Lithium Ion Batteries - An introduction
Lithium Ion batteries are a marvel of modern technology and manufacturing.
Customers always ask questions about the longevity and performance of the lithium batteries in our devices.
Customers always ask questions about the longevity and performance of the lithium batteries in our devices.
So we’ve produced this article to try and answer these questions in a way which will give insights into this.
Lithium Ion rechargeable battery technology has come a long way in recent years, and lithium ion batteries are a marvel of modern technology and manufacturing.
Low voltage devices that can make use of battery power are now everywhere.
Therefore it makes sense to standardise and package batteries to run these devices efficiently, and reduce waste.
And batteries can be produced cheaply due to economies of scale.
This article explains how lithium ion batteries are put together and package.
It’s so that our device owners can learn for themselves how effective the batteries are in their device.
Lithium ion batteries require some care if we want to get the maximum life and performance out of them.
And here we provide tips on what steps should be followed to take good care of the batteries.
Also, why these steps are important to the health of the batteries.
What's so special about Lithium Ion Batteries
The 18650 cell is slightly larger than a standard AA cell (see the picture for comparison).
And the 18650 cells are each usually a standard voltage of 3.675V.
They can range from 2 Amp Hrs (Ah) to 4Ah in power.
A lot can be researched about these cells, for example from Wikipedia.
A lot can be researched about these cells, for example from Wikipedia.
How are they packaged?
The 18650 cells can be packaged together in banks:
- When wired in series, this will increase Voltage (eg. 3.675v, 7.35v, 11.02v, 14.7v, 29.4v, etc…)
- When cells (or banks) wired parallel, will increase Ampage. (eg. 2.2Ah, 4.4Ah; 6.6Ah; 8.8Ah)
- A bank of 8x 3.675V / 2.2Ah cells in series will deliver 29.4V max (or 24V nominal).
- A pack of 3 of these banks wired in parallel will deliver 6.6Ah.
- This pack would be called 8s3p (ie. eight cells to a bank in series, three banks in parallel
And so it goes: Cells > > Banks > > Packs
What's a BMS?
A battery management system (BMS) circuit board is attached so the pack (see the picture).
The purpose of the BMS is to protect and regulate each of the individual cells in the pack.
The BMS works to ensure no cell runs below a min of 2.7V, or above a max of 4.2V, for optimum life:
- Below the 2.7V threshold, a chemical reaction may occur that can damage the cell.
- Above 4.2V the cell may overheat, which is dangerous for the cell, and for the pack.
Having more cells, reduces the impact of a failure in any single cell.
However, if one cell in one bank becomes damaged, it will reduce the maximum voltage of the pack.
However, if one cell in one bank becomes damaged, it will reduce the maximum voltage of the pack.
Even a Tesla uses these standard 18650 cells – about 7,000 of them in the floor pan of the car.
For example a Tesla Model S uses a standard 3.66V / 3400mAh cell within modular battery packs.
The configuration of each module is 6s74p, or 444 cells, and there are 16 modules.
That means there are 7,104 cells in total, to deliver 85 KWh.
Caring For Lithium Ion Batteries
It is important that lithium ion battery cells are maintained well. This means ensuring that the power of any cell is not allowed to run down below about 2.8 volts.
Below this threshold, a cemical reaction occurs within the cell which can permanently damage the cell.
What this post shows is how intricate the lithium ion battery packs are, and how critical it is to keep them recharged, even if you are not using the device for extended periods.