High-Concentration Li-Ion Electrolytes With Low Viscosity
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Solution Overview
Problem
Conventional lithium-ion battery electrolytes face issues with volatility, flammability, increased cost, and decreased lithium-ion conductivity due to high lithium salt concentrations, which affect the safety and performance of battery cells over multiple charging cycles.
Innovation Solution
The development of electrolytes with a non-carbonate-containing ester compound solvent, a diluent that includes a fluorinated organic compound, and a phosphorous-containing additive, allowing for high lithium salt concentrations above 2 moles/liter while maintaining low viscosity and reducing free solvent molecules, thereby minimizing volatility and flammability and enhancing conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If lithium salt concentration is increased above conventional levels, then volatility and flammability are reduced, but viscosity increases and lithium-ion conductivity decreases
Solution Approach 1:
The patent changes the chemical parameters of the electrolyte system by introducing fluorinated cyclic carbonate compounds with specific molecular structures (Formula 1) and controlling their concentration ratios (5-50 vol%). This parameter change allows the system to achieve both high lithium salt concentration (reduced volatility/flammability) and maintained lithium-ion conductivity through optimized molecular composition rather than simply increasing salt concentration alone.
Solution Approach 2:
The patent creates a composite electrolyte system combining fluorinated cyclic carbonate (Formula 1), non-fluorinated cyclic carbonate, and chain carbonate in specific proportions. This composite approach allows the fluorinated component to provide structural stability and ion conduction pathways while the other components contribute to overall electrolyte performance, resolving the contradiction between conductivity and safety.
2Object-affected harmful factors
If lithium salt concentration is increased above conventional levels, then safety is improved, but manufacturing cost increases
Solution Approach 1:
The patent optimizes the concentration parameter of fluorinated cyclic carbonate to 5-50 vol%, which provides sufficient safety improvement while avoiding excessive material costs. This parameter optimization allows manufacturers to achieve safety goals with moderate amounts of expensive fluorinated compounds rather than requiring extreme concentrations that would be prohibitively costly.
Solution Approach 2:
The fluorinated cyclic carbonate acts as an intermediary substance that enables the use of high lithium salt concentrations for safety while the specific molecular structure prevents excessive viscosity increases. This intermediary role allows the system to achieve safety benefits without proportionally increasing manufacturing costs through other means.
3Object-affected harmful factors
If free solvent molecules are reduced through high lithium salt concentration, then volatility is reduced, but electrical resistance increases
Solution Approach 1:
The patent replaces the conventional mechanism of reducing volatility simply by increasing salt concentration (which increases viscosity and resistance) with a chemical substitution approach. The fluorinated cyclic carbonate molecules substitute for conventional carbonate molecules, providing similar solvation functions while enabling higher salt concentrations without proportional viscosity increases, thus maintaining electrical conductivity.
Solution Approach 2:
The patent changes the molecular parameter of the carbonate component by introducing fluorinated cyclic carbonates with specific structural characteristics (Formula 1). This parameter change in molecular structure allows the electrolyte to maintain low viscosity and good ion conductivity even at high lithium salt concentrations, resolving the volatility-resistance contradiction.
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 results in lithium-ion battery cells with reduced electrical impedance, improved cycle life, and enhanced safety by minimizing swelling and impedance growth over hundreds of charge-discharge cycles, while maintaining low viscosity and stability.
Implementation Method 1
the decrease in lithium-ion conductivity caused by the increase in viscosity that occurs when the salt becomes more concentrated in the electrolyte
Implementation Method 2
when the lithium salt is more concentrated in the electrolyte, there are fewer free solvent molecules present because more are tied up in solvent aggregates with the ions of the lithium salt
Data Source
AI summary
Electrolytes for lithium-containing battery cells are described. The electrolytes may include a solvent that includes at least one non-carbonate-containing ester compound. The electrolytes may further include one or more lithium salts, where the lithium salts have a concentration of greater than or about 2 mols/liter in the electrolyte. The electrolytes may still further include a diluent that includes an aromatic fluorocarbon.