Cathode Binder Solvent Exchange for Low-Moisture Insulating Coatings
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Solution Overview
Problem
Existing methods for manufacturing cathode binders or insulating solutions for lithium secondary batteries face challenges in preventing physical short circuits between the anode and cathode, particularly due to limitations in separator heat resistance and the complexity of insulation tape application.
Innovation Solution
A method involving the replacement of water as a dispersion solvent for conjugated diene latex with a non-aqueous organic solvent, such as N-methyl-pyrrolidone, is used to manufacture a cathode binder or insulating solution. This process includes heating and decompressing to achieve a moisture content of 10,000 ppm or less, allowing for simultaneous coating of the cathode mixture layer and insulating coating layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a microporous membrane separator is used to maintain electrical insulation between cathode and anode, then electrical insulation is achieved, but the separator shrinks at high temperatures (120-160°C) causing thermal runaway and internal short circuits
Solution Approach 1:
The patent applies composite materials by combining polyolefin resin (separator) with heat-resistant inorganic particles (alumina, silica, or boehmite) to create a composite insulating layer. This composite structure maintains the electrical insulation function of the separator while adding high-temperature stability from the inorganic particles, preventing shrinkage and thermal runaway at temperatures above 160°C.
Solution Approach 2:
The patent changes the thermal parameters of the insulating layer by incorporating inorganic particles with high melting points (alumina: 2050°C, silica: 1710°C, boehmite: 300°C). This parameter change enables the insulating layer to maintain its structural integrity and insulating properties at temperatures where conventional separators would fail, thereby resolving the heat resistance limitation.
2Reliability
If insulation tape is attached on the electrode tab to prevent short circuits, then physical short circuit prevention is improved, but the winding process becomes complicated and electrode assembly thickness increases
Solution Approach 1:
The patent merges the insulating function with the electrode structure itself by forming an insulating layer directly on the electrode tab surface through coating processes. This integration eliminates the need for separate insulation tape components and their complex winding processes, while maintaining effective insulation against short circuits between the tab and current collector.
Solution Approach 2:
The patent extracts the insulation function from the separate tape component and integrates it directly into the electrode assembly structure. By forming the insulating layer as part of the electrode coating process, the design removes the complexity of tape application while maintaining the essential insulation function.
3Reliability
If non-aqueous binder (PVDF) is used to form insulating layer on tab portion, then insulating properties are improved, but wet adhesion decreases causing lithium ion migration and capacity loss
Solution Approach 1:
The patent uses composite materials by combining PVDF binder with inorganic particles (alumina, silica, or boehmite) in the insulating layer formulation. This composite approach maintains the excellent insulating properties of PVDF while the inorganic particles provide structural stability and improve adhesion, preventing lithium ion migration and capacity loss.
Solution Approach 2:
The patent applies local quality by creating an insulating layer with specific local properties on the tab portion where insulation is most critical. The layer is formulated with appropriate PVDF and inorganic particle content to provide both insulating properties and adhesion specifically at the tab-current collector interface, where short circuit prevention is most important.
4Strength
If aqueous styrene-butadiene copolymer (SBL) binder is used for insulating coating, then adhesion is improved, but gelation of PVDF occurs and moisture causes side reactions
Solution Approach 1:
The patent changes the chemical composition parameters by replacing aqueous SBL binder with non-aqueous PVDF binder in the insulating layer formulation. This parameter change eliminates moisture-related side reactions and gelation issues while maintaining adhesion through the PVDF-inorganic particle composite system, thereby improving chemical stability.
Solution Approach 2:
The patent replaces the problematic aqueous SBL binder with PVDF, which, while requiring careful handling, eliminates the need for moisture control and prevents gelation. This substitution trades the adhesion benefits of SBL for the chemical stability and process simplicity of PVDF in the non-aqueous insulating layer system.
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 solution effectively prevents physical short circuits between the anode and cathode by maintaining the particle shape of conjugated diene latex and achieving a low moisture content, thereby ensuring excellent adhesion and insulation properties in lithium secondary batteries.
Implementation Method 1
adding a non-aqueous organic solvent to a water-dispersed conjugated diene latex, followed by heating and decompressing
Implementation Method 2
adding a non-aqueous organic solvent to a water-dispersed conjugated diene latex, followed by heating and decompressing
Data Source
AI summary
A manufacturing method of a cathode binder or a cathode insulating solution for a lithium secondary battery includes: adding a non-aqueous organic solvent to a water-dispersed conjugated diene latex, followed by heating and decompressing, to replace water, which is a dispersion solvent of conjugated diene latex particles, with a non-aqueous organic solvent. A cathode binder or a cathode insulating solution and a lithium secondary battery including the cathode binder or the cathode insulation solution prepared according to the method is also provided.