meeting report

44th Power Sources Conference

Las Vegas, NV USA

June 14-17, 2010

• Jaime Navarrete
• Freudenberg Nonwovens LP
• Owensboro, Kentucky

The 44th Power Sources Conference moved this year out of its long-standing site around the Philadelphia/Cherry Hill region to Las Vegas. The Power Sources Conference focuses on energy-generation and storage technology that is of interest to the Department of Defense, other government agencies and to the civilian marketplace. Although the conference covers work in the four technology sectors mentioned later by Marc Geitter’s Technology Roadmap, only a small portion will be covered here due to the extensive amount of information and topics presented.

The second day of the conference started with the Plenary Session and T. Killion, U.S. Army SAAL-IT discussing the need to invest in technology that will power the army of the future. One example Killion gave of the changing power requirements was the change in Humvee. Initially the Humvee had a power system supported by a 40A alternator. Now, a 400A alternator is required to support the increased use of sophisticated electronic gear. Killion indicated the development of an energy strategy that defines the next generation energy technology while supporting technology that supports soldiers today.

This energy strategy was presented by Marc D. Gietter, Army Power Division, at the poster session. Marc’s poster showed a Technology Roadmap to assure that state of the art power sources are available. The Roadmap attempts to identify performance gaps, proposed corrective actions to fill that gap along with a rough estimate of the required investment. For some technologies there is no proposed investment. The Roadmap focuses on man-portable power sources divided into four technology sectors: (1) non-rechargeable batteries, (2) rechargeable batteries, (3) thermal/reserve batteries and (4) 1 watt to 1 kilowatt fuel cells. Each technology is further broken down by chemistry (for batteries) and fuel source (for fuel cells). Each chemistry/fuel source is matched against a common set of performance requirements, and to determine if the chemistry/fuel source is capable of meeting requirements now, five and ten years in the future. Figure 1 depicts a simplified roadmap for primary batteries. Access to the DOD Power Sources Technology Roadmap is available to any current government contractor. Please contact Marc Geitter at email: marc.d.gietter@us.army.mil for further information.

Extending the Operating Temperature for Li-ion Batteries

One of the performance gaps being investigated is extending the operating temperature range (-40oC to +70oC) of lithium-ion batteries. The principal issues for extended temperature range performance of lithium-ion batteries are rate capability at low temperature and stability/cycle life at high temperature. Low temperatures reduce the conductivity of the electrolyte system and increase charge transfer resistance for electrochemical cell reactions. At elevated temperatures stability of components is the primary problem. Most efforts to resolve this problem result in performance improvements either at low temperatures or elevated temperatures, but not both. Finding a solution is not simple, as indicated by the following three summaries describing the work being done at TIAXX, U.S. Army Research Lab and California Institute of Technology.

Bookeun Oh, TIAX, discussed efforts to develop a novel electrolyte system comprised of LiPF6 salt with nitriles as cosolvents that could work at both elevated and low temperatures. The results demonstrated the novel electrolyte composition with nitriles/TSF additive, improved the discharge performance at elevated temperatures compared to the control EDE cell (Figure 2) and without compromising room temperature performance. At low temperatures, the addition of nitrile (specifically butyronitrile) was able to significantly increase ionic conductivity. However, a stable SEI was not able to form with the addition of nitriles to the electrolyte. This required the addition of another additive, TSF — a proprietary SEI-forming additive. In addition, the amount of TSF had to be controlled because too much would build a thick SEI layer, which was not desirable.

Arthur von Wald Cresce, Electrochemistry Division, Sensors and Electron Devices Directorate, U.S. Army Research Laboratory, discussed investigations looking at replacing the standard ethylene carbonate (EC) solvent system with linear and cyclic sulfones (tetramethylene sulfone) for the potential to increase the operating voltage in lithium-ion batteries in the vicinity of 5V. The pursuit of a high voltage lithium-ion secondary battery is motivated by the need for higher density energy storage and delivery (or discharge) at a higher voltage. Lithium-ion batteries operating at higher voltages demand electrolyte systems with excellent chemical and thermal stability while retaining good lithium solvation and transport characteristics. But as in the case with TIAX development, additives need to be added to the sulfone-based systems to aid in forming a protective and Li-ion-conducting SEI layer. Wald Cresce showed the addition of sulfolane could be partially substituted for ethylene carbonate to improve cycling performance of LiMnO spinel cells. However, the results indicated the benefits of SL can only be achieved in the presence of EC. In Figure 3 Cresce stated more fundamental work is needed before SL can be considered a real alternative for EC in high voltage Li-on battery electrolytes.

SL works only in the presence of EC.

Marshall C. Smart, California Institute of Technology, presented results obtained with prototype Li-ion cells (manufactured by Quallion, LLC) which included various wide operating temperature range electrolytes developed by both JPL and Quallion. Differentiation in performance between range of electrolytes being tested cells was only observed at the higher 5oC discharge rates at -40oC. (Figure 4.) And when cells were cycled at alternating high and low temperatures, performance at the low temperatures continued to drop as the cells were cycled, indicating instability in the system. Of the various electrolytes tested the ethyl butyrate-based electrolyte system showed the best overall performance over operating temperature range investigated.

Not to Be Left out

Even Zn/MnO2 chemistries, which are considered mature, can still be improved. Silke Spiesshoefer of Engineering Systems Solutions presented efforts to improve high capacity and/or miniaturization of alkaline batteries by replacing microparticles used in present technology with nanoparticles. Due to the higher surface area, nanoparticles are expected to improve the energy density and active material utility efficiency.

Sameer Singhal, CDF Research Corp., probably had the most unique energy source of the conference. CDF has developed a Bio-Battery which uses enzymes to convert sugar and other renewable fuels directly into electrical energy. Figure 5 demonstrates the working principle of a Bio-Battery. Besides being applicable for military use, a Bio-Battery could also see use in biomedical devices, where power generation from physiological fluids could lead to improved implantable monitors and drug delivery systems. The latest results show a power density of >1mW/cm2, enough to drive low power electronic circuits.

Jessica Mitchell, general manager of NDC Power, also had a demonstration power source (a 300W direct alcohol fuel cell — DAFC) running at their booth (Figure 6). A direct alcohol fuel cell (DAFC) that consumes any primary alcohol (examples: methanol, ethanol, ethylene glycol, butanol, propanol, etc). The alcohol is fed to the anode and directly oxidized in a liquid state (a reformer is not required). The charge balance is maintained via a liquid electrolyte in the center of the cell. Thus the fuel/electrolyte blend that is active on the anode is also in contact with the cathode. This is allowed because unlike other fuel cells (e.g. methanol fuel cell), the DAFC does not require a perm-selective membrane. The electrodes themselves contain selective catalysts (the anode can only oxidize alcohols and the cathode can only reduce air).

NDC Power has a contract with the Army to further develop this technology. There is also commercial interest that the fuel source is ethanol as opposed to methanol, which is more toxic, and doesn’t require expensive platinum catalysts or expensive perm-selective membranes. NDC is seeking strategic partnerships to bring their technology into larger commercial use.

Announcement at Power Sources Conference

Advanced Membrane Systems (AMS) announced the opening of their new manufacturing facility for Li-ion battery separators as well as the introduction of their new separator product (Figure 7).

AMS has entered into a joint venture agreement with Biax Laboratories to open a 25,000 square-foot manufacturing plant in Rutherfordton, North Carolina. The new venture is called UltraLith LLC. The patent pending UltraLith-HP is a single layer non-shutdown polyolefin separator engineered for high power and high density lithium batteries (LIBs) used in such applications as electric drive vehicles. According to Abbas Samii, president and chief scientist, UltraLith-HP provides 70% porosity, improved safety due to high melt integrity performance and lower cost due to a simplified manufacturing process.

Also available for consumer applications is UltraLith-SD. UltraLith-SD is a single layer membrane with shutdown capability (melt temperature 145oC to 155oC).

Dave Lucero, director of alternative energy storage for Eagle Picher announced a recent Advanced Research Prospects Agency — Energy (ARPA-E) award for $7.2 million. The project focuses on planar sodium (Na)-beta batteries (NBB) as a low-cost energy storage solution for grid applications. Dave mentioned the current technology, using thick tubular beta-Al2O3 electrolytes that suffer from reliability issues and high costs. The research team, led by Eagle Picher Technologies (EPT), will focus on developing and demonstrating new planar-stacked NBB architectures that achieve the necessary performance at substantially lower operating temperatures. This new architecture is also expected to reduce the cost by using inexpensive stack construction materials and low-cost manufacturing techniques. The project will demonstrate a 5kW-10kWh modular system (scalable to >10MW power) and work to establish a viable NBB manufacturing industry in the U.S.

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