A battery separator for an alkaline battery is described. The separator comprises a cross linked copolymer of vinyl alcohol units and unsaturated carboxylic acid units. The cross linked copolymer is insoluble in water, has excellent zincate diffusion and oxygen gas barrier properties and a low electrical resistivity. Cross linking with a polyaldehyde cross linking agent is preferred

Gonzalez-Sanabria, O. D.

Hsu, L. C.

Philipp, W. H.

Sheibley, D. W.

English

NASA Technical Reports Server

United States Patent 
Hsu et al. 
[I]] Patent Number: 4,505,998 
[45] Date of Patent: Mar. 19, 1985 
[54] ALKALINE BATTERY CONTAINING A 
SEPARATOR OF A CROSS-LINKED 
COPOLYMER OF VINYL ALCOHOL AND 
UNSATURATED CARBOXYLIC ACID 
[75] Inventors: Li-Chen Hsu, Westlake; Warren H. 
Philipp, N. Olmsted; Dean W. 
Sheibley, Sandusky; Olga D. 
Gonzalez-Sanabria, N. Olmsted, all 
of Ohio 
represented by the Administrator of 
the National Aeronautics and Space 
Administration, Washington, D.C. 
[73] Assignee: The United States of America as 
[21] Appl. NO.: 282,298 
[22] Filed: Jul. 10, 1981 
[51] Int. c1.3 .............................................. HOlM 6/04 
[52] U.S. C1. ..................................... 429/206; 429/249 
[58] Field of Search ............... 429/249, 254, 250, 251, 
429/252, 206 
2' 
1561 References Cited 
U.S. PATENT DOCUMENTS 
4,109,066 8/1978 Dick et al. ...................... 429/254 X 
4,157,423 6/1979 Gadessand ...................... 429/249 X 
4,277,572 7/1981 Fujiwara et al. ............... 429/249 X 
4,287,275 9/1981 Davis .............................. 429/254 X 
4,290,833 9/1981 Kadija et al. ................... 429/249 X 
Primary Examiner-Charles F. LeFevour 
Attorney, Agent, or Firm-Norman T. Musial; John R. 
Manning; James A. Mackin 
P I  ABSTRACT 
A battery separator for an alkaline battery. The separa- 
tor comprises a cross-linked copolymer of vinyl alcohol 
units and unsaturated carboxylic acid units. The cross- 
linked copolymer is insoluble in water, has excellent 
zincate diffusion and oxygen gas barrier properties and 
a low electrical resistivity. Cross-linking with a polyal- 
dehyde cross-linking agent is preferred. 
1 Claim, 1 Drawing Figure 
c5 
'I 
- 3  
https://ntrs.nasa.gov/search.jsp?R=19850020832 2020-03-22T19:40:03+00:00Z
U.S. Patent Mar. 19,1985 4,505,998 
E 
2 
4,505,998 
1 
ALKALINE BATTERY CONTAINING A 
SEPARATOR OF A CROSS-LINKED COPOLYMER 
OF VINYL ALCOHOL AND UNSATURATED - 
CARBOXYLIC ACID 
ORIGIN OF THE INVENTION 
The invention described herein was made by employ- 
ees of the U.S. Government and may be manufactured 
and used by or for the Government without the pay- lo line battery. 
ment of any royalties thereon or therefor. 
a battery comprising an alkaline electrolyte, a negative 
electrode, a positive electrode, and a separator inter- 
posed between the electrodes, a separator comprising a 
cross-linked copolymer comprising I to 99 mole % 
5 vinyl alcohol units and from 99 to 1 mole % carboxylic 
acid units. 
DESCRIPTION OF THE DRAWING 
The drawing is a diagrammatic illustration of an alka- 
DESCRIPTION OF PREFERRED 
FIELD O F  THE INVENTION EMBODIMENTS 
The present invention relates to a battery separator With reference to the drawing, a conventional alka- 
for an alkaline battery containing an alkaline electro- l 5  line battery includes a casing 1 comprising a positive 
lyte, and positive and negative electrodes. The battery electrode chamber 2 and a negative electrode chamber 
separator is positioned between the electrodes. 3. An alkaline electrolyte 4 is contained within the cas- 
ing. A battery separator 5 is interposed between a posi- 
tive electrode 6 and a negative electrode 7. Electrical BACKGROUND OF THE INVENTION 
This invention relates to alkaline batteries. More par- *O leads may be connected to the electrodes for communi- 
ticularly, the invention relates to separators for alkaline cation with an external electrical circuit. 
batteries. Still more PartiCUlarly, the invention relates to According to the invention, the separator comprises a 
such separators which comprise cross-linked polyvinyl cross-linked copolymer comprising from 1 to 99 mole 
alcohol copolymers. % of vinyl alcohol units and 10-50 mole % unsaturated 
Alkaline batteries are well known and are described 25 carboxylic acid units. A separator of this compos~t~on 
in considerable detail in the literature, including U.S. has excellent oxygen gas barrier and zincate barrier 
Pat. No. 296359127 Of Yardney et al; u.s. Pat. No. 
29648,717 of Ross et a]; U.S. Pat. No. 4,269,869 of Men- 
delsohn; and US. Pat. No. 4,1577423 of Gaddesaud, the 
properties and a low electrical resistivity. The cross- 
linked copo~ymer is aiso insoluble in boiling water. 
The copo~ymer may be prepared by reacting an ap- 
Of each Of which is incorporated herein by 30 propriate ratio of vinyl ester and unsaturated carboxylic 
acid or an ester or anhydride thereof. The vinyl ester 
may be 99-1 mole % of the ingredients, but is preferably 
90-50 mole %. The carboxylic acid may be 1-99 mole 
%, but is preferably 10-50 mole % of the mix. Still more 
acid is 3-7:l. The resulting vinyl ester-unsaturated car- 
boxylic acid copolymer is hydrolyzed to the desired 
vinyl alcohol-unsaturated carboxylic acid copolymer. 
40 The vinyl alcohol-unsaturated carboxylic acid COP@ 
reference. 
battery is the 
separator, a membrane which is interposed between the 
electrodes of the battery and which is in contact with 
the alkaline electrolyte. Battery separators are discussed 35 
including the following patents: u.s. pat, No, 4,085,241 
of Sheibley; U.S. Pat. No. 4,154,912 ofphilipp et al.; and 
U.S. Pat. No. 4,224,393 of Fienberg et al., the disclosure 
of each of which is incorporated herein by reference. 
One Of the key Of an 
at Some length in the foregoing patents and elsewhere, preferably, the ratio Of to 
One type of battery separator which has received IYner is a fih-former and preferably has a molecular 
considerable attention, and which is referred to in sev- weight in 
era1 of the foregoing patents, comprises cross-linked In order to Produce a battery separator, a film is cast 
polyvinyl alcohol. These separators are typically made from an aqueous solution of the copolymer. After dry- 
by casting an aqueous solution containing 540% by 45 ing, the film is cross linked in any suitable manner. 
weight of film-forming polyvinyl alcohol into a film, Cross linking with a polyaldehyde, in acidic medium, is 
and drying and cross-linking the film. Cross-linking preferred. Cross linking Of the copolymer makes it in- 
may be achieved in any of several ways, such as by soluble in water and the cross linked copolymer has 
treatment of the polyvinyl alcohol film with an acid excellent oxygen gas and zincate barrier Properties, low 
solution of an aldehyde cross-linking agent. Suitable 50 electrical resistivity, and high electrolyte retention ca- 
methods include those disclosed in U.S. Pat. No. pabilities, making it ideal for use as an alkaline battery 
4,157,423 of Gaddesaud; U.S. application Ser. No. separator. 
145,271, now U.S. Pat. No. 4,272,470 of Hsu et al; and Cross linking may be effected chemically by mixing 
U.S. Pat. No. 4,262,067 of Philipp et al., the disclosure the aqueous copolymer with a known cross-linking 
of each of which is incorporated herein by reference. 55 agent, such as those described in U.S. Pat. No. 4,640,734 
While the cross-linked polyvinyl alcohol battery sep- of Oppenheimer et al.; U.S. Pat. NO. 4,154,912 of Phi- 
arators known heretofore have proven to be satisfac- lipp et al.; or U.S. Pat. NO. 4,262,067 of Philipp et al., 
tory, there is a continuing need for improvement, par- before casting a film. Alternatively, the copolymeric 
ticularly in battery performance. It is an object of the film may be cross-linked by exposure to irradiation with 
present invention to provide a battery having a battery 60 accelerated electrons. The dried film may be submersed 
separator which enhances alkaline battery performance in acid and then irradiated, or the film may be cast and 
and to provide alkaline batteries with enhanced perfor- irradiated while wet. 
mance. 
Of 509000. 
The following examples illustrate the invention: 
BRIEF SUMMARY OF THE INVENTION 65 EXAMPLE 1 
The foregoing and other objects which will be appar- 
ent to those of ordinary skill in the art are achieved in 
accordance with the present invention by providing, in 
A copolymer of vinyl alcohol and acrylic acid, with 
molecular weight in excess of 50,000 is prepared as 
follows: 
4,505,998 
3 4 
A solution of 150 ml H20, 45.5 ml vinyl acetate, 5 ml 
5% K2S208 and 1 gr PVA (88% hydrolyzed) is stirred 
continuously in a three neck flask. The solution is 
treated under reflux for 30 minutes. A burette solution is 
prepared containing 50 ml H20) 7.6 ml acrylic acid and 5 tivity tivity Rate Rate 
5 ml 5% K2S2O8. Then, 15 ml of the burette solution is Material (Rcmz) (Rcm) (cm/min) (mole/cm?min) 
added to the flask to start copolymerization. The rest of 7VA-lAA" ,062 5.276 2,975 10-3 1.900 10-6 
the burette solution is added slowly in 15-30 minutes. 6VA-1AA ,154 6.082 2.335 X 2.572 X 
Reflux follows for four hours. The solution is cooled SVA-lAA ,102 3.656 4.989 X 2.988 X 
,110 8.619 6.479 X lop4 1.358 X 
and the resulting white precipitate is filtered, rinsed and 10 i:2::22 ,058 2.640 1.619 X 
dried. A flask solution is then prepared containing 10 gr 
of the copolymer and 200 ml CH30H. Heat is applied 
and the mix is refluxed for 30 minutes. A burette solu- 
tion containing 5 gr CH3ONa and 50 ml CH30H is 
TABLE 1 
Copolymer - 10% GDA' Acid XL 
Zinc Dendrite Area 
Resis- Resis- Penetration Zn Diffusion 
.Glutar=ldehyde cross-linker 
**Where XVA-YAA is the molecular units ratio: e.g., 7VA-IAA is 7 vinyl acrtatr 
moles per one acrylic acid mole. 
TABLE 2 
Copolymer 6VA-1AA Acid XL 
Zinc Dendrite 
Area Volume Penetration Zn + 2  OH - 
Cross- Resistivity Resistivity Rate Diffusion Diffusion 
linker (ncm2) (ncm) (cm/min) (mole/cm2min) (mole/cm'rnin) 
10% GDA ,154 6.082 2.335 X 2.572 X IOp6  - 
10% TPA* .03 1 2.820 4.45 X IOp4 9.49 X low7 3.189 X IO-' 
10% DAF** ,126 14.282 2.88 x lo-' 7.00 X I O w 7  4.083 x lo-' 
'Terephthaldehyde 
**Dialdehyde of furan 
prepared. Initially 15 ml of burette solution is added to 
the flask, then the rest is added slowly in 15-30 minutes. 
The solution is neutralized with dilute acid and cooled. 
The precipitate is filtered, rinsed and dried. 
EXAMPLE 2 
Cross-linking of the vinyl alcohol-acrylic acid co- 
polymer is effected by mixing 100 gr of a 5% aqueous 
solution of the copolymer with 0.81 gr glutaraldehyde, 
25 gr H20 and 2 gr Triton x 100 solution and heating to 
100"-120" C. The solution is put under vacuum and is 
then cast on a flat surface, such as a glass plate. The film 
is dried overnight, then heated in an acid solution for 
one hour at 90" C. The film is then rinsed. The acid 
solution may comprise 40 ml conc. H2S04 and 200 gr 
Na2S04 dissolved in 2 1 of water. 
EXAMPLE 3 
A 5% solution of the vinyl alcohol-acrylic acid co- 
polymer is cast into a film and dried. The film is placed 
in an acid solution and exposed to a 2 mev accelerator at 
10 pa for 10 minutes. The irradiated film is then taken 
out of the solution, rinsed and dried. Alternatively, a 
film of a 5% aqueous solution (acid pH) of the copoly- 
mer is cast and irradiated while wet at 2 pa for 10 min- 
utes. The film is then dried at room temperature. 
Tables 1 and 2 which follow illustrate the properties 
of battery separators made with various proportions of 
vinyl alcohol and acrylic alcohol in accordance with 
the foregoing examples. Table 1 shows area resistivity, 
volume resistivity, zinc dendrite penetration rate and 
zincate diffusion rates for varying ratios of vinyl alcohol 
to carboxylic acid. The copolymer is acid cross-linked 
with 10% glutaraldehyde. Table 2 shows changes in 
these same properties as a result of the use of different 
aldehyde cross-linkers. 
It will be seen from the table that battery separators in 
accordance with the present invention have excellent 
properties such as low electrical resistivity, low zincate 
30 diffusion rate, and low zinc dendrite penetration rates. 
Preferred battery separators in accordance with the 
present invention have the following properties: 
Area Resistivity (ohm-cm2): 1 
Volume Resistivity (ohm-cm): 20 
Zinc Dendrite Penetration Rate (cm/min): 5 X 
Zincate Diffusion Rate (mole/cmzmin): 2 X 10-6 
In the foregoing examples, vinyl acetate and acrylic 
acid are employed. However, other hydrolyzable esters 
of vinyl alcohol and other unsaturated carboxylic acids 
40 can be used. The copolymers, methods of making them, 
and suitable monomers are well known. Vinyl acetate is 
widely used and is the preferred hydrolyzable ester of 
vinyl alcohol. The copolymerizable acid can vary 
widely and can be the free acid or an ester thereof or, in 
45 the case of polycarboxylic acids, an anhydride thereof. 
Suitable monomers include: acrylic acid or esters 
thereof such as methyl acrylate; maleic acid or half of 
full esters thereof; maleic anhydride; fumaric acid; and 
itaconic acid. 
It will be understood by those having ordinary skill in 
the art that the copolymer making up a battery separa- 
tor in accordance with the present invention is made by 
hydrolyzing and cross linking copolymer made by re- 
acting a vinyl ester, such as vinyl acetate, and an unsatu- 
55  rated carboxylic acid or ester or anhydride thereof. The 
hydrolyzed copolymer contains hydroxyl groups re- 
sulting from the hydrolysis of the polymerized vinyl 
acetate and carboxylic acid groups which were either 
35 
60 
65 
present on the saturated ca;box;lic acid reactant or, 
where an ester or anhydride of that acid was employed, 
resulted from the hydrolysis of the polymerized anhy- 
dride or ester. It will thus be readily apparent that the 
copolymer does not contain any vinyl unsaturation 
since the vinyl acetate monomer was polymerized. For 
this reason, in naming the copolymer, the expression 
"units" has been used to make it clear that the "vinyl 
alcohol" portion of the copolymer does not contain 
vinyl unsaturation. Similarly, where a mono- 
4,505,998 
5 6 
unsaturated carboxylic acid, ester or anhydride mono- 
mer is copolymerized with the vinyl ester, the resulting 
copolymer contains no unsaturation in that portion of 
the copolymer derived from the mono-unsaturated car- 
boxyiic acid, ester, or anhydride. Accordingly, the term 5 crosslinked copolymer is formed by reacting a 
“units” has been used to make it clear that the carbox- 
ylic acid portion of the copolymer does not necessarily 
contain any unsaturation. 
What is claimed is: 
able to gaseous oxygen, the improvement wherein said 
separator comprises a cross-linked copolymer compris- 
ing from 1 to 99 mole % vinyl alcohol units and from 99 
to mole % carboxylic acid units and wherein said 
ester and an unsaturated carboxylic acid, or ester or 
anhydride thereof to form a vinyl ester-carboxylic acid 
or ester copolymer, followed by hydrolysis to form a 
Said vinyl alcohol-carboxYlic acid copolymer is subse- 
quently cross-linked. 
1. In an alkaline battery comprising an alkaline elec- 10 vinyl alcohol-carboxYlic acid copolymer, and wherein 
trolyte, a positive electrode, a negative electrode, and a 
separator interposed between said electrodes and per- 
meated by said electrolyte but substantially imperme- * * * * *  
15 
20 
25 
30 
35 
45 
50 
55 
60 
65 


Alkaline battery containing a separator of a cross-linked copolymer of vinyl alcohol and unsaturated carboxylic acid

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server