Cycles, nickel hydroxides

Nickel hydroxides have been used as the active material in the positive electrodes of several alkaline batteries for over century [1], These materials continue to attract much attention because of the commercial importance of nickel-cadmium and nickel-metal hydride batteries. In addition to being the cathode active material in nickel-metal hydride batteries, Ni(OH)2 is an important corrosion product of the anode during cycling. There are several reviews of work in the field [2-10],... 

For alkaline storage batteries requirements are often demanded exceeding by far those for lead storage batteries. The reason is that the suitable materials for the positive electrode are very expensive (silver oxide, nickel hydroxide) and thus the use of these storage batteries is only justified where requirements as to weight, number of cycles, or temperature range prohibit other solutions. Besides a few standardized versions — mainly for nickel-cadmium batteries — this has led to the existence of a large diversity of constructions for special applications [4-6, 108, 109],... 

Srinivasan F., Weidner J. W., and Newman J. Hysteresis during Cycling of the Nickel Hydroxide Electrode. J. Electrochem Soc. 2001 148 A969-80. 

The active material used in pocket plate cells consists of Ni(OH)2 together with up to 5% of Co(OH)2, Ba(OH)2, etc. to improve cell capacity and cycle life, and 20% of graphite in various forms to increase the electronic conductivity. The nickel hydroxide is precipitated from nickel sulphate in a controlled manner to produce fine particles of large surface area. As in the case of the cadmium electrode, the nickel hydroxide powder may be formed into pellets before insertion into the pockets. 

Ion intercalation into nickel oxide is often performed in aqueous media. On immersion of nickel oxide into an alkaline solution, such as aqueous KOH, a spontaneous chemical conversion of NiO into a hydrous metal oxide phase Ni(OH)2 proceeds [25]. Hydrous NiO resembles V2O5 in respect to the two-dimensional layered host structure. The Ni(II)/Ni(III) couple responsible for the reversible color change on electrochemical cycling has been identified as the nickel hydroxide/oxy-hydroxide phases [25, 26]... 

Ref. [154] with permission.) (c) SEM of platinum nanoparticles electrodeposited on BDD microelectrodes after two deposition cycles. (Taken from Ref. [149] with permission.) (d) AFM image of nickel hydroxide nanoparticles deposited on free-standing polished MC BDD by electrochemically generating OH" in the presence of NP+. (Taken from Ref. [146] with permission.)... 

The sintered nickel substrate for the cathode is similar to that used for Ni-Cd and Ni-MH cell constructions. The nickel active materials are loaded into the sinter plate using either an aqueous (Bellcore) or alcoholic-based (Air Force or Pickett) electrochemical impregnation process. A 5-10% cobalt additive is deposited with nickel hydroxide to improve charge acceptance. These electrodes have a significantly longer cycle life over the standard vacuum impregnated or pasted nickel electrodes used in commercial Ni-Cd cells. 

The internal oxygen cycle, formed by oxygen evolution at the nickel-hydroxide electrode and its subsequent reduction at the cadmium electrode, was already detected in the 1940s as a possibility to avoid gas escape during overcharging, and the sealed nickel/cadmium battery appeared on the market in the 1950s. Immobilization of the alkaline electrolyte is achieved by absorption in mats of fibers of polyamide or polypropylene. Formation of a gel, as described in Section... 

Nickel hydroxide for use in NiMH batteries is fundamentally the same as that used in nickel eadmium and niekel-iron batteries, and from a simple viewpoint, the basic compound is the same as that used by Thomas Edison 100 years ago. Today s high performance nickel hydroxide is mueh more complieated and eontinues to improve in capacity and utilization, power and diseharge rate capability, cycle life, high temperature charging efficiency, simplified manufaeturing processes and eost. 

A similar study showed that the effect of the zinc electrode on the nickel electrode was primarily mechanical. Previous speculation of the effect of nickel-hydroxyzincates or nickel zinc double hydroxides on capacity degradation in the nickel electrode were not found to be significant. However, significant increases in the resistivity of cycled nickel electrodes were observed which corresponded with mechanical damage observed by optical microscopy. 

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