Working of Lithium-ion Batteries : Simple Understanding

Introduction:

Lithium Batteries are one of the most used rechargeable batteries for many portable devices or gadgets. They are also used much in electric vehicles(EV) and other military, Aerospace applications.
Before the entry of this lithium ion batteries, Nickel-cadmium is only sustainable portable battery. 

From early 1990's  Nickel-metal hydride and lithium ion batteries are used, and the future is lithium ion batteries for their advantages. Lithium ion batteries are continuously getting more advanced and many changes have been taken part without any safety problems.

Structure & Features:

The structure of lithium ion battery is clear enough from the following figure. There are many tyoes of lithium ion batteries, namely Lithium Cobalt Oxide (LiCoO2), Lithium Manganese Oxide(LiMn2O4)....The positive electrode consists of Lithium Metal Oxide containing Lithium ions and the negative eletrode consists of Graphite layer. These two layers are separated by Separator Electrolyte. As lithium is highly electro positive, it loses electrons and form lithium ion, the ejected electrons travel through the external circuit and reaches the negative terminal and settles in the graphite layers (it cannot passes through electrolyte, hence journey in internal circuit or within the battery is not possible). 

This process takes place till all the lithium losses it electron to form lithium ion, this process is called discharging. Here is a problem arose, as electrons from positive terminal settles more and more at graphite layer, the layer becomes negatively charged and no more electrons can reach. This is solved simply by adding addition of gel which acts as a guard that allow lithium ions from positive side to graphite side hence positively charged ions and electrons are neutralized, it does not allow, electrons from graphite to positive side. This all happens while discharging. While charging, reverse process takes place.

• The efficiency of lithium ion batteries is higher than any other types. 
• The efficiency is around 80% to 90% both charging and discharging.
• It is noted that the energy density is 0.90-2.43 MJ/L.
• The Specific energy of lithium-ion battery is 0.36-0.875MJ/kg
• The number of cycles it can be worked is around 400-1200cycles and still in development.

 

The Structure of Lithium ion battery (source: wikipedia)

ADVANTAGES:

• High energy density- potential for yet higher capacities.
• Does not need prolonged priming when new. One regular charge is all that's Need.
• Relatively low self-discharge - It is less than half that of nickel-based batteries.
• Low-maintenance - no periodic discharge is needed; there is no memory.
• Specialty cells can provide very hugh current to applications such as power tools. 

LIMITATIONS:

• Requires protection circuit to maintain voltage and current within safe limits.
• Subject to aging, even if not in use - storage in a cool place at 40% charge reduces the aging effect.
• Transportation restrictions - shipment of larger quantities may be subjects to regulatory control. This restriction does apply to personal carry on batteries.
• Expensive to manufacture - about 40% higher in cost than nickel-cadmium.
• Not fully mature - metals and chemicals are changing continuing basis.

This way lithium-ion batteries are going to rule the electronic gadgets in the future, and we post why lithium-ion batteries are the future? content soon.

Also Read: Use of Lithium-ion Battery in EV