Week 1 Understanding Different Battery Chemistry
Objective-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.
Li-ion Cell
Lithium-ion cells are rechargeable cells, they use lithium as one of the key components in the construction of the cell. The development of Li-ion cells started in the early 70s, and their advancement and potential to catapult the energy storage systems making the adoption of EV’s a reality caused its inventors to win a Nobel Prize in Chemistry in 2019. These are rechargeable cells commonly used in portable electronics to something as large as Discoms for storing energy produced from renewable energy. There is a tremendous amount of research going on in the Li-ion batteries which cause the capacity of battery to increase drastically in the coming future. In the past 3 decades, the cost of battery has decreased by 97% and since the last decade, it has fallen by 88%.
Components of Li-ion Cell
Like any other cell, Li-ion cells are also made up of different components. These internal components help in shaping the features and other characteristics of a Li-ion cell. The Li-ion cell has 4 main components that are Cathode, Anode, Electrolyte, and Separator. The image below shows the different components of a Li-ion cell.
Cathode:
The material used in the cathode determines the capacity and voltage of Li-ion battery. This material is called the active material. The active material plays a crucial role in the chemical reaction in the battery which causes the flow of current. The capacity of a cell depends on the size of the active material at the cathode, i.e. for higher capacity of the cell, we need to have bigger cathodes. Meanwhile, the voltage of the cathode depends on the element used as a cathode.
The nomenclature of the battery usually depends on the cathode, like a Lithium-ion battery has a cathode made up of Lithium. But because lithium is highly reactive and unstable making it difficult to contain and use directly, therefore a combination of lithium and oxygen is used as a cathode.
Anode:
Similar to the cathode, an anode is the other electrode, which is also coated with an active material. It is the negative electrode and its property decides the rate of charge and discharge of the battery. We try to maximize the surface area of the anode which affects the rate of flow of electric current through the external circuit, resulting in a higher rate of absorption or emission of lithium ions released from the cathode. Anode stores the lithium ions during the charge cycle of the battery. The image below shows the discharging and charging states of the battery showing the flow of electrons and ions during the process.
The most commonly used anodes in Li-ion cells are graphite and the oxide spinel Li4Ti5O12. Graphene is being investigated and is considered a better alternative that can increase the power density as well as the charge and discharge rate of the cell.
Electrolyte:
An electrolyte solution is an electrically neutral solution, both the electrodes are submerged in the electrolyte solution. Although the solution is neutral but when an electric potential is applied, the ions start flowing towards the electrode. During the charge cycle, the lithium ions move from cathode to anode, while in the discharge cycle the reverse happens. Electrolyte plays a major role in the movement of ions thus making the flow of current possible. The movement of anions and cations in opposite directions in the electrolyte causes the flow of current.
For a Li-ion cell, the electrolyte needs to be a lithium salt, hence the most commonly used electrolyte in a Li-Ion battery is LiPF6 dissolved in an organic solvent.
Separator:
The separator plays an important role in the functioning of the battery. The electrolyte acts as a medium between the electrodes while the separator is placed between the electrodes to isolate them from each other so that no electron flows through them while allowing the ions to flow between them. The separator forms a catalyst when covered with the electrolyte thus facilitating the movement of ions between anode and cathode while stopping the electrons. When excessive heat is applied, the pores of separator get clogged by the melting process, this property can be employed as a safety feature, making the separator act as a fuse, stopping the flow of current in case of overheating thus safeguarding the battery from fire.
Most batteries for mobile phones and tablets which need to be kept lightweight and do not have a very rugged use have a single polyethylene separator while larger industrial batteries deploy tri-layered separator that acts like a fuse, protecting fires during extreme temperatures and on multi-cell configurations.
Types of Li-ion Battery
Li-ion batteries can be classified based on the combination of anode and cathodes used. There are six categories of lithium-ion battery readily available in the market, these are Lithium Cobalt Oxide (LCO), Lithium Manganese Oxide (LMO), Lithium Nickel Manganese Cobalt Oxide (NMO), Lithium Iron Phosphate (LFP), Lithium Nickel Cobalt Aluminum Oxide (NCA), and Lithium Titanate (LTO). Apart from the LTO battery, all other Li-ion battery has graphite as an anode. All the above Li-ion chemistries have different properties and we need to know their properties, their operating conditions and other parameters in order to select the best battery for our application. The properties of all the chemistries are given below.
1. LITHIUM COBALT OXIDE (LCO): Energy Dense but Low Thermal Stability
Lithium cobalt oxide battery have cobalt as the main active material in its cathode. It was invented in 1991 and has been extensively used because of its high energy density of 150-200 Wh/kg. Although this battery chemistry is energy dense, but other options are being investigated as the experts are claiming that the world could face a cobalt supply shortage soon. This is due to the surge in sales of electric vehicles where this battery chemistry is extensively used, leading to increase in cost over time.
Cobalt is a highly volatile metal, which limits the current handling capabilities of LCO battery due the risk of overheating. Furthermore, LCO batteries have lower thermal stability, that makes them sensitive to higher operating temperatures and overcharging.
LCO batteries are extensively used in portable electronics such as phones, cameras, laptops and have a high demand in electric vehicles.
Reactions of LCO batteries-
2. LITHIUM MANGANESE OXIDE (LMO): The Safest Li-ion Chemistry
The lithium /manganese dioxide (Li /MnO2) battery was one of the first lithium / solid-cathode systems to be used commercially and is now the most widely used primary lithium battery. It is available in many configurations (including coin, bobbin, spirally wound cylindrical, and prismatic configurations in multicell batteries, and in designs for low, moderate, and moderately high drain applications. The capacity of batteries available commercially ranges up to 2.5 Ah. Larger sized batteries are available for special applications and have been commercially. Its attractive properties include a high cell voltage (nominal voltage 3 V), specific energy above 230 Wh/kg and an energy density above 535 Wh/L, depending on design and application, good performance over a wide temperature range, long shelf life, storability even at elevated temperatures, and low cost.
The Li/MnO2 battery is used in a wide variety of applications such as long-term memory backup, safety and security devices, cameras, many consumer devices and in military electronics. It has gained an excellent safety record during the period since it was introduced.The performance of a Li /MnO2 battery is compared with comparable mercury, silver oxide, and zinc batteries in Sec. 7.3 illustrating the higher energy output of the Li/MnO2 battery.
Chemical Reactions-
The Li/MnO2 cell uses lithium for the anode, and electrolyte containing lithium salts in a mixed organic solvent such as propylene carbonate and 1,2-dimethoxyethane, and a specially prepared heat-treated form of MnO2 for the active cathode material.
The cell reactions for this system are-
Manganese dioxide, an intercalation compound, is reduced from the tetravalent to the trivalent state producing LixMnO2 as the Li+ ion enters into the MnO2 crystal lattice.1,38 The theoretical voltage of the total cell reaction is about 3.5 V, but an open circuit voltage of a new cell is typically 3.3 V. Cells are typically predischarged to lower the open circuit voltage to reduce corrosion.
3. LITHIUM NICKEL COBALT ALUMINUM OXIDE (LINICOALO2) NCA: High Energy with Long Life
Lithium Nickle Cobalt batteries, also known as NCA batteries have a combination of nickel, cobalt and aluminum as active material in its cathode. These batteries have a high life cycle and are one of the most energy-dense Li-ion chemistry with energy density as high as 260Wh/kg and a nominal voltage of 3.6V. But the main disadvantage of this battery is its lower thermal stability and high cost making them an unviable option for consumer electronics. They are a good option for EVs due to their energy density, the NCA batteries must be used in cars with extra safety measures to monitor their performance and other data to keep the drivers secure.
The NCA batteries are becoming increasingly important in electric powertrains such as in Tesla and find application in grid storage due to their lifespan and energy density.
Reactions of NCA batteries-
4. LITHIUM NICKEL MANGANESE COBALT OXIDE (NMC): Expensive but High Performing Battery
Lithium Nickel Manganese Cobalt Oxide (NMC) Batteries uses a combination of nickel, manganese and cobalt as the active material for its cathode. The most commonly used ratio is 60 percent nickel mixed with 20 percent each of manganese and cobalt to form the alloy. Changing the ratio of these metals can alter the property and we can either attain a high specific energy density or a high specific power. These batteries are cheaper than other Li-ion batteries and have a very low self-heating rate and a nominal voltage of 3.7V. NMC batteries have energy density of 150-220 Wh/kg, which is higher than most other chemistries.
This battery is commonly used to power medical equipment, power tools and is considered as one of the preferred battery chemistries for EVs.
Reactions of NMC batteries-
5. LITHIUM IRON PHOSPHATE (LFP): Affordable, Safe, and Reliable
Lithium iron phosphate batteries use phosphate as active material in the cathode. These batteries are one of the most used chemistries in electric motorcycles, e-rikshaw as well as other applications that need a long lifecycle and significant safety. These batteries have a moderately high energy density of 90-160 Wh/kg. Similar to LMO, LFP chemistry have low internal resistance resulting in higher thermal stability. Unlike the LCO battery, these batteries are durable and have a long lifecycle with low self-discharge rates. LFP batteries have one of the best life cycles making them a very cost-effective option considering their long operations life. However, the nominal voltage of 3.2V of the li-phosphate battery means that it has less energy than other types of lithium batteries.
LFP batteries are used in industrial equipment and heavy machinery due to their high thermal stability and great life cycles. They are widely used in EVs, especially in e-bikes, e-rikshaw, and many cars because of their ability to withstand a lot of mechanical and thermal abuse.
Reactions of LFP batteries-
6. Lithium titanate LTO: Long life, fast charge using advanced Nanotechnology
Lithium titanate, also known as li-titanate are one of the newly developed Li-ion chemistries. They have advanced nanotechnology and replace the graphite used in the anode with lithium titanate as the active material. The large surface area of Li-titanate allows a larger quantity of electrons to enter and exit the anode faster, making a very high rate of charging and discharging possible without compromising on safety. The main drawback of this battery is that it suffers from is the low nominal voltage and low energy density of 2.4V and 50-80Wh/kg respectively. What makes this battery special is its ability to provide discharge rate exceeding 30 C for a short period of time. The use of advance nanotechnology makes it one of the safest chemistries available in today’s time.
Currently, a lot of big manufacturers of electric vehicles and bikes such as Mitsubishi, Honda, etc., use li-titanate batteries, and there is potential for this type of battery to be used in electric buses for public transportation.
LTO batteries have potential scope in aerospace, military and are used in battery energy storage systems for storing wind energy and solar energy and for creating smart grids. Their ability to sustain high discharge rates make them a preferred option for frequency control devices for grid applications.
Reactions of LTO batteries-
Objective-2.Compare the differences between each type of Li+ion batteries based on their characteristics.
Table for different Li-ion batteries-
Comparison of Parameters-
Conclusion- All the objectives has been achieved.