I decided I’m still not ready to spring for a new iPhone 8 or iPhone X. So I went to the Apple store here in Seattle, to inquire about a replacement battery for my old iPhone 6s. (Apple has a special offer of $29 for battery replacements for certain older phones. Normally they charge $79).
Well – it turned out that I’m going to get the battery for free. The analysis they ran at the store showed that the battery in my phone has gone through 533 charging cycles, and its capacity is now down to 80%. It is also from a batch of batteries that had since been marked as slightly flawed – hence its free replacement.
Here’s how a typical modern mobile phone Li-ion battery works, highly simplified. The positive electrodes (cathodes) are typically lithium-doped cobalt oxide; the negative electrodes (anodes) are graphite, with a separator in between. There is also an electrolyte, lithium salts in an organic solvent. A large number of these electrode layers are ‘jelly-rolled’ into the pouch to increase the current that the battery can discharge during its use. Lithium ions migrate back and forth depending if the phone is used, or charged. The electrolyte and electrodes degrade over time, though. Some researchers are working hard to find a solid-state solution (a battery with no electrolyte). They believe these solid-state batteries would last tens of thousands of cycles instead of a few hundred. [Picture: Infographic for Galaxy 7 Note phone, by Samsung]
