At the 40th Power Sources Conference...Part 1
Battery and Fuel Cell Innovation Prevailed
by Shirley and Doanld Georgi
Summer heat and humidity perked up in Cherry Hill, New Jersey on the week of June 10, 2002. Concurrently, the eclectic combination of presentations on batteries, fuel cells and ancillaries at the 40th Power Sources Conference showed that research and development continues to expand capabilities now and offer increased performance in the future. The non-attendee might wrongly classify this conference as military-only because it is cosponsored by the Army Communications Electronic Command and the Sensors and Electronic Devices Directorate. True, the exhibitors were strongly focused on power packs for Humvees and Land Warriors, but the presentations provided scientific evidence of continuing progress in all aspects of battery and fuel cell understanding which will ultimately extend to commercial, medical and recreational devices.
This conference has depth. It includes primary and secondary batteries, fuel cells, safety, testing, quality, power management and even non-electrochemical power sources. The conference is so deep and that it is almost its worst enemy. To cover all the presentations in four days there are either two or three parallel tracks held simultaneously. The attendee is torn between choosing a hybrid fuel cells session or a primary lithium presentation. Without the complete 570 page hardbound proceedings, dutifully presented to each attendee before the conference starts, one could have been too frustrated to be able to choose from this ‘candy store’ of knowledge. Organizers of the conference recognize this depth and accommodate track switching by keeping each presentation on a rigorous time schedule. For example, such on-time schedules allow the attendee to move from a presentation in the aqueous battery track to another track where a secondary lithium session is being given. Few battery conferences can match this rigorous combination of prepared materials, schedules and implementations.
After excellent organization, the true test of the meeting is in the range and richness of the material presented, and here again the 40th Power Sources conference excelled. Eleven major topic areas were available with 154 sessions. Lithium secondary topics garnered a peak of 34 presentations. Let’s take a brief overview of some of these sessions:
The keynote speaker, Gilbert V. Herrera, Deputy Director of Corporate Business Development and Partnerships for Sandia National Laboratories in Albuquerque, New Mexico, addressed the attendees on a topic entitled, “Power System Technologies for the Dismounted Solider.” He based his presentation on the results of the U.S. Army Science Board 2001 Summer Study Power Panel. Mr. Herrera noted that the military will be taking a holistic approach in making decisions about the requirements of the power system for the dismounted soldier; such requirements will be based on assessing the needs and goals for logistics, generation, management and storage. He also discussed how the military will be continuing to strive for an integrated package. As a result, he sees the military looking at a hybrid of technologies (various battery chemistries, fuel cells, hydrogen, supercapacitors, ect.) which combine to produce optimum power and energy to maximize functionality for the soldier.
Primary Lithium batteries are used by the military for general land warrior applications and for special applications such as the power supply in interceptor type missions. Some of the chemistries discussed which are utilized in these batteries were: Lithium/ Chlorinated Sulfur Chloride, Lithium/Sodium Dioxide, and Lithium/Manganese Dioxide.
A paper given by Marc Roberts of the US Army CECOM explained the experimental results of a method to extract bonded water (a known ‘poison’) from manganese dioxide cathode materials.
One entire section (four papers) concentrated on primary reserve batteries, where the highly acidic form of the electrolyte is stored in a separate reservoir and then injected into the dry electrode plate stack to activate the battery.
Dr. Patrick McDermott of Zentek Corporation discussed an alternate design where the plate stack is flooded with neutral electrolyte during periods of storage, but activated to high current operation through injection of a highly acidic form of the electrolyte from a separate reservoir.
A unique presentation by Joseph McDermott of Infinite Power Solutions in the primary Lithium section dealt with a ‘thin film rechargeable.’ Although this solid state Lithium battery is rechargeable, the focus of the paper was to discuss how it could be used in primary military applications that need a very small battery that can deliver microAmps to milliAmps after many years of storage.
As expected, Lithium-ion received more attention than any other one chemistry or topic. Seven separate sessions were devoted strictly to this rechargeable chemistry, and it was also discussed in the sections on safety/testing and advanced materials. Lithium technology is popular for military applications due to its high specific energy, power and long cycle life. Very abbreviated summaries are given to provide the essence of work being done.
Why is Lithium-ion technology being considered for unmanned vehicle (UV) applications?
- Higher Cell Voltage - One lithium-ion equivalent to three NiCd or NiMH
- Excellent Energy Density - Extended service hours, lower in weight and smaller in size
- Volumetric, Wh/liter - 300, Two times higher than NiCd
- Gravimetric, Wh/Kg: 145 - Three times high than Ni/Cd
- Excellent Power Capability - 135/Whg and 2900 W/liter
- Low Self-Discharge or Superior Charge Retention -
Li-ion< 5% year, NiMH and NiCd: 20-25% Month
- No memory effect
- Saft Li-ion can be shallow discharged at any depth without degradation - shallow cycling improves
the cycle life up to 100,000 cycles
- Fast charge Capability - 80% of full charge in one hour,
97% of full charge in two hours
- Cycle Life and Calendar Life - >3000 cycles at 100% depth of discharge (95% cap. remaining), 15 years as calendar life
- Broad Operating Temperature Range: -200 C to +600 C
- Hermetically sealed and no gassing
- Maintenance free
Information from “Lithium-Ion Batteries for Unmanned Underwater Vehicles,” presented by N.S. Raman of Saft at the PowerSources Conference, June 2002
Pouch cell designs, also referred to as the soft package technology, are also being investigated. Properly executed, this design can have an advantage over the welded design . Christo Brand of Eagle Picher Energy Products discussed their program with Li/MnO2 cell chemistry. He pointed out the two main advantages of the design: 1) space - With an elliptically wound cell, the volume can be fully utilized. 2) enhanced safety - “If a ‘pouch’ cell is placed under external short-circuit, the temperature of the tabs will increase to the point where the seal is broken and the electrolyte will leak out, effectively shutting down the cell.” During their nail penetration test, only a small drop in open circuit Voltage was observed. After 30 minutes and removal of the nail, the cell can be discharged and still deliver 75% capacity of an undamaged cell.
Research on anodes - 1) T/J Technologies studied the low temperature performance of tin-based anodes and found a significant low-temperature performance benefit for their nano-composite materials when compared to graphite.
2) In another paper, the Army Research Laboratory reported that their copper-tin anodes also have potential as replacement for the graphite.
3) Yardney Technical Products’/Lithion, Inc.’s research is showing promise for their carbon/silicon and copper/silicon composites as anodes.
4) Sandia National Laboratories found that in working with carbon/carbon composite samples prepared by pyrolysis, the pyrolysis results proved to be very sensitive to the experimental conditions and sample size.
Material investigations - The need for improved power sources at low temperature and improved safety for larger sized cells requires new electrolyte formulations.
1) The U.S. Army Laboratory is experimenting with three different chelating agents.
2) Arthur D. Little (now TIAX) is working on improving the energy density of the graphite anode and LiCoO2 and Li-Ni-Co-O2 cathode materials. In Christina Lampe-Onnerud’s presentation (from TIAX), she stressed the key challenge of working with the Ni-based compound because of the surrounding safety issues associated with the more reactive Ni materials.
3) Nanocomposite materials may prove to be a key to enhance the electromechanical performance of both the cathode and anode; Nanopowder Enterprises, Inc. found that SnOx/C nanocomposites exhibited excellent cyclability, and rate capabilities of ultra fine Li4Ti5O12 showed promise.
4) U.S. NanocorpR’s research centered on nanostructured MnO2 for high energy lithium rechargeable batteries. “The longer cycle life of the Li/MnO2 is expected because flexible nanoparticles of MnO2 are more stable in morphology and structure compared with conventional manganese dioxide with regular shaped particles.” Further reliable battery tests need to verify the cycle performance.
New cells - 1) A.G. Ritchie and P.G. Bowles of QinetiQ Ltd. in England have shown that a lithium-ion/iron disulfide battery can be made by chemically synthesizing lithium iron sulphide and using this as the cathode for a Lithium-ion battery; thus, by replacing cobalt (the standard cathode material) with iron, a Lithium-ion system could be cheaper to produce, an especially important consideration for larger size applications.
2) Based on the efforts undertaken at Lithium Energy Associates, Inc., work can now commence on 25 to 40 Ahr cells, in demountable and welded metal cases, for the rechargeable Li/CuCl2 battery system with a LiAlCl4/SO2 based electrolyte; these batteries would be used in launch applications.
Improved materials - 1) At the U.S. Army CECOM Research and Engineering Center, development work shows that low crystalline LixMnO2 phased with MnO2•B2O3 is a promising cathode active material that shows excellent charge capability.
2) New lithium salts, a potential lower cost alternative to LiPF8, are being prepared and evaluated by Yardney Technical Products/Lithion; it appears that these salts may be more thermally stable than LiPF6.
Showing support for the Power Systems Conference with a product display of battery charging and testing products at the exhibition was Isidor Buchmann, who fills many roles. He is the CEO and founder of Cadex; he gave the presentation on Battery Quick Testing: A Technology that Has come of Age , and he is the regular contributing author of the ‘Ask Isidor’ column in BD. (See pp. 13-15.)
Engineering studies - Battery related studies are also being pursued in engineering departments.
1) Z.R. Ma from the Center for Interdisciplinary Magnetic Resonance, National High Magnetic Field Laboratory at Florida State University discussed the on going studies of the structural arrangement of a Li/membrane/ LixV2O3 cell using AC impedance and NMR spectroscopes; results show that capacity degradation of the cells were mainly due to degradation of the anode electrode.
2) At Sandia National Laboratories, work is being conducted to understand the fundamental causes for power and capacity degradation in high-power Lithium-ion cells by looking at the correlation of impedance increase with electrical performance degradation; observations suggest that the increase in the charge transfer resistance at the cathode electrolyte interface with aging may be the cause.
New forms, shapes and sizes - 1) LiTech, LLC. and the U.S. Air Force Wright Laboratory examined nano-particle electrodes under high rate pulse power conditions on prototype Lithium-ion pouch cells; additional work was recommended on the electrodes to improve specific power and power density for the pulse power mode of operation.
2) Work on disc-shaped Lithium-ion cells for high rate applications is being done by InvenTek Corporation; Thomas Kaun states that the improved performance and safety of this Lithium-ion cell may provide advantages for a variety of defense applications. ( A 5 Ah cell exhibits the power density of a 2.5 kW/kg ultracapacitor but with the specific energy of a high performance battery, 75-100 Wh/kg.)
3) Anthony Pellegrino of the U.S. Army CECOM RDEC described his ongoing work with Rayovac in developing the FAT D Lithium-ion cells.
Modifying standard Lithium-ion cells for space and defense Through testing and demonstration, Saft has shown that their Lithium-ion technology can be adapted to the specification of different applications by mechanical and/or electrochemical adjustment; high reproducibility and low cost are the advantages.
Key concerns in battery development - Quallion and the U.S. Army CECOM discussed the development of their new battery with deep discharge storage capability; their main concern was that the design be “a cut above the conventional technology.” Therefore, discussions centered on mechanical stability and safety evaluation to make a battery that is lightweight, hermetically sealed, electromechanically stable and yet be safe under field abuse conditions.
Experimental testing 1) Japan Storage Battery reviewed their process in determining experimental equations to calculate the calendar life and cycle life in their 100 Ah Lithium-ion cells used for space applications. By using experimental equations, they tried to calculate the capacity fading of typical GEO and typical LEO batteries.
2) In presenting “The Effect on Low Earth Orbit (LEO) cycling performance due to Physiochemical Changes in Aerospace Lithium-ion Cell Electrodes,” J.W. Baker of Mine Safety Appliances Co. stressed the need for use of experimental design methods, beyond basic cell hardware testing, to aid in the optimization of electrode formulation. By utilizing statistical analysis , the results indicated that electrode interactions exist and that particle-to-particle optimization is very important for designing electrodes that are capable of sustaining the rates required for a LEO cycling regime.
Novel Batteries J.P. Thomas of the Naval Research Laboratory described his work with Geo-Centers, Inc., Telecordia Technologies and AeroVironment Inc. to combine rechargeable plastic Lithium-ion batteries with structure enhancing materials to create a new type of multifunction structure-battery material for use in unmanned air vehicles. Structure-battery materials serve in a structural capacity while also providing a propulsion energy storage function, so the goal is to replace unifunctional structure material with multifunctional structure-battery material to increase the energy storage capacity and achieve gains in UAV endurance (time-of-flight) or range.
Testing programs of Lithium-ion cells Sandia National Laboratories (R. Jungst., D Doughty, Bor Yann Liaw, G. Nagasubramanian, H. Case and E. Thomas) is studying the capacity and power fade of high-power Lithium-ion cells for the Advanced Technology Development (ATD) Program. The initial objective was to develop an efficient protocol for verifying the life of these cells, specifically for hybrid electric vehicles (HEVs). The behavior of the 18650-size cells were characterized under a variety of accelerating conditions, then a selected a range of test parameters allowed life predictions to be made for nominal HEV operating conditions. The group found that they can accelerate power fade with storage at higher temperatures and state of charge with life times between 51 and 89 weeks. Validation is underway.
Yardney Technical Products, Inc./Lithion, Inc. is studying prismatic cell design optimization based on considerations in thermal analysis. As more demands are placed upon the cell and battery, coupled with cell designs in excess of 50 Ahrs., thermal considerations become increasingly important. In developing their thermal model, the guidelines developed allow for the efficient dissipation of heat, while maintaining a light weight, electrically efficient design. Guidelines for testing include the following: 1) Electrode design should be such that the length and width of the electrode are equal. 2) A plot of electrode area vs. cell temperature rise is generated. 3) A plot of cell case weight vs electrode is superimposed over previous plot. 4) The intersection of the two plots is found.
AGM Batteries Ltd. and AEA Technology Battery Systems presented data on high performance Lithium-ion cells for military applications. Tony Jeffrey and Bill Macklin reported success on the development of the AGM Lithium-ion D cell by noting improvement in cycle life , discharge efficiency and low temperature performance. Cycle life in excess of 1,000 cycles to 60% of nominal capacity has been demonstrated, and useful capacity down to -400C is obtainable. Currently, three D cell variants are in manufacture at AGM’s plant in Scotland. Further studies are planned.
The Idaho National Engineering and Environmental Laboratory, Argonne National Laboratory, Sandia National Laboratories and the U.S. Department of Energy, in conjunction with the Partnership for a New Generation of Vehicles (PNGV), are testing a second generation of Lithium-ion cells consisting of a baseline and three variant chemistries in the Advanced Technology Development Program. Although the results are very detailed, in general, it appears that the Variant C cell chemistry, having an increase of the aluminum dopant from 5% to 10% and a decrease to the cobalt from 14% to 10% in the cathode (i.e. LiNi0.8C00.1Al0.1O2), will reach end of life sooner than the Baseline Chemistry. Deterioration in both the initial capacity and the power fade during aging were noted.
Ed. note: This conference has so much material that we will have to continue this overview in following issues.