Lithium Ion Battery Electrolyte Impurity Control
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Solution Overview
Problem
Lithium ion secondary cells face safety issues during overcharging, internal short circuits, and high-temperature environments, with existing nonaqueous electrolytes exhibiting reduced discharge capacity and cycle degradation.
Innovation Solution
A lithium ion secondary cell design incorporating a nonaqueous electrolyte with a reduced amount of specific impurities, including fluorine-containing ethers and hydroxy group-containing compounds, optimized to improve high-temperature storage and high-voltage cycle characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If fluorine-containing ether is used to improve safety and voltage, then safety and voltage are improved, but discharge capacity is reduced when left in high temperature environment or repeatedly charged and discharged
Solution Approach 1:
The patent changes the chemical composition parameters of the electrolyte by specifying precise proportions of fluorine-containing ether (15-30 vol%), cyclic carbonate (65-80 vol%), and chain carbonate (5-20 vol%). This parameter optimization resolves the contradiction by achieving both improved safety and maintained discharge capacity through balanced formulation.
Solution Approach 2:
The patent uses a composite electrolyte system combining fluorine-containing ether with cyclic carbonate and chain carbonate. This composite approach leverages the safety benefits of fluorine-containing ether while the carbonate components maintain discharge capacity and cycle stability, resolving the contradiction between safety improvement and capacity retention.
2Power
If fluorine-containing ether is used to achieve higher voltage, then voltage is improved, but cycle characteristics deteriorate when repeatedly charged and discharged
Solution Approach 1:
The patent creates a composite electrolyte where fluorine-containing ether provides high voltage capability while cyclic carbonate and chain carbonate components ensure good cycle characteristics. The synergistic combination resolves the contradiction between achieving higher voltage and maintaining durable cycle performance.
Solution Approach 2:
The patent optimizes the volume ratio parameters, specifically setting fluorine-containing ether at 15-30 vol% rather than higher concentrations. This parameter control allows achieving high voltage while limiting the degradation of cycle characteristics that would occur with excessive fluorine-containing ether content.
3Quantity of substance
If conventional electrolyte composition is used to maintain discharge capacity, then discharge capacity is maintained, but safety is insufficient during overcharging, internal short circuit, or penetration
Solution Approach 1:
The patent extracts and incorporates fluorine-containing ether into the electrolyte composition to specifically address safety concerns during overcharging, internal short circuits, and penetration. This extraction of the safety-enhancing component while maintaining overall electrolyte balance resolves the contradiction between maintaining discharge capacity and improving safety.
4Reliability
If fluorine-containing ether concentration is increased to improve safety, then safety is improved, but manufacturing complexity increases due to purification requirements
Solution Approach 1:
The patent sets the fluorine-containing ether concentration at an optimized range of 15-30 vol%, which is high enough to provide safety benefits but controlled enough to avoid excessive purification complexity. This parameter optimization resolves the contradiction between improving safety and managing manufacturing complexity.
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 enhances the cell's safety and performance by maintaining high discharge capacity and cycle stability, even under high-voltage and high-temperature conditions, through the use of purified fluorine-containing ethers and controlled amounts of impurities in the electrolyte.
Implementation Method 1
a nonaqueous electrolyte containing nonaqueous solvents and an electrolyte salt, the nonaqueous solvents including a fluorine-containing ether
Data Source
AI summary
The present invention provides a lithium ion secondary cell excellent in high-temperature storage characteristics and high voltage cycle characteristics; and a nonaqueous electrolyte for the cell. The present invention relates to a lithium ion secondary cell, comprising a positive electrode, a negative electrode, and a nonaqueous electrolyte containing nonaqueous solvents and an electrolyte salt, the nonaqueous solvents comprising a fluorine-containing ether represented by the formula (1): Rf1-O-Rf2 (1) wherein Rf1 and Rf2 are the same as or different from each other, each being a C1-10 alkyl group or a C1-10 fluoroalkyl group; and at least one of Rf1 and Rf2 is a fluoroalkyl group, and the following compounds (I) and (II): (I) a fluorine-containing unsaturated compound; and (II) a hydroxy group-containing compound represented by the formula (2): Rf1OH (2) wherein Rf1 is the same as above, and the nonaqueous solvents comprising the compounds (I) and (II) in a total amount of 5000 ppm or less for the fluorine-containing ether.