Cellulose-Coated Battery Separator for Heat Stability and Air Permeability
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Solution Overview
Problem
Conventional lithium secondary battery separators made from polyolefin-based polymers suffer from thermal deformation, reduced porosity, and decreased air permeability, leading to instability and ion conductivity issues, which are exacerbated by the use of inorganic particles and cellulose nanocrystals that compromise mechanical strength and ion migration.
Innovation Solution
A secondary battery separator with a cellulose coating layer containing cellulose nanofibers and nanocrystals on a porous support, using a mixed solvent of water and an organic solvent with a higher boiling point, forming a continuous phase with chain entanglement and a dispersed phase, enhancing puncture strength, air permeability, and heat resistance without the need for 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 porosity and air permeability are reduced
Solution Approach 1:
The patent uses a porous support as the base separator structure, maintaining inherent porosity and air permeability. The coating layer is applied in a controlled manner that preserves the porous structure, allowing ion migration while providing heat resistance without requiring inorganic particles that would block pores.
Solution Approach 2:
The patent creates a composite structure combining the porous support with a coating layer containing cellulose derivatives and binder. This composite approach provides heat resistance through the coating while the porous support maintains the necessary porosity and air permeability for ion conductivity.
2Strength
If cellulose nanocrystals are introduced to improve puncture strength, then mechanical strength is improved, but air permeability is significantly decreased
Solution Approach 1:
The patent uses a binder with specific local properties (low viscosity, high flexibility) that allows the coating layer to maintain puncture strength without requiring high concentrations of cellulose nanocrystals. The binder's unique characteristics enable strength enhancement while preserving air permeability.
Solution Approach 2:
The patent changes the key parameter of the binder from conventional high-viscosity materials to low-viscosity, high-flexibility materials. This parameter change allows for a coating composition that provides puncture strength through flexible bonding rather than dense packing of nanocrystals, thus maintaining air permeability.
3Ease of manufacture
If polyolefin-based polymer is used for the separator, then ease of manufacture is improved, but thermal deformation occurs leading to reduced stability
Solution Approach 1:
The patent introduces a coating layer as an intermediary between the polyolefin support and the thermal environment. This coating layer, containing cellulose derivatives and a specialized binder, acts as a protective barrier that prevents thermal deformation of the polyolefin while maintaining ease of manufacture of the base support.
Solution Approach 2:
The patent changes the thermal properties of the separator by adding a coating layer with different thermal characteristics. The coating layer's glass transition temperature and thermal stability parameters are optimized to prevent heat shrinking at battery operating temperatures, while the polyolefin support retains its manufacturing advantages.
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 provides a lightweight separator with improved ion conductivity, wettability, and heat stability, significantly reducing the risk of battery explosions due to internal short-circuits, while maintaining excellent air permeability and puncture strength.
Implementation Method 1
a continuous phase formed from a plurality of cellulose nanofibers having a chain entanglement structure
Implementation Method 2
a cellulose coating layer containing cellulose nanofibers and cellulose nanocrystals on one surface or both surfaces of a porous support, wherein the cellulose coating layer includes a continuous phase formed from a plurality of cellulose nanofibers having a chain entanglement structure and a dispersed phase formed from the cellulose nanocrystals
Data Source
AI summary
Disclosed is a secondary battery separator including a cellulose coating layer containing cellulose nanofibers and cellulose nanocrystals on a porous support. The secondary battery separator has a light weight, excellent air permeability and excellent puncture strength, and thus can provide a lithium secondary battery with excellent physical properties, including ion conductivity, wettability with an electrolyte and heat stability.