This study investigates the thermal runaway characteristics of LiFePO4 (LFP) and LiNi0.5Co0.2Mn0.3O2 (NCM523) energy storage batteries under external heating abuse conditions. The findings provide critical insights for early warning systems and fire safety protocols in energy storage applications.
Thermal Runaway Behavior
The LFP energy storage battery released white smoke without combustion, reaching a maximum temperature of 534.2°C. In contrast, the ternary NCM523 battery exhibited violent combustion with jet flames, achieving a peak temperature of 1,052.4°C. Key temperature metrics are summarized below:
| Battery Type | Max Temp. (°C) | Time to Peak (s) | Avg. Heating Rate (°C/s) |
|---|---|---|---|
| LFP | 534.2 | 2,894 | 0.79 |
| NCM523 | 1,052.4 | 1,964 | 10.52 |
Heat Release Dynamics
Energy release parameters were calculated using oxygen consumption calorimetry. The total heat release (THR) and peak heat release rate (PHRR) demonstrate significant differences:
$$ \text{PHRR} = E \cdot \left( \dot{m}_{O_2}^0 – \dot{m}_{O_2} \right) $$
Where \( E = 13.1 \, \text{kJ/g} \), representing the energy released per unit mass of consumed oxygen.
| Parameter | LFP | NCM523 |
|---|---|---|
| THR (MJ) | 0.162 | 3.147 |
| PHRR (kW) | 1.81 | 134.85 |
| Smoke Release Rate (m²/s) | 7.54 | 2.28 |
Gas Emission Profiles
Both energy storage battery types produced similar gas compositions during thermal runaway:
$$ \text{CO}_2 + 2\text{Li}^+ + 2e^- \rightarrow \text{Li}_2\text{CO}_3 + \text{CO} $$
$$ \text{C}_3\text{H}_6\text{O}_3 \, (\text{DMC}) + 2\text{Li} \rightarrow \text{Li}_2\text{CO}_3 + \text{C}_2\text{H}_6 $$
| Gas Component | LFP (vol%) | NCM523 (vol%) |
|---|---|---|
| H2 | 38.2 | 32.7 |
| CO | 21.4 | 25.9 |
| CO2 | 17.8 | 28.1 |
Voltage Response Characteristics
Both energy storage battery types exhibited two-stage voltage drops during thermal runaway:
$$ \Delta V_1 = V_{\text{initial}} – V_{\text{plateau}} $$
$$ \Delta V_2 = V_{\text{plateau}} – 0 $$
| Event | LFP Time (s) | NCM523 Time (s) |
|---|---|---|
| First Voltage Drop | 2,237 | 1,949 |
| Second Voltage Drop | 2,576 | 1,960 |
| Thermal Runaway Onset | 2,610 | 1,995 |
Early Warning Implications
For energy storage battery systems, voltage signals provided earlier warnings than temperature measurements:
$$ t_{\text{warning}} = t_{\text{voltage}} – t_{\text{thermal}} $$
LFP batteries showed 373s advance warning, while NCM523 exhibited 46s lead time. Implementing multi-parameter monitoring (voltage, temperature, gas composition) significantly enhances safety in energy storage battery applications.