Graphite-Epoxy Bipolar Plate for Fuel Cell
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Solution Overview
Problem
Existing fuel cell bipolar plates face challenges in achieving sufficient strength and flexibility while maintaining minimal thickness variation, especially when made thin-walled, leading to potential breakage during assembly and assembly-related damage.
Innovation Solution
A fuel cell bipolar plate is manufactured using a composition comprising porous artificial graphite, o-cresol novolak epoxy resin, phenol novolak resin, and an internal mold release agent, which enhances mechanical properties, moldability, and reduces thickness variation, allowing for thin-walled production with improved strength and flexibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the bipolar plate is made thin-walled to reduce fuel cell volume, then compactness is improved, but strength and flexibility deteriorate leading to breakage during assembly
Solution Approach 1:
The bipolar plate uses a composite material consisting of graphite powder (5-30 mass%) dispersed in a polyimide matrix. This composite structure provides both the thin-walled capability and the necessary strength-flexibility balance, preventing breakage during assembly while enabling compact fuel cell design
Solution Approach 2:
The invention optimizes specific parameters including graphite particle size (3-10 μm), graphite content (5-30 mass%), and plate thickness (0.1-0.3 mm) to achieve the desired balance between compactness and mechanical performance. The polyimide matrix molecular weight is controlled at 20,000-50,000 to ensure appropriate flexibility
2Strength
If short carbon fibers or metal fibers are mixed with molding material to increase strength, then flexural strength is improved, but elastic modulus becomes very high causing breakage at reduced thickness
Solution Approach 1:
Instead of using fibrous reinforcements, the invention uses graphite powder with controlled particle size (3-10 μm) and optimizes the polyimide matrix molecular weight (20,000-50,000) to achieve the desired strength-flexibility balance without excessive elastic modulus that would cause brittleness in thin-walled structures
Solution Approach 2:
The bipolar plate incorporates a porous structure with controlled void content (5-30%) which provides impact absorption and maintains flexibility while preserving sufficient strength, avoiding the brittleness associated with fibrous composites
3Stability of the object's composition
If a porous artificial graphite with high binder resin content is used to improve impact absorption, then flexibility is improved, but binder resin has high melt viscosity causing non-uniform flow and thickness variation
Solution Approach 1:
The invention controls the binder resin content at an optimal level (5-30 mass%) and uses graphite powder with specific particle size (3-10 μm) to ensure uniform flow during molding while maintaining sufficient impact absorption. The polyimide matrix molecular weight is optimized to balance viscosity and mechanical properties
Solution Approach 2:
The bipolar plate design incorporates varying local densities and porosity distributions, with different regions optimized for their specific functions while maintaining overall thickness uniformity through controlled molding parameters
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution results in bipolar plates with sufficient strength, flexibility, and precise thickness control, reducing the likelihood of breakage during assembly and enabling the production of thinner, more compact fuel cells with improved surface flatness and handleability.
Implementation Method 1
molding a composition which includes a given porous artificial graphite material, o-cresol novolak epoxy resin, phenol novolak resin and an internal mold release agent
Implementation Method 2
a composition which includes 100 parts by weight of a porous artificial graphite material... from 19 to 30 parts by weight of an epoxy resin comprised of a base resin and a curing agent
Implementation Method 3
from 0.1 to 1.0 part by weight of an internal mold release agent
Data Source
AI summary
This invention provides a bipolar plate for a fuel cell, produced by molding a composition comprising 100 parts by mass of a porous artificial graphite material having a true density of 1.63 to 2.20 g/ml and an average particle diameter (d = 50) of 20 to 100 µm, 19 to 30 parts by mass of an epoxy resin comprising a main agent and a curing agent, and 0.1 to 1.0 part by mass of an internal release agent. The main agent is an o-cresol novolak-type epoxy resin having an epoxy equivalent of 195 to 216 g/eq and an ICI viscosity of 0.20 to 1.00 Pa·s at 150°C. The curing agent is a phenol novolak resin having a hydroxyl equivalent of 103 to 106 g/eq and an ICI viscosity of 0.03 to 0.50 Pa·s at 150°C. The average thickness of a thin wall part is 0.12 to 0.20 mm. This bipolar plate is much superior in mechanical properties such as flexural strength and flexural strain and moldability to the conventional bipolar plate and, even in a reduced thickness, is satisfactorily strong and flexible and, at the same time, is also excellent in accuracy of the thickness.