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Primary batteries

Zinc-carbon battery

The zinc-carbon battery, also called zinc-carbon dry cell, is a very popular and cheap type of battery. Inside of the battery, zinc is oxidized at the anode, following the reaction:

Zn(s) → Zn2+(aq) + e-

The characters written in brackets () indicate the condition of the substance:
(s) - solid, (g) - gas, (aq) - aqueous solution, (l) - liquid
At the cathode, manganese is reduced:

2MnO2(s) + H2O(l) + 2e- → 2MnO(OH)(s) + 2OH-(aq)

The needed water molecules come from the following reaction of the ammonium chloride:

2NH4+(aq) + 2OH-(aq) → 2NH3(aq) + H2O(l)

The ammonia, formed at the previous chemical reaction, is not gaseous, but bond in a zinc complex:

Zn2+(aq) + 2NH3(aq) → [Zn(NH3)2]2+(aq)

The whole reaction is given by:

Zn(s) + 2MnO2(s) + 2NH4Cl → 2MnO(OH) + [Zn(NH3)2]Cl2(aq)

This kind of battery is named zinc-carbon, because the used material for the cathode is carbon. The conductivity of manganese oxide isn't very well, so a solid carbon rod, surrounded by a mixture of manganese dioxide and carbon powder is used for the positive terminal to reduce the resistance. The negative terminal (anode) consists of a zinc can, which serves as a container for the battery, too. The electrolyte is a paste of zinc chloride and ammonium chloride dissolved in water. The voltage output is about 1.5V.

Alkaline battery

The alkaline battery is very similar to the zinc-carbon type described above. The substances providing electric energy are manganese dioxide and zinc, too. Instead of the acidic ammonium chloride of the zinc-carbon batteries, an alkaline electrolyte of potassium hydroxide is used. The reaction inside of the cell is given by:

Zn(s) + 2MnO2(s) + H2O(l) → ZnO(s) + 2MnO(OH)(s)

Water is consumed by the given reaction, so the electrolyte is drying-out during the discharging procedure of the battery.
The can of the alkaline battery serves as the positive terminal. The mixture of manganese dioxide and carbon powder, acting as cathode, is arranged at the inner surface of the can. The anode (negative terminal) is at the center of the cathode and consists of a dispersion of zinc powder in a gel, containing the potassium hydroxide electrolyte. Between cathode and anode is a thin layer of a separator material.

Silver-zinc battery

Silver-zinc batteries, also called silver oxide batteries are commonly available as small single cell batteries, shaped as a squat cylinder (button cell).
The anode of a silver-zinc battery consists of zinc powder, the cathode of silver oxide with usually sodium hydroxide (NaOH) or potassium hydroxide (KOH) as electrolyte. The following chemical reaction takes place inside of the battery:

Zn(s) + Ag2O(s) → ZnO(s) + 2Ag(s)

The voltage output is about 1.5V.
The energy density is 130Wh/kg, respectively 500Wh/dm3.

Zinc-air battery

Inside of a zinc-air battery, zinc particles form a porous anode, which is saturated with an electrolyte. At the half reaction of the cathode, oxygen and water molecules react to hydroxide ions:

O2(g) + 2H2O(l) + 4e- → 4OH-(aq)

At the anode, zinc atoms are oxidized, following the half reaction:

Zn + 4OH-(aq) → Zn(OH)42-(aq) + 2e-

The zincate decays into zinc oxide and water returns to the electrolyte:

Zn(OH)42-(aq) → ZnO + H2O + 2OH-

The total reaction is given by the equation:

2Zn(s) + 2O2 → 2ZnO(s)

The theoretical voltage output is 1.65 volts, but this is reduced to 1.4-1.35 V in available cells to achieve compatibility with other battery types (e.g. silver-zinc).
The energy density is 470Wh/kg, respectively 1480Wh/dm3. Theoretically maximum values are: 1370Wh/kg, respectively 9780Wh/dm3.

Lithium battery

There is a multitude of batteries available with an anode made of lithium. The most common type uses metallic lithium as anode and manganese dioxide as cathode. Metallic lithium is highly reactive to water, moist air or oxygen. For this reason, a salt of lithium, dissolved in an organic solvent is used as electrolyte. The chemical reaction at the anode is given by:

Li → Li+ + e-

At the cathode, the following reaction consumes the electrons of the anode:

MnO2 + Li+ + e- → LiMnO2

The total reaction is given by the equation:

MnO2 + Li → LiMnO2

The voltage output of a lithium-manganese dioxide battery is 3.0V.
The energy density is 280Wh/kg, respectively 580Wh/dm3.

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