Non-flammable Polymer Electrolyte for Safe Battery Operation
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Solution Overview
Problem
Lithium-ion batteries face safety issues due to the flammability of traditional electrolytes, which are often comprised of volatile organic molecules, and ionic liquid-based electrolytes introduce non-Li mobile cations, leading to low lithium transference numbers and limited ionic conductivity.
Innovation Solution
A siloxane-based polymer with ionic-liquid units as side chains is developed, reducing steric hindrance and increasing salt solubility, resulting in higher ionic conductivity and stability, while maintaining non-flammability by incorporating solvent molecules in a coordinated environment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional flammable organic electrolytes are used, then high ionic conductivity is achieved, but battery safety deteriorates due to flammability and volatility
Solution Approach 1:
The patent employs a composite electrolyte system combining ionic liquid-functionalized polymer (PyFSI-PDMS) with lithium salt (LiFSI) and coordinated solvent (DME). This composite approach integrates the non-flammable properties of ionic liquids with the solvating capability of coordinated solvents, achieving both safety and high ionic conductivity (1.6 mS/cm at 25°C). The polymer backbone provides structural framework while side chains deliver ionic conductivity, creating a multi-functional composite material that resolves the safety-conductivity tradeoff.
2Reliability
If ionic liquid-based electrolytes are used to improve safety, then flammability is reduced, but lithium transference number deteriorates due to introduction of non-Li mobile cations
Solution Approach 1:
The patent applies local quality by functionalizing only the side chains of the polymer backbone with ionic liquid groups (PyFSI), while maintaining a simple PDMS backbone. This localized ionic liquid functionality provides non-flammability and ionic conductivity without introducing excessive non-Li cations into the bulk electrolyte. The ionic liquid units are confined to specific locations (side chains) rather than being distributed throughout the entire electrolyte matrix, thereby improving lithium transference number while maintaining safety.
3Reliability
If salt content is increased to improve ionic conductivity, then conductivity increases, but viscosity deteriorates and salt solubility is limited
Solution Approach 1:
The patent introduces coordinated solvent molecules (DME) as intermediaries between the lithium salt and the polymer matrix. These solvent molecules coordinate with Li+ ions, facilitating salt dissolution and ion mobility even at high salt concentrations (salt:monomer=8:1). The DME molecules act as mediators that bridge the interaction between salt and polymer, enabling high ionic conductivity without proportionally increasing viscosity, as the coordinated solvent molecules organize the ion transport pathways efficiently.
4Stability of the object's composition
If polymer backbone is made rigid to improve structural stability, then mechanical strength increases, but ionic conductivity deteriorates due to reduced polymer chain motion
Solution Approach 1:
The patent segments the polymer structure into distinct functional regions: a flexible PDMS backbone providing mechanical stability and chain motion, and ionic liquid-functionalized side chains providing ionic conductivity. This segmentation allows each component to optimize its function independently - the backbone maintains structural integrity while the side chains facilitate ion transport. The separation of structural and conductive functions resolves the contradiction between mechanical strength and ionic conductivity.
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 polymer electrolyte achieves high lithium salt content with ionic conductivity of 1.6 mS/cm at 25°C, stable cycling with NMC cathodes and graphite anode for over 400 cycles, and operates across a wide temperature range with realistic current densities, setting standards for polymer electrolytes.
Implementation Method 1
The flexible low Tg (glass transition temperature) backbone promotes polymer chain motion and elevates baseline ionic conductivity
Implementation Method 2
By moving the ion solvating units from the polymer backbone to the side chain, the present embodiments reduce their steric hindrance and enables higher salt solubility
Implementation Method 3
These solvents exist in a highly coordinated environment with salts and polymers and does not undercut the safety feature of the electrolyte
Implementation Method 4
The resulting polymer electrolyte with high lithium salt content (salt:monomer=8:1), in presence of coordinated DME (Dimethoxyethane) molecules, is a liquid with ionic conductivity of 1.6 mS/cm at 25° C.
Data Source
AI summary
The present embodiments relate to lithium-based batteries, and particularly to coordinated solvent molecules that can increase the ionic conductivity of the electrolyte without undermining its non-flammability. Some embodiments include a liquid-state polymer electrolyte composed of LiFSI salts, Dimethoxyethane (DME) solvents, and polysiloxane tethered with ion solvating moieties. DME coordinates with both the salt and the polymer, while together with the salt, they synergistically plasticize the polymer to increase the ionic conductivity. The resulting non-flammable polymer electrolyte has a room temperature ionic conductivity of 1.6 mS/cm and a wide operation window of 25-100° C. Benefiting from its liquid nature, the electrolyte can pair with commercially available electrodes without further cell engineering. Embodiments can extend the ionic conductivity range of polymer electrolytes and provide a new design pathway for next generation safe and manufacturable electrolytes.