Nickel-hydrogen batteries separators

In year 2000, Japan supplied over 90% of the nickel-hydrogen battery separators globally. °... 

Nickel—hydrogen batteries offer long cycle life that exceeds that of other maintenance-free secondary battery systems and accordingly makes it suitable for many space applications. Three types of separator materials have been used for aerospace Ni—H2 cells— asbestos (fuel-cell-grade asbestos paper), Zircar (untreated knit ZYK-15 Zircar cloth),and nylon. 

Mostly in batteries the reacting substances are stored within the electrodes (the active material ), but there are also systems where the electrolyte participates, as in lead-acid batteries, or where the reacting substances are stored in separate tanks, e.g. Zn/Cl, Zn/Br, and vanadium redox batteries (Section 1.8.5), or as a gas in the container of nickel-hydrogen batteries (Section 1.8.3). 

The nickel-metal hydride batteries employ PP with modified surface by either chemical grafting of acrylic acid or sulfonation. For nickel-hydrogen batteries, asbestos, Zircor cloth, and nylon have been used as separators. 

In normal battery operation several electrochemical reactions occur on the nickel hydroxide electrode. These are the redox reactions of the active material, oxygen evolution, and in the case of nickel-hydrogen and nickel-metal hydride batteries, hydrogen oxidation. In addition there are parasitic reactions such as the corrosion of nickel current collector materials and the oxidation of organic materials from separators. The initial reaction in the corrosion process is the conversion of Ni to Ni(OH)2. 

Zirconia fiber cloths, such as those made by the relic process (see Chapter 8), are used as separators in aerospace nickel-hydrogen and nickel-cadmium batteries [9j. These fibers display a high resistance to many corrosive media, including hot potassium hydroxide. Zirconia fiber felts are also present in aerospace solid oxide fuel cells. 

The nickel-based batteries are nickel-iron, nickel-cadmium, nickel-hydrogen, and nickel-zinc, and the separators are simple absorbent materials. The nickel-cadmium vented battery use nonwoven nylon felt. Nonwoven fibers of PE or PP are used in the sealed version, where gaseous oxygen permeability is an essential feature of a separator. 

Zn(OH)2 is soluble in the alkaline solution as [Zn(OH)3]- until the solution is saturated with K[Zn(OH)3]. In addition Zn(OH)2 can be dehydrated to ZnO. An enhanced power density (when compared with the - Leclanche cell) is accomplished by using particulate zinc (flakes) soaked with the alkaline electrolyte solution. This anode cannot be used as a cell vessel like in the Leclanche cell. Instead it is mounted in the core of the cell surrounded by the separator the manganese dioxide cathode is pressed on the inside of the nickel-plated steel can used as battery container. In order to limit self-discharge by corrosion of zinc in early cells mercury was added, which coated the zinc effectively and suppressed hydrogen evolution because of the extremely low exchange current density... 

Tang et al. (2013) studied the recycling of NiMH household batteries. The main parts of a NiMH battery are the cathode, the anode, the electrolyte, a separator, and the steel case. REEs are found in the anode, which consists of a hydrogen storage alloy based on misch metal and nickel alloys. The misch metal contains mainly cerium, lanthanum, praseodymium and neodymium. 

Nickel/metal hydride (Ni/MH) battery is a secondary battery using hydrogen storage alloy for the negative electrode, Ni(OH)2 for the positive electrode, and alkaline solution for the electrolyte. Polypropylene nonwoven fabric is usually selected for the separator. The theoretical voltage is about 1.32 V, and the operating voltage is about 1.2 V which is almost the same as that of Ni/Cd battery [1]. The Ni/MH battery has been put to practical use for portable electric equipments in 1990 and for HEV (hybrid electric vehicle) in 1997 [2, 3]. 

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