Week 1 Understanding Different Battery Chemistry

1. Li-ion Batteries

A lithium-ion battery or Li-ion battery is a type of rechargeable battery. Lithium-ion batteries are commonly used for portable electronics and electric vehicles and are growing in popularity for military and aerospace applications.

Similar to the lead- and nickel-based architecture, lithium-ion uses a cathode (positive electrode), an anode (negative electrode) and electrolyte as conductor. The cathode is a metal oxide and the anode consists of porous carbon. During discharge, the ions flow from the anode to the cathode through the electrolyte and separator; charge reverses the direction and the ions flow from the cathode to the anode. Figure 1 illustrates the process.

Types of Li-ion Cells

Lithium Cobalt Oxide(LiCoO2) — LCO
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).

Lithium Manganese Oxide (LiMn2O4) — LMO
Li-ion with manganese spinel was first published in the Materials Research Bulletin in 1983. 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.

Lithium Nickel Cobalt Aluminum Oxide (LiNiCoAlO2) — NCA
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. NCA is a further development of lithium nickel oxide; adding aluminum gives the chemistry greater stability.

Lithium Nickel Manganese Cobalt Oxide (LiNiMnCoO2) — NMC
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. For example, NMC in an 18650 cell for moderate load condition has a capacity of about 2,800mAh and can deliver 4A to 5A; NMC in the same cell optimized for specific power has a capacity of only about 2,000mAh but delivers a continuous discharge current of 20A.

Lithium Iron Phosphate(LiFePO4) — LFP
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.

Lithium Titanate (Li2TiO3) — LTO
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.

The materials & chemical reactions occurring at the anode, cathode and overall reactions of all the types of Li-ion cells are given in the table below

2. Lithium Nickel Manganese Cobalt Oxide (NMC)

NMC batteries use a cathode chemistry composed of nickel, manganese, and cobalt. They offer high energy density, moderate cost, and less susceptibility to overheating compared to other lithium-ion batteries. This makes them a popular choice for electric vehicles:

• High energy density is well-suited for the EV range.
• Good cycle life for battery pack longevity
• High specific power for improved acceleration
• Relatively stable chemistry

The percentage makeup of nickel, manganese, and cobalt can be adjusted to tweak performance metrics. For example, increasing nickel content raises energy density, while boosting manganese improves stability and safety.

Lithium Iron Phosphate (LFP)

LFP batteries use a cathode chemistry based on iron phosphate. They have a lower energy density than NMC but offer other advantages:

• Excellent safety record due to stability
• Long-cycle life and service life
• Good specific power rating
• Low cost due to abundance of iron

The tradeoff is less driving range compared to NMC for a similarly sized battery pack. However, new advancements in LFP energy density continue to close this gap.

Lithium Titanate Oxide (LTO)

LTO batteries substitute titanium oxide for the traditional graphite anode. They charge extremely rapidly and have a high cycle count, making them most suitable for hybrid EVs.

• Rapid recharging capability
• Excellent, high-current performance
• Outstanding low-temperature discharge characteristics
• Longer cycle life compared to other lithium-ion chemistries

The high cost and lower energy density make LTO less ideal for pure battery electric vehicles needing extended range.

Lithium Cobalt Oxide (LCO)

Lithium-cobalt oxide batteries offer high specific energy but low stability. This makes them suitable for compact consumer electronics like mobile phones and tablets, which require optimum energy density. The cathode in an LCO battery contains cobalt oxide material.

Key features:

– High specific energy density

– Low thermal stability

Medium-specific power

– Average cycle life

– Used in mobile phones, tablets, and cameras

Lithium Manganese Oxide (LMO)

Lithium manganese oxide, or LMO, batteries offer improved thermal stability over LCO batteries. They also have a higher operating voltage. But they come with less specific energy. LMO batteries find use in both consumer gadgets as well as electric powertrains.

Key features:

– Better thermal stability than LCO

– Higher operating voltage

– Lower energy density than LCO

– Often used with LCO cathodes in blends

– Used in power tools, medical devices, and electric bicycles

Lithium Nickel Cobalt Aluminum Oxide (NCA)

NCA cathode chemistry contains a mix of nickel, cobalt, and aluminum. They are related to NMC batteries but use aluminum instead of manganese. NCA batteries offer very high capacity and good energy density, comparable to LCO. But stability is inferior to NMC, and cycle life is also lower.

Key features:

– Very high capacity

– Good energy density

– Lower stability than NMC batteries

– Used in electric vehicles and laptops

Solid-State Batteries

Solid-state batteries utilize solid electrodes and solid electrolytes rather than liquid- or gel-based electrodes found in conventional Li-ion batteries. They offer better safety and stability while delivering increased energy density. Currently, solid-state batteries are under intense R&D across the industry.

Key features:

– Improved safety

– Increased energy density potential

– Longer cycle life

– High cost as of now

– Still under development