Separator with Oriented Scaly Particles for Thermal Stability

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Solution Overview

Problem

Conventional lithium ion battery separators face issues with thermal contraction leading to potential ignition and short circuits due to inadequate pore blocking, high cost of heat-resistant materials, and challenges in uniformly filling inorganic particles in nonwoven fabrics, which affect safety and energy density.

Innovation Solution

A separator structure is developed with scaly particles oriented in the thickness direction and fibrous materials interposed among them, maintaining high porosity and puncture resistance while preventing short circuits, using scaly particles with an average diameter of 15 µm to 200 µm and a porosity of 70% to 95%, ensuring the scaly particles are 30 vol.% to 90 vol.% of the total volume.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If polyethylene separator is used to block pores by melting at low temperature, then shut-down effect is improved, but thermal contraction causes short circuit at high temperature

Engineering Contradiction:

Improveshut-down effectVSAvoidthermal contraction

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The separator uses a composite structure combining polyethylene resin (for shut-down function) with heat-resistant resin (for thermal stability). This composite approach allows the separator to both block pores at low temperature and resist thermal contraction at high temperature, resolving the contradiction between shut-down effect and thermal stability.

Inventive Principle:

Principle #40Composite materials

2Object-affected harmful factors

If heat-resistant resin is used for separator, then thermal contraction is prevented, but cost increases

Engineering Contradiction:

Improvethermal contractionVSAvoidcost

Core Design Contradiction:

Object-affected harmful factorsVSEase of manufacture

Solution Approach 1:

Instead of using heat-resistant resin throughout the entire separator, the invention applies heat-resistant resin locally in specific regions or layers where thermal resistance is most needed. This localized approach maintains thermal contraction resistance while reducing overall material cost compared to using heat-resistant resin for the entire separator structure.

Inventive Principle:

Principle #3Local quality

3Reliability

If inorganic fine particles are densely filled in nonwoven fabric, then short circuit is prevented, but porosity decreases and resistance increases

Engineering Contradiction:

Improveshort circuit preventionVSAvoidporosity

Core Design Contradiction:

ReliabilityVSQuantity of substance

Solution Approach 1:

The invention uses a nonwoven fabric base material that inherently provides porous structure, and combines it with inorganic fine particles. The porous nature of the nonwoven fabric allows maintaining high porosity (70-95%) even with particle filling, while the particles provide short circuit prevention. This resolves the contradiction by using a porous base material that accommodates particles without sacrificing overall porosity.

Inventive Principle:

Principle #31Porous materials

4Quantity of substance

If inorganic fine particles are sparsely filled in nonwoven fabric, then porosity is maintained, but puncture resistance becomes low

Engineering Contradiction:

ImproveporosityVSAvoidpuncture resistance

Core Design Contradiction:

Quantity of substanceVSStrength

Solution Approach 1:

The invention creates a composite structure where inorganic fine particles are combined with a nonwoven fabric matrix. The nonwoven fabric provides mechanical strength and puncture resistance, while the inorganic particles provide thermal stability and short circuit prevention. This composite approach allows maintaining adequate porosity without sacrificing puncture resistance, as the fabric matrix supports the structure even with reduced particle density.

Inventive Principle:

Principle #40Composite 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

This configuration enhances puncture resistance and maintains low electrical resistance, effectively preventing lithium dendrite formation and ensuring safety without compromising energy density.

Implementation Method 1

a separator is formed to orient flat surfaces of scaly particles in an extending direction of a surface of the separator

Methodology Applied

Scientific EffectOrientation:

Implementation Method 2

the porosity of the separator is 70% or more and 95% or less

Methodology Applied

Scientific EffectPorosity: Porosity

Implementation Method 3

to interpose fibrous materials among the scaly particles

Methodology Applied

Scientific EffectInterposition:

Implementation Method 4

This kind of separator has strain caused by the orientation in the film, which leads to a problem of contraction caused by residual stress when exposed to a high temperature

Methodology Applied

Scientific EffectThermal contraction resistance: Thermal Contraction

Data Source

PatentEP2605311B1Separator

Publication Date: 2019.05.29 NIPPON SHEET GLASS CO LTD

Figure 1~2

AI summary

The present invention provides an inexpensive separator having excellent heat resistance and causing no contraction even in a high temperature circumstance nor short circuit while maintaining a high porosity. This separator is characterized in that the flat surfaces of scaly particles are oriented in the extending direction of the surface of the separator, the scaly particles being arranged in layers in the thickness direction of the separator, and fibrous materials are interposed among the scaly particles.