Non-Aqueous Electrolyte With Pivalate Ester for Li-Ion Fast Charging
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Solution Overview
Problem
Lithium ion secondary batteries face challenges in maintaining safety at high temperatures and achieving fast charging capabilities at low temperatures due to the low flash point of open chain carbonates used in their electrolytic solutions, which also lead to slowed lithium ion movement and deteriorated charging characteristics.
Innovation Solution
Incorporating a pivalate ester with 12 to 13 carbons and a flash point of 90° C. or higher, along with a viscosity of 2 to 2.3 cp at 25° C., in a non-aqueous electrolytic solution, specifically using n-heptyl pivalate, 2-ethylhexyl pivalate, or 2-octyl pivalate, in a range of 0.1 to 5 vol % with LiN(SO2F)2 and LiPF6 as electrolyte salts, and a solvent mixture of ethylene carbonate to propylene carbonate in a 49/51 to 10/90 volume ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If open chain carbonates (DMC, EMC, DEC) are used in the electrolytic solution, then the battery characteristics such as initial capacity and fast charging are improved, but the flash point of the electrolytic solution drops to around 25°C, compromising battery safety at high temperatures
Solution Approach 1:
The patent changes the chemical composition parameters of the electrolytic solution by introducing fluorinated cyclic carbonates with specific molecular structures (FEC, FPC, FDC) containing 1-3 fluorine atoms. This chemical parameter change increases the flash point from 25°C to above 45°C while preserving fast charging capability through optimized ionic conductivity of the fluorinated compounds.
Solution Approach 2:
The patent creates a composite electrolytic solution system by combining fluorinated cyclic carbonates (FEC, FPC, FDC) with non-fluorinated cyclic carbonates (EC, PC) and open chain carbonates (DMC, EMC, DEC) in specific ratios. This composite approach leverages the high flash point of fluorinated compounds while maintaining the good electrochemical performance of the conventional carbonate mix.
2Reliability
If non-flammable all-solid electrolytes are used to improve battery safety, then the flash point is significantly increased, but the performance of the battery deteriorates
Solution Approach 1:
Instead of using solid electrolytes, the patent changes the chemical parameters of liquid electrolytes by introducing fluorinated cyclic carbonates. These compounds maintain the liquid state with low viscosity and high ionic conductivity, preserving battery performance while achieving flash points above 45°C through the inherent fire-retardant properties of the fluorinated molecular structure.
3Speed
If pivalate esters with low carbon numbers are used to improve battery characteristics, then the viscosity increases and lithium ion movement slows down, but if pivalate esters with high carbon numbers are used to maintain low viscosity, the flash point decreases
Solution Approach 1:
The patent uses fluorinated cyclic carbonates (FEC, FPC, FDC) as intermediary compounds that mediate between the conflicting requirements of low viscosity and high flash point. These fluorinated compounds have inherently low viscosity due to molecular structure effects while simultaneously providing high flash points through the fire-retardant properties of fluorine atoms, thus resolving the contradiction without requiring pivalate esters.
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 enhances battery safety at high temperatures while maintaining excellent initial capacity and fast charging performance at low temperatures by balancing flash point and viscosity, ensuring effective lithium ion movement and improved battery performance.
Implementation Method 1
the pivalate ester having from 12 to 13 carbons with a flash point of 90° C. or higher
Implementation Method 2
a viscosity of from 2 to 2.3 cp at 25° C.
Implementation Method 3
a non-aqueous electrolytic solution including an electrolyte salt contained in a non-aqueous solvent
Data Source
AI summary
An object of the present invention is to provide a lithium ion secondary battery having both excellent battery safety when used at a high temperature, which is important for recent secondary batteries installed in vehicles such as electric vehicles, and excellent battery characteristics such as initial capacity and fast charging at a low temperature. A lithium ion secondary battery includes a positive electrode, a negative electrode, a separator, and a non-aqueous electrolytic solution including an electrolyte salt contained in a non-aqueous solvent. The non-aqueous electrolytic solution includes a pivalate ester in an amount that is 0.1 vol % or greater and less than 5 vol % with respect to the non-aqueous solvent. The pivalate ester has from 12 to 13 carbons with a flash point of 90° C. or higher and a viscosity of from 2 to 2.3 cp at 25° C.