PIM Membranes for Ion Separation in Redox Flow Batteries

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Solution Overview

Problem

Commercial battery separators are freely permeable to active materials in redox flow batteries and electrolyte intermediates, leading to device shorting, electrode fouling, and irreversible capacity loss, and existing membrane solutions like Nafion restrict the use of certain electrode types, while rational design rules for ion-selective transport via sieving in battery membranes are lacking.

Innovation Solution

The use of polymers of intrinsic microporosity (PIMs) as membrane materials, which are synthesized to have sub-nm pore dimensions and high surface area, allowing selective ion transport through size sieving and potentially electrostatic restrictions, blocking polysulfide crossover in lithium-sulfur batteries while maintaining high ionic conductivity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If commercial battery separators with shape-persistent mesopores are used, then ionic conduction is enabled, but active materials freely permeate through the separator causing device shorting and capacity loss

Engineering Contradiction:

Improveprevention of active material crossoverVSAvoidionic conductivity

Core Design Contradiction:

ReliabilityVSQuantity of substance

Solution Approach 1:

The patent employs polymers of intrinsic microporosity (PIMs) with precisely controlled sub-nm pore dimensions to achieve size-selective ion transport. The microporous structure allows small ions to pass while blocking larger active materials, resolving the contradiction between preventing crossover and maintaining ionic conductivity.

Inventive Principle:

Principle #31Porous materials

Solution Approach 2:

The invention changes the pore size parameter from mesoporous (commercial separators) to microporous (PIMs), enabling selective transport based on ion size. This parameter change allows the separator to distinguish between small ions (which should pass) and large active materials (which should be blocked).

Inventive Principle:

Principle #35Parameter changes

2Reliability

If Nafion membranes are used to prevent active material crossover, then ion selectivity is improved, but the use of certain flowable electrode types is restricted

Engineering Contradiction:

Improveactive material blocking capabilityVSAvoidcompatibility with different electrode types

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The patent applies local quality by creating regions of different pore sizes within the separator structure. The microporous regions provide size-selective blocking while maintaining overall compatibility with various electrode types, unlike Nafion's uniform structure that restricts electrode choices.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

PIMs provide universal applicability across different battery chemistries and electrode types while maintaining size-selective transport. The microporous structure can accommodate various ion sizes and electrode configurations, making the separator versatile for different applications.

Inventive Principle:

Principle #6Universality (Multi-functionality)

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

PIM membranes demonstrate a 500-fold reduction in polysulfide crossover, significantly improving battery performance by preventing polysulfide shuttling and maintaining high ionic conductivity, thus addressing the limitations of existing separators and enabling flexible battery chemistries.

Implementation Method 1

polymers of intrinsic microporosity may be advantageous for separator systems. Polymers of intrinsic microporosity may advantageously be selected based on their inherent pore size to selectively restrict large ions by size sieving, while allowing smaller ions to transport through the pores.

Methodology Applied

Scientific EffectSize sieving: Molecular Sieve

Implementation Method 2

polymers of intrinsic microporosity may be modified to aid in the restriction of ion transport, such as by imparting negative charges to the polymer structure, which may further provide an electrostatic restriction on anionic species

Methodology Applied

Scientific EffectElectrostatic restriction: Ion Repulsion/Attraction

Implementation Method 3

by crosslinking the polymer, which may provide for further improved size sieving properties

Methodology Applied

Scientific EffectCrosslinking: Chemical Bonding

Implementation Method 4

Membranes (or separators) are critical for ionic conduction and electronic isolation in many electrochemical devices

Methodology Applied

Scientific EffectIonic conduction: Conduction (electrical)

Data Source

PatentUS11318455B2Polymeric materials for electrochemical cells and ion separation processes

Publication Date: 2022.05.03 RGT UNIV OF CALIFORNIA

AI summary

Polymers of intrinsic microporosity are provided herein. Disclosed polymers of intrinsic microporosity include modified polymers of intrinsic microporosity that include negatively charged sites or crosslinking between monomer units. Systems making use of polymers of intrinsic microporosity and modified polymers of intrinsic microporosity are also described, such as electrochemical cells and ion separation systems. Methods for making and using polymers of intrinsic microporosity and modified polymers of intrinsic microporosity are also disclosed.