ISSUE NUMBER 11 FEBRUARY 1997 ISSN # 1086-9727 Concentrated Battery Business and Technology Summaries for Decision Makers Considerations for Primary Cell Selection1 by Sol Jacobs * The technical press pays a lot of atten- bon-zinc 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 manganese dioxide, zinc and communications applications. But there a caustic potassium hydroxide-zinc are categories of applications that can Primary Battery Specific Energy oxide electrolyte. 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-carbon-ammonium chloride (Leclanche cell), zinc-carbon- In the past, alkaline batteries were The Lithium Thionyl Chloride battery zinc chloride, 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 ion, 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. Mercury, an environ- mental pollutant, is used in alkaline batteries as an anti-passivation stabilizer for the zinc electrode. 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 hydrogen 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 electrolytes 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 anodes 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- ☛ Anode: 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 cathode, +150°C. While incinera- tions having relatively high continu- prevents internal shorts while enabling ions to tion or other exposure to ous- or pulse-current requirements, move freely between the electrodes. 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 lithium battery 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.