Water-Based Binder for Li-Ion Cathode Coating
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Solution Overview
Problem
Existing binders for high voltage Li-ion batteries, such as PVDF in organic solvents, are costly, environmentally harmful, flammable, and toxic, while water-based binders face challenges in achieving adequate coating thickness and stability for cathode materials like Spinel LiNi0.5Mn1.5O4 (LMNO) with good cycling performance and capacity retention.
Innovation Solution
A combination of carboxymethylcellulose (CMC) and a low glass transition temperature polyacrylic polymer, such as SX-50 or PAA, is used as a water-based binder to form a cathode layer with adequate thickness and stability, ensuring good adhesion and electrochemical performance without organic solvents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If PVDF binder with organic solvent (NMP) is used, then good adhesion and film quality are achieved, but environmental harm, cost, and safety issues arise
Solution Approach 1:
The invention changes the fundamental parameter of the binder system from organic-based (PVDF/NMP) to water-based (CMC/polyacrylic), transforming the chemical composition and solvent type while maintaining binding functionality. This parameter change eliminates environmental and safety issues associated with organic solvents while preserving adhesion properties through the synergistic combination of CMC and polyacrylic polymers.
Solution Approach 2:
The invention uses a composite binder system combining two different water-based polymers (CMC and polyacrylic) to achieve the adhesion and film quality previously only attainable with organic binders. The composite structure leverages the complementary properties of each polymer: CMC provides structural integrity and adhesion, while polyacrylic with low Tg provides flexibility and crack resistance, together replacing the performance of PVDF/NMP systems.
2Object-affected harmful factors
If water-based binder is used, then environmental friendliness and cost-effectiveness improve, but coating thickness and film quality deteriorate
Solution Approach 1:
The composite binder system combines CMC and polyacrylic in specific ratios to achieve adequate coating thickness and superior film quality. The polyacrylic component with low glass transition temperature provides flexibility that prevents cracking during coating formation, while CMC ensures proper adhesion and structural integrity, together enabling water-based binders to achieve thicknesses greater than 100 microns with excellent film quality.
Solution Approach 2:
The invention changes the physical and chemical parameters of the water-based binder, specifically selecting polyacrylic with glass transition temperature around 0°C or lower, to improve coating flexibility and crack resistance. This parameter optimization enables the water-based system to achieve adequate coating thickness and maintain film quality without the limitations previously associated with water-based binders.
3Object-affected harmful factors
If water-based binder is used, then environmental safety improves, but cycling performance and capacity retention worsen
Solution Approach 1:
The composite binder system combines the adhesion benefits of CMC with the flexibility of low-Tg polyacrylic to achieve cycling performance and capacity retention comparable to or exceeding traditional PVDF binders. The synergistic interaction between the two polymers maintains electrode structural integrity during repeated charge-discharge cycles, preventing particle detachment and maintaining electrical contact, thereby achieving superior reliability in high voltage Li-ion batteries.
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 water-based binder system achieves coating thicknesses greater than 100 microns with no cracking, excellent adhesion, and superior cycling and capacity retention, comparable to or exceeding performance with traditional PVDF binders, while being environmentally friendly and cost-effective.
Implementation Method 1
a polyacrylic characterized as having low glass transition temperature, Tg, around 0° C. or lower, and good adhesion to Al
Implementation Method 2
The binder commonly used is PVDF (polyvinylidene difluoride) dispersed in an organic solvent... An example of the second water compatible polymer according to some embodiments of the present invention is a polyacrylic characterized as having low glass transition temperature, Tg, around 0° C. or lower, and good adhesion to Al
Implementation Method 3
coating a conductive substrate with the slurry; and drying the coated substrate, forming a cathode layer on the substrate
Implementation Method 4
drying the coated substrate, forming a cathode layer on the substrate
Data Source
AI summary
The present invention generally relates to using water-based binders for high voltage cathode materials, such as LMNO (spinel LiNi0.5Mn1.5O4), in Li-ion batteries. An example of a water compatible polymer binder according to some embodiments of the present invention is a combination of CMC (carboxymethylcellulose) and a second water compatible polymer that produce coatings of adequate thickness and loading (mAh/cm2). A method of forming a cathode for a Li-ion battery may include: preparing an aqueous solution of CMC; mixing together LMNO and carbon black; combining the LMNO and carbon black mixture with the CMC solution, an aqueous polyacrylic solution and distilled water, and mixing to form a slurry; coating a conductive substrate with the slurry; and drying the coated substrate, forming a cathode layer on the substrate. Furthermore, this invention describes a cathode for Li-ion batteries and tools for carrying out the above method.