Fluorinated Carbonate Electrolyte Impurity Control
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Solution Overview
Problem
Nonaqueous electrolytes for electrochemical devices, such as lithium ion secondary batteries, face challenges in maintaining high temperature storage characteristics and cycling performance due to decomposition at high voltages and impurities in the solvent.
Innovation Solution
A nonaqueous electrolyte with a fluorinated linear carbonate solvent and specific impurities (RfOH, ROH, ROCOC1) in controlled amounts (not more than 5000 ppm) is used, which improves the electrochemical device's storage and cycling characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If fluorinated linear carbonate is used as nonaqueous solvent, then oxidation resistance and high voltage stability are improved, but discharge capacity is lowered when left in high-temperature environment
Solution Approach 1:
The patent changes the chemical composition parameters of the electrolyte by strictly controlling the amounts of specific compounds (I) RfOH, (II) ROH, and (III) ROCOCl to be each 50 ppm or less relative to fluorinated linear carbonate. This parameter control resolves the contradiction by eliminating impurities that cause capacity loss while preserving the oxidation resistance of the fluorinated solvent.
Solution Approach 2:
The patent converts the potential harm of trace impurities in fluorinated linear carbonate into a benefit by establishing precise purity standards. By controlling impurities to 50 ppm or less, the patent transforms what would normally be unacceptable contamination into a defined specification that enables both oxidation resistance and capacity retention.
2Reliability
If fluorinated linear carbonate is used as nonaqueous solvent, then high voltage stability is improved, but cycling characteristics are lowered after repetitive charge-discharge cycles
Solution Approach 1:
The patent changes the chemical purity parameters by limiting compounds (I) RfOH, (II) ROH, and (III) ROCOCl to 50 ppm or less. This parameter control resolves the contradiction by removing impurities that degrade during cycling while maintaining the high voltage stability provided by the fluorinated linear carbonate structure.
3Ease of manufacture
If conventional nonaqueous electrolyte is used, then manufacturing is simpler, but electrolyte decomposition occurs at high voltage
Solution Approach 1:
The patent changes the purity specification parameters from conventional standards to ultra-high purity standards (50 ppm or less for specific compounds). This parameter change enables high voltage stability while remaining compatible with existing electrolyte preparation processes, thus resolving the contradiction between ease of manufacture and electrolyte stability.
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 controlled impurity levels enhance the electrochemical device's capacity, load, and cycling characteristics, reducing degradation and maintaining performance at high temperatures.
Implementation Method 1
Commonly used nonaqueous electrolytes for electrochemical devices such as lithium ion secondary batteries are electrolytes containing an electrolyte salt (e.g., LiPF6, LiBF4) dissolved in a nonaqueous solvent (e.g., ethylene carbonate, propylene carbonate, dimethyl carbonate). Such hydrocarbon solvents, however, have a low oxidation potential, and therefore the electrolyte may be decomposed in high voltage batteries produced in the future.
Implementation Method 2
The nonaqueous solvent contains a fluorinated linear carbonate represented by the formula (1), and further contains following compounds of (I) to (III) in a total amount of not more than 5000 ppm relative to the fluorinated linear carbonate: (I) a compound represented by the formula (2) RfOH; (II) a compound represented by the formula (3) ROH; and (III) a compound represented by the formula (4) ROCOCl
Data Source
AI summary
The present invention aims to provide an electrochemical device excellent in high temperature storage characteristics and cycling characteristics at high voltages, and a nonaqueous electrolyte for the electrochemical device. The present invention relates to an electrochemical device including: a positive electrode; a negative electrode; and a nonaqueous electrolyte containing a nonaqueous solvent and an electrolyte salt, wherein the nonaqueous solvent contains a fluorinated linear carbonate represented by the formula (1): RfOCOOR (1) (wherein Rf represents a C1-4 fluorinated alkyl group and R represents a C1-4 alkyl group), and further contains following compounds of (I) to (III) in a total amount of not more than 5000 ppm relative to the fluorinated linear carbonate: (I) a compound represented by the formula (2) RfOH (2) (wherein Rf is defined as above); (II) a compound represented by the formula (3) ROH (3) (wherein R is defined as above); and (III) a compound represented by the formula (4) ROCOCl (4) (wherein R is defined as above).