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.

Primary Cells (Disposable Batteries)
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)		 1.1 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)		 1.1 V
* originally sulfuric acid (H2SO4)
 
Secondary Cells (Rechargeable Batteries)
example anode (−) electrolyte cathode (+) voltage
lead acid lead
(Pb)		 sulfuric acid
(H2SO4)		 lead oxide
(PbO2)		 2.2 V
nicad nickel hydroxide
(Ni(OH)2)		 potassium hydroxide
(KOH)		 cadmium hydroxide
(Cd(OH)2)		 1.35 V
nickel metal hydride nickel
(Ni)		 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
** typically a mixture of LiPF6, LiBF4, LiClO4 in diethyl ether ((C2H5)2O) 

Loose notes:

The Physics Hypertextbook

  • No condition is permanent.