How Lithium-ion Batteries Work

Lithium-ion batteries are popular because they have a number of important advantages over competing technologies:

  • They’re generally much lighter than other types of rechargeable batteries of the same size. The electrodes of a lithium-ion battery are made of lightweight lithium and carbon. Lithium is also a highly reactive element, meaning that a lot of energy can be stored in its atomic bonds. This translates into a very high energy density for lithium-ion batteries. Here is a way to get a perspective on the energy density. A typical lithium-ion battery can store 150 watt-hours of electricity in 1 kilogram of battery. A NiMH (nickel-metal hydride) battery pack can store perhaps 100 watt-hours per kilogram, although 60 to 70 watt-hours might be more typical. A lead-acid battery can store only 25 watt-hours per kilogram. Using lead-acid technology, it takes 6 kilograms to store the same amount of energy that a 1 kilogram lithium-ion battery can handle. That’s a huge difference [Source: Everything2.com].
  • They hold their charge. A lithium-ion battery pack loses only about 5 percent of its charge per month, compared to a 20 percent loss per month for NiMH batteries.
  • They have no memory effect, which means that you do not have to completely discharge them before recharging, as with some other battery chemistries.
  • Lithium-ion batteries can handle hundreds of charge/discharge cycles.

That is not to say that lithium-ion batteries are flawless. They have a few disadvantages as well:

  • They start degrading as soon as they leave the factory. They will only last two or three years from the date of manufacture whether you use them or not.
  • They are extremely sensitive to high temperatures. Heat causes lithium-ion battery packs to degrade much faster than they normally would.
  • If you completely discharge a lithium-ion battery, it is ruined.
  • A lithium-ion battery pack must have an on-board computer to manage the battery. This makes them even more expensive than they already are.
  • There is a small chance that, if a lithium-ion battery pack fails, it will burst into flame.

Lithium-ion Batteries
Many of these characteristics can be understood by looking at the chemistry inside a lithium-ion cell. We’ll look at this next. ­

Inside a Lithium-ion Battery Pack and Cell

Lithium-ion battery packs come in all shapes and sizes, but they all look about the same on the inside. If you were to take apart a laptop battery pack (something that we DO NOT recommend because of the possibility of shorting out a battery and starting a fire) you would find the following:

  • The lithium-ion cells can be either cylindrical batteries that look almost identical to AA cells, or they can be prismatic, which means they are square or rectangular The computer, which comprises:
  • One or more temperature sensors to monitor the battery temperature
  • A voltage converter and regulator circuit to maintain safe levels of voltage and current
  • A shielded notebook connector that lets power and information flow in and out of the battery pack
  • A voltage tap, which monitors the energy capacity of individual cells in the battery pack
  • A battery charge state monitor, which is a small computer that handles the whole charging process to make sure the batteries charge as quickly and fully as possible.

If the battery pack gets too hot during charging or use, the computer will shut down the flow of power to try to cool things down. If you leave your laptop in an extremely hot car and try to use the laptop, this computer may prevent you from powering up until things cool off. If the cells ever become completely discharged, the battery pack will shut down because the cells are ruined. It may also keep track of the number of charge/discharge cycles and send out information so the laptop’s battery meter can tell you how much charge is left in the battery.
It’s a pretty sophisticated little computer, and it draws power from the batteries. This power draw is one reason why lithium-ion batteries lose 5 percent of their power every month when sitting idle.

Lithium-ion Cells

As with most batteries you have an outer case made of metal. The use of metal is particularly important here because the battery is pressurized. This metal case has some kind of pressure-sensitive vent hole. If the battery ever gets so hot that it risks exploding from over-pressure, this vent will release the extra pressure. The battery will probably be useless afterwards, so this is something to avoid. The vent is strictly there as a safety measure. So is the Positive Temperature Coefficient (PTC) switch, a device that is supposed to keep the battery from overheating.
For more Detail: How Lithium-ion Batteries Work


About The Author

Ibrar Ayyub

I am an experienced technical writer with a Master's degree in computer science from BZU Multan University. I have written for various industries, mainly home automation and engineering. My writing style is clear and simple, and I am skilled in using infographics and diagrams. I am a great researcher and am able to present information in a well-organized and logical manner.

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