from June 2011 ABT

meeting report

28th International Battery Seminar and Exhibition

Ft. Lauderdale, FL USA

March 14-17, 2011

The International Battery Seminar and Exhibit is an annual event held at the Broward County Convention Center in Ft. Lauderdale, Florida. It is organized by Dr. Sumner P. "Shep" Wolsky and Dr. A. Harry Taylor and is administered by Mr. Tom DeVita.

The 28th seminar was highly successful, attracting approximately 500 attendees despite the lingering effects of the economic downturn and the occurrence of a devastating earthquake and tsunami off the coast of northern Japan only a few days before it began. More than 50 presentations were given on various topics, but with two particular areas of emphasis: lithium ion (Li ion) batteries and large-format batteries for both electric vehicles and stationary applications. More than 100 exhibitors and sponsors confirmed the seminar as a premier event for industrial and academic battery professionals. As in previous years, the seminar opened with two tutorials.

Chesworth_Gibbard

Editor Jo Chesworth and Dr. H. Frank Gibbard at the ABT booth.

The first tutorial, given on Monday morning by Prof. Doron Aurbach of the Department of Chemistry of Bar University in Israel, was entitled "Advanced Materials (anode, cathode, electrolytes, separators) for Li Ion Batteries, Their Appropriate Selections and Characterization." In keeping with the general themes of the seminar, Prof. Aurbach emphasized lithium ion cells for the EV application, reviewing the present state of the art and advances now being pursued at many laboratories. The implications of thermodynamic instabilities of both the anode and the cathode of high-voltage lithium ion cells, with respect to reactions with the electrolyte, were discussed. The use of many analytical techniques (an area of special expertise of Prof. Aurbach) to study electrodes, electrolytes and current collectors, was described for various materials. He debunked the idea that nanotechnology could contribute positively to most areas of battery technology, pointing out areas in which the use of nanomaterials can be either advantageous or deleterious. Among the research needs identified for lithium ion EV batteries, the development of electrolytes with improved low-temperature performance was singled out.

The second tutorial, entitled "Worldwide Market Update on Secondary Batteries for Portable Devices, Automotive and ESS," was scheduled to be given by Hideo Takeshita of the Institute for Information Technology of Japan. This year Takeshita, like many other Japanese planned participants, was unable to travel to the seminar. In his absence, Dr. Brian Barnett of TIAX gave a presentation of the slides that Takeshita was able to send, supplemented by materials based on studies of Barnett and his colleagues at TIAX. Market trends were presented for lithium ion cells in portable electronic devices, and projections were given for a very large growth in lithium ion batteries for EV applications, from a small base in 2011. Norman Allen also gave a brief but informative discussion of the situation in the U.S. for venture capital investments in battery ventures for mobile, EV and energy storage applications.

Copies of both tutorials are available on CD from the seminar organizers at www.PowerSources.net.

The first presentation at the Plenary Session on Monday afternoon was given by James Barnes of the U.S. Department of Energy, who spoke on "U.S. DOE Electric Drive Vehicle Battery Manufacturing and R&D Progress." This presentation began with an overview of DOE’s funding of energy storage, including science and technology for the near term (manufacturing and material supply of first-generation lithium-ion batteries), applied research and technology development (next-generation lithium batteries), "transformational research" supported under the Advanced Research Projects Agency-Energy (ARPA-e) program, and long-term basic research on battery materials and phenomena under the office of Basic Energy Sciences. The emphasis of this talk was on electric drive vehicle energy storage technology, though DOE supports other work on stationary energy storage. This limitation enabled a rather comprehensive description of the activities relating to electric-vehicle energy storage.

Data were presented on the specific institutions supported by DOE funding (including universities and government laboratories as well as for-profit companies), on funding trends over the past several years, and on DOE goals for Plug-in Hybrid Electric Vehicles (PHEV’s). The value chain for advanced battery manufacturing was presented for "commercial ready technologies" in terms of material supply, cell components, cell fabrication, pack assembly and battery recycling. The DOE’s support of these activities at the level of $1.5 billion, at 20 different companies throughout the U.S., was presented as a strong stimulus to the achievement of the Administration’s goal of one million PHEVs on the roads by 2015.

M. Lord, speaking for Toyota, next presented Preparation for PHEV Market Introduction, a review of Toyota’s EV program from the 1990’s to date. He described the introduction of three generations of the Prius automobile, culminating in the demonstration of 600 Prius PHEVs since 2010. The lithium ion battery was described as comprising 288 prismatic cells of 5Ah capacity, with a battery voltage of 345V. Extensive tests were performed in five countries, with 13 vehicles being exposed to durability tests. Toyota conducted interviews with drivers of the test vehicles, comparing their expectations with their experience

The next paper, titled Lithium Ion Battery Technology: What Lies Ahead and How We Can Get There,was given by S. Ahn of LG Chemical. The author began with a brief review of LG Chemical, which began as a small cosmetics company in 1947. Work on battery technology began in 1995, when the company realized the potential for rapid growth of battery-powered products; their investments in battery R&D have resulted in a portfolio of approximately 800 patents on battery materials. Primary areas of R&D on lithium ion batteries are the cathode (reduction of Co content), safety (ceramic-coated separator), and electrolytes (higher voltage window). The following market trends were noted: the need for higher energy density in batteries for smart phones, and for wider and thinner polymer cells for tablet computers, and growth in the market for 18650 cells partly driven by their adoption for use in electric vehicles. An informative graph was presented showing the increase in energy density of 18650 cells over the past decade and with projections for the future, though the projections for "separator-free" cells struck some participants as overly optimistic. The author also cited the need for cathode materials to pair with silicon anodes.

After a break, the Plenary Session continued with a contribution from H. Uchi, Chemi-Con (Japan), entitled Nippon Chemi-Con Nanotechnology for Capacitors, Hybrid Energy Storage Devices and Lithium Ion Batteries. Nippon Chemi-Con was described as a vertically integrated, billion-dollar aluminum capacitor company. Their larger (300 Farads and up) double-layer capacitors are used in a variety of applications requiring large energy pulses of short duration, such as lifting and lowering loads by cranes, digging operations with hydraulic excavators, and UPS installations up to 2MW. Their current research interests are to increase operating temperatures to 85ºC and to address stop-and-start systems for automobiles. They are exploring the use of carbon nanotubes in combination with Li4Ti5O12 (LTO), with the ultimate goal of achieving specific power comparable to that of lithium ion batteries but capable of much higher discharge rates.

The next paper, presented by Jeff Dahn of Dalhousie University, was titled How Can You Tell if a Li Ion Battery Will Last for 30 Years: An Experiment That Takes 3 Weeks. The author argued that very highly accurate cycling measurements can enable better insights into failure mechanisms, and that present-day commercial cycling equipment is severely lacking in the precision necessary to make such measurements. The main point of this argument is that failure mechanisms encountered in lithium ion batteries will result in coulombic inefficiencies that can be measured and used for predictions of cell life. The audience was referred to various recent studies in the literature by the author’s research group.

Dr. Brian Barnett presented the next paper, New Safety Technologies for Li Ion. This paper described a study of the effects of internal shorts in lithium ion cells that can lead to safety incidents in the field. The author pointed out that although the rate of occurrence of such incidents may be reduced, even to one part in 10 million cells, it can never be completely eliminated. The concept of a "safe zone" for cells was described, such that cell shorts having a relative energy and a relative power below certain measureable thresholds would not cause a thermal runaway. Finite-element thermal models were described for PHEV cells, with the interesting result that prismatic cells are generally safer than cylindrical cells of the same energy. In experimental studies, cells were constructed with deliberately-induced short circuits; among other results, it was found that the occurrence of a short that can lead to a thermal runaway must be detected several cycles prior to the runaway event. TIAX continues to develop safety technologies to detect incipient thermal runaways, and to intervene and contain them.

Steve Lambouses of Texas Instruments presented Monday’s final paper, Building Better Batteries with Battery Management. He spoke of the need for robust and cost-effective systems for monitoring, protecting and charging batteries, and recent improvements in the design of battery management systems. Whereas such systems previously had been available for laptop computers and cell phones, a much larger selection of battery management systems is becoming available for a much larger variety of applications. Of particular interest was the recent availability of wireless battery charging systems, which in the past had been limited to low-power devices such as electric toothbrushes and certain medical rechargeable batteries.

The first paper on Tuesday morning, U.S. and International Regulatory and Legislative Issues Impacting Battery Industry, was presented by George Kerchner of PRBA, The Rechargeable Battery Association. Changes in regulations for the shipment of lithium primary and rechargeable batteries, in the U.S. and foreign countries, were described. New regulations on "product stewardship," including the collection and disposal of used batteries, were covered; and the shipment of waste and damaged lithium batteries was described from a regulatory standpoint.

Kevin White of Exponent Failure Analysis Associates presented a paper entitled, Thermal Stability of Lithium-ion Cells as Functions of Chemistry, Design and Energy. The objective of this work was to develop "apples-to-apples" comparisons of lithium-ion cell thermal stability, independent of their chemistry. To this end, accelerating rate calorimetry (ARC) studies were made on 18650 cells at various states of charge, and comparisons were made on the basis of cell energy. Four types of cells were employed: iron phosphate, LMO/NCM, LCO (high power) and LCO (low power). Some general conclusions resulted, the most important of which was that cell energy dominates both the onset of self-heating and the rate of self-heating, i.e., that cell chemistry and cell design are relatively unimportant in determining these safety metrics. A concise "takeaway" message also emerged from the studies: "Don’t charge your batteries (with high-voltage cathodes) fully if you don’t have to; you’ll get longer life and greater safety."

John Zhang of Celgard presented the paper, Li-ion in EDV and Safety Perspectives, and began his presentation with an interesting table rating five lithium ion chemical systems for electric-drive vehicles (EDV) according to eight criteria, on a five-point scale. He considered the question of whether EDV batteries should employ large or small cells and came down strongly on the side of small cells in parallel configurations vs. large cells of the same capacity. His reasoning had to do with the multiple safety features that could be incorporated in or on the small cells (fuses, separator shut-down, electrode shut-down, PTC, and others) that would be more difficult or impossible to use in large cells. Additionally, heat dissipation from large cells is lower, owing to the longer heat-transfer paths. Other findings promoting safety were found to be the use of a lower state of charge for lithium ion cells, and the design of cells so as to have low shorting power and electrodes that tend not to propagate thermal runaway. The most intractable problem he found was lithium deposition, which he stated occurs in 90% of lithium ion cells, but nearly always in a benign condition.

Michael Sanders of DuPont presented the next paper, Advanced Separators for High Performance Lithium Ion Batteries. After reviewing the various materials that DuPont makes that find use in lithium ion cells and packs, including electrolytes, cathode active materials and binders, and battery back insulators, he concentrated on a new class of nanofiber separators based on polyimide materials, sold under the trade name Energain™. These materials were said to provide high temperature stability, high power performance, and good chemical resistance and wetability to battery electrolytes.

In a contribution from Argonne National Laboratory and EnerDel, Ilias Belharouak presented the paper, Understanding Power Fade Mechanism in Li4Ti5O12/LiMn2O4 Cells. This lithium ion battery system has exceptionally high power density, low-temperature performance and excellent safety, but due to its low cell voltage of 1.5V, is not rated as a high-energy-density system. This paper addresses the cause of fading power and capacity when the cells are cycled at 60ºC. Many possible causes for these losses in performance were evaluated by careful analytical studies. The most significant findings were from XPS and SEM studies of the electrodes, where it was found that reaction of the salt from the electrolyte had reacted with the negative active material, forming an amorphous material that completely obscured the presence of Ti. No solution to this problem has been applied, but promising approaches have been identified.

Eric Maki of MEGTEC Systems Inc. next spoke on Advanced Coating and Drying Techniques for increasing the speed and lowering the cost of electrode processing in lithium ion cells. He reviewed the present manufacturing methods for coating and drying, and identified new approaches to achieve up to 50% reduction in cost and increases in productivity. For coating, this comprised dual-side operation, line speeds of more than 50m/min, web widths of more than 1m, and the use of ultra clean rooms, e.g., ISO Class 5.

The first paper of the Tuesday afternoon session was presented by Takehiko Ishii of Sony Energy Devices Corp., with the title of Sony’s Lithium Ion Battery Using Olivine-type LFP Cathode and New Energy Storage Module. This paper described Sony’s 18650 and 26650 cells that employ the olivine LiFePO4 positive electrode material. The two cells, with nominal capacities of 1100mAh and 3000mAh, respectively, at 3.2V, are intended for use in power tools, electric motorcycles, and for energy storage applications. They show excellent high-rate performance and resistance to high-temperature storage (recovery of 85% capacity at 10A discharge after storage for two years at 60ºC), and are projected to have lifetimes of 10 years.

Next, Shinya Miyazaki of Sanyo Electric Co. Ltd. presented a paper titled, Latest Developments of Li Ion Batteries. Sanyo’s 18650 cell development efforts have resulted in segmentation into three designs for different markets: a 3000mAh cell for high-capacity needs, a model for high power, with either 1200mAh or 1600mAh, and a model with 2000-2250mAh providing a compromise between low cost and adequate performance. Present and projected prismatic designs (thinner but with greater area) were shown that demonstrate Sanyo’s intention of supplying power solutions for a wide range of consumer and industrial applications, from digital devices to electric vehicles and power tools and, in the future, solar energy systems.

Continuing the series of presentations from major Japanese lithium ion manufacturers, H. Matsuno of Panasonic presented a paper entitled, Lithium-Ion Batteries Using Ni-based Cathode Material for High Capacity and Reliability. This paper described the extension of Panasonic’s line of lithium ion cells based on NNP positive electrodes containing nickel (for high capacity), cobalt (for structural stability) and aluminum (for thermal stability). The line of products contains cylindrical cells rated at 700-2900mAh and prismatic cells with nominal capacity of 700-1320mAh. A roadmap showing increases in capacity density of prismatic cells to 500Wh/L attributed an increase of 12% to use of the NNP cathode material, 4% to use of a denser anode material, and 2% to mechanical effects, i.e., the use of thinner parts.

Next, John Wozniak of HP Mobile Computing spoke on Quantifying and Improving Battery Quality to Increase Customer Satisfaction. This presentation gave an interesting and succinct explanation of the conflict between laptop computers customer’s expectations for (a) long run time and (b) long calendar life. Since the fraction of laptop users who are truly mobile has increased over the past few years, maintaining long run time over the life of the pack has become more important. Charging to a higher cell voltage (e.g., 4.2V/cell) yields more run time but shortens battery pack life. Thus it would appear that a lower charging voltage would provide greater customer satisfaction, but this runs counter to the industry trend to rate batteries by their initial run time.

Andy Keates of Intel next presented a paper on Hybrid Power Boost for Mobile Computing. The objectives of the work described in this paper were to provide the customer-perceived quality of "snappiness" of operation of laptop computers without the use of a large AC adapter and without sacrificing much if any battery life. These goals were apparently achieved by the use of a "hybrid power boost" that detects when higher power is needed (for short times, on the order of a few milliseconds) by the host device and "borrows" power from the battery to supplement that drawn from the AC adapter. The charger then "pays back" the energy borrowed from the battery during lower-power operation. The performance goals were achieved at the possible cost of shorter battery life for some, but not all, device users.

The next paper was a contribution from Shanghai Changyuan Wayon Circuit Protection Co., entitled Application of Fuzzy Algorithm and Active Balancing in BMS, presented by W. Tao. This paper described the development of a fuzzy-logic algorithm to determine the state of charge of lithium ion batteries, based on measurements of capacity, discharge rate, charge rate, temperature, self-discharge, and aging. The use of a fuzzy-logic algorithm was dictated by the complex, nonlinear relationships among the state of charge and the experimental parameters. Based on the state of charge, the battery management system (BMS) performs balancing (apparently at the cell level) during all states of the battery: charge, discharge, and rest. Battery management systems were stated to be applicable to power tools, large and small vehicles, and for communications applications.

The final presentation on Tuesday afternoon was made by Henry Mao of China BAK Battery Inc., as was titled, Advances in EV Battery Cell Design and Process Control. This presentation was given in two disparate parts the first devoted to a description of the company, its lithium iron phosphate products and markets, and the second comprising rather detailed descriptions of two design and manufacturing issues. The company’s products range from power sources for electronic devices notebook PCs, cell phones, and other handheld devices to electric vehicles, including bikes, cars, and buses. Since the bus batteries contain up to 22,000 cells, risk mitigation, including design and testing, is paramount. The range of design activities extends from cells to strings to modules and complete batteries, as well as battery management systems.

The author presented two manufacturing challenges: inconsistent cells in parallel connections, and rheological considerations in slurry consistency (for electrode coating). Large-format prismatic cells were described, and the principal conclusion was that the manufacturing for individual sub-cells must produce closely matched electrodes, just as the capacities for smaller cells in parallel arrays must be. A detailed description of viscoelastic processes and rheological analyses was presented, with the conclusion that much work was necessary to get products of the needed quality.