ISSUE NUMBER 11 FEBRUARY 1997 ISSN # 1086-9727

Concentrated Battery Business and Technology Summaries for Decision Makers

Considerations for Selection1 by Sol Jacobs *

The technical press pays a lot of atten- bon- chloride system, a heavy-duty By far, the leading primary battery tion to rechargeable, or secondary bat- version of the Leclanche cell, consti- technology, in terms of units sold in the teries, mainly because of the growing United States, is the alkaline system, number of portable-computing and based on , zinc and communications applications. But there a caustic potassium hydroxide-zinc are categories of applications that can Primary Battery Specific Energy oxide . Alkaline-cell technol- be addressed only by the less glam- ogy offers greater capacity for a given orous class of primary batteries. Alkaline cell size compared with Leclanche types, but it typically costs 50% more Li/12 These applications can be organized and weighs about 25% more. into groups that help to rationalize the Li/(CFX)x choice of primary battery technology. There have been some apparent Li/SO2 However, an overview of existing bat- improvements in alkaline cell perfor- tery technologies is a necessary first Li/MnO2 mance in recent years, but these have step in the decision-making process. been a result of changes in packaging Li/SOCL2 0 250 500 750 and manufacturing techniques rather The types of primary battery than any improvements to the basic chemistries available today include Watthours/kg. chemical system. traditional zinc--ammonium chloride (Leclanche cell), zinc-carbon- In the past, alkaline batteries were The Thionyl Chloride battery , alkaline (the leading type made with complex sealing systems has the highest energy density of pro- for consumer use), zinc-air and a and thick steel outer cases and end duction primary batteries. Just as with variety of lithium-based chemistries. caps. Several years ago, a method was other chemistries such as lithium , developed that allowed manufacturers lithium thyonyl shloride performance is The chemical systems employed in the to use thinner packaging materials and manufacturer dependent. Tadiran’s most widely used primary battery types more volumetrically efficient seals. have the highest energy density, voltage have been around for quite some time. That created room for more active and temperature range. The zinc-carbon-ammonium chloride material within a given standard cell “dry,” or Leclanche cell, system is size and increased capacity. more than 75 years old and still accounts for a little less than 10 per- The next change to come in alkaline- cent of all of the primary battery units tutes a similar portion of U.S. primary cell technology may actually be a step sold in the United States. The zinc-car- battery consumption. backward in capacity, but for a good

Issue No. 11, Feb., 1997, © 1997 by Teksym Corp. Maple Plain, MN, 55359, Phone 612-479-6190, Fax 612-479-3657, E Mail [email protected], Page 1 cause. , an environ- mental pollutant, is used in alkaline batteries as an anti-passivation stabilizer for the zinc . Without mercury, chemical processes within the battery cause the zinc to function less efficiently as discharge proceeds because of passivation of zinc surface, thus limiting useful battery life.

In the interest of keeping as much mercury out of the envi- ronment as possible, several states have developed propos- als to reduce the mercury con- tent of alkaline batteries. The current target for mercury con- tent is 250 ppm. The European Union has developed similar rules, also with the allowable mercury content of 250 ppm.

Major producers of alkaline cells are conducting research to find gen is absorbed into the electrolyte metals. Lithium is also the lightest environmentally suitable replacements through a gas-permeable, liquid-tight non-gaseous metal. Batteries based on for mercury. By the time mercury is membrane. With the removal of a seal- lithium chemistries have the highest phased out, it is likely the end user will ing tab, oxygen from the air is intro- specific energy (energy per unit not notice any changes in alkaline bat- duced into the cell. A zinc-air battery weight) and energy density (energy per tery performance. typically reaches full operating voltage unit volume) of all types. The high within 5 seconds of being unsealed. energy density is a result of lithium’s Mercury cells were once widely used The zinc-air system, while sealed, has high potential and the fact that lithium in many applications that required excellent shelf life, with a self-dis- reacts strongly with water. miniature or subminiature size and rel- charge rate of only 2 percent per year. atively low drain. Coin-sized versions That precludes the use of any aqueous Now, zinc-air battery technology, origi- (water-containing) electrolyte—-but nally developed in the mid-1980’s, has Zinc-air batteries are available in but- that turns out to be a benefit. Because become a high-capacity, high-energy- ton sizes for direct replacement of the oxygen and in water dis- density replacement for mercury. other button types, but recently intro- sociate in the presence of a potential Compared with mercury cells of the duced coin-sized versions are designed above 2 V, cells using aqueous elec- same physical size, zinc-air batteries, for pagers as well as personal medical trolytes are limited in voltage. Lithium with a nominal Open Circuit Voltage equipment, such as cardiac monitors cells, all of which use a non-aqueous (OCV) of 1.4 V, are up to 40 percent and transmitters. electrolyte, have nominal OCVs of lighter and have twice the capacity. between 2.7 and 3.6 V. However, the Zinc-air batteries offer much higher Of all the primary battery chemistries, use of non-aqueous results energy density than any alkaline bat- lithium has stirred the most interest in those cells having a relatively high tery type. among members of the electronics internal impedance. industry. Lithium is an ideal material Batteries using zinc-air technology are for battery because its intrinsic Lithium batteries also have extended energized only when atmospheric oxy- negative potential exceeds that of all operating-temperature ranges, made

Page 2 Issue No. 11, Feb., 1997, © 1997 by Teksym Corp. Maple Plain, MN, 55359, Phone 612-479-6190, Fax 612-479-3657, E Mail [email protected] possible by the absence of Manganese dioxide lithium cells are water and the chemical also available in standard cylindrical Lithium Thionyl Chloride and physical stability of and coin sizes. They are in many ways Components and Materials the materials. Some lithi- equivalent to poly (carbon monofluo- ☛ : Made of battery grade lithium foil, um-based systems, ride) cells in terms of construction, which is pressed on to the inner surface of the including Tadiran’s inor- energy density, safety and OCV, but cell can provide a mechanically sound and reli- ganic system, can operate typically have only about half the ser- able electrical connection. at temperatures as low as vice life. However, manganese dioxide- -55°C and as high as lithium cells are well-suited to applica- ☛ Separator: Between the anode and , +150°C. While incinera- tions having relatively high continu- prevents internal shorts while enabling to tion or other exposure to ous- or pulse-current requirements, move freely between the . It is made of very high temperature can since the cell internal impedance is non woven glass. cause the casings of lithi- somewhat lower than for other types. ☛ Cathode: Made of highly porous teflon-bond- um batteries to fail cata- ed carbon powder. Thyonyl chloride cathodic strophically, other battery A proprietary lithium-iodine technolo- reduction occurs on the cathode surface when a types behave similarly gy is offered by some manufacturers, load is connected. The high porosity of the car- under similar conditions. and that approach offers very good bon results in a true surface area compatible with safety, since it uses only solid con- the current capability of the cell. Under the broad category stituents. The separator in a lithium- ☛ Electrolyte: A solution of lithium aluminum of primary iodine cell can “heal” itself if cracks tetrachloride in thionyl chloride, which is highly types, there are several occur. This battery type powers the ionic conductive over the entire temperature chemical systems in majority of implanted cardiac pace- range. This temperature range and negligible mainstream use, each makers. The major drawback to the mass transport loss in the electrochemical sys- with its own set of perfor- lithium-iodine system is its high inter- tem contribute to the outstanding voltage stability mance and safety charac- nal impedance, which limits its use to of lithium thionyl chloride cells. The low freezing teristics. They are poly very low-drain applications. point (-105°C) and relatively high boiling point (carbon monofluoride) (>79°C) of the electrolyte result in a battery capa- lithium, or (CF)X-Li; Sulfur dioxide-lithium cells are used ble of operating over a wide temperature range. manganese dioxide lithium, almost exclusively in military/aero- ☛ Current Collector: A metal surface provides or MnO2Li; thionyl space applications and have somewhat

the electrical connection between the porous car- chloride lithium, or SOCi2 lower energy density than manganese bon cathode and the positive terminal of the bat- Li; sulfur dioxide lithium, dioxide-lithium or poly (carbon mono-

tery. or SO2Li; and iodine fluoride) lithium cells. Their service

☛ Can and Cover: Made of nickel-plated cold- lithium, or I2Li. life and energy density are less than rolled steel, the can is designed to withstand the half that of thionyl chloride lithium mechanical stresses that would be encountered Poly (carbon monofluo- cells. For safety, and “emergency” vent over the anticipated wide range of environmental ride) cells have an OCV structure is required in the hermetically service conditions. of 2.8 V and moderately welded case. ☛ Hermetic Seal: The positive cell termination is high energy density. insulated from the cell cover, which is the nega- Cylindrical types are High Energy tive termination, by a glass-to-metal seal that manufactured with a spi- uses compression sealing technology. In addition, ral-shaped cathode and Thionyl chloride lithium cells have the the cell cover is welded to the cell can by a laser crimped elastomer seals. highest energy density of all lithium seam welding process. The resultant ultra-high Though generally safe, types and are manufactured in welded, hermetically and mechanical integrity are major under extreme conditions hermetically sealed cases. Service life contributors to the excellent shelf-life obtained. the elastomer seals can is an unmatched 15 to 20 years and fail before the case fails, holds for all case types—-cylindrical ☛ : thus allowing the relative- and coin or wafer. The cells are best ➝ + - At the anode: 4Li 4Li + 4e ly reactive cell con- suited for applications having very low ➝ - - At the cathode: 2SOCl2 SO2 + S + 4Cl - 4e stituents to escape. The continuous-current and moderate pulse- ➝ Overall: 4Li + 2SOCl2 4LiCl + S + SO2 cells are available in all current requirements. Their extremely standard cylindrical sizes long service life and low self-discharge as well as coin types. rate make them ideal where physical

Issue No. 11, Feb., 1997, © 1997 by Teksym Corp. Maple Plain, MN, 55359, Phone 612-479-6190, Fax 612-479-3657, E Mail [email protected], Page 3 PRIMARY Lithium Battery Technologies

Chemistry Cathode Specific Voltage Operating Maximum Construction Application Material Energy Temperature Service Class Range Life TADIRAN Thionyl Chloride 700 Wh/kg 3.6 -55¡C to 150¡C 15-20 years Bobbin Industrial/commerial Li/SOCI2 hermetic weld Li/SO2 Sulfur Dioxide 260 Wh/kg 2.8 -55¡C to 70¡C 5 years Spiral, hermetic Military/ welded, vented aerospace

Li/MnO2 Manganese 330Wh/kg 3.0 -20¡ to 60¡C 5 years Spiral, crimped Consumer Dioxide elastomer seal

Li/(CF)x Poly (carbon 310 Wh/kg 2.8 -20¡ to 60¡C 5 years Spiral, crimped Consumer monofluoride) elastomer seal

Li/I2 Iodine 230 Wh/kg 2.7 0¡ to 70¡C 10 years Welded Implanted Medical Devices

access is limited, such as for remote ride) or manganese-dioxide lithium cell mum shock experienced by delicate sensing systems. of the same size. equipment or other goods during ship- ping. The information is stored until it Lithium battery chemistries differ in Remote sensing is retrieved for display by one of a several important characteristics. bank of LEDs. A typical version of the Carefully matching those characteris- Other remote sensing applications have device records maximum shock in four tics to the conditions of a particular made good use of lithium-battery char- ranges: for example, 10g, 20g, 30g and application is key to safe and reliable acteristics. At Sandia National 40g. The user interrogates the unit, and operation of the system. Laboratories (Albuquerque, N.M.), a the LED corresponding to the maxi- system of remote motion sensors of mum recorded shock is lit. The critical considerations are: nomi- undisclosed type was developed to help nal, minimum and maximum voltage; safeguard the fissionable materials—- Though the ShockRanger units are initial, average and maximum dis- primarily —-that have been intended for one-time disposable use, charge current; continuous or intermit- accumulated during the United States’ choice of a battery technology was tent operation; if intermittent, the ongoing nuclear-weapons-dismantling important to the designers. Quiescent amplitude and duration of minimum activities. The battery is required to current drain is in the hundreds of uA and peak current drains; required ser- supply a current in the range of several and increases to hundreds of mA when vice life; operating-temperature range; uA when the system is “asleep” and an LED is lit. a worst-case analysis, including highest 100 mA at low duty cycle during peri- expected current at lowest expected odic system interrogations. A cell Required service life is one year. But temperature and permitted voltage-rise working voltage greater than 3 V was the shelf life was key, as was the tem- time to minimum voltage: and storage required to bias the sensors and power perature independence of the self-dis- duration and conditions. the associated microsensors and power charge rate. The expected storage and at the associated microprocessor. operating temperature range is 0° C to Remote wireless-sensing applications Required service life is 10 years under 150° C. are also ideal for lithium primary bat- controlled-temperature conditions, but teries. For example, wireless passive long shelf life with potential high-tem- infrared (PIR) sensors used in security perature excursions was also an issue. * Sol Jacobs is the General Manager systems typically draw very small cur- of the Battery Division of Tadiran rents (tens of µA) in quiescent mode Dallas Instruments Inc. employs a Electronic Industires, Inc. He has a BS and 7.5 mA to 10 mA when transmit- thionyl chloride lithium wafer cell in in engineering, andan MBA. He has ting. Under those operating conditions, its ShockRanger R-1 single-axis shock been involved in international market- a thionyl chloride/lithium cell offers a monitor. The device consists of a ing and management for many years. service life up to 2-1/2 times longer piezoelectric “bimorph bender” that than either a poly (carbon monofluo- senses, along a single axis, the maxi-

Page 4 Issue No. 11, Feb., 1997, © 1997 by Teksym Corp. Maple Plain, MN, 55359, Phone 612-479-6190, Fax 612-479-3657, E Mail [email protected]