OCV-SOC Curves: NMC vs LFP

Open-Circuit Voltage as a function of State of Charge — two dominant EV chemistries

NMC — Sloped Curve Voltage varies meaningfully across the full SOC range (3.0 V → 4.2 V). This slope makes voltage-based SOC estimation reasonably reliable, especially outside the 40–60% mid-range where the curve is slightly flatter.

LFP — Flat Plateau (20–80%) Voltage is nearly constant (~3.27–3.32 V) across the usable range. A 10 mV measurement error corresponds to a ~30% SOC uncertainty. LFP BMS must rely on Coulomb counting, EIS, or OCV at rest.

Data: representative published OCV-SOC curves. Exact values vary by manufacturer, temperature, and C-rate. Measured at 25 °C, ~C/20 quasi-static sweep.