Ageing Sensitivity of Pulse-Derived Descriptors in Lithium-Ion Cathode Chemistry Classification Under Health-Shifted Evaluation

Cathode chemistry governs a retired cell’s route; labelling of cells now retiring was recommended rather than required, so it must be read from the cell itself, here from 5 s pulses. Published data from 270 battery-states and 215 cells test this capability beyond the training health range. Named descriptors replace the raw turning points; loss of discrimination can then be attributed to an electrochemical quantity. Under a shared health distribution, the task saturates: one decision tree using rested open-circuit voltage (OCV) classifies three chemistries perfectly, and seven configurations achieve at least 97.8% accuracy, although chemistry is confounded with capacity, format, and fleet. Trained at or above a state-of-health (SoH) of 0.88 and tested below 0.85, configurations retaining OCV achieve 0.886 macro-recall versus 0.744 for pulse dynamics alone, a within-replicate gap of 0.144 across 25 seeded fits [0.118, 0.152]. Because state-of-charge (SoC) references nominal capacity, true SoC varies with health; true-SoC matching reduces the gap to 0.105 [0.088, 0.120]. By chemistry, the matched gap arises only where health and format shift together, whilst two of the three OCV-free configurations decline further with distance. These descriptors vary with health under the examined conditions, which weakens them as chemistry markers outside that range.