Substrate-Free Battery Separator Structure for Swelling Stability

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Solution Overview

Problem

Conventional separators for secondary batteries without a polyolefin substrate face issues with dimensional stability and swelling resistance in electrolyte solutions, leading to increased cell resistance and potential short circuits due to dimensional changes.

Innovation Solution

A separator with a layer structure comprising a fibrous support, such as cellulose nanofibers or aramid fibers, and inorganic particles, along with a binder, which provides improved dimensional stability and swelling resistance, preventing dimensional changes and maintaining ion conductivity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Temperature

If a separator without a polyolefin substrate is used, then thermal stability is improved, but dimensional stability deteriorates due to swelling in electrolyte solution

Engineering Contradiction:

Improvethermal stabilityVSAvoiddimensional stability

Core Design Contradiction:

TemperatureVSStability of the object's composition

Solution Approach 1:

The separator uses a composite structure combining inorganic fibers (alumina, silica, boehmite) with organic binder polymers (carboxymethyl cellulose, styrene-butadiene rubber). This composite material provides both thermal stability from the inorganic components and controlled dimensional stability through the binder matrix that resists excessive swelling in electrolyte solution.

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The patent optimizes specific parameters including fiber diameter (0.5-5 μm), binder content (5-30 wt%), and pore size (1-10 μm) to balance thermal stability and dimensional stability. By controlling these parameters, the separator maintains structural integrity at high temperatures while limiting swelling-induced dimensional changes in electrolyte.

Inventive Principle:

Principle #35Parameter changes

2Strength

If the separator thickness is increased to improve mechanical strength, then strength is improved, but dimensional change increases due to swelling

Engineering Contradiction:

Improvemechanical strengthVSAvoiddimensional change

Core Design Contradiction:

StrengthVSStability of the object's composition

Solution Approach 1:

The separator employs locally optimized properties through controlled fiber distribution and pore structure. The inorganic fibers provide localized mechanical reinforcement while the binder matrix controls local swelling behavior, achieving adequate strength without proportional increase in overall dimensional change.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The separator uses a porous structure with controlled pore size (1-10 μm) and porosity (30-70%). This porous architecture provides mechanical strength through the fiber network while the controlled pore distribution limits excessive swelling, as the pore structure accommodates electrolyte uptake without causing disproportionate dimensional expansion.

Inventive Principle:

Principle #31Porous materials

3Temperature

If inorganic particles are added to improve thermal stability, then thermal stability is improved, but adhesion between separator and electrode deteriorates

Engineering Contradiction:

Improvethermal stabilityVSAvoidadhesion force

Core Design Contradiction:

TemperatureVSForce

Solution Approach 1:

The separator combines inorganic particles (alumina, silica, boehmite) with organic binder polymers to create a composite material that balances thermal stability and adhesion. The inorganic provide heat resistance while the organic binder matrix ensures adequate adhesion to electrodes through its polymeric nature and ability to form bonding interfaces.

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The patent optimizes particle size (0.1-10 μm), particle content (20-80 wt%), and binder type to balance thermal stability and adhesion. By controlling these parameters, the separator achieves sufficient thermal resistance from inorganic particles while maintaining adequate bonding strength to electrodes through the optimized binder system.

Inventive Principle:

Principle #35Parameter changes

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 effectively reduces dimensional changes and maintains ion conductivity, preventing increased resistance and short circuits, while ensuring thermal stability and improved adhesion between electrodes.

Implementation Method 1

a separator for secondary batteries configured to provide insulation between a positive electrode and a negative electrode, wherein the separator does not include a polyolefin substrate, and comprises a layer structure including a fibrous support, inorganic particles, and a binder

Methodology Applied

Scientific EffectSwelling resistance:

Implementation Method 2

exhibit high ion permeability, high mechanical strength and stability at high temperature such that an electrolytic solution can pass smoothly through the separator

Methodology Applied

Scientific EffectIon permeability: Permeation

Data Source

PatentUS11757155B2Separator for secondary batteries having no separator substrate

Publication Date: 2023.09.12 LG ENERGY SOLUTION LTD

AI summary

Disclosed herein is a separator for secondary batteries, configured to provide insulation between a positive electrode and a negative electrode, wherein the separator comprises no polyolefin substrate, is configured to have a layer structure comprising a fibrous support, inorganic particles, and a binder, and has improved dimensional stability.