Aqueous Binder System for Lithium Battery Anode Swelling Control
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Solution Overview
Problem
Conventional lithium secondary batteries face issues with charge and discharge capacity deterioration due to separation of electrode active material components and volume expansion during charging and discharging, leading to reduced battery capacity and lifespan, which existing binders like polyvinylidene fluoride fail to address effectively.
Innovation Solution
A lithium secondary battery using an anode mixture with carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) as aqueous binders, which provide strong adhesive strength and structural stability, allowing for increased anode active material ratio and reduced swelling, thereby enhancing battery capacity and processability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional organic solvent-based binder (PVdF) is used, then ease of manufacture is improved, but adhesive strength and structural stability are insufficient leading to electrode separation
Solution Approach 1:
The patent changes the chemical composition parameters of the binder from conventional PVdF to a specific aqueous binder system containing CMC (carboxymethyl cellulose) and SBR (styrene-butadiene rubber) with defined molecular weights and ratios. This parameter change enables both strong adhesion to graphite particles and structural stability during volume expansion, while maintaining ease of manufacture through aqueous-based processing.
Solution Approach 2:
The patent employs a composite binder system combining CMC and SBR in specific ratios. CMC provides structural stability and adhesion through its carboxymethyl groups, while SBR contributes elasticity and adhesion through its polymer structure. This composite approach achieves superior adhesive strength and structural stability compared to single-component binders, preventing electrode separation during charging-discharging cycles.
2Quantity of substance
If high ratio of anode active material is used to increase capacity, then energy density is improved, but electrode coating amount increases causing swelling and reduced cycle lifespan
Solution Approach 1:
The patent optimizes the binder composition parameters (CMC molecular weight: 500,000-900,000, CMC:SBR ratio: 1:0.1 to 1:5) to enable higher anode active material content (95-99 wt%) while maintaining electrode integrity. The specific parameter ranges of the binder components provide sufficient adhesion and swelling control to maintain cycle lifespan even with high active material ratios.
Solution Approach 2:
The aqueous binder system with CMC and SBR provides beforehand cushioning against volume expansion during charging-discharging cycles. The binder's physical properties (viscosity, elasticity) are designed to accommodate and cushion the expansion forces before they can cause electrode separation, thereby maintaining reliability with high active material content.
3Strength
If aqueous binder (CMC and SBR) is used to increase adhesive strength, then structural stability is improved, but slurry viscosity increases reducing processability
Solution Approach 1:
The patent carefully controls the molecular weight of CMC (500,000-900,000) and the particle size of SBR (90-150 nm) to optimize the balance between adhesive strength and slurry processability. These parameter specifications ensure sufficient adhesion while preventing excessive viscosity that would hinder coating and manufacturing processes.
Solution Approach 2:
The patent applies local quality by using SBR with specific particle size (90-150 nm) that provides localized adhesion at particle interfaces, while CMC provides bulk structural stability. This localized functional distribution achieves high adhesive strength without requiring uniformly high viscosity throughout the entire slurry, thereby maintaining processability.
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 use of CMC and SBR as aqueous binders in the anode mixture increases the solid content of the slurry, reduces swelling, and maintains battery characteristics even with higher electrode coating amounts, resulting in improved cycle lifespan and energy density.
Implementation Method 1
the anode mixture includes, as aqueous binders, carboxymethyl cellulose (CMC) having a degree of substitution of a hydroxyl group (—OH) with a carboxymethyl group (—CH2CO2H) of 0.7 to 1.2, a molecular weight (Mn) of 500,000 to 900,000, and a pH of 6.5 to 8.0 and styrene-butadiene rubber (SBR) having a particle diameter of 90 nm to 150 nm and a tensile strength of 90 kgf to 160 kgf
Data Source
AI summary
Disclosed is a lithium secondary battery that includes an anode coated with an anode mixture including an anode active material, a cathode coated with a cathode mixture including a cathode active material, and a non-aqueous electrolyte, wherein the anode mixture includes, as aqueous binders, carboxymethyl cellulose (CMC) having a degree of substitution of a hydroxyl group (—OH) with a carboxymethyl group (—CH2CO2H) of 0.7 to 1.2, a molecular weight (Mn) of 500,000 to 900,000, and a pH of 6.5 to 8.0 and styrene-butadiene rubber (SBR) having a particle diameter of 90 nm to 150 nm and a tensile strength of 90 kgf to 160 kgf, and the anode has an electrode coating amount of 10 to 20 mg/cm2 and that enhances electrode processability and reduces a swelling phenomenon.