High Compressive Strength Graphite for Battery Contact
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Solution Overview
Problem
Non-aqueous electrolyte secondary batteries with exposed negative electrode current collectors face challenges in maintaining effective electric contact with the battery case, leading to increased internal resistance and deteriorated current collecting properties.
Innovation Solution
Incorporating graphite particles with a compressive strength of 15 MPa or more as the negative electrode active material, which enhances the state of electric contact between the exposed negative electrode current collector and the battery case by increasing the stress relaxation force, thereby reducing internal resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the negative electrode current collector is exposed on the outer peripheral surface of the wound-type electrode assembly to contact the inner surface of the metal exterior body, then the battery structure is simplified and volume is reduced, but the state of electric contact deteriorates and internal resistance increases
Solution Approach 1:
The patent changes the physical parameter of graphite particles by specifying a compressive strength of 15 MPa or more. This parameter change enables the graphite particles to generate sufficient stress relaxation force that pushes the negative electrode current collector outward, improving contact with the battery case while maintaining the simplified exposed structure.
Solution Approach 2:
The patent introduces graphite particles as an intermediary medium between the negative electrode current collector and the battery case. These particles serve dual functions: they maintain structural integrity during winding and provide stress relaxation force to ensure good electric contact, thus resolving the contradiction between structural simplification and contact quality.
2Volume of stationary object
If the negative electrode current collector is exposed on the outer peripheral surface of the wound-type electrode assembly, then the battery volume is reduced, but the contact area with the battery case is insufficient and internal resistance increases
Solution Approach 1:
The patent specifies graphite particles with compressive strength of 15 MPa or more, which generates sufficient stress relaxation force to push the negative electrode current collector outward against the battery case. This ensures adequate contact area and good electric contact while maintaining the compact exposed structure, thus resolving the volume-contact area contradiction.
3Ease of manufacture
If graphite particles with low compressive strength are used, then the negative electrode mixture layer is easy to form, but the stress relaxation force is insufficient and electric contact deteriorates
Solution Approach 1:
The patent establishes a specific threshold for graphite particle compressive strength (15 MPa or more) that balances manufacturability and performance. This parameter specification ensures that the graphite particles are sufficiently strong to generate stress relaxation force for good electric contact, while still being workable for forming the negative electrode mixture layer.
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 use of high-compressive-strength graphite particles improves the contact between the negative electrode and the battery case, resulting in decreased internal resistance, enhanced current discharge capabilities, and increased safety against external shorts.
Implementation Method 1
the graphite particles have a compressive strength of 15 MPa or more... enhances the state of electric contact between the exposed negative electrode current collector and the battery case by increasing the stress relaxation force
Data Source
AI summary
A nonaqueous electrolyte secondary battery (10) according to one embodiment of the present disclosure is provided with: an electrode body (14) which is obtained by winding a positive electrode (30) and a negative electrode (40), with a separator (50) being interposed therebetween; a nonaqueous electrolyte; and a battery case (15) which is formed of a metal and contains the electrode body (14) and the nonaqueous electrolyte. The negative electrode (40) comprises a negative electrode collector (41) and a negative electrode active material layer (42) that contains graphite particles as a negative electrode active material; the outer circumferential surface of the electrode body (14) is provided with an exposure part (43) from which the negative electrode collector (41) is exposed so as to be in contact with the inner circumferential surface of the battery case (15); and the graphite particles have a compressive strength of 15 MPa or more.