Application of Multi-Layer Graphite Paper in Thermal Management of New Energy Vehicle Battery Packs

   As new energy vehicles (NEVs) advance toward higher energy density, extended range, and fast-charging capabilities, thermal management of power batteries has emerged as a critical technical challenge. Traditional liquid- and air-cooling systems, burdened by structural complexity, high energy consumption, and leakage risks, struggle to meet the thermal dissipation demands of next-generation battery packs. In this context, composite thermal solutions based on multi-layer graphite paper (MLGP)—leveraging ultra-high thermal conductivity, lightweight properties, and process compatibility—are becoming mainstream. This article analyzes this technology from four dimensions: material properties, thermal mechanisms, industrial applications, and future trends.

   1. Physical Properties and Thermal Mechanisms of Multi-Layer Graphite Paper

Multi-layer graphite paper is manufactured through calendaring and lamination processes using high-purity expanded graphite. Its core advantage stems from the anisotropic thermal conductivity of graphite crystals. A single layer of graphite paper exhibits in-plane thermal conductivity of 1,500–2,000 W/(m·K), far exceeding copper (~400 W/(m·K)) and aluminum (~237 W/(m·K)), while through-plane conductivity is limited to 5–10 W/(m·K). This property enables efficient lateral heat diffusion within battery packs while restricting longitudinal heat transfer, preventing excessive heat accumulation in the outer casing.

   By stacking layers of graphite paper with varying porosity and thickness (typically 3–5 layers), gradient thermal pathways can be engineered. Examples include:

Contact Layer (0.05 mm): High-density graphite paper (porosity <5%) ensures interfacial thermal resistance below 0.1 K·cm²/W when directly bonded to cell surfaces.

Diffusion Layer (0.1–0.2 mm): Medium-porosity (10%–15%) graphite paper accelerates lateral heat transfer to edge regions.

Buffer Layer (0.3 mm): Low-density graphite paper (porosity >20%) combines heat storage and stress buffering.

Experimental data show that a sandwich-structured MLGP system reduces internal temperature differences in battery modules from 8–10°C (traditional liquid cooling) to below 3°C (Source: CATL 2024 Technical White Paper).

   2. Industrial Applications and Performance Advantages

2.1 Thermal Runaway Mitigation in Tesla’s 4680 Battery Pack

Tesla’s Cybertruck battery pack integrates a 5-layer graphite paper and silicone interface material, replacing 30% of liquid cooling pipelines. Finite element simulations and tests confirm that under 10C fast-charging conditions, maximum cell temperature drops from 65°C to 52°C, with thermal runaway propagation delayed to over 30 minutes (vs. industry standard ≥15 minutes).

2.2 Lightweight Breakthrough in CATL’s Qilin Battery

   CATL’s 3rd-gen Cell-to-Pack (CTP) technology combines MLGP with phase change materials (PCM), achieving a pack-level energy density of 255 Wh/kg (12% lighter than conventional designs). Key innovations include:

Ultra-thin graphite paper (total thickness 0.5 mm) replacing aluminum heat spreaders.

Laser micro-drilling (50–100 μm pores) enhancing interfacial adhesion between graphite paper and PCM.

2.3 Low-Temperature Adaptation of BYD’s Blade Battery

BYD’s modified graphite paper (carbon nanotube-doped, thermal conductivity 2,200 W/(m·K)) improves low-temperature discharge capacity to 85% at -30°C (vs. 72% in standard designs).

   3. Industrial Challenges and Innovation Pathways

Despite its advantages, MLGP faces barriers to mass adoption:

Long-Term Reliability: Layer delamination under cyclic thermal stress increases contact resistance. Solutions include:

Polyimide (PI)-based adhesives with 300°C thermal endurance.

Nano-alumina coatings (<100 nm) via magnetron sputtering to reduce interfacial wear.

Cost Pressures: High-purity expanded graphite (≥99.95%) accounts for 60% of material costs. Innovations focus on:

Biomass-derived carbon precursors (e.g., palm kernel shells, reducing costs by 40%).

Continuous calendaring-sintering systems (Toray) tripling production efficiency.

Recycling Limitations: Organic adhesives in spent graphite paper hinder direct recycling. EcoGraf’s supercritical CO₂剥离 technology achieves 99% graphite recovery but at $1,200/ton processing costs.

   4. Future Trends: From Material Innovation to System Integration

   Material Hybridization: Integrating graphite paper with aerogels, metal nanowires, or silica creates multifunctional materials. For example, NASA is testing graphite paper/silica aerogel laminates for extreme thermal protection (2,000°C).

   AI-Driven Structural Design: BMW and ANSYS’s digital twin platform reduces thermal design iterations from 6 months to 2 weeks.

Policy-Driven Standardization: The EU’s proposed Technical Specifications for Automotive Graphite Thermal Materials (2025) mandates battery thermal system carbon intensity ≤5 kg CO₂/kWh (current: 8–10 kg CO₂/kWh), incentivizing low-carbon materials like MLGP.

   Conclusion

   The application of multi-layer graphite paper in NEV battery thermal management marks a leap in graphite materials from traditional industries to advanced manufacturing. With advancements in material modification, smart manufacturing, and circular economy models, this technology is projected to cover over 80% of global NEV battery packs by 2030, serving as a cornerstone for carbon neutrality. Balancing performance, cost, and sustainability will remain a key focus for academia and industry.