The Great Recall
Samsung announced that all Galaxy 7 Note devices should be recalled as users have reported overheating batteries, fires, and even explosions. The Galaxy 7 Note was released on September 2nd (pre-orders from August 16th) and has only been on the shelves for a month. However, this does not imply that all Samsung devices are dangerous as there have been 92 reports out of a total of 1 million devices in the US.
Even so, these incidents have gotten a lot of media attention given that the damage caused by the devices has been enough to burn people and cause fires (as one individual found out when he left his Note 7 in his Jeep charging).
But why are these batteries catching fire? What is it about lithium-ion batteries that make the susceptible to such an explosive end? To answer these questions, we need to understand how a lithium-ion battery works.
Like most batteries, Li-ion batteries consist of three main parts: the anode (+ terminal), an electrolyte, and a cathode (-).
In Li-ion batteries, the anode is usually made from Lithium-Cobalt Oxide (new batteries may use Lithium Iron Phosphate) and the cathode is made of carbon. The electrolyte in such batteries must be able to transfer positive ions between electrodes but be an insulator to an electrical current (electron flow). Electrolytes vary between batteries but are commonly lithium salts in an organic solvent.
Simple cutaway of the Li-ion battery. Image courtesy of Tkarcher (own work) [CC BY-SA 3.0]
When a Li-ion battery is charged, lithium ions are removed from the anode and embed themselves into the porous carbon cathode. At the same time, electrons from the anode are removed and electrons flow to the cathode where they bond with the lithium ions to deposit lithium metal into the carbon.
During a discharge cycle (when a load is connected across the battery terminals), electrons from the cathode are attracted to the anode which results in the embedded lithium ions in the carbon cathode to travel through the electrolyte and back to the anode where again they combine with electrons to form metallic lithium.
The electron flow and ion flow in the electrolyte complement each other and the charge process can only occur if both processes are active. If one stops (for example, the electron flow), then so will the other process (in this case, the ion flow).
So why do Li-ion batteries have a bad habit of overheating and catching fire?
The issue comes down to two factors:
- Speed of lithium ion deposition on the carbon cathode
- Temperature of the battery
When a lithium battery is being charged, the Li ions need to be embedded into the cathode which is known as intercalation. This process is very important because, instead of depositing metallic lithium on the surface of the cathode, the lithium ions penetrate the porous regions of the cathode.
If a Li-ion battery is charged too quickly, the Li ions are deposited on the surface of the cathode as plated lithium instead of being trapped the porous regions. This is serious as the distance between two plates in a typical Li-ion battery is very small (measuring in mm’s). As the lithium-plated layer becomes thicker, it can eventually make contact with the anode which creates a short circuit.
Electroplating showing how the cathode increases in physical dimension.
This short circuit can then lead to a massive amount of current discharge which heats up the battery. As the battery heats up, it runs the risk of entering thermal runaway where the increase in temperature makes the reaction occur faster which loops back to increasing the temperature. This can lead to the cell smoking, igniting, and even exploding.
So how is such an issue overcome?
The answer involves electronics that constantly monitor the batteries' temperature, voltage, and current output. During charging, the battery is carefully monitored and the charge current is kept low. This intentionally increases the time taken to charge the battery but results in the lack of lithium plating on the cathode. When batteries are in use, the controller can keep measuring the temperature of the battery and shut down cells if needed to prevent further damage.
The situation with Samsung and their potentially dangerous batteries is not new. In fact, it is very common to hear about Li-ion batteries causing damage and fires including hoverboards, Apple iPhones, and even laptops.
So why are these batteries still in use if they can present a very real danger?
In short, we keep using Li-ion batteries because they have a number advantages over other rechargeable batteries and regular batteries.
Firstly, Li-ion batteries are rechargeable, unlike normal batteries that you may find in some cameras, remotes, and toys.
Secondly, Li-ion batteries do not suffer from a phenomenon called “memory effect” as much as other rechargeable batteries (such as NiMH and NiCd). Simply stated, memory effect is when a battery loses its ability to store charge if it isn't completely discharged before being charged again.
Li-ion batteries are also lightweight and have a higher energy density as compared to other rechargeable technologies. This makes Li-ion the choice for portable devices, power tools, and even electric vehicles.
- Battery Construction: Batteries and Power Systems
- How Lithium-Metal Doubles the Energy Density of Rechargeable Batteries
- New Liquid Battery Chemistry Could Be a Game Changer
Li-ion batteries are heavily used for their properties in weight and energy density, but this comes at a cost that some of these batteries may fail and cause damage.
If incidences continue to rise with faulty Li-ion batteries, then it may not be long before government intervention may change the rules with such power sources.
New technologies, smarter devices, and better materials may reduce the risk of such devices failing—but these changes may need to come sooner rather than later because it won’t be long before someone becomes seriously hurt from one of these power sources.