WO2000069005A1

WO2000069005A1 - Cadmium negative electrode

Info

Publication number: WO2000069005A1
Application number: PCT/US2000/013033
Authority: WO
Inventors: Priyadarshani Bendale; John J. Weckesser; David R. Atherton
Original assignee: Moltech Power Systems, Inc.
Priority date: 1999-05-12
Filing date: 2000-05-11
Publication date: 2000-11-16

Abstract

This invention relates to a high-tap density Cd(OH)2, to non-sintered negative electrodes formed from high-tap density Cd(OH)2, to rechargeable electrochemical cells utilizing high-tap density Cd(OH)2 in the formation of electrodes, and to methods of producing such electrodes and cells.

Description

CADMIUM NEGATIVE ELECTRODE

BACKGROUND OF THE INVENTION

This invention relates generally to cadmium negative electrodes for use in a rechargeable electrochemical cell.

Cadmium-based negative electrodes are commonly used in rechargeable electrochemical cells, such as commercially available nickel-cadmium (NiCd) cells. The active material for the positive electrode is generally nickel oxyhydroxide (NiOOH), which is reduced to nickel hydroxide (Ni(OH)₂) on discharge. The active material for the negative electrode is cadmium metal (Cd ), which is oxidized to cadmium hydroxide (Cd(OH)₂) during discharge. The electrolyte is generally potassium hydroxide (KOH) and common separator materials may include woven and non-woven fabrics or porous plastic. Battery manufacturers use cadmium oxide powder (CdO) or other cadmium salts as the negative starting electrode material. For example, U.S. Patent No. 3,986,893 to Stephenson describes the use of cadmium nitrate Cd(N0₃)₂ for producing a sintered negative electrode. In non-sintered negative electrodes, CdO is the traditional starting material. Representative references of this approach include U.S. Patent No. 5,071,722 to Yoshimura, U.S. Patent No. 4,988,589 to Awajitani et al, and U.S. Patent No. 4,983,477 to Takemura et al.. which describe the use of CdO as the starting material for the production of pasted negative electrodes.

Non-sintered CdO electrodes are incorporated into cells where they come in contact with an aqueous electrolyte, typically a solution of caustic alkali such as potassium hydroxide, sodium hydroxide (NaOH), lithium hydroxide (LiOH), or mixtures thereof. Upon contact with this aqueous solution, the CdO converts to Cd(OH) , an electrochemically active form of cadmium. The following equations illustrate the interrelationship between the various forms of cadmium in the negative electrode and their ultimate derivation from the CdO starting material. CdO Traditional Starting Material

+ H. O Hydration

Cd^u Cd(OH)₂ Charged and Uncharged Forms

(Cd(OH)₃ ^" _(aq)) Hydroxylated Soluble Form

The key conversion is the cycling of the solid state redox reaction between Cd(OH)? and Cd°. Upon charging. Cd(OH)₂ is reduced to Cd°; upon discharge Cd° is oxidized back to Cd(OH)₂ with the release of two electrons. This redox reaction is supported by the diffusion of electrolyte throughout the electrode. In other reactions in the charged electrode, some Cd(OH)₂ and or Cd° becomes complexed with hydroxide ions supplied by the electrolyte to form soluble species such as cadmiate (Cd(OH)₃ ^"(aq)). Cadmiate reprecipitates as Cd(OH)₂ upon discharge. Reprecipitated Cd(OH)₂ is shown in Fig. 1.

In a conventional non-sintered CdO electrode, some of the CdO is hydrated during electrode manufacturing. Additional unreacted CdO undergoes hydration following exposure to electrolyte. However, because only about 75 percent of CdO is converted to Cd(OH) , the use of CdO as the starting material for negative electrodes results in an inherent limitation of their electrochemical capacity. While it is desirable for up to 100 percent of the negative electrode to comprise the active form of cadmium, about 25 percent remains inactive. Moreover, because the conversion of CdO to Cd(OH)₂ in the cell is a hydration reaction, water supplied by the electrolyte solvent is consumed thereby increasing the concentration of caustic alkali present in the cell by as much as 15 percent or more. The hydration reaction causes the negative electrode material to undergo a significant expansion, nearly doubling in volume, its density changing from about 7.9 g cc (CdO) to about 4.8 g/cc (Cd(OH) ₂). This subsequently results in densification of the electrode. In addition, because CdO powder fines are readily dispersible in air, its use in electrode manufacturing presents a health hazard. The present inventors have recognized the desirability of replacing CdO with

Cd(OH)₂ as a starting material for non-sintered negative electrode manufacturing to avoid the problems presented by the conversion inefficiency of CdO to Cd(OH)₂, the fluctuations in electrolyte concentration, and the net densifϊcation of the negative electrode. U.S. Patent No. 4,988,589 to Awajitani et al., U.S. Patent No. 4,983,477 to Takemura et al, U.S. Patent No. 4,649,092 to Chang et al, and U.S. Patent No. 4,414,303 to Williamson et al. only note in passing that a paste of Cd(OH) may be applied to an electrode substrate but do not address nor overcome the problems of using Cd(OH)₂ as described below, nor do they suggest the desirability of replacing CdO with Cd(OH) as a starting material. There are many problems in using Cd(OH)₂ as a starting material. The inventors have recognized that Cd(OH)₂ starting materials generally have a tap density (i.e. , weight of sample divided by tapped volume) of only about 0.6-0.8 g/cc, and thus, the requisite electrode packing density to provide acceptable energy density is unattainable. This is because the void spaces between the Cd(OH)₂ particles on the electrode become relatively small as the electrode packing density is increased. The re-precipitation of cadmiate as Cd(OH)₂ during cell cycling over time deposits within or over the orifices of the small voids in the electrode, blocking the diffusion of electrolyte between the Cd(OH) particles, as shown in Fig. 2. This blockage mechanism reduces diffusion of the electrolyte to a significant portion of the negative electrode, creating areas within the bulk of the negative material that are prevented from efficiently discharging. This decreases the effective capacity of the cell, especially for high drain rate applications.

The buildup of reprecipitated Cd(OH)₂ has a pronounced effect, turning the material from porous to densified and glassy, and producing losses of about one-third of cell capacity within approximately 20 cell charge-discharge cycles as shown in Fig. 3. Cells based on such electrodes have a radically reduced cycle life, on the order of less than 10 percent the cycle life of currently available cells. For example, in comparison with the 20-cycle life of Cd(OH)₂ based cells, CdO-based cells retain as much as 80-90 percent of their capacity over several hundred cycles. This means that, in practical terms of cell capacity and life, such Cd(OH)₂ produced electrodes with tap densities less than about 0.8 g/cc are inferior to CdO produced electrodes. Moreover, the use of Cd(OH) with such tap densities as a starting material makes for very brittle electrodes. In a conventional NiCd cell using CdO as a starting material, a common cause of failure is shorting due to the formation of cadmium dendrites. Cadmiate ions may migrate through the separator towards the positive electrode. During subsequent cycling, Cd dendritic structures are formed during charge, leading to internal shorts in cells as they reach the positive electrode. Thus, it is important to reduce cadmiate migration through the separator and thereby increase the reliability of NiCd cells.

Growth of Cd(OH)₂ crystals results in capacity fading and affects the dischargeability of NiCd cells. To prevent this crystal growth from occurring, additives, which can be either organic or inorganic, are added to the cadmium electrode. These are also classified as anti-agglomerants. Ni(OH)₂ is commonly added to cadmium electrodes. One to five percent of this additive is mechanically mixed with CdO prior to pasting the electrode. The Ni(OH)₂ additive inhibits agglomeration, reduces the size of the crystals formed on the cadmium electrode, provides large surface area for reactions to proceed, and consequently improves dischargeability and increases cycle life.

SUMMARY OF THE INVENTION

Accordingly, it is an aspect of the present invention to solve the above problems by providing methods for producing non-sintered cadmium negative electrodes that do not require the use of CdO. A further aspect of the present invention is to produce such electrodes that comprise a high percentage of Cd(OH)₂. Still another aspect of the present invention is to produce non-brittle cadmium negative electrodes. An additional aspect of the present invention is to produce electrochemical cells comprising such negative electrodes. Yet another aspect of the present invention is to produce cells which have a cycle life exceeding that of CdO produced electrodes and that retain their useful capacity throughout that life.

To achieve the foregoing and other aspects and advantages, the non-sintered negative electrode of the present invention comprises an electrically conductive electrode support and a active material applied to the electrode support that includes Cd(OH)₂ particles having a tap density of at least about 1.2 g/cc. An additional aspect of the present invention is to provide a method for more uniformly distributing an anti-agglomerant additive within the cadmium negative material. To achieve this and other aspects and advantages, the method according to the present invention includes the steps of providing a dry preparation including Cd(OH) co- precipitated with an anti-agglomerant, mixing said preparation with a solvent and applying the preparation to an electrically conductive electrode support.

These and other features, advantages, and objects of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification, claims, and appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a scanning electron micrograph of re -precipitated Cd(OH)₂ on the surface of a cadmium electrode.

Fig. 2 is a scanning electron micrograph of a cross section of a cadmium electrode showing blockage of surface sites by re-precipitated Cd(OH)_;.

Fig. 3 is a graph of capacity (mAH) versus cycle number for conventional NiCd cells made with CdO and low tap density Cd(OH)₂.

Fig. 4 is a graph of capacity (mAH) versus cycle number for NiCd cells made with high tap density Cd(OH)₂ in accordance with the present invention.

Fig. 5 is a graph of capacity (mAH) versus cycle number for NiCd cells made with high tap density co-precipitated and non-co-precipitated Cd(OH)₂ in accordance with the present invention.

Fig. 6 is a graph of capacity (mAH) versus cycle number for NiCd cells made with high tap density co-precipitated and non-co-precipitated Cd(OH)₂ in accordance with the present invention.

Fig. 7 is a graph of capacity (mAH) versus cycle number for NiCd cells made with high tap density co-precipitated Cd(OH)₂ with varying amounts of Ni(OH). as a co- precipitant in accordance with the present invention. Fig. 8 is a graph of mid-point voltage (MPV) versus cycle number for NiCd cells made with high tap density co-precipitated Cd(OH)₂ with varying amounts of Ni(OH), as a co-precipitant in accordance with the present invention.

Fig. 9 is a graph of capacity (mAH) versus cycle number for NiCd cells made with high tap density co-precipitated Cd(OH)₂ with varying amounts of Ni(OH). as a co- precipitant in accordance with the present invention.

Fig. 10 is a graph of mid-point voltage (MPV) versus cycle number for NiCd cells made with high tap density co-precipitated Cd(OH)₂ with varying amounts of Ni(OH)₂ as a co-precipitant in accordance with the present invention.

Fig. 1 1 is a graph of capacity (mAH) versus cycle number for conventional NiCd cells made with CdO.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention uses high-tap density Cd(OH)₂ (e.g., at least about 1.2 g/cc) as a starting material for forming non-sintered negative electrodes. Such high-tap density Cd(OH)₂ is available from Shepherd Chemical Company of Cincinnati, Ohio, U.S.A., product no. 1254. As used herein, the term "tap density" is the density obtained by dividing the weight of the sample by its tapped volume. One commercial tap density analyzer is Quantachrome's Dual Autotap.

Methods of making high-tap density Cd(OH) that involve the precipitation of particles of Cd(OH)₂ offer the advantage of allowing the co-precipitation of anti- agglomerant additives. As used herein, "co-precipitation" refers to the substitution of the anti-agglomerant within the Cd(OH)₂ crystal lattice. Representative examples of co- precipitants include compounds of nickel, copper, magnesium, yttrium, indium, or other metals. In the methods of the present invention, either Cd(OH)₂ particles or co- precipitated Cd(OH) particles may be used. Where co-precipitated Cd(OH)₂ particles are used, preferred co-precipitants include anti-agglomerants such as Ni(OH)₂ and magnesium hydroxide Mg(OH)₂. The amount of Ni(OH) co-precipitant is preferably from about 3 to about 13 weight percent (wt%), and more preferably from about 7 to about 13 weight percent. By co-precipitating an anti-agglomerant with the Cd(OH)₂ particles, the anti- agglomerant may be more uniformly distributed within the negative electrode paste than is the case when the CdO or Cd(OH)₂ particles are physically mixed with the anti- agglomerant particles to form the negative electrode paste. Thus, the anti-agglomerant is more likely to be effective. High-tap density Cd(OH)₂ co-precipitated with Ni(OH)₂ is available from Shepherd Chemical Company of Cincinnati, Ohio, U.S.A., product code D88380.

The Cd(OH)₂ particles used in the present invention have a tap density of at least about 1.2 g/cc, preferably at least about 1.8 g/cc, and more preferably at least about 2.3 g/cc. The particles selected are those with a median size of about 1 to about 30μm, preferably about 4 to about 28 μm, more preferably about 5 to about 20 μm, yet more preferably about 6 to about 16 μm, and most preferably about 5 to about 12 μm. These particles also have process-favorable physical characteristics in that they are highly flowable and low-dusting. An electrode using these materials has a porosity of at least about 15 percent to a maximum of about 50 percent. The porosity is preferably at least about 25 percent and more preferably about 30 percent.

In the methods of the present invention, a dry preparation of these particles is mixed with a solvent and applied to an electrically conductive support to form a non- sintered electrode. The non-sintered electrode produced by these methods may be of various types. The electrode may be, for example, a three-dimensional nickel foam matrix in which the electroactive material is forced into the matrix, or a pasted electrode in which the electroactive material is compressed or extruded onto and across the surface or surfaces of the conductive strip. In a preferred embodiment, the negative electrode is an extruded electrode.

Such an electrode is produced by mixing the Cd(OH)₂ particles with a binder and a liquid vehicle to form the Cd(OH)₂ paste. The amount of liquid vehicle used is that which is effective to produce a composition having a paste-like consistency. The binder may be one or more of any of those commonly used in the field. Representative examples of binders include synthetic polymers, such as polypropylene or nylon; fluoropolymers, such as PTFE; and natural or synthetic cellulose and its derivative, e.g., alkylcellulosics and hydroxyalkylcellulosics. Preferably, the binder is Kraton® 1654 available from Shell

Chemical Company, Houston, Texas, U.S.A., used in conjunction with the preferred non- aqueous liquid vehicle, which is Kwik Dri® brand mineral spirits available from Ashland Chemical Company, Dublin, Ohio, U.S.A. The amount of binder used is that which is effective to maintain electrode integrity during production and normal use of the cell.

The negative electrode paste may also comprise any of various additives mechanically distributed throughout the paste. Representative examples of such additives include carbon, Ni(OH)₂, graphite, Cd , and nickel metal (Ni ). Where the electrode to be produced is a pasted electrode, particles or powders of one or more of such additives are mixed into the dry paste.

The paste preparation is applied onto one or both surfaces of an electrically conductive strip support. Preferably, the strip is perforated metal, such as nickel or nickel- plated steel, and the paste is applied onto both sides of the strip. The strip is then dried to form a negative electrode. Any such positive electrode as is commonly known in the field may be used. Examples of positive electrodes include nickel hydroxide positive electrodes, and may be of the sintered or foam substrate type.

Comparative examples are described below to illustrate procedures for practicing the present invention and to highlight the advantages provided by the present invention. These examples should not be construed as limiting the scope of the present invention. First, to illustrate the advantages of increased tap density, three groups of cells were constructed using different Cd(OH)₂ starting materials each having a different tap density. The first cell group (Sample A) constructed was a control group using Cd(OH)₂ with a tap density of 0.8 g/cc. However, electrodes fabricated with the low tap density (0.8 g/cc.) Cd(OH)₂ material could not be used because the electrode was very dense and could not be wound into a cell. The second and third groups of cells were successfully constructed and tested. The second cell group (Sample B) used Cd(OH)₂ with a tap density of 1.2 g/cc, and the third cell group (Sample C) used Cd(OH) with a tap density of 2.3 g/cc. Specifically, the cells of each group were constructed by mechanically mixing Cd(OH)₂ (73.0 percent by weight), Ni(OH)₂ (1.0 percent by weight), cadmium metal (25.0 percent by weight), and Kraton® 1654 binder (1.0 percent by weight) to form a dry paste, and then adding and mixing Kwik Dri® solvent (16-18 percent by weight of the dry paste) to form the wet paste. The paste was then applied onto a carrier, calendered to the desired thickness of 0.021 inches (0.533 mm) and wound into a cell with a sintered positive electrode to form AA size NiCd cells with a standard potassium hydroxide electrolyte. Fig. 4 shows the cycle life trend for the NiCd AA cell groups. The capacity fade on cycling of NiCd cells decreases significantly with increasing tap density of the Cd(OH)₂ starting material.

As discussed above, the inventors' attempts to improve electrode efficiency resulted in the development of a co-precipitated Cd(OH)₂. In this process, Ni(OH)₂ precipitation is performed simultaneously with the Cd(OH)₂ in order to obtain a homogeneously distributed anti-agglomerant. To illustrate the advantages of co- precipitating Ni(OH)₂ with the Cd(OH)₂, two NiCd AA cell groups were constructed where one group (Sample E) used co-precipitated Ni(OH)₂ and the other group (Sample D) used mechanically mixed Ni(OH)₂. The cells in Sample D were in the manner described above with the exception that Cd(OH)₂ was used that had a tap density of 1.8 g/cc. The cells in Sample E were constructed by first forming a negative electrode paste made by mechanically mixing Cd(OH)₂ with Ni(OH)₂ as a co-precipitant (73.5 percent by weight), cadmium metal (25.5 percent by weight), and Kraton® 1654 binder (1.0 percent by weight) to form a dry paste, and then mixing in 16-18 percent by weight Kwik Dri® solvent to form a wet paste. The co-precipitated Cd(OH)₂ used in preparing the cells of Sample E also had a tap density of 1.8 g/cc. The paste was then applied onto a carrier, calendered to the desired thickness of 0.021 inches and wound with a sintered positive electrode to form AA size NiCd cells. It should be noted that the cells from Sample D were made with 1.0 weight percent Ni(OH)₂ mechanically mixed with the Cd(OH)₂ whereas the other cell group (Sample E) was made with 7.6 weight percent Ni(OH)₂ co- precipitated with the Cd(OH)₂. The 1.0 weight percent of mechanically mixed Ni(OH)₂ was selected as opposed to 7.6 weight percent since the 1.0 weight percent additive is typically used when the anti-agglomerant is mechanically mixed. The two powders used had the same range of particle size. The physical properties of these powders are outlined in Table A below. Also listed in Table A below are the weight percentages of carbonate in the negative electrode paste. Carbonate levels should be kept low, since high concentrations of carbonates in NiCd cells result in poor cycle life performance. TABLE A

Fig. 5 shows the cycle life trend for the two groups of cells. The capacity of the cells constructed using co-precipitated Ni(OH)₂ was significantly higher than those constructed using mechanically mixed Ni(OH)₂. Fig. 6 shows and compares the cycle life trends for groups of cells of the above Samples B and E, as well as a group of cells (Sample F) that are constructed the same as Sample B with the exception that the Cd(OH)₂ used had a tap density of 2.0 g/cc. As apparent from Fig. 6. the co-precipitation of Ni(OH)₂ improves performance to such a degree that cells made using co-precipitated Cd(OH) (Sample E), have better performance than cells made using non-co-precipitated Cd(OH)₂ having a higher tap density (Sample F).

As apparent from Figs. 4 through 6, the tap density of Cd(OH) powder and the co- precipitation of Ni(OH)₂ play important roles in the performance of NiCd cells. As will be apparent from Fig. 7, the amount of Ni(OH)₂ co-precipitated with Cd(OH) also plays a role in the performance of NiCd cells. To determine the optimum percentage of Ni(OH)₂ to be co-precipitated, five cell groups were constructed. Three of the cell groups (Samples G, H, and I) were constructed with a 1.8 g/cc tap density Cd(OH)₂. These cells were constructed in the same manner as Sample E above with the following exceptions. Cell group Sample G was made with 3.2 weight percent co-precipitated Ni(OFI)₂, cell group Sample H was made with 7.6 weight percent co-precipitated Ni(OH)₂, and cell group Sample I was made with 13.0 weight percent co-precipitated Ni(OH)₂. The other two groups (Samples J and K) were constructed with a 1.4 g/cc tap density Cd(OH)₂ where cell group Sample J was made with 7.6 weight percent co-precipitated Ni(OH)₂ and cell group Sample K was made with 13.0 weight percent co-precipitated Ni(OH)₂. The half- cell energy densities of each of these powders was determined to help design cells with the same cell balance. These numbers were optimized to account for co-precipitated Ni(OH)₂. This was done so that the cycle life would not be skewed by the addition of Ni(OH)₂. The physical properties of Cd(OH)₂ samples G-K are shown in Table B below.

TABLE B

Fig. 7 shows cycle life data for the groups of cells made with samples G-I. Fig. 8 shows the mid-point voltages (MPV) for the groups of cells made with samples G-I. Fig. 9 shows cycle life data for the groups of cells made with samples J and K. Fig. 10 shows the mid-point voltages for the groups of cells made with samples J and K. The above data indicates that a 7.6 weight percent level of anti-agglomerant Ni(OH)₂ co-precipitated with Cd(OH)₂ improves cycle life. However, at a 13 weight percent concentration of Ni(OH)₂, the cycle life is adversely affected.

For purposes of comparison, the cycle life trend of a group of AA NiCd cells made using conventional CdO negative electrodes is shown in Fig. 1 1. Based upon a comparison of the capacity trends of the conventional and inventive NiCd cells, it is clear that the cells constructed according to the present invention provide significantly improved performance. While not all of the embodiments of the present invention have initial capacities that exceed that of the conventional NiCd cells, they generally have greater cycle life. Further, the embodiments of the present invention avoid the health hazards associated with the use and handling of CdO fine powders used to make the conventional NiCd cells.

Based on all the tests conducted to date, the following properties of Cd(OH)₂ gave the best performance.

Variations of the methods and resulting electrodes and cells described herein as the preferred embodiment may be apparent to those skilled in the art once they have studied the above description. Variations such as these are considered to be within the scope of the invention, which is intended to be limited only to the scope of the claims and the reasonably equivalent materials and methods to those defined therein. The foregoing examples illustrate a preferred embodiment of the invention. Various changes can be made without departing from the invention as defined in the appended claims.

Claims

CLAIMSThe invention claimed is:

1. A method for producing a non-sintered negative electrode comprising the steps of: (a) providing a dry preparation including Cd(OH)₂ particles having a tap density of at least about 1.2 g/cc;

(b) combining said preparation with a solvent to form a paste; and

(c) applying said paste to an electrically conductive electrode support.

2. The method according to claim 1 , wherein said tap density is at least about 1.8 g/cc.

3. The method according to claim 1 , wherein said tap density is about 2.3 g/cc.

4. The method according to any one of claims 1-3, wherein said Cd(OH)₂ particles comprise Cd(OH)₂ which has been produced in a co-precipitation process with at least one co-precipitant selected from the group consisting of Ni(OH)₂ and Mg(OH)₂.

5. The method according to claim 4, wherein the co-precipitant is Ni(OH)₂.

6. The method according to claim 5, wherein the Ni(OH)₂ in the preparation is from about 3 weight percent to about 13 weight percent.

7. The method according to claim 6, wherein the Ni(OH)₂ in the preparation is from about 7 weight percent.

8. The method according to any one of claims 1-7, wherein said Cd(OH) particles have a median size between about 1 μm and about 30μm.

9. The method according to any one of claims 1 -7, wherein said Cd(OH)₂ particles have a median size of about 4μm to about 28μm.

10. The method according to any one of claims 1-7, wherein said Cd(OH)₂ particles have a median size of about 5μm to about 20μm.

1 1. The method according to any one of claims 1-7, wherein said Cd(OH)₂ particles have a median size of about 6μm to about 16μm.

12. The method according to any one of claims 1-1 1 , wherein said Cd(OH) electrode has a degree of paste porosity of about 15 percent to about 50 percent.

13. The method according to claim 12, wherein said paste porosity is at least about 25 percent.

14. The method according to claim 12, wherein said paste porosity is at least about 30 percent.

15. An electrode prepared according to the method of claim 3.

16. An electrode prepared according to the method of claim 7.

17. An electrode prepared according to the method of claim 1 1.

18. An electrode prepared according to the method of claim 14.

19. The method according to any one of claims 1-14, wherein said non-sintered negative electrode is of a form selected from the group consisting of foamed and pasted electrodes.

20. The method according to claim 19, wherein said negative electrode is a pasted electrode.

21. An electrode prepared according to the method of claim 20.

22. A non-sintered negative electrode for an electrochemical cell comprising:

(a) an electrically conductive electrode support; and

(b) a paste applied to said support, said paste comprising a dry preparation and a solvent, said preparation comprising Cd(OH)₂ particles having a tap density of at least about 1.2 g/cc.

23. The electrode as defined in claim 22, wherein said Cd(OH)₂ particles have a tap density of at least about 1.8 g/cc.

24. The electrode as defined in claim 22, wherein said Cd(OH)₂ particles have a tap density of at least about 2.3 g/cc.

25. The electrode as defined in any one of claims 22-24, wherein said Cd(OH)₂ particles comprising Cd(OH)₂ which has been produced in a co-precipitation process with at least one co-precipitant selected from the group comprising Ni(OH)₂ and Mg(OH)₂.

26. The electrode as defined in claim 25, wherein the co-precipitant is Ni(OH)₂.

27. The electrode as defined in claim 25 or 26, wherein the weight percent of Ni(OH)₂ in the preparation is from about 3 percent to about 13 percent.

28. The electrode as defined in claim 27, wherein the weight percent of Ni(OH)₂ in the preparation is at least about 7 percent.

29. The electrode as defined in any one of claims 22-28, wherein said Cd(OH)₂ particles have a median size between about lμm and about 30μm.

30. The electrode as defined in any one of claims 22-28, wherein said Cd(OH)₂ particles have a median size of about 4μm to about 28μm.

31. The electrode as defined in any one of claims 22-28, wherein said Cd(OH)₂ particles have a median size of about 5μm to about 20μm.

32. The electrode as defined in any one of claims 22-28, wherein said Cd(OH)₂ particles have a median size of about 6μm to about 16μm.

33. The electrode as defined in any one of claims 22-32, wherein said Cd(OH)₂ electrode has a degree of paste porosity of about 15 percent to about 50 percent.

34. The electrode as defined in claim 33, wherein said paste porosity is at least about 25 percent.

35. The electrode as defined in claim 34, wherein said paste porosity is at least about 30 percent.

36. The electrode as defined in any one of claims 22-35, wherein said electrode support is a three-dimensional nickel foam.

37. The electrode as defined in any one of claims 22-35, wherein said electrode support is nickel plated steel.