Lithium Battery Separator Coating for Adhesive Force
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Solution Overview
Problem
Lithium batteries face issues with low adhesive force between the separator and electrodes, leading to increased distance between electrodes during charging and discharging, reduced capacity and energy density, and decreased lifetime characteristics due to volumetric changes and potential gap or destruction of the separator.
Innovation Solution
A separator with a porous base material layer coated with a polymer layer containing a fluorinated copolymer and a non-fluorinated copolymer at a weight ratio of 3:1 to 1:3, enhancing adhesive force and stability, and suppressing volumetric changes during charging and discharging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a conventional separator is used, then the battery structure is simple, but the adhesive force between the separator and electrodes is low
Solution Approach 1:
The separator is constructed as a composite material consisting of a base layer and a coating layer with different functional properties. The base layer provides mechanical strength and porosity, while the coating layer containing fluorinated copolymer and non-fluorinated copolymer provides enhanced adhesive force to the electrodes, resolving the contradiction between simplicity and adhesion.
Solution Approach 2:
The adhesive force is improved by changing the chemical composition parameters of the separator surface through the coating layer. By controlling the weight ratio of fluorinated copolymer to non-fluorinated copolymer (1:9 to 9:1) and the thickness of the coating layer (1-10 μm), the separator achieves optimal adhesion without excessive structural complexity.
2Stability of the object's composition
If the separator has low adhesive force, then the manufacturing process is simple, but the distance between electrodes increases during charging and discharging
Solution Approach 1:
The coating layer is applied to the base layer in advance during the separator manufacturing process. This preliminary action of coating ensures that when the separator is assembled into the battery, the electrodes are already positioned stably with high adhesive force, preventing distance increase during charging and discharging cycles.
Solution Approach 2:
By optimizing the coating layer parameters including polymer composition (fluorinated copolymer content), coating thickness (1-10 μm), and drying conditions, the separator achieves sufficient adhesive force to maintain electrode position stability while remaining manufacturable through conventional coating and drying processes.
3Duration of action of stationary object
If the separator adhesive force is insufficient, then the initial battery capacity is acceptable, but the capacity and energy density reduce over time
Solution Approach 1:
The coating layer acts as a protective cushion between the separator and electrodes, preventing direct mechanical stress and volumetric changes from damaging the separator structure. This beforehand cushioning effect maintains separator integrity and adhesive force throughout the battery's lifetime, preventing capacity and energy density reduction that would occur with separator degradation.
Solution Approach 2:
The composite structure with fluorinated copolymer and non-fluorinated copolymer in the coating layer provides both mechanical stability and chemical stability. This composite material composition ensures the separator maintains its adhesive properties and structural integrity over extended battery operation, preserving capacity and energy density throughout the battery's service life.
4Force
If a thicker coating layer is used to increase adhesive force, then the adhesion improves, but the manufacturing complexity and cost increase
Solution Approach 1:
The coating layer thickness is optimized to a specific range of 1-10 μm, which provides sufficient adhesive force through the polymer composition and surface properties rather than relying on excessive thickness. This parameter optimization maintains ease of manufacture by using thin coatings that can be applied with conventional techniques while achieving the required adhesion performance.
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 improved adhesive force and stability of the separator enhance the operational characteristics and life expectancy of lithium batteries by maintaining electrode integrity and preventing capacity and energy density reduction.
Implementation Method 1
a polymer coating layer formed on at least a surface of the base material layer
Implementation Method 2
immersing the coated porous base material layer in a non-solvent; and drying the coated porous base material layer to remove the non-solvent
Data Source
AI summary
A separator for a battery having a porous base material layer and a polymer coating layer formed on at least a surface of the base material layer. The polymer coating layer includes a first fluorinated copolymer and a non-fluorinated polymer. A weight ratio of the first fluorinated copolymer to the non-fluorinated polymer is in a range of 3:1 to 1:3.