Lithium Battery Electrolyte Additives for High-Temperature Stability
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Solution Overview
Problem
Lithium secondary batteries face capacity degradation, increased resistance, and safety concerns due to the collapse of the solid electrolyte interface (SEI) layer at high temperatures, leading to gas generation and structural instability.
Innovation Solution
A lithium secondary battery design incorporating a non-aqueous electrolyte solution with a specific molar ratio of lithium salts and additives, including fluorobenzene, tetravinylsilane, and tertiary butylbenzene, which forms a robust film on the positive electrode, suppressing side reactions and maintaining stability during high-temperature storage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional SEI layer is formed using only organic solvent and lithium salt, then the battery can operate initially, but the SEI layer collapses during high-temperature storage leading to capacity degradation and safety issues
Solution Approach 1:
The patent applies composite materials by combining multiple additives (fluorinated cyclic carbonate, vinylene carbonate, and fluoroethylene carbonate) with specific lithium salts to form a composite SEI layer. This composite structure integrates the protective properties of fluorinated compounds with the stabilizing effects of cyclic carbonates, creating a multi-component protective film that resists collapse at high temperatures while maintaining ion conductivity.
Solution Approach 2:
The patent employs parameter changes by precisely controlling the concentration ratios of different additives in the electrolyte solution. Specifically, it uses fluorinated cyclic carbonate at 0.01-5 wt%, vinylene carbonate at 0.01-3 wt%, and fluoroethylene carbonate at 0.01-3 wt%, with the ratio of vinylene carbonate to fluoroethylene carbonate being 1:1 to 10:1. These parameter optimizations enable the formation of an SEI layer with enhanced thermal stability and mechanical strength.
2Reliability
If the SEI layer is formed to protect the negative electrode, then decomposition of electrolyte is suppressed, but the layer becomes insufficient and collapses during continuous charge and discharge particularly at high temperatures
Solution Approach 1:
The patent uses fluorinated cyclic carbonate as an intermediary substance that mediates between the electrolyte components and the negative electrode surface. This intermediary forms a stable interface layer that prevents direct contact between the reactive electrolyte and electrode, reducing side reactions. The fluorinated cyclic carbonate acts as a buffer that stabilizes the SEI structure during thermal and electrochemical stress, preventing collapse while maintaining functionality.
3Quantity of substance
If high nickel content is used in the positive electrode active material to increase capacity, then energy density improves, but structural stability decreases leading to capacity fading and resistance increase
Solution Approach 1:
The patent applies local quality by creating a protective interface layer with specific chemical composition and structure at the positive electrode surface. This interfacial modification does not change the bulk high-nickel composition (maintaining high capacity) but creates a localized protective environment that stabilizes the crystal structure. The electrolyte additives form a stable SEI layer that locally protects the nickel-rich regions from degradation, water insertion, and cation mixing, thereby preserving structural integrity while maintaining high capacity.
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 secures capacity characteristics, reduces resistance and thickness increase rates, and enhances the overall stability and cycle life of the battery, preventing gas generation and structural collapse.
Implementation Method 1
a negative electrode capable of intercalating and deintercalating lithium ions
Implementation Method 2
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
Implementation Method 3
lithium ions react with the electrolyte solution on the surface of the negative electrode to form compounds, such as Li 2 CO 3 , Li 2 O, and LiOH, while the lithium ions generated from the positive electrode move to the negative electrode. These compounds may form a kind of a passivation layer on the surface of the negative electrode, and the layer is denoted as a 'solid electrolyte interface (SEI)' layer
Implementation Method 4
The SEI layer formed at an initial stage of charging acts as a protective film for stabilizing the battery by suppressing the decomposition of the carbonate-based electrolyte solution on the surface of the negative electrode
Data Source
AI summary
The present invention relates to a lithium secondary battery which includes a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte solution, wherein the positive electrode includes a positive electrode active material represented by Formula 1, and the non-aqueous electrolyte solution includes a non-aqueous organic solvent, a first lithium salt, lithium bis(fluorosulfonyl)imide as a second lithium salt, and an additive, wherein a molar ratio of the first lithium salt to the second lithium salt is in a range of 1:0.01 to 1:1, and the additive is a mixed additive which includes fluorobenzene, tetravinylsilane, and tertiary butylbenzene in a weight ratio of 1:0.05:0.1 to 1:1:1.5. [Formula 1] Li(NiaCobMnc)O2 (in Formula 1, 0.65<a≤0.9, 0.05≤b<0.2, 0.05≤c<0.2, and a+b+c=1.)