LiFSI and Phosphazene Additives for Rigid SEI Layer Formation
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Solution Overview
Problem
Lithium secondary batteries face challenges in maintaining output properties and lifespan due to the formation of non-uniform solid electrolyte interfaces (SEI) and decomposition of electrodes at high temperatures, especially when using common electrolyte solutions without effective additives.
Innovation Solution
A non-aqueous electrolyte solution comprising lithium bis(fluorosulfonyl)imide (LiFSI) and a phosphazene compound, along with a lithium-nickel-manganese-cobalt-based oxide positive electrode active material, is used to form a rigid SEI layer, preventing decomposition and oxidation reactions, and enhancing the battery's output and lifespan.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a common electrolyte solution without effective additives is used, then the device complexity is reduced, but the output properties and lifespan deteriorate due to non-uniform SEI formation and electrode decomposition at high temperatures
Solution Approach 1:
The patent changes the chemical composition parameters of the electrolyte solution by introducing specific additives (cyclic carboxylate compound at 0.1-5 wt% and sulfur compound at 0.1-5 wt%) to transform the SEI formation characteristics and electrode surface properties, thereby improving reliability without excessive complexity increase
Solution Approach 2:
The patent creates a composite electrolyte system combining multiple components (lithium salt, cyclic carbonate, chain carbonate, cyclic carboxylate additive, and sulfur compound additive) that work synergistically to form a stable protective interface, resolving the contradiction between simple composition and reliable performance
2Reliability
If an electrolyte additive is included to improve SEI formation, then the output properties improve, but the positive electrode surface may be decomposed or oxidation reactions may occur at high temperatures, increasing irreversible capacity
Solution Approach 1:
The cyclic carboxylate compound and sulfur compound act as intermediary substances that form a protective intermediate layer on the electrode surface, preventing direct harmful interactions between the electrolyte and electrode materials at high temperatures, thus reducing irreversible capacity
Solution Approach 2:
The patent applies different functional additives to different aspects of the electrolyte system: cyclic carboxylate for SEI stabilization and sulfur compound for high-temperature oxidative stability, creating localized protective effects that prevent electrode decomposition while maintaining output properties
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 improves output properties at low temperatures and extends the battery's lifespan by forming a stable SEI layer, preventing electrode decomposition and oxidation reactions, thereby enhancing performance and stability at high temperatures.
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, and organic solvents of an electrolyte solution having high molecular weight may induce co-intercalation at the carbon negative electrode, thereby preventing the breaking of the structure of the carbon negative electrode
Implementation Method 5
Once the SEI layer is formed during an initial charging, the SEI layer prevents the reaction of the lithium ions with the negative electrode or other materials during repeating charging and discharging
Data Source
AI summary
The present invention relates to a lithium secondary battery comprising a non-aqueous electrolyte solution comprising lithium bis(fluorosulfonyl)imide (LiFSI) and a phosphazene 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 electrolyte solution 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.