Si-Based Negative Electrode Granules for Capacity Retention
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Solution Overview
Problem
Existing negative electrodes for lithium ion secondary batteries using Si-based active materials face challenges with capacity deterioration due to expansion and contraction, which cannot be sufficiently reduced, and high-strength binders like polyimides increase resistance and limit their usage.
Innovation Solution
A method of producing a negative electrode involving granule particles with a Si-based active material, a conductive material, and a first binder with an imide framework, combined with graphite particles and a second binder without an imide framework, applied to a current collector and dried, where the weight percentage of the first binder is between 5% and 15%, and the granule particles have an average diameter of 50 μm or less.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high-strength binders such as polyimide binders are used to address expansion and contraction of Si-based active materials, then capacity deterioration is reduced, but resistance increases and conductivity decreases
Solution Approach 1:
The patent optimizes the weight percentage of polyimide binder within a specific range (5-15%) to achieve the right balance between mechanical strength for capacity retention and electrical conductivity. This parameter optimization resolves the contradiction by finding the optimal concentration that provides sufficient binding strength while minimizing resistance increase.
Solution Approach 2:
The patent creates a composite negative electrode structure combining Si-based active material particles with polyimide binder and conductive material. This composite approach allows the polyimide to provide mechanical strength and capacity retention while the conductive material compensates for the resistance increase, thus resolving the contradiction between reliability and harmful factors.
2Reliability
If polyimide binders are added in large amounts to improve capacity retention, then expansion and contraction are better managed, but resistance increases significantly
Solution Approach 1:
The patent establishes an optimal weight percentage range (5-15%) for polyimide binder content, preventing excessive addition that would cause significant resistance increase. This parameter control resolves the contradiction by limiting the binder amount to the minimum necessary for capacity retention while avoiding excessive resistance.
Solution Approach 2:
The patent incorporates conductive material within the granule particles to compensate for the resistance introduced by polyimide binder. This copying approach replicates the conductive network that would otherwise be disrupted by the insulating binder, thus resolving the contradiction between reliability improvement and resistance reduction.
3Ease of manufacture
If granule particles with larger size are used, then manufacturing is easier, but capacity retention and performance are reduced
Solution Approach 1:
The patent optimizes the average diameter of granule particles to 50 μm or less, finding the optimal size balance between ease of manufacture and capacity retention performance. This parameter optimization resolves the contradiction by selecting a particle size that is sufficiently small for good performance but large enough for practical manufacturing.
Data Source
AI summary
A method of producing a negative electrode includes a process of preparing granule particles containing a Si-based active material, a conductive material, and a first binder having an imide framework, a process of preparing a negative electrode mixture containing the granule particles, graphite particles, and a second binder having no imide framework, and a process of applying the negative electrode mixture to a current collector and performing drying, wherein the weight percentage of the first binder contained in the granule particles is 5% or more and 15% or less, and the granule particles have an average diameter of 50 μm or less.