Lithium-Ion Batteries: How does it work?
This document explains what a lithium ion battery is made of and how it works to power cell
phones and other consumer electronics to the general public.
Introduction
Have you ever wondered what powers your cell phone battery and how it can be recharged? In
today’s consumer electronics, the Lithium-Ion battery is the source that powers virtually every
product that emerges. These batteries power devices due to some simple chemistry that
involves the flow of lithium ions from one terminal to the other. In chemistry, an ion is just a
charged particle; therefore, a lithium ion is simply a positively charged lithium particle.
The Makeup of the Battery
A battery has 3 main parts; a positively charged terminal called the cathode, a negatively
charged terminal called the cathode and an electrolyte. Typically the negative terminal in a
lithium ion battery is made of the element carbon in the form of graphite. The positive
terminal often consists of a metal oxide such as lithium cobalt oxide. A metal oxide is a metal
or multiple positively charged metal ions bonded to oxygen in order to neutralize that charge.
The electrolyte component of a lithium ion battery is often a liquid mixture of organic
carbonates such as ethylene or diethyl carbonate that contain lithium ions. Electrolytes are
substances that ionize or dissociate in water or other appropriate solvents. The electrolyte in a
battery can be found between the cathode and the anode and acts as a carrier between them
for lithium ions.
In addition to these chemical components to a lithium ion battery, there are also a few parts
that make the battery that aid in the performance of electronic devices. Batteries in electronics
come equipped with voltage regulators, temperature sensors, and charge monitors that
regulate the amount of current in and out of the battery. These accessories to the pure battery
improve performance and add a factor of safety so that the battery will not short circuit. Most
times the materials inside a battery are placed in a plastic casing. The entire battery can take on
many shapes and sizes to fit whatever electronic device it is designed to power.
The Chemistry of Charging and Discharging
Inside a lithium ion battery, power is generated via chemical reaction involving the electrolyte
and the negative and positive terminals (electrodes). The electrolyte serves as a conductive
medium for Lithium ions to move between the two electrodes. The direction of this flow of
lithium ions is determined by whether the battery is charging or discharging. Discharging refers
to the action of producing energy that would power the device. When discharging, the
positively charged lithium ions move from the positively charged terminal made of graphite to
the negatively charged, lithium containing metal oxide. This movement of the Lithium ions is
caused by a chemical reaction that is occurring inside the battery. The overall reaction
occurring is displayed below:
Overall reaction: Li+ + e- +LiCoO2 → Li2O + CoO
This reaction can be broken down into two half reactions occurring at the anode and the
cathode. Where x is a coefficient that represents the number of lithium ions involved in the
reaction taking place in the battery.
Cathode: LiCoO2 ↔ Li1-xCoO2 + xLi+ + xeAnode: xC6 + xLi+ + xe- ↔ xLiC6
The lithium ions are transported to and from the anode by reducing the cobalt from Co 4+ to
Co3+ during discharge. The movement of the positively charged lithium ions causes a flow of
electrons from the anode to cathode during discharge. This flow of electrons carries an electric
charge called a current. Current causes a voltage that can be used to do work or act as a power
source. This energy can be harnessed and used by whatever device the battery is powering.
*http://theelectricenergy.com/lithium-and-lithium-ion-battery/
When all of the lithium ions have been transferred to the cathode, there is no longer a current
being produced and no voltage to power the device. At this time the battery needs to be
charged. During charging, an external power source applies a higher voltage in the opposite
direction reversing the direction of the current. This reversal of current causes the lithium ions
migrate back from the cathode to the anode and the cobalt to be oxidized from Co3+ to Co4+.
Since the lithium ions are returned to the cathode, when the power source is removed, the
discharging reaction will occur again. The process of charging and discharging allows batteries
to be extremely useful in electronics.
Conclusion
The lithium ion battery is made of specific compounds that undergo repeated chemical
reactions that create a movement from anode to cathode. This movement causes current that
powers the device it is connected to. Once the battery has completely discharged, it can be
recharged again. The ability to recharge makes the lithium ion battery useful to power portable
electronics.