Secondary Battery Electrode Structure for Interlayer Cohesive Strength
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Solution Overview
Problem
Lithium secondary batteries face cohesive failure issues, particularly interlayer cohesive failure, due to differences in adhesion and strength between electrode active materials, leading to degraded life characteristics and capacity, especially in multilayer electrodes with artificial and natural graphite.
Innovation Solution
An electrode structure with a current collector and electrode material mixture layers containing negative electrode active materials, conductive agents, and binders, where the ratio of maximum to minimum shear strength is 1.7 or less, as measured by surface and interfacial cutting analysis, minimizing cohesive failure and enhancing life and capacity characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the amount of polymer binder is decreased to increase electrode capacity, then capacity increases, but cohesive failure occurs due to decreased binding force
Solution Approach 1:
The patent changes the chemical composition parameters of the binder from conventional polymers to carboxymethyl cellulose (CMC) and styrene butadiene rubber (SBR) with specific weight ratios (CMC: 1-5 parts, SBR: 1-5 parts based on 100 parts active material). This parameter change enables the binder to provide sufficient adhesion at lower quantities, resolving the contradiction between minimizing binder amount and maintaining cohesive strength.
Solution Approach 2:
The patent uses a composite binder system combining CMC and SBR rather than a single polymer. CMC provides strong adhesion to graphite particles while SBR contributes elasticity and cohesive strength. This composite approach allows reduced total binder quantity while maintaining or improving resistance to cohesive failure during electrode expansion and contraction.
2Reliability
If multilayer electrode structure is used to improve life characteristics and capacity, then performance improves, but interlayer cohesive failure occurs due to differences in adhesion and strength
Solution Approach 1:
The patent applies different binder compositions to different layers of the multilayer electrode structure. Each layer containing graphite-based active materials uses the CMC-SBR binder system, providing locally optimized adhesion properties tailored to the specific requirements of graphite particles in each layer. This local quality approach ensures consistent interlayer bonding across the entire multilayer structure.
Solution Approach 2:
The CMC-SBR binder acts as an intermediary material between different graphite-based active material layers. It mediates the interface between layers with different adhesion characteristics, providing a common bonding mechanism that prevents interlayer cohesive failure. The binder's dual-component chemistry allows it to adhere to various graphite surface properties, bridging the adhesion gap between layers.
Data Source
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AI summary
Anelectrode for a secondary battery including a current collector, and at least oneelectrode material mixture layer on a surface of the current collector, the electrode material mixture layer including a negative electrode active material, a conductive agent, and a binderwherein, the electrode has a property such that in a regression curve obtained by regression analysis of shear strength data according to a cutting depth which are measured whileobliquely cutting the electrode material mixture layer from a surface thereofuntil reaching the current collector using a surface and interfacial cutting analysis system (SAICAS), a ratio of a maximum value (σmax) to a minimum value (σmin) of shear strength is 1.7 or less.