• Energy Research

AbstractThe protic ionic liquid (PIL) N‐butylimidazolium trifluoromethanesulfonate ([BIm][TfO]) was obtained for the first time and incorporated into a sol–gel‐derived di‐ureasil matrix with a concentration of X=5, 10, and 30 %, where X is the ratio of the mass of PIL per mass of poly(oxyethylene). Four years after their synthesis, the resulting quasi‐anhydrous electrolytes remained amorphous, homogeneous, flexible, and thermally stable below 200 °C. SEM/EDS data revealed the presence of the PIL at the surface of the xerogels with X>5 %, demonstrating that this type of morphological characterization is mandatory to avoid misleading ionic conductivity values. The highest ionic conductivity was produced in the washed sample with X=30 % (3.5×10−5 and 2.1×10−3 S cm−1 at 25 and 170 °C, respectively). The present family of electrolytes yielded higher conductivities than the N‐ethylimidazolium trifluoromethanesulfonate‐based analogues introduced earlier by our group and may thus be considered as promising candidates for applications in fuel cells.

To address the challenges of the next generation of smart windows for energy-efficient buildings, new electrochromic devices (ECDs) are introduced. These include indium molybdenum oxide (IMO), a conducting oxide transparent in the near-infrared (NIR) region, and a NIR-emitting electrolyte. The novel electrolytes are based on a sol-gel-derived di-urethane cross-linked siloxane-based host structure, including short chains of poly (ε-caprolactone) (PCL(530) (where 530 represents the average molecular weight in g mol−1). This hybrid framework was doped with a combination of either, lithium triflate (LiTrif) and erbium triflate (ErTrif3), or LiTrif and bisaquatris (thenoyltrifluoroacetonate) erbium (III) ([Er(tta)3(H2O)2]). The ECD@LiTrif-[Er(tta)3(H2O)2] device presents a typical Er3+ NIR emission around 1550 nm. The figures of merit of these devices are high cycling stability, good reversibility, and unusually high coloration efficiency (CE = ΔOD/ΔQ, where Q is the inserted/de-inserted charge density). CE values of −8824/+6569 cm2 C−1 and −8243/+5200 cm2 C−1 were achieved at 555 nm on the 400th cycle, for ECD@LiTrif-ErTrif3 and ECD@LiTrif-[Er(tta)3(H2O)2], respectively.

Lithium-ion batteries (LIBs) are nowadays widely used in many energy storage devices, which have certain requirements on size, weight, and performance. State-of-the-art LIBs operate very reliably and with good performance under restricted and controlled conditions but lack in efficiency and safety when these conditions are exceeded. In this work, the influence of outranging conditions in terms of charging rate and operating temperature on electrochemical characteristics was studied on the example of lithium titanate (Li$_4$Ti$_5$O$_{12}$, LTO) electrodes. Structural processes in the electrode, cycled with ultrafast charge and discharge, were evaluated by operando synchrotron powder diffraction and ex situ X-ray absorption spectroscopy. On the basis of the Rietveld refinement, it was shown that the electrochemical storage mechanism is based on the Li-intercalation process at least up to current rates of 5C, meaning full battery charge within 12 min. For applications at temperatures between ���30 and 60 ��C, four carbonate-based electrolyte systems with different additives were tested for cycling performance in half-cells with LTO and metallic lithium as electrodes. It was shown that the addition of 30 wt % [PYR$_{14}$][PF$_6$] to the conventional LP30 electrolyte, usually used in LIBs, significantly decreases its melting point, which enables the successful low-temperature application at least down to ���30 ��C, in contrast to LP30, which freezes below ���10 ��C, making battery operation impossible. Moreover, at elevated temperatures up to 60 ��C, batteries with the LP30/[PYR$_{14}$][PF$_6$] electrolyte exhibit stable long-term cycling behavior very close to LP30. Our findings provide a guideline for the application of LTO in LIBs beyond conventional conditions and show how to overcome limitations by designing appropriate electrolytes. ACS applied materials & interfaces 12(33), 37227 - 37238 (2020). doi:10.1021/acsami.0c10576 Published by Soc., Washington, DC

The widespread use of lithium‐ion batteries underlines the criticality of a more sustainable cell fabrication. Here, three biopolymers gelatin, pectin, and deoxyribonucleic acid (DNA) are investigated as binders for the TiNb2O7 anode material in Li cells in a temperature range between 0 and 60 ºC and compared to conventional binder polyvinylidene fluoride (PVDF). The use of biopolymers is motivated by their own environmental friendliness and the possibility to implement an aqueous electrode processing. A specific charge capacity of at least 200 mAh g−1 is found for all binders at 0 °C when testing the cycling performance of TiNb2O7 at 77.5 mA g−1 (1C rate). However, low‐rate cycling at 60 °C shows decreasing capacity for all biopolymers due to the swelling effect and continuous contact loss to the current collector, what also reflects in lowering the overall Li‐diffusion coefficient. This effect becomes less pronounced at 0 °C and high current densities, making biopolymers competitive with commercial PVDF. The electrodes with DNA binder demonstrate overall the most stable performance, arising from the biopolymer intactness and a thin solid–electrolyte interface layer. At 0 °C, the electrode with DNA provides 150 mAh g−1 at 775 mA g−1 for at least 500 discharge–charge cycles.

Abstract Ionically conductive membranes of gelatin and d-PCL(530)/siloxane doped with cyano-based ionic liquids (ILs) were prepared through solvent casting and sol-gel methods, respectively. The membranes were characterized in terms of ionic conductivity, thermal behavior, morphology, and structure. All samples, except the d-PCL(530)/siloxane matrix, exhibited a predominantly amorphous morphology. The samples prepared through solvent casting and sol-gel displayed a minimum thermal stability of 170 and 230 °C, respectively. The ionic conductivity varied according with the type, quantity, and length of the alkyl chain of the cation of the ILs. The sample with the highest ionic conductivity was gelatin 0.5 [C 2 mim][N(CN) 2 ] with 2.40×10 −3 S cm −1 at 25 °C and 1.68×10 −2 S cm −1 at 95 °C. The good results of ionic conductivity encouraged the assembly and characterization of prototypes of electrochromic devices (ECDs). The best results were obtained with glass/ITO/WO 3 /gelatin 1 [C 2 mim][SCN]/CeO 2 -TiO 2 /ITO/glass configuration that showed a fast color switching time (~15 s) and a good open circuit memory (~4 h). The ECD changed its color from pale blue to transparent, and its charge density decreased from −17.53 to −2.71 mC cm −2 during 640 color/bleaching cycles.

Abstract P(VDF-TrFE), solid polymer electrolytes were prepared using the ionic liquid N,N,N-trimethyl-N-(2-hydroxyethyl)ammonium bis(trifluoromethylsulfonyl)imide, [N1 1 1 2(OH)][NTf2]. The morphology, polymer phase, and thermal and electrochemical properties have been determined by scanning electron microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR), differential scanning calorimetry (DSC) and impedance spectroscopy, respectively. The addition of the ILs in P(VDF-TrFE) affects the microstructure, thermal stability and ionic conductivity of the polymer membrane. It was found that the ionic conductivity increases as the ionic liquid (IL) content increases with a maximum value at room temperature of 1.7 × 10− 5 S·cm− 1 for an IL composition of 32 wt.%. The temperature behavior in the ionic conductivity is thermally activated, following the Arrhenius equation, the high ionic conductivity resulting from the large carrier numbers of the IL. The electrochemical potential window shows 1.0 V at 4.0 V that these solid polymer electrolytes are adequate for energy storage devices.