NL8501874A - ELECTROCHEMICAL CELL AND METHOD FOR REDUCING CORROSION AND GAS GENERATION THEREIN. - Google Patents

Description

J ·. N.0. 33308 *. * 'F

Electrochemical cell as well as a method of reducing corrosion and gassing therein

The invention relates to an electrochemical cell as well as to methods of reducing the corrosion and gassing in aqueous electrochemical cells, especially in alkaline cells with zinc anodes.

A problem in aqueous electrochemical cells is the development of hydrogen gas in the sealed cell container. Such gassing results in corrosion, leakage of the electrolyte from the cell, breakage and deformation of the cell holder and a potentially hazardous situation when the cell is exposed to fire. Various methods and means have been used to prevent, minimize and control such hydrogen gas development and its consequences. The most common, most effective as well as the oldest agent (especially in alkaline electrolyte containing cells) is the use of mercury to amalgamate the anode material, such as zinc, to increase the normally high hydrogen over potential and to provide an even equipotential surface on the anode metal. With environmental considerations becoming more and more important, intensive efforts are being made to reduce or eliminate mercury without at the same time causing a significant increase in cell corrosion or gassing.

The object of the invention is to provide a method for reducing or eliminating mercury in cell anodes without loss of corrosion protection and without increasing gas formation in the cell.

The invention generally relates to a method of manufacturing an electrochemical cell, in which reduced cell formation occurs, by using specific materials in specific states; on such materials as well as on the cell as such. The method is particularly suitable for an anodic cell consisting of a mercury-amalgamated powdered metal, such as zinc. According to the method of the invention, the powdered metal is mainly formed in its individual monocrystals and a small amount of one or more of the elements indium, cadmium, gallium, thallium, bismuth, tin and lead is added to the anodic material, that is, the powdered metal (whether or not amalgamated) or mercury, which is then amalgamated with the powdered metal. The mercury and the additive hereby form - »J * ·. f ΓΓ * ’V * / i'ï k,, τ <2 the process generally referred to as an alloy on the surface on each of the particles.

While the use of a single crystal line anode material and the use of an indium and / or other additives are known separately to effectively allow for some reduction of the mercury content in the anode without a detrimental increase in gas formation, it has surprisingly been found that effect of the combination is significantly greater than the sum of the individual measures. For example, in cells with amalgamated single crystal zinc anodes, the amount of mercury in the amalgam can be effectively reduced from about 6-7% by weight to about 4% by weight. Similarly, the use of an indium additive in polycrystalline zinc amalgam anodes allows for a mercury reduction of from about 6-7 wt% to about 3.5 wt%. According to the present invention, a combination of the two measures, ie a single crystal line of zinc amalgam with an indium additive, surprisingly allows an effective reduction in the amount of mercury to about 1.5% by weight. Of course, a combination of gas-reducing agents usually does not provide an added effect, and excessive use of additives does not. The monocrystalline and zinc are preferably prepared as described in Belgian Patent 899,191. Such a process involves the formation of a thin skin on each of the zinc particles by oxidation in air at a temperature just below the melting point (419 ° C) of the zinc, heating the skin-surrounded zinc particles in an inert atmosphere above the melting point of the zinc and then cooling slowly, removing the oxide skins. The size of the zinc particles is generally between 80 and 600 microns for use in electrochemical cells, and the described method provides an effective means for the production of single crystal particles of such small dimensions.

Generally, the amounts of indium or other additives added to the anode metal can range from 25-5000 ppm, preferably 100-1000 ppm. Such material can be added directly to the mercury as such. For example, indium is very soluble in mercury and can be added directly to it in the form of powder or granules. Alternatively, the additive may be applied to the surface of the anode material using its salts for amalgamation with mercury. Such salts include the halides, especially chlorides, oxides and acetates of the materials such as indium. It has been found that the additives such as indium 5501374 r3 ....... both by addition to the mercury and by deposition on the monocrystalline anode metal particles do not in fact have the monocrystalline nature thereof. interfere to some degree, which is surprising.

The amount of mercury in the anode amalgam may range from 0-4% by weight, depending on the application of the cell and the tolerated degree of gassing.

The amalgamated monocrystalline metal particles with additives such as indium are then anodes for electrochemical cells, especially alkaline electrochemical cells. Such cells generally contain zinc anodes and cathodes of materials such as manganese dioxide, silver oxide, mercury (II) oxide and the like. Electrolytes in such cells are generally alkaline and usually include hydroxide solutions, such as sodium or potassium hydroxide. Other anode metals, from which monocrystalline powders can be formed and useful in electrochemical cells, include Al, Cd, Ca, Cu, Pb, Mg, Ni and Sn. It is noted that with anodes of these metals, the additive is not the same as the anode-active material, but is electrochemically less active.

The effects of the present invention can be more clearly demonstrated by comparing the gaseous rates and discharge capacities, as shown in the following examples.

EXAMPLE I

Zinc powder amalgams containing 1.5 wt% mercury are prepared using only polycrystalline zinc, polycrystalline zinc with 0.1 wt% in-25 dium as an element added with the mercury, monocrystalline zinc and monocrystalline zinc with 0.1 wt .% indium as an element added with the mercury. Equal amounts of the amalgam powders are then charged in equal amounts of 37% KOH solution (a typical electrolyte solution for alkaline cells) and examined for gas formation at a temperature of 71 ° C. The amount of gas formed, measured in microliters / gram per day (/ ul / g day) and the factors of the reduction of the amount (where the polycrystalline zinc used as control is 1) are shown in Table A.

. > * A ** “5 / C o L - ^ - v V ··.

4

TABLE A

ANODE MATERIAL QUANTITY AMOUNT OF THE

FORMED GAS REDUCTION OF

5 THE QUANTITY

polycrystalline zinc, 1.5 wt% Hg 295 1 polycrystalline zinc, 1.5 wt% Hg 105 2.8 0.1 wt% indium monocrystalline zinc, 1.5 wt% Hg 140 2.1 10 monocrystalline line zinc, 1.5 wt% Hg 9.8 9.8 wt% indium

It would be expected that the amount reduction factor (if any) could be at most about 5.9 (2.8 x 2.1) 15 for a combined use of a single crystal line of zinc and indium with a reduction in the amount of gas formed to about 50 µl / g day. However, the combination synergistically reduces gassing to about double the expected reduction.

EXAMPLE II

Fifteen amalgams of monocrystalline zinc particles with various combinations of additive material and of indium, thallium, gallium and lead are prepared and tested for corrosion. The additive material and are applied to the zinc particles from its salts. All amal-25 games contained 1.5 wt% mercury. The amounts of the individual additive materials (denoted by "+" or if not present, respectively) are 0.1 wt% indium (In), 0.01 wt% thallium (Tl), 0.005 wt% gallium (Ga), and 0.04 wt% lead (Pb). Two grams of each of the amalgams are placed in a 37 wt% KOH solution as the electrolyte, measuring the gas formation at 90 ° C after a period of 24 and 48 hours, this gas formation being representative of the corrosion. As controls, two amalgams are prepared, the first containing no additive material but 1.5 wt% mercury and the other containing polycrystalline zinc containing 7 wt% mercury, which is equal to the amount usually found in cells of the alkaline type. The results of the tests described are shown in Table B.

3SfM o 7 £ v- J y i g / *} -. - J »5

TABLE B

ADDITION ELEMENT GAS VOLUME (ml), 90 ° C

In T1 Ga Pb 24 hours 48 hours 5 + - - 0.17 0.51 + - 0.13 0.49 + - 0.42 1.35 + 0.40 1.15 + + - 0.13 0.36 10 + - + - 0.17 0.47 + - + 0.15 0.42 ++ - 0.12 0.40 + - + 0.12 0.56 + + 0.40 1.13 15 + + + - 0.13 0.42 + + - + 0.11 0.32 + + + 0.15 0.60 + - + + 0.14 0.44 + + + + 0.10 0.28 20 - - - - (control) 0.41 1.39 control: polycrystalline zinc with 0.16 0.43 7 wt% Hg

As shown in the table above, indium and / or thallium provide the most effective reduction of gaseous formation and thus these materials are preferred embodiments of the present invention. However, an increase in the percentage of gallium or lead is expected to provide similar effects. Similarly, other materials having a similar effect to indium, such as cadium, tin and bis-30 mut, can be expected to provide the improved effect of the present invention.

EXAMPLE III

Seven zinc amalgams containing 1.5 wt% Hg are prepared, three consisting of monocrystalline zinc (prepared as described above) and four consisting of polycrystalline zinc. The amalgams containing monocrystalline zinc comprise two amalgams with 0.1% by weight of indium (added in one case to the mercury for the amalgamation and in the other case for the amalgamation applied to the surface of the zinc particles) and an amalgam without indium. The polycrystalline 40 zinc amalgams comprise three unleaded amalgams for a direct comparison to the monocrystalline zinc, which contains no lead and a polycrystalline line amalgam with lead, as commonly used in electrochemical cells. The lead-free polycrystalline amalgams are directly analogous to the three monocrystalline zinc amalgams. The polycrystalline, lead-containing zinc amalgam contains 0.02% by weight of indium. A control of polycrystalline zinc with lead and 7 wt% mercury (as is commonly used in alkaline cells) is also prepared. Two grams of the samples from each of the above-described amalgams are assayed for gassing at elevated temperatures (71 ° C and 90 ° C) for various periods of time to determine the total gas volume and gassing rates for comparison, such as shown in Table C.

EXAMPLE IV

Cells are prepared with the amalgams of monocrystal line zinc with 0.1 wt% indium (both types), polycrystalline zinc with 0.1 wt% indium, applied to the zinc particles, polycrystallized as described in example III. line zinc with 0.02 wt% indium added to the mercury and a control of polycrystal line zinc with no indium and 7 wt% mercury (a typical alkaline cell). Each of the cells of the AA 20 standard size contains an anode of 2.7 grams (1.75 wt% starch graft copolymer as gelling agent), 2.6 grams of a 37 wt% K0H electrolyte and a manganese dioxide cathode, where the cell is anode-limited. Five cells are assayed for gas formation at 71 ° C for various periods without discharge and five are assayed correspondingly but after partial discharge at 3-9 ohms for 1 hour. The total gas volume and gas formation rates are shown in Table C.

3531874 2l 7 α.

+ j ε <U 3 Dl ε -r-a:

—- T3 CU CT> CM CM ID CO N IN H CO ΟΊ <3Ί O Γ- ~ · CO

cïïre- <n re · cn cm σι <t in r-4 co re- σ h in V * t- · O A n K <t A A A A A A A A ««

S 3 S_ OOr-4r-4 OOOO Ο Ο O r-4 Ο O

• r- C Yl + Y N (U DC <U O E Or "o • r-> σ

! - IE

<ea® · + j · a® «13 · • I- <U 3 HOIHDI encode» COHLOIN oo s_ σι ε cu cm re- σι cm CM PN σι CM cm cn cm co in cm 3 {5¾ A ft A ft ft A ft ft ft A ft ft ft ft 5 »CM 1-> —4 CM CO in Ο Ο O r-4 Ο O rl« tf- O'-Ι r— σ Ό m Ο «E *

CL O «r * r — I

σ a: a® a® • + · 3 5 U1C0DH OOO CO O CM CO OOl cu ε <u <t ie οι η I ^ γνο cm in o in io re- 15¾ g 05 ft ft A ft] ft ft 91. ft ft ft ft ft ft> r- r-l CM CO m Ο O r-4 i- O O rH CM O r-4 .Ο ΗΌΙΛ 3 CL «C« 3 O (- 1—4

E r-t-I

cu cu CU CTO cu ex ar ό ω c a® 3¾¾ T3 cu

JaC ·> 1— · 4-

E 3 5 C OCMO «3 * - 3 Pn. I — I

r- cu Έ οι cu in in co co e t i i i re? iiii re- cm ND13D5 + J «« «.« aj till <u iiii ««

• r- -r- r-4 CM CO re "" D D> O i — I

E t — I Ό in 3 CCS

• r— »e * _q r— ε

r- O T- r-1 - + J .E

r- Ε O

es f— ε o z re σι «3 I σι i-i + j ε ze re + j« S «1 3 σ ω co QC * ι— · ι— a® i—! - - o i. to · «on e n σι co> E 3 ε 1—4 t" * - I I * —r IIII · | - 1 1 t I COIN.

io>) T- cu re «*> ιι iiii _o. i f I f «« <C i— cn <t in I— r- (re-

o ο ε σ cu E

- cl. cu in cm o cu

Qi «Ό ο σ> τ-4 r- cu re ε re? r-

_j -P

LU σ CU E E

ca a: ε <- <o <C 3 Η— a® a® - • + · ai— 3 3> HCOOIO ΟΊ Γ- »CO re * cu 00 O CM CO O CJl ω ε cu en re-σι r- »O hcoicoi a r-4 co re- <x> cm io

0¾ 3 05 (Q ft A ft ft ft ft ft ft ft ft ft ft ft A.

• I- C3 00> -lCM OOOO CU OOOO OO

HDin re? " E *

O 'P-T-4 E

I — I

-S4 CT

E re n aft cr aft • * r * «e 3 3 rem in. in t *. co io cm hhcoh ο co ό cu ε d re * σ> m cm r-ι re- m σι cMcore-o cm m «(-> 0) 0 0 ft ft ft ft ft A ft ft ft ft A ft Aft

I-OOHCM OOOO OOOr-10 OO

. i— h rein re «c« + i O v- r-i «1 4. O!

S4 SI

O 3 E * r— ¾¾ ore? · In cm oo in coco ΣΙ e 3 ui in co in iiii iiii in oo • r— <u «« «« till 111! «« Σι> —4 co m in ο «-4 E ^ -n cu in r—

(You «C_J CU

CD r-l. - - Ο O

o o ο σι cu

r — 4 -O

1-- -r-j

N— *! - E

-D CU

e r-. re-4 co o pn re · oo ο γν. re- oo -p re · co cu r-ι cm cm t — i cm i — 4 cm ε v— cm re- σ cu 3 re s- jd Q = Γ— 3S ft * 1 = -. 0 υ i U / *} * 's | 8 α.

• p ε 0) 3 0)

J, -5 ^ 0J rH in COCO-1

CS ^ I— CO (-! CO Ο) CO Γ— LO UJ ΙΠ ΙΟ CO CO rH ΗΗ os τ- · ο foncortrortn c 3 s- · <- c οι -μ ν <υ σ> c <υ ο c cnh 'ο • Γ-5 • r— γ— σι

τ— X

Π3 3¾ • Ρ · 3% V) 3 · • r- 4) 3 s_ σι Ε 0J ιο η η σι σι οco co r ~ »σ co co co r ~ * co ιη 3CT co O) o σι co o σι cm <h rH co i — i cm co lo

> 1 CM · Γ- rH τ — I

γ— OOLfl, • ο * c «CL · ο · γ- γΗ cn

X

3¾ 3¾ • + * ω ε S Ή d * 'co * —ι cm co ι — ι r ^ oicocoo γ ^ -cmooo o) 30ir— o oo σι co σι co σι ι — ι <—ι <- <-— · -T cm cm ^ co r- ~. · Ι— Cl) τ — ι s- jQ rH XJ ΙΟ O = Q_ Λ C * 3

Ο -r- rH <U

C Ό <- *

CD

φ Oil C 4>

Ol X 0J "Ο

r-. s_- + J C

cn 3¾ C 3¾ ·· “<U

r— ^ · »i— * 3 * oc 3 3 .α 3> · ι- <υεο) '-to rs ο io ro c Ό i-NO) 3CT Ol— N rv cn N CO (1) IIII ι <DII ι ι ι φ · Γ- O) rH XJ O)> c rH -a in co to _

- 'ι-5 «C« Ό I— E

R- O T- rH I -P -C

.—. r— U) CO

Or- ^ O

x ra or— ι σι i-H 4J ε X 3 Ρ *

S W) 3 "S- 4J CO

OS · ι— -1-3¾ -r- O S- XJ · C Ό 5 »^ c3 co σι co> - · · ι- (/)>! <- a) (/) σ cn ι ι r ~ - ι ι ι ι ι ι ι -Ω iiiii e £, - σ) »σ CM CM CM I— ο oc σ> <uc

• - Q. cu LO O QJ

0) ·> XJ XJ

o oh ε <u («S- Ό r—

_ Y O -P

lu cn> c c - ca x aj rH o <CD - 'P- 3¾ 3¾ • 4- XJ r— 3 3 ·· - 0) aj ε <u a) o

O) 3 CJ) -C OIHHNLO (JICM OrHOOO CO CO CO cn rH

• I — r— CM CO CO τ — I rH rH rH rH 4) rH rH

rH xj cn aj ό «e« <u

O'rH> C

<u HH

O

CT X.

C X

N 3¾ C 3¾ • <1— · c 3 3 • 1-5 <U ε 4) • r- σ> 3 σι h co σι co ο co ο ο o coco co in h

.1— CO (O Cf Cf d ci Cf Η HHH rH rH

I— rH XJ If) <a ·> c ·>

4-) O - rH

1 /) ΊΕΙ σι ε x O 3 C m— 3¾ O XJ ·

s; c3 rH rH ΟΊ CO CO rH CO IIIII I I III

• I— <u rH «d · CO CO CM cn CO IIIII iiiii

O) rH t — I ι — I rH rH τ — I rH

c aj cn cu «DJrH r— 'o 0

rH

Γ ~ τ «4 * rH CO * nf · CO 00« 3 "CO CO <d-« d * co co

C r ^ * rH CM CM rH CM CM IsHHNCM ISHHCMCM

CU I I I I I I I IIIII IIIII

cn ΟΝ'ΐΗΟ'ίΟ ONO-i O ONCiO

fO rH CM rH rH rH

o 35 0 1 8 / 4ί 9

EXAMPLE V

Cells are manufactured as in Example IV and each is discharged to various cut-off voltages at a 3.9 ohm load, the capacities in hours of use being shown in Table D.

TABLE D

(Ont1adi ngskarakteri sti eken) (Hours run at 3.9 ohms)

Cut-off Monocrystalline zinc _ Polycrystalline zinc_ 10 stress- 0.1 wt% 0.1 wt% 0.02 wt% 0.1 wt% None In gene In + In in In in In + 7 wt% _ 1 .5 wt.% Hg 1.5 wt. Hg 1.5 wt% Hg 1.5 wt% Hg Hg Ctrl 1.2 0.660 0.668 0.533 0.688 0.623 1.1 1.616 1.638 1.457 1.712 1.553 15 1.0 2.826 2.859 2.480 2.926 2.598 0.9 3.535 3.652 3.235 3.619 3.295 0.8 3,800 3,967 3,498 3,883 3,599 0.65 3,986 4,179 3,594 4,020 3,684 It is clear from the above examples and tables that the monocrystalline zinc with one or more additives of the invention is remarkably effective in significantly reducing the amount of mercury without an increase in gas formation in the cells, while at the same time improving the discharge characteristics of the cell as compared to the conventional commercially available alkaline cells, which contain a high content of mercury carbon.

3501874

Claims (13)

An electrochemical cell comprising an anode, a cathode and an aqueous electrolyte, characterized in that the anode consists of monocrystalline anode metal particles and one or more of the elements 5 indium, cadmium, gallium, thallium, bismuth, tin and lead. Cell according to claim 1, characterized in that one or more of the elements in the anode are present in an amount in the range of 25-5000 ppm. 3. Cell according to claim 1 or 2, characterized in that the anode consists of monocrystalline anode metal particles and indium. Cell according to claims 1-3, characterized in that the anode metal is zinc. 5. Cell according to claims 1-4, characterized in that mercury is present in the anode in an amount of at most 1.5% by weight, based on the weight of the anode. Cell according to claims 1-5, characterized in that the cathode consists of manganese dioxide and the aqueous electrolyte is a potassium hydroxide solution. 7. A process for the production of an electrochemical cell 20 with reduced gas formation, characterized in that the following steps are carried out: the production of monocrystalline particles of the metal, which is used as the active anode of said cell, adding a or more additives selected from the group consisting of indium, cadmium, gallium, thallium, bismuth, tin and lead to the monocrystalline particles and using the monocrystalline particles with one or more additives as the anode of the cell. 8. Process according to claim 7, characterized in that the monocrystalline metal particles are prepared by forming separate thin oxide coatings on polycrystalline metal particles by oxidation of these polycrystalline metal particles in air at a temperature below melting point of the metal, heating the metal particles in an inert atmosphere above the melting point of the metal, slowly cooling the metal particles and removing the coatings. 9. A method according to claim 7 or 8, characterized in that the metal is zinc. Method according to claims 7-9, characterized in that one or more additives make up 25-5000 ppm of the anode. 11. A method according to claims 7-10, characterized in that mercury is present in the anode in an amount of up to 1.5% by weight, based on the anode. 8501874 11 A method according to claim 11, characterized in that one or more additives are applied to the monocrystalline zinc particles for the amalgamation of these particles with mercury. A method according to claim 11, characterized in that one or more additives are mixed with the mercury to amalgamate the monocrystalline zinc particles with this mercury. ++++++++++++++ «BoOI874