Storing Electrical Energy
A battery is a device consisting of one or more electrochemical cells with external connections for powering electrical devices. It is a practical application of a galvanic (or voltaic) cell, which converts stored chemical energy into electrical energy.
The Galvanic Cell
Every battery is based on a spontaneous redox reaction. Its key components are:
Anode (-): The negative electrode where oxidation (loss of electrons) occurs.
Cathode (+): The positive electrode where reduction (gain of electrons) occurs.
Electrolyte: An ion-conducting medium that allows ions to flow between the electrodes, completing the circuit internally.
Separator: A porous membrane that keeps the anode and cathode from touching (which would cause a short circuit) but allows ions to pass through.
Electrons flow from the anode, through the external circuit (powering a device), to the cathode.
Primary vs. Secondary Batteries
Primary Batteries (Non-rechargeable): The electrochemical reaction is not easily reversible. Once the reactants are consumed, the battery is 'dead'.
Example: Alkaline batteries (like AA, AAA). The anode is zinc and the cathode is manganese dioxide.
Secondary Batteries (Rechargeable): The electrochemical reaction can be reversed by applying an external electric current. This process, called charging, regenerates the original reactants at the electrodes.
Example: Lead-acid batteries (in cars), Nickel-cadmium (NiCd) batteries, and Lithium-ion batteries.
Lithium-Ion Batteries
This is the dominant technology for modern portable electronics (phones, laptops) and electric vehicles due to its high energy density (it can store a lot of energy for its weight and volume).
Basic Principle:
Discharging: Lithium ions (Li⁺) move from the anode (typically graphite) through the electrolyte to the cathode (typically a metal oxide like LiCoO₂). At the same time, electrons flow from the anode through the external circuit to the cathode.
Charging: An external voltage forces the lithium ions and electrons to move back from the cathode to the anode, restoring the battery's potential.
Key Advantage: Lithium is the lightest metal and has a very high electrochemical potential, allowing for very lightweight, high-voltage batteries.