Modified cellulose ether films having an increased electrolytic conductivity and a useable flexibility and in certain instances an increased flexibility are presented. Battery separator membranes comprising a cellulose ether and a minor proportion of a compatible water soluble base selected from the group consisting of alkali metal and ammonium hydroxides, aliphatic amines, and aliphatic hydroxyamines are used

Hoyt, H. E.

Pfluger, H. L.

English

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20546
Reply lo Ann of: GP—4
APR 3 0 1982
TO: NST-44/Scientific and Technical Information Division
Attn: Shirley Peigare
FROM: GP-4/Office of Assistant General Counsel
for Patent Matters
SUBJECT: Announcement of NASA-Owned U.S. Patents in STAR
In accordance with the procedures agreed upon by Code GP-4 and
Code NST-44, the attached NASA-owned U.S. Patent is being
forwarded for abstracting and announcement in NASA STAR.
The following information is provided:
U.S. Patent No. :
Government or
Contractor Employee:
NASA Case No. :
}\J
NOTE - If this patent covers an invention made by a contractor
employee under a NASA contract, the following is applicable:
YES /Y7 NO /~7
Pursuant to Section 305(a) of the National Aeronautics and Space
Act, the name of the Administrator of NASA appears on the first
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invention of...."
R E C E I V E D
TI FACILITY
ACCESS DEPT.
(NASA-Case-G'SC-100 17-1) SEPABATOB FOB"
ALKALINE ELECTRIC CELLS AND METHOD OF HAKIBG
Patent (NASA) 3 p CSCL. 10A
00/44
82-2 46 4 3
Unclas
20222
https://ntrs.nasa.gov/search.jsp?R=19820016767 2020-03-21T16:46:23+00:00Z
1,519,434
Patented July 7, 1970
. 3,519,484
SEPARATOR FOR ALKALINE ELECTRIC CELLS
AND METHOD OF MAKING
Helmulh louts PHuger and Howard Eugene Hoyt, Hunt-
. ingdon Valley, Pa., assignors to Borden, Inc., New
York, N.y., a corporation of New Jersey
No Drawing. Ffled Nov. 2, 1967, Ser. No. 679,996
Int. CL HOlm 3/00, 35/00
V& CL 136—6 11 Claims
10
ABSTRACT OF THE DISCLOSURE
• This invention relates to the battery separator mem-
branes of high electrolytic conductivity comprising a
cellulose ether and a compatible water-soluble base and 15
to batteries utilizing said membranes.
Origin of the invention
The invention described herein was made in the per-
formance of work under a NASA contract and is subject
to the provisions of Section 305 of the National Aero-
nautics and Space Act of 1958, Public Law 85-568 (72
Slat. 435; 42 U.S.C. 2457).
Background of the invention
The cycle life of rechargeable battery cells is known to
be limited by the tendency of the electrodes to short cir-
cuit and this tendency can be slowed down by the use of
a separator membrane between the electrodes. In the par-
ticular case of alkaline cells such as silver-zinc, silver-
cadmium, nickel-cadmium, and the like such a separator
must be able to withstand the oxidizing power of silver
oxide and the penetration of metallic zinc, nickel, and
cadmium, and must also have low resistance to the pas-
sage of an electrolytic current. Films of cellulose ethers,
and particularly methyl cellulose, have excellent with-
standing powers against both silver oxidation and metal
penetration. In spite of these advantages, the use of
methyl cellulose by itself has not been successful because
its resistance to passage of an electrolytic current is pro-
hibitively high in the 30 to 45% alkali metal hydroxide
solutions customarily used in batte:-:y cells. It is known,
as shown in U.S. Pat. No. 2,858,353, that by incorpora-
tion within methyl cellulose films of certain polymeric
acid materials a certain limited increase in conductivity
can be obtained. For optimum performance, however, a
greater electrolytic conductivity is required. Moreover,
films modified in this manner are not as flexible in the
dry state as unmodified methyl cellulose films and require
special control of humidity in order to insure freedom
from damage during handling.
Summary of the invention
We have now found modified cellulose ether films hav-
ing an increased electrolytic conductivity and a useable
flexibility; p.nd in certain instances an increased flexibility
"as compared to films of unmodified cellulose ethers.
Our invention comprises battery separator membranes
comprising a cellulose ether and &. minor proportion of
a compatible water soluble base selected i'rom the grjup
consisting of alkali metal and ammonium hydroxides, ali-
phatic amines, and aliphatic hydroxyamines.
* Detailed description of the invention
This invention may be applied to any water-soluble or
water-sweliable and alkali insoluble cellulose ether, such
as methyl cellulose, ethyl cellulose, propyl cellulose, mix-
tures iliereof, and the like.
-' The preferred ether is methyl cellulose, particularly
methyl cellulose in which 1.6 to 1.9 out of every 3.0
20
25
30
40
. 45
50
55
65
70
2
available hydroxyl units of cellulose have been etherified.
Methods for etherifying cellulose to different degrees and
using a variety of ether groups are known to the art and
are not a subject of the instant invention.
The base used may be selected from any waler-selubte
alkali metal hydroxide as well as hydroxides of ammo-
nium and substituted ammonium ions, including quater-
nary r.rnmonium ions, also waler-solubk organic bases
including aliphatic primary, secondary and tertiary
amines and hydroxyamines. Specific examples of such
bases are potassium hydroxide, sodium hydroxide, lithium
hydroxide, cesium hydroxide, rubidium hydroxide, am-
monium hydroxide, methyl ammonium hydroxide, methyl
ethyl ammonium hydroxide, tetraaethyl ammonium hy-
droxide, benzyltrimethyl ammonium hydroxide, tri-
ethanolammonium hydroxide, diethylamine, hydroxy-
propylamice, ethanolamine, diethanolamine, and Iri-
ethanolamine.
The amount of base may vary from 2 to 20% by
weight based on the cellulose ether. Preferred amounts
are in the range 5 to 15%, the choice being determined
by the degree of resistance lowering desired (electrolytic
conductivity increase desired) and by the necessity of
avoiding frosting out of the base from the film which
occurs at varying threshold levels.depending on the base
used.
In addition to the methyl cellulose, the polymeric com-
position of the film may also include minor amounts
of more polar polymeric materials such as polyaerylic
acid or the 1:1 copolymer of vinyl methyl ether and
maleic anhydride. The polar polymeric substance may
vary in concentration up to 40% by weight, but it is gen-
erally preferred not to exceed 33% because of the stiffen-
ing and non-flexibilizing effects which such components
impart.
The membrane may be prepared by combining aqueous
solutions respectively of methyl cellulose and of the
other additives. The w.uliing composition may be cast in
sheet form and evaporated to dryness. Other forms may
be made as for example plates, slabs, "buttons," films
and the like. Solutions of the components should not be
so concentrated as to precipitate the components before
drying.
Good flexibility in the film is of particular importance
in the construction of the individual battery cells during
the operation of wrapping the separators around the elec-
trodes. In one common technique a so-called U wrap is
made whereby two positive electrodes are placed butt
end to butt end on a sheet of separator and after, for
example, six wraps of the pair the wrapped assembly
is folded at the junction in the form of the fetter U. When
separators of poorer flexibility are used cracks tend to
occur in the separator at the base of the U, particularly
in the outer wraps, thus destroying the utility of the
separator at these points. We have found experimentally
that this is particularly likely to occur below a certain
critical threshold of flexibility, corresponding to with-
standing at least about 800 flex cycles as measured by
the ASTM Folding Endurance Test D643-43 with 200
grams tension on the specimen.
The invention will be further illustrated by description
in connection with the following specific examples of the
practice of it, the proportions here and elsev/here herein
being expressed as parts by weight except where indicated
specifically to the contrary.
EXAMPLE t
30 grams of 5% potassium hydroxide solution in water
was heated to 80° C. Ten (10) grams of methyl cellulose
(Methocel 15) was added and stirred at the same tempera-
ture for five minutes. Sixty grams of ice was then stirred
into the mixture. After standing 5a the cold for release of
3,519,484
bubbles the solution was cast,, using a doctor blade at
22 mil clearance. The dried film was much improved in
clarity. Unexpectedly the electrolytic resistance of the film
in 45% potassium hydroxide was lowered to 31 millf-
ohms-in.2 compared to 7250 milliohm-in.2 for a corre-
sponding methyl cellulose film.
EXAMPLE 2
A solution was prepared of 480 grams of methyl cellu-
lose (Methocel 15) in 4320 grams of water. To this solu-
tion was added, with stining, 480 grams of a 10% aqueous
solution of tetramethyl ammonium hydroxide. The result-
ing clear homogeneous- solution was cast on a level glass
plate, using a doctor blade set at 21 mils clearance.
Evaporation to dryness resulted in a flexible film of 1-5
mils thickness. The properties of'this film v.ere compared
against those of a corresponding unmodified methyl cellu-
lose film with the following results:
4
EXAMPLE 8
Unmodified
The film methyl
of this cellulose
example lilm
Kesistanco. milliohins-hi.1:
Equilibrated with 3(1% KOH
Equilibrated with 45% KOH
MIT Fltx Test, cycles (using ASTM Folding
Endurance Test 1) 643-43 with 200 grains
tension on lilm, at 50% relative humidity
tmd71°F.)
Tenitte strength, p.s:i :..
1.4
22.8
50.8
6,992
7,4«>
1.5
712
7,250
3,937
7, ISO
\
Thus the modified film had the double advantage of
both low electrolytic resistance and improved dry flexi-
bility.
EXAMPLE 3
By the procedure of Example 1, 3 parts sodium hy-
droxide per 100 parts methyl cellulose were incorporated
into a film of 1.4 mils thickness. Resistance after equilibra-
tion with 45% potassium hydroxide solution was 1655
millif>hms-in.2, MIT flex of the dry film was 2858 cycles
and tensile strength was 11,100 p.s.i.
EXAMPLE 4
By the procedure of Example 1, 6 parts sodium hy-
droxide per '00 parts of methyl cellulose were incorpo-
rated into a film of 1.6 mils thickness. Reristance after
equilibration with 45% potassium hydroxide solution was
330 miliiohms-in.2, MIT flex of the dry film was 2233
cycles and tensile strength was 8500 p.s.i.
EXAMPLE 5
By the procedure of Example 1, fourteen parts of 3-
hydroxypropyJamine pef 100 parts of methyl cellulose
were incorporated into a film of 1.7 mils thickness. Re-
sistance after equilibration with 45% potassium hydroxide
was 573 milliohms-in.2, MIT flex was 3216 cycles and
tensile strength was 8140 p.s.i.
EXAMPLE 6
By the procedure of Example 1, six parts of potassium
hydroxide per 100 parts of methyl cellulose were incorpo-
rated into a film of 1.4 mils thickness. Resistance after
equilibration with 45% potassium hydroxide was 330
milliohms-in.2. After equilibration with 30% potassium
hydroxide another specimen of this film had a resistance
of only 60 milliohms-in.2. MIT flex of the dry film was
3100 cycles and tensile strength was 8870 p.s.i.
EXAMPLE 7
By the procedure of Example 1, nine parts of potassium
hydroxide per 100 parts of methyl cellulose were in-
corporated into a film of L5 mils thickness. Resistance
after equilibration with 45% potassium hydroxide was 244
milliohms.-in.*. After equilibration with 30% potassium
hydroxide another specimen of this film had a resistance
of only 42 milliohms-in.2. MIT flex of the dry firm was
2272 cycles and tensile strength was 7350 p.s.i.
By the procedure of Example I, 67 parts methyl cellu-
lose; 33 parts polyacrylic acid (Acrysol A5) and 14.4
parts 3-hydroxypropylamine were incorporated into a film
of 1.6 mils thickness. Resistance after equilibration with
45% potassium hydroxide was only 14 milliohms-in.z and
M IT flex was 4958 cycles.
EXAMPLE 9
]0 By. the procedure of Example 1, 80 parts methyl cellu-
lose,-. 20 parts polyacrylic acid and 10 parts triethanol-
amine were incorporated into a film of 1.3 mils thickness.
Resistance after equilibration with 45% potassium hy-
droxide was only 245 milliohms-in.2 and MIT flex was
15 9850 cycles. Tensile strength v/as 7000 p.sj.
EXAMPLE 10
By the procedure of Example 1, 80 parts methyl cellu-
lose, 20 parts polyacrylic acid and 20 parts triethanol-
20 amine were incorporated into a film of 1.4 mils thickness.
Resistance Met equilibration with 45% potassium hy-
droxide v:as only -60 milliohms-in.* and MIT flex was
21,000 cycles. Tensile strength was 5,220 p.s.i.
25 EXAMPLE 11
By, the procedure of Example 1, 80 parts methyl cellu-
lose, 30 parts of the 1:1 copolymer of vinyl methyl ether,
maleic anhydride (Gantrez AN) and 20 parts triethanol-
amine were incorporated into a film of 1.4 mils thickness.
30 Resistance after equilibration with 45% potassium hydrox-
ide was only 29 miiliohms-in.2 and MIT flex was 15,850
cycles. Tensile strength was 4870 p.sJ.
EXAMPLE 12
aa
 Representative films of this invention were stirred for
72 hours in 30% potassium hydroxide saturated with
silver oxide, conditions which oxidize and degrade PUDO
cellophane customarily used in alkaline battery cells so
drastically that the cellophane no longer has any break-
ing strength. Corresponding samples of the same films of
this invention were also stirred for 72 hours in 30%
potassium hydroxide in fee absence of stiver oxide. Both
sets of film were broken in a tensile testing machine. The
difference in strength between the samples exposed to
45 silver oxide and the sample not so exposed was found
lo be statistically insignificant. Thus, for example, the
ffim of Example 7 had breaking strength 4660 p.s.i., after
swelling in 30% potassium hydroxide and 4600 p.s.i.
after the exposure to silver oxide. The film of Example
50 jo had breaking strength 1990 p.s.i. after swelling in
30% potassium hydroxide and 2100 pjj. after the ex-
posure to silver oxide.
Thus, the films of this invention are superior to the
customarily used cellophane in withstanding the oxida-
55
 tion power of silver oxide which is a normal constituent
of the electrolyte in silver-zinc and silver-cadmium cells.
It will be understood that it is intended to cover all
changes and modifications of the examples of the inven-
tion herein chosen for the purpose of illustration which
60
 do not constitute departures from the spirit and scope
of the invention.
What is claimed is:
1. A substantially dry battery separator membrane for
alkaline electrochemical cells prepared by
(a) making an aqueous solution comprising a cellulose
ether and a compatible water-soluble base selected
from the group consisting of alkali metal hydroxides,
ammonium hydroxides, aliphatic amines and ali-
phatic hydroxyamines, said base being in the pro-
portion of from about 2 to about 20 parts by weight
for each 100 parts of cellulose ether.
(b) casting said solution in sheet ioim, and
(c) evaporating said sheet to dryness.
2. The membrane of claim 1 wherein the cellulose
5
 ether is methyl cellulose.
•jo r
Go
70
3,519,484
3. The membrane of claim 1 wherein the cellulose
ether is methyl cellulose with degree of substitution in
the range 1.6-1.9 ont of every 3.0 available hydroxyl
units.
4. An alkaline electrochemical cell comprising elec-
trodes, a concentrated aqueous alkali fluid, and the bat-
tery separator of claim 1 interposed between the elec-
trodes.
5. An alkaline silver cell comprising electrodes, a con-
centrated aqueous alkaline fluid, and the battery sepa-
rator of claim 2 interposed between the electrodes.
6. An alkali silver-zinc cell comprising a silver elec-
trode, a zinc electrode, a concentrated aqueous alkali
fluid, and the battery separator of claim 3 interposed be-
tween the electrodes..
7. A substantially dry membrane capable of develop-
ing high electrolytic conductance after equilibration with
concentrated aqueous alkali, said membrane being pre-
pared by
(a) making a solution comprising methyl cellulose 20
with a degree of substitution in fhe range of about
1.6-1.9 and a base selected from the group consist-
ing of potassium hydroxide, tetramethylammonium
hydroxide, sodium hydroxide, 3-hydroxypropylamine
and triethanolamine, said base being in a propor- 25
tion of. from about 5% to about 15% by weight
of the methyl cellulose,
(b) casting said solution in sheet form, and
(c) evaporating said sheet to dryness.
10
15
weight for each 100 parts of cellulose ether, said
base being selected from the group consisting of
alkali metal hydroxides, ammonium hydroxides, ali-
phatic amines and aliphatic hydroxyamines,
(b) casting said solution in sheet form, and
(c) evaporating said sheet to dryness.
10. A method for making a dry membrane capable
of developing a high electrolytic conductance after
equilibration with concentrated aqueous alkali, which
method comprises
(a) making an aqueous solution comprising methyl
cellulose with a degree of substitution in the range
of about 1.6-1.9 and a base in the proportion of
from about 5 to about 15 parts by weight for each
100 parts of methyl cellulose, said base being se-
lected from the group consisting of potassium hy-
droxide, tetramethylammonium hydroxide, sodium
hydroxide, 3-hydroxypropylamine and- triethanol-
amine, !
(b) casting said solution in sheet form, and
(c) evaporating said sheet to dry-ness.
11. A method for making a silver-zinc cell which com-
prises interposing between silver and zinc electrodes a
substantially dry battery separator, membrane prepared
by making an aqueous solution comprising methyl cellu-
lose with a degree of substitution.in the range of about
1.6-1.9 and a compatible water-soluble base in the pro-
portion of from about 5 to about 15 parts by weight for
each 100 parts methyl cellulose, said base being selected
References Cited
UNITED STATES PATENTS
8. An alkaline silver-zinc cell comprising a silver elec- 30 from the group consisting of alkali metal hydroxides,
trode, a zinc electrode, a concentrated aqueous alkali ammonium hydroxides, aliphatic amines and aliphatic
fluid and as a battery separator interposed between the hydroxyamines, casting said solution in sheet form, and
electrodes, a membrane prepared by evaporating said sheet to dryness, placing the assembly
(a) making an aqueous solution comprising methyl of said electrodes and membrane in a cell vessel and add-
cellulose with a degree of substitution in the range 35 ing thereto a concentrated aqueous alkali fluid.
of about 1.6-1.9 and a compatible water-soluble
base, in the proportion of from about 5 to about 15
parts by weight for each 100 parts methyl cellulose,
said base being selected from the group consisting
of alkali metal hydroxides, ammonium hydroxides,
aliphatic amines and aliphatic hydroxyamines,
(b) casting said solution in sheet form, and
(c) evaporating said sheet to dryness.
9. A method for making a dry membrane capable of
 45
developing high electrolytic conductance after equilibra-
tion with concentrated aqueous alkali, which method
comprises
(a) making an aqueous solution comprising a cellulose
ether and a compatible water-soluble base in the 50 106—186; 136 146, 148; 260 232
proportion of from abr 2 to about 20 parts by
2,438,975
2,696,515
2,771,377
2,858,353
2,900,433
4/19.48
12/1954
10/1958
8/1959
Jones 106—186
Keren et aL 136—146
Gwjuiager 106—186
Mendelsohn 136—146
Cahoon et aL 136—146
WINSTON A. DOUGLAS, Examiner
D. L. WALTON, Assistant Examiner
U.S. CL XJL


Separator for alkaline electric cells and method of making

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