July 14th 1999
Transcribed by Remy Chevalier, Electrifying Times, from the introduction to the Nickel Hydroxide Active Material For Electro Chemical Cells patent by Evercel inventors: Franklin Martin, Allen Charkey &Virgil Handberry.
[What you are about to read means, in plain English, that the specs for Evercelís Nickel Zinc batteries are about to improve dramatically. Keep in mind Evercelís parent company, Energy Research Corporation, has provided nickel components to Ovonics breakthrough Nickel Metal Hydride. ERCís history developing batteries for the military puts it at the cutting edge of nickel research for electrical applications. Promising much lower cost than nickel metal hydride, nearly comparable to good olífashion lead acid, a wide market has opened for nickel zinc in Asia. The Evercel plant in China is up and running. Letís hope it catches on in the USA. For more technical details beyond the comprehension of this humble journalist, please contact Virgil Handberry, Chemical Engineer Assistant, directly at www.evercel.com. To read an interview with Evercel president Robert Kanode by Bill Moore go to http://www.evworld.com/interviews2/rkanode.html.]
Alpha phase nickel hydroxide is produced by driving the nickel to the plus four oxidation state. Due to this oxidation state, the alpha phase nickel hydroxide can exchange as high as 1.67 electrons per nickel atom for thin film electrodes. This represents an 85 percent improvement in the electrodeís storage capacity, as compared to an electrode using the beta phase material.
This invention relates to active materials for use in the cathodes or positive electrodes of electrochemical cells and in particular, to nickel hydroxide active material and cathodes or positive electrodes formed from such nickel hydroxide active material.
Active material containing nickel hydroxide has long been used in the cathodes or positive electrodes of rechargeable or secondary batteries and, in particular, in alkaline rechargeable batteries. Typical batteries which have used this material include nickel metal hydride, nickel cadmium, nickel hydrogen, nickel iron and nickel zinc.
The molecular structure of hydroxide active material is well known. There are two phases of the material, the alpha phase and the beta phase. Currently, the beta phase nickel hydroxide is most widely used in battery cathodes. The beta phase material is generally oxidized and reduced between the plus two and plus three oxidation states. Commercially available beta nickel hydroxide exchanges 0.9 electrons per nickel atom.
However, due to the instability of the alpha phase material, it is not currently used in commercial battery electrodes. In spite of this, the possibility of realizing electrodes with a significantly higher overall storage capacity continues to drive researchers to develop a stabilized alpha material.
Several research efforts have resulted in alpha materials which are stable when exposed quiescently to potassium hydroxide of 5 to 8 molar concentration. However, the true test for stability is whether the material remains stable when subjected to repeated charging and discharging cycles at various rates. In most of the reported research, under these conditions, the alpha materials slowly develop an undesired secondary beta phase and the effect of multi-electron transfer is short lived.
Other research efforts have identified that partial substitution of the nickel cations with trivalent cations such as aluminum, cobalt or iron at greater than 20 wt. percent appears to stabilize the alpha phase structure of the double layered nickel hydroxide material. Some researchers have also purposely introduced various anions such as Cl-, NO3-, C03-2, or S04-2 along with the trivalent cation additions in order to evaluate the physical changes occurring within the brucite structure. It has been reported that using the trivalent aluminum cation in greater than 20 wt. percent along with the deliberate addition of the CO3-2 anion could stabilize the alpha structure for reversible electrode applications.
While anions have been added to promote stability of the alpha phase nickel hydroxide, it is known in nickel battery technology that these anions also act as contaminants which are detrimental to battery performance. Thus, nitrates (NO3) are known to promote self discharge of the positive electrode through the well known nitrate shuttle. In some specific applications, ternary electrolytes containing potassium carbonate have been found to reduce shape change of the zinc anode, but generally any carbonates are looked upon as undesired. Chlorides and sulfates as well are viewed in various other battery systems as contaminants detrimental to the proper battery performance.
It is, therefor, an object of the present invention to provide an improved alpha phase nickel hydroxide material having increased stability.
It is a further object of the present invention to provide a positive or cathode electrode using such an improved alpha phase nickel hydroxide.