Lithium-Ion Separator Copolyester Film for Thin Solid Electrolytes

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Solution Overview

Problem

Lithium-ion batteries face safety concerns due to the flammability and mechanical weakness of polyolefin films used as separators, which can lead to short-circuiting and thermal runaway, and existing solid-state batteries struggle with maintaining conductivity and mechanical strength at low thicknesses.

Innovation Solution

Development of a copolyester film comprising repeating units derived from an aliphatic diol, an aromatic dicarboxylic acid, and poly(alkylene oxide) with incorporated lithium ions, which provides a combination of high conductivity and mechanical strength while being easy to form and process, suitable for use as a solid electrolyte in lithium-ion batteries.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If polyolefin films are used as separators, then separation function is achieved, but mechanical strength and safety deteriorate due to low tensile strength and flammability

Engineering Contradiction:

ImprovesafetyVSAvoidtensile strength

Core Design Contradiction:

ReliabilityVSStrength

Solution Approach 1:

The patent uses a block copolymer composite consisting of polyethylene terephthalate hard blocks and polypropylene oxide soft blocks. This composite structure combines the high mechanical strength and thermal stability of PET with the lithium ion conductivity and flexibility of PPO, resolving the contradiction between strength and safety.

Inventive Principle:

Principle #40Composite materials

2Productivity

If separator thickness is reduced, then energy density improves, but mechanical strength and conductivity deteriorate

Engineering Contradiction:

Improveenergy densityVSAvoidmechanical strength

Core Design Contradiction:

ProductivityVSStrength

Solution Approach 1:

The patent changes the chemical composition parameters by incorporating lithium ions into the block copolymer structure and optimizing the hard block to soft block ratio. This enables the production of ultra-thin separators (20μm or less) that maintain both mechanical strength and lithium ion conductivity, achieving high energy density without sacrificing performance.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If inorganic lithium-ion conductors are used, then conductivity improves, but device complexity and processing difficulty increase due to sputtering requirements

Engineering Contradiction:

ImproveconductivityVSAvoidprocessing complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent replaces complex inorganic conductor systems with an organic block copolymer system that provides inherent lithium ion conductivity. The PPO soft blocks create continuous conductive pathways for lithium ions, eliminating the need for sputtering equipment and complex inorganic material processing while achieving comparable or superior conductivity.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

4Reliability

If separator rigidity is increased, then dendrite prevention improves, but adaptability to electrode volume changes deteriorates

Engineering Contradiction:

Improvedendrite preventionVSAvoidvolume variation tolerance

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The patent creates a dynamic separator structure where the PPO soft blocks provide flexibility and elasticity, allowing the separator to deform and adapt to electrode volume changes during charging and discharging cycles. The block copolymer architecture maintains structural integrity while accommodating dynamic dimensional changes, preventing dendrite formation without compromising adaptability.

Inventive Principle:

Principle #15Dynamics

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 copolyester film exhibits excellent dimensional stability and conductivity, tolerating electrode volume variations during battery cycling, and maintains mechanical strength at elevated temperatures, enhancing the safety and performance of lithium-ion batteries.

Implementation Method 1

the separator must enable migration of the lithium ions within its structure

Methodology Applied

Scientific EffectIon migration: Diffusion

Implementation Method 2

a solid separator between the cathode and anode, which prevents contact between the electrodes

Methodology Applied

Scientific EffectPhysical barrier: Physical Containment

Data Source

PatentEP4169966B1Copolyesters derived from aliphatic glycols, aromatic dicarboxylic acids and poly(alkylene-oxides) and films made therefrom

Publication Date: 2024.11.20 MYLAR SPECIALTY FILMS U S LLP

AI summary

An optionally oriented copolyester film comprising a copolyester which comprises repeating units derived from an aliphatic diol, an aromatic dicarboxylic acid and a poly(alkylene oxide), wherein the copolyester film further comprises lithium ions, and wherein the film has a thickness of no more than about 25µm. The copolyester film is suitable for use a separator in a lithium-ion rechargeable battery