Separator Binder Copolymer for Thermal Shrinkage Resistance
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Solution Overview
Problem
Current lithium ion batteries face safety issues due to severe thermal shrinkage of polyolefin-based separators, leading to potential electric short circuits and explosions, especially at high temperatures, and require enhanced bonding with electrodes to improve safety and discharge capacity.
Innovation Solution
A separator with a porous organic-inorganic coating layer featuring a binder polymer with a copolymer containing vinylidenefluoride, hexafluoropropylene, and maleic acid monomethyl ester units, which provides strong integration with electrodes and improved interfacial resistance, reducing the risk of thermal runaway.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a porous coating layer is formed on the separator to improve safety, then thermal shrinkage resistance is improved, but manufacturing complexity increases
Solution Approach 1:
The patent changes the chemical composition parameters of the binder polymer to achieve optimal balance between safety and manufacturability. Specifically, it uses a copolymer containing vinylidenefluoride (50-95 wt%), hexafluoropropylene (5-40 wt%), and maleic acid monomethyl ester (0.1-5 wt%), where the maleic acid monomethyl ester content is controlled at 0.1-5 wt% to provide sufficient adhesion without excessive complexity in coating formulation
Solution Approach 2:
The patent creates a composite porous coating layer combining inorganic particles with a specifically formulated copolymer binder. This composite structure provides thermal shrinkage resistance from the inorganic particles while the copolymer matrix ensures adhesion and allows for straightforward coating processing, resolving the contradiction between safety improvement and manufacturing complexity
2Reliability
If the bonding between separator and electrodes is increased to improve safety, then thermal runaway risk is reduced, but interfacial resistance increases
Solution Approach 1:
The patent optimizes the chemical composition parameters of the binder polymer to achieve the right balance between bonding strength and electrical conductivity. The copolymer contains vinylidenefluoride (50-95 wt%) for thermal stability, hexafluoropropylene (5-40 wt%) for mechanical properties, and maleic acid monomethyl ester (0.1-5 wt%) for adhesion. This specific composition range ensures strong bonding without excessive interfacial resistance
Solution Approach 2:
The patent applies local quality by creating a coating layer with specific compositional gradients and thickness variations (1-10 μm) to optimize local adhesion properties while maintaining overall electrical conductivity. The maleic acid monomethyl ester units are strategically incorporated to provide localized bonding sites at the separator-electrode interface without compromising the bulk electrical properties
3Reliability
If a porous coating layer is added to enhance safety, then thermal shrinkage resistance is improved, but air permeability decreases
Solution Approach 1:
The patent employs a porous coating layer structure with controlled porosity to maintain air permeability while providing thermal shrinkage resistance. The porous structure allows electrolyte and gas transport necessary for battery operation, while the inorganic particles and copolymer matrix provide the required thermal stability and mechanical strength
Solution Approach 2:
The patent controls the physical parameters of the coating layer including thickness (1-10 μm), porosity, and particle size distribution to optimize the balance between safety and permeability. The specific copolymer composition with low maleic acid monomethyl ester content (0.1-5 wt%) ensures the coating remains sufficiently permeable while providing adequate thermal protection
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 separator enhances adherence to electrodes, improves cycling characteristics, and reduces the risk of thermal shrinkage and explosions by forming a high-adherence binder layer without additional processing steps, thereby ensuring safer and more efficient battery performance.
Implementation Method 1
a binder polymer disposed on part or all of the inorganic particles' surface to connect and immobilize the inorganic particles
Implementation Method 2
the binder polymer includes a copolymer with a vinylidenefluoride-derived repeat unit, a hexafluoropropylene-derived repeat unit, and a maleic acid monomethyl ester-derived repeat unit
Data Source
AI summary
Disclosed are a separator and an electrochemical device comprising the same, the separator comprising: a porous substrate having a plurality of pores; and a porous coating layer formed on at least one surface of the porous substrate and in at least one type of region of the pores of the porous substrate, the porous coating layer containing a plurality of inorganic particles and a binder polymer disposed on a part or the entirety of the surface of the inorganic particles to connect and fix the inorganic particles, wherein the binder polymer contains a copolymer including a vinylidene fluoride-derived repeat unit, a hexafluoropropylene-derived repeat unit, and a maleic acid monomethyl ester-derived repeat unit.