Leclanché element

The Leclanché element is a historical galvanic element that was developed by Georges Leclanché and patented in 1866. It represents an electrical battery (primary element) and was equipped with liquid electrolyte in its original form . Improvements resulted in a gelled electrolyte, and it is a precursor to dry batteries such as the zinc-carbon element and the alkaline-manganese battery .

General

Leclanché element

The Leclanché element has a terminal voltage of 1.5  V and consists of an anode made of zinc , which represents the negative connection and is usually shaped into a cup (receptacle), an electrolyte made from thickened with swelling agents (flour, starch , methyl cellulose ) Ammonium chloride solution , and a cathode made of a pressed mixture of manganese dioxide and carbon (in the form of graphite or "acetylene black" → soot ) with a graphite rod as a discharge, which is positioned centrally and represents the positive connection of the cell. The cathode is surrounded by manganese dioxide towards the electrolyte, which acts as a depolarizer .

The Leclanché element was economically successful for many decades and was used, among other things, to supply railroad telegraphs and doorbells . The element went through continuous improvements over the years: A significant improvement and the first step towards the dry element was made by replacing the liquid electrolyte (ammonium chloride solution) with the addition of swelling agents. Subsequently, the gelled electrolyte was divided into sectors by thin separator paper and the energy density was increased by adding zinc chloride . In the area of ​​the zinc anode, various metal alloys and locking systems were used to reduce the generation of hydrogen during discharge or to increase the shelf life of the elements by excluding air.

One of the disadvantages of the Leclanché element is the chemical decomposition of the zinc anode when the cell is discharged. Since the anode is formed by the outer zinc cup, the chemical components leak out at the end of use. This design disadvantage, which also exists with the similarly constructed zinc-carbon element, was only solved by the alkali-manganese battery.

Electrochemistry

Sectional view and structure

The reaction equation when the cell is discharged is:

Negative electrode ( anode ):

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

Positive electrode ( cathode ):

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

Electrolyte solution ( complex formation ):

${\displaystyle \mathrm {Zn^{2+}+2NH_{4}^{+}+2Cl^{-}\rightarrow [Zn(NH_{3})_{2}]Cl_{2}+2H^{+}} \,}$

The overall reaction is:

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

Literature sources

• Lucien F. Trueb, Paul Rüetschi: Batteries and accumulators . 1st edition. Springer, 1998, ISBN 3-540-62997-1 .
• HA Kiehn: Battery Technology Handbook . 2nd Edition. Marcel Dekker Inc., 2003, ISBN 0-8247-4249-4 .

Individual evidence

1. ↑ Georges Leclanché: French Patent No. 71 865, granted in 1866

Web links

Commons : Leclanché cell  - collection of images, videos and audio files