Types of Lithium-ion

The casual battery user may think there is only one lithium-ion battery. As there are many species of apple trees, so do also lithium-ion batteries vary and the difference lies mainly in the cathode materials. Innovative materials are also appearing in the anode to modify or replace graphite.

Scientists prefer to name batteries by their chemical name and the material used, and unless you are a chemist, these terms might get confusing. Table 1 offers clarity by listing these batteries by their full name, chemical definition, abbreviations and short form. (When appropriate, this essay will use the short form.) To complete the list of popular Li-ion batteries, the table also includes NCA and Li-titanate, two lesser-known members of the Li-ion family. 
 

Table 1: Reference names for Li-ion batteries.We willuse the short form when appropriate.

¹  Cathode material        ²  Anode material

To learn more about the unique characters and limitations of the six most common lithium-ion batteries, we use spider charts and look at the overall performance. We begin with Li-cobalt, the most commonly used battery for high-end consumer products, and then move to Li-manganese and Li- phosphate, batteries deployed in power tools, and finally address the newer players such as NME, NCA and Li-titanate. 

Lithium Cobalt Oxide(LiCoO₂)

Its high specific energy make Li-cobalt the popular choice for cell 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 and limited load capabilities (specific power). Figure 2 illustrates the structure.

Li-cobalt cannot be charged and discharged at a current higher than its 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 1920mA. [BU-402, What is C-rate?] The mandatory battery protection circuit limits the charge and discharge rate to a safe level of about 1C.

Figure 3 summarizes the performance of Li-cobalt in terms of specific energy,or capacity; specific power,or the ability to deliver high current; safety; performanceat hot and cold temperatures; life spanreflecting cycle life and longevity; and cost.The hexagonal spider web provides a quick and easy performance analysis of the battery characteristics.

Lithium Manganese Oxide (LiMn₂O₄)

Lithium insertion in manganese spinels was first published in the Materials Research Bulletin in 1983. In 1996, Moli Energy commercialized a Li-ion cell with lithium manganese oxide as a cathode material. The architecture forms a three-dimensional spinel structure that improves ion flow on the electrode, which results in lower internal resistance and improves 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 is key to 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 4 shows the crystalline formation of the cathode in a three-dimensional framework. This spinel structure, which is usually composed of diamond shapes connected into a lattice, appears after initial formation.

Li-manganese has a capacity that is roughly one-third lower compared to Li-cobalt but
the battery still offers about 50 percent more energy than nickel-based chemistries. 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 1,100mAh; the high-capacity version is 1,500mAh but has a reduced service life. Laptop manufacturers would likely choose the high-capacity version for maximum runtime; whereas the maker of cars with the electric powertrain would take the long-life version with high specific power and sacrifice on runtime.

Figure 5 shows the spider web of a typical Li-manganese battery. In this chart, all characteristics are marginal; however, newer designs have improved in terms of specific power, safety and life span.
 

Lithium Iron Phosphate(LiFePO₄)

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 enhanced safety, good thermal stability, tolerant to abuse, high current rating and long cycle life. Storing a fully charged battery has minimal impact on the life span. As trade-off, the lower voltage of 3.3V/cell reduces the specific energy to slightly less than Li-manganese. In addition, cold temperature reduces performance, and elevated storage temperature shortens the service life (better than lead acid, NiCd or NiMH). Li-phosphate has a higher self-discharge than other Li-ion batteries, which can cause balancing issues with aging. Figure 6 summarizes the attributes of Li-phosphate.

Lithium Nickel Manganese Cobalt Oxide (LiNiMnCoO₂)

Leading battery manufacturers focus on a cathode combination of nickel-manganese-cobalt (NMC). Similar to Li-manganese, these systems can also be tailored to high specific energy or high specific power, but not both. For example, NMC in an 18650 cell for consumer use can be tweaked to 2,250mAh, but the specific power is moderate. NMC in the same cell optimized for high specific power has a capacity of only 1,500mAh. A silicon-based anode will be able to go to 4,000mAh; however, the specific power and the cycle life may be compromised.

The secret of NMC lies in combining nickel and manganese. An analogy of this is table salt, in which the main ingredients of 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 low stability; manganese has the benefit of forming a spinel structure to achieve very low internal resistance but offers a low specific energy. Combining the metals brings out the best in each.

NMC is the battery of choice for power tools and powertrains for vehicles. The cathode combination of one-third nickel, one-third manganese and one-third cobalt offers a unique blend that also lowers raw material cost due to reduced cobalt content. Striking the right balance is important and manufacturers keep their recipes a well-guarded secret. Figure 7 demonstrates the characteristics of the NMC.
 

Lithium Nickel Cobalt Aluminum Oxide (LiNiCoAlO₂)

The Lithium Nickel Cobalt Aluminum Oxide battery, or NCA, is less commonly used in the consumer market; however, high specific energy and power densities, as well as a long life span, get the attention of the automotive industry. Less flattering are safety and cost. Figure 8 demonstrates the strong points against areas for further development.

Lithium Titanate (Li₄Ti₅O₁₂)

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. 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; the battery is safe, has excellent low-temperature discharge characteristics and obtains a capacity of 80 percent at –30°C (–22°F). At 65Wh/kg, the specific energy is low. Li-titanate charges to 2.80V/cell, and the end of discharge is 1.80V/cell. Figure 9 illustrates the characteristics of the Li-titanate battery.
 

Figure 10 compares the specific energy of lead, nickel- and lithium-based systems. While Li-cobalt is the clear winner by being able to store more capacity than other systems, this only applies to specific energy. In terms of specific power (load characteristics) and thermal stability, Li-manganese and Li-phosphate are superior. As we move towards electric powertrains, safety and cycle life will become more important than capacity.

Figure 10: Typical energy densities of lead, nickel- and lithium-based batteries
Lithium-cobalt enjoys the highest specific energy; however, manganese and phosphate are superior in terms of specific power and thermal stability.

Courtesy of Cadex

Comments

On April 19, 2011 at 1:45pm

Mike wrote:

Not correct: “on charge the flow is from anode to cathode”

On charge, Li+ ion flow is from cathode to anode. On discharge, flow is from anode to cathode.  This is easy to remember.  The battery is assembled in a discharged state, where only the cathode contains lithium (e.g. LiCoO2) and the anode is pure carbon containing no lithium.  Thus on charging, the Li+ flow must be from cathode to anode.

On July 10, 2011 at 4:08am

Ken Neal wrote:

I just want decent battery life for my Mesmerise Phone.

On July 21, 2011 at 9:59am

karl wrote:

Danke für die vergleichende Darstellung der verschiedenen Li-Elemente.
Die Parameter.Grafiken geben einen raschen Überblick.
MFG karl!

On February 1, 2012 at 12:47am

Victor wrote:

Not Correct “Not correct: “on charge the flow is from anode to cathode” “

Lithium ion flow is ALWAYS from anode to cathode, both charge and discharge.  You are confusing the negative and positive electrodes (which are the same on charge and discharge) with the sites of oxidation and reduction (which are respectively the anode and cathode and reverse on charge to discharge and vice / versa).  Battery engineers (me included) use this mistaken nomenclature for the electrodes as a historical artifact of primary (non-rechargeable) batteries which operate only in the discharge mode.

On March 14, 2012 at 2:08pm

Tom Blakley wrote:

Victor’s comments clear up the misunderstanding that Mike voiced concerning the phrase “on charge, the flow is from anode to cathode”, which is found in the first paragraph of the section describing Lithium Cobalt Oxide.
Another (more wordy) way of stating what Victor is teaching is to say that: On Discharge, the negative electrode is called the anode and the positive electrode is called the cathode. However, on Charge, the negative electrode is now called the cathode, while the positive electrode is called the anode.
We swap the names (functions) of the physical negative and positive electrodes depending on whether discharging or charging is occuring.
Another point: The negative electode is always labeled as the negative terminal (-) and the positive electrode is always the positive terminal (+).

On March 20, 2012 at 2:01am

Shivbraham Singh Rajawat wrote:

Very Good Material on Batteries

On March 28, 2012 at 12:44pm

Robert Bernal wrote:

MORE info for the LiFePo4 (lithium iron phosphate) battery… please!
They should not be grouped with the other li-ion chemistries in the “safety” table.
Anyways, they (and I guess, all li-ion types) need to be charged constant current until reaching charged voltage, then constant voltage just for maintaining. I hear that CC/CV is how the li-ion smart chargers do it.
What I want to know, is if it is alright to simply put a low drop out voltage regulator on a 6v SOLAR panel, set to the 3.5 or 3.6v (not 4.2v as with li-ion), would it be Ok? I visualize such that “it can’t get filled up past that point no matter how large the charging source is, as long as the input voltage remains below the recommended charge cut off”. I tried to search this many times but nobody’s doing it.
Bty, they do not have thermal issues and have about 4x the charge discharge cycles (about 2,000 complete) wheras li-ion is prone to thermal issues (catch fire) and only last a few hundred cycles.
For this reason, the LiFePO4 battery should be on the top of everybody’s list and that we all should DEMAND robotic factories that mass produce them cheap enough to be used in solar and electric car applications. The ONLY trade off (other than current high costs) is that it is not quite as energy dense as li-ion. There are enough raw materials in this planet’s crust to safely mine and base an entire global infrastructure on it, too!

On May 15, 2012 at 9:53am

ron davison wrote:

Robert,
Add a current limiting diode to your idea and whne the battery voltage is very low you will not draw more current than the battey will take without damage.

Caveat…at very very low voltages this current limit is very low and mAY NOT ALLOW FOR A FAST ENOUGH CHARGE if you protect current fore below cot-off chARGING.

a SERIES RESistor with a fet across it (in //) that closes when the battery voltage is above the cut-off voltage (without charge current). So the state of the switch needs to be set with the LDO off. So a timing circuit that turns off the LDo and checks voltage is needed this can be low duty cycle. Starting to not be a simple circuit…

Name (required): Email (required): Add A Comment: Remember my personal information?
Notify me of follow up comments?

Please enter the word you see in the image below:

Submit