Cell-to-cell variations play a significant role in the commercialisation of sodium-ion batteries (SIB). With first SIBs entering the open market in consumer-friendly 18650 packages, this work aims to provide insight into the typical cell metrics as well as the effects of cyclic ageing on these cells. To provide a baseline, the results are compared to 18650 LFP cells from the same manufacturer which also have the same rated capacity of 1500 mAh.

For the investigation, several initial tests were conducted, incl.:
– EIS measurements as a function of SoC,
– capacity tests,
– HPPC tests as a function of SoC, and
– incremental OCV measurements.

After that, full cycles with maximum continuous charge and discharge currents were applied to the cells in order to get fast ageing results for a preliminary evaluation of the general ageing behaviour. Intermediate checkups were conducted every 50 cycles. This poster presents the current status of the ageing process, with two of the cells (one LFP, one SIB) already at an SoH of 0 %. Further tests using the lower, recommended currents are planned.

The experiments show significant differences in the behaviour of SIB compared to LFP cells. Electrical characterisation using EIS or HPPC tests needs to take the impedance increase from high to low frequencies into account. Deviations in impedance of SIBs at begin of life (BoL) also correlate with a faster loss of SoH under full cycles. However, high variations of the investigated LFP cells imply general production issues with cells from that manufacturer, which might have skewed the results.