Polyurethane Binder for Lithium Secondary Cell Electrodes
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Solution Overview
Problem
Conventional lithium secondary battery electrodes face issues with adhesiveness to collectors, flexibility, and resistance to electrolytic solutions, leading to problems such as electrode release during press molding and reduced battery capacity retention.
Innovation Solution
A binder for lithium secondary battery electrodes is developed, comprising a water dispersion of polyurethane formed from a polyisocyanate, a compound with two or more active hydrogen groups, a compound with one or more active hydrogen groups and a hydrophilic group, and a chain extending agent, specifically using olefinic polyol and polycarbonate diol, which enhances adhesiveness and flexibility while maintaining resistance to electrolytic solutions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If fluorine resin is used as binder, then adhesive force to active material is provided, but adhesiveness to metal current collector is insufficient and flexibility is poor
Solution Approach 1:
The invention uses a composite binder system combining SBR (styrene-butadiene rubber) and CMBR (chloroprene-methylvinyl butadiene rubber) in specific ratios. This composite approach leverages the strengths of each component: SBR provides flexibility and adhesion to active material, while CMBR contributes oil resistance and structural stability, resolving the contradiction between flexibility and adhesive performance.
2Adaptability or versatility
If styrene-butadiene latex is used as binder, then flexibility and adhesiveness to metal current collector are improved, but adhesive force is weak and electrode structure cannot be maintained
Solution Approach 1:
The patent combines SBR and CMBR in a specific ratio range (70:30 to 30:70) to create a binder with balanced properties. CMBR compensates for the weak adhesive force of SBR while SBR maintains the flexibility advantage, enabling the electrode to maintain its structure during charging-discharging cycles.
Solution Approach 2:
The invention optimizes the molecular weight, glass transition temperature, and composition ratio of the binder components. By controlling the glass transition temperature within a specific range and adjusting the SBR/CMBR ratio, the binder achieves both sufficient flexibility and adhesive strength.
3Quantity of substance
If binder content is decreased to enhance battery capacity, then capacity increases, but electrode layer is liable to be released during press molding
Solution Approach 1:
The patent optimizes the binder content within a specific range (3-15 wt% of total electrode weight) and adjusts the molecular weight and glass transition temperature of the binder polymers. This parameter optimization ensures sufficient adhesion at minimal binder content, preventing electrode release during press molding while maximizing battery capacity.
4Adaptability or versatility
If polymer with low glass transition temperature is used as binder, then flexibility is improved, but electrode layer is liable to be released from collector during press molding
Solution Approach 1:
The patent specifies a glass transition temperature range for the binder (below room temperature for SBR, below -50°C for CMBR) and optimizes the crosslinking density. This controlled parameter approach ensures the binder remains flexible enough to prevent cracking while maintaining sufficient adhesive stability during press molding operations.
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 binder provides high adhesiveness to collectors, prevents electrode release during press molding, and improves charge and discharge characteristics, resulting in enhanced battery performance and capacity retention.
Implementation Method 1
a water dispersion of a polyurethane formed of (A) a polyisocyanate, (B) a compound having two or more active hydrogen groups
Implementation Method 2
the (B) compound having two or more active hydrogen groups contains an olefinic polyol and/or a polycarbonate diol having a carbon number between carbonate bond chains of less than 6
Data Source
AI summary
A binder for an electrode of a lithium secondary battery contains a water dispersion of a polyurethane. The polyurethane has been formed of (A) a polyisocyanate, (B) a compound having two or more active hydrogen groups, (C) a compound having one or more active hydrogen groups and a hydrophilic group, and (D) a chain extending agent. The (B) compound having two or more active hydrogen groups contains an olefinic polyol and/or a carbonate diol having a carbon number between carbonate bond chains of less than 6. The binder has high adhesiveness to a collector, does not cause release in press molding, has high flexibility, and is excellent in bindability and resistance to an electrolytic solution.