Using carbon as a negative additive in VRLA battery

27 Aug 2021

Several types of carbon find various uses in many types of electrochemical power sources. In this article, we focus on implementations of its elemental forms in presently used lead-acid batteries, as well as potential future improvements to their construction that carbon can bring. Unique properties of carbon and a variety of its allotropes allow it to find a use in different parts of lead-acid battery, namely in its negative or positive active mass, a part of the electrode or current collectors.

Additives to negative active mass (NAM), the so-called expanders, were introduced after the World War II. Their three main components were lignosulfonates, barium sulfate, and active carbon. They were used to prevent formation of a passive lead (II) sulfate layer, increase fraction of the active mass involved in electrochemical reactions, and improve current conductivity when the plate is discharged and is composed mainly of the isolating sulfate. Nowadays, many types of carbon are employed in this role, e.g., active carbon, graphite, acetylene black, or carbon black.

The effects of carbon additive are positive. It greatly improves the cycle life of batteries and the charge acceptance during an operation. The significant rise of the durability and the number of battery discharge/charge cycles allow the lead-acid battery to become competitive in relation to other more expensive types of electrochemical power sources, e.g., Ni-Cd cells. Bellow figures shows how adding carbon on the grid can prevent sulfate layer (sulfation) to happen.

Without carbon

With carbon

Now-a-days, carbon finds use in lead-acid batteries mostly as an additive to the negative active mass to improve its electrochemical properties. This additive works mainly in the following three ways: increasing the portion of the active mass where electrochemical reactions of lead can proceed, storing the energy in the electrical double layer as a capacitor, and physically restricting the growth of the large and hard to reduce lead sulfate crystals. The use of carbon gives a real possibility of the lead-acid battery implementation in hybrid vehicles, as it improves cycle life and reduces the negative plate sulfation occurring during the operation in such vehicles. The most effective carbon additives have a large specific surface area, good conductivity, and high lead affinity. In recent years, investigations of carbon nanostructures or composite materials for this role have started. Carbon has also the potential to be the next breakthrough in lead-acid battery technology in the near future. Its use in current collectors can lead to improvement in the weakest point of lead-acid batteries, namely their low specific energy.

Reticulated carbon collectors ensure a lower weight, better active mass utilization, and mechanical support. The improvement of lead-acid batteries parameters can allow them to better compete with newer battery types, like lithium-ion, in different areas (e.g., in energy storage, hybrid vehicles). Carbon can also be used in the battery construction as a capacitor electrode allowing them to achieve a higher power density. Spread of mentioned carbon-based improvements in the lead-acid battery construction can lead to many further years of the economically feasible use of this type of batteries. Despite their long history, lead-acid batteries do not seem to lose their current standing and can even reach new implementations in the future.
EverExceed uses Nano-carbon in their Modular Range VRLA batteries. That's why these batteries are one of the most popular VRLA solutions in the market right now due to their heavy duty performance and long life.

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