4 ms·

I was talking to a founder of a battery company the other day and he said "there are two kinds of moving parts in your iphone, the buttons and the battery". The

I was talking to a founder of a battery company the other day and he said "there are two kinds of moving parts in your iphone, the buttons and the battery". The lithium literally moves from side to side as it charges and discharges.

speedgoose 3y ago
There is also the speakers, the microphones, the lens (focus), the vibrating motors, and probably a few other things.
- bongobingo1 3y ago
  The glass moves quite a lot once I drop it.
  - NavinF 3y ago
    Not so much with modern phones; the glass has gotten a lot stronger over the years. I can drop mine on hardwood with no visible effects and dropping it on concrete only causes cosmetic issues (chipped edges) without affecting functionality. I went caseless and screenprotector-less ~10 years ago and never regretted it.
- deepserket 3y ago
  The gyroscope and the accelerometer https://youtu.be/9X4frIQo7x0 https://youtu.be/9X4frIQo7x0
- hwillis 3y ago
  Most/all of the capacitors (which are mostly piezoelectric), the inductors, any ferrite beads, and of course thermal expansion. I'd also bet that liquid crystals change pressure when they rotate, but idk.
Someone 3y ago
So, can we, in theory (I guess the effect will be small), measure battery charge by measuring the center of gravity and/or rotational inertia of batteries or even smartphones?
- hwillis 3y ago
  No- the inside of a li-ion battery looks like this: https://www.researchgate.net/profile/Jigang-Zhou/publication/310734722/figure/fig2/AS:431587125927942@1479909797975/Full-three-dimensional-rendering-of-jellyroll-assembly-inside-the-pouch-cell-The-heat.png https://www.researchgate.net/profile/Jigang-Zhou/publication... Li-ion battery comes off the production line as one continuous, miles-long tape that is rolled into shape and then sliced off. The tape is made of a few layers, and li ions move from one layer to another. All of the movement cancels out. You could measure the state of charge by mass, though! As electrons are moved from anode to cathode, they occupy a lower energy state and therefore have less mass. You'd measure that in eV, electron-volts: convert amp-hours to coulombs and you have the number of electrons, and the average voltage change is from roughly 3.7 volts to 3.2 volts. Or you could use the much easier formula- E=MC^2 :D
  - Someone 3y ago
    > All of the movement cancels out. For the center of mass, that’s right, but that will change the moment of rotational inertia, won’t it? Mass will either move inwards or outwards as the battery gets discharged.
    - hwillis 3y ago
      Well, for the outside layer only, since the inside layers are effectively just shifting slightly. The battery as a whole swells slightly due to the stress of intercalation, which is certainly a much larger effect.
hwillis 3y ago
Well, side-to-side as in less than 100 microns. The inside of the battery is a very long tape that is rolled up like folded paper. The tape is: 1: Aluminum foil (about 1/10th as thick as household foil) 2: Cathode material (metal oxides, like NMC or NCA) 3. Separator film (polypropylene + polyethylene, which blocks electrical short circuits but lets li ions through- only ~20 microns thick) 4. Spheroidal graphite anode (mostly artificial, some natural) 5. Copper foil The ions (and some amount of solvent- the solvation sheath!) travel from cathode <-> anode.

speedgoose 3y ago

There is also the speakers, the microphones, the lens (focus), the vibrating motors, and probably a few other things.

bongobingo1 3y ago
The glass moves quite a lot once I drop it.
- NavinF 3y ago
  Not so much with modern phones; the glass has gotten a lot stronger over the years. I can drop mine on hardwood with no visible effects and dropping it on concrete only causes cosmetic issues (chipped edges) without affecting functionality. I went caseless and screenprotector-less ~10 years ago and never regretted it.
deepserket 3y ago
The gyroscope and the accelerometer https://youtu.be/9X4frIQo7x0 https://youtu.be/9X4frIQo7x0
hwillis 3y ago
Most/all of the capacitors (which are mostly piezoelectric), the inductors, any ferrite beads, and of course thermal expansion. I'd also bet that liquid crystals change pressure when they rotate, but idk.

Someone 3y ago

So, can we, in theory (I guess the effect will be small), measure battery charge by measuring the center of gravity and/or rotational inertia of batteries or even smartphones?

hwillis 3y ago
No- the inside of a li-ion battery looks like this: https://www.researchgate.net/profile/Jigang-Zhou/publication/310734722/figure/fig2/AS:431587125927942@1479909797975/Full-three-dimensional-rendering-of-jellyroll-assembly-inside-the-pouch-cell-The-heat.png https://www.researchgate.net/profile/Jigang-Zhou/publication... Li-ion battery comes off the production line as one continuous, miles-long tape that is rolled into shape and then sliced off. The tape is made of a few layers, and li ions move from one layer to another. All of the movement cancels out. You could measure the state of charge by mass, though! As electrons are moved from anode to cathode, they occupy a lower energy state and therefore have less mass. You'd measure that in eV, electron-volts: convert amp-hours to coulombs and you have the number of electrons, and the average voltage change is from roughly 3.7 volts to 3.2 volts. Or you could use the much easier formula- E=MC^2 :D
- Someone 3y ago
  > All of the movement cancels out. For the center of mass, that’s right, but that will change the moment of rotational inertia, won’t it? Mass will either move inwards or outwards as the battery gets discharged.
  - hwillis 3y ago
    Well, for the outside layer only, since the inside layers are effectively just shifting slightly. The battery as a whole swells slightly due to the stress of intercalation, which is certainly a much larger effect.

hwillis 3y ago

Well, side-to-side as in less than 100 microns. The inside of the battery is a very long tape that is rolled up like folded paper. The tape is: 1: Aluminum foil (about 1/10th as thick as household foil) 2: Cathode material (metal oxides, like NMC or NCA) 3. Separator film (polypropylene + polyethylene, which blocks electrical short circuits but lets li ions through- only ~20 microns thick) 4. Spheroidal graphite anode (mostly artificial, some natural) 5. Copper foil The ions (and some amount of solvent- the solvation sheath!) travel from cathode <-> anode.