Flat Lyocell Fibre Separators With Low-Energy Fibrillation
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Solution Overview
Problem
Current battery separator papers made from cellulosic fibres, such as lyocell, face challenges in achieving desired properties like density, porosity, and dimensional stability due to the energy-intensive fibrillation process, which shortens fibre lengths and compromises mechanical properties.
Innovation Solution
The use of lyocell fibres with a modified cross-sectional aspect ratio, produced through specific spinning processes, allows for efficient fibrillation with reduced energy and time, resulting in non-woven fibre fleeces with aligned fibrils and solid cores that enhance tensile properties and reduce thickness while maintaining mechanical strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If lyocell fibres are fibrillated to high degrees of freeness through refining, then the porosity and ion mobility of the separator are improved, but the fibre length is reduced and mechanical properties deteriorate
Solution Approach 1:
The patent changes the physical parameter of fibre cross-sectional shape from round to flat, which fundamentally alters how the fibres respond to refining. Flat fibres achieve the desired freeness level with significantly less refining intensity, thereby preserving fibre length and mechanical strength while still achieving high porosity and ion mobility
2Ease of manufacture
If standard round lyocell fibres are used, then the fibre production is straightforward, but the residual core diameter after refining is too large for thin separator applications
Solution Approach 1:
The patent applies asymmetry by changing the fibre cross-section from a symmetric round shape to a flat asymmetric shape. This geometric modification causes the fibres to fibrillate differently during refining, resulting in a much smaller residual core diameter (approximately half of round fibres) while maintaining ease of manufacture through standard flat fibre spinning processes
3Length of stationary object
If the fibrillation process is extended to reduce fibre diameter, then the residual core size is reduced, but the energy consumption and processing time increase significantly
Solution Approach 1:
The patent changes the initial fibre geometry parameter from round to flat cross-section, which fundamentally alters the fibrillation kinetics. This parameter change enables achieving the same residual core diameter with approximately 50% less refining energy and shorter processing time, as the flat structure naturally exposes more surface area for fibrillation
Data Source
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AI summary
The invention relates to the use of a lyocell fibre (1) for the manufacture of a nonwoven fibre fleece (10, 100). To manufacture a thin nonwoven fibre fleece with sufficient mechanical properties, the use of a lyocell fibre is proposed, where the fibre (1) has a cross-sectional aspect ratio of at least 1.8. The invention further relates to a nonwoven fibre fleece (10, 100). In order to manufacture a thin nonwoven fibre fleece (10, 100) suitable for use as a battery seperator, it is proposed, that the fibre fleece comprises at least two layers (11, 12) of fibrillated lyocell fibres (13), with the fibrillated lyocell fibres (13) having solid cores (14, 110) and fibrils (15) protruding from said cores (14), the fibres and fibrils (15) being intermingled to form the fibre fleece (10), embedding the solid cores (14) therein, whereby the solid cores (14, 110) of the fibrillated lyocell fibres (13) have an average cross-sectional aspect ratio k of at least 1.5.