LiFSI Electrolyte for Lithium Battery SEI Uniformity
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Solution Overview
Problem
Lithium secondary batteries face challenges in achieving high-rate charge and discharge characteristics, suppressing gas generation during high-temperature storage, and improving life characteristics due to non-uniform solid electrolyte interfaces (SEI) formed by conventional electrolytes, especially when electrolyte additives with poor characteristics are used.
Innovation Solution
An electrolyte composition for lithium secondary batteries incorporating lithium bis(fluorosulfonyl)imide (LiFSI) as a lithium salt, a borate-based lithium compound, and a non-aqueous organic solvent, along with specific additives like succinonitrile and vinyl silane, which form a robust and uniform SEI, enhancing the battery's performance by preventing decomposition and oxidation reactions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional electrolyte additives are used, then the electrolyte can be manufactured with simple composition, but the SEI formed is non-uniform leading to poor high-rate charge and discharge characteristics
Solution Approach 1:
The patent uses a composite electrolyte additive system combining lithium bis(fluorosulfonyl)imide (LiFSI) with specific ratios of cyclic carbonate and chain carbonate solvents. This composite composition creates a uniform SEI layer that enables high-rate charge and discharge while maintaining structural integrity, directly resolving the contradiction between charge/discharge rate and SEI uniformity.
Solution Approach 2:
The patent optimizes specific parameters including the ratio of cyclic to chain carbonate (0.3 to 2.0 by volume), LiFSI concentration (0.5 to 2.0 M), and additive composition ratios. These parameter changes transform the electrolyte system to form uniform SEI while maintaining high conductivity for fast charge and discharge operations.
2Temperature
If electrolyte additive is included to improve SEI formation, then low-temperature output may be improved, but the additive decomposes at high temperature causing oxidation reactions and increased irreversible capacity
Solution Approach 1:
The patent selects LiFSI as the lithium salt with optimal concentration (0.5 to 2.0 M) and combines it with specific carbonate solvent ratios. This parameter optimization ensures the SEI remains stable across a wide temperature range, preventing decomposition and oxidation reactions at high temperatures while maintaining low-temperature output performance.
Solution Approach 2:
The patent employs a carefully formulated electrolyte composition where the additive system is designed to form a stable, long-lasting SEI layer that protects against high-temperature degradation. The specific combination of LiFSI and carbonate solvents creates a protective interface that prevents harmful oxidation reactions during high-temperature operation.
3Temperature
If high amount of electrolyte additive is added to improve SEI robustness, then high-temperature performance may be improved, but the amount of gas generated during high-temperature storage increases
Solution Approach 1:
The patent optimizes the LiFSI concentration to a specific range (0.5 to 2.0 M) and controls the ratio of cyclic to chain carbonates (0.3 to 2.0 by volume). These parameter changes achieve robust SEI formation that maintains high-temperature performance while minimizing gas generation during storage, avoiding the need for excessive additive amounts.
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 proposed electrolyte composition significantly improves high-rate charge and discharge capabilities, reduces gas generation during high-temperature storage, and extends the battery's life by stabilizing the SEI, leading to better high-temperature performance and capacity retention.
Implementation Method 1
Charge and discharge of the lithium secondary battery is performed while a process of intercalating and deintercalating lithium ions from a lithium metal oxide positive electrode into and out of a graphite negative electrode is repeated.
Implementation Method 2
The SEI only passes the lithium ions by acting as an ion tunnel.
Implementation Method 3
since lithium is highly reactive, the lithium reacts with the carbon electrode to form Li2CO3, LiO, or LiOH
Implementation Method 4
a robust SEI must be formed on the negative electrode of the lithium secondary battery
Data Source
AI summary
An electrolyte for a lithium secondary battery of the present invention may improve high-rate charge and discharge characteristics and high-temperature storage and life characteristics of a lithium secondary battery and may achieve an effect of increasing reversible capacity by simultaneously including lithium bis(fluorosulfonyl)imide (LiFSI) and a second lithium salt, as a lithium salt, while including a second additive as well as a novel borate-based lithium compound, as an additive.