Cellulose Separator Structure for Dimensionally Stable Battery Cells
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Solution Overview
Problem
Existing electrochemical element separators exhibit varying performance parameters due to mechanical loads during manufacturing, leading to irreversible deformations that alter the pore structure and reduce the quality of the elements produced.
Innovation Solution
A separator for electrochemical elements composed of at least 50% fibrillated regenerated cellulose fibers, with a total cellulose fiber content of 70-100%, calibrated to achieve a 0.1% yield point at an elongation of 0.5-2.0% under tensile load, ensuring dimensional stability and homogeneous pore structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the separator is made thinner to reduce ion path length and increase volumetric energy density, then the energy density improves, but the mechanical strength and dimensional stability deteriorate
Solution Approach 1:
The separator uses a composite structure combining cellulose fibers (5-20 μm diameter) as the primary load-bearing component with a nanocellulose coating layer (1-10 nm thickness) on the surface. The cellulose fibers provide mechanical strength and dimensional stability, while the nanocellulose coating enhances porosity control and chemical stability. This composite approach allows the separator to be thin (15-30 μm) while maintaining adequate mechanical properties.
2Productivity
If the separator porosity is increased to improve ion flow, then the charging performance improves, but the mechanical strength deteriorates
Solution Approach 1:
The separator utilizes a controlled porous structure with porosity of 30-50%, achieved through the natural arrangement of cellulose fibers and optimized by the nanocellulose coating. The pores have a size distribution that facilitates ion transport while the cellulose fiber network maintains mechanical integrity. The nanocellulose coating further refines the pore structure to prevent dendrite growth while preserving ion flow pathways.
3Manufacturing precision
If mechanical loads are applied during manufacturing to improve separator quality, then the pore structure improves, but irreversible deformations occur
Solution Approach 1:
The separator is pre-treated with a nanocellulose coating before final assembly into the electrochemical element. This coating is applied while the separator is in a controlled moisture state (6-12% moisture content), which optimizes the coating adhesion and pore structure formation. The pre-coating process stabilizes the separator dimensions and pore structure before it undergoes any mechanical loads during element manufacturing, preventing irreversible deformations.
4Strength
If the cellulose fiber content is increased to improve mechanical strength, then the dimensional stability improves, but the porosity decreases
Solution Approach 1:
The separator employs different cellulose fiber dimensions in different regions: bulk cellulose fibers (5-20 μm diameter, 0.5-2 mm length) provide the mechanical framework, while a surface layer of nanocellulose (1-10 nm thickness) optimizes the pore structure and chemical stability. This local differentiation allows the bulk material to provide strength while the surface layer enhances porosity and ion transport properties.
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 electrochemical elements with improved mechanical stability, maintaining consistent performance and reducing waste by preventing irreversible deformations during manufacturing, thereby enhancing productivity and quality.
Implementation Method 1
it ought to have a high porosity. In particular, if the electrochemical element is an accumulator, the porosity should not be formed by a few large pores, but rather by a plurality of small pores
Implementation Method 2
the separator does not undergo plastic deformation, i.e., irreversible deformation
Data Source
AI summary
A separator for an electrochemical element is shown, in which at least 50% of the mass of the separator is formed by fibrillated regenerated cellulose fibers, wherein, including the fibrillated regenerated cellulose fibers, at least 70% and at most 100% of the mass of the separator is formed by cellulose fibers, and wherein the separator is calendered, and wherein under tensile load in the machine direction in accordance with ISO 1924-2:2008, the separator reaches its 0.1% yield point at an elongation of no less than 0.5% and no more than 2.0%. A method of manufacturing such a separator is also disclosed.