The improvement of water-soluble cellulose ether membranes for use as separators in concentrated alkaline battery cells is discussed. The process of contacting membranes with an aqueous alkali solution of concentration less than that of the alkali solution to be used in the battery but above that at which the membrane is soluble is described

Hoyt, H. E.

Pfluger, H. L.

English

NASA Technical Reports Server

(VI/NSA
National Aeronautics and
Space Administration
Washington, D.C.
20546
Reply to Atlnol: GP—4
APR 30 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. :
'/ Zi/ic.
, It
NOTE - If this patent covers an invention made by a contractor
employee under a NASA contract, the following is applicable:
YES 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
page of the patent; however, the name of the actual inventor
(author) appears at the heading of Column No. 1 of the
specification, following the words "...with respect to an
invention of...."
(HASA~Case-GSC-10019- 1} PROCESS "OF TREATING
CEILULOSIC MEflBJBAME AND A1KA1OE WITH
MEMBRANE SEJPABATOE Patent (RASA) 3 p
CSCL 10C
00/44
1*82-24641
Onclas
20220
https://ntrs.nasa.gov/search.jsp?R=19820016765 2020-03-21T16:46:37+00:00Z
EB
3/98,841
Patented Mar. 3, 1970
3,498,841
PROCESS OF TREATING CELLULOSIC MEMBRANE
AND ALKALINE.WITH MEMBRANE SEPARATOR
Howard Eugene Hoyt aad Helmuth Louis Pflrger, Hun-
tingdon Valley, Pa, assignors to Borden, Inc., New
York, N.Y., a corporation of New Jersey
No Drawing. Filed Nov. 2, 1967, Ser. No. 680>048
Int. CL HOlm 35/02,^/02
US. Cl. 136—6 10 Claims
10
ABSTRACT OF THE DISCLOSURE
This invention relates to the improvement of water-
soluble cellulose ether membrane for use as separators
in concentrated alkaline battery cells by contacting said 15 amine. Suitable salts of organic acids arc the alkali metal
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 this patent application. •**•
The film, or membrane, tc be treated may also con-
tain a minor proportion, up to 30%, of a modifying
agent to help increase conductivity and/or increase flexi-
bility. -Examples are hydroxide bases of inorganic or
organic cations, organic nitrogen bases, salts'of organic
acids, glycols, and polymeric acids.
Examples of hydroxide bases are potassium hydroxide,
sodium hydroxide and tetramethylammonium hydroxide.
Organic nitrogen bases that can be used include aliphatic
primary, secondary and tertiary amines and hydroxy
amines, in particular hydroxypropylamine and triethanol-
membrane with an aqueous alkali solution of concentra-
tion less than that of the alkali solution to be used in the
battery but above that at -which the membrane is soluble
therein.
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 (73
Stat. 435; 42 U.S.C. 2457).
BACKGROUND OF THE INVENTION
salts of acetic, propionic, butyric, salicyclic, succmic,
glutaric, maleic, and fumaric acids. Potassium salts are
preferred when the cell electrolyte is to be potassium
hydroxide. The glycol used can be, for example, glyc-
20 erine, ethylene glycol, tetraethylene glycol, and the poly-
ethylene glycols. As to polycneric acids, polyacrylic acid,
such as Acrysol A5, and the 1:1 copolymer of vinyl
methyl ether and maleic anhydride, such as Gantrez AN
can be used.
25
 The alkali used in the lower concentrated solutions
may be aqueous solutions of the hydroxide of any alkali
melai including the hydroxides of sodium, potassium,
lithium, rubidium or cesium as well as the hydroxide of
organic cations such as tetramethyl ammonium hydrox-
ide. The preferred alkali is potassium hydroxide which
is also the preferred alkali of commercial silver-zinc and
silver-cadmium cells.
The concentration of potassium hydroxide used in this
invention for the pre-soak is between about 10% to about
30It is known that the cycle life of rechargeable bat-
tery cells is limited by the tendency of the electrodes
to short circuit and that this tendency can be slowed down
by the use of a separator membrane between the elec-
trodes. In the particular case of alkaline silver-zinc cells,
such a separator must also withstand ?'ae oxidizing power 35 30% by weight, in water, but sufficiently high to avoid
of silver oxide and the penetration of metallic zinc, but disintegration of the membrane. In preparation of straight
must also have Jow resistance to the passage of an elec- methyl cellulose films for improved separator use in 30-
trolytic current. Films of cellulose ethers, particularly 45% potassium hydroxide solutions, it is preferred to use
methyl cellulose, have excellent withstanding powers as presoaking solution a potassium hydroxide solution of
against both silver oxidation and zinc metal penetration 40 concentration 13-17% by weight,
but not the low electrolytic resistance required; partial- The membrane to be treated may be in the form of an
electrode wrap as, for example, in the fonn known in thelarly in the 30 to 45% potassium hydroxide solution
customarily required for efficient operation of silver-zinc,
silver-cadmium and other alkaline batteries.
SUMMARY OF THE INVENTION
It has now been found that cellulose ether films may
be made electrolytfcally conductive in concentrated alka-
line battery solutions to provide battery separators with
extended life and superior performance. Moreover, it
has surprisingly been found that the resistance remains
low for indefinite periods of time and does not revert to
the high resistance it would have had if placed directly
in 30-45% potassium hydroxide.
The present invention is directed to the process of
increasing the electorlytic conductivity of a water-soluble
cellulose ether membrane for concentrated alkaline bat-
teries comprising contacting said"membrane with an aque-
ous alkali solution of concentration less than that of
the alkali solut?cn in the battery but above that at which
the membrane is soluble therein until the said membrane
is essentially equilibrated and to the resulting stabilized
membrane.
DETAILED DESCRIPTION
This invention may be applied to any waior-soluble or
water-swellable and alkali insoluble cellulose ether, such
as methyl cellulose, ethyl cellulose, propyl cellulose,
modified hydroxy ethyl cellulose, and mixtures thereof.
art as a U wrap. In a preferred application of this in-
vention, the battery cell is first assembled with positive and
negative electrodes properly separated by the membrane
material. The assembled cell is next filled with the less
concentrated presoaking alkali solution. Then after equil-
ibration, the presoak solution is removed aud replaced
by electrolyte of the concentration at which the cell is
expected to operate.
In carrying out this invention it is preferred that the
presoak in less concentrated alkali be carried out at the
same temperature at which the cell will eventually be
operated after equilibration with the more concentrated
alkali. However, a wide range of temperatures may be
used. The membrane can be preceded to very low tem-
peratures (below about 10° C.) in contact with the
alkali solution.
As used herein, the term "stabilized" refers to the fact
60
 that the membranes will not revert to the conductivity
levels that the nembranes had before being processed in
accordance wu.i the present invention.
The invention will be further described in connection
with the following examples which are set forth for the
65 purpose of illustration only and wherein proportions are
in parts by weight unless specifically stated to the contrary.
EXAMPLE 1
45
50
55
A 1.5 mil film of methyl cellulose was soaked in 15%
The preferred material is methyl cellulose, particularly 7C KOH for three days, blotted, then stirred for seven days
methyl cellulose in which l.<5 to 1.9 out of every 3.0 in a large excess of 45% KOH. The resistance of the film
available hydroxyl units of cellulose have been etherified. in 45% KOH was determined, the percent weight increase
3,498,841
on the blotted film and Ae percent KOH in the blotted
film by sulfate ash analysis. A control film of methyl cel-
lulose was equilibrated directly in 45% KOH and ana-
lyzed in a similar manner. Results are shown in Table I:
TABLS r,
30% KOH and half were stirred in 30% KOH saturated
with silver oxide. The breaking strength of the oxidized
cellophane was then compared with that found for cello-
phane treated with KOH only. Results are shown in
Table IV.
Wt. increase, percent. - ,
KOH in blotted film by asb analysis, "
KOH in blotted film, calculated,
percent • . .
Resistance, millionms-in.>_ _
Film pie-
soak eri In
15% KOH,
then equil-
ibrated in
45% KOH
61.2
20L1
19.7
60
Control
film equil-
ibrated
directly
in 45%
KOH
22.0
1L9
It 6
6,080
TABLE IV.-
-EFFECT OF SILVER OXIDE ON STRENGTH OF
FILMS
10
Methyl
Cellulose
Modified
as in
Example 2
PUDO
Cellophane
EXAMPLE 2
Strength after 72 hoars In 30% KOH
only, p.s.l. (A)
Strength after 72 hours In 30% KOH
+Ag>O, p.s.1. (B)
B/A
2340
2130
.904
1010
148
.143
The procedure was repeated on a similar film except
that after soaking in 15% KOH h was stirred for three The greater stability toward oxidizing action of the
days in 30% KOH. Electrolytic resistance, weight gain 20 si.lver oxide no™^ present in the electrolyte of silver/
were then compared to values on the same film equili- zinc cells is readily apparent.
brated directly in 30% KOH, as shown in Table II:
TATIT V TT
EXAMPLES
A series of equilibrations are made using the process
and membrane of Example 1, with the exception that the
low concentrated KOH solution therein used is replaced,
separately and in turn, by an equal concentration of tetra-
methyl ammonium hydroxide, sodium hydroxide, lithium
hydroxide, rubidium hydroxide, and cesium hydroxide.
J
«s 30 Membranes of increased conductivity are obtained in each
instance as compared to membranes equilibrated directly
in the battery alkali.
Although the exact mechanism of the invention is not
known it has been observed that when cellulosic mem-
-- - —— - --•- " " " , ' " " , , 9- branes are pre-swollen in dilute KOH, then equilibratedformulations with polyacrylic acid and a methyl cellulose *> -m KOH concentrations of 30% KOH or higher that the
formulation with potassium acetate were cast as films.
 wej fat pickup of ^ st r a,kaii fe sisnificantly greater
Clear, one-phase films were obtained of the compositions
 than when ^ membrane is equilibrated directly in the
and designations shown: stronger alkali. Furthermore, ash analysis on such mem-
Resistance, railliohms-in."
illmpre-
soakedin
15% KOH,
then equil-
ibrated In
30% KOH
64.9
17. S
Control
film equil-
ibrated
directly
in 30%
KOH
25 0
498
EXAMPLE 3
Two methyl cellulose formulations with poly (vinyl ^
methyl ether-maleic anhydride), two methyl cellulose _ Cranes"
Cl: 10% PVMMA—90% methyl cellulose
C2: 20% PVMMA—80% methyl cellulose
B3.3: 33% PAA—67% methyl cellulose
B2: 20% PAA—80% methyl cellulose
KA: 25% KOAc—75% methyl cellulose
The air dry fi!.-ns were soaked in 15% KOH overnight,
 45
then sample sections were soaked in 30% and 45% KOH
respectively. The electrolytic resistances of the specimens
thus processed are compared to the corresponding values
obtained when the dry films were soaked directly in 30%
and 45% KOH respectively.
TABLE m
Resistance, mUltohms-ln.'
KA Cl C2 B3.3 B2
40 branes reveals a metal content corresponding to replace-
ment of 15% electrolyte by electrolyte of the stronger
concentration. It appears from this that the precondition-
ing of the film in dilute alkali according to the invention
results in an increased free volume in the membrane for
imbibition of strong electrolyte.
Membranes prepared by this procedure are markedly
more resistant to oxidation than cellophane of prior art
and hence can be used in oxidizing environments with-
out losing their physical integrity.
•It will be understood that it is intended to cover all
50 changes and modifications of the examples of the inven-
tion herein chosen for the purpose of illustration which
do not constitute departures from the spirit and scope of
the invention.
What is claimed is:
65 1. A process for increasing the electrolytic conductivity
of a water-soluble cellulose 'ether membrane when in
contact with an aqueous solution A, said solution compris-
ing an alkali hydroxide selected from the group consist-
ing of potassium hydroxide, tetramethyl ammonium hy-
60 droxide, sodium hydroxide, lithium hydroxide, rubidium
EXAMPLE 4 hydroxide and cesium hydroxide, the concentration of
said alkali hydroxide being selected from the range be-
Uniform strips of 15 mm. width were cut for tensile tween about 30% a*4 abont 45% by weight of said solu-
testing, using PUDO cellophane and methyl cellulose. tion, said process comprising first contacting said mem-
The methyl cellulose film strips were conditioned in 15% 85 brane with an aqueous alkali hydroxide conditioning sOlu-
KOM, *» -ta 30% KOH as in Example 2. One half the' tion B of concentration less than the concentration selected
strips were removed and suspended in a bath of 30% for solution A but above that at which the membrane
KOH saturated with dissolved silver oxide for a period is soluble therein until the membrane is essentially equili-
of 72 hours, under gentle stirring of the solution. The brated, then removing the conditioned membrane from
strips were then rercoved, blotted and immediately broken 70 said conditioning solution B and placing the conditioned
on a tensile testing machine. The breaking strength so ob-. membrane in the alkali hydroxide solution A having the
tained was compared with that found for the unoxidized selected concentration.
strips. 2. The process of claim 1 wherein the membrane is first
For comparison, uniform strips of cellophane of 15mm. interposed in the dry state between the electrodes of a
width were cut Half of these were stared ia a baft of 75 battery cell, the conditioning with solution B is carried
Film soaked directly In 30%
KOH
Film soaked in 15% KOH,
then 30% KOH
Film soaked directly In 45%
KOH
Film soaked in 15% KOH.
then 45% KOH
2B.O
6.9
54.0
6.6
72.8
10.3
905
It 2
22.4
0 1
733
7.4
23 9
3.2
47*
4.9
24.3
6.8
953
It 2
3,498,841
out in- the battery cell, the removal of the conditioned
membrane from solution B is effected by pouring solu-
tion B from the cell and solution. A is then poured into
the cell.
3. The process of claim 1 wherein the alkali used in
both solution A and solution B is potassium hydroxide,
the concentration of solution A. being from about 30%'
to about 40% by weight and the concentration in the
conditioning solution B being below 30% but above
about 10%.
4. The process of claim 3 wherein the alkali condition-
ing solution B is an aqueous potassium hydroxide solu-
tion of concentration 13-17% by weight.
5. A cellulose ether membrane, suitable as a battery
separator for alkaline electrochemical cells, conditioned: 15 tery separator of claim 7.
and stabilized by the process of claim 1^
6. The membrane of claim 5 wherein the cellulose
ether is methyl cellulose.
7. The membrane of claim 6 wherein the degree of sub-
stitution in the methyl cellulose is in the range of 1.6-1.9.
8. An alkaline electrochemical cell comprising elec-
trodes, an aqueous alkali fluid comprising between about
30% and about 45% by weight of an alkali hydroxide
selected from the group consisting of potassium hydrox-
ide, tetramethyl ammonium hydroxide, sodium hy-
droxide, lithilim hydroxide, rubidium hydroxide and
cesium hydroxide, and the stabilized battery separator
Of claim 5.
9. An alkaline silver cell comprising electrodes, an
aqueous alkali fluid comprising between about 30% and
about 45% by weight of an alkali hydroxide selected
from the group consisting- of potassium hydroxide, tetra-
methyl ammonium hydroxide, sodium hydroxide, lithium
hydroxide, rubidium hydroxide and cesium hydroxide,
and the stabilized battery separator of claim 5.
10. An alkaline silver zinc cell comprising a silver elec-
trode, a zinc electrode, an aqueous alkali fluid comprising
between about 30% and about 45% by weight of an
alkali hydroxide selected from the group consisting of
potassium hydroxide, tetramethyl ammonium hydroxide,
sodium hydroxide, lithium- hydroxide, rubidium hy-
droxide and cesium hydroxide, and the stabilized bat-
20 2,419,3412,696,515
3,245,839
References Cited
UNITED STATES PATENTS
4/1947 Edelstein 106—197 XR
12/1954 Korenetal. 136—154 XR
4/1966 Rosseretal. 136—146
WINSTON A. DOUGLAS, Primary Examiner
25 DONALD L. WALTON, Assistant Examiner
U.S.G1.XJR.
106—197; 136—148; 264—195


Process of treating cellulosic membrane and alkaline with membrane separator

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server