Lithium Battery Electrolyte Additives for Cycle Life
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Solution Overview
Problem
Rechargeable lithium batteries with non-carbon-based negative electrodes suffer from poor cycle life due to volume expansion and pulverization of metal materials like Si, Sn, and Al during charge-discharge cycles, limiting their commercialization and capacity retention.
Innovation Solution
A rechargeable lithium battery design incorporating a non-carbon-based negative active material with an electrolyte comprising ethylene carbonate in 20 volume % or less, LiPF6 as a lithium salt, a first additive represented by Formula 1, and a second additive LiB(C2O4), which forms a stable passivation film to improve cycle-life characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If non-carbon-based negative active material (Si, Sn, Al) is used to provide high capacity, then battery capacity is improved, but cycle life deteriorates due to volume expansion and pulverization
Solution Approach 1:
A solid electrolyte interface (SEI) film is formed as an intermediary layer between the non-carbon-based negative active material and the electrolyte. This SEI film acts as a protective barrier that prevents direct contact and harmful reactions, while allowing lithium ion transport. The film is formed through controlled decomposition of vinylene carbonate and fluoroethylene carbonate additives during initial charging cycles, creating a stable interface that resolves the contradiction between high capacity and cycle life.
Solution Approach 2:
The electrolyte composition is optimized with specific parameters: vinylene carbonate at 0.5-5 volume% and fluoroethylene carbonate at 5-20 volume%, with ethylene carbonate limited to 20 volume% or less. These parameter changes in electrolyte composition enable the formation of a stable SEI film that improves cycle life while maintaining high capacity characteristics of non-carbon-based materials.
2Quantity of substance
If amorphous Si oxide alloy material is used to improve initial capacity retention, then initial capacity is improved, but capacity retention sharply decreases after repeated charge-discharge cycles
Solution Approach 1:
The SEI film formed from vinylene carbonate and fluoroethylene carbonate additives serves as a stable intermediary layer that protects the amorphous Si oxide alloy material during repeated charge-discharge cycles. This film prevents electrolyte decomposition and maintains structural integrity, resolving the sharp decrease in capacity retention after cycling by providing continuous protection throughout the battery's operational life.
3Reliability
If halogen-containing carbonate (4-fluoroethylene carbonate) is added to improve cycle life, then cycle life is improved, but the improvement is limited
Solution Approach 1:
The patent combines multiple additives with complementary functions: vinylene carbonate (0.5-5 volume%) for SEI formation, fluoroethylene carbonate (5-20 volume%) for cycle life improvement, and ethylene carbonate (20 volume% or less) for lithium ion conductivity. This merging of multiple additives creates a synergistic effect that simultaneously improves cycle life and maintains high capacity retention, overcoming the limitations of using halogen-containing carbonate alone.
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 battery exhibits enhanced cycle-life characteristics with improved capacity retention and reduced electrolyte viscosity, maintaining performance over multiple charge-discharge cycles without significant capacity loss.
Implementation Method 1
A stable passivation film at the interface of a non-carbon-based negative electrode and an electrolyte improves cycle-life characteristics of a rechargeable lithium battery
Implementation Method 2
a positive electrode including a positive active material that reversibly intercalates and deintercalates lithium ions
Implementation Method 3
The electrolyte has a viscosity of 3.02 cP or less
Data Source
AI summary
The rechargeable lithium battery includes: a negative electrode including a non-carbon-based negative active material; a positive electrode including a positive active material that reversibly intercalates and deintercalates lithium ions; and an electrolyte that includes a non-aqueous organic solvent that includes ethylene carbonate in an amount of 20 volume % or less, a lithium salt including LiPF6, a first additive represented by the following Formula 1 and a second additive that is LiB(C2O4)2. The electrolyte has a viscosity of 3.02 cP or less:wherein, R1 and R2 are independently selected from the group consisting of hydrogen, a halogen, a cyano (CN), a nitro (NO2), and a C1 to C5 fluoroalkyl, provided that at least one of R1 and R2 is selected from the group consisting of a halogen, a cyano (CN), a nitro (NO2), and a C1 to C5 fluoroalkyl.