Reformate hydrogen from biogas is an attractive fuel alternative for energy conversion in PEM fuel cells. However, in the reformate traces of ammonia may be found, e.g. if the biogas is produced from agricultural resources. In this investigation the effect of ammonia in the fuel gas, on each part of the fuel cell, is studied by cyclic voltammetry, electrochemical impedance spectroscopy (EIS), symmetrical hydrogen cell (H2|H2)- and real fuel cell operation. A considerable degradation in performance is observed by introducing 200 ppm ammonia. The results show that ammonia not only affects the polymer electrolyte membrane but also the oxygen reduction reaction (ORR) and catalyst ionomer in both electrodes, whereas the hydrogen oxidation reaction (HOR) is the worst affected. In the short-term, the performance is reversible if running the cell on neat hydrogen after ammonia exposure, but this does not apply for long-term exposure. A mitigation method with air bleed is tested but gives no improvement of the performance.

Sinusoidal ripple-current charging has previously been reported to increase both charging efficiency and energy efficiency and decrease charging time when used to charge lithium-ion battery cells. In this paper, we show that no such effect exists in lithium-ion battery cells, based on an experimental study of large-size prismatic cells. Additionally, we use a physics-based model to show that no such effect should exist, based on the underlying electrochemical principles.

The effects of external compression on the performance and ageing of NMC(1/3)/Graphite single-layer Li-ion pouch cells are investigated using a spring-loaded fixture. The influence of pressure (0.66, 0.99, 1.32, and 1.98 MPa) on impedance is characterized in fresh cells that are subsequently cycled at the given pressure levels. The aged cells are analyzed for capacity fade and impedance rise at the cell and electrode level. The effect of pressure distribution that may occur in large-format cells or in a battery pack is simulated using parallel connected cells. The results show that the kinetic and mass transport resistance increases with pressure in a fresh cell. An optimum pressure around 1.3 MPa is shown to be beneficial to reduce cyclable-lithium loss during cycling. The minor active mass losses observed in the electrodes are independent of the ageing pressure, whereas ageing pressure affects the charge transfer resistance of both NMC and graphite electrodes and the ohmic resistance of the cell. Pressure distribution induces current distribution but the enhanced current throughput at lower pressures cell does not accelerate its ageing. Conclusions from this work can explain some of the discrepancies in non-uniform ageing reported in the literature and indicate coupling between electrochemistry and mechanics.

For the promising Li-O-2 battery to be commercialized, further understanding of its constituents is needed. This study deals with the role of O-2 in Li-O-2 batteries, both its influence on electrochemical performance and its solubility in lithium-salt-containing dimethyl sulfoxide (DMSO) electrolytes. Experimentally, the electrochemical performance was evaluated using cylindrical ultramicroelectrodes. Two independent techniques, using a mass spectrometer and an optical sensor, were used to evaluate the O-2 solubility, expressed as Henry's constant. Furthermore, the ionic conductivity, dynamic viscosity, and density were also measured. Density functional theory calculations were made of the interaction energy between O-2 and the different species in the electrolytes. When varying O-2 partial pressure, the current was larger at high pressures confirming that the O-2 concentration is of key importance when studying the kinetics of this system. Compared with neat DMSO, the O-2 solubility increased with addition of LiTFSI and decreased with addition of LiClO4, indicating that the salt influences the solubility. This solubility trend is best explained in terms of apparent molar volume and interaction energy between O-2 and the salt anion. In conclusion, this study shows the importance of O-2 concentration, not just its partial pressure, and that the choice of Li salt can make this concentration increase or decrease.

Lignin-based carbon fibers (LCFs) from the renewable resource softwood kraft lignin were synthesized via oxidative thermostabilization of pure melt-spun lignin and carbonization at different temperatures from 1000 degrees C to 1700 degrees C. The resulting LCFs were characterized by tensile testing, scanning electron microscopy (SEM), X-ray diffraction (XRD) and confocal Raman spectroscopy. The microstructure is mainly amorphous carbon with some nanocrystalline domains. The strength and stiffness are inversely proportional to the carbonization temperature, while the LCFs carbonized at 1000 degrees C exhibit a strength of 628 MPa and a stiffness of 37 GPa. Furthermore, the application potential of LCFs was evaluated as negative electrodes in a lithium-ion battery (LIB) by electrochemical cycling at different current rates in a half-cell setup. The capacity drops with the carbonization temperature and the LCFs carbonized at 1000 degrees C have a capacity of 335 mAh g(-1). All LCFs showed good cycling stability. Because of the mechanical integrity and conductivity of the LCFs, there is no need to apply current collectors, conductive additives or binders. The advantage is an increased gravimetric energy density compared to graphite, which is the most common negative electrode material. LCFs show a promising multifunctional behavior, including good mechanical integrity, conductivity and an ability to intercalate lithium for LIBs.

Beyond conductivity and viscosity, little is often known about the mass transport properties of next generation lithium battery electrolytes, thus, making performance estimation uncertain when concentration gradients are present, as conductivity only describes performance in the absence of these gradients. This study experimentally measured the diffusion resistivity, originating from voltage loss due to a concentration gradient, together with the ohmic resistivity, obtained from ionic conductivity measurements, hence, evaluating electrolytes both with and without the presence of concentration gradients. Under galvanostatic conditions, the concentration gradients, of all electrolytes examined, developed quickly and the diffusion resistivity rapidly dominated the ohmic resistivity. The electrolytes investigated consisted of lithium salt in: room temperature ionic liquids (RTIL), RTIL mixed organic carbonates, dimethyl sulfoxide (DMSO), and a conventional Li-ion battery electrolyte. At steady state the RTIL electrolytes displayed a diffusion resistivity similar to 20 times greater than the ohmic resistivity. The DMSO-based electrolyte showed mass transport properties similar to the conventional Li-ion battery electrolyte. In conclusion, the results presented in this study show that the diffusion polarization must be considered in applications where high energy and power density are desired.

Carboxylated cellulose nanofibers (CNF) prepared using the TEMPO-route are good binders of electrode components in flexible lithium-ion batteries (LIB). However, the different parameters employed for the defibrillation of CNF such as charge density and degree of homogenization affect its properties when used as binder. This work presents a systematic study of CNF prepared with different surface charge densities and varying degrees of homogenization and their performance as binder for flexible LiFePO4 electrodes. The results show that the CNF with high charge density had shorter fiber lengths compared with those of CNF with low charge density, as observed with atomic force microscopy. Also, CNF processed with a large number of passes in the homogenizer showed a better fiber dispersibility, as observed from rheological measurements. The electrodes fabricated with highly charged CNF exhibited the best mechanical and electrochemical properties. The CNF at the highest charge density (ISSO mu mol g(-1)) and lowest degree of homogenization (3 + 3 passes in the homogenizer) achieved the overall best performance, including a high Young's modulus of approximately 311 MPa and a good rate capability with a stable specific capacity of 116 mAh g(-1) even up to 1 C. This work allows a better understanding of the influence of the processing parameters of CNF on their performance as binder for flexible electrodes. The results also contribute to the understanding of the optimal processing parameters of CNF to fabricate other materials, e.g., membranes or separators.

At electric vehicle fast-charging stations, it is generally recommended to avoid charging beyond similar to 80% State-of-Charge (SOC) since topping-off to full capacity disproportionately increases the charging time. This necessitates studying its long-term impact compared to slower rate charging to full capacity typical of home or residential charging. Here we present the long-term ageing effects on commercial 18650 NMC-LMO/graphite cell cycled between 2.6-4.2 V at three different charging protocols: 1.5 C-rate fast-partial charging ( to 82.5% SOC), 0.5 C-rate slow standard charging without or with a constant-voltage step (to 93% or 100% SOC). Quantitative discharge-curve and postmortem analyses are used to evaluate ageing. The results show that ageing rate increases in the order: fast-partial charging < standard charging < standard charging with constant-voltage period, indicating that higher SOC-range near full capacity is more detrimental to battery life than fast-charging. The capacity fade is totally dominated by cyclable-lithium loss. The similar to 8% NMC-LMO active material loss has negligible impact on the cell capacity fade due to the electrodes excess material in the fresh cell and its moderate loss rate with ageing compared to the cyclable-lithium. Similar ageing modes in terms of capacity fade and impedance rise are found irrespective of the charging protocol.

This study evaluates the use of energy storage technologies coupled to renewable energy sources in rural electrification as a way to address the energy access challenge. Characteristic energy demanding applications will differently affect the operating conditions for off-grid renewable energy systems. This paper discusses and evaluates simulated photovoltaic power output and battery state of charge profiles, using estimated climate data and electricity load profiles for the Altiplanic highland location of Patacamaya in Bolivia to determine the loss of load probability as optimization parameter. Simulations are performed for three rural applications: household, school, and health center. Increase in battery size prevents risk of electricity blackouts while increasing the energy reliability of the system. Moreover, increase of PV module size leads to energy excess conditions for the system reducing its efficiency. The results obtained here are important for the application of off-grid PV-battery systems design in rural electrification projects, as an efficient and reliable source of electricity.

In this paper, the harmonic content of the battery current in a commercial hybrid vehicle (bus) is measured and analyzed for a number of different driving situations. It is found that the most prominent harmonic reaches peak magnitudes that can be higher than 10% of the maximum dc-current level with a maximum frequency less than 150 Hz. Further, it is found that this harmonic can be approximated using a fitted, simple analytical expression with reasonable agreement for all driving situations considered.