Poly(arylene alkylene)s functionalized with perfluorosulfonic acid groups as proton exchange membranes for vanadium redox flow batteries

With the aim to develop vanadium redox flow battery (VRFB) membranes beyond state of the art, we have in the present work functionalized poly(p-terphenylene)s with highly acidic perfluorosulfonic groups and investigated their performance as proton exchange membranes (PEMs). Consequently, two poly(p-terphenylene alkylene)s tethered with perfluoroalkylsulfonic acid and perfluorophenylsulfonic acid, respectively, were synthesized through superacid-mediated polyhydroxyalkylations and cast into PEMs. Compared with Nafion 212, the PEM carrying perfluorophenylsulfonic acid groups (PTPF-Phenyl-SA) was found to exhibited higher ionic conductivity and eight times lower vanadium (IV) permeation rate. The latter explains the longer self-discharge duration of the VRFB based on the PTPF-Phenyl-SA. In addition, the VRFB assembled with the PTPF-Phenyl-SA PEM exhibited a high average coulombic efficiency of 99.6% for over 100 cycles with a capacity fade of 0.24% per cycle, which was 50% lower than when Nafion 212 was used. More importantly, an excellent capacity retention was achieved through electrochemical rate performance experiments at different current densities

LiFePO4-coated carbon fibers as positive electrodes in structural batteries: Insights from spray coating technique

This study presents the fabrication of LiFePO4 (LFP)-coated carbon fibers (CFs) as a positive electrode component for structural batteries, utilizing a spray coating technique. The successful coating of CFs through this method demonstrated their usefulness as efficient current collectors. The electrodes obtained using this method underwent electrochemical evaluations. Throughout the extended cycling tests at C/7, the maximum specific discharge capacity reached 146 mAh/g, maintaining a 77% capacity retention after 100 cycles. In rate performance assessments at the faster C-rate of 1.5C, the capacity measured 123 mAh/g, with a retention of 96%. The application of spray coating emerges as a promising technique for electrode production in structural batteries, showcasing its potential for optimizing performance in multifunctional energy storage systems

Highly proton conductive membranes based on carboxylated cellulose nanofibres and their performance in proton exchange membrane fuel cells

The performance of thin carboxylated cellulose nanofiber-based (CNF) membranes as proton exchange membranes in fuel cells has been measured in-situ as a function of CNF surface charge density (600 and 1550 µmol g-1), counterion (H+or Na+), membrane thickness and fuel cell relative humidity (RH 55 to 95 %). The structural evolution of the membranes as a function of RH, as measured by Small Angle X-ray scattering, shows that water channels are formed only above 75 % RH. The amount of absorbed water was shown to depend on the membrane surface charge and counter ions (Na+or H+). The high affinity of CNF for water and the high aspect ratio of the nanofibers, together with a well-defined and homogenous membrane structure, ensures a proton conductivity exceeding 1 mS cm-1at 30 °C between 65 and 95 % RH. This is two orders of magnitude larger than previously reported values for cellulose materials and only one order of magnitude lower than Nafion 212. Moreover, the CNF membranes are characterized by a lower hydrogen crossover than Nafion, despite being ≈ 30 % thinner. Thanks to their environmental compatibility and promising fuel cell performance the CNF membranes should be considered for new generation proton exchange membrane fuel cells.</p

Highly proton conductive membranes based on carboxylated cellulose nanofibres and their performance in proton exchange membrane fuel cells

The performance of thin carboxylated cellulose nanofiber-based (CNF) membranes as proton exchange membranes in fuel cells has been measured in situ as a function of CNF surface charge density (600 and 1550 μmol g$^{−1}$), counterion (H$^+$ or Na$^+$), membrane thickness and fuel cell relative humidity (RH 55 to 95%). The structural evolution of the membranes as a function of RH, as measured by Small Angle X-ray Scattering, shows that water channels are formed only above 75% RH. The amount of absorbed water was shown to depend on the membrane surface charge and counter ions (H$^+$ or Na$^+$). The high affinity of CNF for water and the high aspect ratio of the nanofibers, together with a well-defined and homogenous membrane structure, ensures a proton conductivity exceeding 1 mS cm$^{−1}$ at 30 °C between 65 and 95% RH. This is two orders of magnitude larger than previously reported values for cellulose materials and only one order of magnitude lower than Nafion 212. Moreover, the CNF membranes are characterized by a lower hydrogen crossover than Nafion, despite being ≈30% thinner. Thanks to their environmental compatibility and promising fuel cell performance the CNF membranes should be considered for new generation proton exchange membrane fuel cells

Evaluating performance and cycle life improvements in the latest generations of prismatic lithium-ion batteries

The last decade has seen an enormous improvement of energy density for lithium-ion battery cells, particularly for automotive grade cells intended for use in electrified vehicles. This has led to vastly improved range for battery electric vehicles as well as for plug-in hybrids. However, the challenge of uncertain battery lifetime remains. The ageing effect due to fast charging is especially difficult to predict due to its non-linear dependence on charge rate, state-of-charge and temperature. We here present results from fast charging (1C and 3C in a 20 % to 80 % SOC-level) of several energy-optimized, prismatic lithium-ion battery cell generations utilizing NMC/graphite chemistry through comparison of capacity retention, resistance and dQ/dV analysis. Considerable improvements are observed throughout cell generations and the results imply that acceptable cycle life can be expected, even under fast charging, when restricting the usage of the available battery capacity. Even though this approach reduces the useable energy density of a battery system, this trade-off could still be acceptable for vehicle applications where conventional overnight charging is not possible. The tested cell format (the VDA PHEV2-standard) has been used for a decade in different electrified vehicles. The ongoing development and improvement of this cell format by several battery cell manufacturers suggests it will continue to be a good choice for future vehicles