Aqueous localized high-concentration electrolyte and preparation method thereof, and sodium-ion battery
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Solution Overview
Problem
Water-in-salt electrolytes for sodium-ion batteries face challenges such as high viscosity, poor wettability, and high cost, which affect the electrochemical performance and stability of the batteries.
Innovation Solution
An aqueous localized high-concentration electrolyte (LHCE) is formulated using a specific ratio of sodium salt, water, organic solvent, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, optimizing the volume and molar ratios to enhance miscibility and reduce viscosity, thereby improving wettability and conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high-concentration salts are used to wrap water molecules to form water-in-salt electrolyte, then the electrochemical stability window is broadened, but the viscosity increases and wettability deteriorates
Solution Approach 1:
The patent changes the concentration parameter by using localized high-concentration electrolyte (LHCE) instead of uniform high-concentration electrolyte. The electrolyte contains 3-5 mol/kg sodium salt, with water content controlled at 10-30 wt% and organic solvent at 70-85 wt%, creating regions of high salt concentration near electrodes while maintaining bulk流动性. This parameter optimization resolves the contradiction between electrochemical stability and fluidity.
Solution Approach 2:
The patent applies local quality by creating localized high-concentration regions near the electrode surfaces where salt wrapping occurs, while the bulk electrolyte maintains lower concentration for good流动性. The organic solvent (cyclic carbonate like EC or PC combined with chain carbonate like DMC or DEC) ensures the bulk remains fluid while the electrode interface provides the necessary high-concentration protective effect.
2Reliability
If high-solubility imide salts are added to broaden the electrochemical window, then the electrochemical stability improves, but the cost increases
Solution Approach 1:
The patent optimizes the salt concentration parameter to 3-5 mol/kg, which is high enough to provide electrochemical stability (achieving 3.0-3.8V windows) but not excessively high to avoid prohibitive costs. This moderate high-concentration approach uses common salts like NaClO4, NaPF6, or NaTFSI at economically viable levels rather than requiring extreme concentrations of expensive imide salts.
Solution Approach 2:
The patent employs relatively inexpensive sodium salts (perchlorate, hexafluorophosphate, or trifluoromethanesulfonylimide) rather than expensive specialized imide salts. The electrolyte formulation achieves good performance with these cheaper salts at optimized concentrations, reducing material costs while maintaining electrochemical stability through proper concentration control and solvent selection.
3Ease of operation
If diluents are introduced into high-concentration electrolytes to reduce viscosity, then the wettability improves, but the electrolyte concentration decreases
Solution Approach 1:
The patent implements local quality by creating a spatial gradient in concentration: high salt concentration (3-5 mol/kg) localized near electrode surfaces provides protective wrapping and electrochemical stability, while the bulk electrolyte contains more organic solvent for good wettability and流动性. This local differentiation allows both high concentration benefits and good wettability without compromise.
Solution Approach 2:
The patent uses composite electrolyte formulation combining multiple components: sodium salts (3-5 mol/kg), water (10-30 wt%), cyclic carbonates (EC or PC, 20-50 wt%), and chain carbonates (DMC or DEC, 30-50 wt%). This composite structure integrates the high-concentration protective effect with the low-viscosity wettability benefits of organic solvents, achieving synergistic performance that neither component could provide alone.
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 aqueous LHCE achieves a wide electrochemical stability window of about 3.4 V, maintaining stable operation of carbon-coated sodium vanadium phosphate electrodes and a capacity retention rate of approximately 100% after 100 cycles, enhancing battery performance.
Implementation Method 1
effectively fix the water molecules through a high concentration of salts to form a special solvent sheath, thereby limiting a direct reaction between the water molecules with active materials in the battery
Implementation Method 2
high conductivity, and thereby could improve an electrochemical performance of the battery
Data Source
AI summary
Disclosed are an aqueous localized high-concentration electrolyte (LHCE) and a preparation method thereof, and a sodium-ion battery, which belong to the technical field of electrolyte materials. The aqueous LHCE includes a sodium salt, water, an organic solvent, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, wherein a volume ratio of the water to the organic solvent is in a range of 1:5 to 1:7; and an amount of the 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether in moles is not larger than an amount of the organic solvent in moles.