Icon-YouTube(250x93px).png
Icon-LinkedIn(250x93px).png

© 2017 Ian Watts

Battery Chemistry

I'm sure we've all heard of battery horror stories; from packs that explode, packs that catch fire when charging, packs that just stop working after a few charges and batteries that simply do not live up to expectations.

Indeed, above and beyond proper manufacturing practices and quality control, it is predominantly battery chemistry that impacts battery safety. By 'chemistry', I mean the metals and electrolytes that make up a battery giving it its specific characteristics. Here are a few chemistry types :

          Lithium manganese oxide                         Lithium nickel manganese cobalt

          Lithium nickel cobalt aluminum oxide          Lithium nickel cobalt oxide

          Lithium cobalt oxide                                Lithium iron phosphate

          Lithium Titanic Oxide

I guess, I should point out that I will use the terms 'battery' and 'cell' interchangeably - which is generally technically incorrect but I'm sure we'll all get the idea !. In fact, a battery is most-often a combination of individual cells, electrically connected in order to provide the required battery Voltage, Capacity and Power output. For example a 12V car battery is generally made up of 6 cells, in series, each cell having a nominal voltage of 2V (6 x 2V = 12V). Conversely, a flashlight may only have one cell as its battery, say, a 1.5V AA cell, in which case, it would be technically correct to use 'cell' or 'battery' interchangeably.

So, just for some clarity / background, what exactly is an 18650 Li-ion battery ?

The '18650' refers to the cell's format, In this particular case, cylindrical, anode (+ve) at one end and cathode (-ve) at the other. Typically an 18650 cell is around 18mm in diameter and 65mm long (whereas a more 'typical' AA cell is around 14mm diameter and 50mm long - sometimes referred to as a 14500 cell).

Generally, an 18650 cell will weigh around 47 - 48gms.

The 'Li-...' refers to a family of batteries that use a Lithium electrolyte and various chemicals for the anode and cathode.

The '...-ion' refers to the ions (molecules with a net electric charge - generally due to the loss (discharge) or gain (charge) of one or more electrons) that move between the electrodes. Li-ion batteries do NOT suffer from memory effects (unlike Ni-Cd or NiMh batteries).

More generally, a battery consists of three parts: the cathode, the anode, and the electrolyte.

Lithium-ion batteries generate current through the movement of ions and electrons. When the battery discharges, the lithium ions move through an electrolyte from one electrode (the anode) to another (the cathode).

The lithium ions collecting on the cathode add positive charge, which attracts negatively charged electrons.

As the electrons exit the anode, move through an external circuit to the ions on the cathode, they create the current that powers the device (flashlight, motor...). During charging, this process occurs in reverse.

Typically a cathode that has a high energy density is required - one that can absorb and expel as many lithium ions as possible in the smallest volume (size) possible in the fastest time possible without generating dangerous, damaging and wasteful heat.

 

The anode of all 18650 li-ion batteries is basically the same: carbon/silicon and graphite.

The cathode, however, is where batteries differ; different batteries use different chemistry in the make-up of the cathode. The cathode plays such a critical role because it is largely responsible for enabling the flow of electrons. It is the cathode that gives each model its unique characteristics and determines a battery's specific characteristics such as :

energy content (capacity),

power output,

safety and

life span.

Some of the trade-offs with 'cathode chemistry' are between these 4 characteristics. For instance, ICR (cobalt-based) chemistries are both high power and high energy but not particularly safe. IMR (manganese-based) chemistries are safer, but have lower energy capacity/capacity, whilst adding nickel to manganese (IMR) gives it a higher specific energy, increasing , size-for-size the energy content/capacity but not to ICR levels...

So... it's important to note that by changing the chemistry of a cell, we can change the rate at which the cell is 'happy' to charge at or the rate at which it is 'happy' to discharge at, or the temperature range it is 'happy' to operate within. We can also change the cell weight and the cell size, cell longevity and cell safety characteristics and, therefore, the necessary precautions associated therewith...

Naturally, when thinking of batteries (and the cells within them) we all want the highest capacity and highest energy density, the longest life-span (number of recharges), the minimum of self-discharge, the coolest running, the highest power output, the fastest charge rate, the widest temperature range over which the battery can operate and the safest battery we can possibly have. All at the lowest cost of course !

Unfortunately, ALL of these things are not achieved with the same chemistry. By changing the battery chemistry, we can change the characteristics - from max discharge rate to fastest charge rate, from weight to safety and from expensive to cheap(er)..

Anyways, when I was starting out, I looked far and wide for stuff that would explain the differences and the pros 'n' the cons of each chemistry type in a simple kind of way... cells aren't cheap and I wanted to make sure I weighed up my options before parting with the the best part of +500€ for a number of 18650 cells.

In the end, I cobbled a load of stuff together from sites such as BatteryBro, BatterySpace, BatteryUniverstity, CobaltInstitute, Google, LG, Panasonic, ResearchGate, Samsung, Wikipedia and YouTube. I then (as best I could) researched any conflicting statements (there were quite a few) and created the following notes for myself...

Here is a (non-exhaustive) list of some of the the major/ more common 18650 battery chemistries and their abbreviations:

Lithium manganese oxide : LiMn2O4 : IMR / LMO : Li-manganese

Lithium nickel manganese cobalt : LiNiMnCoO2 : INR / NMC : --- Li-Manganese Cobalt

Lithium nickel cobalt aluminum oxide : LiNiCoAlO2 : --- : NCA : Li-Aluminum

Lithium nickel cobalt oxide : LiNiCoO2 : --- : NCO : --- Li-Nickel Cobalt

Lithium cobalt oxide : LiCoO2 : ICR / LCO : Li-Cobalt

Lithium iron phosphate : LiFePO4 : IFR / LFP : Li-Ferrous Phosphate

Lithium Titanic Oxide : (Li4Ti5O12 : LTO : Lithium Titanate

One more thing I feel I should mention before looking at the advantages and disadvantages of battery chemistries​; I mentioned, above, that battery chemistry affects, amongst other things, a cell's charge and discharge rate. Both the charge and discharge rate are measured as a multiplier of 'C', e.g. 1C, 3C, 10C etc. The point here is that 'C' refers to the cell's quoted Capacity in mAHr, i.e.:

the Samsung ICR-18650-26F is a Lithium Cobalt Oxide cell with a capacity, or 'C', of 2600mAHr

          it's max. standard charge rate is 0.7 - 1C (1830mAHr - 2600mAHr) with a 3Hr charge time

          it's max. stated continuous discharge rate is 2C (5200mAHr)

the Sanyo/PanasonicNCR-18650-GA is a Lithium Ferrous Phosphate cell with a capacity, or 'C', of  3350mAHr

          it's max. standard charge rate is 0.44 - 0.5C (1475mAHr - 1675mAHr) with a 4Hr - 4.5Hr full charge time

          it's max. stated continuous discharge rate is 3C (10A)

Now that we know what a Li-Ion battery / cell is and that various chemistries are employed to give various types of Li-Ion cells with specific feature-sets, here is a more in-depth look at some of the associated advantages and disadvantages of each. First, let's understand what exactly these names mean...

(the chemical formulas below refer to the battery's cathode).

IMR - LMO - Lithium Manganese Oxide

Cathode = Lithium Manganese Oxide

Anode = Graphite carbon

LMO forms the cathode which results in lower internal resistance and, therefore, high current handling (charge & discharge) capability and high thermal stability = enhanced safety. Life cycle and shelf life are limited compared to other Lithium cells. Many of the high-drain batteries used in vaping, flashlights, newer (2017) power tools and hybrid batteries have IMR chemistry. The reason is that manganese is awesome. It allows batteries to discharge at a high current while maintaining low temperatures. This means that it's safer than many of the older ICR batteries. Most IMR batteries don't require extensive built-in protective circuitry. 

 

Cell V : 3V7 (nom)

Charging : 'Standard' constant current / constant voltage

Charge : 0.7C - 1C (typ), 3C (Max)

Cut-Off V : 2V5 - 4V2

Cycles / Durability : 300 - 700 cycles

Discharge : 1C - 10C (some cells), 30C (2.5s pulse)

Energy Density : 100 - 150 WH/Kg

Safety : safer than LiCo

Typical uses : medical equipment, power tools, e-bikes, laptops and EVs.

 

However, most modern high-drain batteries add nickel to the mix...

 

INR - NMC - Lithium Nickel Manganese Cobalt

Cathode = Nickel, manganese, cobalt (60,20,20 mix%)

Anode = graphite carbon

The reigning champ of the 18650 vaping world. This cathode chemistry adds nickel and cobalt to the IMR chemistry above, making it a "hybrid" chemistry. It combines the safety and low resistance of manganese and the high energy of nickel but also reduces the number of cycles / recharges to around 200 before noticeable degradation (which then flattens out considerably, quite soon thereafter).

The resulting battery chemistry provides a reasonably high capacity and a high discharge current. Importantly for vapers, the chemistry is very stable, meaning that expensive built-in protective circuits are unnecessary.

There is extensive innovation within this chemistry as well. Sony, Samsung, and LG are all developing next-gen INR batteries with different ratios of manganese, nickel, and cobalt.

Popular INR 18650 models:

  • Samsung 25R

  • Sony VTC4

  • Sony VTC5

  • LG HE2

 

Cell V : 3V7 (nom)

Charging : 'Standard' constant current / constant voltage

Charge : 0.7C - 1C (typ), >1C reduces life

Cut-Off V : 2V5 - 4V2

Cycles / Durability : 1,000 - 2,000 cycles

Discharge : 1C - 2C (some cells)

Energy Density : 150 - 220 WH/Kg

Safety :

Typical uses : Power tools & EVs

 

NCA - Li-Nickel Cobalt Aluminum

Cathode = Li-Nickel Cobalt Aluminum

Anode = graphite carbon

This chemistry is similar to INR, but without the benefit of manganese. These batteries tend to support lower discharge currents, but make up for it with great capacities and cycle life. They also tend to be more resistant to physical shock, making them good options for e-bikes. Tesla uses them for its awesome electric cars.

Popular NCA models:

  • Panasonic 18650PF

  • Panasonic 18650B

  • LG MH1

 

Cell V : 3V6 (nom)

Charging : 'Standard' constant current / constant voltage

Charge : 0.7C (typ), >1C reduces life

Cut-Off V : 3V0 - 4V2

Cycles / Durability : circa 500 cycles

Discharge : 1C

Energy Density : 200 - 260 WH/Kg

Safety :

Typical uses : EVs, grid energy storage

 

NCO - Lithium Nickel Cobalt Oxide

Cathode = Lithium Nickel Cobalt Oxide

Anode = graphite carbon

This is a very rare chemistry. The only model found is the Samsung 29E, which has 2900 mAh and a max continuous discharge current of 8.2A.

 

ICR - LCO - Li-thium Cobalt Oxide

Cathode = Cobalt oxide

Anode = graphite carbon

The big boys! This chemistry delivers the highest specific energy of any 18650 battery chemistry - but at a cost. They are the most dangerous li-ion 18650 batteries out there. This is also a problem for high-current discharging, as they can't be safely discharged at a higher current than their mAh rating. Additional (built-in / added-on) protective circuitry is a must - which most often should be undertaken by a third-party company - like Trustfire. 

 

Cell V : 3V6 (nom)

Charging : 'Standard' constant current / constant voltage

Charge : 0.7C - 1C (typ), >1C reduces life

Cut-Off V : 2.5 - 4.2V

Cycles / Durability : 500 - 1,000 cycles

Discharge : 1C, >1C reduces life

Energy Density : 150 - 240 WH/Kg

Safety : Poor, low thermal stability, limited load capability, cobalt is expensive

Typical uses : Laptops

 

These batteries are not good for EVs or flashlights, for example, but you might have them in your laptop. Good, cheap batteries - but finicky.

 

IFR - LFP - Lithium Ferrous phosphate

Cathode = Lithium Ferrous Phosphate

Anode = Graphite carbon.

These batteries are excellent in many ways, but they can (depending upon manufacturer) 'suffer' from lower (3V2) voltages (as opposed to the other types at 3V6 / 3V7). They also self-discharge at higher rates than other chemistries BUT, on the flip side, can be cycled around a 1000 times without noticeable degradation, have high current ratings, even getting up to 30C, while still maintaining somewhat high capacities and are more chemically and structurally stable than cobalt alternatives. 

 

Cell V : 3V2 / 3V6 (nom)

Charging : 'Standard' constant current / constant voltage

Charge : 0.5C (typ), >1C reduces life

Cut-Off V : 2.5 - 4.2V

Cycles / Durability : 1,000 - 2,000 cycles

Discharge : 1C - 25C (some cells), 40A (2s pulse)

Energy Density : 90 - 120 WH/Kg

Safety : Very, one of the safest Li-Ion cells

Typical uses : e-Motorbikes and EVs

Then, I stumbled across the LTO chemistry type... so I'll include the details here...

LTO - Lithium Titanic Oxide

Cathode = Lithium Titanic Oxide

Anode = nano tech. Graphite carbon

These batteries are a pretty new technology (2017) and are excellent in many ways, but they 'suffer' from lower (2V4) nominal voltages (as opposed to the other types at 3V2 - 3V7) and, as a consequence, lower energy density. They are known for their VERY fast charging, low internal resistance, high charge and discharge capability, VERY long endurance / life cycle (number of times they can be recharged) with low irreversibility and EXCELLENT safety (<0.2% volumetric change between charged (Li7Ti5O12) and discharged (Li4Ti5O12) states.

One major reason for the LTO characteristics previously itemised is the fact that LTO cells utilise nano-crystal technology on the ANODE effectively increasing the anode's surface area from circa 3m2 (standard carbon based Li cell anodes) to >100m2 allowing electrons to enter / exit the anode far more quickly and, therefore, generate far less heat.

 

Cell V : 2V4 (nom)

Charging : 'Standard' constant current / constant voltage

Charge : 1C (typ), >1C reduces life

Cut-Off V : 1V8 - 2V8

Cycles / Durability : 6,000 - 10,000 cycles

Discharge : 1C - 25C

Energy Density : 50 - 80 WH/Kg

Safety : Very, among the safest Li-Ion cells

Typical Uses : EVs and Power storage

My choice of Chemistry : LiFePo4

After doing all my research, whilst accepting that the LTO cells are best for longevity, charge rate and safety, their size (energy density @ 2V4) and cost coupled with difficulties (at present) of locating suitable BMS and charge systems, currently make them unsuitable for my particular uses but I'm hopeful that in the near future this may change...

In the end, I selected​ LiFePo4 cell chemistry.

Whilst not the most energy dense (energy to weight), this chemistry does offer a good nominal cell voltage (3V6) with a 4V2 high cut-off, a more than reasonable (1C) charge rate, a respectable discharge rate (up to 10+C), low self-discharge, good longevity (1000-2000+re-charges before substantial degradation), very stable structural and chemical makeup = great safety and 'reasonable' price.

In addition, the use of Phosphate reduces the environmental concerns (big win) and higher costs associated with Cobalt. To boot, suitable charger and BMS systems are readily available.

I did, however, then find I had further research to do in order to select both a manufacturer and re-seller for the highest individual cell capacity (3300mAHr). In the end it I selected Sanyo / Panasonic NCR18650GA 3350mAh - 10A .

Cell V : 3V2 / 3V6 (nom)

Charging : 'Standard' constant current / constant voltage

Charge : 1C (typ), >1C reduces life

Cut-Off V : 2.5 - 4.2V

Cycles / Durability : 1,000 - 2,000 cycles

Discharge : 1C - 25C

Energy Density : 90 - 120 WH/Kg

Safety : Very Good, one of the safest Li-Ion cells

I tend to use LiFePo4 chemistry for ALL my projects and buy them in batches of 150 - 200 18650 cells at a time. I usually design the cell holders (specific to the project at the time)  in SketchUp and print them out on my Prusa i3 mk3 3D printer.

 

I'm not yet sure, however, what chemistry & cell size I'm going to use when I finally buy the batteries for my 1971 Triumph GT6 conversion. It's true I'll have more space ... but... more space could equate to more capacity (LiFePo4 chemistry) or super-fast recharge and longevity of LTO - and greater weight :-(. I still have a lot more research to do here before I commit.