Alkaline batteries, separators

S. Tanso, J. Okamoto, I. Ishigaki, T. Sugo, K. Murata, K. Senoo and T. Takayama, A new alkaline battery separator made by pre-irradiation graft polymerization, Yuasa Jiho, 1983, 54, 57. 

Gancarz, L, Kunicki, J. and Ciszewski, A. 2008. Application of plasma-induced grafting for modification of alkaline battery separator. Chem. Listy 102 467 72. 

Cylindrical alkaline cells are made in only a few standard si2es and have only one important chemistry. In contrast, miniature alkaline cells are made in a large number of different si2es, using many different chemical systems. Whereas the cylindrical alkaline batteries are multipurpose batteries, used for a wide variety of devices under a variety of discharge conditions, miniature alkaline batteries are highly speciali2ed, with the cathode material, separator type, and electrolyte all chosen to match the particular appHcation. 

The design of a AA-size alkaline manganese dioxide cell is shown in Fig. 1 (Sec. 3.1). Primary and secondary alkaline batteries are constructed in the same way and can be manufactured on essentially the same machinery. The separator material, electrode formulation, and the Mn02 Zn balance are different. Rechargeable cells are zinc-limited to prevent a discharge beyond the first electron-equivalent of the MnOz reduction. The electrolyte is 7-9 mol L KOH. The electrode reactions are ... 

Of all possible manufacturing proceses for macroporous separators to be employed in alkaline batteries, the wet-fleece process using paper machines is the predominant one [130] it permits a very uniform ( cloud-free ) production of such material and the use of different types of fibers as well as of short and very thin fibers, thus achieving a uniform structure of small pores (Table 15). 

Very different microporous separators for alkaline batteries are included in Table 16. The very thin (-25 ftm) films of stretched polypropylene ( Celgard ) are generally employed in combination with... 

The development of stable, effectively ion-separating membranes for rechargeable alkaline batteries remains a persistent challenge, in which the separator can provide decisive contributions to the advancement of storage batteries of high power and energy density. 

In most batteries, the separators are either made of nonwoven fabrics or microporous polymeric films. Batteries that operate near ambient temperatures usually use separators fabricated from organic materials such as cellulosic papers, polymers, and other fabrics, as well as inorganic materials such as asbestos, glass wool, and Si02. In alkaline batteries, the separators used are either regenerated cellulose or microporous polymer films. The lithium batteries with organic electrolytes mostly use microporous films. 

The performance and capacity advantages of alkaline batteries vs carbon—zinc is resulting in the continuous decline of this battery. The low cost of the carbon zinc cell is a major reason for its continued use. Thus, cost is a major consideration in the development and selection of separators for this system. 

The first practical silver—zinc battery was developed more then 60 years ago. Since then, primary and secondary silver—zinc batteries have attracted a variety of applications due to their high specific energy, proven reliability and safety, and the highest power output per unit weight and volume of all commercially available batteries. However, they find very limited use in commercial applications, because of their high price and limited cycle life. Development of a battery separator which will improve the performance and life of zinc based alkaline cells has been... 

For battery separators, regenerated cellulose is placed on the surface of nonwoven so that the nonwoven is available to promote the wicking of the electrolyte. The nonwovens should not allow the penetration of viscose into itself. Suitable nonwovens are made from polypropylene, poly(vinyl alcohol), and hardwood hemps. Regenerated cellulose films are commonly used in alkaline manganese cells, both primary and secondary, in NiCd industrial batteries, as well as in silver—zinc batteries. 

A large quantity of homogeneous ion-exchange membranes are made annually for separators in alkaline batteries. See also Batteries. 

Hydroxide. Potassium hydroxide, [CAS 1310-58-3]. caustic potash, potassium hydrate, KOH, white solid, soluble, mp 380 C, formed (1) by reaction of potassium carbonate and calcium hydroxide in H2O, and then separation of the solution and evaporation. (2) by electrolysis of potassium chloride under the proper conditions, and evaporation. Used in the preparation of potassium salts f 1) in solution, and (2) upon fusion. Also used 111 the manufacture of (3) soaps, (4) drugs. (5) dyes, (6) alkaline batteries, (7) adhesives, (8) fertilizers, (9) alkylates, (10) for purifying industrial gases, (11) for scrubbing out traces of hydrofluoric add in processing equipment, (12) as a drain-pipe cleaner, and (13) in asphalt emulsions. 

Batteries that require a liquid electrolyte are called wet batteries. Corrosive battery fluid refers to either acid electrolytes syn. battery acid, like the common lead-acid automobile battery which uses a solution of sulphuric acid, or alkali electrolytes syn. alkaline corrosive battery fluid, like potassium hydroxide (1310-58-3) solutions in nickel-cadmium and other alkaline battery systems. Dry batteries or dry cells, like all primary batteries, use electrolytes immobilized in pastes, gels, or absorbed into separator materials. Some batteries are loaded with a dry, solid chemical (e.g., potassium hydroxide) which is diluted with water to become a liquid electrolyte. The hazards associated with handling and transportation prior to use are thereby reduced. 

Pyrotechnics plays a more subordinate role in other galvanic cells of high storage life where the inactivity is achieved by separation of hattery proper and of electrolyte. In ammonia activated batteries, pyrochemical heat aids in transfer of the ammonia, and in certain alkaline batteries, a concentrated potassium hydroxide solution is projected into the battery cavity with the help of a propellant-gas cartridge. 

The most common primary (nonrechargeable) battery is the alkaline battery ( Figure 20.20). The anode is powdered zinc metal immobilized in a gel in contact with a concentrated solution of KOH (hence, the name alkaline battery). The cathode is a mixture of Mn02 (s) and graphite, separated from the anode by a porous fabric. The battery is sealed in a steel can to reduce the risk of any of the concentrated KOH escaping. The cell reactions are complex but can be approximately represented as follows ... 

It is implicit in the permeability requirement that typically Li-Ion battery separators have a porosity of 40%. Control of porosity is very important for battery separators. Specification of percent porosity is commonly an integral part of separator acceptance criteria. The porosity of separators used in alkaline zinc MnO cells is typically around 80-90%. 

If the PECH content was further increased to the blend ratio of 1 0.5 to 1 1, phase separation was observed and the film exhibited a sticky surface. These issues posed problems for PVA/PECH SPE for alkaline battery system, although it had lower activation energy of 1-3 kJ mol and excellent mechanical strength of 58.9 MPa. As a result, it was foimd that the blend ratio of 1 1 sample exhibited the lowest KOH content and thus low ionic conductivity. 

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