With the second implementation phase of Firefly’s Microcell^TMfoam grid technology, dubbed 3D², this new battery architecture achieves its fullest potential.  While the 3D technology is a significant evolutionary improvement over existing lead-acid technology, the ultimate potential of the foam technology is limited by the conventional positive plate, which acts as a “brake” on the cell performance in fast charging and during high-rate/low-temperature discharges.  In addition, the cell lifetime is still limited by the failure modes associated with the positive plate.  Building on the 3D product design, the 3D² product takes advantage of the porous material for both the negative and positive plates, replacing up to 70% of the lead utilized in traditional lead-acid batteries. This delivers a formidable jump in power, energy, and cycle life beyond the 3D product, and approximates the performance of lithium and nickel metal hydride batteries without the high cost and/or potential safety issues. 

Replacing the conventional lead metal-based positive plate with a foam electrode eliminates positive grid growth and corrosion, but it also introduces a different set of challenges.  Various foams used in the positive plate are affected to varying degrees when exposed to extreme overcharge conditions. As a matter of thermodynamics, foams can corrode (oxidize) in the positive potential region similar to the way lead grids corrode; however, electrochemical testing by Firefly has found that foams composed of certain materials react differently in the upper potential ranges commonly experienced during recharge of the positive plate.  Firefly is actively refining and stabilizing foam chemistry as well as increasing the robustness of the foams used in positive plates through manipulation of both foam chemistry and processing, as well as methods of plate preparation.  At present, these chemistries and processes are trade-secret intellectual property, for which Firefly is actively pursuing patent protection.

It should be noted that the Firefly foam positive “grid” and pasted plate are fundamentally different from conventional lead-acid positives.  Conventional positive plates contain lead alloy grids that are over-pasted and subsequently formed.  These conventional positives can fail in a variety of ways that are not likely to occur with a foam-based positive plate.  Lead alloy grids can fail due to grid growth and/or grid corrosion.  Growth can cause failure due to plate-to-top-lead shorting or battery container rupture; grid corrosion, when extreme, results in mechanical degradation of the plate structure and severe, fatal reduction in current-carrying capabilities during discharge and charge.  Extended life in both float and cyclic applications should be possible with foam technology due to elimination of these failure modes.  .

3D²    Performance Summary

Thus, Firefly’s 3D² technology involves having foam-based “grids” for both plates.  Positive plates are pasted in the same way as foam negatives in the 3D product.  With both electrodes having high-surface-area foam structures, 3D² batteries will have the following packaging and performance characteristics:

•  Significantly lower volumes and weights (by up to ~50%) relative to comparable lead-acid products in terms of energy output; greater differences may accrue in high-power applications such as engine start, UPS and HEV
• Lower plate mass results in a high level of vibration resistance. 
• Can be constructed in either flooded or VRLA configurations
• Extremely rapid recharge capability
• Superior discharge performance
• Longer cycle life compared to existing lead-acid products, particularly in PSoC-type applications
• Longer float lifetimes, particularly in high-temperature usage

In summary, 3D² will be a “breakthrough” technology in that it enables the true power of lead acid chemistry to be realized;  allowing the use of lead-acid chemistry in many new applications, some of which are currently being served by NiCad, NiMH and/or Li-Ion, as well as improving performance and life in existing lead-acid battery applications.