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Thermal Runaway Behavior of Ni-Rich NCM 9-Series Lithium-Ion Batteries

2023.02.02

Nickel-cobalt-manganese (NCM) lithium-ion batteries exhibit inherent thermal stability limitations. The cathode materials undergo violent decomposition at 250-300℃, releasing oxygen that triggers electrolyte combustion and potential battery explosion.

Current industry development has progressed from low-nickel NCM 3-series to high-nickel 8-series and ultra-high-nickel 9-series batteries. Theoretically, this increasing active metal content reduces cathode material thermal stability, consequently elevating thermal runaway risks.

Our testing with the BAC-420AE Large Battery Adiabatic Calorimeter demonstrates that 9-series batteries exhibit significantly more severe thermal runaway characteristics compared to other NCM battery types.

Experimental Conditions

  • Sample: NCM9-Series pouch-type lithium-ion battery (5Ah)
  • Instruments: BAC-420AE Large Battery Adiabatic Calorimeter, battery charge/discharge system, TP700 multi-channel temperature recorder
  • Test modes: HWS-R mode, temperature difference baseline mode
  • Recording frequency: 1–100 Hz
  • Self-Heating detection threshold: 0.02 ℃/min
  • Thermocouple locations: center point of battery main surface (sample thermocouple), positive electrode (additional thermocouple)

Experimental Result

Test data showed that the NCM9-series lithium-ion battery had a self-heating onset temperature (Tonset) of 86.78℃ and thermal runaway onset temperature (TTR) of 202.76℃, with the battery voltage plunge point basically consistent with TTR.

After reaching TTR, the battery exhibited an extremely high temperature rise rate, achieving the peak thermal runaway temperature of 1109℃ on its surface within 2 seconds, with a maximum heating rate of approximately 48,900℃/min.

Compared with the 9-series battery, as shown in Figure 2, the 6-series battery required 70 seconds from TTR to Tmax with a maximum heating rate of about 6,500℃/min, while the 8-series battery needed 5 seconds with a maximum heating rate of around 20,600℃/min, demonstrating that the severity of battery thermal runaway increases progressively with higher nickel content.

Thermal runaway of 9-series Li-ion ternary battery
Figure 1. Thermal runaway characteristics of NCM9-series lithium-ion batteries: (a) temperature-voltage profiles and (b) heating rate versus temperature curve

Self-heating onset temperature（Tonset***）/℃

Thermal Runaway Onset Temperature（
TTR***）
/℃

Maximum Thermal Runaway Temperature（
Tmax）/℃

Maximum Rate of Temperature Rise(dT/dt)max/（
℃*min1）

Mass Loss Rate%

86.78

202.76

1059.05

48896.05

56.53

Table 1 Key thermal runaway parameters of NCM9-series lithium-ion batteries*
*All above parameters were calculated based on temperatures measured at the sample thermocouple contact point; **Tonset determination criterion: dT/dt ≥0.02℃/min; ***TTR determination criterion: dT/dt ≥60℃/min.
6-series ternary temperature rise rate-temperature
Figure 2. (a) Heating rate versus temperature curve for NCM6-series and (b) heating rate versus temperature curve for NCM8-series batteries
Fig. 3 Sample Li-ion battery (a) Thermal runaway video and (b) Post-experiment cavity photo

Experimental Conclusions

This experiment measured the thermal runaway characteristic parameters of 9-series NCM lithium batteries using the BAC-420AE Large Battery Adiabatic Calorimeter. The experimental data obtained will facilitate improvements in this battery type to enhance its safety performance.

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