Week 1 Understanding Different Battery Chemistry

Lithium ion Batteries

It was not until the early 1970s that the first non-rechargeable lithium batteries became commercially available. Attempts to develop rechargeable lithium batteries followed in the 1980s but the endeavor failed because of instabilities in the metallic lithium used as anode material.

Lithium is the lightest of all metals, has the greatest electrochemical potential and provides the largest specific energy per weight. Rechargeable batteries with lithium metal on the anode (negative electrodes) could provide extraordinarily high energy densities, however, cycling produced unwanted dendrites on the anode that could penetrate the separator and cause an electrical short. The cell temperature would rise quickly and approaches the melting point of lithium, causing thermal runaway, also known as “venting with flame.” The inherent instability of lithium metal, especially during charging, shifted research to a non-metallic solution using lithium ions. Although lower in specific energy than lithium-metal, Li-ion is safe, provided cell manufacturers and battery packers follow safety measures in keeping voltage and currents to secure levels. In 1991, Sony commercialized the first Li-ion battery, and today this chemistry has become the most promising and fastest growing on the market. Meanwhile, research continues to develop a safe metallic lithium battery in the hope to make it safe.

In 1994, it cost more than $10 to manufacture Li-ion in the 18650* cylindrical cell delivering a capacity of 1,100mAh. In 2001, the price dropped to $2 and the capacity rose to 1,900mAh. Today, high energy-dense 18650 cells deliver over 3,000mAh and the costs have dropped further. Cost reduction, increase in specific energy and the absence of toxic material paved the road to make Li-ion the universally acceptable battery for portable application, first in the consumer industry and now increasingly also in heavy industry, including electric powertrains for vehicles.

Types of Lithium ion Battery:

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 illustrates the process.

A lithium-ion (Li-ion) battery is an advanced battery technology that uses lithium ions as a key component of its electrochemistry. During a discharge cycle, lithium atoms in the anode are ionized and separated from their electrons. The lithium ions move from the anode and pass through the electrolyte until they reach the cathode, where they recombine with their electrons and electrically neutralize. The lithium ions are small enough to be able to move through a micro-permeable separator between the anode and cathode. In part because of lithium’s small size (third only to hydrogen and helium), Li-ion batteries are capable of having a very high voltage and charge storage per unit mass and unit volume.

Li-ion batteries can use a number of different materials as electrodes. The most common combination is that of lithium cobalt oxide (cathode) and graphite (anode), which is most commonly found in portable electronic devices such as cellphones and laptops. Other cathode materials include lithium manganese oxide (used in hybrid electric and electric automobiles) and lithium iron phosphate. Li-ion batteries typically use ether (a class of organic compounds) as an electrolyte.

Question 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.

Solution 1: Table below shows a detailed information regarding Lithium-ion batteries:

LITHIUM ION CELLS	Material		Chemical reaction
	Cathode	Anode	Cathode	Anode	Overall Reaction
LCO	Cobalt oxide	graphite carbon	`〖Li〗_(1-x) 〖CoO〗_2+x〖Li〗^++xe^- □(→┴( ) ) 〖LiCoO〗_2`	`〖LiC〗_6 □(→┴( ) xLi+〖xe〗^-+C_6 )`	`C_6+〖LiCoO〗_2 □(↔┴( ) ) 〖Li〗_x C_6+〖〖Li〗_(1-x) CoO〗_2`
LMO	lithium-manganese spinel	Graphite	`MnO_2+〖Li〗^++ e^- □(→┴( ) MnOOLi)`	`Li□(→┴( ) 〖Li〗^++e^- )`	`MnO_2 □(+Li→┴( ) ) MnOOLi`
NCA	Lithium nickel cobalt aluminum oxide (9% Co)	Graphite	`〖NiCoAlO〗_2+ 〖Li〗^++e^- □(↔┴( ) 〖LiNiCoAlO〗_2 )`	`〖LiC〗_6 □(↔┴( ) ) C_6+〖Li〗^++e^-`	`〖LiC〗_6+〖NiCoAlO〗_2 □(↔┴( ) C_6+ 〖LiNiCoAlO〗_2 )`
NMC	Lithium nickel manganese cobalt oxide	Graphite	`〖NiMnCoO〗_2+ 〖Li〗^++e^- □(↔┴( ) 〖LiNiMnCoO〗_2 )`	`〖LiC〗_6 □(↔┴( ) C_6+ 〖Li〗^++e^- )`	`〖LiC〗_6+ 〖NiMnCoO〗_2 □(↔┴( ) C_6+ 〖LiNiMnCoO〗_2 )`
LFP	Iron Phosphate	Graphite	`〖FePO〗_4+〖Li〗^++e^- □(↔┴( ) ) 〖LiFePO〗_4`	`〖LiC〗_6 □(↔┴( ) C_6+ 〖Li〗^++e^- )`	`〖LiC〗_6+ 〖FePO〗_4 □(↔┴( ) C_6+ 〖LiFePO〗_4 )`
LTO	Manganese oxide	Titanate	`〖Mn_2 O〗_4+〖Li〗^++e^- □(↔┴( ) ) 〖Li〖Mn〗_2 O〗_4`	`〖Li〗_2 〖TiO〗_3 □(█(↔┴( ) 〖TiO〗_3+〖2Li〗^+@+〖2e〗^- ))`	`〖Li〗_2 〖TiO〗_3+ 〖2Mn_2 O〗_4 □(↔┴( ) 〖TiO〗_3+ 〖2Li〖Mn〗_2 O〗_4 )`

• 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 cathode has a layered structure. During discharge the lithium ions move from the anode to the cathode; on charge the flow is from cathode to anode.

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 (SEI), 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 Li-cobalt is losing favor to Li-manganese, but especially NMC and NCA because of the high cost of cobalt and improved performance by blending with other active cathode materials.

• Lithium magnesium 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 is 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. Figure 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 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.

The cathode crystalline formation of lithium manganese oxide has a three-dimensional framework structure that appears after initial formation. Spinel provides low resistance but has a more moderate specific energy than cobalt.

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). For example, the long-life version in the 18650 cell has a moderate capacity of only 1,100mAh; the high-capacity version is 1,500mAh.

Figure 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.

Although moderate in overall performance, newer designs of Li-manganese offer improvements in specific power, safety and life span.

• Lithium nickel-manganese-cobalt oxide:

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 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. Cobalt is expensive and in limited supply. Battery manufacturers are reducing the cobalt content with some compromise in performance. A successful combination is NCM532 with 5 parts nickel, 3 parts cobalt and 2 parts manganese.

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

NMC has good overall performance and excels on specific energy. This battery is the preferred candidate for the electric vehicle and has the lowest self-heating rate.

• Lithium Iron Phosphate:

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.

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 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.

Li-phosphate has excellent safety and long life span but moderate specific energy and elevated self-discharge.

• Lithium nickel cobalt aluminum oxide:

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. Figure 11 summarizes the six key characteristics. NCA is a further development of lithium nickel oxide; adding aluminum gives the chemistry greater stability.

High energy and power densities, as well as good life span, make NCA a candidate for EV powertrains. High cost and marginal safety are negatives.

• Lithium Titanate:

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

Li-titanate excels in safety, low-temperature performance and life span. Efforts are being made to improve the specific energy and lower cost.

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

Solution 2:

Specifications	Li-cobalt	Li-manganese	Li-phosphate	NMC
Voltage	3.60V	3.70V	3.30V	3.60/3.70V
Charge limit	4.20V	4.20V	3.60V	4.20V
Cycle life 2	500	500–1,000	1,000–2,000	1,000–2,000
Operating temperature	Average	Average	Good	Good
Specific energy	150–190Wh/kg	100–135Wh/kg	90–120Wh/kg	140Wh/kg
Specific power	1C	10C, 40C pulse	35C continuous	10C
Safety	Average. Requires protection circuit and cell balancing of multi cell pack. Requirements for small formats with 1 or 2 cells can be relaxed		Very good, needs cell balancing and V protection	Good, needs cell balancing and voltage protection
Thermal runaway 3	150°C (302°F)	250°C (482°F)	270°C (518°F)	210°C (410°F)
Cost	Raw material high	Material 30% less than cobalt	High	High
In use since	1994	2002	1999	2003
Researchers, manufacturers	Sony, Sanyo, FDK, Saft	NEC, Samsung, Hitachi	UT, QH, MIT A123, Valence	Sony, Sanyo, Nissan Motor
Notes/ Application	Very high specific energy, limited power; for cell phones, laptops	High power, average to high specific energy, power tools, medical, EVs	High power, average specific energy, higher self-discharge than other Li-ion	Very high specific energy, high power; tools, medical, EVs
Drawback	short life cycle, low thermal stability, and smaller load capabilities	Overheat, Leak if not handle properly	Lower energy density, Poor performance under low temperature, Low tap density	Slightly lower voltage than cobalt systems.