RecentRecent DevelopmentsDevelopments inin BatteriesBatteries forfor PortablePortable ConsumerConsumer ElectronicsElectronics ApplicationsApplications by Ralph J. Brodd

he engine that powers the growth the production volume was lower. This medium drain applications but lack the in batteries, especially primary is a remarkable growth rate for a new high current capability, shelf life, and and small rechargeable varieties, battery system. The alkaline primary bat- leakage resistance of the alkaline cell. has been, and will continue to be, tery was introduced in about 1960 and it Worldwide, there were about 15 billion the proliferation of portable elec- took over 15 years to equal the sales carbon-zinc cells produced in 1998. In tronic devices the U.S., there has Tthat find use in our been a shift away from 300 daily lives. The world- Ni-Cd the traditional carbon wide battery market zinc (Zn-MnO with 250 Ni-MH 2 in 1997 was about NH4Cl or ZnCl2 elec- $34 billion of which Li-ion trolyte) dry cell con- the primary market 200 structions to the segment was about higher performance $10 billion. The 150 alkaline (Zn-MnO2 growth in primary with KOH electrolyte) batteries has closely 100 cells. Both the followed the increased Leclanché and zinc use of “boom” boxes, chloride are now Sales Value, Yen Billion Sales Value, 50 Walkman portable imported into the U.S. cassette and disc (the last major pro- players, and the like. 0 ducer of carbon zinc in The worldwide 1990 1991 1992 1993 1994 1995 1996 1997 the U.S. has just dis- rechargeable market Year continued produc- segment in 1997 was tion). This shift to about $24 billion with FIG. 1. Growth of the small rechargeable cell market segment. H. Takeshita, Proceedings of Power alkaline cells has been lead acid accounting ’98, Giga Information Group and Arthur D. Little, Santa Clara CA, October 4-6, 1998. slower to occur in for over half of this Europe and Japan value. The double-digit growth of small value of the carbon-zinc in the U.S. where the consumer is more conscious rechargeable cells has paralleled the Japan dominates the production of the of the cost-performance ratio. spectacular growth of cellular phones rechargeable cells and sets the standard Alkaline cells now dominate the U.S. and laptop computers. These devices for quality and performance. market for primary cells with the U.S. demanded greater performance than producers setting the standard for was available from rechargeable nickel Primary Batteries quality and performance. There has cadmium (Ni-Cd) and alkaline primary been a shift in product mix away from cells. In response to this demand and Figure 2 illustrates the energy the larger D- and C-cells to the smaller the environmental pressure on Ni-Cd, storage capability of the common pri- AA- and AAA-size cells. Strong competi- the lithium-ion (Li-ion) and nickel metal mary battery. Since the energy deliv- tion has led the major producers to hydride (Ni-MH) rechargeable battery ered by a battery varies depending on institute significant service improve- systems have been developed. Figure 1 the design, current drain, temperature, ments to meet the competition. Service depicts the growth in the rechargeable etc., the energy storage capability in life has increased over 30% compared to market and the shift from Ni-Cd to Li- Fig. 2 is depicted as a field, rather than 10 years ago. The high current pulse ion and Ni-MH. The market for Ni-Cd the single “best” value, to illustrate the capability has also been improved. has remained fairly constant while Ni- variation in performance in its area of These improvements were accom- MH and Li-ion have supplied the application. The carbon zinc cells, both plished by a major redesign of the growth. In 1997, the sales value of the Leclanché and zinc chloride versions, internal structure and composition of Li-ion surpassed that of Ni-Cd although are more cost effective for low to the components of the alkaline cell. The

20 The Electrochemical Society Interface • Fall 1999 outside label has remained intact so the tions. Mercury cells have been phased wrap constructions of the lithium man- public perception is that little change out from consumer applications. Only a ganese dioxide (Li-MnO2) and lithium has occurred over the past ten years. few highly specialized medical and mili- carbon monofluoride (Li-CFx) cell sys- The three major components of the tary applications still use the mercury tems have captured the camera market alkaline cell—the anode, cathode, and cell to power the devices. while coin cells service the memory separator—all have undergone signifi- Lithium metal anode primary cells protection applications. Both Li-MnO2 cant changes. The specifications of the have high energy storage capability but and Li-CFx coin cells are widely used as composition of the manganese dioxide lack high power capability. The thin (4- memory protection in CMOS circuitry cathode active material now applications. Electrolyte modi- require control of critical impu- fications have improved the rities to less than parts-per-mil- 1000 high temperature performance lion level with improved in response to higher oper- current carrying capability. The ating temperatures found in Lithium Cylindrical internal structure of the 500 the newer high performance cathode active mass has been Zinc Air devices. The thin postage modified to improve the diffu- Lithium Coin stamp sized lithium cells have sion into the mass and to found a niche market in secu- Alkaline increase the surface area for rity cards, but their envisioned better performance at high cur- Silver use in powered “smart cards” rents. New zinc powder anode has not yet occurred. compositions have eliminated The Li-FeS AA-size cell has 100 2 mercury. Other zinc alloying been developed for photoflash Log Energy Density, Wh/kg Log Energy Density, Mercury agents and added organic cor- applications. This system was rosion inhibitors provide the Carbon-Zinc originally developed to pro- control of zinc corrosion 50 vide a low cost alternate to (hydrogen gas generation) to 100 1000 5000 silver-zinc cells. Although the essentially the same levels as Log Energy Density, Wh/I lithium metal anodes do not when mercury was the main have good high current capa- corrosion inhibitor. The par- FIG. 2. Comparison of the energy storage capability of various primary bat- bility, the combination of thin ticle size distribution of the tery systems. Please note the different scales in Figures 2 and 3. electrodes with large geometric zinc powders has also changed. surface area, combined with The composition and stability an innovative opposite-end of the KOH gelling agents, current collection, yields a cell which hold the zinc powders 400 Lithium Metal design with very uniform cur- in the anode compartment, Li-Ion/SPE rent distribution. This gives has also been modified. the cell excellent pulse capa- Although the basic overall bility. The fact that the manufacturing processes for 300 cathode decreases in resistance the new cells are the same, during discharge gives the cell these changes in materials and low internal resistance and internal construction have Zn-MnO2 uniform fast response, even to Ni-MH required extensive modifica- 200 the end of the service life. tions to the unit manufac- turing processes. The state of Ni-Cd Rechargeable Cells charge indicator on the label of alkaline cells, that was intro- Wh/l Energy Density, 100 Lead Acid Rechargeable batteries can duced as a marketing feature, be discharged and then will likely be removed in the restored to their original con- future. It is inaccurate and of dition for reuse. The energy questionable usefulness to the 0 storage capability of the 0 50 100 150 200 average consumer. Also, when common rechargeable cells is activated, it discharges the cell Energy Density, Wh/kg shown in Fig. 3. A rule-of- and lowers the service life. thumb states that a cell should The zinc-air (Zn-air) button FIG. 3. Comparison of the energy storage capability of various be capable of delivering 300 rechargeable battery systems. Please note the different scales in cell has the highest energy complete discharge-charge FIGS. 2 and 3. storage capability of all con- cycles to 80% of its original sumer cells. It has captured almost 95% 8 Å) protective film that forms on the capacity for it to be classified as a of the hearing aid market. Zn-air cells lithium surface by reaction with cell rechargeable battery system. In the have twice the capacity of the same size electrolyte results in a low exchange past, the energy storage capability of zinc-silver button cells. A new construc- current density. As a result, although rechargeable cells was significantly tion concept described in U.S. Patent they have higher energy storage poten- lower than that of primary cells. The 5,691,074 restricts airflow to the oxygen tial, lithium cells have not replaced advantage of the rechargeable batteries electrode. New constructions, based on alkaline cells for most applications. is their high current capability and this development, could open the way Lithium anode cells now provide the their ability to accept recharging to to commercialize Zn-air cells in cylin- power for most camera and memory restore their capacity to the original drical format or in battery pack construc- protect applications. Wound or spiral- level. For the first time, the energy

The Electrochemical Society Interface • Fall 1999 21 storage capability of rechargeable bat- Wh/l and 200 Wh/kg in the future. “solid electrolyte interface” often teries is almost equal to that of pri- Considerable effort is being devoted to termed, SEI. These reactions consume mary cells. The newer rechargeable develop the Ni-MH for use in electric a portion of the lithium ions and make Li-ion and Ni-MH systems have nearly vehicles. them unavailable for use later in the the same volumetric energy storage The Li-ion battery system, first energy producing battery reactions. capability as that of alkaline cells. The introduced by Sony in 1991, has This is often termed “first cycle loss.” Li-ion cell is inherently lighter. The enjoyed spectacular growth as noted in The graphitic materials tend to have a recycling of rechargeable batteries Fig. 1. Li-ion has been termed a lower first cycle loss than the “hard” makes them even more environmen- “rocking chair” or “swing” battery carbons or cokes. tally friendly. system since the cell reactions essen- The Li-ion is the system of choice to The rechargeable alkaline Zn-MnO2 tially transport lithium ions from one power many portable energy devices reappeared as the Renewal® brand in electrode to the other and back again. because of its lightweight and good the U.S. The internal structure and During charge, the lithium ions from overall performance. Li-ion polymer design of the primary alkaline cell has the lithium cobalt oxide (LiCoO2) cells with a solid polymer electrolyte been modified at the cost of capacity cathode active mass intercalate into (gel) are now appearing on the market. to produce the rechargeable version. It the crystal structure of the These cells can be produced in large offers a low cost alternative to other carbon/graphite negative active mate- footprint (8˝ x 10˝) thin formats. The rechargeable systems. It also has lower rials. On discharge, the ions reverse Li-ion polymer cells could satisfy the cycle life than the industry standard. direction, leave the carbon and re- demand for a 100 Wh battery pack that For many years the Ni-Cd was the enter the cathode structure. Although would allow a traveler to use a note- major small rechargeable cell system. It Li-ion is used to designate the cell book computer on cross-country used a simple charger and had better chemistry, there is no lithium metal in flights. It would also allow additional cycle life and high rate performance the cell. Lithium refers to the Li+ ions “power-hungry” features to be incorpo- than the lead acid system. Since it is intercalated into the crystal structure rated in the notebook computer. At the more costly than lead acid, it has of the carbon and cobalt oxide active present time, the Li-ion does not have found wide use only in the smaller materials and the ions of the elec- the high power capability applications spiral wound constructions. The Ni-Cd trolyte that transport current during or the low temperature performance of has a designed-in overcharge and cell operation. either Ni-Cd or Ni-MH. Nonetheless, overdischarge protection system based The cathode active material supplies the light weight of the Li-ion has made on a chemical shuttle mechanism. It is the lithium for cell operation. Initially, it the system of choice for laptops and very robust and can tolerate abuse con- the Li-ion system was developed using cellular phones. In situations where the ditions. It can be stored in a discharged LiCoO2 as the active material. Its crystal phone is given away for agreeing to a condition without serious damage. structure undergoes an irreversible service contract, the heavier but lower The Ni-MH system was developed change if the cell voltage exceeds 4.2 cost Ni-Cd still prevails. as an alternative to the Ni-Cd. The volts or falls below 2.7 volts. Electronic A notable side benefit of the environmentally threatened cadmium controls are required to limit charge requirement for voltage and current negative electrode in Ni-Cd was and discharge voltages between these control of the Li-ion system has been replaced by a hydrogen absorbing two levels on an individual cell basis. the advent of “power management” alloy negative electrode. The voltage of The electronic controls also function as for all rechargeable systems. The cir- the two systems is essentially the same. a safety feature by stopping cell opera- cuitry and software developed to allow The change in chemistry allowed a tion if the cell exceeds a current limit or the exchange of information between new internal cell balance with signifi- a preset temperature. the battery and the device has greatly cantly increased energy storage capa- Other transition metal oxides of enhanced safety and improved run- bility. New, high density, spherical nickel and manganese are also poten- time. Power management is imple- nickel oxide cathode materials, cou- tial cathode active materials for the Li- mented by the incorporation of an IC pled with non-woven nickel fiber cur- ion system. The lithium nickel oxide package that monitors and controls rent collectors, have significantly (LiNiO2) has a higher capacity but is the pack operation on a cell-by-cell improved the performance of the difficult to prepare and may have basis for both discharge and charge. nickel electrode for both Ni-Cd and Ni- potential safety problems. Recently, These same features also improve the MH. The same simple charging sys- mixed oxides of cobalt and nickel operation of Ni-Cd and Ni-MH. As a tems can be used with minor (20% to 30% nickel) are employed to result, the control circuitry and modifications for either system. increase the cell capacity while chargers for rechargeable batteries is an The hydrogen absorbing alloys used avoiding the potential safety problems active technology development area. in the Ni-MH cells are based on two of the pure nickel oxide. The man- Power management has become a hot different alloy systems. One, termed ganese spinels (LiMn2O4) have topic in over-all system design. With AB5, is based on misch metal alloys received intensive study and are in the advent of the Li-ion cell and its and the other, termed AB2, is based on limited use. They possess lower need for electronic control to prevent transition metal alloys. Both alloy sys- capacity than the cobalt materials, but abuse conditions from developing, tems contain numerous components are lower in cost. Cells employing the new concepts for charging have to improve hydrogen storage, corro- spinel are reported to require simpler emerged. sion, structural stability, etc. Competi- electronic controls. The control circuitry has been tion is strong and manufacturers have During the first charge (formation) extended to include charging opera- steadily increased the cell capacity as of the Li-ion cells, a portion of the tions of other rechargeable battery sys- manufacturing and design improve- lithium ions react with the electrolyte tems. The IC chip in “smart” chargers ments are instituted. It is estimated and the active oxygen species on the can identify the type of battery from that the Ni-MH can deliver almost 400 surface of the carbon to produce a its response to the pulse, and then

22 The Electrochemical Society Interface • Fall 1999 select the optimum charge regime. It alent series resistance, and low energy tems will likely appear in the future. may be possible to eliminate the storage capability of 5 to 10 Wh/kg. These include: memory effect of Ni-Cd by the choice Most devices are based on high surface • Lithium metal anode rechargeable of charging regime. Not surprisingly, area carbon (250 to over 700 m2/g) cells with polymer electrolyte. The the new chargers with power manage- electrode structures. Other materials, lithium polymer battery now ment capability also improve the per- such as nitrides and carbides, show under development for use in elec- formance of the older lead acid promise as electrode materials. tric vehicles is a forerunner of battery. Pulse charging techniques these new systems. The avail- have been developed to rapidly and On the Horizon ability of solid electrolytes with safely charge. good room temperature conduc- The principal use of lead acid bat- Several issues face the battery tivity will spur this development teries is for automotive starting, industry. The first is the environ- for consumer applications. lighting, and ignition applications. mental impact of spent batteries. Lead • Very thin, large footprint recharge- While growth in lead acid batteries is acid batteries are an excellent example able Li-ion polymer batteries. This slow and closely follows the GNP, a of the success of recycling. About 95% freedom of format offered by the significant change is imminent in this to 98% of spent lead acid batteries are polymer cells will encourage area. The automotive industry is recycled. The lead is refined and designers to develop new, longer preparing to shift to higher voltage returned for use as the grid and active running devices. These will have systems to handle the larger power mass. The plastic is ground into small about the same energy as the needs of the new accessories. System chunks and blended to mold new bat- liquid electrolyte version but with voltages in the range of 36 to 48 volts tery cases. New electrolytic processes a large footprint. For instance, a Li- are under consideration with the final with low or no lead emissions have ion polymer battery could deliver decision on voltage to be made in the been developed to replace the conven- 100 Wh in a 8˝ x 12˝ x 0.5˝ config- next year or two. Introduction of cars tional hydrothermal refining tech- uration. with the higher voltage systems is niques. • Zinc-air primary cells with creative likely to occur by the year 2005. The There is a move to require the recy- air management systems. The Zn- voltage change will require completely cling of all batteries in an effort to pro- air system has the capability to new cell designs and sizes. This will tect the environment. Several states in equal or exceed the lithium sys- open an opportunity for new concepts the U.S. already have laws in place but tems in energy storage. A Zn-air D- such as the small cylindrical lead acid have delayed implementation. The cell could more than double the cells and the Li-ion polymer battery cost and the reluctance, on the part of service life of the present alkaline ■ system. The spiral-wrap lead acid cells the consumer, to return batteries for Zn-MnO2 D-size cell. incorporate very thin foil electrodes collection and recycling are delaying and are capable of delivering energy action. The small rechargeable battery pulses of well over 1000 W/kg. The Li- industry group recently formed an ion polymer cells also offer very thin independent company, the Recharge- About the Author cell construction with one-third the able Battery Recycling Corporation to weight and one-half the volume of the recycle Ni-Cd batteries. Convenient Ralph J. Brodd is President of his same energy lead acid battery. collection centers have been estab- consulting company, Broddarp of New battery-like systems termed lished in major stores such as Radio Nevada, Inc. He has over 30 years “double layer” capacitors or ultraca- Shack, Kmart and Wal-Mart as well as experience in the battery field and pacitors have been under development by municipalities. Eventually, the recy- has worked on all the major primary for several years. The devices draw cling of primary cells will also be and secondary battery systems. His their character from the double layer required. Suitable technology appears work experience includes technical and reaction capacitance that develops to be available for economic recovery. and marketing activities spanning a at the electrode-solution interface of The cost of recovering and recycling is wide range of applications as bench all electrodes. Capacitances of up to 20 almost equal to the initial manufac- chemist, technical manager, and farads are possible in a common AA- turing cost. vice president of marketing for var- size cell. The ultracapacitor can handle The second issue involves the ship- ious battery companies. He is Past (smooth out) very high current pulses ping of lithium and Li-ion batteries. President and Honorary Member of that occur in an electric circuit. They The shipping of all cells containing The Electrochemical Society. have specific power capability of over lithium metal are regulated by the Dr. Brodd has served as a 10 kW/kg. It is reported that an ultra- Department of Transportation, the National Secretary and Vice-Presi- capacitor, in parallel with a primary details of which are found in the Code dent of the International Society of alkaline cell, can extend the perfor- of Federal Regulations, CFR49.185.173. Electrochemistry, and Chairman of mance of an alkaline cell by 3 to 5 The United Nations also has developed the 1979 Gordon Research Confer- times for pulse applications such as are shipping regulations that have been ence in Electrochemistry. Case found in digital cellular phones. adopted by various transport groups. Western Reserve University named Research and development activity has The new proposed regulations include him Centennial Fellow in 1980. He accelerated as the usefulness of these Li-ion batteries in the same category as has served on several government devices has been recognized. Commer- lithium metal anode cells. These regu- advisory committeess and has over cial systems are now on the market for lations will likely be modified over the 80 publications and patents. use in memory protection, ground next several years to reflect the good insulation, and uninterruptible power safety record of these systems. supplies. The main disadvantages are Although the crystal ball is dim, the low operating voltage, high equiv- several new high-energy battery sys-

The Electrochemical Society Interface • Fall 1999 23