Batteries

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:

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
Primary cells (disposable batteries) * originally sulfuric acid (H2SO4)
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
Secondary cells (rechargeable batteries) ** typically a mixture of LiPF6, LiBF4, LiClO4 in diethyl ether ((C2H5)2O)