Week 1 Understanding Different Battery Chemistry

Lithium-ion uses a cathode (positive electrode), an anode (negative electrode) and electrolyte as conductor. (The anode of a discharging battery is negative and the cathode positive). The cathode is metal oxide and the anode consists of porous carbon/graphite. 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.

When the cell charges and discharges, ions shuttle between cathode (positive electrode) and anode (negative electrode). On discharge, the anode undergoes oxidation, or loss of electrons, and the cathode sees a reduction, or a gain of electrons. Charge reverses the movement.

General Discharging process

Anode:

LiC₆ ----->Li⁺+ e^-+6C

Here oxidation happening by releasing electron

Cathode:

LiXO_y + Li⁺+ e^------> LiXO_y

where X is any Metal which may be Co,Mn,CoMn,NiCoAl,Ti

Overall Reaction for discharge

LiC₆ + LiXO_y -----> LiXO_y + 6C

While recharging the reverse reaction happening

Components of Li Ion cells

Li-ion batteries consist of largely four main components: cathode, anode, electrolyte, and separator.
Every single component of a Li-ion battery is essential as it cannot function when one of the components is missing.

1)Cathode

A Lithium-ion battery generates electricity through chemical reactions of lithium.This is why, of course, lithium is inserted and that space for lithium is called cathode.

However, since lithium is unstable in the element form, the combination of lithium and oxygen along with other metal oxides are used for cathode.

The material that intervenes the electrode reaction of the actual battery just like lithium oxide is called ”active material”.

In other words, in the cathode of a Li-ion battery, lithium oxide is used as an active material.

A thin aluminum foil used to hold the frame of the cathode coated with a compound made up of active material,conductive additive and binder.

The active material contains lithium ions, the conductive additive is added to increase conductivity.

The binder acts as an adhesive which helps the active material and the conductive additive to settle well on the aluminum substrate.

Cathode plays an important role in determining the characteristics of the battery as the battery’s capacity and voltage are determined by active material type used for cathode.

The higher amount of lithium, bigger the capacity; and the bigger potential difference between cathode and anode, higher the voltage.

2)Anode

Like the cathode, the anode substrate is also coated with active material.

The anode’s active material performs the role of enabling electric current to flow through the external circuit,while allowing reversible absorption/emission of lithium ions released from the cathode.

When the battery is being charged, lithium ions are stored in the anode. At this point, when the conducting wire connects the cathode to the anode (discharge state),lithium ions naturally flow back to the cathode through the electrolyte,and the electrons(e-) separated from lithium ions move along the wire generating electricity.

For anode graphite which has a stable structure is used, and the anode substrate is coated with active material,conductive additive and a binder.

3)Electrolyte

When explaining about cathode and anode, it was mentioned that lithium ions move through the electrolyte and electrons move through the wire.

It serves as the medium that enables the movement of only lithium ions between the cathode and anode.

For the electrolyte, materials with high ionic conductivity are mainly used so that lithium ions move back and forth easily.

4)Seperator

While the cathode and anode determine the basic performance of a battery, electrolyte and separator determine the safety of a battery. The separator functions as a physical barrier keeping cathode and anode apart. It prevents the direct flow of electrons and carefully lets only the ions pass through the internal microscopic hole. Therefore, it must satisfy all the physical and electrochemical conditions

Table showing materials & chemical reactions occurring at the anode and cathode of LCO, LMO, NCA, NMC, LFP and LTO type of lithium ion cells

SNo	Battery type	Electrolyte		Anode	Cathode	Anode Reaction	Cathode Reaction
		Salt	Solvent
1	Lithium Cobalt — LCO	Lithium hexafluoro Phosphate (LiPF6)	Ethylene Carbonate	Graphite(C6)	Lithium Cobalt Oxide-LiCoO2	LiC6 ↔ Li+ + e- + C6	CoO2 + Li+ + e- ↔ LiCoO2
						{Discharging L to R (-->) & Recharging R to L(<--)}	{Discharging L to R (-->) & Recharging R to L(<--)}
2	Lithium Manganese — LMO	Lithium hexafluoro Phosphate (LiPF6)	Ethylene Carbonate	Graphite(C6)	Lithium Manganese Oxide-LiMn2O4	LiC6 ↔ Li+ + e- + C6	Mn2O4 + Li+ + e- ↔ LiMn2O4
						{Discharging L to R (-->) & Recharging R to L(<--)}	{Discharging L to R (-->) & Recharging R to L(<--)}
3	Lithium Nickel Cobalt Aluminum — NCA	Lithium hexafluoro Phosphate (LiPF6)	Ethylene Carbonate	Graphite(C6)	Lithium Nickel Cobalt Aluminum Oxide-LiNiCoAlO2	LiC6 ↔ Li+ + e- + C6	NiCoAlO2 + Li+ + e- ↔ LiNiCoAlO2
						{Discharging L to R (-->) & Recharging R to L(<--)}	{Discharging L to R (-->) & Recharging R to L(<--)}
4	Lithium Nickel Manganese Cobalt - NMC	Lithium hexafluoro Phosphate (LiPF6)	Ethylene Carbonate	Graphite(C6)	Lithium Nickel Manganese Cobalt Oxide-LiNiMnCoO2	LiC6 ↔ Li+ + e- + C6	NiMnCoO2 + Li+ + e- ↔ LiNiMnCoO2
						{Discharging L to R (-->) & Recharging R to L(<--)}	{Discharging L to R (-->) & Recharging R to L(<--)}
5	Lithium Iron Phosphate — LFP	Lithium hexafluoro Phosphate (LiPF6)	Ethylene Carbonate	Graphite(C6)	Lithium Iron Phosphate-LiFePO4	LiC6 ↔ Li+ + e- + C6	FePO4 + Li+ + e- ↔ LiFePO4
						{Discharging L to R (-->) & Recharging R to L(<--)}	{Discharging L to R (-->) & Recharging R to L(<--)}
6	Lithium Titanate — LTO	Lithium hexafluoro Phosphate (LiPF6)	Ethylene Carbonate	Titanite (Ti5O12)	Lithium Manganese oxide - LiMn2O4	Li4Ti5O12 ↔Ti5O12 + 4Li++ 4e−	4Mn2O4 + 4Li+ + 4e− ↔ 4LiMn2O4
						{Discharging L to R (-->) & Recharging R to L(<--)}	{Discharging L to R (-->) & Recharging R to L(<--)}

Types of Li-ion Battery

1)Lithium Cobalt Oxide (LiCoO2) — LCO

2)Lithium Manganese Oxide (LiMn2O4) — LMO

3)Lithium Nickel Cobalt Aluminum Oxide (LiNiCoAlO2) — NCA

4)Lithium Nickel Manganese Cobalt Oxide (LiNiMnCoO2) - NMC

5)Lithium Iron Phosphate (LiFePO4) — LFP

6)Lithium Titanate (Li2TiO3) — LTO

1)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).

Figure illustrates the structure

The hexagonal spider graphic (figure below) summarizes the performance of Li-cobalt in terms of specific energy or capacity that relates to runtime; specific power or the ability to deliver high current; safety; performance at hot and cold temperatures; life span reflecting cycle life and longevity; and cost.

SUMMARY TABLE

2)Lithium Manganese Oxide (LiMn2O4) — LMO

It 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.

Figure below illustrates the formation of a three-dimensional crystalline framework on the cathode of a Li-manganese battery. This spinel structure, which is usually composed of diamond shapes connected into a lattice, appears after initial formation.

Figure below shows the spider web of a typical Li-manganese battery. The characteristics appear marginal but newer designs have improved in terms of specific power, safety and life span. Pure Li-manganese batteries are no longer common today; they may only be used for special applications.

SUMMARY TABLE

3)Lithium Nickel Cobalt Aluminum Oxide (LiNiCoAlO2) — NCA

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. Figure below summarizes the six key characteristics. NCA is a further development of lithium nickel oxide; adding aluminum gives the chemistry greater stability.

SUMMARY TABLE

4)Lithium Nickel Manganese Cobalt Oxide (LiNiMnCoO2) - NMC

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 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.

New electrolytes and additives enable charging to 4.4V/cell and higher to boost capacity. Figure below demonstrates the characteristics of the NMC.

SUMMARY TABLE

5)Lithium Iron Phosphate (LiFePO4) — LFP

The 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. Figure below summarizes the attributes of Li-phosphate.

Li-phosphate is often used to replace the lead acid starter battery. Four cells in series produce 12.80V, a similar voltage to six 2V lead acid cells in series. Vehicles charge lead acid to 14.40V (2.40V/cell) and maintain a topping charge. Topping charge is applied to maintain full charge level and prevent sulfation on lead acid batteries.

With four Li-phosphate cells in series, each cell tops at 3.60V, which is the correct full-charge voltage. At this point, the charge should be disconnected but the topping charge continues while driving. Li-phosphate is tolerant to some overcharge; however, keeping the voltage at 14.40V for a prolonged time, as most vehicles do on a long road trip, could stress Li-phosphate. Time will tell how durable Li-Phosphate will be as a lead acid replacement with a regular vehicle charging system. Cold temperature also reduces performance of Li-ion and this could affect the cranking ability in extreme cases.

SUMMARY TABLE

6)Lithium Titanate (Li2TiO3) — LTO

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. Figure below illustrates the characteristics of the Li-titanate battery. Typical uses are electric powertrains, UPS and solar-powered street lighting.

SUMMARY TABLE

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

Sl.no.	Battery Type			Cathode	Anode	Advantages	Drawbacks	Applications	Performance graph
1	(LiCoO2) — LCO			Li Cobalt oxide	Graphite carbon	high specific energy	short life span, low thermal stability and limited load capabilities (specific power), Cobalt is expensive	mobile phones, laptops and digital cameras
2	(LiMn2O4) — LMO			lithium manganese oxide	Graphite carbon	lower internal resistance and improved current handling, high thermal stability and enhanced safety	cycle and calendar life are limited	Electric vehicles such as the Nissan Leaf, Chevy Volt and BMW i3, Power tools, medical devices, electric powertrains
3	(LiNiMnCoO2) — NMC			Lithium Nickel Manganese Cobalt Oxide	Graphite carbon	good overall performance and excels on specific energy, lowest self-heating rate	high cost due to cobalt	E-bikes, medical devices, EVs, industrial
4	(LiFePO4) — LFP			Lithium Iron Phosphate	Graphite carbon	high current rating and long cycle life, besides good thermal stability, enhanced safety and tolerance if abused.	higher self-discharge, less specific energy	Portable and stationary needing high load currents and endurance
5	(LiNiCoAlO2) — NCA			Lithium Nickel Cobalt Aluminum Oxide	Graphite carbon	high specific energy, reasonably good specific power, long life span	High cost and marginal safety	Medical devices, industrial, electric powertrain (Tesla)
6	(Li2TiO3) — LTO			lithium manganese oxide or NMC	Li2TiO3 (titanate)	Fast charging, safe, high discharge current of 10C	Low specific energy	UPS, electric powertrain (Mitsubishi i-MiEV, Honda Fit EV), solar-powered street lighting