Hi all,
it is generally agreed (i guess?) that there is a correlation of a li-ion cells quality (Soh) and its IR. In most cases an increasing IR indicates a decreasing Soh, decreasing capacitance and increasing self discharge rate (SDR). I recently tested all my salvaged 18650 with my new YR1035+ to measure actual voltage and IR.
I came across a few cells from an ebike battery pack made of Sony SE US18650V2 (NMC, 2100 mAh) from which i knew they had quite high SDR and others which are fine SDR-wise. When i talk of high SDR i mean something like dropping 400 - 600 mV in 6 months! The IR of these cells is only insignificantly higher (43...44 mR) compared to the good cells of the same pack (with an IR or 40...41) which only drop around 10 mV in the same time (6 months).
At least, there is an increasing IR, but its not as significant as i would expect.
For other cells the IR difference is much bigger for the bad cells and goes up to 100...200 mR but often with less SDR than the ones mentioned above.
Anyone with similar experience?
BTW: this topic should be in "general cell testing and recycling"
P.S. i charged some bad cells to nearly full and did the measurement again: even the slight difference in IR nearly disapeared so they really look like the other good cells with no increased SDR. Probably the temperature went also up a bit - so that might bias the IR readings. As a result: there is not always a direct relation between high SDR and high IR.
it is generally agreed (i guess?) that there is a correlation of a li-ion cells quality (Soh) and its IR. In most cases an increasing IR indicates a decreasing Soh, decreasing capacitance and increasing self discharge rate (SDR). I recently tested all my salvaged 18650 with my new YR1035+ to measure actual voltage and IR.
I came across a few cells from an ebike battery pack made of Sony SE US18650V2 (NMC, 2100 mAh) from which i knew they had quite high SDR and others which are fine SDR-wise. When i talk of high SDR i mean something like dropping 400 - 600 mV in 6 months! The IR of these cells is only insignificantly higher (43...44 mR) compared to the good cells of the same pack (with an IR or 40...41) which only drop around 10 mV in the same time (6 months).
At least, there is an increasing IR, but its not as significant as i would expect.
For other cells the IR difference is much bigger for the bad cells and goes up to 100...200 mR but often with less SDR than the ones mentioned above.
Anyone with similar experience?
BTW: this topic should be in "general cell testing and recycling"
P.S. i charged some bad cells to nearly full and did the measurement again: even the slight difference in IR nearly disapeared so they really look like the other good cells with no increased SDR. Probably the temperature went also up a bit - so that might bias the IR readings. As a result: there is not always a direct relation between high SDR and high IR.
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