Ionic liquid (IL)-based electrolytes containing molecular solvents were shown to be attractive for extreme temperature applications in electric double layer capacitors (EDLCs). In particular, the IL-butyronitrile (BuCN) mixture provides high capacitance (around 125 F g 21 at 500 mA g 21 ) independent of testing temperature, and superior performance at high current rates (reduced current dependence at high rates). Importantly, the IL-BuCN electrolyte can safely operate between 220 and + 80 uC, which overcomes the high temperature limitations of current commercial EDLCs. An additional advantage of IL-solvent mixtures is that the higher concentration of IL ions in the mixtures allows a greater specific capacitance (F g 21 ) to be achieved. The conductivity of the ionic liquid N-butyl-n-methylpyrrolidinium bis(trifluoromethane sulfonyl) imide (PYR 14 TFSI) could be increased from 2.48 mS cm 21 up to 45 mS cm 21 by mixing with an appropriate solvent. Importantly, these solvent mixtures also retain a wide electrochemical voltage window, in the range 4-6 V.

Boronium-cation-based room-temperature ionic liquids (RTILs) were applied for the first time as novel supporting electrolytes in rechargeable Li|LiFePO4 batteries. The physicochemical properties of three different materials (L1L2)BH2−NTf2, 3a (L1, L2 = 1-methyl imidazole (mim)), 3b (L1, L2 = 1-butylimidazole (bim), and 3c (L1 = trimethylamine (N111), L2 = dimethylethylamine (N112)), which are readily synthesized from inexpensive and commercially available starting materials, were established by DSC, TGA, conductivity, and cyclic voltammetry. These RTILs are stable up to between 238 and 335 °C and display sufficient conductivities and electrochemical windows (4.3−5.8 V) to be compatible with the Li anode of a battery. Stable battery cycling with good capacity retention was possible for >300 cycles with (N111)(N112)BH2−NTf2 + LiNTf2 solutions at charge − discharge rates C/10 and C/5 between 50 and 30 °C. By contrast, a C4mpyr−NTf2 + LiNTf2 electrolyte system performed less well under the same conditions despite the higher conductivity of C4mpyr−NTf2 compared to the boronium RTIL 3c. Li battery cycling was also possible with the imidazole units containing material (bim)2BH2−NTf2 for 140 cycles at 80 °C. These new materials could emerge as important electrolytes for various electrochemical applications.

Through the interpretation of porosity and intrusion data, and correlation to the electrochemical response, this study has confirmed that are not only carbon blacks (CBs) very effective in improving the electrical connectivity of a carbon electrode coating, but they also significantly modify the porosity of the electrode coating and thereby also influence ionic diffusion. CBs are more effective conductive fillers than graphites in EDLC electrodes. The highly branched structure of CBs allows multiple electrical contact points and results in a lower electrode electronic resistance. CBs can decrease inter‐particle porosity (both volume and size) and introduce additional porosity that is characteristic of the type of carbon employed. It is observed that electrode coatings prepared from a carbon slurry have a highly macroporous structure and that electrolyte accessibility to individual activated carbon particles is unlikely to be the limiting factor to accessing capacitance. Electrochemical testing has confirmed the strong relationship between bulk electrode resistance and the accessibility of capacitance at different rates.

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Solid state microbatteries are highly sought after for emerging microsensor technologies. To overcome the problem of the dwarfing capacity resulting from the miniaturization of the battery, 3D-structured platform consisting of high surface area micropillar-shaped electrodes are used. However, applying a conformal and continuous solid polymer electrolyte films onto the intricate 3D electrodes is a crucial step toward achieving functional microbatteries. In this work, we present our approach for the development of polyethylene oxide (PEO)-acrylate based ion conducting polymer thin films which function as solid polymer electrolyte (SPE) and a separator. The SPEs were electrochemically deposited on the 3D electrodes resulting in ultrathin, continuous, conformal, and pinhole-free polymer films. The electrochemical and Li + ions transport properties of the SPEs were characterized by EIS measurements and cyclic voltammetry. Furthermore, the homogenous composition of the SPEs at various depths were confirmed by XPS depth profiling techniques.

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