Separators nickel-zinc batteries

The nickel—zinc (NiZn) system is attractive as a secondary cell because of its high energy density and low material cost and the low level of potential pollutants contained. The widespread use of nickel-zinc batteries, particularly as electric vehicle power sources, would be strongly enhanced by significantly extending the deep-discharge cycle life beyond the current level of 100—300 cycles. Considerable work has been done in the past to develop a suitable separator for nickel— and silver—zinc batteries. 272 An excellent discussion of separator development is contained in a comprehensive review. 2 ... 

There are two broad classes of separators employed in nickel—zinc batteries a main separator, which exhibits resistance to dendrite penetration, and an interseparator, which principally acts as an electrolyte reservoir and wicking layer. Both main and interseparator should be resistant to chemical attack by the alkaline electrolyte and resistant to oxidative attack by nascent oxygen, permanently wettable by the electrolyte, flexible, heat sealable, tear resistant, and inexpensive. 

Nickel—zinc batteries containing a vibrating zinc anode has been reported (83). In this system zinc oxide active material is added to the electrolyte as a slurry. During ckaige the anode substrates are vibrated and the zinc is electroplated onto the surface in a uniform manner. The stationary positive electrodes (nickel) are encased in a thin, open plastic netting which constitutes the entire separator system. 

For nickel-zinc batteries, the cellophane remains the material of choice for separators, and for zinc-air batteries it is usually PP membrane. Microporous separators have been used for zinc-bromine batteries. 

With the development of new separators and improved zinc electrodes, the nickel-zinc battery has now become competitive with the more familiar battery systems. It has a good cycle life and has load-voltage characteristics higher than those of the silver-zinc system. The energy per unit of weight and volume are slightly lower than those of the silver-cadmium system. Good capacity retention (up to 6 months) has made the nickel-zinc battery a more direct competitor of the silver-zinc and silver-cadmium systems. Nickel-zinc batteries aie not yet available in a sealed form. 

With the development of new types of separator and zinc electrodes, the nickel-zinc battery has now... 

IBMA 43rd Convention, Chicago, 1980, 49-53 Landers, J. J. (1970) Requirements and characteristics of secondary battery separators. In Proceedingsofthe Meeting of the ElectrochemicalSociety, February 1970, pp. 4-24 Lundquist, J. T. Jr (1983) Separators for nickel-zinc batteries. 

Bermion, D. N. A review of membrane separators and Zinc-Nickel oxide battery development. Prepared for Argorme Na tional Laboratory under Contract No. 31 109 38 5455, October 1980. 

Electrochemical Design. The electrochemical design of the cell consists primarily of balancing the active materials present in the electrodes. This previously has been discussed for each of the two electrodes separately, the nickel positive electrode and the zinc negative electrode. When combined in the cell, the two active materials must be present in some ratio with respect to each other. As with most other alkaline nickel batteries, the nickel-zinc system is typically positive (nickel electrode) limited. This means that the cell contains more zinc active material, on an Ampere-hour basis, than nickel active material. This must take into account the active materials present in the cell in addition to the active material utilization of each. 

As discussed in previous chapters, the separators are an integral part of liquid electrolyte batteries including nonaqueous batteries such as lithium-ion, lithium-polymer, hthium-ion gel polymer, and aqueous batteries such as zinc-carbon, zinc-manganese oxide, lead-acid, nickel-based batteries, and zinc-based batteries. 

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. 

Table 11. Separators and Their Manufacturers for Nickel and Zinc Based Battery Systems...

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... 

Accurate sorting relies on the identification of a number of different properties of a battery. These include the physical size and shape, the weight, the electromagnet properties and any surface identifiers such as colour or unique markings. These properties can be analysed in a number of different combinations in order to sort batteries into nickel cadmium, nickel metal hydride, lithium, lead acid, mercuric oxide, alkaline and zinc carbon batteries. Due to an voluntary marking initiative introduced by the european battery industry, it is now also possible to separate the alkaline and zinc carbon cells further into mercury free and mercury containing streams. 

Alkaline cells use the same zinc-manganese dioxide couple as Leclanche cells. However, the ammonium chloride electrolyte is replaced with a solution of about 30 wt% potassium hydroxide (KOH) to improve ionic conductivity. The ceU reactions are identical to those above, but the battery construction is rather different (Figure 9.7). The negative material is zinc powder, and the anode (negative terminal) is a brass pin. The positive component is a mixture of Mn02 and carbon powder that surrounds the anode. A porous cylindrical barrier separates these components. The positive terminal (cathode) is the container, which is a nickel-plated steel can. 

The active material of the positive electrode (1) consisting of mercury oxide HgO and 5-15% fine purified graphite is pressed into the nickel-plated steel case (6). Zinc powder (2) is pressed into the steel cover (4) and amalgamated. The separator (3) consists of several layers of a special alkali-resistant filter paper. The separator and the powdered zinc electrode are impregnated with a 40% KOH solution saturated with zincate. After assembly the battery is sealed by bending the edges of the case (6). The terminals (case and cover) are insulated by a mbber or plastic spacer (5). 

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