Lithium Secondary Battery Electrolyte Additive for SEI Stability
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Solution Overview
Problem
Lithium secondary batteries face challenges in maintaining high-temperature cycle characteristics and low-temperature output due to the degradation of the solid electrolyte interface (SEI) layer, leading to battery swelling, internal pressure increase, and potential fire or explosion risks, while existing methods to improve SEI formation often degrade cycle life characteristics.
Innovation Solution
A non-aqueous electrolyte solution for lithium secondary batteries is developed, incorporating lithium bis(fluorosulfonyl)imide (LiFSI) as a first lithium salt, a second lithium salt, and a compound represented by Formula 1, which forms a robust ion conductive film on the negative electrode, enhancing the SEI layer's stability and preventing side reactions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an SEI forming material is added to prevent SEI collapse during high-temperature storage, then high-temperature cycle characteristics are improved, but cycle life characteristics are degraded due to side effects of the electrolyte solution additive
Solution Approach 1:
The patent changes the chemical composition parameters of the electrolyte solution by introducing a specific additive (lithium 2,3-dimethyl-2,3-butandiolyl carbonate) with defined molecular structure and properties. This additive forms a stable SEI layer that prevents collapse during high-temperature storage without causing harmful side effects, thus improving high-temperature cycle characteristics while maintaining cycle life
Solution Approach 2:
The patent creates a composite electrolyte system by combining the specific additive (lithium 2,3-dimethyl-2,3-butandiolyl carbonate) with conventional electrolyte components. This composite approach produces a synergistic effect where the additive forms a protective SEI layer that stabilizes the electrode interface during high-temperature storage without compromising overall battery performance and cycle life
2Reliability
If the organic solvent is stored for a long period at high temperature, then the battery may be charged and discharged initially, but gas is generated through oxidation by transition metal oxide, causing battery swelling and electrode assembly deformation
Solution Approach 1:
The patent applies preliminary anti-action by having the additive (lithium 2,3-dimethyl-2,3-butandiolyl carbonate) proactively form a protective SEI layer on the electrode surface before oxidation can occur. This pre-formed barrier prevents the organic solvent from being oxidized by transition metal oxide during high-temperature storage, thereby preventing gas generation and maintaining battery structural stability
Solution Approach 2:
The patent converts the potentially harmful oxidation reaction into a beneficial process by directing it toward the additive instead of the organic solvent. The additive sacrificially forms a stable SEI layer that protects the main electrolyte components, transforming what would be a harmful degradation pathway into a protective mechanism that prevents battery swelling and deformation
3Reliability
If the SEI layer collapses during high-temperature storage in a fully charged state, then the negative electrode becomes exposed and reacts with the electrolyte solution, but this leads to continuous side reactions and gas generation increasing internal pressure
Solution Approach 1:
The patent implements preliminary action by having the additive form a robust SEI layer during initial charging cycles before high-temperature storage begins. This pre-formed SEI layer maintains its integrity during subsequent high-temperature storage in fully charged states, preventing electrode exposure and the subsequent harmful side reactions that would generate gas and increase internal pressure
Solution Approach 2:
The patent uses a small amount of additive (lithium 2,3-dimethyl-2,3-butandiolyl carbonate) that is consumed during initial SEI formation. This disposable-like behavior of the additive is beneficial because it sacrificially forms a stable protective layer that prevents ongoing degradation, gas generation, and internal pressure increase during the battery's operational life
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 initial capacity and cycle life characteristics of lithium secondary batteries by forming a stable SEI layer, maintaining performance under high-temperature conditions and reducing the risk of battery degradation, while minimizing side effects.
Implementation Method 1
a passivation layer is formed on a surface of the negative electrode while some of electrolyte solution additive components and organic solvents are decomposed in a voltage range of 0.5 V to 3.5 V during initial charge and the negative electrode reacts with the electrolyte solution. The layer is denoted as a 'solid electrolyte interface (SEI) layer'.
Implementation Method 2
lithium ions, which are deintercalated from the positive electrode by charging, are intercalated into the carbon-based negative electrode and again deintercalated during discharging
Implementation Method 3
The SEI layer formed during the initial charge may not only act as an ion tunnel to only pass lithium ions, but may also prevent a reaction of the lithium ions with the carbon-based negative electrode or other materials during charge and discharge
Implementation Method 4
gas is generated while the organic solvent is oxidized by the transition metal oxide discharged from the positive electrode
Data Source
AI summary
A non-aqueous electrolyte solution for a lithium secondary battery, and a lithium second battery including the same are disclosed herein. In some embodiments, the lithium electrolyte includes lithium bis(fluorosulfonyl)imide as a first lithium salt, a second lithium salt, an organic solvent, and a compound represented by Formula 1. In some embodiments, the lithium second battery includes a positive electrode having a positive electrode active material represented by Formula 2.