Nonaqueous Electrolyte Composition for Li-Ion Gas Suppression
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Solution Overview
Problem
Lithium-ion secondary batteries with Si-based negative electrode active materials face issues such as volume changes during charging/discharging, leading to breakage, and the degradation of nonaqueous electrolytes like fluoroethylene carbonate, which causes gas generation and reduces battery life due to increased internal pressure.
Innovation Solution
A nonaqueous electrolyte for lithium-ion secondary batteries containing a cyclic carbonate, such as ethylene carbonate or monofluoroethylene carbonate, and a high-molecular-weight organic compound with polar functional groups, which suppresses gas generation and improves capacity retention by stabilizing the electrolyte and enhancing SEI formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If fluoroethylene carbonate is used to improve SEI formation and prevent direct contact between electrolyte and active material, then battery life is improved, but gas generation increases during high temperature storage
Solution Approach 1:
The patent combines fluoroethylene carbonate (for SEI formation) with ethylene carbonate (to suppress gas generation) in a specific ratio. This merging of two different cyclic carbonate compounds allows the system to simultaneously achieve good SEI formation properties and reduced gas generation during high temperature storage.
Solution Approach 2:
The patent specifies precise content ranges for fluoroethylene carbonate (0.1-5 mass%) and ethylene carbonate (5-30 mass%) to optimize the balance between SEI formation quality and gas suppression. By controlling these parameter ranges, the electrolyte achieves both improved battery life and reduced gas generation.
2Reliability
If cyclic carbonates are used to enhance SEI formation, then battery performance is improved, but internal pressure increases due to gas generation
Solution Approach 1:
The patent converts the harmful gas generation effect into a beneficial outcome by using ethylene carbonate to suppress the gas generation caused by fluoroethylene carbonate. The combination transforms the individual weakness of each compound into a strength when used together, maintaining battery performance while controlling internal pressure.
Solution Approach 2:
The electrolyte uses a composite approach by combining two different cyclic carbonate compounds (fluoroethylene carbonate and ethylene carbonate) with distinct properties. This composite electrolyte system leverages the SEI-forming capability of fluoroethylene carbonate while using ethylene carbonate to suppress gas generation and control internal pressure.
3Quantity of substance
If Si-based negative electrode active material is used to increase capacity density, then energy density is improved, but volume changes cause breakage and isolation from current collector
Solution Approach 1:
The electrolyte composition with ethylene carbonate and fluoroethylene carbonate promotes formation of a stable SEI layer on the Si-based anode before significant volume expansion occurs. This pre-formed protective layer acts as a cushion that accommodates volume changes and prevents direct mechanical stress on the Si particles, reducing breakage and isolation.
Solution Approach 2:
The patent modifies the electrolyte composition parameters (adding specific cyclic carbonates in controlled amounts) to change the properties of the SEI layer formed on the Si-based anode. This parameter change in electrolyte composition leads to formation of a more flexible and adherent SEI that can accommodate Si volume changes during cycling.
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 configuration effectively reduces gas generation, leading to improved battery life and capacity retention by preventing electrolyte degradation and maintaining internal pressure, thus extending the battery's lifespan.
Implementation Method 1
a nonaqueous electrolyte for lithium-ion secondary batteries containing a cyclic carbonate, such as ethylene carbonate or monofluoroethylene carbonate, and a high-molecular-weight organic compound with polar functional groups, which suppresses gas generation and improves capacity retention by stabilizing the electrolyte
Implementation Method 2
Since fluoroethylene carbonate has an oxidation-reduction potential and is easily reduced and decomposed, SEI can be suitably formed and direct contact and reaction between the electrolyte and the active material can be prevented
Implementation Method 3
SEI can be suitably formed and direct contact and reaction between the electrolyte and the active material can be prevented
Data Source
AI summary
A nonaqueous electrolyte for use in a lithium-ion secondary battery, capable of reducing gas generation due to degradation of nonaqueous electrolyte, is provided. The nonaqueous electrolyte disclosed herein is for use in a lithium-ion secondary battery wherein a negative electrode active material in a negative electrode includes at least one of a Si-based negative electrode active material including Si as a component and capable of reversibly absorbing and releasing lithium ions or a graphite-based carbon negative electrode active material. The nonaqueous electrolyte contains a nonaqueous solvent and an electrolyte dissolved in the nonaqueous solvent, and further contains a cyclic carbonate and a high-molecular-weight organic compound having a weight-average molecular weight of 1000 or higher.