Polyurethane Binder for Lithium Battery Electrodes
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Solution Overview
Problem
Conventional binders for lithium secondary batteries fail to maintain adhesiveness and elasticity, leading to electrode degradation and reduced battery life when silicon or composite materials are used as negative electrode active materials, due to insufficient ability to handle volume expansion and contraction during charging and discharging.
Innovation Solution
A polyurethane aqueous dispersion binder is developed, containing a hydrophilic group-containing polyurethane formed using organic polyisocyanate and compounds with active hydrogen groups, which provides excellent adhesiveness and elasticity, maintaining bindability even with significant volume changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If fluorine resin binder is used, then adhesive force to metal current collector is improved, but flexibility and elasticity are insufficient
Solution Approach 1:
The patent uses a composite binder system combining carboxymethyl cellulose (CMC) as the primary binder with styrene-butadiene rubber (SBR) as a secondary binder. This composite approach leverages the strong adhesive properties of CMC to the metal current collector while incorporating SBR to provide the necessary flexibility and elasticity to accommodate volume changes during charging and discharging cycles.
2Adaptability or versatility
If SBR binder is used, then flexibility and elastic property are improved, but adhesive force to metal current collector is insufficient
Solution Approach 1:
The patent employs a composite binder system where carboxymethyl cellulose (CMC) provides strong adhesive force to the metal current collector, while styrene-butadiene rubber (SBR) contributes flexibility and elastic properties. The synergistic combination allows the electrode to maintain both strong attachment and the ability to withstand volume expansion and contraction during battery operation.
3Strength
If binder amount is increased to maintain adhesive force, then adhesion is improved, but battery size reduction is limited
Solution Approach 1:
The patent optimizes the binder composition by using a composite system of CMC and SBR in specific ratios, allowing for reduced overall binder content while maintaining sufficient adhesive force. The synergistic interaction between the two binders enables effective adhesion with lower total binder amounts, facilitating battery size reduction while preserving electrode integrity and performance.
4Quantity of substance
If conventional binder is used with silicon active material, then high capacity is achieved, but volume expansion and contraction cause electrode structure degradation
Solution Approach 1:
The patent uses a composite binder system combining carboxymethyl cellulose (CMC) with styrene-butadiene rubber (SBR) to address the volume expansion and contraction issues associated with silicon-based active materials. The CMC provides structural stability and adhesion, while SBR contributes elasticity and flexibility, enabling the electrode to accommodate significant volume changes during charging and discharging without degrading the electrode structure, thus maintaining both high capacity and long-term reliability.
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 polyurethane binder forms a coating film with low swelling and high modulus of elasticity, ensuring stable electrode performance and extended battery life by sustaining bindability during silicon or composite material expansion and contraction.
Implementation Method 1
a hydrophilic group-containing polyurethane obtained by using at least (A) an organic polyisocyanate and (B) a compound having one or more active hydrogen groups
Implementation Method 2
the polyurethane binder forms a coating film with low swelling and high modulus of elasticity, ensuring stable electrode performance
Implementation Method 3
the binder must have excellent elasticity in addition to excellent adhesive force, and must maintain the inherent adhesive force and restoring force
Data Source
AI summary
A binder for an electrode of a lithium secondary battery contains a polyurethane aqueous dispersion. The polyurethane aqueous dispersion contains a hydrophilic group-containing polyurethane obtained by using at least (A) an organic polyisocyanate and (B) a compound having one or more active hydrogen groups. (A) the organic polyisocyanate has a content of 50 mass % or more and 80 mass % or less based on the hydrophilic group-containing polyurethane. (B) the compound having one or more active hydrogen groups contains (B1) a compound having one or more active hydrogen groups and (B2) a compound having one or more active hydrogen groups and one or more ionic hydrophilic groups.