Negative Electrode Binder Swelling for Battery Cycle Life
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Solution Overview
Problem
During the winding of non-aqueous electrolyte secondary battery electrode assemblies, the inner mixture layer is compressed, leading to reduced electrolyte liquid passage and increased ion dispersity, while the outer mixture layer experiences cracking and peeling due to expansion and contraction, resulting in poor cycle characteristics.
Innovation Solution
A non-aqueous electrolyte secondary battery design where the negative electrode has an outer mixture layer with a higher degree of binder swelling (150-250%) and an inner mixture layer with lower binder swelling (100-150%), preventing peeling and enhancing cycle characteristics by ensuring uniform electrode reactions and maintaining adhesion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the electrode assembly is wound tightly to improve space utilization, then the battery density increases, but the inner mixture layer is compressed causing reduced electrolyte passage and poor ion dispersity
Solution Approach 1:
The patent applies local quality by using binders with different degrees of swelling in different regions of the mixture layer. The inner mixture layer (near the winding center) contains binders with lower degree of swelling to maintain structural integrity under compression, while the outer mixture layer contains binders with higher degree of swelling to accommodate expansion and maintain electrolyte passages. This spatial differentiation of binder properties resolves the contradiction between tight winding density and ion dispersity.
2Reliability
If the outer mixture layer is made more flexible to prevent cracking during winding, then cycle characteristics improve, but the inner mixture layer loses adhesion and peeling occurs
Solution Approach 1:
The patent implements local quality by assigning different binder characteristics to different radial positions in the mixture layer. The inner layer uses binders with lower swelling (50-150%) that maintain strong adhesion to the current collector under compression, preventing peeling. The outer layer uses binders with higher swelling (150-300%) that provide flexibility and prevent cracking during charge-discharge cycles. This localized differentiation simultaneously achieves both adhesion and cycle stability.
3Ease of manufacture
If a uniform binder is used throughout the mixture layer to simplify manufacturing, then production cost decreases, but both cracking and peeling occur due to incompatible mechanical properties in different regions
Solution Approach 1:
The patent applies local quality by dividing the mixture layer into inner and outer regions with different binder specifications. The inner mixture layer uses binders with lower degree of swelling (50-150%) optimized for adhesion under compression, while the outer mixture layer uses binders with higher degree of swelling (150-300%) optimized for flexibility during expansion. This regional differentiation prevents both peeling and cracking, achieving electrode integrity despite increased manufacturing complexity.
Solution Approach 2:
The patent employs composite materials by combining different types of binders with distinct swelling characteristics within the same electrode structure. The inner layer uses binders such as polyvinylidene fluoride or carboxymethyl cellulose with lower swelling, while the outer layer uses binders like styrene-butadiene rubber with higher swelling. This composite approach creates a functionally graded material structure that accommodates the mechanical contradictions in different radial zones.
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 battery achieves improved cycle characteristics by preventing peeling of the outer mixture layer and maintaining ion dispersity within the inner layer, leading to enhanced performance and capacity maintenance.
Implementation Method 1
a degree of swelling of the binder included in the outer negative electrode mixture layer is higher than a degree of swelling of the binder included in the inner negative electrode mixture layer, and the outer negative electrode mixture layer includes a binder having a degree of swelling of 150 to 250%
Implementation Method 2
the inner negative electrode mixture layer is compressed, and the outer mixture layer is elongated. Thus, a passage for an electrolyte liquid shrinks in the inner mixture layer to lower dispersity of Li ions
Data Source
AI summary
A nonaqueous electrolyte secondary battery according to one embodiment of the present disclosure is provided with a wound-type electrode body. A negative electrode has: a negative electrode collector; and negative electrode mixture layers that are formed on both lateral surfaces of the negative electrode collector, while containing at least a negative electrode active material and a binder. The negative electrode mixture layers include an inner negative electrode mixture layer that is positioned on the inner circumference side of the negative electrode collector and an outer negative electrode mixture layer that is positioned on the outer circumference side. The swelling degree of the binder contained in the outer negative electrode mixture layer is higher than the swelling degree of the binder contained in the inner negative electrode mixture layer; and the outer negative electrode mixture layer contains a binder that has a swelling degree of from 150% to 250%.