Sodium−metal chloride batteries are usually operated at a relatively high temperature (270−350 °C) to achieve adequate electrochemical performance. Such a high operating temperature may cause several issues and limit their widespread applications. Lowering the operating temperature may alleviate these issues, which can be achieved by reducing the ohmic resistance of a Na−β″-Al 2 O 3 solid electrolyte (BASE) and incorporating a low-melting-point catholyte. Herein, a planar sodium−copper chloride battery is evaluated at intermediate temperatures (from 100 to 175 °C) with a thin BASE disk (500 μm) and a roomtemperature ionic liquid (RTIL). The RTILs at various concentrations (0.1−0.75 mol L −1 ) are prepared by dissolving different amounts of sodium bis-(trifluoromethanesulfon)imide (NaTFSI) into 1-ethyl-3-methylimidazolium bis-(trifluoromethylsulfonyl)imide ([EMIm][TFSI]) and used as the catholyte. The effect of NaTFSI addition in [EMIm][TFSI] on the physical properties of the catholyte is examined. With 0.5 mol L −1 NaTFSI in [EMIm][TFSI] ionic liquid to assemble the Na/CuCl 2 battery, the fabricated cell delivers a capacity up to 146.5 mAh g −1 when cycled at 175 °C with the current density of 2 mA cm −2 and retains 94.5% capacity after 20 cycles. Moreover, the battery can run steadily at 130 °C and show a reversible capacity of 79.2 mAh g −1 when the operation temperature is set as low as 100 °C. To the best of our knowledge, these are the lowest operation temperatures reported thus far for sodium−metal-chloride-based cells.
Cobalt sulphides attract much attention as anode materials for Li-ion batteries (LIBs). However, its poor conductivity, low initial column efficiency and large volume changes during cycling have hindered its further development. Herein, novel interlaced CoS nanosheets were firstly prepared on Carbon Fiber Cloth (CFC) by two hydrothermal reactions followed with carbon coating via carbonizing dopamine (CoS NS@C/CFC). As a freestanding anode, the nanosheet structure of CoS not only accommodates the volume variation, but also provides a large interface area to proceed the charge transfer reaction. In addition, CFC works as both a three-dimensional skeleton and an active substance which can further improve the areal capacity of the resulting electrode. Furthermore, the coated carbon combined with the CFC work as a 3D conductive network to facilitate the electron conduction. The obtained CoS NS@C/CFC, and the contrast sample prepared with the same procedure but without carbon coating (CoS NS/CFC), are characterized with XRD, SEM, TEM, XPS and electrochemical measurements. The results show that the CoS NS@C/CFC possesses much improved electrochemical performance due to the synergistic effect of nanosheet CoS, the coated carbon and the CFC substrate, exhibiting high initial columbic efficiency (~87%), high areal capacity (2.5 at 0.15 mA cm −2 ), excellent rate performance (1.6 at 2.73 mA cm −2 ) and improved cycle stability (87.5% capacity retention after 300 cycles). This work may provide a new route to explore freestanding anodes with high areal specific capacity for LIBs.
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