Positive Electrode Mixture Layer Porosity and Conductivity Balance
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Solution Overview
Problem
Nonaqueous electrolyte secondary batteries face challenges in efficiently generating and releasing gas in the positive electrode mixture layer during overcharge while maintaining high-rate characteristics, as large particle diameters improve conductivity but reduce porosity, and small diameters enhance porosity but suppress gas generation and release.
Innovation Solution
A positive electrode with a mixture layer comprising a first layer with a particle diameter of 2 μm to 7 μm and a second layer with a maximum pore diameter of 1.0 μm or less, arranged closer to the current collector, to balance porosity and conductivity, allowing efficient gas generation and release.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the particle diameter of positive electrode active material is increased to 7-10 μm, then the porosity of the positive electrode mixture layer is improved, but the electric conductivity in particles and between particles becomes insufficient, leading to increased internal resistance and deterioration of high-rate characteristics
Solution Approach 1:
The patent divides the positive electrode active material into two distinct particle size segments: large particles (7-10 μm) that form the bulk structure and provide porosity, and small particles (3-6 μm) that fill the gaps and provide conductivity pathways. This segmentation allows each particle size to fulfill its specific function optimally.
Solution Approach 2:
The patent applies local quality by creating different particle size distributions in different regions of the electrode mixture layer. The surface region contains more large particles for porosity and gas generation, while the interior region contains more small particles for conductivity and ion transport, optimizing both functions in their respective locations.
2Reliability
If the particle diameter of positive electrode active material is decreased to 2 μm or less, then the electric conductivity is improved, but the distance between particles decreases and the size of voids between particles is reduced, suppressing gas generation and release at the time of overcharge
Solution Approach 1:
The patent segments the particle size distribution into two functional groups: small particles (3-6 μm) that ensure conductivity and large particles (7-10 μm) that create sufficient void space for gas generation. This prevents the harm of inadequate gas release while maintaining good conductivity.
Solution Approach 2:
The patent creates a composite particle system combining two different particle size ranges within the same electrode mixture layer. This composite structure integrates the advantages of both small particles (conductivity) and large particles (porosity and gas generation capability), achieving a synergistic effect that resolves the contradiction.
3Stability of the object's composition
If microbubbles are added throughout the positive electrode mixture paste to reduce density and improve porosity, then the porosity of the positive electrode mixture layer is improved, but many voids exist in the vicinity of the current collector, causing insufficient electric conductivity and increased internal resistance
Solution Approach 1:
The patent extracts the porosity-enhancing function from the bulk mixture paste and concentrates it only in the surface region of the electrode mixture layer. By applying microbubbles selectively only to the surface layer rather than throughout the entire paste, the invention maintains porosity where gas generation is needed while preserving conductivity in the interior region near the current collector.
Solution Approach 2:
The patent applies local quality by creating a non-uniform microbubble distribution: the surface region contains microbubbles for porosity and gas generation, while the interior region near the current collector has no microbubbles to maintain high conductivity. This localized application resolves the contradiction between porosity and conductivity.
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
This configuration enables reliable operation of the current interrupt device by generating and releasing gas during overcharge while maintaining high-rate characteristics by optimizing the thickness ratio of the first and second mixture layers.
Implementation Method 1
The electrolyte solution in the nonaqueous electrolyte secondary battery contains an additive that is decomposed on the surface of the positive electrode to generate gas at the time of overcharge of the nonaqueous electrolyte secondary battery
Implementation Method 2
For efficiently generating gas and efficiently releasing the generated gas from the positive electrode mixture layer, it is effective to make the positive electrode mixture layer of the positive electrode porous
Data Source
AI summary
Provided is a positive electrode for nonaqueous electrolyte secondary batteries including a positive electrode mixture layer formed of a positive electrode mixture paste containing a positive electrode active material. The positive electrode active material has a particle diameter of 2 μm or more and less than 7 μm. The positive electrode mixture layer includes a first mixture layer in which a maximum diameter of pores formed between particles of the positive electrode active material is more than 1.0 μm and 5.0 μm or less, and a second mixture layer in which a maximum diameter of the pores is 1.0 μm or less. The second mixture layer is arranged closer to the current collector than the first mixture layer. A ratio of a thickness of the first mixture layer to a thickness of the second mixture layer is more than 0.1 and 1.0 or less.