Phase Inversion Battery Separators for Thermal Stability

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Conventional lithium ion and lithium sulfur battery separators exhibit thermal instability, leading to shrinkage and increased risk of battery shorting when exposed to heat, due to the precise stretching required in their fabrication process.

Innovation Solution

A method for producing thermally stable battery separators using a phase inversion process involving a liquid precursor material with a polymer having high cohesive energy, melting temperature, and molecular weight, along with a volatile second solvent, applied to a substrate and processed to form a polymer membrane with improved mechanical and ionic conductance properties.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If conventional wet or dry processes are used to create pores in battery separators, then adequate porosity is achieved, but thermal stability deteriorates due to shrinkage when exposed to heat

Engineering Contradiction:

ImproveporosityVSAvoidthermal stability

Core Design Contradiction:

Quantity of substanceVSReliability

Solution Approach 1:

The patent changes the chemical and physical parameters of the separator material by using a phase inversion process with specific polymers (polyacrylonitrile, polyvinylidene fluoride, or their copolymers) and controlled solvent systems (N-methyl-2-pyrrolidone with water or alcohol). This creates a porous structure with different thermal properties than conventional separators, achieving both adequate porosity and improved thermal stability with shrinkage resistance above the melting point of polyethylene.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent creates a composite porous structure through phase inversion, combining polymer materials with specific pore architectures that provide both porosity for ion transport and thermal stability. The resulting separator comprises a porous polymer matrix with controlled pore size and distribution, achieving the dual requirement of ion conductivity and heat resistance.

Inventive Principle:

Principle #40Composite materials

2Quantity of substance

If precise stretching is applied to extruded thin film to create pores, then adequate porosity is achieved, but manufacturing complexity increases

Engineering Contradiction:

ImproveporosityVSAvoidmanufacturing process complexity

Core Design Contradiction:

Quantity of substanceVSDevice complexity

Solution Approach 1:

The patent replaces the mechanical stretching process with a chemical/physical phase inversion process. Instead of mechanically stretching extruded film to create pores, the invention uses controlled precipitation of polymer from solvent systems to spontaneously form porous structures. This substitution eliminates complex stretching equipment and precise mechanical control requirements while achieving adequate porosity.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent utilizes phase transition during the precipitation process where polymer separates from the solvent system (N-methyl-2-pyrrolidone with water or alcohol) to form a porous solid structure. This phase inversion naturally creates the desired porosity without requiring subsequent mechanical stretching operations, simplifying the manufacturing process.

Inventive Principle:

Principle #36Phase transitions

3Ease of manufacture

If conventional separators are used, then manufacturing is simpler, but abuse tolerance deteriorates due to shrinkage at elevated temperatures

Engineering Contradiction:

Improvemanufacturing simplicityVSAvoidabuse tolerance

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The patent changes the thermal parameters of the separator by selecting polymers with appropriate glass transition temperatures and using phase inversion to create a porous structure that maintains dimensional stability at elevated temperatures. The resulting separator exhibits shrinkage resistance above the melting point of polyethylene, significantly improving abuse tolerance while maintaining manufacturing feasibility through the direct phase inversion process.

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 method generates separators with reduced shrinkage at elevated temperatures, enhanced abuse tolerance, and improved cycling performance, while maintaining high production rates and solvent resistance.

Implementation Method 1

precipitating the polymer from the liquid precursor material in the coating layer to form a polymer membrane

Methodology Applied

Scientific EffectPhase inversion: Phase Change

Implementation Method 2

evaporating a portion of the second solvent

Methodology Applied

Scientific EffectEvaporation: Evaporation

Data Source

PatentUS10056590B2Methods of making separators for lithium ion batteries

Publication Date: 2018.08.21 GM GLOBAL TECHNOLOGY OPERATIONS LLC

AI summary

Methods for producing a battery separator are provided. The methods include applying a liquid precursor material to a substrate to generate a coating layer on the substrate. The liquid precursor material includes a polymer, and a first solvent. The methods also include precipitating the polymer from the liquid precursor material in the coating layer to form a polymer membrane, and drying the polymer membrane to generate a battery separator.