Hydrofluoroether Electrolyte Suppresses Gas Generation
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Solution Overview
Problem
Nonaqueous electrolyte solutions containing fluorine-containing ethers do not adequately suppress gas generation in lithium ion secondary batteries with high potential positive electrodes, leading to suboptimal battery characteristics.
Innovation Solution
A nonaqueous electrolyte solution containing a hydrofluoroether compound with a specific diether structure, such as CF3CF2CF2OCHFCF2OR1, where R1 represents various fluorinated groups, is used to suppress gas generation and improve battery characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional fluorine-containing ethers are used in the electrolyte solution, then the electrolyte provides basic battery function, but gas generation occurs on the positive electrode surface due to oxidative decomposition
Solution Approach 1:
The patent changes the chemical parameters of the electrolyte by introducing a specific hydrofluoroether compound with the formula CF3CF2CF2OCHFCF2OR1 where R1 is a fluorinated alkyl group. This parameter change in the electrolyte composition suppresses oxidative decomposition at the positive electrode, thereby reducing gas generation while maintaining battery functionality.
Solution Approach 2:
The patent uses a composite electrolyte system combining the hydrofluoroether compound (Formula 1) with conventional carbonate solvents (cyclic and chain carbonates) and lithium salts. This composite approach leverages the protective film-forming capability of the hydrofluoroether while maintaining the ionic conductivity and solvation properties of the carbonate-based electrolyte, effectively suppressing gas generation without compromising battery performance.
2Use of energy by moving object
If high potential positive electrodes are used to increase energy density, then battery voltage and energy density improve, but oxidative decomposition of solvent increases leading to more gas generation
Solution Approach 1:
The hydrofluoroether compound performs preliminary protective action by forming a stable surface film on the high potential positive electrode before significant oxidative decomposition of the bulk electrolyte can occur. This pre-formed protective layer prevents or reduces oxidative decomposition reactions, thereby suppressing gas generation while enabling the battery to operate at high voltages (4.5V or more) for increased energy density.
Solution Approach 2:
The patent changes the electrochemical stability parameters of the electrolyte system by incorporating the hydrofluoroether compound, which raises the oxidative stability threshold. This allows the battery to operate at higher potentials (increasing energy density) without experiencing excessive oxidative decomposition and gas generation that would normally occur at such high voltages.
3Reliability
If conventional additives like vinylene carbonate or fluoroethylene carbonate are used, then protective coating forms on the negative electrode, but these additives are insufficient to suppress gas generation from positive electrode decomposition
Solution Approach 1:
The hydrofluoroether compound exhibits multi-functionality by performing both negative electrode protection (forming protective coating via reductive decomposition) and positive electrode protection (suppressing oxidative decomposition and gas generation). This universal protective capability against both electrodes makes it superior to conventional single-function additives that only protect the negative electrode.
Solution Approach 2:
The hydrofluoroether compound acts as an intermediary substance that mediates between the electrolyte and both electrode surfaces. It forms protective interfaces at both the negative electrode (through reductive decomposition) and the positive electrode (by suppressing oxidative decomposition), thereby preventing gas generation from both electrodes while maintaining electrolyte functionality.
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 use of the hydrofluoroether compound in the nonaqueous electrolyte solution effectively reduces gas generation, enhancing the energy density, cycle stability, and long-term reliability of lithium ion secondary batteries.
Implementation Method 1
on the electrode surface of the negative electrode, a solvent in the electrolyte solution causes a reductive decomposition, whereby the decomposition product deposits on the negative electrode surface
Implementation Method 2
on the electrode surface of the positive electrode, the solvent causes an oxidative decomposition, whereby the decomposition product deposits on the positive electrode surface
Data Source
AI summary
A nonaqueous electrolyte solution including a hydrofluoroether compound represented by the following formula (1):[Formula 1]CF3CF2CF2OCHFCF2OR1 (1)wherein R1 represents a difluoromethyl group, a 2,2-difluoroethyl group, a 2,2,2-trifluoroethyl group, a 2,2,3,3,3-pentafluoropropyl group, a 2,2,3,3-tetrafluoropropyl group, a 1,1,1,3,3,3-hexafluoroisopropyl group, a 2,2,3,3,4,4,4-heptafluorobutyl group, a 2,2,3,3,4,4-hexafluorobutyl group, or a 2,2,3,3,4,4,5,5-octafluoropentyl group.