Lithium ion batteries

-----| this whole blog is under construction, for updates keep subscribed |-----

A battery is a transducer that converts chemical energy into electrical energy. They are the source of energy which can be stored and also mobile. Batteries which can be used only once are called as primary batteries while which are rechargable and used more than one time are called as rechargeable or secondary batteries. Lithium is used in both primary as well as secondary batteries but the term lithium ion batteries is generally used for secondary batteries. They come in various shapes (coin, cylindrical and pouch) and sizes depending upon the energy density and the area of applications.

Developments

Recent developments of lithium-ion (Li-ion) batteries based on new and improved chemistries have resulted in batteries with high performance, long lifetime and increased safety. It not only became the ultimate choice for any portable power equipment but also in standalone systems like UPS and energy grid for power backup. Thanks to the decrease in cell prices with advances in research, which makes it affordable for everyone and everything.

Nevertheless, there are some issues

• Majorly the efficiency and life depends on temperature, load current and state of charge. 
• High input cost for industrial production.

Even though the competitors at present in market, i,e Lead Acid Batteries which can overcome these issues to some extent but the portability with high energy density factor cannot be replaced. Therefore, LIB rules the market at present and the near future.

Importance

With rise of electronic gadgets, the need of batteries has grown from high power to portable high energy density. We have been addicted to gadgets in every activity, whether it is for leisure, work or for essential activities like health control and monitoring. Lithium ion batteries are always the favourite because of the two aspects portability and high energy storage. Yet issues of fire explosion due to flammable electrolyte is a concern for many. Older battery technologies are still equipped because of this fire safety issue and ofcourse they are cheaper. The hunger of energy storage whether its for your pocket or home or electric grid, LIB's has the answer. In mobiles and hand held devices there is no replacement for LIB's, energy storage for home is not a viable option since its slightly costlier than older technologies while for the power grid LIB's has a definite answer and its already been installed in some places.

Battery Life:

While using a battery we have a decrease in maximum capacity it can hold at 100% charge these are due to parasitic and other reactions inside the cell. A battery which can hold 10% charge is really impractical to use since it gives a backup for a very less time. The capacity of a battery for a device is generally designed by the manufacturer and they only defined the useful capacity till which the battery is good to use, i.e., 80%. The number of cycles a battery can charge and discharge till the loss of capacity to 80% is called as battery life. In our daily life we do not charge a battery till it completely drains out and therefore we cant track the battery life properly. In laboratory, the cells are tested to charge and discharge at a constant rate continuously till they reach to 80% of its capacity. This life is generally called as calendar life.

Chemistry:

Battery are made of number of components among them only three components are of great interest viz., cathode, anode and electrolyte.

Among the three, cathode is the one which is talked about mostly among both researchers as well as manufacturers. Cathode is called to be the limiting factor in defining capacity since it is lower than the carbon anode which is mostly used while the electrolytes is used to facilitate the movement of ions.

Researchers have found quite a many chemistry in cathode and it is difficult for a normal mind to keep track all the properties of it, especially the voltage part which is very important. A wrong charger with a wrong battery would either or both decrease the life of a battery or explode. An NMC chemistry battery has a nominal voltage of 4.2 while LFP has 3.3 V.

Charging and discharging:

Generally, LIB's have carbon as anode and they do not have any lithium in them. While charging, under the application of voltage, the lithium ions migrate from cathode to anode through electrolyte (electrons flow in the reverse direction outside the battery). In this process (for charging a battery), the positive terminal is anode while negative terminal is cathode. The lithium ions are stored in the cages of carbon like prisoner with gates closed, and they wait to be released.

 When discharging, the positive terminal is cathode and negative terminal is anode. The reverse migration of lithium ions from anode to cathode takes place without any intervention of any external source while itself acting as a voltage source.

Cell are charged in two methods: constant voltage (CV) and constant current (CC), At low charge CV method is used to increase the voltage of the battery to some extent and from there when we have some charge in the battery, CC method is used.

Rate of Charge/Discharge: The flow of lithium ions or electrons can be tuned with the load while voltage (typically~4.2-3) depends upon the state of charge. As a convention, if the cell discharges with a rate that it exhausts in a hour then it is called as 1C rate. If it takes half an hour then the rate is called as 2C and 10 min then 6C similarly a cell can take long time to discharge like if it takes 6hrs then the rate is C/6. the same convention is applied to charge the cell.