LiFSI Electrolyte for Rigid SEI Layer Formation
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Solution Overview
Problem
Lithium secondary batteries face challenges in maintaining high temperature storage properties and lifespan due to non-uniform solid electrolyte interface (SEI) layer formation and electrolyte additive-related issues, leading to decomposition and oxidation reactions.
Innovation Solution
A non-aqueous liquid electrolyte comprising lithium bis(fluorosulfonyl)imide (LiFSI) and a fluorinated ether compound, along with a lithium-nickel-manganese-cobalt-based oxide positive electrode active material, is used to form a rigid SEI layer, controlling the concentration of LiFSI and adding a lithium salt to prevent decomposition and oxidation, thereby enhancing storage and lifespan properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a common electrolyte or electrolyte with inferior additives is used, then the battery can operate, but the SEI layer formed is non-uniform leading to poor high-temperature storage properties and reduced lifespan
Solution Approach 1:
The patent changes the chemical composition parameters of the electrolyte by introducing specific additives (cyclic carbonate 10-30 vol%, linear carbonate 70-90 vol%, and fluoroethylene carbonate 0.5-5 vol%) to transform the SEI layer formation process, achieving a more uniform and stable SEI layer that improves high-temperature storage properties and battery lifespan
Solution Approach 2:
The patent uses a composite electrolyte system combining multiple carbonate solvents (cyclic and linear) with a small amount of fluoroethylene carbonate additive. This composite approach creates synergistic effects where the bulk carbonates provide stable SEI formation and the FEC additive enhances uniformity, resolving the contradiction between SEI uniformity and storage stability
2Productivity
If electrolyte additive is added to improve SEI layer formation, then low-temperature output improves, but excessive additive causes decomposition of positive electrode surface and oxidation reactions at high temperature
Solution Approach 1:
The patent precisely controls the concentration parameter of the fluoroethylene carbonate additive at 0.5-5 vol%, which is sufficient to improve low-temperature output through better SEI formation but low enough to prevent decomposition and oxidation reactions at high temperature. This parameter optimization resolves the contradiction between low-temperature performance and high-temperature stability
Solution Approach 2:
The fluoroethylene carbonate acts as an intermediary substance that mediates between the electrolyte and electrode surfaces. It forms a protective SEI layer that enables low-temperature ion transport while preventing harmful reactions at high temperature, thus resolving the contradiction through its dual protective function
3Reliability
If the amount of electrolyte additive is not controlled, then SEI layer formation is enhanced, but the positive electrode surface decomposes and oxidation reactions increase irreversible capacity
Solution Approach 1:
The patent optimizes the additive concentration parameter to 0.5-5 vol%, which is the critical threshold that ensures sufficient SEI layer formation quality while preventing excessive additive that would cause decomposition and oxidation. This precise parameter control minimizes irreversible capacity loss while maintaining reliable SEI formation
Solution Approach 2:
The patent applies a small but sufficient amount of fluoroethylene carbonate (0.5-5 vol%) that provides just enough SEI formation enhancement without excess that would cause harmful side reactions. This partial action approach achieves the necessary SEI quality while avoiding the detrimental effects of excessive additive
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 effectively forms a thin, rigid SEI layer that minimizes gas generation and electrode decomposition, improving high-temperature storage and lifespan properties by preventing side reactions and maintaining smooth lithium ion movement.
Implementation Method 1
lithium ions repeat intercalation and deintercalation from a lithium metal oxide of a positive electrode to a carbon electrode to conduct charging and discharging
Implementation Method 2
lithium is strongly reactive and reacts with the carbon electrode to produce Li2CO3, LiO, LiOH, etc. to form a coated layer on the surface of a negative electrode
Implementation Method 3
the SEI layer performs the role of an ion tunnel and passes only the lithium ions
Implementation Method 4
The ion tunnel may induce the solvation of the lithium ions
Data Source
AI summary
The present invention relates to a lithium secondary battery comprising a non-aqueous liquid electrolyte comprising lithium bis(fluorosulfonyl)imide (LiFSI) and a fluorinated ether compound as additives, a positive electrode comprising a lithium-nickel-manganese-cobalt-based oxide as a positive electrode active material, a negative electrode and a separator. According to a non-aqueous liquid electrolyte for a lithium secondary battery of the present invention, a rigid SEI layer may be formed at a negative electrode during the initial charging of the lithium secondary battery comprising the same, the output properties of the lithium secondary battery may be improved, and the output properties after storing at high temperature and capacity properties may be increased.