Cellulose-Coated Battery Separator for Heat Resistance and Air Permeability
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Solution Overview
Problem
Conventional lithium secondary battery separators made from polyolefin-based polymers suffer from thermal deformation (heat shrinking) during charge/discharge cycles, leading to stability degradation, and the use of inorganic particles for coating results in non-uniform coatings, reduced porosity, and air permeability, as well as mechanical strength issues.
Innovation Solution
A secondary battery separator with a cellulose coating layer containing cellulose nanofibers and microfibers, along with a dispersant, is applied to a porous support, forming a continuous phase with chain entanglement and a dispersed phase, which enhances puncture strength, air permeability, and heat resistance without using inorganic particles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If inorganic particles are coated on the separator to prevent heat shrinking, then heat resistance is improved, but coating uniformity deteriorates and porosity is reduced
Solution Approach 1:
The patent changes the material parameters from inorganic particles to cellulose fibers (nanofibers and microfibers), which have different physical and chemical properties that enable uniform coating while maintaining heat resistance. The cellulose fibers can be dispersed more evenly in the coating composition and form a uniform layer on the separator surface.
Solution Approach 2:
The patent uses a composite structure combining cellulose nanofibers and cellulose microfibers in the coating layer. This composite material approach allows the coating to achieve both uniformity and heat resistance, as the different fiber sizes work synergistically to form a consistent coating structure.
2Temperature
If inorganic particles are coated on the separator to prevent heat shrinking, then heat resistance is improved, but air permeability is reduced
Solution Approach 1:
The patent employs porous cellulose fiber materials in the coating layer that maintain high air permeability. The fibrous structure creates interconnected pores that allow air and lithium ions to pass through while the cellulose material itself provides heat resistance, unlike dense inorganic particle coatings.
Solution Approach 2:
The patent changes from inorganic particles to cellulose fibers, fundamentally altering the coating's physical structure from a particle-based dense coating to a fiber-based porous network, thereby maintaining air permeability while achieving heat resistance.
3Temperature
If inorganic particles are coated on the separator to prevent heat shrinking, then heat resistance is improved, but mechanical strength deteriorates
Solution Approach 1:
The patent creates a composite coating layer with cellulose nanofibers and microfibers that work together to enhance mechanical strength. The nanofibers provide reinforcement at the molecular level while microfibers provide structural integrity, resulting in superior puncture strength compared to inorganic particle coatings.
Solution Approach 2:
The patent segments the coating into two distinct fiber size components (nano and micro), where each segment contributes differently to the overall mechanical properties. The nanofibers entangle to provide strength at the micro-scale, while microfibers provide macro-scale structural support.
4Ease of manufacture
If polyolefin-based polymer is used for the separator, then manufacturing ease is improved, but thermal stability deteriorates
Solution Approach 1:
The patent creates a composite structure with a polyolefin-based porous support (maintaining manufacturing ease) combined with a cellulose fiber coating layer (providing thermal stability). This composite approach allows the separator to benefit from both the ease of polyolefin manufacturing and the heat resistance of cellulose.
Solution Approach 2:
The patent applies local quality by placing the heat-resistant cellulose coating only on the surfaces of the polyolefin support, rather than making the entire separator from heat-resistant material. This allows the bulk polyolefin structure to maintain its manufacturing advantages while the surface coating provides the necessary thermal stability.
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 cellulose coating layer provides improved puncture strength, heat resistance, and air permeability, ensuring excellent lithium-ion conductivity and wettability with the electrolyte, while maintaining a lightweight design.
Implementation Method 1
a continuous phase formed from a plurality of cellulose nanofibers having a chain entanglement structure
Implementation Method 2
it is vulnerable to heat and causes a fatal problem in that it undergoes thermal deformation (heat shrinking) due to the heat generated during the charge/discharge of a secondary battery
Implementation Method 3
ensuring a sufficient level of porosity and air permeability to provide high lithium-ion conductivity
Implementation Method 4
a cellulose coating composition having a suitable level of viscosity and improved dispersibility
Data Source
AI summary
Disclosed is a secondary battery separator including a cellulose coating layer containing cellulose nanofibers and cellulose microfibers and prepared by using a specific content of dispersant, on a porous support layer. The secondary battery separator has a light weight, improved air permeability and excellent puncture strength, and thus realizes excellent physical properties, such as lithium-ion conductivity, wettability with an electrolyte and heat stability.