Negative Electrode Carbon Fiber Network for Cycle Stability
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Solution Overview
Problem
Current lithium-ion secondary batteries face challenges in improving cycle characteristics, particularly with the use of silicon and tin as negative electrode active materials, where expansion and shrinkage during charging and discharging lead to conductive path collapse and reduced battery performance.
Innovation Solution
Incorporating a combination of first and second carbon fibers with specific diameter and length ranges into the negative electrode active material, where the first carbon fiber (70 nm to 150 nm in diameter and 1 μm to 10 μm in length) secures electron paths on the surface and the second carbon fiber (150 nm or greater in diameter or 10 μm or longer) contributes to a conductive network between particles, enhancing cycle stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If silicon or tin is used as negative electrode active material to increase theoretical capacity, then energy density is improved, but conductive path collapse occurs due to expansion and shrinkage during charging and discharging
Solution Approach 1:
The patent uses a composite material system consisting of silicon or tin negative electrode active material particles combined with carbon fibers of two different size ranges. The carbon fibers form a conductive network that maintains electrical conductivity even when the silicon/tin particles expand and shrink during charging and discharging cycles, thus preserving both high energy density and conductive path stability.
Solution Approach 2:
The patent specifies precise parameter ranges for carbon fiber dimensions: first carbon fibers with diameter of 0.5 μm or less and length of 10 μm or more, and second carbon fibers with diameter of 1 μm or more. These parameter specifications optimize the balance between flexibility (to accommodate particle expansion/shrinkage) and structural integrity (to maintain conductive paths), resolving the contradiction between energy density and conductive path stability.
2Reliability
If carbon fibers are added to maintain conductive paths, then cycle characteristics are improved, but device complexity increases due to multiple fiber specifications
Solution Approach 1:
The patent divides the carbon fiber conductive agent into two distinct size categories with specific parameter ranges. This segmentation allows each fiber type to perform specialized functions: finer fibers for flexibility and surface coverage, coarser fibers for structural framework. While this increases material specification complexity, it actually simplifies the overall design by clearly defining functional roles for each component type.
Solution Approach 2:
The carbon fibers serve multiple functions simultaneously: they act as conductive agents, provide mechanical support during expansion/shrinkage cycles, and form a flexible network that accommodates particle movement. This multi-functionality reduces the need for additional separate components, thereby managing device complexity while improving cycle characteristics.
Data Source
AI summary
Provided are a negative electrode, a battery, a battery pack, an electronic apparatus, an electrically driven vehicle, an electrical storage device, and an electric power system which are capable of improving cycle characteristics.