Does anyone know what to think about the very strange jagged IMR discharge pattern?
You got a really bad quality cell. I recommend not using it.
IMR cells use LiMn2O4 as the cathode material instead of the more common LiCoO2. LiMn2O4 is also commonly referred to as LMO or "spinel".
In as much as you can generalize about lithium-ion chemistries, here are a few things to know about cells made with LiMn2O4:
1. LiMn2O4 has a slightly lower capacity and has historically had less cycle life than LiCoO2. This is why LiCoO2 has become the dominate cathode chemistry, despite it being more expensive.
2. You can make a higher power cell with LiMn2O4 because the diffusion rate of lithium ions in that material is higher than in LiCoO2.
3. LiMn2O4 tends to be safer than LiCoO2 because it cannot be "overcharged". Now, let me explain this a bit. You can certainly damage a IMR cell by charging at too high of a current and/or voltage, so don't try it. The difference is that you cannot put excess capacity into the cell because at full state of charge, all of the lithium is extracted from the LiMn2O4 (so when the cell is fully charged (~4.2V), the cathode is essentially MnO2). In this respect, IMR cells are similar to cells that use lithium iron phosphate as the cathode. With an LiCoO2 cathode, only half of the lithium is extracted at full state of charge, and if the cell is charged to a higher voltage, more lithium is extracted from the cathode, leading to all sorts of safety problems.
Given the better high power (high drain) and safety characteristics, IMR cells are usually designed for high power applications where the cell is likely going to be exposed to high current drains and higher temperatures.
So, the reason that many people like IMR cells is that they are generally higher power and safer than other lithium-ion cells that charge to 4.2V.
This does not mean that all IMR cells are high power and/or safe. You can certainly build a low power cell with LiMn2O4, but there are other, better cathode materials to choose from. You can also build a crappy, low quality IMR cell that will catch on fire.
Just remember that "IMR" simply denotes the chemistry of the cell. Just like you can have NiMH cells with various performance characteristics from different manufacturers, the same is true for IMR cells.
Hope this helps.
Cheers,
Battery Guy
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