Separators for alkaline batteries

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... 

P. Kritzer, J.A. Cook, Nonwovens as separators for alkaline batteries, an overview, J Electrochem Soc 154 (5) (2007) A481-A494. 

Very different microporous separators for alkaline batteries are included in Table 11.16. The very thin ( 25 xm) films of stretched polypropylene ( Celgard ) are generally employed in combination with fleeces, while separators of sintered PVC or filled UHMW PE find use also in single separation of alkaline industrial batteries. Their production process corresponds to the analogous version for lead-acid batteries and is described in detail in Sections 11.2.2.1 and 11.2.2.2 respectively. 

J.J. Lander, R. D. Weaver, A.J. Salkind, J.J. Kelley in Characteristics of Separators for Alkaline Silver Oxide Zinc Secondary Batteries. Screening Methods (Eds. J.E. Cooper, A. Fleischer), NASA Technical Report NAS 5-2860,1964. 

Danko, T. Properties of cellulose separators for alkaline secondary batteries. Proceedings of the 10th Annual Battery Conference on Applications 8z Advances, IEEE New York, 1995 p 261. 

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

Lander JJ, Weaver RD, Salkind AJ, Kelley JJ (1964) In Cooper JE, Fleischer A (eds) Characteristics of separators for alkaline silver oxide zinc secondary batteries. Screening methods. NASA Technical Report NAS 5-2860... 

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. 

Nonwovens have been well established as traditional materials for alkaline batteries, NiCd and NiMH cells, and for absorbed glass matt (AGM) lead—acid batteries. Alkaline batteries use a variety of materials, mostly composed of wet-laid cellulose and polyvinyl alcohol (PVA). NiCd and NiMH use a variety of materials, from spunbond and melt blown to dry-laid materials. Lead—acid AGM batteries use a wet-laid glass matt as the separator, often in conjunction with another membrane. These materials range in thickness from 100 to 300 pm. One review article in 2007 even states that for lithium ion cells, nonwoven not possible. However, these traditional nonwovens are a significant industrial market for several manufacturers, with total sales into these types of cells of 450 million globally. 

No attempt has been made so far to relate the membrane phctse concentration of an ion to its external concentration. A relation of the type (3.3.120e, f) may be derived by using the relation (3.3.118b) for Donnan equilibrium as well as the electroneutrality relations in the membrane and in the external solution. The ionic flux of any ion through an ion exchange membrane may then be obtained from the Nernst-Plank equation (3.1.106). If is to be eliminated from such an equation, then the following procedure may be adopted. Write down the flux for /J and /j. If there is some constraint like Jl 0 (as in (3.4.121)), the problem is easily solved. In some cases, /J = (for example, in battery separators for alkaline Ni/Zn batteries, KOH is the electrolyte and/k+ = /oh-)- This will also allow elimination of V(i. Then one can express / in terms of the concentrations of two solutions on the two sides of the membrane by integrating across the battery separator membrane at steady state. 

Separators for Alkaline Storage Batteries JJ5 Table 11.15 Nonwoven materials for alkaline batteries. 

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 prime requirements for the separators in alkaline storage batteries are on the one hand to maintain durably the distance between the electrodes, and on the other to permit the ionic current flow in as unhindered a manner as possible. Since the electrolyte participates only indirectly in the electrochemical reactions, and serves mainly as ion-transport medium, no excess of electrolyte is required, i.e., the electrodes can be spaced closely together in order not to suffer unnecessary power loss through additional electrolyte resistance. The separator is generally flat, without ribs. It has to be sufficiently absorbent and it also has to retain the electrolyte by capillary forces. The porosity should be at a maximum to keep the electrical resistance low (see Sec. 9.1.2.3) the pore size is governed by the risk of electronic shorts. For systems where the electrode substance... 

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). 

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. 

Nonwovens are widely utilized as separators for several types of batteries. Lightweight, wet laid nonwovens made from cellulose, poly (vinyl alcohol), and other fibers have achieved considerable success as separators for popular primary alkaline cells of various sizes. The key nonwoven attributes include consistently uniform basis weight, thickness, porosity and resistance to degradation by electrolytes. Nonwovens are also successfully employed as separators in NiCd s. 

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