Li-Ion Battery

 "Science behind the Lithium-Ion battery"

About Lithium-Ion battery

A Lithium Ion or Li -ion battery is a type of rechargeable battery. Li-ion batteries are commonly used in portable electronics devices like Mobiles, Laptops, Drones and Electric vehicles etc.

A prototype Li-ion battery was developed by Akira Yoshino in 1985, based on earlier research by John Goodenough, M. Stanley Whittingham, Rachid Yazami and Koichi Mizushima during the 1970s–1980s, and then a commercial Li-ion battery was developed by a Sony and Asahi Kasei team led by Yoshio Nishi in 1991.

The Four Components of Li-Ion battery:-

1. Anode.

2. Cathode.

3. Electrolyte.

4. Separator.

Every single component of a Li-Ion battery is essential as it cannot function when on of the component is missing. 

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

 A Lithium-ion battery generates electricity through chemical reactions of lithium.

This is why, of course, lithium is inserted into the battery and that space for lithium is called “cathode”.

However, since lithium is unstable in the element form, the combination of lithium and oxygen, lithium oxide is used for cathode.

The material that intervenes the electrode reaction of the actual battery just like lithium oxide is called ”active material”.

In other words, in the cathode of a Li-ion battery, lithium oxide is used as an active material.

If you take a closer look at the cathode, you will find a thin aluminium foil used to hold the frame of the cathode coated

with a compound made up of active material, conductive additive and binder.

The active material contains lithium ions, the conductive additive is added to increase conductivity;

and the binder acts as an adhesive which helps the active material and the conductive additive to settle well on the aluminium substrate.

 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 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 cathode, the potential difference is relatively high in general.

As such, the cathode plays a significant role in determining the voltage of the battery. 

▶ ”Anode” sends electrons through a wire

 Just like the cathode, the anode substrate is also coated with active material.

The anode’s active material performs the role of enabling electric current to flow through the external circuit while allowing reversible absorption/emission of lithium ions released from the cathode.

 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.

For anode graphite which has a stable structure is used, and the anode substrate is coated with active material,

conductive additive and a binder.

Thanks to graphite’s 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 anode.

▶ “Electrolyte” allows the movement of ions only

 When explaining about cathode and anode, it was mentioned that lithium ions move through the electrolyte

and electrons move through the wire.

This is the key in enabling the use of electricity in a battery.

If ions flow through the electrolyte, not only can’t we use electricity but safety will be jeopardized.

 

Electrolyte is the component which plays this important role.

It serves as the medium that enables the movement of only lithium ions between the cathode and anode.

For the electrolyte, materials with high ionic conductivity are mainly used so that lithium ions move back and forth easily. 

The electrolyte is composed of salts, solvents and additives.

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

and the additives are added in small amounts for specific purposes. 

Electrolyte created in this way only allows ions to move to the electrodes and doesn’t let electrons to pass.

In addition, the movement speed of lithium ions depends on the electrolyte type.

Thus, only the electrolytes that meet stringent conditions can be used.

▶ ”Separator”, the absolute barrier between cathode and anode

 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.

Therefore, it must satisfy all the physical and electrochemical conditions.

Commercialized separators we have today are synthetic resin such as polyethylene (PE) and polypropylene (PP).

So far, we have looked at the four main components which determine the performance of Li-ion batteries.

Currently, Samsung SDI is strengthening R&D of new materials for the enhancement of battery performance

while ceaselessly continuing its efforts to improve the performance of existing materials and core technologies.

Through high capacity/high efficiency Li-ion battery innovation,

Samsung SDI seeks to take the lead in the future battery industry which will enrich the lives of human beings all across the world.  

Overall Reaction in Li-Ion Battery

 

The following equations exemplify the chemistry.

The positive electrode (cathode) half-reaction in the lithium-doped cobalt oxide substrate is

${\displaystyle {\ce {CoO2 + Li+ + e- <=> LiCoO2}}}$

The negative electrode (anode) half-reaction for the graphite is

${\displaystyle {\ce {LiC6 <=> C6 + Li+ + e^-}}}$

The full reaction (left to right: discharging, right to left: charging) being

${\displaystyle {\ce {LiC6 + CoO2 <=> C6 + LiCoO2}}}$

The overall reaction has its limits. Over discharging supersaturates lithium cobalt oxide, leading to the production of lithium oxide, possibly by the following irreversible reaction:

${\displaystyle {\ce {Li+ + e^- + LiCoO2 -> Li2O + CoO}}}$

Overcharging up to 5.2 volts leads to the synthesis of cobalt(IV) oxide, as evidenced by x-ray diffraction

${\displaystyle {\ce {LiCoO2 -> Li+ + CoO2 + e^-}}}$

In a lithium-ion battery, the lithium ions are transported to and from the positive or negative electrodes by oxidizing the transition metal, cobalt (Co), in Li
1-xCoO
2 from Co3+
 to Co4+
 during charge, and reducing from Co4+
 to Co3+
 during discharge. The cobalt electrode reaction is only reversible for x < 0.5 (x in mole units), limiting the depth of discharge allowable. This chemistry was used in the Li-ion cells developed by Sony in 1990.

The cell's energy is equal to the voltage times the charge. Each gram of lithium represents Faraday's constant/6.941, or 13,901 coulombs. At 3 V, this gives 41.7 kJ per gram of lithium, or 11.6 kWh per kilogram of lithium. This is a bit more than the heat of combustion of gasoline, but does not consider the other materials that go into a lithium battery and that make lithium batteries many times heavier per unit of energy.

How does recharging a lithium-ion battery work?

When the lithium-ion battery in your mobile phone is powering it, positively charged lithium ions (Li+) move from the negative anode to the positive cathode. They do this by moving through the electrolyte until they reach the positive electrode. There, they are deposited. The electrons, on the other hand, move from the anode to the cathode.

When you charge a lithium-ion battery, the exact opposite process happens. The lithium ions move back from the cathode to the anode. The electrons move from the anode to the cathode.

Battery during Charging

Video Link:-https://www.youtube.com/watch?v=G5McJw4KkG8