Mechanism of action of electrochemically active carbons on the processes that take place at the negative plates of lead-acid batteries

It is known that negative plates of lead-acid batteries have low charge acceptance when cycled at high rates and progressively accumulate lead sulphate on high-rate partial-state-of-charge (HRPSoC) operation in hybrid-electric vehicle (HEV) applications. Addition of some carbon or graphite forms to the negative paste mix improves the charge efficiency and slows down sulfation of the negative plates. The present investigation aims to elucidate the contribution of electrochemically active carbon (EAC) additives to the mechanism of the electrochemical reactions of charge of the negative plates. Test cells are assembled with four types of EAC added to the negative paste mix in five different concentrations. Through analysis of the structure of NAM (including specific surface and pore radius measurements) and of the electrochemical parameters of the test cells on HRPSoC cycling, it is established that the electrochemical reaction of charge Pb²⁺ + 2e⁻ → Pb proceeds at 300-400 mV lower over-potentials on negative plates doped with EAC additives as compared to the charge potentials of cells with no carbon additives. Hence, electrochemically active carbons have a highly catalytic effect on the charge reaction and are directly involved in it. Consequently, the reversibility of the charge/discharge processes is improved, which eventually leads to longer battery cycle life. Thus, charging of the negative plates proceeds via a parallel mechanism on the surfaces of both Pb and EAC particles, at a higher rate on the EAC phase. Cells with EAC in NAM have the longest cycle life when their NAM specific surface is up to 4 m² g⁻¹ against 0.5 m² g⁻¹ for the lead surface. The proposed parallel mechanism of charge is verified experimentally on model Pb/EAC/PbSO₄ and Pb/EAC electrodes. During the charge and discharge cycles of the HRPSoC test, the EAC particles are involved in dynamic adsorption/desorption on the lead sulfate and lead surfaces. Another effect of electrochemically active carbons is also evidenced namely that, above a definite concentration, some EAC forms reduce the mean pore radius of NAM. When it diminishes to less than 1.5 μm, access of sulfuric acid into the pores is impeded and PbO forms instead of PbSO₄ in the pores of NAM during discharge. Thus, it may be presumed that electrochemically active carbons change the overall electrochemical reaction of charge and discharge of lead-acid cells when operated under HRPSoC cycling conditions.     

Influence of carbons on the structure of the negative active material of lead-acid batteries and on battery performance

It has been established that addition of carbon additives to the lead negative active material (NAM) of lead-acid batteries increase battery charge acceptance in hybrid electric vehicle mode of operation. The present work studies three types of activated carbons and two types of carbon blacks with the aim to evaluate their efficiency in improving the charge acceptance of lead-acid batteries. It has been established that the size of carbon particles and their affinity to lead are essential. If carbon particles are of nanosizes, they are incorporated into the bulk of the skeleton branches of NAM and may thus increase the latter's ohmic resistance. Their content in NAM should not exceed 0.2-0.5 wt.%. At this loading level, carbon grains are adsorbed only on the surface of NAM contributing to the increase of its specific surface area and thus improving its charge acceptance. When carbon particles are of micron sizes and have high affinity to lead, they are integrated into the skeleton structure of NAM as a structural component and act as super-capacitors, i.e. electric charges are concentrated in them and then the current is distributed along the adjacent branches of the lead skeleton with the lowest ohmic resistance. This eventually improves the charge acceptance of the negative battery plates.     

Consequences of including carbon in the negative plates of Valve-regulated Lead-Acid batteries exposed to high-rate partial-state-of-charge operation

In power-assist hybrid electric vehicles (HEVs) batteries are required to operate from a partial-state-of-charge baseline and to provide, and to accept, charge, for short periods, at very high rates. Under this regime conventional lead-acid batteries accumulate lead sulfate on the negative plate and fail quickly. This failure mode can be effectively countered by the inclusion of certain forms of carbon at greater concentrations than have been used in lead-acid batteries in the past. So effective is this preventive measure that VRLA batteries benefiting from the inclusion of such carbon have been able to substitute for nickel metal hydride batteries in power-assist HEVs with no significant loss of performance. There has been much speculation about the function of the carbon that is providing this remarkable improvement. This paper aims to review the several mechanisms that have been proposed as possibly playing some contributory role.     

VRLA Ultrabattery for high-rate partial-state-of-charge operation

The objective of this study is to produce and test the hybrid valve-regulated Ultrabattery designed specifically for hybrid-electric vehicle duty, i.e., high-rate partial-state-of-charge operation. The Ultrabattery developed by CSIRO Energy Technology is a hybrid energy-storage device, which combines an asymmetric supercapacitor, and a lead-acid battery in one unit cells, taking the best from both technologies without the need for extra, expensive electronic controls. The capacitor will enhance the power and lifespan of the lead-acid battery as it acts as a buffer during high-rate discharging and charging. Consequently, this hybrid technology is able to provide and absorb charge rapidly during vehicle acceleration and braking. The work programme of this study is divided into two main parts, namely, field trial of prototype Ultrabatteries in a Honda Insight HEV and laboratory tests of prototype batteries. In this paper, the performance of prototype Ultrabatteries under different laboratory tests is reported.     

Influence of expander components on the processes at the negative plates of lead-acid cells on high-rate partial-state-of-charge cycling. Part I: Effect of lignosulfonates and BaSO4 on the processes of charge and discharge of negative plates

This study investigates the influence of the organic expander component (Vanisperse A) and of BaSO₄ on the performance of negative lead-acid battery plates on high-rate partial-state-of-charge (HRPSoC) cycling. Batteries operating in the HRPSoC mode should be classified as a separate type of lead-acid batteries. Hence, the additives to the negative plates should differ from the conventional expander composition. It has been established that lignosulfonates are adsorbed onto the lead surface and thus impede the charge processes, which results in impaired reversibility of the charge-discharge processes and hence shorter cycle life on HRPSoC operation, limited by sulfation of the negative plates. BaSO₄ exerts the opposite effect: it improves the reversibility of the processes in the HRPSoC mode and hence prolongs the cycle life of the cells. The most pronounced effect of BaSO₄ has been registered when it is added in concentration of 1.0 wt.% versus the leady oxide (LO) used for paste preparation. It has also been established that BaSO₄ lowers the overpotential of PbSO₄ nucleation. The results of the present investigation indicate that BaSO₄ affects also the crystallization process of Pb during cell charging. Thus, BaSO₄ eventually improves the performance characteristics of lead-acid cells on HRPSoC cycling.     

全钒液流电池用电极及双极板研究进展

全钒氧化还原液流储能电池是一种新型的储能装置,电极及双极板是其关键材料。介绍了全钒液流储能电池的两种电极（金属电极、碳素电极）和三种双极板（金属双极板、碳塑双极板和石墨双极板）以及一体化电极双极板的研究进展。     

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.     

石灰石直接硫化实验研究

进行了在高CO2浓度下石灰石直接硫化实验研究。实验研究了温度、CO2分压、O2分压及SO2浓度对石灰石直接硫化的影响。结果表明,温度对直接硫化反应速率影响很大,随温度的升高直接硫化速率增大,在所试验的时间内,当温度为1173K时,Ca转化率可以达到87%,当转化率≈0时,测得表观活化能为93.5kJ/mol,且表观活化能随Ca转化率的升高而增加;与温度相比,CO2分压对石灰石直接硫化几乎没有影响,增加CO2分压只是延缓石灰石的分解,提高石灰石的分解温度;在5%以下随O2分压的增加,直接硫化速率随之增加,O2分压超过5%以后,O2分压对石灰石直接硫化就没有什么影响;随SO2浓度的增加,直接硫化速率升高。     

High performance silicon carbon composite anode materials for lithium ion batteries

Silicon and silicon containing compounds are attractive anode materials for lithium batteries because of their low electrochemical potential vs. lithium and high theoretical capacities. In this work the relationship between the electrochemical performance of silicon powders and their particle sizes was studied. It is found that the material with nano particle sizes gives the best performance. New silicon/carbon composite anode materials were synthesized and their structures and electrochemical performance were investigated. The results of these studies are reported in this paper.     

Preparation and application of bamboo-like carbon nanotubes in lithium ion batteries

CNTs with bamboo-like structure (B-CNTs) has been prepared via a CVD process with novel carbon precursor. The potential application of B-CNTs as electric conductive additive and anode materials for lithium ion batteries was explored. The EIS spectra prove that it is better electric conductive additive than multiwalled CNTs and traditional carbon black (CB). The electric resistance of the electrode is decreased around 20 Ω when B-CNTs is used instead of CB. The cycle stability is also enhanced. However, the test cell with B-CNTs as anode material shows low reversible capacity of 135 mAh g⁻¹ and very low initial cycle efficiency of 17.3%, which indicates that so-prepared B-CNTs is not suitable for anode material.     

Graphite materials prepared by HTT of unburned carbon from coal combustion fly ashes: Performance as anodes in lithium-ion batteries

The behaviour as the potential negative electrode in lithium-ion batteries of graphite-like materials that were prepared by high temperature treatment of unburned carbon concentrates from coal combustion fly ashes was investigated by galvanostatic cycling. Emphasis was placed on the relation between the structural/morphological and electrochemical characteristics of the materials. In addition, since good electrode capacity retention on cycling is an important requirement for the manufacturing of the lithium-ion batteries, the reversible capacity provided by the materials prepared on prolonged cycling (50 cycles) was studied and the results were compared with those of petroleum-based graphite which is commercialized as anodic material for lithium-ion batteries. The graphite-like materials prepared lead to battery reversible capacities up to ∼310 mA hg⁻¹ after 50 cycles, these values were similar to those of the reference graphite. Moreover, they showed a remarkable stable capacity along cycling and low irreversible capacity. Apparently, both the high degree of crystallinity and the irregular particle shape with no flakes appear to contribute to the good anodic performance in lithium-ion batteries of these materials, thus making feasible their utilization to this end.