How to Distinguish Positive and Negative of Lithium Battery?

What is an 18650 battery?
An 18650 battery is normally a lithium ion or lifepo4 battery. The height is 650mm. and diameter is 18mm. As we can see from the dimensions. The 18650 battery is named from its size. So, if any cell rated this size, we can call it 18650 cells. 18650 battery is one kind of cylindrical lithium battery. The structure of a typical 18650 lithium battery : shell, cap, positive electrode, negative electrode, diaphragm, electrolyte, PTC element, washer, safety valve, etc. Generally, the battery shell is the negative electrode of the battery, the cap is the positive electrode of the battery. Different kinds of Li-ion batteries can be formed into cylindrical, for example, LiFePO4 battery, NMC battery, LCO battery, LTO battery, LMO battery and etc.

What are Cathode and Anode for a lithium battery?
The negative electrode in a cell is called the anode. The positive side is called the cathode. During charging, the lithium ions move from the cathode, through the separator, to the anode. During discharge, the flow reverses. The most popular material used for the anode is graphite. Common materials for the cathode are lithium cobalt oxide, lithium iron phosphate, and lithium manganese oxide. These different chemistries provide different benefits and voltages.

Cathode: it is the electrode at which reduction takes place– Electronation
Anode: It is the electrode at which oxidation takes place–De-electronation

In a galvanic or a voltaic cell, the electrons generated due to oxidation flow through an external wire from anode to cathode. At the cathode electrons are consumed due to reduction. Hence the anode in a galvanic cell is given a -Ve sign as the negatively charged electrons flow from it. So the cathode is +Ve. In case of an Electrolytic Cell, an external DC source transfers the electrond from the anode to the cathode. As a result, the anode becomes positively charged and the cathode is negatively charged.

How do you know the positive and negative battery packs?
All battery cells with positive and negative pole. Same for 18650 battery cells. but we should have different way to find out the positive and negative pole of it. This is very important to know before you insert the battery to the device. Wrong setting would lead a fire or other problem if there is no protection circuit.

Check by sight.
We can find out the positive and negative by just see it. The flat side is negative most of the time. and top bottom side is positive. This a normal design as most of the battery cell like this. However, this is not 100% for sure.  Because sometimes both sides are flat. And some batteries positive and negative just in one side like following photo shows.

Check by meter.
We strongly recommend to check the 18650-cell pole by a volt meter. This will be 100% safety before you place the battery to any devices.
(1) Open the DC voltage gear.
(2) Use the red and black test pens of the multimeter to contact the two sides of the button battery respectively.
(3) When the displayed voltage value is positive, the red test lead of the multimeter is connected to the positive electrode, and the black test lead is connected to the negative electrode.
(4) When the displayed voltage value is negative, the black pen of the multimeter is connected to the positive pole, and the red pen is connected to the negative pole. The above are 5 ways how to check the positive and negative poles of a button battery. In general, either look at the signs (“+, -“) or look at the shapes.

The button battery has won the praise of the public with its excellent volume advantage, high-cost performance, and excellent service life. Button batteries have also been widely used in daily life, such as car keys, TWS headphones, smartwatches, etc. How much do you know about button batteries? Do you check the positive and negative poles of the button battery when you replace the button battery every day? For the positive and negative electrodes of the button battery, look at the + sign, the + sign indicates the positive electrode, and the – sign indicates the negative electrode. One side of the button battery is directly marked with the + sign, then this side is the positive electrode, and the other side is the negative electrode.

What’s the Meaning of Numbers on the Lithium Battery?

The Rule of Naming a Lithium Battery
Some may confused about numbers mentioned above:14650, 17490, 18650, 21700…
Let’s have a look about these numbers.
All of them are names of cylindrical cells.According to name of cylindrical battery given by manufacturers, we can easily know its basic information.

For cylindrical lithium cells,
Naming Rule: Three letters+ Five numbers+ normal capacity

Five Letters refer to main electrode materials of cell
The first letter: anode material
“I”– lithium ion
“L”– lithium or lithium alloy
The second letter: cathode electrode material
“C”– Cobalt electrode
“N”– Nickle electrode
“M”– Manganese electrode
“V”– Lead electrode
The third letter:“R”– cylindrical cell

Five numbers refer to its outer dimensions
The first and second number: the diameter of cell(mm)
The third and fourth number :the height of battery (mm)
The last number “0”: cylindrical battery

The normal capacity: usually use milliampere( mAh) as unit

Just take “ICR18650 2200mh “as an example.
We can know that this is a Li-ion cylindrical cell with cobalt cathode. Its diameter is 18mm with height of 65mm. And its normal capacity is about 2200mAh.

It is simple, right?

Here are other cells, you can have a try

Actually, for convenience, we always call them with its five numbers, that is, its outer dimensions.
For example: 14650, 17490, 18650, 21700, 26650

All of them are easily understood now according to above explanations, right?

For prismatic lithium battery, here is a subtly different point
Naming Rule: Three letters+ Six numbers+ normal capacity
Six numbers refer to its outer dimensions
The first two numbers: the thickness of cell(mm)
The third and fourth numbers :the width of battery (mm)
The last two numbers: the height of battery (mm)

Pay attention!!!

Thickness, width, height≥100mm, must add “/”among three sizes
ICP35/78/131 INP34/63/110

One of Thickness, width, height≤1mm, the letter “t”should be add before this size
ICPt73448 INP35t968

IMPt73448: a square secondary lithium-ion battery, the cathode material is Manganese, its thickness is about 0.7mm, the width is about 34mm and the height is about 48mm.

For example

ICP103450: a prismatic secondary lithium-ion battery, the cathode material is Cobalt, its thickness is about 10mm, the width is about 34mm, and the height is about 50mm.

INPO8/34/150 : a prismatic secondary lithium-ion battery, the cathode material is Nickle, its thickness is about 8mm, the width is about 34mm and the height is about 150mm.