Zinc-carbon cell

The zinc-carbon cell or zinc-carbon element , commonly referred to as zinc-carbon battery or zinc-carbon dry battery , is a galvanic element and is a chemical energy storage device for delivering electrical energy . The zinc-carbon cell is a variant of the zinc-manganese dioxide cells and represents a further development of the historical Leclanché element .

Different types of zinc-carbon cells

General

The zinc-carbon cell is one of the primary elements because, unlike accumulators , it is not rechargeable. It was widely used in various sizes until the 1970s , but has since been largely replaced by the technically better and more leak-proof alkali-manganese cells .

The cell delivers a voltage of about 1.5  volts . By arranging several cells in a common housing in series connection to form a battery , the available terminal voltage can be increased. Types with 4.5 V (3R12, " flat battery "), 6 V (4R25, " lantern battery ") or 9 V (6F22, " 9-volt block battery ") are still in use. Even in the smaller and more widespread sizes AAA , AA , C and D , they are still occasionally available because of their lower price compared to Alkaline.

construction

Zinc-carbon cell in section

The zinc-carbon element consists of a cup made of zinc (negative pole, anode) and manganese dioxide ( manganese dioxide ) as the positive pole (cathode), and a central rod made of graphite for the contacting of the manganese dioxide with a metal cap as an electrical lead. A 20 percent ammonium chloride solution is used as the electrolyte . The electrical consumer is switched between the two electrodes .

The zinc cup, which encloses the electrolyte and the "brownstone", represents the anode, which is chemically decomposed by the discharge. When the batteries are discharged, the zinc cup is almost used up and the chemical substances can "leak out". Some zinc-carbon cells only had a cardboard sleeve as the outer casing, which only partially absorbs the electrolyte that escapes. A wrapped metal casing can increase the mechanical stability of the cell and, by means of a plastic film under the metal casing, the leakproofness of the cell, but makes the cell more expensive. The graphite pencil in the middle of the manganese dioxide casing is pulled out slightly as the positive external contact of the cell for better contacting and is provided with a metal cap.

Alkali-manganese cells can be distinguished from zinc-carbon cells by the arrangement of the electrodes: In the case of alkaline-manganese cells with a circular design, the metallic outer jacket, the area below the plastic film used for manufacturer labeling, is at positive potential. In the case of zinc-carbon cells, the cylinder jacket has a negative potential.

Problems

Several zinc-carbon cells with different depths of discharge. The chemical decomposition of the zinc cup in the event of deep discharge is clearly visible (right)

Zinc-carbon cells are cheaper to manufacture than alkaline-manganese cells, but their technical data are worse. The main problem with the carbon-zinc cell is leakage at the end of its useful life. Batteries supplied in the entertainment electronics sector and for remote controls are sometimes zinc-carbon batteries for reasons of price.

The main problems of the zinc-carbon cell are:

• Zinc-carbon cells are in principle not leakproof ( English leak proof ), the zinc electrode is located outside and is eaten at discharge or self-discharge. Leaking electrolyte often destroys battery contacts and circuit boards . For this reason, cells of this type should not be used in devices where they will remain for longer.
• As with the historical Leclanché element, the problem that a zinc complex (diammine zinc chloride, [Zn (NH ₃ ) ₂ ] Cl ₂ ) precipitates. This poorly soluble complex is deposited on the electrodes of the element, which increases the electrical resistance, so that the maximum output that can be delivered quickly drops.
• The initial voltage, which drops rapidly during use, and the low current carrying capacity make the cell unsuitable for many applications with higher loads.
• The self-discharge of zinc-carbon elements is about an order of magnitude higher than that of alkali-manganese cells, which makes them unusable for devices that are used sporadically or for storage purposes. Many devices with briefly high power consumption (e.g. some digital cameras with AA cells) no longer work with zinc-carbon cells.

Reaction (discharges)

Negative pole (anode):

${\displaystyle \mathrm {Zn\rightarrow Zn^{2+}+2e^{-}} }$

Positive pole (cathode):

${\displaystyle \mathrm {2MnO_{2}+2H_{2}O+2e^{-}\rightarrow 2MnO(OH)+2OH^{-}} }$

Subsequent delivery of the necessary water from the ammonium chloride electrolyte:

${\displaystyle \mathrm {NH_{4}^{+}+OH^{-}\rightarrow NH_{3}+H_{2}O} }$

The resulting ammonia molecules are bound by the zinc ion complex:

${\displaystyle \mathrm {Zn^{2+}+2NH_{3}\rightarrow [Zn(NH_{3})_{2}]^{2+}} }$

The reaction of this complex with the chloride ions from the ammonium chloride:

${\displaystyle \mathrm {[Zn(NH_{3})_{2}]^{2+}+2Cl^{-}\rightarrow [Zn(NH_{3})_{2}]Cl_{2}} }$

Overall equation:

${\displaystyle \mathrm {Zn+2MnO_{2}+2NH_{4}Cl\rightarrow 2MnO(OH)+[Zn(NH_{3})_{2}]Cl_{2}} }$

disposal

Batteries and accumulators do not belong in the household waste or in the environment, as they contain environmentally relevant and recyclable substances. In Germany and Austria, zinc-carbon batteries, like other batteries, must be properly disposed of. Retail stores that sell batteries, many recycling centers, and supermarkets have set up collection bins for this purpose.

literature

• Lucien F. Trueb, Paul Rüetschi: Batteries and accumulators . Springer, 1998, ISBN 3-540-62997-1 .

Web links

Commons : Zinc Carbon Cells  - Collection of Pictures, Videos, and Audio Files

Wikisource: Bunsen's improved carbon battery and some attempts at the same  - sources and full texts

Individual evidence

1. ↑ Battery types : This is how electricity is generated for on the go. In: test.de 02/2006. Stiftung Warentest - multi-colored cross-section to compare "zinc-carbon battery" = zinc-manganese dioxide cell and alkali-manganese battery, accessed August 7, 2012