Lithium-Ion Battery Electrolyte Coatings for High Flash Point Output
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Solution Overview
Problem
Lithium ion secondary batteries face issues with the volatilization of flammable nonaqueous solvents and the release of oxygen due to degradation of lithium composite oxide at high temperatures, which affects their durability and performance, especially in cold conditions.
Innovation Solution
The use of γ-butyrolactone as a nonaqueous solvent is combined with the formation of a coat containing components derived from vinylene carbonate on the negative electrode and monoalkyl sulfate ions on the positive electrode, to reduce degradation and enhance durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If γ-butyrolactone is used as a nonaqueous solvent to increase flash point, then the flash point increases, but the battery output decreases due to degradation product
Solution Approach 1:
Vinylene carbonate acts as an intermediary substance that forms a protective SEI layer on the negative electrode, preventing direct contact between γ-butyrolactone and the electrode surface. This mediator layer blocks the degradation pathway while allowing ion transport, thus preventing battery output decrease while maintaining the high flash point benefit
Solution Approach 2:
The invention changes the chemical composition parameters of the electrolyte by adding vinylene carbonate at specific concentrations (0.1-5 wt%). This parameter change transforms the electrolyte system from one where γ-butyrolactone directly contacts electrodes to one where a stable SEI layer mediates the interaction, preventing degradation while maintaining desired thermal properties
2Power
If γ-butyrolactone is used as a nonaqueous solvent to improve cold output, then the cold output improves, but cycle deterioration occurs due to degradation
Solution Approach 1:
Vinylene carbonate performs a preliminary action by forming a stable SEI layer on the negative electrode during initial charging cycles. This pre-formed protective layer prevents subsequent degradation of γ-butyrolactone during cycling, thereby preserving cycle durability while maintaining the improved cold output characteristics
Solution Approach 2:
The invention converts the potentially harmful degradation reaction into a beneficial process by controlling it to occur only for vinylene carbonate (forming protective SEI) rather than γ-butyrolactone. The degradation of vinylene carbonate becomes a protective mechanism that prevents worse degradation of the main solvent and electrode materials over cycles
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
This configuration increases the flash point of the battery, improves its output in cold conditions, and enhances its durability by preventing cycle deterioration and maintaining high output properties for a long period.
Implementation Method 1
a coat (SEI layer) containing a component derived from vinylene carbonate (hereinafter 'VC'), on the surface of the negative electrode active material layer
Implementation Method 2
a coat containing a component derived from monoalkyl sulfate ions, on a surface of the positive electrode active material layer
Implementation Method 3
The nonaqueous electrolyte is obtained by dissolving a lithium salt in a nonaqueous solvent such as ethylene carbonate, propylene carbonate, and dimethyl carbonate
Data Source
AI summary
A lithium ion secondary battery includes: a positive electrode having a positive electrode active material layer on a surface of a positive electrode collector; a negative electrode a having a negative electrode active material layer on a surface of a negative electrode collector; and a nonaqueous electrolyte. The positive electrode, the negative electrode, and the nonaqueous electrolyte are accommodated in a battery case. The nonaqueous electrolyte contains γ-butyrolactone as a main component of a nonaqueous solvent. A monoalkyl sulfate ion-derived coat is formed on the surface of the positive electrode active material layer. A VC-derived coat is formed on the surface of the negative electrode active material layer.