#1 Understanding Different Battery Chemistry

1)Objective:

To 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

Fundamental Science in Li-ion Battery Materials
Among the rechargeable batteries, Li-ion batteries have dominated the field of advanced power sources due to their high gravimetric and volumetric energy density. The most common Li-ion battery applications in the market are for portable electronics, power tools, and transportation.

MAIN COMPONENTS OF LITHIUM ION BATTERY

• Anode

The electrode at which the oxidation occurs is called the anode. The charge on the anode is negative.

Characteristics

• Efficiency as a reducing agent.
• High coulombic output (Ah/g)
• Good conductivity
• Stability

Example

graphite, Metals

• Cathode

The electrode at which reduction occurs is termed as the cathode. The charge on the cathode is positive.

Characteristics

• Good oxidizing agent.
• Must stable when contact with electrolyte.
• To achieve high performance.
• Should be conductive.

Example

Metallic oxides

• Electrolyte

The ionic conductor which provides the medium for transfer of charge, as ions, inside the cell between the anode and cathode is called as an electrolyte.

Characteristics

• Good ionic conductivity
• Low viscosity and high dielectric constant
• Non reactivity with electrode materials

Example

Sulphuric acid, LiPF₆, in 1:1 (Ethylene carbonate and diethylene carbonate)

• Separator

An ion permeable and electronically nonconductive, spacer or material which prevents electronic contact between electrodes of opposite polarity in the same cell.

Characteristics

• Chemical stability
• Low thickness
• Mechanical strength
• High porosity & permeability

Examples

Polypropylene, Glass, Non-Woven glass.

• Current collector

An inert member of high electrical conductivity used to conduct current from or to an electrode during discharge or charge.

Characteristics

• Excellent bulk electrical conductivity
• Minimal thickness / weight
• Excellent surface conductivity

Examples

Aluminium foil, Copper foil and Nickel mesh.

OPERATING PRINCIPLE OF CELL

• Discharge

When the cell is connected to an external load, electrons flow from the anode, which is oxidized, through the external load to the cathode, where the electrons are accepted and the cathode material is reduced. The electric circuit is completed in the electrolyte by the flow of anions (negative ions) and cations (positive ions) to the anode and cathode, respectively.

• Charge

During the recharge of a rechargeable or storage cell, the current flow is reversed and oxidation takes place at the positive electrode and reduction at the negative electrode. As the anode is, by definition, the electrode at which oxidation occurs and the cathode is the electrode where reduction takes place. Thus, the positive electrode is the anode and the negative electrode is the cathode.

A lithium-ion battery starts its life in a state of full discharge: all its lithium ions are intercalated within the cathode and its chemistry does not yet have the ability to produce any electricity. Before you can use the battery, you need to charge it. As the battery is charged, an oxidation reaction occurs at the cathode, meaning that it loses some negatively charged electrons. To maintain the charge balance in the cathode, an equal number of some of the positively charged intercalated lithium ions are dissolved into the electrolyte solution. These travel over to the anode, where they are intercalated within the graphite. This intercalation reaction also deposits electrons into the graphite anode, to ‘tie’ up the lithium ion.

During discharge, the lithium ions are de-intercalated from the anode and travel back through the electrolyte to the cathode. This also releases the electrons that were tying them to the anode, and these flow through an external wire, providing the electric current that we used to do work. It’s the connection of the external wire that enables the reaction to proceed—when the electrons are free to travel, so are the positively charged lithium ions that will balance the movement of their negative charge.

When the cathode becomes full of lithium ions, the reaction stops and the battery is flat. Then we recharge our lithium-ion batteries again, and the external electric charge that we apply pushes the lithium ions back into the anode from the cathode.

The Prospective cathode materials for lithium ion batteries

• LCO - Lithium Cobalt oxide(LicoO2)
• LMO - Lithium Manganese oxide(LiMn2O4)
• NCA- Lithium Nickel Cobalt Aluminium Oxide (LiNiCoAlO2)
• NMC- Lithium Nickel Manganese Cobalt Oxide (LiNiMnCoO2)
• LFP- Lithium Iron Phosphate (LiFePO4)
• LTO- Lithium Titanate

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).

The drawback of Li-cobalt is a relatively short life span, low thermal stability and limited load capabilities (specific power). Like other cobalt-blended Li-ion, Li-cobalt has a graphite anode that limits the cycle life by a changing solid electrolyte interface, thickening on the anode and lithium plating while fast charging and charging at low temperature. Newer systems include nickel, manganese and/or aluminum to improve longevity, loading capabilities and cost.

Li-cobalt should not be charged and discharged at a current higher than its C-rating. This means that an 18650 cell with 2,400mAh can only be charged and discharged at 2,400mA. Forcing a fast charge or applying a load higher than 2,400mA causes overheating and undue stress. For optimal fast charge, the manufacturer recommends a C-rate of 0.8C or about 2,000mA. 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 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.

Low internal cell resistance enables fast charging and high-current discharging. In an 18650 package, Li-manganese can be discharged at currents of 20–30A with moderate heat buildup. It is also possible to apply one-second load pulses of up to 50A. A continuous high load at this current would cause heat buildup and the cell temperature cannot exceed 80°C (176°F). Li-manganese is used for power tools, medical instruments, as well as hybrid and electric vehicles.

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. 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.

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. There is a move towards NMC-blended Li-ion as the system can be built economically and it achieves a good performance. The three active materials of nickel, manganese and cobalt can easily be blended to suit a wide range of applications for automotive and energy storage systems (EES) that need frequent cycling. The NMC family is growing in its diversity.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 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 Iron Phosphate(LiFePO₄) — LFP

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. Figure 9 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 sulpation 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.

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 (–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. Typical uses are electric powertrains, UPS and solar-powered street lighting.

2)Objective:

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

Types of lithium ion battery	Lithium Cobalt Oxide: LiCoO2 cathode (~60% Co), graphite anode Short form: LCO or Li-cobalt. Since 1991	Lithium Manganese Oxide: LiMn2O4 cathode. graphite anode Short form: LMO or Li-manganese (spinel structure) Since 1996	Lithium Nickel Manganese Cobalt Oxide: LiNiMnCoO2. cathode, graphite anode Short form: NMC (NCM, CMN, CNM, MNC, MCN similar with different metal combinations) Since 2008	Lithium Nickel Cobalt Aluminum Oxide: LiNiCoAlO2 cathode (~9% Co), graphite anode Short form: NCA or Li-aluminum. Since 1999	Lithium Iron Phosphate: LiFePO4 cathode, graphite anode Short form: LFP or Li-phosphate Since 1996	Lithium Titanate: Cathode can be lithium manganese oxide or NMC; Li2TiO3 (titanate) anode Short form: LTO or Li-titanate Commercially available since about 2008
Voltages	3.60V nominal; typical operating range 3.0–4.2V/cell	3.70V (3.80V) nominal; typical operating range 3.0–4.2V/cell	3.60V, 3.70V nominal; typical operating range 3.0–4.2V/cell, or higher	3.60V nominal; typical operating range 3.0–4.2V/cell	3.20, 3.30V nominal; typical operating range 2.5–3.65V/cell	2.40V nominal; typical operating range 1.8–2.85V/cell
Specific energy (capacity)	150–200Wh/kg. Specialty cells provide up to 240Wh/kg.	100–150Wh/kg	150–220Wh/kg	200-260Wh/kg; 300Wh/kg predictable	90–120Wh/kg	50–80Wh/kg
Charge (C-rate)	0.7–1C, charges to 4.20V (most cells); 3h charge typical. Charge current above 1C shortens battery life.	0.7–1C typical, 3C maximum, charges to 4.20V (most cells)	0.7–1C, charges to 4.20V, some go to 4.30V; 3h charge typical. Charge current above 1C shortens battery life.	0.7C, charges to 4.20V (most cells), 3h charge typical, fast charge possible with some cells	1C typical, charges to 3.65V; 3h charge time typical	1C typical; 5C maximum, charges to 2.85V
Discharge (C-rate)	1C; 2.50V cut off. Discharge current above 1C shortens battery life.	1C; 10C possible with some cells, 30C pulse (5s), 2.50V cut-off	1C; 2C possible on some cells; 2.50V cut-off	1C typical; 3.00V cut-off; high discharge rate shortens battery life	1C, 25C on some cells; 40A pulse (2s); 2.50V cut-off (lower that 2V causes damage)	10C possible, 30C 5s pulse; 1.80V cut-off on LCO/LTO
Cycle life	500–1000, related to depth of discharge, load, temperature	300–700 (related to depth of discharge, temperature)	1000–2000 (related to depth of discharge, temperature)	500 (related to depth of discharge, temperature)	2000 and higher (related to depth of discharge, temperature)	3,000–7,000
Thermal runaway	150°C (302°F). Full charge promotes thermal runaway	250°C (482°F) typical. High charge promotes thermal runaway	210°C (410°F) typical. High charge promotes thermal runaway	150°C (302°F) typical, High charge promotes thermal runaway	270°C (518°F) Very safe battery even if fully charged	One of safest Li-ion batteries
Applications	Mobile phones, tablets, laptops, cameras	Power tools, medical devices, electric powertrains	E-bikes, medical devices, EVs, industrial	Medical devices, industrial, electric powertrain (Tesla)	Portable and stationary needing high load currents and endurance	UPS, electric powertrain (Mitsubishi i-MiEV, Honda Fit EV),
Comments	Very high specific energy, limited specific power. Cobalt is expensive. Serves as Energy Cell. Market share has stabilized.	High power but less capacity; safer than Li-cobalt; commonly mixed with NMC to improve performance.	Provides high capacity and high power. Serves as Hybrid Cell. Favorite chemistry for many uses; market share is increasing.	Shares similarities with Li-cobalt. Serves as Energy Cell.	Very flat voltage discharge curve but low capacity. One of safest	solar-powered street lighting
2019 update:	Early version; no longer relevant.	Less relevant now; limited growth potential.	Leading system; dominant cathode chemistry.	Mainly used by Panasonic and Tesla; growth potential.	Li-ions. Used for special markets. Elevated self-discharge. Used primarily for energy storage, moderate growth.	Long life, fast charge, wide temperature range but low specific energy and expensive. Among safest Li-ion batteries.Ability to ultra-fast charge; high cost limits to special application.