Taking energy storage to the next level

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Hammond Group, Inc. (HGI), established in 1930, plays a critical role in the global lead acid battery supply chain, with multiple locations in the United States, United Kingdom, Malaysia. HGI supplies battery oxides, specialty lead oxides, and tailored solutions for blended expander formulations. In 2015, we opened a state-of-the-art Lead Acid Battery Laboratory (LAB) at our Hammond facility. The new laboratory boasts more than 3,000 square feet dedicated to the testing and development of specialty additives in various applications for the lead acid (PbA) battery.

Expander is a specialty chemical additive for the negative electrode of the PbA battery. It helps maintain the surface area and functionality over repeated charging and discharging. Historically, expander formulations contained a blend of three basic components (carbon black, lignosulfonate, and barium sulfate) at varying concentrations. Prior to today’s Partial State of Charge (PSoC) applications, PbA battery failure modes were usually related to the positive electrode, so there was no need to alter expander formulations for the negative electrode. Studies have now proven that present day PSoC applications drive the failure mode to the negative electrode. In an effort to meet these new demands, the ALABC (Advanced Lead Acid Battery Consortium) has conducted several projects focused on expander material optimization for batteries running under PSoC duty. One such project focused strictly on carbon additives, holding the organic expander component constant, while another centered on organic materials but kept the carbon fi xed. HGI saw the need and opportunity to study not just the effects of single components in isolation, but how the individual components interact within the negative active material (NAM). Materials and material classes not traditionally used in PbA batteries were trialed in order to step beyond historical material constraints and employ a fresh look at expander formulations. The research originally focused on materials suitable for hybrid electric vehicle demands such as regenerative braking and fast recharge.

The primary measureable was dynamic charge acceptance. A test plan was created containing 70+ material combinations. Factors varied on the organic component included: natural versus synthetic, functional group types and amounts, molecular weight, and pH. Carbon classes tested included: furnace black, acetylene black, natural and synthetic  graphite, and activated carbon. Carbon characteristics within the classes such as porosity, functionality and structure were studied as well.

One of the prevalent theories regarding carbon is that it needs to be highly conductive. Being conductive and present in large amounts would form conductive paths through the dense sulfate layer (failure mode on NAM in PSoC environment) and allow for conversion of the lead sulfate back into sponge lead. Very good results were found with other principally non-conductive carbons. While conductivity seems to be an advantageous factor, other material characteristics like the ratio of micro, meso, and macro pores and surface functionality seem to be equally as important.

Barium additives were compared by varying the material source (precipitated vs. naturally mined/milled) and the particle size influence on performance. What began to emerge was that the key to improved charge acceptance was not solely in the use of specific individual materials, but in the precise combination of carbons, organics, and salt additives.

fig. 1 HPPC Test results. The Hybrid Pulse Power Characterization (HPPC)
test simulates high charge and discharge pulses across the entire state of
charge range. This test correlates well with dynamic charge acceptance.
The graph depicts the point at which the charge and discharge curves
cross yielding equal power 

As more materials were tested, it became evident (Graph 1) that certain combinations would work very well for automotive applications as those require high charge acceptance at high states of charge (SOC). Other combinations exhibited excellent charge acceptance within the various SOC ranges making them prime candidates
for energy storage applications such as renewable energy, peak shaving, grid stabilization, and motive power ORC (opportunity rapid charge). Based on the findings of the interaction  study, HGI introduced its advanced expander product line (Graph 2) catering specifically to the needs of PSoC applications. The result of improved dynamic
charge acceptance leads to enhanced cycle life under partial state of charge conditions. Graph 3 demonstrates the superiority of the advanced expander line in a high rate partial state of charge (HRPSoC) cycling test.

fig. 2 compares an advanced formulation with high charge
acceptance across the entire SOC range to a standard PbA

expander formulation

fig. 3 represents the drastic cycle-life improvements to be
seen in new material combinations (advanced expander line)
over the standard PbA battery expander materials

In conclusion, research results using 2 volt test cells have shown that the right material combinations will enable PbA batteries to operate in all types of partial state of charge applications where previously they were non-competitive. The results put HGI in a position to customize formulations for every application.

The investment in the LAB allows not only the testing of single cells, but also full-scale automotive, motive power, and stationary batteries. Commercial automotive batteries manufactured with advanced expanders are currently on test at both Hammond’s LAB and the Fraunhofer Institute in Germany, where they are being evaluated
against lithium batteries of equivalent size. PbA batteries offer value over alternative chemistries in that they are safe, inexpensive, they have a very strong commercial supply chain structure, and they are nearly 100% recyclable. No other energy storage device option has such a well-developed manufacturing and recycling system
that allows for cradle-to-cradle control. Now, PbA batteries have a long term future as a serious contender in the energy storage arena.

Article posted in EES International Magazine | http://ees-magazine.com/epaper/04_2015/index.html 

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