Non-aqueous Electrolyte for Lithium Battery SEI Formation
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Solution Overview
Problem
Lithium secondary batteries face challenges in maintaining high-temperature cycle characteristics and low-temperature output due to non-uniform solid electrolyte interface (SEI) formation, especially when using non-aqueous organic solvents and lithium salts with poor characteristics, leading to irreversible capacity and reduced output.
Innovation Solution
A non-aqueous electrolyte solution comprising propylene carbonate, an ester-based solvent, and lithium bis(fluorosulfonyl)imide, with a specific mixing ratio of lithium salts, forms a robust SEI on the anode, improving high-temperature and low-temperature output characteristics and capacity retention.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If an ester-based solvent is used to improve output characteristics, then low-temperature and room temperature output characteristics are improved, but high-temperature characteristics deteriorate
Solution Approach 1:
The patent combines ester-based solvent (for low-temperature output improvement) with propylene carbonate and cyclic carbonate solvents (for high-temperature stability) in a specific ratio to create a solvent system that achieves both low-temperature output characteristics and high-temperature cycle characteristics simultaneously
Solution Approach 2:
The patent optimizes the concentration ratio of ester-based solvent to cyclic carbonate solvent within specific ranges (ester-based solvent: 10-40 wt%, cyclic carbonate solvent: 60-80 wt%) to balance the conflicting requirements of low-temperature output and high-temperature stability
2Ease of manufacture
If non-aqueous organic solvent and lithium salt with poor characteristics are used, then manufacturing cost is reduced, but SEI formation uniformity deteriorates
Solution Approach 1:
The patent introduces a specific additive composition (containing fluoroethylene carbonate and vinylene carbonate in controlled amounts) that acts as an intermediary to mediate between the poor-characteristics lithium salt and the electrode surface, enabling uniform SEI formation even with cost-effective lithium salt materials
Solution Approach 2:
The patent creates a composite electrolyte system combining multiple solvents (propylene carbonate, cyclic carbonate, ester-based solvent) and multiple additives in specific ratios to achieve synergistic effects that improve SEI uniformity while maintaining cost-effectiveness
3Reliability
If lithium salt concentration is increased to improve SEI formation, then SEI robustness is improved, but irreversible capacity increases
Solution Approach 1:
The patent optimizes lithium salt concentration within a specific range (0.5-2.0 mol/L) and adjusts the composition ratio of different lithium salts (LiPF6, LiBF4, LiCF3SO3) to achieve sufficient SEI robustness while minimizing irreversible capacity loss through synergistic effects
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 initial and low-temperature output characteristics, suppresses cathode surface decomposition, and maintains high-temperature performance by forming a stable SEI, resulting in improved capacity retention and cycle stability.
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 cathode into and out of a graphite anode is repeated
Implementation Method 2
The SEI may only pass the lithium ions by acting as an ion tunnel
Implementation Method 3
since lithium is highly reactive, lithium reacts with the carbon electrode to form Li 2 CO 3, LiO, or LiOH
Data Source
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AI summary
Provided are a non-aqueous electrolyte solution, which includes a non-aqueous organic solvent including propylene carbonate (PC) and an ester-based solvent, and lithium bis(fluorosulfonyl)imide (LiFSI), and a lithium secondary battery including the non-aqueous electrolyte solution. According to the non-aqueous electrolyte solution of the present invention, since a robust solid electrolyte interface (SEI) may be formed on an anode during initial charge of a lithium secondary battery including the non-aqueous electrolyte solution, high-temperature cycle characteristics and capacity characteristics after high-temperature storage as well as low-temperature, room temperature, and high-temperature output characteristics may be simultaneously improved.