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The choice between round and lithium pouch cells is explained

Flat or round ‘that is the question’


Should I use cylindrical cells, or would it be better to use pouch type?

The most commonly used cells at the moment are the 18650 cylindrical cells. They offer an excellent balance between ease of use and function.
Flat cells (pouch) are not rolled, so the distance inside, to the terminals, is short. As a result, the internal resistance is lower than that of cylindrical cells. The resistance is not always the most important factor.
Which is better: round or flat pouch lithium cells? | Axtrel Battery Management

The electrical differences

Since the advent of the rolled-up cylindrical cell, battery life has improved dramatically. You may be familiar with the flat batteries in cordless telephones. After a year, they bulge considerably, which is detrimental to the operation of the cell.
A disadvantage of rolling up the foils, however, is the increased internal resistance. For power applications, where a lot of current must be supplied, a higher internal resistance (R) contributes to heat development in the cell.
This heat development is proportional to the square of the current.

Heat = I2 x R

At higher currents, the heat development is increasing rapidly. This is why the round cell is not so suitable for high currents.

The round cell is easy to process. You don’t need anything around it, it is already in a solid casing.

The flat (pouch) cells are different. They have a lower internal resistance, so they do not get hot as quickly. become warm. However, they do have a large surface area compared to the round cells, which helps to dissipate heat.
This makes them more suitable for use with larger currents. However, some mechanical provision is needed to keep the keep the cell ‘flat’. If they swell up, they must be pressed flat again.

The mechanical construction is what prevent many from building a flat cell battery.

In all cases, a good BMS for lithium batteries is always required.


Would you like to know how to make a good battery?
A short telephone call will tell you a lot more.

Summarized

  • Round cells are mechanically stable, but electrically somewhat less favourable
  • Flat cells need to be mechanically stabilized, but electrically more favorable
⇛   lithium 18650, lithium 20700, cilindric cells, pouch cells

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