Ionic Liquid Electrolyte for Metal-Air Cell Stability

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Solution Overview

Problem

Conventional metal-air batteries face issues with solvent evaporation, water electrolysis, and self-discharge due to the use of aqueous electrolytes, leading to reduced energy efficiency and operational lifespan, particularly in rechargeable cells.

Innovation Solution

The use of low or room temperature ionic liquids with hydroxamate and N-alkyl sulfamate anions as the ionically conductive medium in metal-air cells, which eliminates solvent evaporation and reduces water content to minimize hydrogen evolution and self-discharge, while maintaining electrochemical reaction efficiency.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If aqueous electrolyte solution is used in metal-air batteries, then ion conductivity is maintained, but solvent evaporation occurs leading to cell inoperability

Engineering Contradiction:

Improvecell operational stabilityVSAvoidelectrolyte solvent evaporation

Core Design Contradiction:

ReliabilityVSLoss of substance

Solution Approach 1:

The patent changes the physical and chemical parameters of the electrolyte by replacing aqueous solutions with ionic liquids. This substitution fundamentally alters the volatility parameter (from high in water to negligible in ionic liquids) while maintaining ionic conductivity, thereby resolving the contradiction between operational stability and solvent loss.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent employs ionic liquids that can be replenished from external reservoirs. While the ionic liquid itself is not disposable, the system design allows for periodic replenishment of the electrolyte medium, addressing the solvent depletion issue without requiring complete system replacement.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

2Productivity

If air electrode is made air permeable to absorb oxygen, then oxygen reduction reaction is enabled, but solvent vapor escapes from the cell

Engineering Contradiction:

Improveoxygen absorption rateVSAvoidsolvent vapor escape

Core Design Contradiction:

ProductivityVSLoss of substance

Solution Approach 1:

The patent changes the volatility parameter of the electrolyte medium by substituting water with ionic liquids. This parameter change allows the air electrode to remain permeable to oxygen while preventing solvent vapor escape, as ionic liquids have negligible vapor pressure compared to aqueous solutions.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If aqueous electrolyte is used to maintain cell performance, then ion conductivity is ensured, but water electrolysis occurs during recharging reducing efficiency

Engineering Contradiction:

Improveelectrolyte ion conductivityVSAvoidenergy loss to hydrogen evolution

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

The patent changes the electrochemical stability window parameter by replacing water with ionic liquids. Ionic liquids possess wider electrochemical stability windows and higher decomposition potentials, which eliminate water electrolysis during recharging while maintaining adequate ion conductivity for electrochemical reactions.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

4Reliability

If high volume of electrolyte solution is added to compensate for evaporation, then solvent depletion is prevented, but cell weight and volume increase

Engineering Contradiction:

Improveelectrolyte level maintenanceVSAvoidcell weight

Core Design Contradiction:

ReliabilityVSWeight of moving object

Solution Approach 1:

The patent changes the volatility parameter of the electrolyte by using ionic liquids with negligible vapor pressure. This parameter change eliminates the need for excessive electrolyte volumes to compensate for evaporation, thereby reducing cell weight while maintaining reliable electrolyte levels throughout the cell lifecycle.

Inventive Principle:

Principle #35Parameter changes

5Productivity

If aqueous electrolyte is used, then electrochemical reactions proceed, but self-discharge occurs due to reaction with water

Engineering Contradiction:

Improveelectrochemical reaction rateVSAvoidself-discharge loss

Core Design Contradiction:

ProductivityVSLoss of energy

Solution Approach 1:

The patent changes the chemical reactivity parameter by replacing water with ionic liquids. Ionic liquids exhibit lower reactivity toward active metal fuels compared to aqueous solutions, thereby reducing parasitic self-discharge reactions while maintaining sufficient ionic conductivity to support electrochemical reaction rates.

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

This approach enhances the energy density and efficiency of metal-air cells by reducing weight and volume, minimizing water-related issues, and maintaining high faradaic efficiency, thereby extending the operational life and performance of the batteries.

Implementation Method 1

an ionic liquid comprising a cation and an anion selected from hydroxamate and N-alkyl sulfamate anions

Methodology Applied

Scientific EffectIon conduction: Conduction (electrical)

Implementation Method 2

a fuel electrode for oxidizing a fuel

Methodology Applied

Scientific EffectOxidation: Oxidation

Implementation Method 3

an air electrode configured to absorb and reduce gaseous oxygen

Methodology Applied

Scientific EffectReduction: Reduction

Data Source

PatentUS9287597B2Ionic liquid containing hydroxamate and N-alkyl sulfamate ions

Publication Date: 2016.03.15 FORM ENERGY INC

AI summary

Embodiments of the invention are related to ionic liquids and more specifically to ionic liquids used in electrochemical metal-air cells in which the ionic liquid includes a cation and an anion selected from hydroxamate and/or N-alkyl sulfamate anions.