Week 1 Understanding Different Battery Chemistry

1. Table which includes materials and chemical reactions occurring at the anode and cathode of LCO, LMO, NCA, NMC, LFP, and LTO:

Lithium-Ion cells are a secondary type, meaning that they are rechargeable and reusable, making them ideal for automotive applications and certain consumer electronics. When two or more lithium-ion cells are connected together in a series arrangement, it is referred to as a lithium-ion battery. Lithium-ion batteries like other batteries rely on the chemical energy stored in the bonds and atoms of elements and compounds and utilize this energy in a chemical reaction occurring inside the cell. The chemical energy from this reaction is converted to electrical energy for us to use. Since lithium-ion cells are rechargeable, they can perform the reverse reaction using electricity as well.

Internal Construction:

Lithium-ion batteries will consist of the following components:

I) Anode.

II) Cathode.

The anode and cathode are the two electrodes that are connected by a wire in an external circuit between which electrons will be transferred during the chemical reaction. This transfer of electrons will result in a flow of charge, meaning a current is produced. The electrode through which conventional current leaves a polarized electrical device is referred to as the cathode. The anode and cathode are not defined by their voltage polarities but instead by the direction of current flowing through them. Often, the cathode is made from a lithium oxide, sulphide or some other compound whereas the anode is made of pure graphite or hard carbon.

III) Separator.

A separator is needed as an insulating barrier between the anode and cathode and prevents internal short-circuiting. The separator is permeable to ions but to electrons due to its micro-porosity.

IV) Electrolyte.

To transfer electrons, there needs to be a chemical reaction involving ions because ions are charged particles that are formed when electrons have been lost or gained by them. This is where an electrolyte is needed. An electrolyte is a medium through which ions can flow between the electrodes but not electrons. Electrolytes can be in solid, liquid, or aqueous states, but in lithium-ion cells, the electrolyte is a non-aqueous type. The ions of the electrolyte will move towards an electrode depending on their polarities as opposites attract. So, a negative ion will move to a positive electrode and vice versa. So, electrolytes permit ionic conduction but not electric conduction as electric conduction will occur through the external circuit. The electrolyte used is a salt of lithium dissolved in an organic solvent.

V) Current collector.

Current collectors are electronic conductors mixed with the electrodes and allow for simple electronic connections to reduce the resistance of an electrode. In lithium-ion cells, the current collector is copper foil at the graphite electrode and aluminium foil at the lithium oxide electrode and they receive electrons.

Working:

Charging:

In the charging mode, a power source is connected to the lithium-ion cell. The positive and negative terminals of the power source will be connected to the lithium oxide and graphite electrodes respectively. The positive terminal will attract and remove electrons from the lithium oxide electrode and will flow from the positive terminal through the external circuit to the negative terminal and get collected at the graphite electrode. This results in the formation of positively charged lithium-ions which will be attracted towards the negative terminal and get trapped in the space between graphite's atomic layers. Once all the lithium-ions have crossed over to the graphite electrode, the cell is fully charged. This creates an unstable state. In this operation, the lithium oxide electrode is the positive anode, and the graphite electrode is the negative cathode. This is because the direction of the current is opposite to the flow of electrons. Electrons flow from the lithium oxide electrode to the graphite electrode, therefore current flows in reverse. By definition, the anode is the electrode through which conventional current enters a polarized device and the cathode is the electrode through which conventional current leaves a polarized device.

Discharging:

In this mode, the power source is replaced with a load instead e.g. a motor. The terminal polarities of the cell are now reversed so that the negative terminal of the load is connected to the lithium oxide electrode and the positive terminal is connected to the graphite electrode. Due to this, the lithium-ions will be attracted back to the lithium oxide electrode so it can regain its stability. Due to the load presence, the electrons will also leave the graphite electrode and return to the lithium oxide electrode. Once all the lithium-ions and electrons have returned to the lithium oxide electrode, the cell is fully charged and the lithium is now in a stable state. In this operation, the graphite electrode is now the anode and the lithium oxide electrode is the cathode. Figure (1) shows the charging and discharging modes of lithium-ion battery. There are several types of Lithium-ion cells, each with different constructions and chemical reactions. They are listed in the table below:

Parameters	Lithium Cobalt Oxide (LCO)	Lithium Manganese Oxide (LMO)	Lithium Nickel Manganese Cobalt Oxide (NMC)	Lithium Iron Phosphate (LFP)	Lithium Nickel Cobalt Aluminium Oxide (NCA)	Lithium Titanium Oxide (LTO)
Chemical Formula	LiCoO2	LiMn2O4	LiNiMnCoO2	LiFePO4	LiNiCoAlO2	Li2TiO3
Anode Material	Graphite Carbon	Graphite Carbon	Graphite Carbon	Graphite Carbon	Graphite Carbon	Lithium Titanium Oxide
Cathode Material	Lithium Cobalt Oxide	Lithium Manganese Oxide	Lithium Nickel Manganese Cobalt Oxide	Lithium Iron Phosphate	Lithium Nickel Cobalt Aluminium Oxide	Lithium Manganese Oxide or NMC
Electrolyte	Lithium salt in an organic solvent.	Lithium Halide dissolved in an organic solvent.	Lithium salt in an organic solvent.	Lithium salt in an organic solvent.	Lithium salt in an organic solvent.	Lithium salt in an organic solvent.
Anode Reaction	6C+(e-) +(Li+)<--> LiC6	LinC6<--> nLi+ + ne−	LinC6<--> Li0C6 + nLi+ + ne−	LinC6<-->Li0C6 + nLi+ + ne−	LinC6<--> Li0C6 + nLi+ + ne−	Li4Ti5O12+(4Li+)+(4e-)<-->4LiMn2O4
Cathode Reaction	LiCoO2<-->CoO2+ Li+ +e-	Lim − nMn2O4 + nLi+ + ne−<--> LimMn2O4	Lim − n(NixMnyCoz)O2 + nLi+ + ne−<--> Lim(NixMnyCoz)O2	Lim − nFePO4 + nLi+ + ne− <-->LimFePO4	Lim − n(NixCoyAlz)O2 + nLi+ + ne−<--> Lim(NixCoyAlz)O2	4Mn2PO4+(4Li+)+(4e-)<-->4LiMn2O4
Overall Reaction	LiCoO2+C6<-->LiC6+CoO2	LinC6 + Lim − nMn2O4<--> Li0C6 + LimMn2O4	LinC6 + Lim − n(NixMnyCoz)O2<--> Li0C6 + Lim(NixMnyCoz)O2	LinC6 + Lim − nFePO4<--> Li0C6 + LimFePO4	LinC6 + Lim − n(NixCoyAlz)O2<--> Li0C6 + Lim(NixCoyAlz)O2	4Mn2O4+Li4Ti5O12<-->4LiMn2O4+Ti4O12
Voltage	Nominal Voltage = 3.6V Operating Range = 3-4.2V per cell.	Nominal Voltage = 3.7-3.8V Operating Range = 3-4.2V per cell.	Nominal Voltage = 3.6-3.7V Operating Range = 3-4.2V per cell.	Nominal Voltage = 3.2-3.3V Operating Range = 2.5-3.65V per cell.	Nominal Voltage = 3.6V Operating Range = 3-4.2V per cell.	Nominal Voltage = 2.4V Operating Range = 1.8-2.85V per cell.
Specific Energy	240Wh/kg	100-150Wh/kg	150-220Wh/kg	90-120Wh/kg	200-260Wh/kg	50-80Wh/kg
Cycle Life	500-1000 cycles.	300-700 cycles.	1000-2000 cycles.	>= 2000 cycles	500 cycles	3000-7000 cycles
Charge/Discharge Rate	Charge Rate: 0.7-1C Discharge Rate: 1C	Charge Rate: 0.7-1C Discharge Rate: 1C	Charge Rate: 0.7-1C Discharge Rate: 1-2C	Charge Rate: 0.7-1C Discharge Rate: 1C	Charge Rate: 0.7C Discharge Rate: 1C	Charge Rate: 1-5C Discharge Rate: 10-30C
Thermal Runaway	150 Degree Celsius	250 Degree Celsius	210 Degree Celsius	270 Degree Celsius	150 Degree Celsius	150 Degree Celsius
Application	Mobile phones, Tablets, Laptops.	Power Tools, Medical devices, Electric Powertrains.	E-Bikes, Medical devices, EVs, Industrial Tools.	Power tools, automotive hybrid systems, PHEV conversions.	Medical devices, Industrial tools, EVs.	UPS, Electric Powertrain.

2. Comparison of differences between each type of Li-ion batteries based on their characteristics:

As we discussed different types of Lithium-ion batteries and comparisons have been shown in tabular form. Here we have summarised different types of lithium-ion and their characteristics.

1. Lithium Cobalt Oxide- LiCoO2 (LCO):

• Also known as lithium cobaltate 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 the anode to the cathode, with the flow reversing when the battery is charging.
• As per the characteristics shown in figure (2), LCO batteries have high specific energy. LCO is a very attractive cathode material because of its relatively high theoretical specific capacity, high theoretical volumetric capacity.
• This type of battery has some drawbacks, including 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. Figure (3) shows the characteristics of LMO batteries.
• Major drawbacks of LMO batteries are shorter lifetime and lower capacity relative to cobalt-based system.

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 as shown in figure (4) which is the characteristics of NCA batteries.

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

• 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 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 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 percentage 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. Figure (5) shows the characteristics of NMC batteries.

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. Figure (6) shows the characteristics of LFP batteries.

6. Lithium Titanium Oxide- LiTiO2 (LTO):

• 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. Figure (7) shows the characteristics of LTO batteries.