Li-Ion Separator Coating with Cellulose Derivatives
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Solution Overview
Problem
Existing Li-ion cell separators face issues with mechanical stability, puncture resistance, and tear propagation, which can lead to internal short circuits and safety concerns, while improving these properties often compromises electrical conductivity and permeability.
Innovation Solution
A separator coated with cellulose derivatives having a chain length of at least 100 repeating units, combined with hard inorganic or organic filler particles and flexible elastomeric binder particles, enhances mechanical stability and homogeneity, achieving high puncture resistance and tear propagation resistance without compromising permeability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the density of the separator is increased to improve puncture resistance, then mechanical stability is improved, but porosity is reduced and electrical resistance increases
Solution Approach 1:
The separator is constructed as a composite material consisting of a polyolefin-based porous film laminated with a particle-containing layer that includes inorganic particles, thermoplastic resin particles, and cellulose-based resin. This composite structure allows the separator to achieve high puncture resistance through the reinforcing particles while maintaining porosity and electrical conductivity through the porous polyolefin matrix and controlled coating density.
Solution Approach 2:
The particle-containing layer is applied selectively on at least one side of the porous film, creating local reinforcement where needed. The coating is designed to provide mechanical strength at the surface while the bulk porous structure maintains its permeability and electrical properties, allowing different regions of the separator to have different functional qualities.
2Stability of the object's composition
If the separator structure is made more dense to improve mechanical stability, then puncture resistance increases, but permeability decreases
Solution Approach 1:
The separator utilizes a porous polyolefin-based film as its base structure, which inherently provides both mechanical stability and high permeability. The porous structure allows electrolyte diffusion while the polyolefin matrix provides mechanical strength. The particle-containing coating layer is designed to reinforce mechanical properties without significantly blocking the pores, thus maintaining permeability.
Solution Approach 2:
By combining the porous polyolefin film with a particle-containing coating layer consisting of inorganic particles, thermoplastic resin particles, and cellulose-based resin, the separator achieves enhanced mechanical stability while the porous nature of the base film and the controlled composition of the coating maintain adequate permeability for electrolyte transport.
3Reliability
If polyolefin membranes are used for good electrical properties, then energy density increases, but thermal and mechanical properties deteriorate
Solution Approach 1:
The separator combines polyolefin-based porous film (providing good electrical properties and electrochemical stability) with a particle-containing coating layer including inorganic particles (providing thermal stability and mechanical reinforcement). This composite structure allows the separator to exhibit both excellent electrical properties for high energy density and improved mechanical properties for enhanced safety.
Solution Approach 2:
The particle-containing layer is applied on at least one side of the porous film to provide localized mechanical reinforcement and thermal stability where needed, while the bulk polyolefin film maintains its excellent electrical properties. This allows different regions to optimize for different functions: the coating layer for mechanical strength and the porous film for electrical conductivity.
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 significantly reduces the risk of internal short circuits, maintains high permeability, and ensures safe operation of Li-ion cells by providing improved mechanical properties and uniform coating, as evidenced by low Gurley numbers and high puncture resistance.
Implementation Method 1
cellulose derivatives having a chain length of at least 100 repeating units
Implementation Method 2
cellulose derivatives having a chain length of at least 100 repeating units
Implementation Method 3
porous separators based on polyolefin membranes
Implementation Method 4
thermoplastic resin particles having a melting point of 100-140°C. The thermoplastic resin particles are said to provide the separator with a shut-down mechanism
Data Source
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AI summary
The invention relates to a separator with a main part which is made of nonwoven material, said main part being provided with a coating. The coating contains filler particles, cellulose, and flexible organic binder particles, said filler particles and flexible organic binder particles being connected to each other by the cellulose. The aim of the invention is to design and develop a separator such that said separator exhibits high permeability with increased mechanical stability. The separator is characterized in that the cellulose contains cellulose derivatives that have a chain length of at least 100 repeating units, preferably a chain length of at least 200 repeating units.