Week 1 Understanding Different Battery Chemistry
Part A:
Primary Cell and Secondary Cell
Primary cells are single-use, non-rechargeable cells, the ones we use in our TV remotes, wall clocks, etc. These are considerably cheaper while having high energy density, which means that they are smaller, weigh less and are more cost-effective. This makes them ideal choice for applications that require lower amount of energy as it helps cut down the cost as well as the weight of the final product.
Secondary cells are energy storage devices that can be reused multiple times. They can perform reversible cell reactions that allow them to recharge, by just reversing the direction of the current. Albeit being more expensive than the primary cells, they can be used multiple times, thus making them a better choice for energy storage applications that require a constant replenishment of energy, such as mobile phones, smart-watches, Electric vehicles, or large Battery Energy Storage systems for homes or discoms, etc.
There are a lot of different types of secondary cells available in the market, there are multiple variants of Lithium-ion cells, Nickel cells, Lead-acid batteries, hydrogen fuel cell, etc., all these batteries have their pros and cons. In this article, we will focus only on different chemistries of Li-ion Batteries.
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.
1. In a lithium cobalt oxide battery cell, chemical reactions takes place in the cell and it generates energy to either charge or discharge the cell.
There is always an anode and a cathode in a cell. In this case, the cathode is the positive electrode which is the lithium cobalt oxide and the anode is the graphite.
Summary Table
| Lithium Cobalt Oxide: LiCoO2 cathode (~60% Co), graphite anode Short form: LCO or Li-cobalt. Since 1991 |
|
| Voltages | 3.60V nominal; typical operating range 3.0–4.2V/cell |
| Specific energy (capacity) | 150–200Wh/kg. Specialty cells provide up to 240Wh/kg. |
| Charge (C-rate) | 0.7–1C, charges to 4.20V (most cells); 3h charge typical. Charge current above 1C shortens battery life. |
| Discharge (C-rate) | 1C; 2.50V cut off. Discharge current above 1C shortens battery life. |
| Cycle life | 500–1000, related to depth of discharge, load, temperature |
| Thermal runaway | 150°C (302°F). Full charge promotes thermal runaway |
| Applications | Mobile phones, tablets, laptops, cameras |
| Comments |
Very high specific energy, limited specific power. Cobalt is expensive. Serves as Energy Cell. Market share has stabilized. Early version; no longer relevant. |
2. Lithium manganate oxide battery refers to the battery that uses lithium manganate oxide as an anode material. Its nominal voltage is 3.7V.
It is the mainstream power battery at present. This kind of battery has ordinary energy density and cycling life. It has environmental protection and no patent limitation.
But lithium manganate oxide is not very stable, easy to decompose gas, may lead to swell, and its high-temperature performance is poor.
Lithium manganate oxide, whose chemical formula is LiMn2O4 (LCM), is one of the promising lithium ion anode materials. Compared with traditional anode materials such as lithium cobalt oxides, lithium manganate oxide has rich resources, low cost, no pollution, good safety and nice rate capability. It is an ideal anode material for power battery.
| Lithium Manganese Oxide: LiMn2O4 cathode. graphite anode Short form: LMO or Li-manganese (spinel structure) Since 1996 |
|
| Voltages | 3.70V (3.80V) nominal; typical operating range 3.0–4.2V/cell |
| Specific energy (capacity) | 100–150Wh/kg |
| Charge (C-rate) | 0.7–1C typical, 3C maximum, charges to 4.20V (most cells) |
| Discharge (C-rate) | 1C; 10C possible with some cells, 30C pulse (5s), 2.50V cut-off |
| Cycle life | 300–700 (related to depth of discharge, temperature) |
| Thermal runaway | 250°C (482°F) typical. High charge promotes thermal runaway |
| Applications | Power tools, medical devices, electric powertrains |
| Comments |
High power but less capacity; safer than Li-cobalt; commonly mixed with NMC to improve performance. Less relevant now; limited growth potential. |
3.
The lithium nickel cobalt aluminium oxides (NCAs) are a group of mixed metal oxides. Some of them are important due to their application in lithium ion batteries.
NCAs are used as active material on the positive pole (which is the cathode when the battery is discharged). NCAs are composed of the cations of the
chemical elements lithium, nickel, cobalt and aluminium. The most important representatives as of this date have the general formula LiNixCoyAlzO2 with x + y + z = 1.
| Lithium Nickel Cobalt Aluminum Oxide: LiNiCoAlO2 cathode (~9% Co), graphite anode Short form: NCA or Li-aluminum. Since 1999 |
|
| Voltages | 3.60V nominal; typical operating range 3.0–4.2V/cell |
| Specific energy (capacity) | 200-260Wh/kg; 300Wh/kg predictable |
| Charge (C-rate) | 0.7C, charges to 4.20V (most cells), 3h charge typical, fast charge possible with some cells |
| Discharge (C-rate) | 1C typical; 3.00V cut-off; high discharge rate shortens battery life |
| Cycle life | 500 (related to depth of discharge, temperature) |
| Thermal runaway | 150°C (302°F) typical, High charge promotes thermal runaway |
| Cost | ~$350 per kWh (Source: RWTH, Aachen) |
| Applications | Medical devices, industrial, electric powertrain (Tesla) |
| Comments |
Shares similarities with Li-cobalt. Serves as Energy Cell. Mainly used by Panasonic and Tesla; growth potential. |
4. Lithium Nickel Manganese Cobalt Oxide Batteries:
NMCs are among the most important storage materials for lithium ions in lithium ion batteries. They are used on the positive side, which acts as the cathode during discharge.
Stoichiometric NMC cathodes are represented as points in the solid solutions between end members, LiCoO 2, LiMnO 2, and LiNiO 2.
For both types of NMC cathodes, there is a formal internal charge transfer that oxidizes the manganese and reduces the nickel cations, rather than all the transition metal cations being trivalent.
While NMC powder can refer to a variety of blends, the formula typically consists of 33% nickel, 33% manganese and 33% cobalt. This blend, so
metimes referred to as 1-1-1, is a popular option for mass-produced cells in applications requiring frequent cycling (automotive, energy storage) due to the reduced material cost resulting from lower cobalt content.
| Lithium Nickel Manganese Cobalt Oxide: LiNiMnCoO2. cathode, graphite anode Short form: NMC (NCM, CMN, CNM, MNC, MCN similar with different metal combinations) Since 2008 |
|
| Voltages | 3.60V, 3.70V nominal; typical operating range 3.0–4.2V/cell, or higher |
| Specific energy (capacity) | 150–220Wh/kg |
| Charge (C-rate) | 0.7–1C, charges to 4.20V, some go to 4.30V; 3h charge typical. Charge current above 1C shortens battery life. |
| Discharge (C-rate) | 1C; 2C possible on some cells; 2.50V cut-off |
| Cycle life | 1000–2000 (related to depth of discharge, temperature) |
| Thermal runaway | 210°C (410°F) typical. High charge promotes thermal runaway |
| Cost | ~$420 per kWh (Source: RWTH, Aachen) |
| Applications | E-bikes, medical devices, EVs, industrial |
| Comments |
Provides high capacity and high power. Serves as Hybrid Cell. Favorite chemistry for many uses; market share is increasing. Leading system; dominant cathode chemistry. |
5.lithium iron phosphate (LFP)
| Lithium Iron Phosphate: LiFePO4 cathode, graphite anode Short form: LFP or Li-phosphate Since 1996 |
|
| Voltages | 3.20, 3.30V nominal; typical operating range 2.5–3.65V/cell |
| Specific energy (capacity) | 90–120Wh/kg |
| Charge (C-rate) | 1C typical, charges to 3.65V; 3h charge time typical |
| Discharge (C-rate) | 1C, 25C on some cells; 40A pulse (2s); 2.50V cut-off (lower that 2V causes damage) |
| Cycle life | 2000 and higher (related to depth of discharge, temperature) |
| Thermal runaway | 270°C (518°F) Very safe battery even if fully charged |
| Cost | ~$580 per kWh (Source: RWTH, Aachen) |
| Applications | Portable and stationary needing high load currents and endurance |
| Comments |
Very flat voltage discharge curve but low capacity. One of safest Li-ions. Used for special markets. Elevated self-discharge. Used primarily for energy storage, moderate growth. |
Lithium titanate battery is a lithium titanate used as a negative electrode material for lithium ion batteries.
It can be combined with lithium manganate, ternary materials or lithium iron phosphate to form a 2.4V or 1.9V lithium ion secondary battery.
Inside a lithium-ion battery, oxidation-reduction (Redox) reactions take place.
Reduction takes place at the cathode. There, cobalt oxide combines with lithium ions to form lithium-cobalt oxide (LiCoO2). The half-reaction is:
CoO2 + Li+ + e- → LiCoO2
Oxidation takes place at the anode. There, the graphite intercalation compound LiC6 forms graphite (C6) and lithium ions. The half-reaction is:
LiC6 → C6 + Li+ + e-
Here is the full reaction (left to right = discharging, right to left = charging):
LiC6 + CoO2 ⇄ C6 + LiCoO2
part B:
Lithium-ion batteries are used in most aspects of our everyday lives. Most devices like smartphones and laptops cannot operate without these batteries.
Lithium-ion batteries have also become very important in the field of electromobility as it is now the battery of choice in most electric vehicles. Its high specific energy gives it an advantage over other batteries.
There are different types of lithium-ion batteries and the main difference between them lies in their cathode materials. Different kinds of lithium-ion batteries offer different features, with trade-offs between specific power, specific energy, safety, lifespan, cost, and performance.
The six lithium-ion battery types that we will be comparing are Lithium Cobalt Oxide, Lithium Manganese Oxide, Lithium Nickel Manganese Cobalt Oxide, Lithium Iron Phosphate, Lithium Nickel Cobalt Aluminium Oxide, and Lithium Titanate.
Cost: Demand for electric vehicles has generally been lower than anticipated and this is mainly due to the cost of lithium-ion batteries. Hence cost is a huge factor when selecting the type of lithium-ion battery.
Table :
| Lithium -Ion battery types | Specific Power | Specific Energy | safety | Lifespan | cost | Performance |
| Lithium Cobalt Oxide | Low | high | Low | Low | Low | moderat |
| Lithium Manganese Oxide | moderat | moderat | moderat | Low | Low | Low |
| Lithium Nickel Manganese Cobalt Oxide | moderat | high | moderat | moderat | Low | moderat |
| Lithium Iron Phosphate | high | low | high | high | Low | moderat |
| Lithium Nickel Cobalt Aluminium Oxide | moderat | high | low | moderat | moderat | moderat |
| Lithium Titanate | moderat | low | High | High | High | High |
The graph shown below compares the nominal voltages of different Li-ion Chemistry
.
From the above graph, we can say that the nominal voltage of NMC, LCO and LMO is higher than other chemistries while that of LTO is lowest. If we compare the data for energy density from the table, we find that the chemistry follows the same trend with LTO having the lowest energy density.
To sum up, it can be said that Li-ion batteries are the future of energy storage, the specification of cell depends on the internal composition, i.e. the material used for the electrodes, separator and the electrolyte. By changing the cathode, properties such as specific energy, charging rates, cycle life, nominal voltage, etc. can be controlled but every chemistry has their own pros and cons which needs to be considered while selecting the li-ion cell for a product.
Lithium Cobalt Oxide :
- has high specific energy as compared to the other batteries which make it the preferred choice for laptops and mobile phones.
- Lithium cobalt oxide battery have cobalt as the main active material in its cathode.
- 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.
- It also has a low cost and a moderate performance. However, it is highly unfavorable in all the other aspects when compared to the other lithium-ion batteries.
- It has low specific power, low safety, and a low lifespan.
Lithium Manganese Oxide has moderate specific power, moderate specific energy, and a moderate level of safety when compared to the other types of lithium-ion batteries.
- It has LiMn2O4 as a cathode.
- These batteries have low internal resistance and high temperature stability which makes them safer than other lithium-ion battery types.
- LMO batteries are capable of delivering current up to 20-30 Amps due to their low internal resistance, thus making fast charging and discharging possible.
- It has the added advantage of a low cost. The downsides are its low performance and low lifespan. It is usually used in medical devices and power tools.
Lithium Nickel Manganese Cobalt Oxide has two major advantages as compared to the other batteries.
- Expensive but High Performing Battery.
- These batteries are cheaper than other Li-ion batteries and have a very low self-heating rate and a nominal voltage of 3.7V.
- The first one is its high specific energy which makes it desirable in electric powertrains, electric vehicles, and electric bikes.
- The other is its low cost.
- It is moderate in terms of specific power, safety, lifespan, and performance when compared to the other lithium-ion batteries.
- It can be optimized to either have high specific power or high specific energy.
- Lithium Iron Phosphate only has one major disadvantage when compared to other types of lithium-ion batteries and that is its low specific energy.
- Other than that, it has moderate to high ratings in all the other characteristics. It has high specific power, offers a high level of safety, has a high lifespan, and comes at a low cost.
- The performance of this battery is also moderate. It is often employed in electric motorcycles and other applications that require a long lifespan and a high level of safety.
- Lithium Nickel Cobalt Aluminium Oxide offers one strong advantage as compared to the five other batteries and that is high specific energy.
- It is pretty moderate in the rest of the characteristics like performance, cost, specific power, and lifespan. The only downside to this battery type is its low level of safety.
- Its high specific energy and moderate lifespan make it a good candidate for electric powertrains.
- Lithium Titanate offers high safety, high performance, and a high lifespan which are very important features every battery should have.
- Its specific energy is low compared to the five other lithium-ion batteries but it compensates for this with moderate specific power.
- The only major disadvantage of lithium titanate as compared to the other lithium-ion batteries is its extremely high cost. Another important feature of this battery worthy of mention is its remarkably fast recharge time.
- It can be used for storing solar energy and creating smart grids.
