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:

Lithium-iron Batteries:

Lithium Cobalt Oxide (LCO): LiCoO2

Its high specific energy makes Li-cobalt the popular choice for mobile phones, laptops and digital cameras. The battery consists of a cobalt oxide cathode and a graphite carbon anode. The cathode has a layered structure and during discharge, lithium ions move from the anode to the cathode. The flow reverses on charge. The drawback of Li-cobalt is a relatively short life span, low thermal stability and limited load capabilities (specific power).

The drawback of Li-cobalt is a relatively short life span, low thermal stability and limited load capabilities (specific power). Li-cobalt should not be charged and discharged at a current higher than its C-rating.

Lithium Manganese Oxide (LMO): LiMn2O4

In 1996, Moli Energy commercialized a Li-ion cell with lithium manganese oxide as cathode material. The architecture forms a three-dimensional spinel structure that improves ion flow on the electrode, which results in lower internal resistance and improved current handling. A further advantage of spinel is high thermal stability and enhanced safety, but the cycle and calendar life are limited.Low internal cell resistance enables fast charging and high-current discharging.

Li-manganese has a capacity that is roughly one-third lower than Li-cobalt. Design flexibility allows engineers to maximize the battery for either optimal longevity (life span), maximum load current (specific power) or high capacity (specific energy).

Most Li-manganese batteries blend with lithium nickel manganese cobalt oxide (NMC) to improve the specific energy and prolong the life span. This combination brings out the best in each system, and the LMO (NMC) is chosen for most electric vehicles, such as the Nissan Leaf, Chevy Volt and BMW i3. The LMO part of the battery, which can be about 30 percent, provides a high current boost on acceleration; the NMC part gives a long driving range.

Lithium Nickel Manganese Cobalt Oxide (NMC): LiNiMnCoO2

One of the most successful Li-ion systems is a cathode combination of nickel-manganese-cobalt (NMC). Similar to Li-manganese, these systems can be tailored to serve as Energy Cells or Power Cells.

The secret of NMC lies in combining nickel and manganese. An analogy of this is table salt in which the main ingredients, sodium and chloride, are toxic on their own but mixing them serves as seasoning salt and food preserver. Nickel is known for its high specific energy but poor stability; manganese has the benefit of forming a spinel structure to achieve low internal resistance but offers a low specific energy. Combining the metals enhances each other's strengths.

NMC is the battery of choice for power tools, e-bikes and other electric powertrains. The cathode combination is typically one-third nickel, one-third manganese and one-third cobalt, also known as 1-1-1. This offers a unique blend that also lowers the raw material cost due to reduced cobalt content. Another successful combination is NCM with 5 parts nickel, 3 parts cobalt and 2 parts manganese (5-3-2). Other combinations using various amounts of cathode materials are possible.

Battery manufacturers move away from cobalt systems toward nickel cathodes because of the high cost of cobalt. Nickel-based systems have higher energy density, lower cost, and longer cycle life than the cobalt-based cells but they have a slightly lower voltage.

Lithium Nickel Cobalt Aluminium Oxide (NCA): LiNiCoAlO2

Lithium nickel cobalt aluminum oxide battery, or NCA, has been around since 1999 for special applications. It shares similarities with NMC by offering high specific energy, reasonably good specific power and a long life span. Less flattering are safety and cost.

Lithium iron Phosphate (LFP): LiFePO4

In 1996, the University of Texas (and other contributors) discovered phosphate as cathode material for rechargeable lithium batteries. Li-phosphate offers good electrochemical performance with low resistance. This is made possible with nano-scale phosphate cathode material. The key benefits are high current rating and long cycle life, besides good thermal stability, enhanced safety and tolerance if abused.

Li-phosphate is more tolerant to full charge conditions and is less stressed than other lithium-ion systems if kept at high voltage for a prolonged time. As a trade-off, its lower nominal voltage of 3.2V/cell reduces the specific energy below that of cobalt-blended lithium-ion. With most batteries, cold temperature reduces performance and elevated storage temperature shortens the service life, and Li-phosphate is no exception. Li-phosphate has a higher self-discharge than other Li-ion batteries, which can cause balancing issues with aging. This can be mitigated by buying high quality cells and/or using sophisticated control electronics, both of which increase the cost of the pack. Cleanliness in manufacturing is of importance for longevity. There is no tolerance for moisture, lest the battery will only deliver 50 cycles.

Lithium Titanate (LTO): Li2TiO3

Batteries with lithium titanate anodes have been known since the 1980s. 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 has a nominal cell voltage of 2.40V, can be fast charged and delivers a high discharge current of 10C, or 10 times the rated capacity. The cycle count is said to be higher than that of a regular Li-ion. Li-titanate is safe, has excellent low-temperature discharge characteristics and obtains a capacity of 80 percent at –30°C (–22°F).

LTO (commonly Li4Ti5O12) has advantages over the conventional cobalt-blended Li-ion with graphite anode by attaining zero-strain property, no SEI film formation and no lithium plating when fast charging and charging at low temperature. Thermal stability under high temperature is also better than other Li-ion systems; however, the battery is expensive. At only 65Wh/kg, the specific energy is low, rivalling that of NiCd. Li-titanate charges to 2.80V/cell, and the end of discharge is 1.80V/cell.

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

Ans.

Lithium Ion battery Comparison:

	LCO	LMO	NCA	NMC	LFP	LTO
Nominal Voltage	3.6 V	3.7 V	3.6 V	3.6 V	3.2 V	2.4 V
Specific Energy	150-200 Wh/Kg	100-150 Wh/Kg	200-260 Wh/Kg	150-220 Wh/Kg	90-120 Wh/Kg	50-80 Wh/Kg
Charge C-Rate	0.7-1C	Typical 0.7-1C Max. 3C	0.7C	0.7-1C	1C	Typical 1C Max. 5C
Discharge C-Rate	1C	Typical 1C Max. 10C	1C	1-2C	1C and on some cell 25C	Upto 10C
Life Cycle	500-1000	300-700	500	1000-2000	2000	3000-7000
Thermal Runaway Temperature	150°C	250°C	150°C	210°C	270°C	One of safest LI-ion batteries
Cost	$ 140 per KWh	$ 402 per KWh	$ 350 per KWh	$ 420 per KWh	$ 580 per KWh	$ 1005 per KWh
Application	Mobile phones, Tablets, Camera, Laptop	Power tools, Medical device, Powertrain	Medical device, Industrial,Electric Powertrain (Tesla)	Medical devices, EV’s, Industrial	Portable and Stationary needing high load current and endurance	UPS, Electric Powertrain, Solar power street Lighting

In the above table we can compare the types of Li-ion batteries on different parameters. Above parameters value are till 2019 and refer from battery university website.

• If we compare on the basis of nominal voltage then all types of batteries nominal voltage are almost the same, only LTO is an exception.
• Specific energy is high in the NCA battery, but Specific power i.e. C-rate is high in the LTO chemistry.
• Similarly in LTO Chemistry life cycle is also higher than other battery chemistry, also one of the safest Li-ion batteries.
• Due to the good performance of the LTO battery, it costs more than other batteries.

In the below figure summarize the six key parameters of lithium ion batteries. This figure gives us a good idea of the lithium-ion battery.