a methyl 3,3,3-trifluoropionate (MTFP)/fluoroethylene carbonate (FEC) (9:1) electrolyte that simultaneously provided high-voltage cathode and Li metal anode reversibility at room temperature. This performance was attributed to the production of fluorine-rich interphases formed in the MTFP-based system, which was investigated by X-ray photoelectron spectroscopy (XPS). Furthermore, the all-fluorinated electrolyte provided 161, 149, and 133 mAh g–1 when discharged at −40, −50, and −60 °C, respectively, far exceeding the performance of the commercial electrolyte. This work provides new design principles for high-voltage batteries capable of ultra-low-temperature operation.

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Thermal management in microelectronic devices has become a crucial issue as the devices are more and more integrated into micro-devices. Recently, free-standing graphene films (GFs) with outstanding thermal conductivity, superb mechanical strength, and low bulk density, have been regarded as promising materials for heat dissipation and for use as thermal interfacial materials in microelectronic devices. Recent studies on free-standing GFs obtained via various approaches are reviewed here. Special attention is paid to their synthesis method, thermal conductivity, and potential applications. In addition, the most important factors that affect the thermal conductivity are outlined and discussed. The scope is to provide a clear overview that researchers can adopt when fabricating GFs with improved thermal conductivity and a large area for industrial applications.

Li||SPAN batteries in the lithium bis(fluorosulfonyl)imide methyl propionate/fluoroethylene carbonate (LiFSI MP/FEC) electrolyte system can charge and discharge at −40 °C with over 78% room temperature capacity retention.

As a promising alternative to the market-leading lithium-ion batteries, low-cost sodium-ion batteries (SIBs) are attractive for applications such as large-scale electrical energy storage systems. The energy density, cycling life, and rate performance of SIBs are fundamentally dependent on dynamic physiochemical reactions, structural change, and morphological evolution. Therefore, it is essential to holistically understand SIBs reaction processes, degradation mechanisms, and thermal/mechanical behaviors in complex working environments. The recent developments of advanced in situ and operando characterization enable the establishment of the structure–​processing–​property–​performance relationship in SIBs under operating conditions. This Review summarizes significant recent progress in SIBs exploiting in situ and operando techniques based on X-ray and electron analyses at different time and length scales. Through the combination of spectroscopy, imaging, and diffraction, local and global changes in SIBs can be elucidated for improving materials design. The fundamental principles and state-of-the-art capabilities of different techniques are presented, followed by elaborative discussions of major challenges and perspectives.