How do Li ion batteries in BEVs work - swapnilmankame1995/EV-course GitHub Wiki

----------- Video Demonstration pending --------

Will be updated on 25th Jan 2021

So we learnt about how motors work! and how they are vital in propelling our automobile! now let's have a look at what powers those motors! Batteries!

Yes, the same ones in your remote and your laptop!

Like any other battery, a rechargeable lithium-ion battery is made of one or more power-generating compartments called cells.

Each cell has essentially four components:

  1. A positive electrode (connected to the battery's positive or + terminal also called the cathode),
  2. A negative electrode (connected to the negative or − terminal also called Anode),
  3. And a chemical called an electrolyte in between them.
  4. A separator

The Four Components of Li-ion Battery​

1526549699390.jpgImage Credits: Samsung sdi

1. Cathode

The Cathode plays an important role in determining the characteristics of the battery as the battery’s capacity and voltage are determined by active material type used for the cathode. The higher amount of lithium, bigger the capacity; and the bigger potential difference between cathode and anode, higher the voltage. The potential difference is small for anode depending on their type but for the cathode, the potential difference is relatively high in general. As such, the cathode plays a significant role in determining the voltage of the battery.

“Cathode” determines the capacity and voltage of a Li-ion battery

2. Anode

The Basic function of an anode is to send "Electrons" through the wire when the battery is getting discharged or is connected to an appliance.

Important note

When the battery is being charged, lithium ions are stored in the anode and not the cathode. At this point, when the conducting wire connects the cathode to the anode (discharge state), lithium ions naturally flow back to the cathode through the electrolyte, and the electrons (e-) separated from lithium ions move along the wire generating electricity.

Because graphite has optimal qualities such as structural stability, low electrochemical reactivity conditions for storing much lithium ions and price, the material is considered suitable to be used for the anode.

3. Electrolyte

The electrolyte is the medium by which the movement of ions happens!

For the electrolyte, materials with high ionic conductivity are mainly used so that lithium ions move back and forth easily. that is why The electrolyte is composed of salts, solvents and additives.

Here the salts are the passage for lithium ions to move, the solvents are organic liquids used to dissolve the salts,

“Electrolyte” allows the movement of ions only

4. Seperator

While the cathode and anode determine the basic performance of a battery, electrolyte and separator determine the safety of a battery.

The separator functions as a physical barrier keeping cathode and anode apart. It prevents the direct flow of electrons and carefully lets only the ions pass through the internal microscopic hole.

Separators are usually made up of synthetic resins such as polyethylene (PE) and polypropylene (PP).

”Separator”, the absolute barrier between cathode and anode

To recap

  • The electrolyte in the centre carries positively charged lithium ions from the anode to the cathode and vice versa through the separator.
  • The movement of the lithium ions creates free electrons in the anode which creates a charge at the Cathode (Blue).
  • The electrical current caused due to the flowing electrons then flows from the cathode through a device being powered to the Anode (Red).
  • The separator (Black) blocks the flow of electrons inside the battery. forcing it to go through the wire connected outside.

ezgif.com-optimize.gif Image chemtube3d.com ChemTube3D by Nick Greeves is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License

Points to remember

  • The negative electrode and positive electrode are capable of storing lithium ions.

  • Energy is stored and released as lithium ions travel between these electrodes through the electrolyte.

  • The negative electrode is generally made from carbon (graphite) and the electrolyte varies from one type of battery to another—but isn't too important in understanding the basic idea of how the battery works.

  • The positive electrode is typically made from a chemical compound called lithium-cobalt oxide (LiCoO2) or, in newer batteries, from lithium iron phosphate (LiFePO4).

Now that we know the basic components of a Li-ion Cell! let's understand more what goes on during charging and discharging!

1. Charging a battery

When the battery is charging up, the lithium-cobalt oxide, positive electrode gives up some of its lithium ions, which move through the electrolyte to the negative, graphite electrode and remain there. The battery takes in and stores energy during this process.

img-06.png Image : Toshiba SIP

  1. The charger passes current to the battery.
  2. Lithium ions move from the cathode to the anode through the electrolyte.
  3. The battery is charged by a potential difference between the two electrodes.

1. Discharging a battery

When the battery is discharging, the lithium ions move back across the electrolyte to the positive electrode, producing the energy that powers the battery. In both cases, electrons flow in the opposite direction to the ions around the outer circuit. Electrons do not flow through the electrolyte: it's effectively an insulating barrier, so far as electrons are concerned.

img-07.png Image : Toshiba SIP

  1. A discharge circuit is formed between the anode and the cathode.
  2. Lithium ions stored in the anode move to the cathode.
  3. Energy is used.

Important points to remember.

  • Lithium-ion chemistry prefers partial discharge to deep discharge, so it's best to avoid taking the battery all the way down to zero. Since lithium-ion chemistry does not have a "memory", you do not harm the battery pack with a partial discharge.

  • If the voltage of a lithium-ion cell drops below a certain level, it's ruined.

  • Lithium-ion batteries age. They only last two to three years, even if they are sitting on a shelf unused. So do not "avoid using" the battery with the thought that the battery pack will last five years. It won't. Also, if you are buying a new battery pack, you want to make sure it really is new.

  • If it has been sitting on a shelf in the store for a year, it won't last very long. Manufacturing dates are important.

  • Avoid heat, which degrades the batteries.