Metal-Air Cell Electrolyte Using Ionic Liquid and Hygroscopic Additive
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Solution Overview
Problem
Conventional metal-air batteries face issues with electrolyte evaporation, water electrolysis, and self-discharge, leading to reduced performance and efficiency, particularly in secondary cells, where the electrolyte cannot be replenished during the recharge cycle, and the use of aqueous electrolytes results in toxic gas production and inefficient hydrogen reduction.
Innovation Solution
An electrochemical cell utilizing a hydrophobic ionic liquid with a hygroscopic additive to maintain a controlled water concentration between 0.1 mol% and 25 mol%, preventing evaporation and enhancing faradaic efficiency by supporting oxygen reduction reactions and stabilizing zinc oxide precipitates, while minimizing hydrogen evolution and self-discharge.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an aqueous electrolyte solution is used in metal-air batteries, then ion conductivity is achieved, but electrolyte evaporation occurs through the air permeable electrode leading to cell inoperability
Solution Approach 1:
The patent changes the physical and chemical parameters of the electrolyte by using an ionic liquid instead of an aqueous solution. The ionic liquid has negligible vapor pressure, eliminating evaporation losses while maintaining ion conductivity. This parameter change directly resolves the contradiction between reliability and substance loss.
Solution Approach 2:
The patent employs a composite electrolyte system combining ionic liquid with specific additives (e.g., ZnCl2, LiClO4) to achieve both non-volatility and high ion conductivity. The composite nature allows the electrolyte to simultaneously prevent evaporation and support electrochemical reactions, resolving the reliability-evaporation contradiction.
2Loss of energy
If aqueous electrolyte is used to maintain ion conductivity, then water electrolysis occurs during recharging causing hydrogen evolution and reducing round trip efficiency
Solution Approach 1:
The patent changes the electrolyte composition from aqueous to ionic liquid-based, which has a much wider electrochemical stability window. This parameter change prevents water electrolysis during charging/discharging cycles, eliminating harmful gas evolution and improving round trip efficiency by ensuring electrons are used for fuel reduction rather than water decomposition.
3Reliability
If a high volume of electrolyte solution is used to compensate for evaporation and maintain performance, then cell size and weight increase without enhancing performance
Solution Approach 1:
The patent changes the electrolyte from aqueous to ionic liquid, which has negligible vapor pressure. This eliminates the need for excess electrolyte volume to compensate for evaporation, allowing the cell to achieve performance stability with minimal electrolyte quantity, thereby reducing overall cell weight while maintaining reliability.
4Loss of energy
If active metal reacts with water and dissolved oxygen in aqueous electrolyte, then self-discharge occurs at high rates reducing cell efficiency
Solution Approach 1:
The patent changes the electrolyte medium from aqueous to ionic liquid, which has extremely low water content. This parameter change eliminates the harmful reactions between active metal and water/dissolved oxygen that cause self-discharge, significantly reducing energy loss and improving cell efficiency.
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 maintains cell performance by controlling water content, reducing electrolyte loss, and enhancing faradaic efficiency, thereby improving the round trip efficiency and extending the operational life of metal-air batteries without the drawbacks of aqueous systems.
Implementation Method 1
The hygroscopic additive modulates the hydrophobicity of the ionic liquid to maintain the concentration of the water in the ionically conductive medium between 0.1 mol % and 25 mol % when exposed to ambient air at standard conditions across a relative humidity of 15% to 95%
Implementation Method 2
an ionically conductive medium comprising a hydrophobic ionic liquid comprising positive ions and negative ions
Implementation Method 3
a hydrophobic ionic liquid that resists moisture and hence do not produce toxic gases
Implementation Method 4
a fuel electrode at which metal fuel is oxidized
Implementation Method 5
an air electrode at which oxygen is reduced
Implementation Method 6
stabilizing zinc oxide precipitates
Data Source
AI summary
An electrochemical cell comprising an electrolyte comprising water and a hydrophobic ionic liquid comprising positive ions and negative ions. The electrochemical cell also includes an air electrode configured to absorb and reduce oxygen. A hydrophilic or hygroscopic additive modulates the hydrophobicity of the ionic liquid to maintain a concentration of the water in the electrolyte is between 0.001 mol % and 25 mol %.