Week 1 Understanding Different Battery Chemistry

Q:- 1.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.Give your detailed explanation on it.

Ans:

Aim:

To make a study and understand about the electrochemistry of different types of lithium ion cells.

Battery:

* A Battery is a device consisting of one or more electrochemical cells with external connections for powering electrical devices such as Flashlights, mobile phones and electric cars.

* When a battery is supplying electric power, its positive terminal is the cathode and its negative terminal is the anode.

* The terminal marked negative is the source of electrons that will flow through an external electric circuit to the positive terminal.

* When a battery is connected to an external electric load, a Redox reaction converts high-energy reactants to lower-energy products, and the free energy difference is delivered to the external circuit as electrical energy.

* There are two types of batteries,

1. Primary cell - These batteries are one time use batteries and they cannot be recharged for further usage.

2. Secondart cell - These batteries can be recharged and can be used for multiple times.

Lithium ion Cell:

* The Lithium ion batteries are secondary type of batteries which can be recharged for further usage.

* The Lithium ion cells have four main Components in it and they are,

(i) Cathode

(ii) Anode

(iii) Electrolyte

(iv) Separator

(i) Cathode:

* They are the positive elctrodes of the cell.

* The cathode elctrode is usually made up of,

1. Layered Transition metal oxides - Has high Capacity but high in cost and poor in safety.

2. Spinels - High power Density but poor in conductivity and stability.

3. Olivines - Lees capacity but has long life and are high in safety.

(ii) Anode:

* They are the negative elctrodes of the cell.

* The anode elctrode is usually made up of,

1. Graphite

2. Hard Carbon, these anodes are less in cost and high in stability and specific capacity.

(iii) Electrolyte:

* The electrolyte is an ionic conductor that provides the medium for internal ionic charge transfer between the electrodes.

* The electrolyte most often comprises a liquid solvent containing dissolved chemicals (the solute) that provide this ionic conductivity.

* The dissolved electrolyte separates into cations and anions, which disperse uniformly through the solvent.

(iv) Separator:

* Battery separators provide a barrier between the anode (negative) and the cathode (positive) while enabling the exchange of lithium ions from one side to the other.

* They are materials that conducts ions but they do not conduct the electrons through them.

* Li-ion cells use polyolefin as a separator. This material has excellent mechanical properties, good chemical stability and is low-cost as well.

schematic diagram of Lithium ion cell:

* Cells are built from a number of principal components. These include a negative electrode, a positive electrode, the electrolyte, and a separator. Certain types of cells also have current collectors that are distinct from the electrodes themselves.

* The negative electrode in an electrochemical cell is often a pure metal, or an alloy, or even hydrogen.

* During discharge, the negative electrode gives up electrons to the external circuit, a process by which the electrode is oxidized: oxidation of a species involves the loss of electrons or, equivalently, an increase in the oxidation state of the species (it becomes more positively charged).

* During charge, the negative electrode accepts electrons from the external circuit and is reduced: reduction of a species involves the gain of electrons or, equivalently, a decrease in its oxidation state (it becomes more negatively charged). Thus, the chemical processes that occur in an electrochemical cell are sometimes called reduction-oxidation or redox reactions.

* The negative electrode is often called the anode. Technically, the anode is the electrode where oxidation occurs. So, the negative electrode is really the anode only when the cell is discharging and is actually the cathode when the cell is charging.

* The positive electrode in an electrochemical cell is often a metallic oxide, sulfide, or oxygen.

* During discharge, the positive electrode accepts electrons from the external circuit, a process by which the electrode is reduced. During charge, the positive electrode gives up electrons to the external circuit and is oxidized.

* The positive electrode is often called the cathode, Technically, the cathode is the electrode where reduction occurs. So, the positive electrode is really the cathode only when the cell is discharging and is actually the anode when the cell is charging.

* During discharge, positively charged ions or cations move through the electrolyte toward the positive electrode, and negatively charged ions or anions (if present) move through the electrolyte toward the negative electrode. During charge, the opposite occurs: cations move
toward the negative electrode and anions move toward the positive electrode.

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)

The Lithium Cobalt Oxide, LiCoO2, battery is a type of lithium-ion battery that find uses in many consumer items of electronic equipment. It provides a very high level of specific energy density along with a good level of safety.

The battery consists of a cobalt oxide cathode with a layered structure. The anode is graphite (carbon). During the discharge cycle, lithium ions move from the anode to the cathode, and in the reverse direction during charge.

The graphite anode limits the battery life as the solid electrolyte interface changes and also as a result of anode thickening. Newer batteries may incorporate nickel or manganese to improve the lifetime as well as reducing manufacturing costs.

One of the drawbacks of the LCO battery is that its current capability in both charge and discharge is limited. As a guide, it should not be charged or discharged at a greater rate than its capacity, i.e. a 2400mAh battery should not be charged or discharged with a current greater than 2400mA. Often figures of 0.8 of the charge level are recommended.

The LCO battery is now being supplanted in some applications by Lithium Manganese, as well as NMC and NCA types. This is occurring as a result of the improved performance of these other types as development improves the performance and as a result of cost.

2. Lithium Manganese Oxide - LiMn2O4 (LMO)

This type of lithium-ion battery uses Lithium Manganese Oxide, LiMn2O4 as its cathode material. This type of lithium-ion battery is structured to allow high currents to flow and this enables it to provide very high current levels and also to be fast charged as well.

It generally uses a three-dimensional spinel structure, i.e. one in which the crystal structure in the cubic, isometric, system, with the oxide anions arranged in a cubic close-packed lattice. This structure improves the flow of ions on the electrode, thereby increasing the current capability and lowering the internal resistance of the cell. A typical 1500mAh battery may be able to deliver steady currents of up to 20 A, obviously for a relatively short time because of the overall battery capacity.

The structure of this type of lithium-ion battery also has the advantage that it improves thermal stability and improves the safety of the cell.

However, the disadvantage of the cell is the limited number of charge-discharge / cycles as well as the limited calendar life

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

Lithium nickel cobalt aluminum 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)

The lithium nickel manganese cobalt oxide lithium battery type uses a cathode comprising a combination of nickel, manganese, and cobalt.

The key to this lithium-ion battery type is the combination of nickel and manganese. Nickel is known for its high specific energy, but poor stability whereas manganese provides low internal resistance but at the cost of low specific energy. Combining both in a cell in the correct manner is able to provide the required balance of the properties of both metals.

The cathode combination often consists of a combination of nickel, manganese and cobalt in equal proportions in a combination known as 1-1-1. This combination reduces cost by reducing the cobalt content.

Another popular combination consists of 5 parts nickel, 3 parts cobalt & 2 parts manganese (5-3-2).

The NMC type of lithium-ion battery can be optimized for either high specific power or high specific energy. With the high cost of cobalt, manufacturers are trying to move away from its use, often increasing the use of nickel, so this is often a major fact in the choice of composition of the battery.

5. Lithium Iron Phosphate - LiFePo4 (LFP)

The Lithium Iron Phosphate, LFP type of lithium-ion battery provides low internal resistance and high current capability.

In order to provide its high of current capability, this type of li-ion battery uses a nano-scale phosphate cathode material.

In terms of performance, this type of lithium-ion battery provides a slightly lower terminal voltage and it has a slightly higher self-discharge rate than other forms.

However, against this, it provides a high current rating, and good thermal stability combined with a good level of, and good thermal stability.

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.

Comparision Table:

Li - ion cell Type	Cathode	Anode	Electrolyte	Seperator	Overall Reaction at Cathode & Anode	Application
LCO	Graphite	Lithium Cobalt Oxide	Ethylene Carbonate + Li salt	Polyolefin	Li1-xCoO2(s) + x Li+ + x e- → LiCoO2(s)	Mobile phones, laptops and digital cameras
LMO	lithium manganese oxide	Graphite carbon	Methyl carbonate + Li salt	Polyolefin	Mn2+ + 2 LiC6 → Mn + 2 Li++ graphite	Power tools, medical devices, electric powertrains
NCA	Comprised of Nickel cobalt & Aluminium	Graphite carbon	Propylene carbonate + Li salt	Polyolefin	Li(1−x)NiO2 → (2 − x)Li(1−x)/(2−x)Ni1/(2−x)O + x/2O2	Medical devices, industrial, electric powertrain (Tesla)
NMC	Comprised of Nickel cobalt & Manganese	Lithium metal Graphite	Methyl carbonate + Li salt	Polyolefin	Li(x)MO2(s) → Li+(org) + Li(x-1)MO2(s) + e-.	E-bikes, medical devices, EVs, industrial
LFP	Comprised of Lithium, Iron & Phosphate	Graphite Carbon	Propylene carbonate + Li salt	Polyolefin		Portable and stationary needing high load currents and endurance
LTO	Comprised of Nickel cobalt & Manganese	Lithium–titanium oxide	Propylene carbonate + Li salt	Polyolefin	Li4Ti5O12 + 3Li+ + 3e → 4 Li7Ti5O12	UPS, electric powertrain (Mitsubishi i-MiEV, Honda Fit EV), solar-powered street lighting

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Q:-2.Compare the differences between each type of Li+ion batteries based on their characteristics

Ans:

Aim: To Compare the differences between each type of Li+ion batteries based on their characteristics

The Major 6 types of lithium-ion batteries were discussed early, Now the major differences in the characteristics can be found when choosing a battery. The major things that can be differentiated from one another.

• Nominal voltage: It is the system voltage at which the device is designed to operate. The rated voltage is usually higher than the nominal voltage to ensure the safe operation of the device.
• Cycle : The charge and discharge when took place for a single time makes a cycle. The higher the cycles can take place, the higher the cycles can takes place then the lifespan is higher.
• Thermal runway : The thermal runway begins when the heat generated within a battery exceeds the amount of heat that is dissipated to its surroundings.Internal battery temperature will continue to rise, causing the battery current to rise creating a domino effect. The rise in temperature in a single battery will begin to affect other batteries nearby and the pattern will continue.
• Specific energy : It is the amount of energy stored per unit mass (Wh/Kg). This is a very important deciding factor that decides how much energy or power from different batteries with the same amount of weight.

Specific energy of different types of lithium based batteries :

The main differences between the lithium ion batteries can be differentiated on the characteristics.

• Nominal Voltage : Most of the batteries are very close when it comes to characteristics. LMO (3.7) has the highest range and LTO (2.4) has the lowest range in volts.
• Cycle life : They differ by a significant amount from each other. LTO battery has the longest life cycle so that it can last longer period of time and it is exactly opposite for the LMO type batteries.
• Charge current rate : Higher the charge current, the less time the battery will take to get fully charged. LTO and LTP are highest NCA comes close to its condenders.
• Discharge current rate : If we need higher discharge rates and faster charging times we should choose a high rated battery instead. LTO has a discharge rate 10 times higher than the others and it t=is one of the safest batteries.
• Thermal runaway : A thermal runaway occurs in situations where an increase in temperature changes the conditions in a way that causes increase in temperature often leading a destructive result. LTO has the highest temperature rating in this and NCA and LCP has its lowest.
• Specific energy : The specific energy density can be calculated by integrating from 0 to t_cutoff. We can obtain the specific energy density in Wh Kg^-1. Lithium ion with cobalt cathodes offer the highest energy densities. This types of applications are cell phones, laptops and digital cameras. Power density indicates how much power a battery can deliver on demand.

For ease of choosing a battery from layman's perspective, the 6 key features are given a value within 0-5 range for all of the, are given with the same parameters which are considered in case of 5 point hexagonal analysis of the batteries. They are

1. Specific energy.
2. Specific power.
3. Safety.
4. Performance.
5. Life span.
6. Cost.

LCO :

Li-cobalt excels on high specific energy but offers only moderate performance-specific power, safety and life span.

LMO :

Although moderate in overall performance, newer designs of Li-manganese offer improvements in specific power, safety and life span.

NMC :

NMC has good overall performance and excels on specific energy. This battery is the preferred candidate for the electric vehicle and has the lowest self heating rate.

LFP :

Li-phosphate has excellent safety and long life span but moderate specific energy and elevated self discharge.

NCA :

High energy and power densities as well as a good life span make NCA a candidate for EV powertrains. High cost and marginal safety are negative.

LTO :

Li-titanate excels in safety, low-temperature performance and life span. Efforts are being made to improve the specific energy and lower the cost.

• These types of lithium-ion batteries are some of the most popular. As technology is continuously seeing more development, new lithium technologies are always being developed and those which exist are being developed.

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