Cellulose Separator Composition for Uniform Battery Pore Structure
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Solution Overview
Problem
Existing separators for electrochemical elements, particularly those using fibrous substrates, face challenges in achieving the required thickness, pore size distribution, strength, and chemical stability, leading to safety and performance issues in lithium-ion batteries due to high variability in cellulose fiber properties and insufficient thermal stability of thermoplastic materials.
Innovation Solution
A separator composed of at least 70% to 95% fibrillated fibers of regenerated cellulose with a branched structure and 3% to 30% pulp having a high fines content, where the fibrillated fibers are refined to retain fines and create a dense network, enhancing mechanical strength and porosity with a small pore size distribution, and the pulp contributes to reducing pore size and standard deviation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If fibrous substrates are used as separators, then safety and ecological benefits are improved, but thickness and pore size control are worsened
Solution Approach 1:
The patent applies parameter changes by controlling the fiber length distribution (L50, L90 parameters) and fines content of cellulose fibers to achieve the desired separator thickness and pore size. By adjusting these parameters, the patent resolves the contradiction between using safe fibrous substrates and achieving thin, controlled thickness.
Solution Approach 2:
The patent uses composite materials by combining cellulose fibers with different length distributions and fines content to create a separator that achieves both safety benefits of fibrous substrates and the thin, controlled thickness required for high energy density.
2Reliability
If fibrous substrates are used as separators, then safety is improved, but pore size distribution uniformity is worsened
Solution Approach 1:
The patent applies parameter changes by precisely controlling the fiber length distribution parameters (L50, L90) and fines content to achieve uniform pore size distribution. This resolves the contradiction between using safe fibrous substrates and achieving consistent pore size uniformity.
Solution Approach 2:
The patent applies local quality by creating specific regions with different fiber length distributions and fines content to control pore size in different areas of the separator, achieving overall uniformity while maintaining safety benefits.
3Volume of moving object
If separator thickness is reduced, then volumetric energy density is improved, but mechanical strength is worsened
Solution Approach 1:
The patent uses composite materials by combining cellulose fibers with optimized length distribution and fines content to create a thin separator that maintains sufficient mechanical strength. This resolves the contradiction between reducing thickness for high energy density and maintaining mechanical strength.
Solution Approach 2:
The patent applies porous materials principles by optimizing the pore size distribution and fines content to achieve a thin, strong separator structure that provides both high volumetric energy density and adequate mechanical strength for handling.
4Manufacturing precision
If plastic films are used as separators, then manufacturing uniformity is improved, but thermal stability is worsened
Solution Approach 1:
The patent uses composite materials by combining cellulose fibers with optimized properties to create a separator that achieves both manufacturing uniformity and high thermal stability. This resolves the contradiction between using uniform plastic films and achieving thermal stability.
Solution Approach 2:
The patent applies parameter changes by controlling the fiber length distribution and fines content to achieve manufacturing uniformity comparable to plastic films, while simultaneously providing the thermal stability benefits of cellulose-based materials.
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 separator with improved mechanical strength, chemical stability, and controlled pore size distribution, enhancing the safety and ecological benefits of cellulose-based separators while maintaining high porosity and conductivity, suitable for use in lithium-ion batteries and other electrochemical elements.
Implementation Method 1
a fiber substrate that consists essentially of fibrillated fibers of regenerated cellulose and pulp having a high fines content
Implementation Method 2
it should absorb the electrolyte into its entire pore volume as quickly as possible in order to obtain a high conductivity for ions
Implementation Method 3
it should also, as far as possible, enable a flow of ions between the electrodes which is as unhindered as possible
Data Source
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.