22nd International Seminar on Primary and Secondary Batteries Fort Lauderdale, Florida

The 22nd International Seminar on Primary and Secondary Batteries was held in Ft. Lauderdale, Florida, on March 14-17. There were over 400 attendees. Several summaries of the presentations at the meeting follow.

George Kershner and Saskia Mooney of Wiley, Rein and Fielding reviewed the shipping regulations and the actions of the U.S. Department of Transportation to further regulate the transport of lithium-ion and fuel cells. The two lithium fires at FedEx involving lithium primary medical batteries and lithium-ion cells for a hybrid car coupled with the LAX airport fire of lithium coin cells has caused DOT to open up a new study. A previous report from England showed that lithium fires were not extinguished by the Halon fire extinguishers used on aircraft. DOT has commissioned a study on Li-ion batteries to identify problems with extinguishing these fires on aircraft. DOT has long wanted to regulate Li-ion batteries as for lithium metal cell regulations. The battery industry prevailed, and DOT permits the carrying of a 96Wh battery pack on aircraft. The Portable Rechargeable Battery Association is pushing for a separate category for Li-ion batteries to help differentiate them from lithium metal batteries. They also are pushing for a 200Wh allowance to ship Li-ion batteries as non-hazardous cargo. In the past several years there have been incidents involving lead acid (20), NiCd and NiMH (4), lithium primary (5), lithium-ion (1), and dry cell (8) batteries. The DOT recently funded a study at the Rochester Institute of Technology to evaluate the E3 impact of methanol cartridges in transportation. A fallout from these studies may impact recycling efforts, if scrap batteries are reclassified as hazardous goods.

M. Sudduth of FedEx related their experience in shipping batteries. Because of the recent incidents, they require shippers of lithium batteries to go through a qualification process before accepting shipments from them. They accept only shipments from the qualified list, and they are taken as Class 9 hazardous goods. Their two recent incidents involved medical primary lithium batteries and 78 Li-ion batteries intended for HEV application. Both incidents were detected before the aircraft took off. The Li-ion cell fire melted the plastic shipping container. It was taken off the aircraft when a worker smelled smoke. It appeared that the cells were not packaged properly and were touching one another. The fire started in one cell and then spread domino fashion to nearby neighbors. He did not identify the source of the cells.

Brian Barnett of TIAX introduced the safety session with a brief description of the thermal runaway scenario. First the cell contents are heated, perhaps by an internal short or from a hot component in the electronic circuitry of a battery pack. As the cell warms up, the reaction of the cathode with the electrolyte increases. Once the point is reached where the heating from internal reactions is greater than the heat dissipated, the cell has reached a critical point/temperature where thermal runaway occurs with disastrous results. That temperature varies with the cathode composition and the electrolyte composition and is different for each cell manufacturer. To raise the temperature for thermal runaway, it will be necessary to engineer the kinetics of the decomposition reactions.

According to Jeff Dahn of Dalhousie University, the success of arriving at a “drug store” battery will depend on the ability to develop a system whose safety is “bulletproof,” whose cost performance is like NiCd or less – safe and does not require electronic circuitry for safety or cell management. Overcharge and overdischarge protection like the NiCd will require an internal redox material with the right potential. The cell includes a LiFePO4 cathode and a Li4/3Ti5/3O4 anode and adding a 2,5 diterbutyl 1,4 dimethoxybenzene as the overcharge/overdischarge protection shuttle. A very safe, long lasting cell can be produced. The cell can be overcharged continuously at moderate rates without overheating the cell.

Linda Nazar of Waterloo University discussed lithium iron phosphate as a cathode material. The ideal LiFePO4 material would have: a) small particle size to limit the path length inside the particle, and b) conductive surface network that does not impede the intercalation and deintercalation of lithium. The carbo-thermal process for producing LiFePO4 produces the conductive Fe2C on the surface of the LiFePO4 particle by a simple surface reduction process. The electronic conductivity of LiFePO4 is about 10-9S/cm and the diffusivity of the Li is about 10-15cm2/sec. This translates into fully charging a 50 nanometer particle will take about 1.75 hours. By comparison the Li diffusivity in LiCoO2 is about 10-10cm2/sec. Both the surface chemistry and the particle size are important in the use of LiFePO4 materials in batteries.

M. Broussely described the Saft lithium-ion (Li-ion) technology applied to a variety of stationary energy storage applications as replacements for lead acid and nickel metal hydride (NiMH). The advantages are very high energy storage (Wh/l and Wh/kg), high efficiency, and maintenance-free (sealed) with predictable end-of-life and state-of-charge characteristics. The Saft preference is for the stabilized lithium cobalt-nickel oxide cathode material, a natural graphite anode with hexafluorophosphate electrolyte with added VC. The cell design and cell balance depend on the application but are generally positive limited. On C/3 cycling to 80% depth of discharge (DOD) the cells show 13% capacity loss after 3200 cycles. On a simulated HEV test the cells cycled 50% state of charge and discharged at 2.2% DOD with 12 sec., 500 amp pulses; cells lost about 15% of their original capacity after 500,000 cycles. The cells have shown minimal degradation after 4.3 years of active life at 40C. A battery management system has been developed to increase safety and service life and controls on a cell-by-cell basis.

M. Fetcenko of Ovonic described their work to improve the performance of NiMH. The state-of-the-art systems now stand at over 100Wh/kg, 400Wh/l and up to 2000W/kg in commercial cells. They have developed a new modified AB2 alloy system with acceptable cycle life (400 cycled to 80%) but lower cost than the AB5 type alloys. The Ni(OH)2 materials have been developed with enhanced specific power and high temperature capability by incorporating nickel fibers and cobalt additions. Ovonics has found a way to enhance the capacity by stabilizing the charge and discharge of the nickel materials to the higher capacity alpha to gamma transition rather than the usual beta to beta for the charge-discharge regime. The smaller AA- and AAA-size cells are replacing alkaline primary cells in digital cameras, and all HEVs use the NiMH system as the power source.    more>