The
concentration polarization, in addition to the activation and
ohmic polarizations, limits the fast operation of electrochemical
cells such as Li-ion batteries (LIBs). We demonstrate an approach
to mitigate the concentration polarization by regulating the effective
concentration (i.e., the mean ionic activity) of Li ions. The use
of an acrylate-based gel polymer electrolyte (A-GPE) improved the
rate capability of LIBs compared with its liquid counterpart. Electrochemical
and spectroscopic evidence confirms that the unexpected power performance
of the A-GPE is ascribed to the unique solvation structure surrounding
the Li ions. The solvation structure suppresses an abnormal increase
in the activity of Li ions and thus mitigates the concentration polarization
during high-rate discharge. Importantly, this study rejects the common
wisdom that the solid or semisolid electrolytes discourage the fast
charge/discharge of LIBs and suggests an avenue to simultaneously
enhance both the safety and high-power performance of rechargeable
batteries.
The gas tungsten arc (GTA) weldability of high-Mn (HMn) steel and austenitic stainless steel (STS) 316L using dissimilar metal welds (DMWs) was investigated, to fabricate a fuel tank for an LNG-fueled ship. Three types of welding fillers, HMn steel, STS 309LMo and Inconel 625, were applied to the DMWs. The weldability of the DMWs was examined by investigating mechanical properties at 25 and -196 o C, followed by microstructural evolution and weld deformation. The GTA welding process was performed with a heat input range of 0.72–1.89 kJ/mm. All of the fillers employed in the study produced reasonable mechanical properties and low levels of precipitation, such as M<sub>7</sub>C<sub>3</sub> and Fe<sub>3</sub>C. However, the DN specimen using the Inconel 625 filler exhibited reduced ductility in the bending test. This was attributed to Nb-carbide precipitations at dendrite boundaries at the root weld. The DM specimen using HMn filler experienced severe thermal deformation because it had a relatively higher coefficient of thermal expansion than the other fillers during heating by arc and solidification. Therefore, STS 309LMo and HMn wires were determined to be the appropriate fillers for the DMW of HMn steel and STS 316L for cryogenic applications, and the HMn wire requires attention to weld deformation.
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