meeting report
43rd Power Sources Conference
Sheraton Philadelphia City Center Hotel
Philadelphia, Pennsylvania
July 7-10, 2008
- Battery Technology and Business Consultant
The 43rd Power Sources Conference was co-sponsored by the Army Power Division, U.S. Army CERDEC at Ft. Monmouth, New Jersey, and the Sensors and Electronic Devices Directorate at the Army Research Lab in Adelphi, Maryland. Once again the event saw participation from a variety of companies offering battery, fuel cell, solar, and other portable and mobile power products and technology to meet the growing need for novel power sources for government applications.
The forum provides a unique opportunity for business and technology development personnel within the industry to showcase their technology and interface with key decision makers at the different branches of DoD, NASA DARPA and DoE. Attendance has grown to well over 700 people with over 50 companies displaying their products and services in the exhibit hall. Special compliments to the conference sponsors and to the event managers from Palisades Convention Management for their hard work in making this event such a pleasure for all attendees.
The program began with a brief welcome address by Ed Plichta, the program chairperson, followed by an interesting keynote address, "Solving the Power and Energy Needs of the Army," by Gary Martin, deputy to the commanding general of USARDEC. Martin pointed out that the fully burdened cost of fuel in the theater today is $41 per gallon, and fuel comprises 70% of the tonnage into the battlefield. Fuel is required for the more than 65,000 power generators in use today that typically consume 1.9 million gallons per year. This demonstrates the importance of improving the efficiency of power generators -- new technology is sought that can reduce the burden of fuel.
Another issue that the Army faces is the number of different types of batteries that the soldier is required to carry today. Martin pointed out that a platoon of 200 soldiers is required to carry more than eight types of batteries totaling 2600 in number. The army is focusing on developing military-unique battery technologies such as Li-air, liquid reserve, thermal reserve, pulse power lithium-ion and lithium sulfur dioxide technologies to help reduce the burden.
The army is also focusing on power and energy density improvements by developing fuel cell and Stirling engines for silent operations, and developing renewable energy technology such as solar for battery charging applications. The land warrior system which is now transitioning to become ground soldier system is expected to significantly improve the infantry platoons' ability at a reduced power burden than what is carried today. Overall, Martin's presentation was very informative and presented a sound argument for the DoD's focus on novel power and energy technologies. Ken Zemach of Exponent Inc. questioned some numbers presented by Martin as being too high regarding the weight burden of batteries carried by the soldiers. He cited conflicting information in some studies that are referenced at the end of this report.
The conference agenda was jam-packed with technical presentations on recent progress from key government and industry professionals that began after the plenary session. As in past Power Sources Conferences, these technical presentations were neatly organized in more than 30 sessions based on the technology areas that included primary and secondary lithium batteries, aqueous batteries, battery safety, fuel cells, molten salt batteries and hybrid power. This year saw the addition of two sessions that focused on developments in advanced materials in battery technology.
Each year it is customary to open the exhibit hall to the public on the first evening of the show with a welcome reception/party. The hall was packed full with conference attendees enjoying their favorite cocktails and hors d'oeuvres, making a mental note of the more interesting exhibits, and contacting friends and acquaintances they want to catch up with during the course of the conference.
Lithium-Air Batteries
This technical session covered talks on both primary and rechargeable lithium-air cells and batteries. Arthur Dobley from Lithion reported on their efforts in developing a lithium-air/lithium-ion hybrid battery system that was tested to deliver 300% of the total capacity of the two batteries when operated individually under the pulse test regime that simulates the power requirements of communications equipment.
K. M. Abraham and collaborators studied the role of conducting salts and solvents on the electrochemistry of oxygen in lithium-air batteries. Initial results indicate that by substituting lithium- and/or sodium-based conducting salts with larger cations like tertiary butylammonium (TBA) results in an increase in the capacity of primary lithium-air cells. The larger cations, TBA and K+, tend to stabilize the superoxide ion formed via the reduction of O2 preventing its precipitation on the electrode surface that leads to passivation of that surface. Their studies on the effect of salts and electrolyte continue with the goal of finding the best electrolyte for non-aqueous lithium-air batteries.
Jeffrey Read from ARL elucidated the utility of un-catalyzed carbon/PTFE electrodes for oxygen reduction in primary lithium-air batteries, particularly for long run-time low discharge-rate applications. They found the electrodes maintained the requisite 1-2mA/cm2 current density over the entire pH range from 0-14, even though the steps related to the oxygen reduction reaction at room temperature vary drastically over that range.
Battery Safety/Quality Testing
Interestingly, the two sessions on this topic covered a wide range of papers that included modeling results, abuse test results on Li/S and Li-ion cells and batteries, papers highlighting the limitations of safety in multi-cell devices s and the effect of disproportionate heat dissipation leading to unbalanced charge distribution in packs constructed by connecting cells in a variety of series/parallel configurations.
Joseph Fellner from Air Force Research Lab (AFRL) reported results on high-rate characterization of commercially available Li-ion cells and batteries. They compared the discharge profile and its temperature dependence and AC impedance data of commercial Li-ion cells from SAFT, A123, Kokam and Quallion at various states of charge. Using SIMULINK and commercial software called "Battery Design Studio" they developed simple equivalent circuit models to simulate cell performance for a variety of discharge profiles.
Eric Darcy from NASA-Johnson Space Center was not shy in pointing out the results of their evaluation to determine the corrosion mechanism of Li-ion pouch cells from a variety of manufacturers, including Electrovaya, Saehan, Kokam, LG and SKC. The corrosion rates normalized wrt to Ah capacity of the cells were the lowest for LG and SKC cells which also had the lowest electrolyte leak rates. These cells also were found to have unique power-to-tab seals, less excess electrolyte and excess separator material near the edge and corner seals.
Brian Barnett of TIAX presented an interesting perspective on mitigating safety incidents in Li-ion cells #8218; what has happened and what may happen when this technology is deployed for automotive applications. He emphasized that the battery community today does not have adequate tests to analyze safety. This is a system issue and not due to single components, according to TIAX's findings. Cells fail due to internal shorts that are developed in field and not in manufacturing. Thermal runaway in these cells occurs during normal operation and not during abuse conditions. In their analysis they have found that there is a threshold power below which there will be no thermal runaway for a given duration of the short.
Rechargeable Lithium Batteries
Yardney has teamed up with BASF to qualify a domestic source for Li-ion battery materials for high rate/low temperature military applications. They presented their results on impedance and LEO cycle testing of MMO cathodes based on lithiated nickel-cobalt oxide and lithiated nickel-cobalt-aluminum oxide. Close on the heels of developing a domestic cathode material source is their effort to develop domestic anode and separator material sources.
Jeff Wolfenstein of ARL presented the results of their study on the effects of Ta (tantalum) dopant on the electronic conductivity of Li4Ti5O12, as a function of heat treatment atmosphere. In their effort to improve the recharge rate of lithium-ion batteries for HEV and soldier power use during short missions, they evaluated LTO as an alternate anode material to graphite. LTO is a zero strain material that should give superior cycling capability and its operating voltage is 1.5V vs. lithium. This is above the plating potential of lithium and above the reduction potential of electrolyte solvents, thus preventing solvent reduction that leads to the formation of the SEI layer, resulting in good low temperature performance and the ability to use nanophase materials. The only disadvantage to using LTO is its extremely low electronic conductivity which their study finds is improved by several orders of magnitude by using Ta dopant and heat treatment in a reducing atmosphere. Researchers from Lithion propose a novel "pseudo three electrode" cell design that they have successfully used to conduct polarization studies on lithium electrode materials.
ARL researchers Jeffrey Read and Dr. Wishvender Behl investigated the use of CoF3 as cathode material in lithium cells. The resulting cells can potentially be of very high energy density due to their high voltage. However, they found CoF3 to react with the sulfolane and PC electrolytes used in their study. Session 12 featured talks on rechargeable battery development by a variety of companies collaborating on government-funded projects to develop novel battery chemistries and technologies.
ElectroEnergy Mobile products of Colorado Springs has developed a high energy lithium-ion battery in the BBx590 configuration that has demonstrated ~ 300Wh/kg and good low temperature performance to -30C. Their approach is based on using mixed metal-oxide cathodes and using a wafer cell design over conventional cylindrical or prismatic designs. AGM batteries of the UK is also using mixed metal oxide cathodes based on Ni, Co and Al and high capacity graphite anodes in pouch cells for BB2590 application. When tested against the D cell (5.2Ah)-based configuration used currently in the UK, Bowman Tactical Communication System, this new battery has exceeded the performance target of 7Ah and also demonstrated -40C discharge capability. Cell level energy density was at 190Wh/kg with future developments targeting 400Wh/kg by 2010. Continuing on the theme of improving the energy density of Li-ion rechargeable batteries via using MMO cathodes and hi-energy anodes, SKC Power Tech pouch cells demonstrated > 260Wh/kg using NMC cathodes and graphite anodes and excellent cycle life. Further work based on silicon graphite composite anodes could improve the energy density to approach 300Wh/kg.
ElectroEnergy has also extended their Li-ion wafer cell development based on NMC cathodes for high power aircraft platforms meeting the performance requirements of USAF F22 Joint Strike Fighter applications. Incidentally, ElectroEnergy has recently acquired a major Li-ion battery manufacturing facility in Gainesville, Florida that positions them as a domestic supplier of 18650 and 26650 cells. The facility has the capability to manufacture 30 million cells annually to meet both low- and high-power application requirements.
The advanced materials and government solutions group of A123 Systems had several presentations on test results of their rechargeable Li-ion batteries based on nanophosphateŽ cathodes that have already entered high volume commercial production for cordless power tool applications. Test results indicate that NP cells offer better performance than NCA cells for silent watch/HEV applications. These cells are also able to operate successfully at an expanded temperature window (-30 to 100C) which is useful for emergency situations, though power and lifetime of the cells is impacted when operated in these conditions. Due to the excellent cycle life capability and improved safety of A123 cells, they have generated interest for other military applications including aircraft, UGV, and robotics as well as for satellite applications when assembled as 28VDC packs. It is interesting to note that A123 is also developing large format battery configurations based on their nanophosphate chemistry cells. These operate at 350VDC nominal, have 100kW pulse power capability and are being evaluated for ground transportation applications such as buses and fleet delivery vehicles as well as special military applications.
Saft continues to improve its lithium-ion technology for high power with the goal of elevating specific power to levels exceeding that of supercapacitors. Their very high power cells are capable of 8kW/kg on two second pulses and 12kW/kg on millisecond pulses. Saft's ultra-high power cells have an increased relative amount of current collector in the same cell dimensions and has been tested to deliver an average specific power of 14kW/kg over a seven second pulse. Specific power of the 200msec pulse approaches 30kW/kg. Additionally, the low temperature performance and cycle life of these cells from Saft is also noteworthy.
Fuel Cells, Fuel Processing and Storage
Interest in this topic was considerably reduced when compared to lithium batteries as evidenced by the scant attendance in the audience during the technical presentations. Noteworthy among the different presentations were Art Homa's discussion on Neah Power's progress in developing porous silicon-based direct methanol fuel cells. Neah completed a full system integrated demonstration in September 2007 and is currently working on improving the power by 2.5 times.
NUWC (Naval Underwater Warfare Center) and SAIC (Science Applications International Corp.) are collaborating on developing a direct borohydride/hydrogen peroxide fuel cell. Latest results show a power density of 2mW/cm2 at 25C with a 60% utilization efficiency for borohydride and 70% for peroxide. The team is conducting scale-up studies that will result in a 2kW demonstration at a predicted energy density of 200-300Wh/kg.
Ensign Bickford has made significant progress since entering the power market only in 2004. Between 2004-2007 they were working on concept development of their amino-borane based hydrogen cartridge system for PEM fuel cell applications. The company is targeting a TRL 4 demonstration of a cartridge packed with fuel elements capable of producing between 0.1-1.8g of hydrogen at 5-500W in 2008. They discussed a 4.5-inch diameter and 12.8-inch long cartridge containing 4.1wt% hydrogen at 100W. The design and testing effort has a major focus on safety to ensure low skin temperature and preventing cross initiation of fuel elements.
Ian Kaye of Ultracell was very upbeat regarding the performance and maturity of their XX25 reformed methanol fuel cell system. He discussed the challenges associated with transitioning their technology into a field-ready product. The system has passed MIL-STD-810F testing, achieved a TRL level of 7 and first shipments from their Dayton, Ohio, plant have been made. Their current cartridge has the same energy as a BA5590 but has demonstrated nearly twice the energy density at 363Wh/kg. With a larger fuel tank they expect to achieve 500Wh/kg.
The conference also had papers from such companies as Eagle Picher, Matsushita Battery, Advanced Thermal Batteries and The ENSER Corp. who are developing novel thermal and molten salt battery systems. GEM power discussed its battery management system that can be used by all battery chemistries. They use a pulse-charging algorithm combined with real time-data analysis.
The breadth and depth of coverage of different topics related to power and energy is not only comprehensive but also very exhaustive. Nevertheless, conference attendees in their eternal quest for knowledge, tirelessly rotate from one session to the other. The conference continued after-hours in the hospitality suites offering food and drink and opportunity for light conversation. The Eagle Picher suite on the top floor featured a jazz band whereas Saft organized "Casino Night," not to forget the good food served at the Yardney and ElectroEnergy events.
Come Thursday morning, it was time to wind up. Most industry participants took off, returning to their respective home bases by noon. But not the government employees. They hung on for an extra day for the Interagency Advanced Power Group's and Chemical Working Group's annual meeting held at the conclusion of the conference. Government participants exchanged information with each other on the different programs they or their department is focusing on. Peter Keller, branch chief of the NSWC Carderock division assumed responsibility as the new chairperson of this working group. I found out from one of the participants that their first day meeting extended till 9:30 p.m. with the group reconvening the next morning to finish up business. No wonder we see so much progress.
Here are the references mentioned before:
