Cellulose Separator Structure for Uniform Battery Pore Control
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Solution Overview
Problem
Existing separators for electrochemical elements, particularly those made from cellulose fibers, face challenges in achieving the required thickness, pore size distribution, strength, and chemical resistance, which are crucial for safety, ecological benefits, and efficient ion flow, while also being thermally stable and capable of absorbing electrolyte effectively.
Innovation Solution
A separator composed of at least 70% to 95% fibrillated regenerated cellulose fibers with a high fines content pulp, where at least 10% of the fibers have a branched structure and a specific pulp with a high fines content is used to create a dense network that retains fines, reducing pore size and achieving a small standard deviation in pore size distribution, thereby enhancing strength and porosity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If fiber substrates are used as separators to improve safety and ecological benefits, then thermal stability and chemical resistance are improved, but the separator becomes too thick and pore size distribution becomes too large with high standard deviation
Solution Approach 1:
The fiber substrate is segmented into two distinct fiber length categories: long fibers (≥1mm) that form the structural framework, and short fibers (<0.2mm) that fill interstices. This segmentation allows each fiber type to perform its specific function - long fibers provide structural integrity while short fibers refine pore size distribution, resolving the contradiction between mechanical strength and pore uniformity
Solution Approach 2:
Different regions of the separator have different fiber length compositions. The surface regions contain predominantly long fibers for structural stability, while the interior regions contain higher proportions of short fibers for pore size control. This local quality differentiation allows the separator to simultaneously achieve structural integrity and uniform pore distribution
2Productivity
If the separator is made thinner to reduce ion path length and increase volumetric energy density, then productivity and energy density are improved, but mechanical strength decreases
Solution Approach 1:
The separator thickness is segmented into functional zones with different fiber length compositions. The thin overall structure (15-50μm) is achieved by using short fibers to fill voids, while long fibers maintain structural integrity throughout the thin profile, enabling both reduced thickness and maintained strength
Solution Approach 2:
The separator is a composite material system combining two fiber length populations (≥1mm and <0.2mm) within a cellulose matrix. This composite structure allows the thin separator to achieve both mechanical strength through long fiber networks and fine pore control through short fiber filling, resolving the thickness-strength contradiction
3Manufacturing precision
If plastic films are used to achieve thin thickness and consistent quality, then manufacturing precision is improved, but thermal resistance deteriorates due to shrinkage at high temperatures
Solution Approach 1:
The material parameter is changed from synthetic plastic to regenerated cellulose, which fundamentally alters the thermal behavior. Cellulose fibers maintain dimensional stability at high temperatures through hydrogen bonding networks, preventing the shrinkage phenomenon observed in plastic films while still achieving thin consistent thickness through controlled fiber assembly
4Reliability
If cellulose fibers with high fines content are used to reduce pore size and improve dendrite prevention, then reliability is improved, but the separator becomes too thick and loses mechanical strength
Solution Approach 1:
The fiber population is segmented into long fibers (≥1mm) for structural strength and short fibers (<0.2mm) for pore refinement. The short fibers provide dendrite prevention by filling pores and creating uniform pathways, while long fibers maintain mechanical strength, resolving the contradiction between reliability and strength
Solution Approach 2:
Short fibers with high fines content are concentrated in specific regions where pore size control is most critical, while long fibers dominate regions requiring structural support. This local quality differentiation allows the separator to achieve both dendrite prevention and mechanical strength simultaneously
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 results in a separator that is thin, strong, chemically resistant, and capable of high ionic conductivity, effectively preventing dendrite growth and ensuring the longevity and performance of electrochemical elements like lithium-ion batteries.
Implementation Method 1
The branched structures connect with each other through hydrogen bonds, forming a network that contributes to high strength and provides the basis for holding additional fibers with a branched structure
Implementation Method 2
these structures contribute significantly to keeping the fines in the fiber substrate. The branched structures are characterized primarily by the fact that the fibrils are not completely separated from one another but remain connected at one end to form a thicker fiber
Implementation Method 3
it should absorb the electrolyte as quickly as possible during production and into its entire pore volume in order to achieve high ionic conductivity
Implementation Method 4
The separator is impregnated with the electrolyte and serves to electrically separate the two electrodes. It should also allow the unhindered flow of ions between the electrodes
Data Source
Figure 1a~1b
Figure 1c~1d
Figure 1e~1f
AI summary
What is shown is a separator for an electrochemical element, wherein at least 70% and at most 95% of the mass of the separator is formed by fibrillated fibers of regenerated cellulose and at least 3% and at most 30% of the mass of the separator is formed by cellulose having a high fines content, wherein at least 10%, based on number, of the fibrillated fibers of regenerated cellulose having a length of at least 1 mm have a branched structure, and wherein, in the cellulose having a high fines content, the proportion of fibers having a length of less than 0.2 mm is at least 70% based on the sum of the length of the fibers in the cellulose having a high fines content.