All Things You Need to Know about Li-ion Battery Package Forms

Li-ion batteries are widely used in many aspect, nowadays.

Have you noticed that?There are many kinds of Li-ion batteries’ shapes, for example, square and cylindrical.

How many kinds of shapes are there?
Do you know their differences?
Do you know why engineers design that?

Read on and make your own mind up.
According to different packaging forms, there are mainly three kinds of Li-ion batteries: Cylindrical lithium ion battery, Prismatic lithium ion battery, and Pouch lithium ion battery.

cylindrical lithium battery

cylindrical  rechargeable lithium ion battery

prismatic lithium battery cell

prismatic lithium battery

pouch lithium battery

Different package structures refer to different characteristics. Let’s break them down one by one.

What is Cylindrical Lithium Battery?

The structure of a typical cylindrical 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.

structure of cylindrical lithium battery

reasons of high market penetration rate

Cylindrical shells divided into two types: steel or alloy material.

Generally speaking, the main battery is cylindrical cylindrical lithium iron phosphate batteries which is based on steel shell.

The earliest cylindrical Li-ion battery was the 18650 Li-ion battery which was invented by SONY in 1992.

There are many models of cylindrical lithium batteries,such as common ones: ‘lithium ion cylindrical battery 3.7V 2200mAh 14650″, “lithium ion  battery 14790”, “lithium rechargeable battery 18650″, ‘”lithium battery 26650”,etc.

Cylindrical lithium batteries are more popular among lithium battery companies in Japan and South Korea, and there are also large-scale companies in China that produce cylindrical lithium batteries.

Application of  cylindriacal lithium battery: Electrical vehicle, Laptop, digital camera, solar lamps, lawn lamps, backup energy, power tools, and toy models, pneumatic tools, portable energy transfer and etc.

Advantages of Cylindrical Lithium Battery:

1.Good Consistency: with mature technology and producing standard, manufacturers can produce productions in large quantity and high quality.

2.Safe: Withstand high voltageand generally sealed batteries, NO SWELLING
3.Goodheat dissipation effect→ Large specific surface area of the cylinde
4.High capacity, such as 15Ah cylindrical lithium ion battery, 20Ah cylindrical lithium battery
5.High output voltage
6.Stable output voltagel
7.Stable electric chemical performance
8.High current discharge
9.Good charge and discharge cycle performance
10.Wide operating temperature range
11.Environmentally friendly
12.Low PACK cost
13.Replaceable battery suppliers

flexible design for cylindrical cell battery pack

Cylindrical battery array with liquid cooling tubes

(A simple lithium battery pack)

Disadvantages of Cylindrical Lithium Battery:

  • Small energy density increasing room
  • The probability of alienation of the characteristics increases
  • High production cost for battery system software level
  • Low packing density because of its shape: can’t fully utilize space in the battery pack
  • Battery performance reaches its limit

What is Prismatic Lithium Battery?

Structure:  Laminated or wound top cover, housing, positive electrode plate, negative electrode plate, diaphragm, insulating parts, safety components, etc.

Although there are steel shell and aluminum shell battery, the aluminum shell one has generally become the mainstream with the market’s pursuit.

Prismatic cells have many anodes, cathodes and separators which of them are rolled up and then pressed into a metallic or hard-plastic shells.

Layer stacking and jelly rolling are both assemble for prismatic electrodes. That is the reason why there are thousands optional types of prismatic cells.

Application of prismatic lithium battery: small electronic devices such as mobile phones.

structure of prismatic lithium battery

Advantages of Prismatic Lithium Battery

  • Flexible Design
  • High reliability in package
  • High energy efficiency in battery system
  • Monitor cells one by one because of simple system composition
  • Simple structure and easily to expand energy density and battery capacity by connecting single cells.

Prismatic battery array with a heat sink conduction matrix

(A simple lithium battery pack)

Disadvantages of Prismatic Lithium Battery:

  • Not easier to find replaceable batteries compared with cylindrical batteries because of large amount of battery models.
  • Cell inconsistency problem is relatively big because there is no very mature standard.
  • Battery pack has shorter life than single cells inside.
  • Relatively expensive model cost.
  • Vulnerability to swelling
  • Lower energy density

What is Pouch Lithium Battery

Structure: Liquid lithium-ion batteries with a layer of polymer shell. The package material is aluminum-plastic composite film which is the most critical and technically difficult material in pouch Li-ion batteries.

Packaging materials have three layers:
Outer barrier– outer protective layer composed of nylon BOPA or PET
Permeable layer– intermediate layer made of aluminum foil
Inner layer–Multifunctional high barrier layer

Application of Pouch lithium battery: Consumer, military, as well as automotive industries.

Mainly used in equipment which has equipment weight requirement or compact space. Pouch batteries are suitable for conditions where the working environment is relatively stable and there are no complex road conditions to ensure the structural stability and service life of lithium battery packs.

structure of pouch lithium battery

Pouch battery array with a heat sink

(A simple lithium battery pack)

Disadvantages of Pouch lithium battery:

  1. High model developing cost of new designed battery
  2. The quantity of existing pouch batteries models can not meet market’s demand
  3. Exposure to high humidity and hot temperature can shorten service life.
  4. Lack of producing standardization

Advantages of Pouch lithium battery:

  • Good Safety Performance
Packed with aluminum-plastic film. In safety hazards, the pouch lithium battery will only swell and crack at most, unlike the steel-shell or aluminum-shell battery, which will explode.
  • Light Weight
40% lighter than that of the steel-shell lithium battery of the same capacity,
20% lighter than that of the aluminum-shell lithium battery of the same capacity.
  • Large Capacity
10 to 15% higher than that of steel-shell batteries of the same specification and size 5 to 10% higher than that of aluminum-shell batteries.
  • Small Internal Resistance
The internal resistance is small, which greatly reduces the self discharge
  • Flexible Design
The shape of the pouch lithium battery can be customized according to customer needs, and new battery models can be developed.

These are all details about cylindrical, prismatic and pouch batteries.

Looking forward, with pouch cells’ optimism , it will move to higher producing efficiency and better performance. Pouch and prismatic formats will be the most used, especially for automotive and energy storage use.

However, it does not means that cylindrical battery will disappear, it will also exist with less dominant stake in the battery market.

Q&A

  • Are pouch batteries better than cylindrical batteries?

Yes. Pouch lithium battery is well kown for its  LIGHTER weight, BETTER safety performance, LARGER lithium battery capacity and SMALLER internal resistance.

At present, if you have other requirement, you can consider pouch batteries. If you do not have weight, space and cost requirements, cylindrical is the optimal choice to save your money and time.

  • Do cylindrical batteries swell?

No, it rarely swell. Because its shell is made by steel or alloy material which is very hard, it can withstand high gas pressure and voltage. Thus cylindrical lithium battery will not swell. While pouch battery has possibility to swell.

  • Why battery shell is important? Whats function?

The following are functions of battery shell

  1. Suppress battery polarization
  2. Reduces thermal effects
  3. Improves magnification performance
  4. Reduce the internal resistance of the battery
  5. Significantly reduce the dynamic internal resistance of the cycle process
  6. Improves consistency and increases the cycle life of the battery
  7. Improve the adhesion of the active substance to the collector fluid
  8. Reduce the manufacturing cost of the pole piece
  9. Protects the collector fluid from being corroded by the electrolyte
  10. Improve the high and low temperature properties of lithium batteries
  11. Improve the processing properties of lithium iron phosphate and lithium titanate materials.

  • What is the advantage of aluminum shell?

1.The lightweight space is large, because the density is 1/3 of steel;
2.Good thermal conductivity,5 times of steel’s;
3.Absorbs twice as much energy per unit weight as steel;
4.Good extension performance;
5.Strong plasticity, good weld-ability, and good productivity;
6.Good casting performance, can be processed into different shapes;
7.Corrosion-resistant, easy to recycle and regenerate
 

  • What is the difference between cylindrical and prismatic battery cells?

shape cylindrical lithium cell pristimatic lithium cell pouch lithium cell
Electrode Arrangement wound wound stacked
Mechanical Strength very hard ++ hard + not hard -
Heat Management not bad- good+ good+
Specific Energy high + high+ very high ++
Energy Density high + very high ++ high +

From the chart below, we can easily gain:

  1. Pouch battery is formed by stacking. Whie the other two are formed by wounding
  2. Cylindrical battery is the hardest one among these three kinds of lithium cell
  3. Pouch battery is soft.
  4. Cylindrical battery is poor in heat management. While the other two are good.
  5. Pouch lithium ion battery has the highest specific energy among them.
  6. Prismatic lithium cell has the highest energy density among them.

  • Naming Rules for batteries

Some may confused about numbers mentioned above:14650, 17490, 18650, 21700…
Lets 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.

How?

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!!

  1. Thickness, width, height100mm, must add /among three sizes

  ICP35/78/131         INP34/63/110
 

  1. One of Thickness, width, height1mm, the letter tshould 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.