Fluorinated Nonaqueous Electrolyte for High-Voltage Capacity Retention
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Solution Overview
Problem
Nonaqueous electrolyte energy storage devices face challenges in maintaining a high capacity retention rate during charge-discharge cycles, especially when the working potential of the positive electrode is noble, such as exceeding 4.4 V, due to insufficient resistance to oxidation and poor miscibility of solvents.
Innovation Solution
A nonaqueous electrolyte composition comprising an alkali metal salt, a first aprotic organic solvent without fluorine, a second aprotic organic solvent with fluorine, and an additive with a polar group and fluorine, optimized in terms of molar ratios and volume percentages, to enhance solubility and ion diffusion while maintaining resistance to oxidation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the working potential of the positive electrode is increased to exceed 4.4 V, then the energy density is improved, but the capacity retention rate deteriorates due to insufficient resistance to oxidation
Solution Approach 1:
The electrolyte uses a composite solvent system combining fluorinated cyclic carbonate (F3EC), fluorinated linear carbonate (FEC), and non-fluorinated cyclic carbonate (PC). This composite approach creates synergistic effects where fluorinated solvents provide oxidation resistance at high potentials while non-fluorinated solvents maintain good ion solubility and conductivity, enabling both high energy density and capacity retention
Solution Approach 2:
The patent optimizes specific parameter ranges: F3EC content at 5-30 vol%, FEC at 10-40 vol%, and PC at 40-80 vol%. It also controls LiPF6 concentration at 0.5-2.0 mol/kg and adds fluoroalkyl phosphoric acid ester at 5-50 vol%. These parameter adjustments balance oxidation resistance with ion solubility and conductivity, allowing high potential operation with good capacity retention
2Reliability
If the concentration of electrolyte salt is increased to improve capacity retention rate, then the solubility is improved, but the viscosity increases and ion diffusion deteriorates
Solution Approach 1:
The patent optimizes electrolyte salt concentration at 0.5-2.0 mol/kg, avoiding excessive concentrations that would cause high viscosity. It controls solvent composition with specific volume ratios where fluorinated carbonates (5-40 vol%) provide good solubility while the dominant non-fluorinated cyclic carbonate (40-80 vol%) maintains low viscosity and high ion mobility
Solution Approach 2:
The electrolyte creates local solvation structures where lithium ions are surrounded by a mix of fluorinated and non-fluorinated solvent molecules. The fluorinated solvents provide stable solvation shells for oxidation resistance, while non-fluorinated solvents provide channels for rapid ion diffusion, achieving both high capacity retention and fast ion transport
3Reliability
If fluorinated solvents are used to improve resistance to oxidation, then the stability is improved, but the miscibility with non-fluorinated solvents deteriorates
Solution Approach 1:
The patent carefully controls the volume ratio of fluorinated to non-fluorinated solvents. F3EC is limited to 5-30 vol% and FEC to 10-40 vol%, while non-fluorinated PC comprises 40-80 vol%. This composition balance ensures sufficient fluorinated content for oxidation resistance while maintaining adequate non-fluorinated content for complete miscibility and homogeneous electrolyte formation
Solution Approach 2:
The non-fluorinated cyclic carbonate (PC) acts as an intermediary solvent that is fully miscible with both fluorinated solvents (F3EC, FEC) and the electrolyte salt LiPF6. This intermediary solvent bridges the fluorinated and non-fluorinated components, ensuring complete mixing and homogeneous electrolyte composition while allowing the fluorinated solvents to provide their oxidation-resistant properties
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 proposed electrolyte composition significantly increases the capacity retention rate of nonaqueous electrolyte energy storage devices, even under conditions allowing high working potentials, by ensuring stable solvent coordination, reduced viscosity, and improved miscibility, thus enhancing both solubility and diffusion of alkali metal ions.
Implementation Method 1
a first aprotic organic solvent which coordinates to an alkali metal ion in the alkali metal salt
Implementation Method 2
the nonaqueous electrolyte... is configured to permit charge-discharge through a transfer of ions between both electrodes
Data Source
Figure 1~2
AI summary
One aspect of the present invention is a nonaqueous electrolyte for an energy storage device comprising: an alkali metal salt; a first aprotic organic solvent coordinating to an alkali metal ion in the alkali metal salt, and not including a fluorine atom; a second aprotic organic solvent including a fluorine atom; and an additive comprising a polar group and a group including a fluorine atom, wherein a content of the alkali metal salt is no less than 0.9 mol/kg and less than 2 mol/kg, a content of the first aprotic organic solvent with respect to the content of the alkali metal salt in terms of a molar ratio is no less than 0.7 and no greater than 4, and a content of the second aprotic organic solvent with respect to a total amount of the first aprotic organic solvent, the second aprotic organic solvent and the additive is no less than 40% by volume.