JPS6148220B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a secondary battery having a cathode comprising zinc material.

Conventionally known silver, zinc, and nickel
Zinc and oxygen (air)-zinc alkaline batteries have not satisfied the battery industry's need to provide secondary batteries of the type described above suitable for powering electric vehicles or similar demand applications. These applications require high (65%) discharge-recharge cycling capacity on the order of 300 cycles or more, which is simply not achievable with previously known zinc-containing secondary batteries.

It is believed that the inability of previously known zinc alkaline batteries to have such cycling capacity is primarily due to various limitations of their cathodes. That is, conventional zinc active material electrodes cannot repeatedly provide uniform surface adhesion due to zinc electrolytically reduced from the state of a solid zinc compound or zinc deposited onto the electrode from an electrolyte. Nakatsuta. The above observations of the inventors are to some extent reflected in Morrison's U.S. Reissue Patent No.
No. 13174, and in the introductory part of that specification, it is stated that electrodes containing zinc-active material, even if not inherently, are depleted from a zinc-containing alkaline electrolyte during repeated discharge-recharge cycling. It is stated that it is impossible to retain the zinc deposited on the electrode. The patent describes that some improvement in short-term cycling may be achieved by preplating the electrode with cadmium or silver and amalgamating it to form a surface suitable for receiving zinc. However, it has been reported that with such improved electrodes, an excess amount of electrolyte must be used over that required to do the required work. In order to solve the above problem, the patent specifies that, apart from the method of using cadmium plating (which it states is impractical), it uses a large number of wires to provide a holding bed for the zinc active material. A mechanical electrode structure including a screen is disclosed.

It is therefore an object of the present invention to provide an improved secondary battery having a zinc cathode.

A more particular object of the invention is a battery of the above-mentioned type having an electrode manufactured using a zinc material, which exhibits improved adhesion to the zinc deposited on the electrode from the electrolyte; It is an object of the present invention to provide a battery that meets the current demand for a much greater discharge-recharge cycling capacity in secondary batteries.

To this end, according to the invention, a cell is provided having an anode with an active substance and a cathode containing a zinc material and particulate cadmium or a cadmium compound dispersed in the zinc material. The respective amounts of anode active material and zinc material are selected as follows. That is, the anode active material is selected to be electrochemically depleted prior to electrochemical depletion of the zinc material upon discharge of the cell. As a result of this quantitative selection, the cadmium material remains electrochemically inert with respect to the anode active material during cell discharge. Therefore, the terminal voltage of the cell according to the invention is ensured by the zinc material and the anode active material during discharge, and no voltage step occurs due to the electrochemical interaction between the anode active material and the cadmium material. The secondary battery according to the present invention exhibits a large discharge-recharge cycling capacity over 300 cycles. The cadmium additive used in accordance with the present invention significantly improves the electrode surface morphology so as to retain zinc electroreduced from the solid zinc compound state or zinc deposited on the electrode from the electrolyte, thus It is believed that this will provide the basis for improving the performance of next-generation batteries.

The above and other features of the present invention will become clearer from the description of specific examples with reference to the drawings below. In addition, reference will be made below to other patent specifications that were considered during the preparation of the present application to aid in understanding the present invention.

The invention of Morrison's U.S. Pat. No. 945,243 is (1) sufficient to prevent hydrogen evolution in an electrode having a copper support, for example, by local reaction between the copper support and zinc deposited on the electrode; The purpose of the present invention is to develop an electrode structure that can retain a sufficient amount of mercury, and (2) limit the penetration of mercury into the support, which may cause the support to become brittle. In order to reconcile these two seemingly contradictory issues, this patent proposes applying an amalgam-retaining or absorbing cadmium coating to a support that prevents mercury penetration. ing. The cadmium layer is electrodeposited on the carrier by electrolysis, and therefore no consideration is given to dispersing particulate cadmium metal.

Werner, US Pat. No. 6,231,95 is directed to a battery having a lead peroxide active material and a thin metal plate anode. The electrodes are electroplated with plywood made from magnesium and cadmium containing zinc. The use of unalloyed cadmium metal or cadmium compounds is not considered, nor is the use of dispersing metallic cadmium particulates.

US Pat. No. 2,013,379 to Drumm et al. provides an electrode support for retaining zinc deposited onto an electrode from a solution. The electrode support is comprised of an iron-nickel or iron-cobalt alloy, which may be further alloyed with various metals, including cadmium, if desired. This patent does not take into account electrode structures that inherently contain zinc active material, nor does it take into account dispersed particulate metallic cadmium.

U.S. Pat. No. 2,942,052 to Bourke et al. discloses a cathode for selected cells of a multi-cell battery, the electrode comprising a plurality of active materials, such as zinc and cadmium, in the following weight ratios: Cadmium is at least 25 percent of the electrode weight). That is, the weight ratio is such that the cell selected will undergo a measurable change in output voltage as the material is electrochemically converted from zinc to cadmium during the discharge period. When constructing the electrode, the multiple active materials may not be physically mixed, and therefore concern with the surface morphology of the zinc-cadmium composite electrode is lacking in this patent. Furthermore, in this patent, no consideration is given at all to the characteristics of metal cadmium particles during electrode production.

U.S. Pat. No. 3,208,880 to Bode relates to a type of secondary battery having a cadmium compound as the active material of the cathode. In order to provide a discharge reserve in the cathode, i.e. to ensure that the anode is consumed before the cathode, the patented invention uses zinc at a rate of 5.0% of the charge-accepting capacity of the cadmium compound.
Since zinc, introduced in amounts up to an equivalent percent, is electrochemically more negative than cadmium, the zinc additive is oxidized to zinc oxide at the start of the cell, while the cadmium compound is converted to cadmium metal. and the desired discharge reserve is provided. In this case, due to the electrochemically inert zinc, the ability of the cathode to provide adhesive properties has no bearing on the subsequent conversion of the cadmium active substance. Furthermore, in the construction of the electrode, the zinc additive can be spatially separated from the cadmium compound.

(Kramer et al., U.S. Pat. No. 3,847,668, which is commonly assigned to and technically related to the Bode patent cited above, is a method for applying zinc to cadmium electrodes in the form of spatially spaced plates). The addition of zinc provides a reserve to the cadmium electrode, and the use of zinc together with the alkaline electrolyte provides for the reduction of anti-polar material in the battery anode. As in the case of the Bode patent, the resulting cell has a cadmium-based cathode and exhibits no particular adhesion for zinc originating from the electrolyte.

As detailed above, none of the above patents that contemplate a cathode structure composed ab initio of zinc and cadmium provide any means for keeping the cadmium material electrochemically inert with respect to the active material of the anode. The policy is also unintended.

Next, preferred embodiments of the present invention will be described in detail.

A cell according to a particularly preferred embodiment of the invention has a cathode comprising a mixture of zinc oxide, cadmium oxide and a binder for both, such as polytetrafluoroethylene (PTFE). That is, these mixtures are kneaded using a non-aqueous lubricant until the dough resembles fresh bread. The kneaded mixture is then rolled to a thickness of 10 to 100 mils, preferably 30 to
Roll into a series of 50 mil sheets. The lubricant is then released and removed from this sheet, resulting in a flexible porous PTFE containing zinc oxide and cadmium oxide.
A sheet is made.

This time, apart from the above, cadmium oxide and PTFE
are mixed separately and kneaded into dough using a non-aqueous lubricant. The kneaded mixture is rolled into a connected sheet 2.0 to 20 mils thick, preferably 2.0 to 5.0 mils thick.

Next, create a sandwich-structured cathode as follows. That is, the above cadmium oxide-PTFE sheets are first applied to both sides of a metal foil current collector, such as a 2.0 mil thick solid copper foil, and then the exposed side of each cadmium oxide-PTFE sheet on the current collector is coated with the cadmium oxide-PTFE sheet. A zinc oxide-cadmium oxide-PTFE sheet prepared as described above is provided.

In the above embodiment, the cadmium oxide may be a commercially available powder known as ASARCO cadmium oxide. Zinc oxide is U.
A commercially available powder named SP12. and known as New Jersey Zinc Oxide may be used. Additionally, the PTFE can be a powder commercially available as Dupont Teflon powder No. 6C. A suitable solvent is Shell
It is a petroleum solvent available on the market as Sol V.
This has a gravity of 70.8APT and an aniline point of 129
(approximately 54°C) and has a composition of 65.5% by volume of paraffinic systems, 32% by weight of naphthenic systems, and 2.5% by volume of aromatic systems. Such solvents are used in an amount of about 50 to 90% by weight of the total weight of solids in the mixture.

Cadmium oxide is preferably used in the electrode structure in an amount of 1.0 to 10% by weight of the zinc active material. In the specific example described above, the amount of cadmium oxide is 5.0% by weight of the total weight of solids in the zinc oxide-cadmium oxide-PTFE sheet, and the weight of PTFE is also 2.5% of the total weight of solids in the sheet. It was hot. cadmium oxide
The same weight ratio of cadmium oxide was used for the PTFE sheet, where the weight of PTFE was 2.0% of the weight of cadmium oxide. Due to the selected thickness of the latter sheet, the weight of cadmium oxide in said sheet is zinc oxide-cadmium oxide-
The content of cadmium oxide in the PTFE sheet can be as low as 15% by weight. As previously mentioned, the total weight of the cadmium additive added to the entire electrode structure is preferably between 1.0 and 10 of the weight of the zinc active material.
%.

In order to obtain the preferred surface morphology for the negative structure described above, the particle size and surface area of the cadmium oxide are preferably selected as follows. That is, the metal cadmium particles present in the electrode structure upon conversion of cadmium oxide are selected to have a particle size not greater than 10 microns and a surface area not less than 1.0 m ² /g. Metallic cadmium powder may be used as a starting material instead of cadmium oxide. In this case, the particle size and surface area of the starting materials are selected directly within the above-mentioned limited ranges. Since both cadmium oxide powder and cadmium hydroxide powder have a lower density than cadmium metal powder, if either of them is used as a starting material, the particle size and surface area of the starting material should be increased by 20 to 30% of the above limitations. Raise it up to. This increase ensures that upon conversion of the starting cadmium compound, the metallic cadmium powder present in the electrode structure falls within the preferred particle size and surface area ranges described above.

An alkaline cell is constructed using the electrode structure thus produced with an amount of zinc oxide active material of 130 g as a cathode and a silver plate containing 140 g of silver active material as its anode. An aqueous electrolyte with 40% potassium hydroxide was used and the cathode and anode were separated by three layers of a commercially available cellulose-like sebarator, like a fibrous sausage bag from Union Carbide. The battery was subjected to discharge-charge (recharge) cycling as follows. That is, discharge at 8 amps for 5 hours to remove 40 amp-hours (Ah) of battery capacity and then charge at 2.5 amps to 2.0 volts.

During the first charge, cadmium oxide is converted to cadmium metal. This is because cadmium is electrochemically more positive than zinc. After this the cadmium metal is inert. This is because during discharge of the cell, the cadmium metal does not participate in the electrochemical oxidation or reduction within the potential region for redox of the zinc active material.

The electrochemical equation during this discharge is shown below: 2AgO+H ₂ O+2e→Ag ₂ O+2OH ^- (1) Ag ₂ O+H ₂ O+2e→2Ag+2OH ^- (2) Zn+2OH ^- →Zn(OH) ₂ +2e (3) Cathode according to the invention As can be seen in Figure 1, which shows a typical discharge curve for a battery with Equation (3) applies to the subsequent process. The discharge cycle in Figure 1 is
Ends when drawn at 40 amps. The two discharge cycles shown, i.e. 5 cycles and
The curves with 200 cycles are almost identical. The above formula
(1) to (3) are reversible, and the reversed equations are applied during charging.

Referring to FIG. 2, the solid curve represents the ampere-hour capacity of the battery over a cycling process of over 300 cycles. This battery delivers its rated capacity of 40 amp-hours throughout its entire cycle. Initially, and after 100 cycles, 200 cycles, and 300 cycles, the cell continued to discharge until its terminal voltage was below 1.5 volts and 1.3 volts. That is, 8.0 amperes were drawn from the battery by continuing to discharge for approximately 0.5 hours beyond the normal 5.0 hour discharge time. During the first discharge, the battery produced a current of 44.5 amp-hours. After 100 cycles of discharge, 43.5 amp-hours were drawn to 1.3 volts. Upon discharge after 200 and 300 cycles, 41.5 and 42 amp-hours are drawn to 1.3 volts, respectively, and the battery maintains its rated capacity for the entire duration of each subsequent standard discharge cycle. did.

In order to evaluate the performance of this cadmium-added battery, FIG. 2 further shows the discharge cycling capacity of the comparative battery as a dashed curve. The comparative cell differs from the cadmium-doped cell of the present invention only in its cathode. The cathode of the comparison cell was 2.0% by weight mercuric oxide, 2.5% by weight PTFE.
and the remainder zinc oxide. The mixture was kneaded with a lubricant and rolled to a thickness of 30 to 50 mils and crimped onto a solid foil copper current collector, as described in the Example for Preparation of a Battery Cathode Structure of the Invention above. .

A comparative cell having an initial ampere-hour capacity as shown in FIG. 2 was subjected to the same discharge-charge cycling experiment as for the cadmium-doped cell. However, the operation of discharging up to 1.3 volts during the first and every 100th cycle thereafter in the cadmium-added battery is excluded. As can be seen in Figure 2, the ampere-hour output of the comparison cell degraded continuously throughout the cycling process, with the cell dropping only 20 amperes in less than 150 cycles.
It becomes nothing more than a current that can be generated at a time.

The reason why the comparative cell was unable to maintain its rated ampere-hour output during such repeated discharge-charge cycles was because its zinc electrode was electrically reduced from a solid zinc compound or zinc deposited on the electrode from an electrolyte. This is because it cannot be properly attached. In a cadmium-doped cell constructed in accordance with the present invention, cadmium metal is always disposed within the cathode in such a manner and shape as to provide a conductive nucleation site for uniform zinc electroreduction or precipitation from solution. I believe that it has been done. This is clear from the results shown in FIGS. 1 and 2.
These excellent results are believed to have been achieved due to the use of particulate cadmium material and the introduction of the cadmium additive into the electrode structure in the form of dispersed particles. Introducing it in the form of dispersed particles is quite different from electroplating or electrodepositing cadmium onto an electrode structure as mentioned in the aforementioned Morrison reissue patent. Furthermore, in the multilayer structure electrode according to the present invention, adding cadmium to the current collector by laminating the current collector with a PTFE-cadmium oxide sheet ensures that zinc is uniformly deposited on the current collector. It serves to provide an electrically conductive nucleation site. Adding cadmium to the zinc active material by dispersing particulate cadmium in the zinc active material serves to provide electrochemically inert conductive nucleation sites for each zinc powder.

A preferred surface form of the electrode structure according to the present invention is:
It could also be provided in ways other than the PTFE bonded multilayer structure described above. For example, a cadmium/cadmium compound powder having the surface area and particle size characteristics described above is applied onto a current collector by a doctor knife or other suitable mechanical means, and a zinc oxide powder is applied onto the cadmium/cadmium compound powder by a doctor knife or other suitable mechanical means. It would also be possible to compress the powder. In this case, during the first charge, the cadmium metal adheres well to both the current collector and the zinc oxide, providing improved adhesion to zinc electroreduced from the solid zinc compound state or deposited from solution. An electrode structure having the following properties is obtained.

In practicing the invention, particulate cadmium metal, cadmium oxide, cadmium sulfate and cadmium hydroxide can be used as the cadmium material, although cadmium oxide powder is preferred.
Because it provides the highest surface area for cadmium metal additives and is more economical than other cadmium materials.

As previously mentioned, the cadmium material of the cathode is electrochemically inert with respect to the active material of the anode during discharge of the cell. This feature of the invention is achieved by selecting the amounts of zinc material and anode active material in advance such that the anode active material is electrochemically depleted during the discharge prior to electrochemical depletion of the zinc material. achieved. This point will be more clearly understood from the examples given below.

A silver-zinc battery with multiple positive and negative plates has a theoretical positive capacity of 77Ah and a theoretical negative capacity of 77Ah.
Make it to be 122Ah. The cathode plate contains a cadmium additive with a capacity of 6.7Ah. 45% of this battery
I filled it with KOH and charged it first with 4 amps to a final voltage of 202 volts. Therefore the input is 62Ah
It is. Next, connect this battery to a final voltage of 8 amps.
Discharging to 1.30 volts, this resulted in an output of 53Ah. A zinc wire reference electrode inserted into the cell showed that the anode plate capacity limited discharge at 1.30 volts, and that capacity was being depleted.

These results show that at the end of the cycle there is still a reserve capacity of 9 Ah of charged zinc and 6.7 Ah of charged cadmium remaining. In the next cycle, the battery was discharged at 8 amps for 5 hours so that 40 Ah was drawn per cycle. At this time, the charge reserve of zinc further increased to 2.2Ah, while the charge reserve of cadmium remained constant at 6.7Ah.

A nickel-zinc battery is constructed with multiple positive and negative plates such that the theoretical positive capacity is 38 Ah and the theoretical negative capacity is 80 Ah. 1 for this battery
Fill with 5% KOH containing %LiOH, and
I first charged it at 2.5 amps for 17 hours, giving me a 42.5Ah input. The battery was then discharged at 6 amps to a final voltage of 1.35 volts with an output of 32 Ah. The zinc wire reference electrode inserted into this battery has an anode plate capacity that limits the discharge of 1-35V,
And he showed that he was exhausted.

These results indicate that at the end of this cycle, the remaining charge on zinc is 10.5Ah and the charge on cadmium is 4.4Ah.
indicates that there is a spare capacity of In the next cycle,
When the cell was discharged at 6 amps for 4.17 hours drawing 25 Ah per cycle, the zinc charge reserve increased further to 17 Ah, while the cadmium charge remained constant at 4.4 Ah.

Two oxygen (air) electrodes and theoretical zinc capacity
An air-zinc cell is made with one zinc electrode containing 25Ah. This zinc electrode contains a cadmium additive with a theoretical capacity of 1.4 Ah. The battery was filled with 35% KOH and first charged at 1-25 amps for 16 hours with a 20Ah input.
Next, this battery goes up to 1.00 volts at 4 amps.
It was discharged with an output of 16Ah.

These results indicate that a reserve capacity of 4 Ah of charged zinc and 1.4 Ah of charged cadmium remains at the end of this cycle. In the next cycle, the cell is discharged at 4 amps for 3 hours, drawing 12Ah per cycle, with the zinc charge reserve increasing further to 8Ah and the cadmium charge reserve increasing further to 8Ah.
1.4Ah remained constant.

As will be apparent to those skilled in the art, various modifications can be made to the embodiments described above. Therefore, the present invention utilizes the above-mentioned silver-zinc, nickel-zinc, oxygen (air)
- Batteries other than zinc batteries are also included.

[Brief explanation of the drawing]

FIG. 1 shows a typical discharge curve for a silver-zinc alkaline secondary battery constructed in accordance with the present invention. FIG. 2 is a curve showing the ampere-hour capacity of a battery according to the invention and a comparative battery not according to the invention.

Claims (1)

[Scope of Claims] 1. A liquid electrolyte, an anode comprising an active material, a cathode comprising a zinc material and a particulate cadmium material dispersed in the zinc material, wherein the amounts of the anode active material and the zinc material are , during cell discharge, the anode active material is electrochemically depleted prior to electrochemical depletion of the zinc material, such that during the cell discharge the particulate cadmium material undergoes electrochemical depletion with respect to the anode active material. an electrically conductive support; the particulate cadmium material and the first
a first layer having a binder; on the first layer;
A battery comprising a second layer having the zinc material, the particulate cadmium material, and a second binder thereof. 2. The battery of claim 1, wherein the anode active material is a silver material. 3. The battery of claim 1, wherein the anode active material is a nickel material. 4. The battery according to claim 1, wherein the anode is an oxygen electrode. 5 The particulate cadmium substance has (a) particle size
Metallic cadmium with a particle size of 10 microns or less and a surface area of 1.0 m ² /g or more; (b) electrochemically determined particle size;
a cadmium compound convertible to metallic cadmium with a size of 10 microns or less and a surface area of 1.0 m ² /g or more;
(c) A battery according to claim 1 selected from the group consisting of a mixture of said cadmium metal and said cadmium compound. 6. The battery of claim 1, wherein the particulate cadmium material is cadmium oxide. 7. The battery of claim 6, wherein the zinc material is zinc oxide. 8. The battery of claim 7, wherein the first and second binders are polytetrafluoroethylene. 9. The battery of claim 1, wherein the particulate cadmium material is cadmium hydroxide. 10. The battery of claim 1, wherein the particulate cadmium material is cadmium sulfate.