Understanding Different Battery Chemistry
AIM: Understanding the Battery Chemistry.
OBJECTIVE:
1. Prepare a table that 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 of it.
2. Compare the differences between each type of Li+ion battery based on their characteristics.
THEORY AND SOLUTION:
A battery is a device consisting of one or more electrochemical cells with external connections for powering electrical devices. 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.
OBJECTIVE 1. Prepare a table that 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 of it.
1. Lithium Cobalt Oxide (LiCoO2) — LCO
It has high specific energy but low specific power which means that charging and discharging with Current Rate (C) above rated values shorten the battery’s life. It has a cobalt Oxide Cathode and Graphite anode. The cathode is layered.
During discharge, the Li-ions move from anode to cathode. The flow reverses during charging. The graphite anode limits its cycle life hence it has a short life span. It has low thermal stability. Its main applications are mobile phones, laptops, cameras, etc.
At the cathode, lithium ions are absorbed by the lithium dioxide and the electrode is reduced as it also receives the electrons from the circuit.
Cathode Reaction:`LiCoO_2↔Li_(1−x)CoO_2+xLi^++xe^−`
At the anode, lithium is oxidized. Lithium ions are released from the carbon, along with electrons.
Anode Reaction: `6C+xe^−+xLi^+↔Li_xC_6`
Overall reaction: `LiCoO_2+6C↔LiC_6+CoO_2`
2. Lithium Manganese Oxide (LiMn2O4) — LMO
The Manganese Oxide forms a 3D-spinel structure that improves the ion flow on the electrode. This results in lower internal resistance, which enables fast charging and high-current discharging. Adding to these, the spinel structure also packs extra thermal stability. Making it safer compared to LCO. The LMO has a lower cycle life.
Most Li-manganese batteries blend with lithium nickel manganese cobalt oxide (NMC) to enhance precise energy and prolong battery life. These three active metals, as well as silicon enhancement, can enhance specific energy (capacity), specific power (load capability), or longevity.
Li-manganese has high power and less capacity. It is used for power tools, medical devices as well as in electric vehicle powertrains.
Cathode Reaction: `LiMnO_2↔Li_(1−x)Mn_2O_4+xLi^++xe^−`
Anode Reaction: `LiMnO_2↔Li_(1−x)Mn_2O_4+xLi^++xe^−`
Overall Reaction:`LiMnO_2↔Li_(1−x)Mn_2O_4+xLi^++xe^−`
*(Order of the equation: Left to Right Charging & Right to Left Discharging)*
3. Lithium Nickel Manganese Cobalt Oxide (LiNiMnCoO2) — NMC
The cathodic combination of Nickel Manganese Cobalt is successful as it can be tailored to be either Energy cells or Power Cells. NMC has a good performance and excels in specific energy. This Lithium-ion battery can deliver a continuous discharge current.
The advantage of Nickel is its high specific energy but it has poor stability. Whereas Manganese achieves low internal resistance by forming a spinal structure. Unlike Nickel, Manganese offers low specific energy.
Their combination enhances each other’s performances. New electrolytes can boost capacity. It has the lowest self-heating rate and improved cycle life. This is a battery of choice for electric powertrains and industrial applications.
Cathode Reaction: `LiMnO_2↔Li_(1−x)MO_2+xLi^++xe^−`
Anode Reaction: `LiMnO_2↔Li_(1−x)MO_2+xLi^++xe^−`
Overall Reaction: `LiMnO_2↔Li_(1−x)MO_2+xLi^++xe^−`
*(Order of the equation: Left to Right Charging & Right to Left Discharging)*
4. Lithium Iron Phosphate (LiFePO4) — LFP
In this type, Li- Phosphate is used as the cathode since it has good electrochemical performance with low resistance. This is because of the nano-scale phosphate cathode material.
Various advantages of this Lithium-ion battery chemistry include – long lifecycle, good thermal stability, high current rating, enhanced safety, and tolerance in case of abuse.
Li-Phosphate is often used to replace lead-acid batteries as it has a moderate specific energy and has a very low tolerance for moisture, which reduces its cycle life drastically.
Other characteristics include a very flat voltage discharge curve but low capacity. LFP is one of the safest Li-ions in the market.
At the cathode, lithium ions are absorbed by the lithium dioxide and the electrode is reduced as it also receives the electrons from the circuit.
Cathode Reaction: `LiFe(III)PO_4↔Li_(1−x)Fe(II)PO_4+xLi^++xe^−`
At the anode, lithium is oxidized. Lithium ions are released from the carbon, along with electrons.
Anode Reaction: `xLi^++xe^−+6C↔Li_xC_6`
Overall Reaction: `LiFePO_4+6C↔LiC_6+FePO_4`
*(Order of the equation: Left to Right Charging & Right to Left Discharging)*
5. Lithium Nickel Cobalt Aluminum Oxide (LiNiCoAlO2) — NCA
NCA batteries are gaining importance in electric powertrains and grid storage. They are not common in the consumer industry but are promising for the automotive Sector. Tesla, the US-based EV manufacturer researches this technology and uses this Lithium-ion battery chemistry.
NCA has the highest Specific Energy, good Specific Power, and a long life span. High cost and marginal safety are the negatives.
Cathode Reaction: `LiNiCoAlO_2↔Li_(1−x)NiCoAlO_2+xLi^++xe^−`
Anode Reaction: `xLi^++xe^−+6C↔Li_xC_6`
Overall Reaction: `6C+LiNiCoAlO_2↔LiC_6+NiCoAlO_2`
*(Order of the equation: Left to Right Charging & Right to Left Discharging)*
6. Lithium Titanate (Li2TiO3) — LTO
In this technology, Li-titanate replaces the graphite in the anode of a typical Lithium-ion battery, and the material forms into a spinel structure.
The cathode can be lithium manganese oxide or NMC. Li-titanate can be fast-charged and delivers a high discharge current 10 times the rated capacity. The cycle count is higher than the regular Li-ion batteries.
Li-titanate excels in safety and has excellent low-temperature discharge characteristics and life span. The applications of this lithium-ion battery chemistry power include electric powertrains, UPS, and solar-powered street lighting.
Cathode Reaction: `4LiMn_2O_4↔4Mn_2O_4+4Li^++4e^−`
Anode Reaction: `Ti_5O_12+4Li^++4e^−↔Li_4Ti_5O_12`
Overall Reaction: `Li_4Ti_5O_12+4Mn_2O_4↔4LiMn_2O_4+Ti_5O_12`
*(Order of the equation: Left to Right Charging & Right to Left Discharging)*
|
Lithium Combat 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 (LOT) |
|
|
Chemical Formula |
`LiCoO_2` |
`LiMn_2O_4` |
`LiNiMnCoO_2` |
`LiFePO_4` |
`LiNiCoAlO_2` |
`Li_2TiO_3` |
|
Anode Material |
Graphite carbon |
Graphic carbon |
Graphic carbon |
Graphic carbon |
Graphic carbon |
Lithium Titanium Oxide |
|
Cathode material |
Lithium Cobalt Oxide |
Lithium Manganese Oxide |
Lithium Nickel Manganese Cobalt Oxide |
Lithium Iron Phosphate |
Lithium Cobalt Aluminium Oxide |
Lithium Manganese oxide |
|
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 |
Charging (L to R) Discharging (R to L) `6C + xe^(-) + xLi^(+) leftrightarrow Li_xC_6` |
Charging (L to R) Discharging (R to L) `6C + xe^(-) + xLi^(+) leftrightarrow Li_xC_6` |
Charging (L to R) Discharging (R to L) `6C + xe^(-) + xLi^(+) leftrightarrow Li_xC_6` |
Charging (L to R) Discharging (R to L) `6C + xe^(-) + xLi^(+) leftrightarrow Li_xC_6` |
Charging (L to R) Discharging (R to L) `6C + xe^(-) + xLi^(+) leftrightarrow Li_xC_6` |
Charging (L to R) Discharging (R to L) `Ti_5O_12 + 4Li^(+) + 4e^(-) leftrightarrow Li_4Ti_5O_12` |
|
Cathod Reaction |
Charging (L to R) Discharging (R to L) `LiCoO_2 leftrightarrow Li_(1-x)CoO_2 + xLi^(+) +xe^(-)` |
Charging (L to R) Discharging (R to L) `LiMnO_2 leftrightarrow Li_(1-x)Mn_2O_4 + xLi^(+) + xe^(-)` |
Charging (L to R) Discharging (R to L) `LiMO_2 leftrightarrow Li_(1-x)MO_2 + xLi^(+) + xe^(-)` |
Charging (L to R) Discharging (R to L) `LiFePO_4 leftrightarrow Li_(1-x)FePO_4 + xLi^(+) + xe^(-)` |
Charging (L to R) Discharging (R to L) `LiNiCoAlO_2 leftrightarrow Li_(1-x)NiCoAlO_2 + xLi^(+) + xe^(-)` |
Charging (L to R) Discharging (R to L) `4LiMn_2O_4 leftrightarrow 4Mn_2O_4 + 4Li^(+) + 4e^(-)` |
|
Overall reaction |
`LiCoO_2 + 6C leftrightarrow CoO_2 + LiC_6` |
`LiMn_2O_4 + 6C leftrightarrow LiC_6 + Mn_2O_4` |
`Li_(1-x)MO_2 + Li_xC_n leftrightarrow LiMO_2 + nC` |
`LiFePO_4 + 6C leftrightarrowLiC_6 + FePO_4` |
`6C + LiNiCoAlO_2 leftrightarrow LiC_6 + NiCoAlO_2` |
`Li_4Ti_5O_12 + 4Mn_2O_4 leftrightarrow 4LiMn_2O_4 + Ti_5O_12` |
OBJECTIVE 2 - Compare the differences between each type of Li+ion battery based on their characteristics
As discussed in problem statement-1, each of the major 6 types of Lithium-ion batteries was discussed briefly. Now, the main differences between their characteristics can be best found out when choosing a battery type that can be best suited for your requirements or which does the job for you more efficiently than the others. In that context, there are certain factors for which the 6 types can be differentiated from one another and can be given in below:
- 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 each for a single time, makes a Cycle. The higher the cycles can take place, the higher is the lifespan.
- The current rate (C): This is used to determine the fast charging capability and short-circuit discharge capability of a battery.
- Thermal Runaway: In simplest terms, thermal runaway begins when the heat generated within a battery exceeds the amount of heat that is dissipated to its surroundings. If the cause of excessive heat creation is not remedied, the condition will worsen. Internal battery temperature will continue to rise, causing 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, thus the term “runaway".
- 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 we are going to get from different batteries with the same amount of weight.
Typical specific energy of different types of lithium-based batteries
The main differences between the 6 types of Li+ ion batteries can be differentiated based on their characteristics and a screenshot of the same is given in a tabular format :
Nominal Voltage: Most of them are very close when it comes to this characteristic. 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 mostly. LTO battery has the longest life cycle that's why it can last for a longer period of time and it is exactly the opposite for the LMO type batteries.
Charge Current Rate: Higher the charge current, the less time the battery will take to get fully charged. LFP and LTO are highest, NCA comes close to its contenders but finishes last in this case.
Discharge Current Rate: In severe cases, you can cause an internal short circuit and/or even an explosion. Most consumer applications require only 1C from their batteries. If you need higher discharge rates and faster charging times, you should definitely choose a high-rate battery instead. LTO has a discharge rate 10 times higher than others, that is why it is one of the safest batteries out there.
Thermal Runaway: It is discussed before, a Thermal runaway occurs in situations where an increase in temperature changes the conditions in a way that causes a further increase in temperature, often leading to a destructive result. It is a kind of uncontrolled positive feedback. We know that the higher the temperature at which the thermal runaway will occur, the safer the battery will be. LTO has the highest temperature rating in this and NCA & LCO has the lowest.
Specific Energy: The Specific energy density can be calculated by integrating from 0 to tcutoff (time to reach the cut-off potential) the expression V(t)*I*A dt and then dividing for (3600*Mw). In this way, you can obtain the specific energy density in Wh kg-1. Lithium-ion with cobalt cathodes(NCA-type batteries) offer the highest energy densities. Typical applications are cell phones, laptops, and digital cameras. Power Density (W/kg) indicates how much power a battery can deliver on-demand.
For ease of choosing a battery from a layman's perspective, the 6 key buying point are being considered and these 6 key features are given a value within 0-5 range for all the 6 types of batteries and then all of them are given with the same parameters which are considered in case of "5 Point Hexagonal Analysis" of the batteries. The 6 factors are as follows:
- Specific Energy
- Specific Power
- Safety
- Performance
- Life Span
- Cost
CONCLUSION
Here we have completely studied all the lithium-ion cells, their performance, reactions, and all other parameters.