The Physics
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Opus in profectus

Batteries

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Discussion

introduction

An electrochemical cell is two different metals in contact through an electrolyte (a liquid with free-moving ions). A set of connected cells is called a battery. Batteries come in two basic types: primary and secondary. The chemical reaction that powers a primary cell is one way. Once the chemicals are exhausted the battery is effectively dead. In contrast, the chemical reaction in a secondary cell is reversible. When the reaction runs in its spontaneous direction, the battery produces a potential difference. When the same potential difference is applied to the battery from an external source, the chemical reaction runs in reverse. A battery made up of secondary cells is said to be rechargeable.

Loose notes:

Primary cells (disposable batteries) * originally sulfuric acid (H2SO4)
example anode (−) electro­lyte cathode (+) voltage
voltaic pile
(1799)		 zinc
(Zn)		 brine
(saltwater)		 copper
(Cu)		 variable
daniell cell
(1836)		 zinc
(Zn)		 zinc sulfate (ZnSO4)*
copper sulfate (CuSO4)		 copper
(Cu)		 1.10 V
leclanché cell
(1866)		 zinc
(Zn)		 ammonium chloride (NH4Cl)
manganese dioxide (MnO2)		 carbon
(C)		 1.58 V
lemon battery zinc
(Zn)		 citric acid
(C6H8O7)		 copper
(Cu)		 1.10 V
Secondary cells (rechargeable batteries) † typically a mixture of LiPF6, LiBF4, LiClO4 in diethyl ether ((C2H5)2O)
example anode (−) electrolyte cathode (+) voltage
lead acid lead
(Pb)		 sulfuric acid
(H2SO4)		 lead oxide
(PbO2)		 2.11 V
nicad nickel hydroxide
(Ni(OH)2)		 potassium hydroxide
(KOH)		 cadmium hydroxide
(Cd(OH)2)		 1.35 V
nife nickel hydroxide
(Ni(OH)2)		 potassium hydroxide
(KOH)		 iron
(Fe)		 1.2 V
nizn nickel hydroxide
(Ni(OH)2)		 potassium hydroxide
(KOH)		 zinc
(Zn)		 1.65 V
nickel metal hydride nickel hydroxide
(Ni(OH)2)		 potassium hydroxide
(KOH)		 inter­metallic
compounds		 1.2 V
lithium ion carbon
(C)		 lithium salts in an organic solvent† lithium cobalt oxide
(LiCoO2)		 3.6 V