THE HYBRID VRLA BATTERIES CONCEPTS

The purpose of this article is to introduce basic concepts regarding VRLA Hybrid AGM-GEL battery technology. For an equivalent capacity, it is possible to state that a GEL battery is physically larger than an AGM battery because it requires more space between the plates to accommodate the GEL, which translates into a larger volume or a decrease in capacity.

Francisco Franco is an engineer with 48 years of experience in the design, production, and manufacturing processes of industrial lead-acid and alkaline batteries. He has worked at the country’s largest companies, holding executive and managerial positions directly related to engineering, quality, and production. Currently, he serves as a technical consultant for projects, engineering, processes, and the production of industrial traction and stationary batteries.

1. INTRODUCTION

The purpose of this article is to introduce basic concepts regarding VRLA Hybrid AGM-GEL battery technology.

For an equivalent capacity, it is possible to state that a GEL battery is physically larger than an AGM battery because it requires more space between the plates to accommodate the GEL, which translates into a larger volume or a decrease in capacity.

2. CHARACTERISTICS OF EACH TECHNOLOGY

AGM Batteries have low internal resistance due to their construction, which incorporates low-resistance electrical separators. This makes them ideal for applications requiring high-intensity current in short periods, such as UPS systems, where runtime is typically less than an hour.

GEL Batteries, on the other hand, excel in cycling performance and are preferred for applications requiring a significant number of cycles. However, the separator materials (such as phenolic resin, PVC, or microporous polymer) increase internal resistance, limiting their use to medium and long-duration discharge applications. As a result, they are not typically designed for high-intensity discharge applications.

3. MARKET OPTIONS

Currently, the market offers the following battery types:

AGM (Original Concept)

GEL (Original Concept)

AGM/GEL Hybrid: A true hybrid battery concept, where AGM separators are used, and the filling electrolyte is gel, which penetrates the separator’s pores. Colloidal silica is commonly used in the formulation of the gel electrolyte.

Note: Another market variation exists, which is a modified hybrid system. In this case, the battery is essentially AGM, but at the end of the manufacturing process, a small amount of gel electrolyte is added over the plates, covering the entire cell. This encapsulation provides a greater volume of acid, improves thermal dissipation, and reduces dry-out effects.

VRLA batteries are produced using two distinct technologies:

Absorbed Glass Mat (AGM) – Known for low internal resistance.

GEL – Offers better thermal stability and superior performance in cycling applications.

By combining these technologies, AGM-GEL hybrid batteries incorporate gel electrolytes with AGM separators, allowing manufacturers to combine the advantages of both technologies.

4. THE HYBRID PRODUCT

The table below illustrates how the combination of both technologies results in a hybrid product with enhanced performance characteristics.

One of the main advantages of AGM-GEL batteries is the extra water content, which results in a longer lifespan.

DRY-OUT, ONE OF THE PRIMARY CAUSES OF FAILURE, CAN BE MINIMIZED WITH GOOD RECOMBINATION EFFICIENCY AND IMPROVED THERMAL RESISTANCE.

Another critical issue is positive grid corrosion, which can also be mitigated by reducing the effects of high temperatures. This is due to the superior thermal dissipation in AGM-GEL batteries.

Regarding the capacity of an AGM-GEL battery: silica does not participate in electrochemical reactions. Thus, it occupies some space within the sulfuric acid, leading to an expected reduction in capacity. Tests must be conducted to achieve gelation with the smallest possible amount of silica, minimizing the reduction in capacity.

DETAILING THE CONCEPT

The concept of the Hybrid AGM-GEL VRLA battery is to merge the advantages of both technologies, resulting in a “premium” battery. As previously mentioned, AGM batteries have lower internal resistance, making them better suited for high discharge rates, while GEL batteries excel in cycling performance. In regions or locations with reliable infrastructure, such cycling performance may not be necessary, and AGM batteries with decent cycle life are often sufficient for certain applications. However, in cases where the infrastructure is unreliable or insecure, a battery with enhanced charge and discharge cycle performance becomes essential. The Hybrid AGM-GEL VRLA battery combines the cycle capacity of a GEL battery without increasing the cell’s volume. The extra thermal dissipation capacity, due to the water content in the colloidal gel, makes these batteries more resistant to high-temperature environments or those experiencing adverse conditions for extended periods.

An AGM separator includes channels that enable the oxygen cycle, and the gel forms fissures that allow oxygen to reach the negative plate and react to prevent hydrogen evolution, thus retaining water. The most suitable gel for constructing a Hybrid VRLA battery would be colloidal silica, as it is simpler and more readily available. As mentioned, the battery’s capacity will be reduced due to the presence of silica in the electrolyte. For this reason, a limited amount of gel should be used in the electrolyte preparation. An optimal concentration must be determined through practical experiments, as it will depend on each product’s design. For example, adding 5% gel could reduce the battery’s capacity by approximately 7%, which would be unacceptable for any application. Therefore, creating prototypes and conducting tests is crucial.

Colloidal gel should be mixed with acid, and filling must be done using a vacuum process to ensure all AGM separator pores and active material are permeated.

The volume of gel electrolyte within the cell should remain above the straps. Filling is relatively straightforward, as colloidal silica and sulfuric acid have similar densities and low viscosity.

It is recommended that the gel electrolyte’s temperature be below 10°C to better control the cell’s temperature during filling.

Gelification of the electrolyte will occur at the end of formation when the acid becomes more concentrated.

The temperature resistance and excellent cycling characteristics directly relate to specific applications, such as photovoltaic systems.

External applications experience temperature fluctuations both seasonally and daily.

The battery’s lifespan follows the well-known Arrhenius equation, indicating that reaction rates depend logarithmically on absolute or thermodynamic temperatures.

Simply put, high temperatures are more damaging than low temperatures are beneficial.

For example, 12 hours at 35°C and 12 hours at 15°C result in a 24-hour average of 25°C. However, the 12-hour temperature excursion at 35°C causes considerable damage

to the battery over time. The Hybrid VRLA battery technology can

mitigate such damage due to its greater heat dissipation capacity. In the scenario above,

the damage to the battery could potentially be reduced by half.

TESTS AND PROTOTYPES

Most factory laboratories can build prototypes and conduct tests using existing AGM batteries from their production line.

To do this, it is enough to provide samples of colloidal gel (Akzo, Cabot, etc.) and experimentally apply the concept to motorcycle or automotive AGM batteries.

This allows for the initial results to verify the necessary adjustments in the gel-acid formulation, filling process, type of separator, etc.

CONCLUSION

Hybrid AGM-GEL VRLA batteries are quite interesting in terms of reliability and longevity of a lead-acid

product. These batteries can be discharged with high current intensity in a short period of time. Their larger amount of electrolyte allows for greater thermal stability and their violability is higher compared to standard AGM batteries.

The effects of stratification are reduced, and all of this results in a longer lifespan.

References

O`Sullivan, Thomas – Hybrid Advanced GEL VRLA Batteries - Power Battery Company

Misra, S.S. et al, Intelec 2003 – Yokohama – Japan , pages 19-20

W.B. Brecht and N.F. O’Leary, “Intelec 881”, Proc. 10th Int. Telecom. Energy Conf., pp. 35-42, 1988.

US Patent – US 2005/0084762 A1 – Apr.21, 2005 – Frank Vaccaro et al.