Optimization studies of carbon additives to negative active material for the purpose of extending the life of VRLA batteries in high-rate partial-state-of-charge operation

The negative plates of lead-acid batteries subjected to partial-state-of-charge (PSOC) operation fail because of the development of an electrically inert film of lead sulfate on their surfaces. It has been found that carbon additives to the negative active material can significantly increase their cycle life in this type of operation. In this paper we show that various types of carbon, including graphite, carbon black eliminate the surface development of lead sulfate and that, in their presence, the lead sulfate becomes homogeneously distributed throughout the active material. Examination of active material by energy dispersive spectroscopy after extensive cycling shows that lead formed during charge of lead sulfate preferentially deposits on the carbon particles that have been embedded in the active material. Electrochemical studies have been carried out on a number of types of carbon additives having a wide range of properties. These included flake, expanded and synthetic graphite, isotropically graphitized carbon, carbon black and activated carbon. We have investigated their effect on the resistivity and surface areas of the negative active material and also on such electrochemical properties as active material utilization and cycle life. Most of the carbon additives increase the utilization of the active material and impressive increases in cycle life have been obtained with over 6000 capacity turnovers having been achieved. However, at this time, we have not been able to correlate either the type or the properties of the carbon with capacity or cycle life. Further work is needed in this area. The increases that have been achieved in cycle life provide evidence that the lead-acid battery is a viable low cost option for hybrid-electric vehicle use.     

Optimization formula of lead-carbon negative electrode by orthogonal experimental design

本工作采用正交实验方法研究了石墨、活性炭、炭黑、硫酸钡与木素在铅炭负极中的含量变化对电池性能的影响,其中石墨和活性炭总含量保持1.5%,改变石墨活性炭的比例,炭黑含量取0~0.5%,硫酸钡含量取0.6%~1.2%,木素含量取0.15%~0.35%。通过容量测试、低温性能测试与循环性能测试对电池进行性能评估。实验结果表明,炭黑与木素对电池低温性能影响比较大,不含炭黑与木素含量为0.35%分别有最佳的低温性能。炭黑、石墨与活性炭的比例对电池循环性能影响比较大,添加炭黑对循环寿命不利,活性炭与石墨按1：1添加时部分荷电态循环性能最好。     

Study of the influence of carbon on the negative lead-acid battery electrodes

Experiments were made with negative lead-acid battery electrodes doped with different concentrations of powdered carbon. It turned out that the rate of formation decreased with the rising concentration of carbon added into the active material. During accelerated cycling in the PSoC regime, the cycle life showed a maximum at a concentration of carbon near 1%, whereas at lower or higher concentrations the cycle life was profoundly lower. A marked increase of the active mass resistance with the cycle number was recorded at carbon concentrations above 2%. Orientation experiments showed that compression of the lead-acid laboratory cells caused an increase of the cycle life of the negative electrode in the studied regime.     

Influence of expander components on the processes at the negative plates of lead-acid cells on high-rate partial-state-of-charge cycling. Part II. Effect of carbon additives on the processes of charge and discharge of negative plates

Lead-acid batteries operated in the high-rate partial-state-of-charge (HRPSoC) duty rapidly lose capacity on cycling, because of sulfation of the negative plates. As the battery operates from a partially discharged state, the small PbSO₄ crystals dissolve and precipitate onto the bigger crystals. The latter have low solubility and hence PbSO₄ accumulates progressively in the negative plates causing capacity loss. In order to suppress this process, the rate of the charge process should be increased.In a previous publication of ours we have established that reduction of Pb²⁺ ions to Pb may proceed on the surface of both Pb and carbon black particles. Hence, the reversibility of the charge-discharge processes improves, which leads to improved cycle life performance of the batteries in the HRPSoC mode. However, not all carbon forms accelerate the charge processes. The present paper discusses the electrochemical properties of two groups of carbon blacks: Printex and active carbons. The influence of Vaniseprse A and BaSO₄ (the other two components of the expander added to the negative plates) on the reversibility of the charge-discharge processes on the negative plates is also considered. It has been established that lignosulfonates are adsorbed onto the lead surface and retard charging of the battery. BaSO₄ has the opposite effect, which improves the reversibility of the processes on cycling and hence prolongs battery life in the HRPSoC duty. It has been established that the cycle life of lead-acid cells depends on the type of carbon black or active carbon added to the negative plates. When the carbon particles are of nano-sizes (<180 nm), the HRPSoC cycle life is between 10,000 and 20,000 cycles. Lignosulfonates suppress this beneficial effect of carbon black and activated carbon additives to about 10,000 cycles. Cells with active carbons have the longest cycle life when they contain also BaSO₄ but no lignosulfonate. A summary of the effects of the three expander components on the elementary processes during charge of negative lead-acid battery plates is presented at the end of the paper.     

Lead-acid batteries for partial-state-of-charge applications

2 V/40 Ah valve-regulated lead-acid (VRLA) cells have been constructed with negative plates employing carbon black as well as an admixture of carbon black + fumed silica as additives in negative active material for partial-state-of-charge (PSoC) applications. Electrical performance of such cells is compared with conventional 2 V/40 Ah VRLA cells for PSoC operation. Active material utilization has been found to be higher for carbon-black + fumed-silica mixed negative plates while formation is faster for cells with carbon-black mixed negative plates. Both faradaic efficiency and percentage capacity delivered have been found to be higher for cells with carbon-black + fumed-silica mixed negative plates. However, a high self-discharge rate is observed for cells with carbon-black + fumed-silica mixed negative plates.     

Advanced management strategies for remote-area power-supply systems

An operating strategy based on partial-state-of-charge (PSoC) operation has been developed for a remote-area power-supply (RAPS) system in Peru. The facility will power an entire village and comprises a photovoltaic array, a bank of gel valve-regulated lead-acid (VRLA) batteries, a diesel generator, and a sophisticated control system. The PSoC schedule involves operation below a full state-of-charge (SoC) for 28 days, followed by an equalization charge. The schedule has been evaluated by operating a 24 V battery bank under simulated RAPS conditions in the laboratory. It is found that operation between 58 and 83% SoC causes the negative-plate potentials to move to significantly more negative values during charging as the PSoC duty progresses. This behaviour is undesirable, because it can lead to the activation of a preset limit and a subsequent reduction in system efficiency. Lowering the PSoC window to 47–72% SoC or 40–65% SoC during the 28-day cycle is found to stabilize the negative-plate potentials. The behaviour of the negative plates in gel batteries is very similar to that observed for absorptive glass mat (AGM) designs of VRLA batteries operated in hybrid electric vehicles.     

Joint-use of activated carbon and carbon black to enhance catalytic stability during chemical looping methane decomposition process

Chemical-looping methane decomposition using activated carbon as a catalyst has been considered a potentially promising approach for high-purity H₂ production with low cost and low CO₂ emission. However, activated carbon is known to deactivate fast despite its high initial catalytic activity. Oppositely, carbon black has shown stable catalytic methane decomposition that even increases slowly with time of reaction. Considering these two different activity trends, activated carbon and carbon black are jointly used to prepare catalysts and then test for the decomposition of the methane via chemical looping in this study that aimed to examine catalyst and reaction properties which may combine the high initial activity of activated carbon with the steady-and-increasing activity of carbon black. These mixed catalysts are examined using X-ray diffraction analysis (XRD), scanning electron microscopy and energy dispersive spectroscopy (SEM/EDS), Brunauer-Emmett-Teller (BET) and high-resolution transmission electron microscopy (HRTEM) before and after reaction testing to reveal chemical and physical constituents which contributed to their reactivities, and the mechanism of long catalytic activity has been discussed. The results point to insights and potential directions for modifying carbonaceous catalysts for chemical looping thermo-catalytic decomposition of methane.     

Effect of carbon types on the electrochemical properties of negative electrodes for Li-ion capacitors

The electrochemical properties of various carbon materials (graphite and hard carbon) have been investigated for use as a negative electrode for Li-ion capacitors. The rate capabilities of the carbon electrodes are tested up to 40C using both half and full cell configurations. It is found that the capacitance of the hard carbon material at 40C could be maintained up to 70% of that at 0.2C in full cells with an activated carbon positive electrode, which is the best among the carbon materials. The cycle performance of the hard carbon demonstrates that the initial capacitance is retained up to 83% even after 10,000 cycles. The outperforming results could be ascribed to the microstructure of hard carbon, which indicates that hard carbon is more suitable as negative electrode materials for high power energy storage applications.     

The use of activated carbon and graphite for the development of lead-acid batteries for hybrid vehicle applications

Future vehicle applications require the development of reliable and long life batteries operating under high-rate partial-state-of-charge (HRPSoC) working conditions. This paper updates work carried out to develop spiral wound valve-regulated batteries for vehicles with different hybridisation degrees, ranging from stop-start to mild hybrid applications.In order to develop a battery that can withstand the hard operating conditions that the work at High Rate Partial-State-of-Charge (HRPSoC) implies, it is necessary to modify the negative AM formulation by using special, additives like carbon and graphite that reduce lead sulphate accumulation during HRPSoC cycling within in the negative plate. Several batches of negative active material (NAM) with the addition of graphites of different types, as well as combinations of graphite and activated carbons, have been made on 6 V 24 Ah Spiral wound modules. Electrical results show a dramatic increase of the charge acceptance at different SoC's that for some combinations approach 200%. On the other hand, on cycle life according to EUCAR Power Assist cycling, values in the range 200,000-220,000 cycles have been obtain in most part of the batch. This represents a capacity turnover of 5000-5500 times the nominal capacity.The paper is divided into three parts. The first part is devoted to identify the cause of failure of the negative plate on Power Assist Cycle Life, that turned to be the development of high amounts of lead sulphate and its accumulation on the surface of the plate. The second part covers the addition of carbon and graphite of low SSA to NAM and finally the third part is dedicated to the test of additions of medium/high SSA carbon to NAM with the specific objective of trying to implement the supercapacitor effect inside the battery.     

Electrochemical performance of different carbon fuels on a hybrid direct carbon fuel cell

In this work, three processed carbon fuels including activated carbon, carbon black and graphite have been employed to investigate influence of the chemical and physical properties of carbon on the HDCFC performance in different anode atmospheres at 650–800 °C. The results reveal that the electrochemical activity is strongly dependent on crystalline structure, thermal stability and textural properties of carbon fuels. The activated carbon samples demonstrate a better performance with a peak power density of 326 mW cm^?2 in CO₂ at 750 °C, compared to 147 and 59 mW cm^?2 with carbon black and graphite samples, respectively. Compared to the ohmic resistance, the polarization resistance plays a more dominated role in the cell performance. When replacing N₂ by CO₂ purge gas, the power density is the strongly temperature dependent due to the Boudouard reaction.     

Enhancement of oxygen reduction activity with addition of carbon support for non-precious metal nitrogen doped carbon catalyst

An improved synthesis scheme of non-precious metal N-doped carbon catalysts for oxygen reduction reaction is reported. The non-precious metal N-doped carbon catalysts were prepared by pyrolysis of the mixture (phenol resin, Ketjen black carbon support and cobalt phenanthroline complex). The drastic improvement of distribution state of Ketjen black supported non-precious metal N-doped carbon catalysts was observed by means of transmission electron microscopy (TEM). In addition, the non-precious metal N-doped carbon catalyst synthesized with Ketjen black carbon support showed much higher oxygen reduction reaction (ORR) activity relative to unsupported non-precious metal N-doped carbon catalyst in O₂-saturated 0.5 mol l⁻¹ H₂SO₄ at 35 °C. Moreover, the highest ORR activity was obtained with addition of optimum amount of Ketjen black carbon support was thirtyfold compared to unsupported non-precious metal N-doped carbon catalyst at 0.7 V. Similarly, the performance of a polymer electrolyte fuel cell (PEFC) using the non-precious metal N-doped carbon catalyst as the cathode electrode catalyst was obviously better than that of the non-precious metal N-doped carbon catalyst before optimization. Microstructure, specific surface area and surface composition of the non-precious metal N-doped carbon catalysts were analyzed by XRD, XPS and BET measurement with nitrogen physisorption, respectively.     

Chemical looping hydrogen production using activated carbon and carbon black as multi-function carriers

The application of a chemical looping process for methane thermo-catalytic decomposition using activated carbon (AC) as a catalyst has been recognized as an advanced process for continuous high-purity H₂ production in the carbon constrained world due to its low CO₂ formation. AC is able to provide reasonable kinetics, however, it suffers from fast deactivation. Deep regeneration of spent AC catalyst using steam is able to eliminate catalytic deactivation, and this process sacrifices part of the catalyst. The catalytic performance of AC and carbon black (CB) catalysts exhibit opposite deactivation behavior with time. AC provides a better activity, but it deactivates quickly. Though the catalytic activity of CB is low, its activity not only can be maintained, but also shows an increase during the test. Our approach for AC modification was inspired by analyzing the factors that lead to the different performance. Results indicate that the catalytic performance of AC and CB exhibit opposite deactivation behavior with time, and the deposited carbon on their surfaces are in different shape, orientation, and chemical structure. The outward growing cone-like graphene layers and tubular-shaped nanostructures are key factors that help maintain the catalyst's porosity and activity; and the cause of different deposit carbon may be attributed to the irregular, cross-linking graphene layers of AC and the spherical bent graphene layers of CB.     

Heat and mass transfer in steam desorption of an activated carbon adsorber

Activated carbon columns are often used for purification of indoor air which is contaminated with solvent vapours. The regeneration of the used activated carbon is practically conducted with steam, which is followed with a drying/cooling process to dry and to cool down the column, as cold and dry carbon is essential for the followed adsorption cycle. A Double-Two-Mechanism-Model was proposed to describe the dynamic steaming process which has been a less understood but an important step in the adsorption cycles. Experiments in a pilot-scale adsorber showed strong evidence of these mechanisms which will lead to a better understanding of steam regeneration process.     

Study on preparation and electrochemical properties of biomass-derived spherical activated carbon

以生物质风化煤系腐殖酸（LHA）为炭质前驱体,通过溶剂蒸发和KOH活化方法制备了球形活性炭。使用扫描电子显微镜（SEM）、N2物理吸脱附仪等手段对球形活性炭形貌和孔道结构进行了表征;还将活性炭组装成扣式电容器,进行了充放电容量、循环伏安特性和交流阻抗行为等电化学性能测试。结果表明：所制备的球形活性炭具有良好的球形度,通过少量碱活化后球形活性炭BET表面积为2034 m2/g、总孔容为1.24 cm3/g、平均孔径为2.38 nm。同时,以球形活性炭作为电极材料应用于水系超级电容器后显示了优异的电化学性能,比电容可达到319 F/g,在进行10000次充放电后,比电容保持率为98.9%。此外,球形活性炭相比于颗粒活性炭具有更好的导电性,也展现了更加优异的倍率性能和循环性能。因此说明LHA基球形活性炭是一种有潜在优势的超级电容器材料。     

Modified carbon materials for high-rate EDLCs application

Porous carbon materials, such as activated carbon and activated carbon aerogel, were modified chemically by using a surfactant sodium oleate to improve their specific capacity for high-rate electrochemical double layer capacitors (EDLCs) application. Main impacting factors have been examined for surface modification of activated carbon. Specific capacity can be improved significantly by the surface modification. The enhancement in specific capacity is mainly attributable to improvement in wettability of carbon materials, resulting in a higher usable surface area and a smaller internal resistance. The effects from surface modification become more marked at higher discharge rates, and a much higher energy density can be achieved for the modified carbon materials. In addition, the modified carbon materials possess comparable cycle stability to the original carbon.     

Influence of bismuth on the charging ability of negative plates in lead–acid batteries

To examine the influence of bismuth on the charging ability of negative plates in lead–acid batteries, plates are made from three types of oxides: (i) leady oxide of high quality which contains virtually no bismuth (termed ‘control oxide’); (ii) control oxide in which bismuth oxide is blended at bismuth levels from 0.01 to 0.12 wt.%; (iii) leady oxide produced from Pasminco VRLA Refined™ lead (0.05–0.06 wt.%Bi). An experimental tool—the ‘conversion indicator’—is developed to assess the charging ability of the test negative plates when cycling under either zero percent state-of-charge (SoC)/full-charge or partial state-of-charge (PSoC) duty. Although the conversion indicator is not the true charging efficiency, the two parameters have a close relationship, namely, the higher the conversion indicator, the greater the charging efficiency. Little difference is found in the charging ability, irrespective of bismuth content and discharge rate, when the plates are subjected to zero percent SoC/full-charge duty; the conversion indicator lies in the range 81–84%. By contrast, there is a marked difference when the negative plates are subjected to PSoC duty, i.e. consecutive cycling through 90–60, 70–40, 80–40 and 90–40% SoC windows. Up to 0.06 wt.%Bi improves the charging ability, especially with a low and narrow PSoC window (40–70% SoC) of the type that will be experienced in 42 V powernet automobile and hybrid electric duties. To maximize this beneficial effect, bismuth must be distributed uniformly in the plates. This is best achieved by using VRLA Refined™ lead for oxide production.     

Surface modification of carbon fuels for direct carbon fuel cells

The direct carbon fuel cell (DCFC) is a promising power-generation device that has much higher efficiency (80%) and less emissions than conventional coal-fired power plants. Two commercial carbons (activated carbon and carbon black) pre-treated with HNO₃, HCl or air plasma are tested in a DCFC. The correlation between the surface properties and electrochemical performance of the carbon fuels is explored. The HNO₃-treated carbon fuels have the highest electrochemical reactivity in the DCFC due to the largest degree of surface oxygen functional groups. The overall effect on changing the electrochemical reactivity of carbon fuels is in the order HNO₃ > air plasma ≈ HCl. Product gas analysis indicates that complete oxidation of carbon to CO₂ can be achieved at 600–700 °C.     

Comparison of multiwalled carbon nanotubes and carbon black as percolative paths in aqueous-based natural graphite negative electrodes with high-rate capability for lithium-ion batteries

The effects of multiwalled carbon nanotubes (MWNTs) and carbon black (CB) as conducting additives on the rate capability of natural graphite negative electrodes in lithium-ion (Li-ion) batteries is investigated within concentration ranges where no degradation of anode capacity is observed. MWNT or CB solutions prepared with Nafion in an 80:20 volume mixture of water:1-propanol are incorporated into graphite precursor suspensions consisting of graphite particulates, carboxymethyl cellulose, and styrene butadiene rubber prepared in an aqueous medium. While negative electrodes with MWNTs demonstrate much better rate behaviour than those without MWNTs at a high C-rate, the rate capability of negative electrodes with MWNTs is not much different from that with CB. The reason for this similar behaviour is investigated with respect to the structural changes and aspect ratio of MWNTs, as well as the density difference between MWNTs and carbon black. Scanning electron microscopy images and Raman spectra for the dispersed MWNTs indicate that MWNTs are significantly damaged and shortened during dispersion, which reduces their electrical conductivity and increases their percolation threshold. This damage negatively affects the rate capability of graphite-nanotube composite electrodes.     

Electrochemical double layer capacitor and lithium-ion capacitor based on carbon black

In this paper we report the physical investigation and the electrochemical performance of the carbon black SC3 from Cabot Corporation. The SC3 carbon black was investigated in terms of BET surface area, pore size distribution, resistivity and morphology. Composite electrodes containing SC3 as active material were prepared and used for the realization of electrochemical double layer capacitor (EDLC) and lithium-ion capacitor (LIC). In EDLC, at 5 mA cm⁻² charge-discharge currents, the carbon black displays a specific capacity of 40 mAh g⁻¹ and a specific capacitance of 115 F g⁻¹. It also displays a very good cycling stability for over 50,000 cycles and excellent performance retention at currents up to 50 mA cm⁻². The performance retention at high currents outstandingly differentiates this carbon black from a few commercially available EDLC-grade activated carbons. Because of the high specific capacity of SC3, the carbon black electrodes were also used in combination with LiFePO₄ electrodes in LIC. The results of this study indicate that SC3 carbon black is an interesting carbonaceous candidate for the realization of LIC.     

A comparative study of the electrochemical hydrogen storage properties of activated carbon and well-aligned carbon nanotubes mixed with copper

We studied the electrochemical hydrogen storage properties of activated carbon (AC) material mixed with copper. The discharge capacity of AC–Cu electrode which reached 510 mAh/g after 384 cycles, is much higher than that of the CNT–Cu electrodes. The plateau of discharge potential for AC–Cu electrode was very long and flat and reached −0.88 V vs. Hg/HgO, which was far from the potential of copper oxidation. The discharge plateau gradually appeared and continually lengthened with the increase of cycle number. Cyclic voltammetric experiments showed that the adsorption and desorption of hydrogen occurred on the surface of activated carbon and the active site increased with the increase of cycle number. The mechanism for electrochemical storage of hydrogen in AC–Cu electrode may be mainly physisorption.