Lyocell Fiber Separator Fleece with Flat Cross-Sections
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Solution Overview
Problem
The existing production of non-woven fleeces, particularly battery separator papers, faces challenges in achieving sufficient strength while maintaining a low thickness due to the energy-intensive fibrillation process of lyocell fibers, which often results in reduced fiber length and mechanical properties.
Innovation Solution
The use of lyocell fibers with a modified cross-sectional aspect ratio, specifically a width-to-height ratio of at least 1.8, allows for more efficient refining with reduced energy and time, enabling the production of thin non-woven fiber fleeces with enhanced tensile properties by aligning the fibers with their thinner axis perpendicular to the sheet plane.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If lyocell fibers are extensively fibrillated to high freeness levels, then porosity and ion mobility are improved, but fiber length is reduced and mechanical properties deteriorate
Solution Approach 1:
The patent changes the physical parameter of fiber cross-sectional shape from round to flat, which fundamentally alters how the fiber responds to refining. Flat fibers achieve the necessary surface fibrillation for ion mobility without the same degree of length reduction that occurs with round fibers, thus resolving the contradiction between porosity requirements and mechanical strength preservation
2Ease of manufacture
If standard round lyocell fibers are used, then fiber production is simpler, but the resulting non-woven fleece requires greater thickness to achieve sufficient strength
Solution Approach 1:
The patent applies asymmetry by using flat cross-sectional fibers instead of symmetric round fibers. This asymmetric geometry provides superior surface area for fibrillation and inter-fiber bonding, enabling thin fleece structures to achieve high strength without complicating the fundamental fiber production process
3Reliability
If lyocell fibers are refined to high degrees of freeness, then fibrillation ability is enhanced, but energy consumption and processing time increase significantly
Solution Approach 1:
Changing the fiber cross-sectional parameter from round to flat creates inherently higher surface area and edge density, which promotes more efficient fibrillation during refining. This geometric parameter change reduces the energy input and processing time required to achieve the necessary fibrillation level for battery separator performance
Data Source
AI summary
The invention relates to the use of a lyocell fiber (1) for the manufacture of a nonwoven fiber fleece (10, 100). To manufacture a thin nonwoven fiber fleece with sufficient mechanical properties, the use of a lyocell fiber is proposed, where the fiber (1) has a cross-sectional aspect ratio of at least 1.8.The invention further relates to a nonwoven fiber fleece (10, 100). In order to manufacture a thin nonwoven fiber fleece (10, 100) suitable for use as a battery separator, it is proposed, that the fiber fleece comprises at least two layers (11, 12) of fibrillated lyocell fibers (13), with the fibrillated lyocell fibers (13) having solid cores (14, 110) and fibrils (15) protruding from said cores (14), the fibers and fibrils (15) being intermingled to form the fiber fleece (10), embedding the solid cores (14) therein, whereby the solid cores (14, 110) of the fibrillated lyocell fibers (13) have an average cross-sectional aspect ratio k of at least 1.5.