The Lithium/Iodine Battery: A Historical Perspective WILSON GREATBATCH and CURTIS F. HOLMES From Greatbatch Gen-Aid, Ltd., Clarence, New York
GREATBATCH, W., ET AL.: The Lithium/Iodine Battery: A Historical Perspective. The Jithium/iodine-
polyvinylpyndine battery, first implanted 20 years ago, has become the power source of choice for the cardiac pacemaker. Over the last 20 years, improvements in ceJ] chemistry, cell design, and modeling of cell performance have been made. CeJJs today exhibit an energy density over three times as great as cells produced in 1972. Well over 2 milJion pacemakers have been implanted with this chemistry, and the system has exhibited excellent reliability. (PACE, Vol. 15, November, Part II 1992] Introduction The precursor of the lithium/iodine-polyvinylpyridine (PVP) battery had its genesis in work done at the Jet Propulsion Laboratory in the mid1960s.* Gutman, Herman, and Rembaum reported the reaction of certain nitrogen containing polymeric compounds with iodine. The reaction product was termed a "charge transfer complex" and was shown to be conductive. Rudimentary cells were reported using a variety of metals, including magnesium and aluminum. Lithium metal was not reported in this work. A few years later, Moser and Schneider^'^ invented the lithium/iodine battery. Wilson Greatbatch became aware of this development and in 1971 an article was published recommending the lithium/iodine-PVP system as a power source for cardiac pacemakers.* Mead^ developed a thermal treatment of the iodine-PVP complex that led to improved performance, and in 1972, in Italy, the first such cell was implanted in a human patient.® The first cells were rather simple in design concept. One side of a lithium anode was exposed to the iodine-PVP cathode material, and a layer of lithium iodide was formed between these components, fabricating in situ the separator and the solid electrolyte. Much inert material was used in the cell to isolate the iodine containing material from the case walls. From this beginning, a 20-
Address for reprints: Wilson Greatbatch, Wilson Greatbatch, Ltd., 10871 Main St., Clarence, NY 14031. Fax: (716) 741-4304.
year history of cell development and fundamental research ensued, producing cells of higher energy density, greater current carrying capability, and great flexibility in cell design. Early Progress in Cell Design The first battery model to achieve real commercial success was known as the Model 702E cell (Wilson Greatbatch, Ltd., Glarence, NY, USA). This cell design featured a central lithium anode that was surrounded by the cathode material. This replacement of a "one-sided" cell design by this central anode concept resulted in a fourfold decrease in cell impedance. The cell contained considerable inert material such as polyester and fluorocarbons to isolate the active components from the stainless steel case walls. The cell was of nominal dimensions, 14 mm by 45 mm by 52 mm, and had a rated capacity of 3.5 A hours. After approximately 17 years on life test, samples of this cell model have completed their discharge in real time at 37°G. Figure 1 shows the discharge curve of a typical cell under a constant resistive load of 100,000 n. Greatbatch, Mead, and Rudolph^ demonstrated that the coating of the anode with pure PVP prior to cell construction led to a dramatic decrease in internal resistance throughout life. This cell design feature was incorporated into all cell models produced by Wilson Greatbatch Ltd. after the 702E. The desire for smaller pacemakers led to the development of smaller, more rounded cells featuring the anode coating procedure as well as
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LITHIUM/IODINE BATTERY HISTORY
2500 - '
2300 • ' Voltage (mV|
Figure 1. Discharge o/a Model 702E Cell under 100 kft load at 37°C.
smaller cells featuring a "lithium envelope" design, in which an external lithium anode completely enclosed the cathode material. These designs still contained inert material in order to ensure that the active components of the cell did not touch the stainless steel case walls. In 1975 it was determined that this material was unnecessary, and the first "case-grounded" cells were produced.^ These cells featured a central lithium anode surrounded by the cathode material. The case itself served as the entire cell enclosure and as the cathode current collector. This design greatly decreased the amount of inert material contained in the cell, and the resultant energy density was more than doubled. Further Design Developments In 1979 Schneider and co-workers^ announced the development of a "pelletized cathode" design. Instead of thermally treating the cathode material to form the final compound, finely powdered iodine and PVP were mixed and pressed into pellets that were placed on either side of a central lithium anode. These cells showed an improved current delivery capability and higher energy density than the "lithium envelope" cells they replaced. The case of the cell, initially fabricated with nickel but later changed to stainless steel, acted as the current collector. Additional design improvements included the development of a "corrugated" anode, which increased anode surface area and reduced macroscopic distortion of the anode during cell dis-
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charge.*" A dual anode design using the pelletized cathode development produced a cell with lower impedance. Alterations to cathode chemistry leading to higher current carrying capability were reported.^^ The process of anode coating as originally invented involved physically "painting" the anode with a solution of PVP in a volatile solvent that was evaporated prior to cell construction. In later years, two alternate methods were developed that allowed tighter control of coating weights and more efficient production. One such method involved the use of a cast film of PVP that was placed onto the anode.^^ The second involved the impregnation of an inert substrate with a solution of PVP, drying the solvent, and cutting the material into the appropriate shape for pressing onto the anode.^^ A significant advance was the development of thinner cells. Gells of 5-mm thickness were introduced in 1984, and today many pacemakers use such power sources. Even thinner cells have been developed and will be used in the future. Fundamental Cell Studies Over the years much work has been done to elucidate the basic chemistry of the cell and allow prediction of real-time cell discharge. The formation of the iodine-PVP complex was studied^^ and fundamental studies of the composition, phase diagram, and chemical nature of the cathode material have been made.^*~'^ The mechanism involved in the improvements due to anode coating
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has been investigated.^''"*^ A physically based modeling technique for determining cell discharge at low rates has been reported.^" All of these studies have indicated that there is much subtle and sophisticated chemisty occurring in what is at first glance an apparently simple battery system. Summary As a result of the investigations and developments occurring in several laboratories for the last
20 years, the lithium/iodine-PVP system has undergone significant improvement in performance, energy density, and flexibility of cell design. Much has also been learned about the fundamental chemistry of the system, allowing better cell design and prediction of discharge characteristics. Further improvements will continue to be made, and this chemistry is likely to see continued significant use as an implantable power source for many more years.
References 1. Gutman F, Herman A, Rembaum A. Solid state electrochemical cells based on charge transfer complexes. J Electrochem Soc 1967; 114:323-329. 2. Moser JR. U.S. Patent 3,660,163, 1972. 3. Schneider AA, Moser JR. U.S. Patent 3,674,562, 1972. 4. Greatbatch W, Lee JH, Mathias W, et al. The solidstae lithium battery: A new improved chemical power source for implantable cardiac pacemakers. IEEE Trans Biomed Eng 1971; BME-18:317-324. 5. Mead RT. U.S. Patent 3,773,557, 1973. 6. Antonioli G, Baggioni F, Gonsiglio F, et al. Stimulatore cardiaco implantabile con nuova battaria a sato solido al litio. Minerva Medica 1973; 64:2298. 7. Greatbatch W, Mead R, Rudolph F. Lithium/iodine battery having coated anode. U.S. Patent No. 3,957,533, 1976. 8. Greatbatch W. U.S. Patent 3,874,929, 1975. 9. Schneider AA, Bowser GG, Foxwell LH. U.S. Patent 4,418,975, 1979. 10. Zayatz RA. U.S. Patent 4,401,736, 1982. 11. Wicelinski SP, Jolson JD, Schneider AA. Biomedical applicaions for low to moderate rate batteries. In: Proceedings of Fifth Battery Gonference on Applications and Advances. 1990, V-2. 12. Skarstad P. U.S. Patent 4,182,798, 1980. 13. Greatbatch W, Holmes GF, Mueller M. Discharge characteristics of the lithium/iodine pacemaker battery. (Abstract 21) In: Extended Abstracts of the Fall 1977 Electrochemical Society Meeting. Princeton, NJ, The Electrochemical Society, 1977, pp. 58-60. 14. Phillips GM, Untereker DF. Phase diagram for the poly-2—vinylpyridine and iodine system. In BB Owens, N Margalit (eds.): Power Sources for Biomedical Implantable Applications and Ambient Temperature Lithium Batteries. Pennington,
NJ, The Electrochemical Society, 1980, pp. 195-206. Brennen KR, Untereker DF. Iodine utilizaion in Li/ I2 (poly-2-vinylpyridine) batteries. In BB Owens, N Margalit (eds.): Power Sources for Biomedical Implantable Applications and Ambient Tempierature Lithium Batteries. Pennington, NJ, Tbe Electrochemical Society, 1980, pp. 161-173. McLean RL, Bleecher J. Halogen induced modification of poly-2-vinylpyridine during lithium-balogen battery life. In BB Owens, N Margalit (eds.): Power Sources for Biomedical Implantable Applications and Ambient Temperature Lithium Batteries. Pennington, NJ, 1980, pp. 207-220. Holmes GF, Brown WR. Effects of anode precoating on the characeristics of the lithium/iodine pacemaker battery. In BB Owens, N Margalit (eds.): Power Sources for Biomedical Implantable Applications and Ambient Temperature Lithium Batteries. Pennington, NJ, The Electrochemical Society, 1980, pp. 187-194. Brown WR, Fairchild WR, Hornung HA, et al. The effects of anode precoating on the stuctural and electrical properties of the solid electrolyte formed in lithium/iodine-polyvinylpyridine batteries. (Abstract 174) In: Extended Abstracts of the Fall 1984 Electrochemical Society Meeting. Pennington, NJ, The Electrochemical Society, 1985, p. 257. Phipps JB, Hayes TG, Skarstad PM, et al. Lithium/ iodine batteries with poly-2-vinylpyridine coated anodes; A microstructural investigation. (Abstract 175) In: Extended Abstracts of the Fall 1984 Electrochemical Society Meeting. Pennington, NJ, The Electrochemical Society, 1985, p. 258. Schmidt G, Skarstad P. Stimulation of performance distribution in lithium/iodine batteries. In: Proceedings of the Seventh Battery Gonference on Applications and Advances. 1992, V-2.
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