Application of Graphite Paper in Thermal Management of Solid-State Batteries

    Introduction

    Solid-state batteries, recognized as the core of next-generation energy storage technologies due to their high energy density and safety, still face critical challenges in thermal management during commercialization. Graphite paper (thickness: 5–100 μm, in-plane thermal conductivity: 1500 W/(m·K)), with its unique anisotropic thermal conduction and interfacial adaptability, offers an innovative solution for thermal management in solid-state batteries. This article analyzes its material characteristics, application scenarios, and technical challenges.

 I. Thermal Management Requirements and Challenges in Solid-State Batteries

    Solid-state batteries encounter two major thermal issues during charge/discharge cycles:Local Hotspot Formation: Joule heat generated by lithium-ion migration at the solid electrolyte/electrode interface can raise local temperatures to over 80°C, exceeding the decomposition threshold of sulfide electrolytes (60°C).Temperature Gradient Degradation: Interface contact resistance is highly temperature-sensitive; a 5°C temperature difference can increase capacity decay by 30%.Traditional metal heat sinks, hindered by high weight and poor through-plane thermal conductivity (e.g., copper foil: ~2 W/(m·K)), are inadequate. Graphite paper’s lightweight properties (density: 2.2 g/cm³) and superior in-plane thermal conduction make it an ideal alternative.

    II. Core Technical Advantages of Graphite Paper

    High-Efficiency In-Plane Thermal Conduction: Utilizing sp²-hybridized carbon layers, graphite paper achieves an in-plane thermal conductivity of 1500 W/(m·K)—3.75 times that of copper foil—effectively eliminating hotspots.Ultra-Thin and Flexible Integration: With a thickness of 50–100 μm, its integration into electrode layers minimally impacts volumetric energy density (<3%). Its flexibility accommodates stacking pressures (10–50 MPa) in solid-state batteries.Chemical Stability: Corrosion-resistant within the operating voltage window of solid-state batteries (0–5 V), compatible with lithium metal anodes and oxide/polymer electrolytes.Dual Conductive-Thermal Functionality: Low resistivity (~5×10⁻⁶ Ω·m) enables uniform current distribution, suppressing lithium dendrite growth.

    III. Application Scenarios and Technological Breakthroughs

1. Thermal Interface Layer at Electrode-Electrolyte Junctions

    Graphite paper is microporous-structured (pore size: 20 μm) and sandwiched between cathodes (e.g., NCM811) and solid electrolytes (e.g., LLZO):Functional Outcomes: Lateral heat diffusion reduces interfacial temperature differences to ≤3°C (experimental data) and extends cycle life by 50% (from 800 to 1200 cycles).Technological Innovation: Vertical carbon nanotube arrays grown via CVD on graphite paper enhance through-plane thermal conductivity to 50 W/(m·K), overcoming traditional longitudinal thermal limitations.

2. Module-Level 3D Thermal Architecture

    Integration of a “cold plate-graphite paper-cell stack” sandwich structure in battery modules:Thermal Simulation Validation: Under 3C charge/discharge conditions, peak module temperature drops from 78°C to 62°C, with temperature gradients reduced from 12°C to 4°C.

Weight Reduction Benefits: Compared to full-metal heat sinks, this design reduces weight by 40%, elevating energy density to 400 Wh/kg.

IV. Technical Challenges and Solutions

    Mechanical Stability Limitations: Electrode volume changes during cycling (e.g., silicon anode expansion >300%) risk graphite paper fracture.Improvement Strategies: Pre-lithiation enhances ductility (tensile strength increases from 15 MPa to 25 MPa), while polyimide fiber composites improve fracture elongation (from 2% to 8%).High-Temperature Oxidation Risks: Prolonged exposure to >80°C environments may degrade graphite paper edges.Countermeasures: Sputtering 100 nm silicon nitride coatings elevates oxidation resistance to 400°C.

V. Cost-Efficiency and Industrialization Prospects

Current graphite paper costs ~50/m².Fora100Ahbatteryrequiring0.2m²,thisadds10 per cell (~3% of total costs), demonstrating commercial feasibility. Continuous roll-to-roll graphitization (production speed: 5 m/min) will align with GWh-scale solid-state battery production post-2025.

Through material modifications (vertical thermal enhancement, surface passivation) and structural optimizations (microporous design, 3D integration), graphite paper delivers a lightweight and reliable thermal management solution for solid-state batteries. Future efforts must tailor compatibility with sulfide/oxide/polymer electrolytes and integrate smart technologies (e.g., embedded sensors). As solid-state battery technology matures, graphite paper is poised to become a cornerstone material in thermal management systems, driving transformative advancements in electric vehicles and energy storage.