Why do battery packs require graphite paper
The optimal operating temperature for lithium batteries is generally between 15-35 ℃. During fast charging or high rate discharge, the surface of the battery cell will instantly accumulate heat, which can easily lead to:
- Single battery cell 'hot spot' too high → accelerated aging, touch heating out of control
- Large temperature difference within the module (>5 ℃) → inconsistent capacity attenuation, high BMS equilibrium pressure
- 800V High Voltage Fast Charging Popularization → Cooling Path Must be Shorter, Lighter, and More Adhesive
The characteristics of graphite paper perfectly match these pain points:
- Strong in-plane thermal conductivity: 150-1500 W/(m · K), with higher in-plane diffusion efficiency than aluminum (237) and copper (401)
- Weak vertical thermal conductivity: 5-15 W/(m · K), with priority given to "horizontal spreading" of heat, without disorderly transfer to the outer shell
- Ultra thin and flexible: 0.03-0.5mm bendable, with no air gap on the side/top/bottom of the battery cell
- Light: Density 1.5-2.1 g/cm ³, approximately 1/4 of copper
- Temperature resistance: -200~600 ℃ stable, flame retardant, low gas emission
Where to stick it in the battery pack and what to do
1. Thermal homogenization layer between battery cells (mainstream)
Insert a layer of 0.1-0.3mm graphite paper between the square shell/blade/soft pack battery cells:
- Transfer the heat from the high heat generating core horizontally to the neighbors
- The temperature difference of the module is reduced from 8-10 ℃ to within 3 ℃
- Suppress the uncontrolled spread of "one hot, nearby explosion" heat
2. Thermal bridge between battery cell and liquid cooled plate
- Stick it on the bottom or side of the battery cell to quickly transfer heat to the liquid cooling plate
- Lighter than a simple thermal pad and not afraid of vibration and detachment
- Can be die cut with adhesive backing, compatible with CTP/CTC non module structure
3. Thermal film for battery pack lining/top cover
- Laying graphite paper inside the package, the overall temperature field is more uniform
- Combined with a heating film in a low-temperature environment, the temperature rises faster and more evenly
4. Composite with phase change material (PCM)
- Graphite paper+phase change material: PCM absorbs heat during fast charging, and graphite paper spreads the heat out
- Kirin Battery and Blade Battery Low Temperature Edition both have similar ideas
5. Thermal runaway barrier auxiliary layer
- The outer layer is equipped with ceramic fiber/aerogel, and graphite paper is responsible for "diverting heat"
- Extend the temperature rise time of adjacent battery cells and leave windows for escape and power outage
Graphite paper vs traditional heat dissipation materials
| Comparison item | Aluminum foil/copper sheet | Thermal conductive silicone pad | Graphite paper |
| In-plane thermal conductivity | Medium (good copper but heavy) | Difference (1-5 W/m · K) | Extremely strong (150-1500) |
| Weight | Heavy | Middle | Light (1/4 copper weight) |
| Flexible bonding | Poor | Good | Excellent, bendable |
| Thickness occupation | 0.2mm+ | 0.5mm+ | 0.03–0.3mm |
| Uniform heating effect | Generally | Weak | Excellent |
| Cost | Upper middle | Middle | Medium (fast cost reduction in mass production) |
Metal is used for "skeleton thermal conductivity", graphite paper is used for "surface uniform heat", and thermal pads are used for "joint filling", complementing each other.
How to choose graphite paper for battery thermal management
| Parameter | Recommended scope | Explanation |
| Thickness | 0.05-0.3mm (between battery cells); 0.1-0.5mm (soaking layer) | Too thin and easy to break, too thick takes up space |
| In-plane thermal conductivity | ≥ 300 W/(m · K) (normal); ≥ 800 (high-power/fast charging) | Check the fast charging rate |
| Vertical thermal conductivity | Do not forcefully chase high, use thermal conductive adhesive/liquid cooling plate | Anisotropy is an advantage, not a disadvantage |
| Density | 1.5–1.8 g/cm³ | Flexible calendered paper |
| Purity | Fixed carbon ≥ 95%, high-purity grade ≥ 99% | Low sulfur, low chlorine, corrosion-resistant |
| Adhesive backing | Single sided PSA, temperature resistance ≥ 120 ℃ | Anti aging adhesive shall be used in the vibration environment of vehicle gauge |
| Flame retardant | UL94 V-0 | Essential car regulations |
| Tensile | ≥ 10MPa (natural); ≥ 15MPa (artificial) | Die cutting does not shed powder or crack |
| Surface treatment | Can be coated with PET/PI film | Insulation, oxidation prevention, and powder shedding prevention |
End
Graphite paper is used in the thermal management of new energy vehicle batteries to horizontally spread heat, vertically transfer heat to liquid cooling, and overall suppress temperature differences.
Choose it based on three things: whether the internal thermal conductivity is sufficient, whether the thickness takes up space, and whether the backing and die-cutting are stable.
It is not a substitute for liquid cooling, but a uniform heating layer that makes liquid cooling "twice the result with half the effort".
