Ionic Liquid Electrolyte Viscosity Reduction via Fluorinated Solvents
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Solution Overview
Problem
Current lithium-ion battery technologies face limitations in electrolyte conductivity and viscosity, particularly at high rates and low temperatures, which restrict their performance and safety in high-power applications.
Innovation Solution
Incorporating low viscosity solvents such as fluorinated alkyl ethers and silanes into the electrolytes to enhance conductivity and reduce viscosity, while maintaining compatibility with silicon anodes and high voltage cathode materials, thereby improving the electrolyte's performance at various temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If room temperature ionic liquids (RTILs) are used as electrolytes to achieve non-flammability and high electrochemical stability, then safety and stability are improved, but viscosity increases and ionic conductivity decreases
Solution Approach 1:
The patent uses composite electrolyte systems combining RTILs with conventional organic electrolytes (carbonates like EC, PC, DMF) and polymer matrices. This composite approach allows the system to inherit the non-flammability and electrochemical stability of RTILs while the organic components reduce viscosity and enhance ionic conductivity, resolving the contradiction between safety and flow properties.
Solution Approach 2:
The patent modifies the chemical composition parameters of the electrolyte by varying RTIL concentration (40-60% by volume), selecting different cation-anion combinations (imidazolium, pyrrolidinium, sulfonium with FSI-, TFSO- anions), and adjusting alkyl chain lengths. These parameter changes optimize the balance between viscosity reduction and maintaining the inherent stability advantages of ionic liquids.
2Temperature
If RTILs with larger ion sizes are used to achieve low melting points and wide temperature stability, then thermal stability is improved, but ionic conductivity decreases due to hindered ion transport
Solution Approach 1:
The patent employs different ionic liquid components with specialized local properties: smaller ions (PYR13+, FSI−) are positioned near electrode interfaces to facilitate charge transfer and form stable SEI layers, while larger RTIL molecules provide bulk thermal stability and non-flammability. This spatial differentiation of ionic liquid functions resolves the contradiction between temperature stability and ionic conductivity.
Solution Approach 2:
Conventional organic electrolyte components (carbonates, DMF) act as intermediary species that mediate between the large RTIL ions and the electrode surfaces. These intermediaries have higher mobility and lower viscosity, facilitating ion transport while the RTILs maintain the stable, non-flammable bulk environment, thus resolving the conductivity-stability trade-off.
3Reliability
If conventional organic electrolytes are used to achieve high ionic conductivity, then conductivity is improved, but flammability increases and electrochemical stability decreases
Solution Approach 1:
The patent merges the advantages of conventional organic electrolytes (high ionic conductivity, low viscosity) with the safety benefits of ionic liquids (non-flammability, electrochemical stability) by creating hybrid electrolyte compositions. The combined system achieves conductivity comparable to pure organic electrolytes while eliminating flammability risks, as demonstrated by the non-flammable behavior of 40-60% RTIL mixtures.
Solution Approach 2:
The patent converts the typically harmful flammability of organic electrolytes into a benefit by using the organic components in controlled, low-concentration formulations (40-60% RTIL content) where they enhance conductivity without compromising safety. The RTIL majority phase acts as a fire-suppressing matrix that tames the flammability risk while preserving the conductive benefits of organic species.
4Quantity of substance
If graphite anodes are used with RTILs to achieve high capacity, then capacity is improved, but irreversible reduction of imidazolium cations occurs leading to unstable SEI and exfoliation
Solution Approach 1:
The patent employs sacrificial additives (small concentrations of conventional electrolyte components) that are consumed during initial cycling to form stable protective SEI layers on graphite anodes. These short-living intermediary species prevent the irreversible reduction of imidazolium cations and protect against graphene exfoliation, enabling long-term stable operation at high capacities.
Solution Approach 2:
Conventional organic electrolyte components serve as intermediary protective layers between the graphite anode and RTIL cations. These intermediaries preferentially react with graphite to form stable SEI structures that block direct contact between imidazolium cations and graphene layers, preventing cointercalation and exfoliation while allowing lithium-ion transport, thus enabling high capacity with stable cycling.
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 integration of these solvents significantly boosts electrolyte conductivity and reduces viscosity, enabling higher rate performance and extended low-temperature operation without compromising the stability of electrode-electrolyte interactions, thus enhancing the overall performance and safety of lithium-ion batteries.
Implementation Method 1
Incorporating low viscosity solvents such as fluorinated alkyl ethers and silanes into the electrolytes to enhance conductivity and reduce viscosity
Implementation Method 2
These materials conduct charge by the transport of one or both of their ions. Ionic conductivity of RTILs is typically on the order of mS cm−1
Implementation Method 3
Use of the bis(fluorosulfonyl)imide (FSI−) anion has been shown to mitigate this issue. This is attributed to the ability of the FSI− anion, especially when paired with certain pyrrolidinium (PYR+) cations, to form a protective, lithium-ion conducting SEI layer that avoids solvent molecules and stops the cations from penetrating the graphene.
Data Source
AI summary
There is disclosed an energy storage device. In an embodiment, the device has an anode including a plurality of active material particles. Each of the plurality of active material particles has a particle size of between about 1 nanometer and about fifty micrometers. One or more of the plurality of active material particles are enclosed by and in contact with a membrane coating permeable to lithium ions, and the membrane coating a thermoplastic polymer treated to a cyclized, non-plastic ladder compound. The device includes a cathode. The device includes an electrolyte coupling the anode to the cathode including a room temperature ionic liquid solvent and at least one wetting agent or viscosity reducing co-solvent and mixtures thereof. Other embodiments are also disclosed.