Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
1998-08-17
2001-05-08
Weiner, Laura (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
C429S220000, C429S221000, C429S224000, C429S229000
Reexamination Certificate
active
06228535
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to optimized nickel hydroxide positive electrode materials, a process for fabricating such materials, positive electrodes fabricated using such materials and nickel metal hydride (“NiMH”) batteries incorporating such materials. More specifically, this invention relates to a multi-element nickel hydroxide positive electrode material characterized by an engineered activation energy and optimized crystallite size. Preferably this is accomplished by the incorporation of modifier elements into the bulk thereof in a single chamber reactor so as to provide a NiMH battery exhibiting multiple electron transfer, improved capacity, high temperature performance, and cycle life.
BACKGROUND OF THE INVENTION
There are many known types of Ni based rechargeable alkaline cells such as nickel cadmium (“NiCd”), NiMH, nickel hydrogen, nickel zinc, and nickel iron (“NiFe”) cells. At one time NiFe and then NiCd batteries were the most widely used. Just as NiFe batteries were displaced by NiCd batteries, NiCd batteries have now been steadily replaced in all applications by NiMH cells. Compared to NiCd cells, NiMH cells made of synthetically engineered materials have superior electrochemical performance parameters, such as specific energy and energy density, and contain no toxic or carcinogenic elements, such as Cd, Pb, and Hg. For purposes of this patent application, the terms “batteries” and “cells” will be used interchangeably when referring to one cell; although the term “battery” can also refer to a plurality of electrically interconnected cells.
While the present discussion focuses on NiMH batteries, it should be understood that the modified nickel hydroxide materials of the present invention can be used in all types of batteries using nickel hydroxide based positive electrode materials. The term “utilization” will be employed in this disclosure to describe the instant invention in the manner well accepted by those ordinarily skilled in the electrochemical art. As used herein “utilization” will refer to the percentage of the electrons of the nickel hydroxide positive electrode electrochemically transferred during the charge/discharge cycling of the electrode relative to the total number of nickel atoms present in the nickel hydroxide material.
In general, NiMH cells employ a negative electrode made of hydrogen storage alloy that is capable of the reversible electrochemical storage of hydrogen. NiMH cells, also employ a positive electrode made from nickel hydroxide active material. The negative and positive electrodes are spaced apart in the alkaline electrolyte. Upon application of an electrical potential across a NiMH cell, water is dissociated into one hydroxyl ion and one hydrogen ion at the surface of the negative electrode. The hydrogen ion combines with one electron and diffuses into the bulk of the hydrogen storage alloy. This reaction is reversible. Upon discharge, the stored hydrogen is released to form a water molecule and release an electron.
The development of commercially viable NiMH batteries began in the 1980s by improving the negative electrode materials by making them “disordered” as taught by Ovshinsky, et al in U.S. Pat. No. 4,623,597. Such disordered negative electrode materials represented a total departure from other teachings of the period that urged the formation of homogeneous and single phase negative electrodes. (For a more detailed discussion, see U.S. Pat. Nos. 5,096,667; 5,104,617; 5,238,756; 5,277,999; 5,407,761 and 5,536,591 and the discussion contained therein. The disclosure of these patents are specifically incorporated herein by reference.)
The use of disordered negative electrode metal hydride materials significantly increases the reversible hydrogen storage characteristics required for efficient and economical battery applications, and results in the commercial production of batteries having high density energy storage, efficient reversibility, high electrical efficiency, bulk hydrogen storage without structural change or poisoning, long cycle life, and deep discharge capability.
As discussed in U.S. Pat. No. 5,348,822, nickel hydroxide positive electrode material in its most basic form has a maximum theoretical specific capacity of 289 mAh/g, when one charge/discharge cycles from a &bgr;II phase to a &bgr;III phase and results in one electron transferred per nickel atom. It was recognized in the prior art that greater than one electron transfer could be realized by deviating from the &bgr;II and &bgr;III limitations and cycling between a highly oxidized &ggr;-phase nickel hydroxide phase and either the &bgr;III phase and/or the ∝-phase. However, it was conventionally recognized dogma that such gamma phase nickel hydroxide formation destroyed reversible structural stability and therefore cycle life was unacceptably degraded. A large number of patents and publications in the technical literature disclosed modifications to nickel hydroxide material designed to inhibit and/or prevent the destructive formation of the transition to the &ggr;-phase.
Attempts to improve nickel hydroxide positive electrode materials began with the addition of elements to compensate for what was perceived as the inherent problems of the material. The use of compositions such as NiCoCd, NiCoZn, NiCoMg, and their analogues are described, for example, in the following patents:
U.S. Pat. No. Re. 34,752, to Oshitani, et al., reissued Oct. 4, 1994, describes a nickel hydroxide active material that contains nickel hydroxide containing 1-10 wt % zinc or 1-3 wt % magnesium to suppress the production of &ggr;-NiOOH. The invention is directed toward increasing utilization and discharge capacity of the positive electrode. Percent utilization and percent discharge capacity are discussed in the presence of various additives.
Oshitani, et al. describe the lengths that routineers in the art thought it was necessary to go to in order to prevent the presence of substantial amounts of &ggr;-NiOOH. The patent states:
Further, since the current density increased in accordance with the reduction of the specific surface area, a large amount of higher oxide &ggr;-NiOOH may be produced, which may cause fatal phenomena such as stepped discharge characteristics and/or swelling. The swelling due to the production of &ggr;-NiOOH in the nickel electrode is caused by the large change of the density from high density &bgr;-NiOOH to low density &ggr;-NiOOH. The inventors have already found that the production of &ggr;-NiOOH can effectively be prevented by addition of a small amount of cadmium in a solid solution into the nickel hydroxide. However, it is desired to achieve the substantially same or more excellent effect by utilizing additive other than the cadmium from the viewpoint of the environmental pollution.”
U.S. Pat. No. 5,366,831, to Watada, et al., issued Nov. 22, 1994, describes the addition of a single Group II element (such as Zn, Ba, and Cd) in a solid solution with nickel hydroxide active material. The Group II element is described as preventing the formation of gamma phase nickel hydroxide thereby reducing swelling, and the cobalt is described as reducing the oxygen overvoltage thereby increasing high temperature charging efficiency. Both oxygen overvoltage and charge efficiency are described as increasing with increasing cobalt.
U.S. Pat. No. 5,451,475, to Ohta, et al., issued Sep. 19, 1995, describes the positive nickel hydroxide electrode material as fabricated with at least one of the following elements added to the surface of the particles thereof: cobalt, cobalt hydroxide, cobalt oxide, carbon powder, and at least one powdery compound of Ca, Sr, Ba, Cu, Ag, and Y. The cobalt, cobalt compound, and carbon are described as constituents of a conductive network to improve charging efficiency and conductivity. The powdery compound is described as adsorbed to the surface of the nickel hydroxide active material where it increases the overvoltage, for evolution of oxygen, thereby increasing nickel hydroxide utilization at high temperatu
Fetcenko Michael A.
Fierro Cristian
Harrison Craig
Ovshinsky Stanford R.
Sommers Beth
Ovonic Battery Company Inc.
Siskind Marvin S.
Watson Dean B.
Weiner Laura
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