Week 1 Understanding Different Battery Chemistry

Q1.

Ans: -

Lithium-ion battery: -

Lithium-ion uses a cathode (positive electrode), an anode (negative electrode), and an electrolyte as a conductor. (The anode of a discharging battery is negative and the cathode positive). 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; the charge reverses the direction and the ions flow from the cathode to the anode.

Most Li-ion batteries share a similar design consisting of a metal oxide positive electrode (cathode) that is coated onto an aluminum current collector, a negative electrode (anode) made from carbon/graphite coated on a copper current collector, a separator and electrolyte made of lithium salt in an organic solvent.

Advantages

• High specific energy and high load capabilities with Power Cells
• Long cycle and extended shelf-life; maintenance-free
• High capacity, low internal resistance, good coulombic efficiency
• Simple charge algorithm and reasonably short charge times
• Low self-discharge (less than half that of NiCd and NiMH)

Limitations

• Requires protection circuit to prevent thermal runaway if stressed
• Degrades at high temperature and when stored at high voltage
• No rapid charge possible at freezing temperatures (<0°C, <32°F)
• Transportation regulations required when shipping in larger quantities

Material and Chemical reaction: -

Li-ion Battery Type	Cathode	Anode	Electrolyte		Cathode Reaction	Anode reaction	Overall reaction
			Salt	Solvent
Lithium Cobalt (LCO)	Lithium Cobalt oxide (LiCoO2)	Graphite carbon	Lithium hexafluoro phosphate (LiPF6)	Ethylene Carbonate	Li1-xCoO2+xLi+ + xe- `⇄` LiCoO2	LixC6 `⇄`xLi+ + xe- +C6	C6 + LiCoO2 `⇄`LiC6 + CoO2
Lithium Manganese (LMO)	lithium manganese oxide (LiMn2O4)	Graphite carbon	Lithium hexafluoro phosphate (LiPF6)	Ethylene Carbonate	Li1-xMn2O4 + xLi++ xe- `⇄` LiMn2O4	LixC6 `⇄` xLi+ + xe- +C6	C6 + LiMn2O4 `⇄` LiC6 + Mn2O4
Lithium Nickel Manganese Cobalt (NMC)	Lithium Nickel Manganese Cobalt Oxide (LiNiMnCoO2)	Graphite carbon	Lithium hexafluoro phosphate (LiPF6)	Ethylene Carbonate	LiNi0.8Mn0.1Co0.1 O2 + xLi. + xe- `⇄`Li1-xNi0.8Mn0.1Co0.1 O2	LixC6 `⇄` xLi+ + xe- +C6	C6 + LiNi0.8Mn0.1Co0.1 O2 `⇄` LiC6 + LiNi0.8Mn0.1Co0.1O2
Lithium Iron Phosphate (LFP)	Lithium Iron Phosphate (LiFePO4)	Graphite carbon	Lithium hexafluoro phosphate (LiPF6)	Ethylene Carbonate	LixFePO4 + xLi + xe- `⇄` LiFePO4	LiC6 `⇄` Li+ + e- +C6	C6+ LiFePO4`⇄`LiC6 + FePO4
Lithium Nickel Cobalt Aluminium (NCA)	Lithium Nickel Cobalt Aluminium Oxide (LiNiCoAlO2)	Graphite carbon	Lithium hexafluoro phosphate (LiPF6)	Ethylene Carbonate	Li1-xNiCoAl02 + xLi+ + xe- `⇄` LiNiCoAl02	LiC6 `⇄` Li+ + e- +C6	C6 + LiNiCoAlO2 `⇄`LiC6+NiCoAlO2
Lithium Titanate (LTO)	lithium manganese oxide or NMC	Li2TiO3 (titanate)	Lithium hexafluoro phosphate (LiPF6)	Ethylene Carbonate	4Li1-xMn2O4 + 4Li+ + 4e- `⇄` 4LiMn2O4	Li4Ti5O12 `⇄` Ti5O12 + 4Li+ + 4e-	Li4Ti5O12 + 4Mn2O4 `⇄`4LiMn2O4 + Ti5O12

Types of lithium-ion batteries: -

Lithium Cobalt Oxide (LiCoO2) (LCO): -

• 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)
• Li-cobalt has a graphite anode that limits the cycle life by a changing solid electrolyte interface (SEI), thickening on the anode and lithium plating while fast charging and charging at low temperature.
• Li-cobalt should not be charged and discharged at a current higher than its C-rating.
• The mandatory battery protection circuit limits the charge and discharge rate to a safe level of about 1C for the Energy Cell.

Lithium Manganese Oxide (LiMn2O4) (LMO): -

• 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 is limited.
• Low internal cell resistance enables fast charging and high-current discharging.
• 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.

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 a 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. A silicon-based anode will go to 4,000mAh and higher but at reduced loading capability and shorter cycle life.
• A silicon-based anode will go to 4,000mAh and higher but at reduced loading capability and shorter cycle life. Silicon added to graphite has the drawback that the anode grows and shrinks with charge and discharge, making the cell mechanically unstable.
• 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 low specific energy. Combining the metals enhances each other strengths.
• 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).

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. With most batteries, the 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 ageing.
• 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.
• 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 the full charge level and prevent sulfation on lead-acid batteries.

Lithium Nickel Cobalt Aluminium Oxide (LiNiCoAlO2) (NCA): -

• Lithium nickel cobalt aluminium 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 aluminium gives the chemistry greater stability.

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 charged fast 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% 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 temperatures 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.

Q.2

Ans: -

Comparison of characteristics of the lithium-ion battery: -

Li-ion Battery Type	Nominal Voltage (V)	SOA (V)	Specific Energy (Wh/Kg)	C-Rate (Charge)	C-Rate (Discharge)	cycle life	Thermal Runaway
Lithium cobalt oxide (LCO)	3.6	3.0 - 4.2	240	0.7–1C, charges to 4.20V (most cells); 3h charge typical. Charge current above 1C shortens battery life.	1C; 2.50V cut off. Discharge current above 1C shortens battery life.	500-100	150
Lithium manganese oxide (LMO)	3.70 - 3.80	3.0 - 4.2	100-150	0.7–1C typical, 3C maximum, charges to 4.20V (most cells)	1C; 10C possible with some cells, 30C pulse (5s), 2.50V cut-off	300-700	250
Lithium Nickel Manganese Cobalt (NMC)	3.60 - 3.70	3.0 - 4.2	150-220	0.7–1C, charges to 4.20V, some go to 4.30V; 3h charge typical. Charge current above 1C shortens battery life.	1C; 2C possible on some cells; 2.50V cut-off	1000-2000	210
Lithium Iron Phosphate (LFP)	3.20 -3.30	2.5 - 3.65	90-120	1C typical charges to 3.65V; 3h charge time typical	1C, 25C on some cells; 40A pulse (2s); 2.50V cut-off (lower than 2V causes damage)	>=2000	270
Lithium Nickel Cobalt Aluminium Oxide (NCA)	3.6	3.0 - 4.2	200-260	0.7C, charges to 4.20V (most cells), 3h charge typical, fast charge possible with some cells	1C typical; 3.00V cut-off; high discharge rate shortens battery life	500	150
Lithium titanate oxide (LTO)	2.4	1.8 - 2.85	50-80	1C typical; 5C maximum, charges to 2.85V	10C possible, 30C 5s pulse; 1.80V cut-off on LCO/LTO	3000-7000	very safe

Datasheet for lithium-ion batteries: -

https://docs.google.com/spreadsheets/d/1GCRZ1H0uwD4i9UovzhPzkl49Yd9d1_0N/edit?usp=sharing&ouid=100530709306493318480&rtpof=true&sd=true