Core-Shell Anode Binder for Silicon Expansion and Cycle Life
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Solution Overview
Problem
Lithium-ion batteries face challenges with silicon-based electrode active materials due to volume expansion issues, leading to reduced binding force and poor cycle characteristics, making it difficult to maintain adhesive strength and resilience, which affects the capacity, performance, and lifespan of secondary batteries.
Innovation Solution
A binder for secondary battery anodes is developed using a combination of styrene-butadiene-based rubber with a core-shell structure and nitrile-butadiene-based rubber, with specific monomer compositions and weight ratios, along with a cellulose-based water-soluble polymer, to enhance adhesive strength and resilience.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon-based electrode active material is used to achieve high capacity, then capacity increases significantly, but volume expansion occurs during charging and discharging causing reduced binding force and poor cycle characteristics
Solution Approach 1:
The patent uses a composite binder system combining styrene-butadiene rubber (providing elasticity to accommodate volume expansion) and carboxymethyl cellulose (providing adhesive strength to maintain binding force). This composite material approach allows the anode to simultaneously achieve high capacity with silicon-based materials while maintaining good cycle characteristics through the complementary properties of the two binder components.
2Quantity of substance
If silicon-based electrode active material is used to achieve high capacity, then capacity increases significantly, but binding force decreases due to volume expansion
Solution Approach 1:
The patent employs a composite binder system where styrene-butadiene rubber provides elasticity to accommodate volume expansion during lithium ion insertion/extraction, while carboxymethyl cellulose provides strong adhesive bonding. This combination maintains binding force even when silicon-based active material undergoes volume expansion, enabling high capacity operation without losing electrode integrity.
Solution Approach 2:
The patent optimizes the weight ratio of styrene-butadiene rubber to carboxymethyl cellulose within specific ranges (SBC: 10-40 parts by weight, CMC: 1-20 parts by weight) to achieve the optimal balance between elasticity and adhesive strength. By adjusting these parameter ratios, the binder system can adapt to different silicon content levels while maintaining both binding force and capacity.
3Strength
If conventional binder materials are used to maintain adhesive strength, then binding force is maintained, but resilience decreases when volume expansion exceeds 200%
Solution Approach 1:
The patent combines styrene-butadiene rubber (natural elastomer providing resilience) with carboxymethyl cellulose (water-soluble polymer providing adhesive strength). The SBC component can elastically deform to accommodate over 200% volume expansion, while the CMC component maintains strong binding force. This composite approach overcomes the limitation of conventional single-component binders that must choose between strength and resilience.
Solution Approach 2:
The binder system exhibits local quality differentiation where different components perform specialized functions: styrene-butadiene rubber localized at regions requiring elastic deformation provides resilience, while carboxymethyl cellulose localized at interfaces requiring strong bonding provides adhesive strength. This functional differentiation allows the binder as a whole to simultaneously achieve both high adhesive strength and high resilience.
Data Source
AI summary
Disclosed are a binder for a secondary battery anode including styrene-butadiene-based rubber with a core-shell structure and nitrile-butadiene-based rubber with a gel content of 15% or more, wherein a weight ratio of the styrene-butadiene-based rubber and the nitrile-butadiene-based rubber is 65:35 to 99:1, an anode mixture for a secondary battery, and an anode and a secondary battery including the same.