PEO-Based Electrolyte for Stable Lithium-Air Cells
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Solution Overview
Problem
Lithium-air batteries face challenges in developing suitable non-aqueous electrolytes that are chemically and electrochemically stable in the presence of oxygen, as traditional solvents like carbonates can be oxidized at low potentials and have high vapor pressures, limiting their use in air-breathing membranes.
Innovation Solution
A lithium-air cell is designed with a non-aqueous electrolyte comprising a poly(ethyleneoxide) solvent and a lithium salt, along with a siloxanyl carbonate co-solvent, which provides stability and facilitates lithium ion and oxygen transport, and includes electrode stabilizing additives to prevent degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If carbonate-based solvents are used in lithium-air batteries, then lithium ion conduction is achieved, but electrochemical stability deteriorates due to oxidation at low potentials in the presence of oxygen
Solution Approach 1:
The patent changes the chemical composition parameters of the electrolyte by replacing traditional carbonate solvents with poly(ethylene oxide) (PEO) as the primary solvent and incorporating fluorinated cyclic carbonate additives. This parameter change fundamentally alters the electrochemical stability window, allowing the electrolyte to remain stable at higher potentials in the presence of oxygen while maintaining lithium ion conductivity.
Solution Approach 2:
The patent creates a composite electrolyte system by combining PEO polymer chains with fluorinated cyclic carbonate molecules. This composite approach leverages the high electrochemical stability of PEO and the beneficial electrochemical properties of fluorinated cyclic carbonates to achieve synergistic effects, resulting in an electrolyte that resists oxidation while facilitating lithium ion transport.
2Reliability
If traditional carbonate solvents are used, then lithium ion transport is enabled, but vapor pressure increases causing issues with air breathing membranes
Solution Approach 1:
The patent changes the physical state parameter of the electrolyte by transitioning from low-viscosity carbonate liquids to higher-viscosity PEO-based electrolytes. This parameter change dramatically reduces vapor pressure, eliminating the harmful evaporation and outgassing issues associated with traditional carbonates while maintaining sufficient ionic conductivity for lithium ion transport.
3Productivity
If lithium-air batteries are designed with air breathing membranes, then oxygen supply to positive electrode is improved, but solvent evaporation increases due to high vapor pressure
Solution Approach 1:
The patent changes the volatility parameter of the electrolyte by using PEO and fluorinated cyclic carbonate components, which have negligible vapor pressures compared to traditional carbonate solvents. This parameter change allows air breathing membranes to function effectively for oxygen supply without the concomitant problem of solvent evaporation and loss.
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 enables the creation of a stable lithium-air cell with enhanced electrochemical performance, overcoming the limitations of traditional solvents by maintaining stability in the presence of oxygen and improving energy density.
Implementation Method 1
the poly(ethyleneoxide) solvent is a compound of Formula Ia, Ib, Ic, Id, IIa, IIb, IIc, or a mixture of any two or more such compounds
Implementation Method 2
a non-aqueous electrolyte including a poly(ethyleneoxide) solvent and a lithium salt
Implementation Method 3
non-aqueous electrolytes are provided that are chemically and electrochemically stable in the presence of oxygen
Data Source
AI summary
Lithium-air cells employing poly(ethyleneoxide) phosphate-based electrolytes may be prepared and exhibit improved charge carrying capacity. Such PEO phosphates generally have the formulas IIa, IIb, IIc, where: