Composite 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 battery's capacity, performance, and lifespan.
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 battery capacity increases, 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) with carboxymethyl cellulose (CMC) and polyacrylic acid (PAA) (providing adhesive strength). This composite approach allows the binder to simultaneously handle the mechanical stress from silicon expansion while maintaining strong attachment to the electrode substrate, thus preserving cycle characteristics while enabling high capacity silicon-based anodes
2Quantity of substance
If silicon-based electrode active material is used to achieve high capacity, then battery capacity increases, but binding force to binder decreases due to volume expansion
Solution Approach 1:
The patent modifies the binder's mechanical parameters by selecting styrene-butadiene rubber with specific glass transition temperature (Tg ≤ -50°C) and elongation at break (≥600%) properties. These parameter changes enable the binder to undergo large elastic deformations during silicon volume expansion cycles while maintaining binding force, thus preserving both high capacity and strong adhesion
3Strength
If conventional binder materials are used to maintain adhesive strength, then binding force is sufficient, but resilience during large volume expansion is insufficient
Solution Approach 1:
The patent merges two distinct binder materials with complementary properties: styrene-butadiene rubber (providing resilience through high elasticity and low Tg) and CMC/PAA (providing adhesive strength through chemical bonding). This combination allows the binder system to simultaneously deliver strong adhesion and high resilience during large volume expansion, overcoming the limitations of conventional single-material binders
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.