Two spherical resorcinol-formaldehyde-based carbons differing in average particle size and external surface area were precursors of two series of modified adsorbents. The modifying agents and modification conditions were chosen to introduce oxygen and/or nitrogen of different content and not to significantly change the porous structure of the samples. The adsorption isotherms of water from the gaseous phase on 16 carbons were the basis for systematic investigations. The differences between them were analyzed in four relative pressure ranges corresponding to subsequent adsorption process stages. The presence of heteroatoms affected the adsorption amount in the low-pressure range, when water molecules directly interact with the oxygen and nitrogen surface groups. However, it also affected the next stage of adsorption: the formation of multimolecular clusters and pore filling. Adsorption in the third range, corresponding to the final plateau, was similar for all the adsorbents and limited by the micropore volume. Differences between the series were revealed in the fourth range (relative pressure close to unity). Adsorption amounts for carbons with more developed external surface area and interparticle porosity were significantly higher, and the isotherms increased more strongly in this part compared to the other series. Qualitative differences between isotherms were also quantified by fitting the data using generalized Barton and Buttersack models. Some of their best-fit parameters were correlated with the content of heteroatoms. Finally, the water adsorption amount for the relative pressure of ca. 0.25 was found as a simple estimate of the heteroatom content in the carbon.

The goal of this work was to predict the dynamic charge acceptance (DCA) for cells using different additives on the negative electrode from the evaluation of small-signal measurements by electrochemical impedance spectroscopy (EIS). Thereby, various operating points were evaluated, such as state of charge (SoC) and prior usage (charge or discharge). The 2V test cells under investigation utilized plates of enhanced flooded 3P2N battery cells (EFB). They contained three positive and two negative electrodes. The latter varied in their additive composition. In total, eight different negative electrodes were investigated, five including specially synthesized amorphous carbon as an additive, two with unknown additive mixes, and one including a commercially available carbon black. The best parameters for predicting the DCA were found within the first semicircle of the negative half-cell spectra measured during a superimposed charging current.

Including a certain amount of carbon in the negative active material is currently the state‐of‐the‐art method to improve the dynamic charge acceptance (DCA) of lead–acid batteries. The DCA is a key parameter of batteries used in microhybrid cars where brake energy recuperation is implemented. To find the optimal carbon additive, it is essential to test the carbon both in short‐term and long‐term tests. This work investigates the long‐term and short‐term DCA of 2 V, 2.5 Ah lead–acid cells and correlates the results with the external surface area of the carbon. Five different carbons with tailored particle size (27–633 nm) and external surface area (7.1–159.3 m2 g−1) are employed as additives in the negative electrodes. The charge acceptance of cells according to the charge acceptance test 2 (SBA), the DCA (EN) test, and the run‐in DCA test (Ford) is increased via an increase in the carbon external surface area. A correlation between the short‐term tests and the first week of the run‐in DCA test is established for the carbon impact. After several weeks of run‐in DCA test, the carbon effect is diminished and only a differentiation between high and low DCA cells is possible.

The active materials of batteries are often tested and selected at the cell level, which prevents comparability to battery-level performance. In the case of a typical lead-acid battery used in a vehicle, the performance after a few months in operation is not necessarily the same as it was during cell-level tests. The goal of this manuscript is to outline the most common reasons for the divergence in test results between cell-level tests and commercial batteries with respect to dynamic charge acceptance (DCA). To do so, this study tested 12 V-70 Ah enhanced flooded batteries (EFB) for their DCA properties. Afterwards, these batteries were dissembled to extract three 2 V test cells, some with a lower number of plates (3P2N and 2P1N). The aim of this investigation was to determine how the DCA of the original battery was affected by changing the plate count and the ratio between the positive active mass, the negative active mass, and the electrolyte by using industrially manufactured cell components - rather than introducing sources of errors by using handmade cells. Both the test batteries and the test cells were subjected to two different constant current discharge tests: the reserve capacity (RC) test and the C20 test. The DCA test according to Japanese Standard SBA S0101 2014 was also conducted. It was particularly important to identify operational conditions and scaling factors (e.g. voltages, currents, and acid densities) on the cell level - for cells with and without lower plate counts. Currently, these are only defined for battery testing according to standard test procedures. Our test cell design, with a reduced, asymmetric set of plates, generated an acid surplus and a PAM surplus, which in turn had major effects on steady-state properties such as the constant current discharge (as the RC test and C20 test showed). DCA battery and cell-level results are not comparable in terms of absolute values, especially for cells with lower plate count. The DCA results for single cells are systematically better for a lower plate count, which may be attributed to excess acid volume.

This study subjected laboratory‐scale test cells to testing methods for dynamic charge acceptance (DCA) that have recently been developed and published for 12 V automotive batteries, particularly enhanced flooded batteries (EFB). The main focus of the study lies on the scaling and geometry effects of different test cell compositions as well as the comparability between the DCA testing methods. The test cells for this study are extracted from industrially manufactured automotive batteries; each cell had either a full set of plates, or a reduced, negative‐limited set of plates. DCA measurements are performed according to SBA S0101:2014, EN 50 342‐6:2015, and a run‐in DCA drive cycle test. The results indicate that DCA generally increases as plate count falls. The correlation between short DCA tests and run‐in DCA under realistic operating conditions is as weak for individual cells as it is known to be for entire batteries. However, DCA stabilized somewhat more quickly in test cells than in batteries.

The subject of this study is test cells extracted from industrially manufactured automotive batteries. Each test cell either had a full set of plates or a reduced, negative-limited set of plates. With these test cells the predictability of the dynamic charge acceptance (DCA) by using electrochemical impedance spectroscopy (EIS) is investigated. Thereby, the DCA was performed according to EN 50342-6:2015 standard. The micro cycling approach was used for the EIS measurements to disregard any influencing factors from previous usage. During the evaluation, Kramers-Kronig (K-K) was used to avoid systematic errors caused by violations of the stationarity, time-invariance or linearity. Furthermore, the analysis of the distribution of relaxation times (DRT) was used to identify a usable equivalent circuit model (ECM) and starting values for the parameter prediction. For all cell types and layouts, the resistance R1, the parameter indicating the size of the first/high-frequency semicircle, is smaller for cells with higher DCA. According to the literature, this semicircle represents the charge transfer reaction, thus confirming that current-enhancing additives may decrease the pore diameter of the negative electrode.

Enhancement of the dynamic charge acceptance (DCA) of advanced lead-acid batteries for micro- and mild-hybrid cars is essential to improve the fuel consumption and CO2 emissions by recuperation of the braking energy. In this work, the effect of carbon surface basicity on the electrochemical activity and the DCA of lead-carbon electrodes is revealed. Five different activated carbons (AC) with different pH values ranging from 9.5 to 11.1 were prepared by ammonia and hydrogen gas treatments. These ACs were used as additives in the negative electrodes of 2 V lead-acid cells. The cyclic voltammetry of the pure carbon as well as lead-carbon (negative) electrodes demonstrates that the hydrogen evolution reaction (HER) activity is increased via higher surface basicity of the ACs. A correlation between the surface basicity of carbon and the DCA can be established in the electrochemical performance. A remarkable impact of carbon pH on the charge currents after the charge history (I-c) as well as final DCA (I-DCA ) is observed. In case of the charge currents after the discharge history (I-d) and during simulated Stop/Start microcycles (I-r), the carbon content in the negative electrodes affects the charge currents. This work demonstrates that the DCA of advanced lead-carbon batteries can be improved by using carbon additives with higher pH in the negative electrodes.

The electrical conductivity of the negative active material in lead-acid batteries has been found to significantly influence the properties of the electrode. Though several publications have addressed this subject, essential information on the conductivity evolution during cycling as well as the influence of additives could yet not be elucidated, even though specific knowledge could support the enhancement of existing lead-acid battery technology. In this study, a novel measurement setup is presented which enables the in-situ and operando measurement of the electrical resistance of bulk electrodes during operation based on the implementation of a four-point probe setup into a laboratory electrode. A comprehensive evaluation of the measurement setup is conducted using the negative electrode of a lead-acid battery as a test material. The experimental results are supported by numerical simulations in order to reflect and include all relevant geometrical and electrical influences from the measurement setup. A direct correlation between active material resistance and conductivity can be established, including the influence of the vertical position of the four-point probes. Finally, the evolution of the discharge capacity, electrical resistance and electrical conductivity of the negative electrode is studied over ten C 5 cycles and correlated to well-known structural developments within the active material.

The surface area of carbon additives has been described as a key property for the enhancement of cycling stability and dynamic charge acceptance (DCA) of negative lead-acid electrodes. However, it is still uncertain if similar performance enhancing effects can be achieved by other inorganic additives of similar structure, or if the electrochemical activity of carbon additives is mandatory for the enhancing effects. In order to elucidate the importance of structure and electrochemical activity of high DCA additives, Stober silica with tailorable particle size and specific external surface area were prepared and incorporated into negative lead-acid electrodes, combined with the addition of carbon black to ensure high cycling stability. The properties and electrical performance of the negative active material were investigated by electrical tests in 2 V laboratory cells and different physical characterization methods. The overall electrochemical activity in terms of hydrogen evolution and double-layer capacitance was not affected by the silica additive and therefore is also independent of the external surface area. In addition, the silica particles led to a slightly reduced, though steady, mass utilization and discharge capacity. Finally the DCA could not be improved by the Stober silica additives, which excludes Stober silica as high DCA additive. In addition, since the DCA performance has not been increased, despite the broad specific surface area range of the additive particles utilized, this study provides a clear indication that the performance enhancement observed with carbon additives also relies on their electrical conductivity.

In vorliegender Dissertation wurde die Wirkweise von Kohlenstoffadditiven auf die verbesserten Ladeeigenschaften negativer Blei-Kohlenstoff Elektroden untersucht, wodurch ein wichtiger Beitrag fur die Weiterentwicklung modernen Blei-Saure Batterien geliefert wurde. Neben der Aufklarung der elektrochemischen Prozesse an Kohlenstoffoberflachen, trug die Arbeit dazu bei, das Verstandnis hinsichtlich der Rolle des Kohlenstoffs zur Erhohung der dynamischen Stromaufnahme zu vertiefen und eine Messmethodik zur Bestimmung der Blei-Affinitat von Graphitpulver zu entwickeln. Die wichtigsten Erkenntnisse dieser drei Themenfelder werden an dieser Stelle noch einmal zusammengefasst. Elektrochemische Untersuchungen an amorphem Kohlenstoff: Um ein grundsatzliches Verstandnis uber die elektrochemische Aktivitat von Kohlenstoff in verdunnter Schwefelsaure zu erhalten, wurden in Kapitel 4 die elektrochemisch ablaufenden Reaktion an der Phasengrenze Kohlenstoff/verdunnte Schwefelsaure bestimmt und diskutiert. Als Messmethode diente eine rotierende Scheibenelektrode aus glasartigem Kohlenstoff. Im Gegensatz zu inerten, metallischen Elektroden, zeigte sich an glasartigem Kohlenstoff ein deutlich komplexeres Verhalten. Die Kohlenstoffoberflache verandert sich in Abhangigkeit des anliegenden Potentials signifikant. Fur Potentiale uber 1,0 V vs. RHE findet eine Oxidation des Kohlenstoffs statt und eine Zersetzung zu CO2. Diese Veranderungen haben wiederum Auswirkungen auf alle anderen elektrochemisch ablaufenden Reaktionen. So wurde durch umfassende zyklovoltammetrische Untersuchungen und mithilfe der differentiellen elektrochemischen Massenspektroskopie erstmals nachgewiesen, dass die Wasserstoffentwicklung durch kurzzeitige Oxidation des Kohlenstoffs signifikant unterdruckt werden kann. Zusatzliche Uberspannungen von uber einem Volt legen den Verdacht nahe, dass die Adsorption von Protonen verhindert wird und die Zersetzung des Elektrolyten erst durch Radikalbildung bei extremen Potentialen unter 2,0 V vs. RHE stattfindet. Zukunftig lasst sich dieser Effekt moglicherweise dazu einsetzen, die Nebenreaktion in Blei-Saure Batterien gezielt zu verringern . Struktur-Eigenschafts-Beziehung zwischen externer Kohlenstoffoberflache und dynamischer Stromaufnahme: Im Anschluss an die elektrochemische Analyse der reinen Kohlenstoffelektrode wurde in Kapitel 5 die Struktur-Eigenschafts-Beziehung von amorphem Kohlenstoff auf die elektrochemische Aktivitat negativer Blei-Kohlenstoff-Elektroden systematisch untersucht. Hierzu wurden Elektroden aus sechs verschiedenen negativen Aktivmasserezepturen hergestellt, welche sich einzig im zugemischten Kohlenstoffadditiv unterschieden. Durch die Verwendung von Kohlenstoffpulver mit gezielt eingestellter spezifischer Oberflache, konnte zum ersten Mal nachgewiesen werden, dass allein die externe Kohlenstoffoberflache relevant fur die Erhohung der Aktivitat der Elektrode ist. Zyklovoltammetrische Messungen zeigten, dass sowohl die Wasserstoffentwicklungsreaktion als auch die Doppelschichtkapazitat durch eine zusatzlich in die Aktivmasse eingebrachte externe Kohlenstoffoberflache verstarkt wird. Erstmals wurde ein linearer Zusammenhang zwischen Doppelschichtkapazitat und dynamischer Stromaufnahme festgestellt, der belegt, dass die Erhohung der dynamischen Stromaufnahme auf einen reinen Oberflacheneffekt zuruckzufuhren ist. Da sowohl der Strom durch die Wasserstoffentwicklung als auch durch die Ladung der Doppelschicht nicht ausreichen, um die erhohte Stromaufnahme zu erkaren, muss davon ausgegangen werden, dass die Bleisulfatreduktion durch den Kohlenstoff katalysiert wird. Erklarungsansatze sind eine vergroserte aktive Oberflache an Bleisulfat aufgrund einer erohten Porositat und die Adsorption des oberflachenaktiven Ligninsulfonats auf der Kohlenstoffoberflache anstelle der des Bleisulfats . Blei-Affinitat von Graphitpulver: Abschliesend wurde in Kapitel 6 eine neue Messmethodik evaluiert, um die Elektrokristallisation von Blei auf Kohlenstoffadditiven zu charakterisieren. Hierfur wurde Bleimetall potentiostatisch aus wassriger Losung auf graphitische Kohlenstoffelektroden abgeschieden und das Kristallwachstum und die Keimzahldichte anhand mikroskopischer Betrachtungen und Modellierung der Strom-Zeit-Transienten analysiert. Es konnte gezeigt werden, dass sich Blei in partikularer Form an definierten Stellen der Graphitkristalle abscheidet und dass die Anzahl an Keimstellen durch die Hohe der Abscheidespannung variiert werden kann. In Anwesenheit von Ligninsulfonat wird das Keimwachstum verlangsamt und die ursprunglich instantane Keimbildung in eine progressive uberfuhrt. Ein fur die Anwendung besonders relevantes Ergebnis lieferte der Vergleich zweier kommerzieller Graphitpulver, welche sowohl im Modellversuch, als auch als Additiv in negativen Bleielektroden eine signifikant unterschiedliche Keimzahldichte aufzeigten. Graphite mit einer hohen Kristallitgrose zeigen eine besonders hohe Bleiaffinitat.

The dynamic charge acceptance (DCA) of modern lead-carbon batteries is one of the key parameters for their future application in micro-and mild-hybrid cars. This work elucidates the impact of the external surface area of carbon additives on the electrochemical performance of lead-carbon electrodes with respect to the DCA. Five specially synthesized amorphous hard carbon powders with different specific external surface area ranging from 13 m(2) g(-1) to 192 m(2) g(-1) were added to the negative active material of laboratory lead-carbon test cells. Results from cyclic voltammetry reveal that the specific external surface area of amorphous carbons exhibits a clear correlation to the electrochemical activity of lead-carbon electrodes. Firstly, an almost linear increase of the activity of the hydrogen evolution reaction with increasing specific external surface area of the carbon additive can be found. Secondly, the specific double-layer capacity of the negative active material is directly linked to the specific external surface area of the additive, as well. Thirdly, a clear correlation to the DCA can be established. In conclusion, a high specific external carbon surface in the negative active material seems to be a key to improve the dynamic charge acceptance of modern lead-carbon batteries. (c) 2017 Elsevier Ltd. All rights reserved.

The improvement of lead-acid batteries with respect to charge acceptance and cycle life in partial state of charge operations due to carbon additives in negative electrodes is state of the art. However, there is still a lack of knowledge about the mechanisms which generate these enhancements. Especially the influence of the physicochemical connection between the carbon additives and the surrounding lead skeleton has not been investigated in much detail yet, but seems to play an important role. Therefore, we developed a new method for characterizing the degree of interaction between lead and carbon additives with focus on graphite materials. By potentiostatic deposition of lead on graphite electrodes, we observe a correlation between the deposition overpotential and the number density of nucleation sites. Chronoamperometry is used to calculate the number density of nucleation sites on graphite electrodes which is in accordance with microscopic observations. We found that expanded graphite exhibits a significantly higher number of nucleation sites than synthetic graphite. Finally, a correlation between this number density of nucleation sites and the integration of the graphite particles in real lead electrodes is observed. Thus, the technique can be used to predict the integration of different graphite particles into the negative active material. (C) 2017 Elsevier Ltd. All rights reserved.

The oxygen reactions in a metal-air battery during discharge (oxygen reduction reaction: ORR) and charge (oxygen evolution reaction: OER) take place on accessible catalyst sites at the gas diffusion electrode (GDE or air-cathode). Typical low-cost catalysts only have function for either the ORR (e.g. MnO2) or the OER (e.g. NiCo2O4). To overcome this issue, either a bifunctional catalyst or a bifunctional GDE is needed. Herein, we focus on the development of such a bifunctional GDE. One key is the use of a carefully tuned binder which allows optimal wetting of the GDE. The combination of carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) can replace conventional binders such as polytetrafluoroethylene (PTFE). Using this binder system, two different approaches to combine the two catalysts γ-MnO2 and NiCo2O4 in one cathode are employed. The first is to mix the ORR catalyst γ-MnO2 and the OER catalyst NiCo2O4 for integration in the same reactive layer. The second is to build a GDE with two reactive layers which are screen printed on top of each other. The reactive layer facing the air side consists of the ORR catalyst γ-MnO2 and the binders CMC/SBR. The second reactive layer, facing the electrolyte, consists of the hydrophilic binder CMC and the OER catalyst NiCo2O4. This double-layer design with two different catalyst species results in a better cycling behavior.

One of the major challenges of metal-air batteries is the impeded oxygen reduction reaction (ORR) during discharge occurring at the gas diffusion electrode (GDE) of the battery. Due to the impeded ORR, high overpotentials emerge and result in a loss of energy efficiency. In order to improve the latter, suitable catalysts have to be employed. Transition metal oxides like manganese oxides (e.g., MnO2, Mn2O3, Mn3O4, Mn5O8, MnOOH) [1,2] are known as good and inexpensive materials for the ORR in alkaline media. A drawback of manganese oxide catalysts is the poor electrical conductivity. Hence, the approach presented in this work aims to enhance the catalytic activity of Mn3O4 and γ–MnO2 by the incorporation of conductive carbon material into the pure manganese oxide. The resulting hybrid catalysts are prepared either by impregnation of Super C 65, Vulcan XC 72, and Kuraray YP 50F via a sol-gel technique employing a MnO2 precursor sol or by direct precipitation of Mn3O4 or γ–MnO2 particles in the presence of the carbon materials mentioned above. Investigations by rotating disc electrode (RDE) show a noticeably higher catalytic activity of the hybrid catalysts than for the pure materials. For verification of the results measured by RDE, screen printed GDEs are prepared and tested in Zn-air full cells.

Stabilization of the Si(553) surface by Au adsorption results in two different atomically defined chain types, one of Au atoms and one of Si. At low temperature these chains develop two- and threefold periodicity, respectively, previously attributed to Peierls instabilities. Here we report evidence from scanning tunneling microscopy that rules out this interpretation. The ×3 superstructure of the Si chains vanishes for low tunneling bias, i.e., close the Fermi level. In addition, the Au chains remain metallic despite their period doubling. Both observations are inconsistent with a Peierls mechanism. On the contrary, our results are in excellent, detailed agreement with the Si(553)-Au ground state predicted by density-functional theory, where the ×2 periodicity of the Au chain is an inherent structural feature and every third Si atom is spin polarized.