Lithium Battery Electrolyte Composition Balancing Conductivity and Heat Safety
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Solution Overview
Problem
Lithium secondary batteries face challenges in maintaining ionic conductivity and mechanical strength while improving output characteristics and high-temperature safety, particularly when using high-concentration lithium salts that increase viscosity and reduce ion mobility.
Innovation Solution
An electrolyte composition for lithium secondary batteries is developed, incorporating a lithium salt concentration of 1.6 M to 5 M, an oligomer mixture with specific structures, and an organic solvent, which includes a first oligomer with a -Si-O- group for surfactant properties and a second oligomer with a carbonate group for improved lithium ion dissociation, along with a halogenated benzene compound for enhanced charge cycle characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high-concentration lithium salt is used in the electrolyte, then output characteristics and high-temperature safety are improved, but viscosity increases and ionic conductivity decreases
Solution Approach 1:
The patent changes the concentration parameter of lithium salt from conventional low concentrations (0.5-2.0 M) to high concentrations (3.0-6.0 M, preferably 4.0-5.0 M). This parameter change increases the degree of lithium ion dissociation and reduces free solvent content, thereby improving high-temperature safety and output characteristics while maintaining acceptable ionic conductivity through optimized solvent composition.
Solution Approach 2:
The patent uses a composite electrolyte system combining multiple components: high-concentration lithium salt (LiPF6, LiBF4), cyclic carbonates (EC, PC), chain carbonates (DMC, DEC, EMC), and additives (VC, GBL). This composite approach allows the electrolyte to simultaneously achieve high lithium ion dissociation, adequate viscosity, and maintained ionic conductivity that would not be possible with single-component systems.
2Productivity
If high-concentration lithium salt is used to improve output characteristics, then lithium ion yield increases, but viscosity increases and ion mobility decreases
Solution Approach 1:
The patent optimizes the lithium salt concentration parameter to 3.0-6.0 M (preferably 4.0-5.0 M), which maximizes lithium ion yield by increasing the degree of dissociation. Simultaneously, the solvent composition is adjusted with cyclic to chain carbonate ratios and viscosity modifiers to compensate for increased viscosity, thereby maintaining adequate ion mobility for practical battery operation.
Solution Approach 2:
The electrolyte employs a composite solvent system with cyclic carbonates (high dielectric constant for dissociation) and chain carbonates (low viscosity for mobility). This composite approach ensures that high lithium salt concentration achieves maximum lithium ion yield while the solvent mixture maintains sufficient ion mobility through its balanced composition.
3Strength
If gel polymer electrolyte is used to improve mechanical strength, then safety is maintained, but ionic conductivity may be reduced
Solution Approach 1:
The patent creates a gel polymer electrolyte by combining polymer matrix (for mechanical strength and safety) with liquid electrolyte components including high-concentration lithium salt and carbonate solvents (for ionic conductivity). The polymer network provides structural integrity while the impregnated liquid electrolyte maintains high ion mobility, achieving both mechanical strength and ionic conductivity simultaneously.
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 electrolyte composition enhances the degree of lithium ion dissociation, improves mechanical strength, and maintains high-temperature safety by reducing exothermic reactions, while maintaining ionic conductivity and interfacial properties, leading to improved battery performance and safety.
Implementation Method 1
enhances the degree of lithium ion dissociation
Implementation Method 2
mobility of ions in the electrolyte is inversely proportional to the viscosity of the electrolyte
Implementation Method 3
the amount of the free solvent may be reduced, and the exothermic reaction may be suppressed to increase the high-temperature safety of the battery
Data Source
AI summary
The present invention provides an electrolyte for a lithium secondary battery which includes a lithium salt present in a concentration of 1.6 M to 5 M, an oligomer mixture including a first oligomer containing a unit represented by Formula 1 and a second oligomer containing a unit represented by Formula 2, and an organic solvent.