Understanding Different Battery Chemistry

Aim:

To understand battery technology in general and the different types of lithium ion cells.

Objective:

To prepare a table which includes materials & chemical reactions occurring at the anode and cathode of LCO, LMO, NCA, NMC, LFP and LTO type of lithium ion cells. We will also study about the BATTERY-TECHNOLOGY and HEV in general using some examples in MATLAB.

Theory:

Battery Definition:

Batteries convert chemical energy directly to electrical energy. In many cases, the electrical energy released is the difference in the cohesive or bond energies of the metals, oxides, or molecules undergoing the electrochemical reaction. For instance, energy can be stored in Zn or Li, which are high-energy metals because they are not stabilized by d-electron bonding, unlike transition metals. Batteries are designed such that the energetically favourable redox reaction can occur only if electrons move through the external part of the circuit.

A battery consists of some number of voltaic cells. Each cell consists of two half-cells connected in series by a conductive electrolyte containing metal cations. One half-cell includes electrolyte and the negative electrode, the electrode to which anions (negatively charged ions) migrate; the other half-cell includes electrolyte and the positive electrode, to which cations (positively charged ions) migrate. Cations are reduced (electrons are added) at the cathode, while metal atoms are oxidized (electrons are removed) at the anode. Some cells use different electrolytes for each half-cell; then a separator is used to prevent mixing of the electrolytes while allowing ions to flow between half-cells to complete the electrical circuit.

Types of Battery:

Batteries are classified into primary and secondary forms:

• Primary batteries are designed to be used until exhausted of energy then discarded. Their chemical reactions are generally not reversible, so they cannot be recharged. When the supply of reactants in the battery is exhausted, the battery stops producing current and is useless.
• Secondary batteries can be recharged; that is, they can have their chemical reactions reversed by applying electric current to the cell. This regenerates the original chemical reactants, so they can be used, recharged, and used again multiple times.

Some types of primary batteries used, for example, for telegraph circuits, were restored to operation by replacing the electrodes. Secondary batteries are not indefinitely rechargeable due to dissipation of the active materials, loss of electrolyte and internal corrosion.

Li-Ion Battery

Li-ion batteries consist of largely four main components: cathode, anode, electrolyte, and separator.

Every single component of a Li-ion battery is essential as it cannot function when one of the components is missing.

Cathode:

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.

Anode:

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.

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

Electrolyte:

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.

Separator:

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.

Working of Li-Ion Battery:

The reactants in the electrochemical reactions in a lithium-ion cell are materials of anode and cathode, both of which are compounds containing lithium atoms. During discharge, an oxidation half-reaction at the anode produces positively charged lithium ions and negatively charged electrons. The oxidation half-reaction may also produce uncharged material that remains at the anode. Lithium ions move through the electrolyte, electrons move through the external circuit, and then they recombine at the cathode (together with the cathode material) in a reduction half-reaction. The electrolyte and external circuit provide conductive media for lithium ions and electrons, respectively, but do not partake in the electrochemical reaction. During discharge, electrons flow from the negative electrode (anode) towards the positive electrode (cathode) through the external circuit. The reactions during discharge lower the chemical potential of the cell, so discharging transfers energy from the cell to wherever the electric current dissipates its energy, mostly in the external circuit. During charging these reactions and transports go in the opposite direction: electrons move from the positive electrode to the negative electrode through the external circuit. To charge the cell the external circuit has to provide electric energy. This energy is then stored as chemical energy in the cell.

Types of Lithium ion battery:

There are some types of lithium ion cells based on their chemical compositions and they are,

1. Lithium cobalt oxide - LiCoO2 (LCO)

Also known as lithium cobaltite or lithium-ion cobalt batteries, lithium cobalt oxide batteries are made from lithium carbonate and cobalt.

They have a cobalt oxide cathode and use graphite carbon as their anode material; during discharge, lithium ions move from anode to cathode, with the flow reversing when the battery is charging.

This type of battery has some drawbacks, including a relatively short battery life and limited specific power. Additionally, these batteries are not as safe as other types.

2. Lithium Manganese Oxide - LiMn2O4 (LMO)

The first commercial lithium-ion cells made with lithium manganese oxide as a cathode material were produced in 1996 by Moli Energy.

Lithium manganese oxide batteries are notable for their high temperature stability and are also safer than other lithium-ion battery types.

For this reason, they are often used in medical equipment and devices, but they may also be used in power tools, electric bikes and more.

It is also possible to use lithium manganese oxide batteries to power laptops and electric powertrain cars.

3. Lithium Nickel Cobalt Aluminium Oxide - LiNiCoAlO2 (NCA)

Lithium nickel cobalt aluminium oxide batteries are also called NCA batteries, and are becoming increasingly important in electric powertrains and in grid storage.

NCA batteries are not common in the consumer industry, but are promising for the automotive industry.

NCA batteries provide a high-energy option with a good lifespan, but they are not as safe as they could be compared to other lithium-ion battery types and are quite costly.

4. Lithium Nickel Manganese Cobalt Oxide - LiMnCoO2 (NMC)

Also known as lithium manganese cobalt oxide or NMC batteries, include a cathode made of a combination of nickel, manganese and cobalt.

Like other lithium-ion battery varieties, NMC batteries can have either a high specific energy density or a high specific power. They cannot, however, have both properties.

This battery type is most common in power tools and in powertrains for vehicles.

The cathode combination ratio is usually 60 percent nickel, 20 percent manganese and 20 percent cobalt. This means that the raw material cost is lower than it is for other lithium-ion battery options, as cobalt can be quite expensive.

These batteries may come down in price further in the future, as some battery makers are planning to switch their battery chemistry to a higher % of Nickel, so that they can use less cobalt.

This battery type is commonly preferred for electric vehicles due to its very low self-heating rate.

5. Lithium Iron Phosphate - LiFePo4 (LFP)

Lithium iron phosphate batteries, also known as li-phosphate batteries, use phosphate as a cathode. They benefit from low resistance properties, which enhance their safety and thermal stability.

Other benefits include durability and a long lifecycle — fully charged batteries can be stored with little change to the total lifespan of the battery’s charge.

Li-phosphate batteries are often the most cost-effective option as well when their long battery life is taken into consideration. However, the lower voltage of the li-phosphate battery means that it has less energy than other types of lithium batteries.

Accordingly, these batteries are often used in electric motorcycles as well as other applications that need a long lifecycle and significant safety.

6. Lithium Titanium Oxide - LiTiO2 (LTO)

Finally, lithium titanate, also known as li-titanate, is a class of battery that allows for ever-increasing applications. The main advantage of the li-titanate battery is its remarkably fast recharge time.

Currently, manufacturers of electric vehicles and bikes use li-titanate batteries, and there is potential for this type of battery to be used in electric buses for public transportation.

However, these batteries have lower inherent voltage, or lower energy density, than other lithium-ion battery varieties, which can present issues with powering vehicles efficiently. Even so, the density of lithium titanate batteries is still higher than other non-lithium-ion batteries, which is a plus.

Table:

S.No.	Li - Ion Battery Type	Cathode	Anode	Electrolyte	Separator
1	(LiCoO2) — LCO	Li Cobalt oxide	Graphite carbon	Ethylene Carbonate + Li salt	Polyolefin
2	(LiMn2O4) — LMO	Lithium manganese oxide	Graphite carbon	Methyl carbonate + Li salt	Polyolefin
3	(LiNiMnCoO2) — NMC	Lithium Nickel Manganese Cobalt Oxide	Graphite carbon	Methyl Carbonate + Li salt	Polyolefin
4	(LiFePO4) — LFP	Lithium Iron Phosphate	Graphite carbon	Propylene Carbonate + Li salt	Polyolefin
5	(LiNiCoAlO2) — NCA	Lithium Nickel Cobalt Aluminium Oxide	Graphite carbon	Propylene Carbonate + Li salt	Polyolefin
6	LTO	Lithium manganese oxide or NMC	Li2TiO3 (Titanate)	Propylene Carbonate + Li salt	Polyolefin

Chemical reactions:

	Lithium Cobalt Oxide (LiCoO2 ) - LCO
Anode reaction	`C_6Li→6C+Li^++e^−`
Cathode reaction	`Li_(1−x)CoO_2+xLi^++xe^− →LiCoO_2`
Overall Cell reaction	`C_6+LiCoO_2↔Li_xC_6+Li_(1−x)CoO2`

	Lithium Manganese Oxide (LiMn2O4) — LMO
Anode reaction	`Li→Li^++e^−`
Cathode reaction	`MnO^2+Li^++e^−→LiMnO^2`
Overall Cell reaction	`Li+MnO^2↔LiMnO^2`

	Lithium Nickel Manganese Cobalt Oxide (LiNiMnCoO2) — NMC
Anode reaction	`Li_xC_n→nC+xLi^++xe^−`
Cathode reaction	`Li_(1−x)(Ni_(1−x−y)Mn_xCo_y)O_2+xLi^++xe^−→LiNiMnCoO_2`
Overall Cell reaction	`Li_xC_n+Li_(1−x)(Ni_(1−x−y)Mn_xCo_y)O_2↔LiNiMnCoO_2+nC`

	Lithium Iron Phosphate(LiFePO4) — LFP
Anode reaction	`Li_xC_n→nC+xLi^+xe^−`
Cathode reaction	`FePo_4+Li^++e^−→LiFePo_4`
Overall Cell reaction	`C_n+LiFePo_4↔FePo_4+LiCn`

	Lithium Nickel Cobalt Aluminum Oxide (LiNiCoAlO2) — NCA
Anode reaction	`C_6Li→6C+Li^++e^−`
Cathode reaction	`NiCoAlO_2+Li^++e^−→LiNiCoAlO_2`
Overall Cell reaction	`C_6Li+NiCoAlO_2↔Li_(1−x)NiCoAlO_2+Li_xC_6`

	Lithium-Titanium oxide (LTO)
Anode reaction	`Li_7Ti_5O_12→Li_4Ti_5O_12+3Li^++3e^−`
Cathode reaction	`3MnO_2+3Li^++3e^−→3LiMnO_2`
Overall Cell reaction	`Li_7Ti_5O_12+3MnO_2↔Li_4Ti_5O_12+3LiMnO_2`