Fluorinated Electrolyte for High-Voltage Lithium Battery
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Solution Overview
Problem
Lithium secondary batteries using high-potential positive electrode materials face issues with electrolyte solution decomposition, leading to gas generation, increased internal pressure, swelling, and reduced cycle characteristics, especially when using carbonate-based solvents at high voltages.
Innovation Solution
Incorporating a fluorine-containing cyclic ether compound and/or a fluorine-containing chain ether or phosphate ester compound in the electrolytic solution to suppress decomposition and improve the battery's cycle characteristics and energy density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a spinel compound such as LiNi0.5Mn1.5O4 is used as a positive electrode active material to achieve high operation voltage, then energy density is improved, but decomposition reaction of the electrolytic solution occurs easily leading to gas generation and swelling
Solution Approach 1:
A fluorinated cyclic carbonate compound is introduced as an intermediary substance in the electrolytic solution that preferentially reacts with the high-potential spinel compound to form a stable interfacial film. This film acts as a protective barrier that prevents direct contact between the electrolyte and electrode, thereby suppressing decomposition reactions and gas generation while allowing ionic transport to continue.
Solution Approach 2:
The chemical composition of the electrolytic solution is modified by incorporating fluorinated cyclic carbonate compounds with specific molecular structures and fluorine content ratios. These parameter changes in the electrolyte composition alter the interfacial chemistry at the electrode surface, creating a more stable environment that prevents unwanted side reactions at high operating voltages.
2Reliability
If a carbonate-based electrolytic solution is used in a lithium secondary battery, then ion conductivity is maintained, but gas generation and capacity degradation are remarkable in high-voltage operation and long-term operation at high temperature
Solution Approach 1:
The electrolytic solution is formulated as a composite system combining conventional carbonate solvents with fluorinated cyclic carbonate compounds. This composite electrolyte leverages the high ion conductivity of carbonates while the fluorinated component provides enhanced interfacial stability and suppressed decomposition, achieving both good conductivity and reduced gas generation during cycling.
3Use of energy by moving object
If the operation voltage of the battery is increased to 4.5 V or more using spinel compound, then energy density is improved, but decomposition reaction of electrolytic solution advances easily at contact portion
Solution Approach 1:
The fluorinated cyclic carbonate compound performs preliminary protective action by reacting first with the high-potential spinel compound during initial cycles to form a stable surface film. This preliminary reaction prevents subsequent decomposition of the bulk electrolyte by creating a protective barrier that withstands high operating voltages, thereby preventing electrolyte decomposition before it can occur.
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 fluorine-containing compounds in the electrolytic solution effectively reduces gas generation, maintains high energy density, and enhances the battery's cycle stability, particularly at high potentials, thereby preventing swelling and internal pressure issues.
Implementation Method 1
when an electrolytic solution contains a fluorine-containing cyclic ether, it is presumed to allow for life improvement by accumulating the fluorine-containing cyclic ether on a negative electrode and by generating a film
Implementation Method 2
accumulating the fluorine-containing cyclic ether on a negative electrode and by generating a film
Implementation Method 3
the operation voltage is defined by oxidation-reduction reaction of cobalt ion or manganese ion (Co3+←→Co4+ or Mn3+←→Mn4+)
Implementation Method 4
decomposition reaction of an electrolytic solution easily advances at a contact portion of the positive electrode and the electrolytic solution
Implementation Method 5
decomposition reaction of an electrolytic solution easily advances at a contact portion of the positive electrode and the electrolytic solution
Data Source
AI summary
There is provided a secondary battery comprising: a positive electrode capable of intercalating and deintercalating a lithium ion; a negative electrode capable of intercalating and deintercalating a lithium ion; and an electrolytic solution, wherein the electrolytic solution comprises: a fluorine-containing cyclic ether compound represented by the following formula (1); and at least one selected from a fluorine-containing chain ether compound or a fluorine-containing phosphate ester compound;wherein R1 to R6 are each independently selected from a hydrogen atom, a fluorine atom, a chlorine atom, or a fluorine-substituted, chlorine-substituted, or unsubstituted alkyl group, and at least one of R1 to R6 is selected from a fluorine atom or a fluorine-substituted alkyl group.