| name | battery-thermal-management |
| description | Battery thermal management — heat generation (Bernardi model), cooling strategies (air/liquid/phase change), thermal runaway, cold plate design, pack temperature uniformity, SOC/SOH. |
| metadata | {"priority":7,"promptSignals":{"phrases":["battery thermal management","battery cooling","thermal runaway","battery pack temperature","cold plate battery","BMS thermal","EV battery cooling"],"minScore":3}} |
Battery Thermal Management — Complete Skill
Heat Generation in Battery Cells
Bernardi Heat Generation Model
Q_gen = I × (U_oc - V_terminal) + I × T × (∂U_oc/∂T)
I = current [A]; U_oc = open-circuit voltage; V = terminal voltage
T × (∂U_oc/∂T) = reversible heat (entropy term; positive for charging, negative for discharging)
Simplified (Joule heating dominant at high C-rate):
Q_gen ≈ I² × R_internal [W/cell]
R_internal: NMC 18650 ≈ 20–50 mΩ; LFP prismatic ≈ 0.5–2 mΩ (varies with SOC, T)
At typical conditions (1C discharge, 50% SOC, 25°C):
Q_gen ≈ 0.2–1.5 W/cell depending on chemistry and format
Cell Chemistries and Thermal Properties
| Chemistry | Nominal V | Energy density [Wh/kg] | T_optimal | T_max | Notes |
|---|
| NMC | 3.6V | 150–260 | 15–35°C | 55°C | EV common; high energy |
| LFP | 3.2V | 90–160 | 20–40°C | 60°C | Long life; safer; lower V |
| NCA | 3.65V | 200–260 | 15–35°C | 50°C | Tesla; highest energy |
| LTO | 2.3V | 50–80 | -30–40°C | 55°C | Long cycle; fast charge |
| LiCoO₂ | 3.7V | 150–200 | 15–35°C | 50°C | Consumer electronics |
Specific heat capacity c_p:
NMC: 1000–1100 J/kg·K; LFP: 1000 J/kg·K
Thermal conductivity:
Radial (in-plane): 20–40 W/m·K (electrolyte + electrode layers)
Axial (through-thickness): 1–3 W/m·K (much lower; determines heat path)
Temperature Uniformity Requirement
ΔT within pack ≤ 5°C (target); ≤ 10°C (acceptable)
Non-uniform T → cell aging imbalance → capacity fade → accelerated degradation
Module design: tab cooling (effective for prismatic); side cooling; bottom cooling
Cooling Strategies
Air Cooling (Forced Convection)
Simplest; lowest cost; lowest thermal performance
h_air ≈ 10–50 W/m²K; limits heat removal to ~500 W/kWh
Turbulent channel:
Nu = 0.023 Re^0.8 Pr^0.4 → h = Nu × k_air / D_h
Air at 25°C: k = 0.026 W/mK; ν = 15.7×10⁻⁶ m²/s; Pr = 0.71
Limitations: poor at high C-rate (>2C); large temperature gradient along flow path; noise
Liquid Cooling (Cold Plate)
Indirect (cold plate under pack):
h_liquid ≈ 1000–5000 W/m²K (turbulent water flow)
Can handle 2–5 kW/module
Cold plate design:
Channels: rectangular, parallel; ΔP = 12μLQ/(nwh³) [laminar flow; n = channels, w = width, h = height]
Target: T_outlet - T_inlet ≤ 5°C; T_cell,max - T_coolant,in ≤ 10°C
Thermal resistance from cell to coolant:
R_thermal = t_cell/(k_cell × A) + R_contact + t_coldplate/(k_Al × A) + 1/(h_channel × A_channel)
Coolant: 50% ethylene glycol/water; k = 0.4 W/mK; operating -40 to +65°C
Immersion Cooling (Direct)
Dielectric fluid (mineral oil, 3M Novec) directly contacts cells
h ≈ 200–1000 W/m²K (natural), 500–5000 W/m²K (forced)
Handles very high power density (> 5C); temperature uniformity excellent
Complexity: fluid containment, dielectric selection, leak risk
Phase Change Material (PCM)
PCM stores latent heat during peak load → releases slowly
Paraffin wax (n-eicosane): T_melt = 36–42°C; h_fg = 240 kJ/kg
k_PCM ≈ 0.2 W/mK → enhance with metal foam or graphite matrix (k → 5–20 W/mK)
Thermal Runaway
Mechanism:
- Heat source (overcharge, short, external heat, dendrite)
- Temperature > 70°C → SEI decomposition
- Temperature > 90–130°C → exothermic reactions (NMC anode + electrolyte)
- Temperature > 150°C → separator melts; internal short
- Temperature > 200°C → cathode decomposition; O₂ release + electrolyte combustion
- Runaway at > 300°C; uncontrolled vent + fire + potentially explosion
Key parameter: Self-Heating Rate
dT/dt|onset = Q_gen / (m × c_p) - Q_cooling / (m × c_p)
Thermal runaway if dT/dt positive and accelerating
Prevention:
BMS (Battery Management System): overvoltage, overtemperature, overcurrent cutoff
Cell-level fuses, PTC (Positive Temperature Coefficient) resistors
Firewall between cells; venting to external; fire suppression spray
State of Charge (SOC) and State of Health (SOH)
SOC = Q_remaining / Q_nominal × 100%
Methods: Coulomb counting (integrating current), OCV lookup, Kalman filter fusion
SOH = Q_current_capacity / Q_initial_capacity × 100%
Degradation mechanisms: lithium plating (low-T), SEI growth, particle cracking, gas evolution
End of life: SOH < 80% (EV); SOH < 70% (stationary storage second life)
Thermal Model
Lumped model (per cell):
m c_p dT/dt = Q_gen - Q_conv - Q_cond
Q_conv = h A (T_cell - T_coolant)
Q_gen = I² R_int
Coupled electro-thermal model:
R_int = R_int(T, SOC) → coupled equations; solve iteratively in MATLAB/Python/COMSOL
Output
Provide: Q_gen per cell [W] at operating C-rate, ΔT expected across pack [°C], cooling strategy recommendation, cold plate flow rate and ΔP [kPa], T_cell,max vs. T_limit, thermal runaway onset temperature, BMS protection triggers.
