Study the various types of Lithium ion batteries and their characteristics.

Aim: To study the various types of Lithium ion batteries and their characteristics.

Objectives:

1.

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

2.

Study the differences between each type of Li-ion batteries based on their characteristics.

Introduction:

Lithium-ion Battery:

As the name suggests, lithium ions (Li+) are involved in the reactions driving the battery. Both electrodes in a lithium-ion cell are made of materials which can intercalate or ‘absorb’ lithium ions. Intercalation is when charged ions of an element can be ‘held’ inside the structure of a host material without significantly disturbing it. In the case of a lithium-ion battery, the lithium ions are ‘tied’ to an electron within the structure of the anode. When the battery discharges, the intercalated lithium ions are released from the anode, and then travel through the electrolyte solution to be absorbed (intercalated) in 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 electrolyte in a lithium-ion cell is usually a solution of lithium salts in a mixture of solvents (like dimethyl carbonate or diethyl carbonate) devised to improve battery performance. Having lithium salts dissolved in the electrolyte means the solution contains lithium ions. This means that individual lithium ions don’t have to make the complete journey from the anode to the cathode to complete the circuit. As ions are kicked out from the anode, others that are already hanging out in the electrolyte, near the electrode surface, can easily be absorbed (intercalated) into the cathode. The reverse happens during recharging.

Being small and light, a lot of lithium can be stored (intercalated) in both the electrodes. This is what gives lithium-ion batteries their high energy density. For example, one lithium ion can be stored for every six carbon atoms in the graphite, and the more lithium ions there are to share the travelling from the anode to the cathode (and back again during recharge cycles), the more electrons there are to balance out their movement and provide the electric current.

The transfer of lithium ions between the electrodes occurs at a much higher voltage than in other battery types and, as they must be balanced by an equal amount of electrons, a single lithium-ion cell can produce a voltage of 3.6 volts or higher, depending on the cathode materials. A typical alkaline cell produces only around 1.5 volts. A standard lead-acid car battery needs six 2-volt cells stacked together to produce 12 volts.

Because of their high energy density, and their comparative lightness, stacking lots of lithium-ion cells together in the one place produces a battery pack far lighter and more compact than stacks made of other battery types. If we stack enough lithium-ion cells together, we can reach a pretty high voltage, such as that required to run an electric car. Sure, all our cars have batteries already, but they’re just to get a petrol or diesel engine going, then the fuel does all the work. An electric car’s battery is its entire energy source, and what gives it the grunt to get up a steep hill. So, it typically will have 96 volts or even more which, even with the high voltage of a lithium-ion cell, requires quite a few cells stacked together.

The anode is usually graphite. However, the repeated insertion of lithium ions into the standard graphite structure in a typical lithium-ion battery eventually breaks apart the graphite. This reduces the battery’s performance and the graphite anode will eventually break down, and the battery will stop working.

In terms of the material used for the cathode, there are quite a few variations—generally made of a combination of lithium, oxygen, and some kind of metal.

Further depending upon the technology and modification as per materials used in Li-ion batteries, these are further categorised as:

1. Lithium-nickle-cobalt-aluminium. (NCA)
2. Lithium-nickle-manganese-cobalt. (NMC)
3. Lithium-manganese spinel. (LMO)
4. Lithium titanate. (LTO)
5. Lithium-iron-phosphate. (LFP)

I. Lithium Nickle Cobalt Aluminium 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.

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.

II. Lithium Nickle 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 voltages.

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.

III. 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.

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.

Most Li-manganese batteries blend with lithium nickel manganese cobalt oxide (NMC) to improve the specific energy and prolong the life span. This combination brings out the best in each system, and the LMO (NMC) is chosen for most electric vehicles, such as the Nissan Leaf, Chevy Volt and BMW i3. The LMO part of the battery, which can be about 30 percent, provides high current boost on acceleration; the NMC part gives the long driving range.

Li-ion research gravitates heavily towards combining Li-manganese with cobalt, nickel, manganese and/or aluminum as active cathode material. In some architecture, a small amount of silicon is added to the anode. This provides a 25 percent capacity boost; however, the gain is commonly connected with a shorter cycle life as silicon grows and shrinks with charge and discharge, causing mechanical stress.

These three active metals, as well as the silicon enhancement can conveniently be chosen to enhance the specific energy (capacity), specific power (load capability) or longevity. While consumer batteries go for high capacity, industrial applications require battery systems that have good loading capabilities, deliver a long life and provide safe and dependable service.

IV. 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.

V. Lithium Iron Phosohate (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 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.

Problem Statement:

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.

2.

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

Solution:

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.

In Li-ion cells / Rechargeable cells, instead of true oxidation and reduction, transport of Lithium ion from one electrode to another electrode through electrolyte by the transport of electron through external circuit.

Therefore, following reactions takes place:

At Positive electrode:

At Negative electrode:

Overall Reaction:

Now we will study thw Anodic and cathodic reactions for the following Li-ion cells:

I. Lithium-nickle-cobalt-aluminium. (NCA)

Lithium ions are positive ions.

During charging phase of the battery positive ions travels from positive electrode (Cathode) towards negative electrode (Anode).

Reaction at anode is called as anodic reaction which takes place while charging of the battery.

For anode of material carbon graphite and cathode of material Lithium-nickle-cobalt-aluminium anodic reaction is given as:

`LiNiCoAl+C_6 rarr Li_(1-x)NiCoAl+Li_xC_6`

During charging of the battery lithium from LiNiCoAl will lose it's ions one by one which will be accumulated by the anode of C6.

If lithium looses x amount of it's ions then it can be written as Li(1-x)NiCoAl.

And if graphite accepts x amount of Lithium ions then it can be written as Li(x)C6.

Whereas during discharge phase positive ions travels from negative electrode (Anode) towards positive electrode (Cathode).

Reaction at cathode is called as cathodic reaction which takes place while discharging of the battery.

For cathode of material carbon graphite and cathode of material Lithium-nickle-cobalt-aluminium cathodic reaction is given as:

`Li_(1-x)NiCoAl+Li_xC_6 rarr Li_(1-x+y)NiCoAl+Li_(x-y)C_6`

If lithium from side anode looses y amount of it's ions then it can be written as Li(x-y)C6.

And if lithium from cathode accepts y amount of it's ions then it can be written as Li(1-x+y)NiCoAl.

II. Lithium-nickle-manganese-cobalt. (NMC)

Lithium ions are positive ions.

During charging phase of the battery positive ions travels from positive electrode (Cathode) towards negative electrode (Anode).

Reaction at anode is called as anodic reaction which takes place while charging of the battery.

For anode of material carbon graphite and cathode of material Lithium-nickle-manganese-cobalt anodic reaction is given as:

`LiNiMnCoO_2+C_6rarrLi_(1-x)NiMnCoO_2+Li_xC_6`

During charging of the battery lithium from LiNiMnCoO2 will lose it's ions one by one which will be accumulated by the anode of C6.

If lithium looses x amount of it's ions then it can be written as Li(1-x)NiMnCoO2.

And if graphite accepts x amount of Lithium ions then it can be written as Li(x)C6.

Whereas during discharge phase positive ions travels from negative electrode (Anode) towards positive electrode (Cathode).

Reaction at cathode is called as cathodic reaction which takes place while discharging of the battery.

For cathode of material carbon graphite and cathode of material Lithium-nickle-manganese-cobalt cathodic reaction is given as:

`Li_(1-x)NiMnCoO_2+Li_xC_6rarrLi_(1-x+y)NiMnCoO_2+Li_x-yC_6`

If lithium from side anode looses y amount of it's ions then it can be written as Li(x-y)C6.

And if lithium from cathode accepts y amount of it's ions then it can be written as Li(1-x+y)NiMnCoO2.

III. Lithium-manganese spinel. (LMO)

Lithium ions are positive ions.

During charging phase of the battery positive ions travels from positive electrode (Cathode) towards negative electrode (Anode).

Reaction at anode is called as anodic reaction which takes place while charging of the battery.

For anode of material carbon graphite and cathode of material Lithium-manganese-Oxide anodic reaction is given as:

`LiMnO_4+C_6rarrLi_(1-x)MnO_4+Li_xC_6`

During charging of the battery lithium from LiMnO4 will lose it's ions one by one which will be accumulated by the anode of C6.

If lithium looses x amount of it's ions then it can be written as Li(1-x)MnO4.

And if graphite accepts x amount of Lithium ions then it can be written as Li(x)C6.

Whereas during discharge phase positive ions travels from negative electrode (Anode) towards positive electrode (Cathode).

Reaction at cathode is called as cathodic reaction which takes place while discharging of the battery.

For cathode of material carbon graphite and cathode of material Lithium-manganese-Oxide cathodic reaction is given as:

`Li_(1-x)MnO_4+Li_xC_6rarrLi_(1-x+y)MnO_4+Li_(x-y)C_6`

If lithium from side anode looses y amount of it's ions then it can be written as Li(x-y)C6.

And if lithium from cathode accepts y amount of it's ions then it can be written as Li(1-x+y)MnO4.

IV. Lithium titanate. (LTO)

Lithium ions are positive ions.

During charging phase of the battery positive ions travels from positive electrode (Cathode) towards negative electrode (Anode).

Reaction at anode is called as anodic reaction which takes place while charging of the battery.

For anode of material carbon graphite and cathode of material Lithium-Titanate-Oxide anodic reaction is given as:

`LiTiO_3+C_6rarrLi_(1-x)TiO_3+Li_xC_6`

During charging of the battery lithium from LiTiO3 will lose it's ions one by one which will be accumulated by the anode of C6.

If lithium looses x amount of it's ions then it can be written as Li(1-x)TiO3.

And if graphite accepts x amount of Lithium ions then it can be written as Li(x)C6.

Whereas during discharge phase positive ions travels from negative electrode (Anode) towards positive electrode (Cathode).

Reaction at cathode is called as cathodic reaction which takes place while discharging of the battery.

For cathode of material carbon graphite and cathode of material Lithium-Titanate-Oxide cathodic reaction is given as:

`Li_(1-x)TiO_3+Li_xC_6rarrLi_(1-x+y)TiO_3+Li_(x-y)C_6`

If lithium from side anode looses y amount of it's ions then it can be written as Li(x-y)C6.

And if lithium from cathode accepts y amount of it's ions then it can be written as Li(1-x+y)TiO3.

V. Lithium-iron-phosphate. (LFP)

Lithium ions are positive ions.

During charging phase of the battery positive ions travels from positive electrode (Cathode) towards negative electrode (Anode).

Reaction at anode is called as anodic reaction which takes place while charging of the battery.

For anode of material carbon graphite and cathode of material Lithium-iron-phosphate anodic reaction is given as:

`LiFePO_4+C_6rarrLi_(1-x)FePO_4+Li_xC_6`

During charging of the battery lithium from LiFePO4 will lose it's ions one by one which will be accumulated by the anode of C6.

If lithium looses x amount of it's ions then it can be written as Li(1-x)FePO4.

And if graphite accepts x amount of Lithium ions then it can be written as Li(x)C6.

Whereas during discharge phase positive ions travels from negative electrode (Anode) towards positive electrode (Cathode).

Reaction at cathode is called as cathodic reaction which takes place while discharging of the battery.

For cathode of material carbon graphite and cathode of material Lithium-iron-phosphate cathodic reaction is given as:

`Li_(1-x)FePO_4+Li_xC_6rarrLi_(1-x+y)FePO_4+Li_(x-y)C_6`

If lithium from side anode looses y amount of it's ions then it can be written as Li(x-y)C6.

And if lithium from cathode accepts y amount of it's ions then it can be written as Li(1-x+y)FePO4.

Type of Li-ion cell	Anode Material	Cathode Material	Anodic Reaction	Cathodic Reaction
Lithium-Nickle-Cobalt-Aluminium	Carbon graphite	Lithium-Nickle-Cobalt-Aluminium oxide	`LiNiCoAl+C_6 rarr Li_(1-x)NiCoAl+Li_xC_6`	`Li_(1-x)NiCoAl+Li_xC_6 rarr Li_(1-x+y)NiCoAl+Li_(x-y)C_6`
Lithium-Nickle-Manganese-Cobalt	Carbon graphite	Lithium-Nickle-Manganese-Cobalt oxide	`LiNiMnCoO_2+C_6rarrLi_(1-x)NiMnCoO_2+Li_xC_6`	`Li_(1-x)NiMnCoO_2+Li_xC_6rarrLi_(1-x+y)NiMnCoO_2+Li_x-yC_6`
Lithium-Manganese-Spinel	Carbon graphite	Lithium-Manganese-oxide	`LiMnO_4+C_6rarrLi_(1-x)MnO_4+Li_xC_6`	`Li_(1-x)MnO_4+Li_xC_6rarrLi_(1-x+y)MnO_4+Li_(x-y)C_6`
Lithium Titanate	Carbon graphite	Lithium Titanate	`LiTiO_3+C_6rarrLi_(1-x)TiO_3+Li_xC_6`	`Li_(1-x)TiO_3+Li_xC_6rarrLi_(1-x+y)TiO_3+Li_(x-y)C_6`
Lithium-Iron-Phosphate	Carbon graphite	Lithium-Iron-Phosphate	`LiFePO_4+C_6rarrLi_(1-x)FePO_4+Li_xC_6`	`Li_(1-x)FePO_4+Li_xC_6rarrLi_(1-x+y)FePO_4+Li_(x-y)C_6`

Table 01: Different types of Li-ion cells, their anodic and cathodic materials and their reactions .

2.

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

Now that we have an understanding of the major battery characteristics, we will use them as the basis for the comparison of our six types of lithium-ion batteries. The characteristics are rated as either high, moderate, or low. The table below provides a simple comparison of the six lithium-ion battery types.

It is important to note that the six types of lithium-ion batteries are compared relative to one another.

Lithium ion Battery Types	Specific power	Specific energy	Safety	Lifespan	Cost	Performance
Lithium Cobalt Oxide	Low	High	Low	Low	Low	Moderate
Lithium Manganese Oxide	Moderate	Moderate	Moderate	Low	Low	Low
Lithium Nickle Manganese Cobalt Oxide	Moderate	High	Moderate	Moderate	Low	Moderate
Lithium Iron Phosphate	High	Low	High	High	Low	Moderate
Lithium Nickle Cobalt Aluminium	Moderate	High	Low	Moderate	Moderate	Moderate
Lithium Titanate	Moderate	Low	High	High	High	High

Table 02: Comparision of Characteristics of different types of Li-ion batteries.

Conclusion:

In this study we learnt the different battery technologies and their characteristics. We also learnt the chemical reactions of the different batteries at their anode and cathode.