Non-Aqueous Electrolyte Composition for Stable SEI and Low Impedance
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Solution Overview
Problem
Existing secondary batteries face challenges in achieving long cycle life, high safety performance, and good rate performance due to the poor thermal stability of lithium hexafluorophosphate and the formation of LiF and PF5, which increase interfacial impedance and lead to corrosion and degradation of the positive electrode.
Innovation Solution
A non-aqueous electrolyte containing specific concentrations of metal cations Men+ and tetrafluoroborate anions BF4−, with D1 ppm of Men+ and D2 ppm of BF4− satisfying D1 is 0.1 to 1250 and D1/D2 is 0.02 to 2, forming a stable and low-impedance SEI film, enhancing cycling, safety, and kinetic performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If lithium hexafluorophosphate is used as the electrolyte, then high ionic conductivity is achieved, but thermal stability deteriorates and LiF/PF5 formation increases interfacial impedance
Solution Approach 1:
The patent changes the chemical composition parameters of the electrolyte by introducing metal cations (Men+) and tetrafluoroborate anions (BF4−) with specific concentration ratios (D1/D2 = 0.02 to 2). This parameter modification transforms the electrolyte system from pure lithium hexafluorophosphate to a composite system that maintains ionic conductivity while improving thermal stability and preventing decomposition product formation.
Solution Approach 2:
The patent creates a composite electrolyte system by combining multiple ionic species (lithium ions, metal cations Men+, and tetrafluoroborate anions BF4−) in specific proportions. This composite approach leverages the synergistic effects of different ions to achieve both high ionic conductivity and enhanced thermal stability, while the metal cations preferentially reduce to form protective SEI films that prevent harmful LiF and PF5 formation.
2Quantity of substance
If lithium hexafluorophosphate is used, then high capacity is achieved, but corrosion and degradation of the positive electrode occurs
Solution Approach 1:
The patent introduces metal cations (Men+) as intermediary substances that mediate between the lithium ions and the positive electrode. These metal cations have more positive standard reduction potentials than lithium ions, causing them to preferentially reduce and form protective SEI films on the electrode surface. This intermediary layer acts as a barrier that prevents direct contact between lithium ions and the positive electrode, thereby preventing corrosion and degradation while maintaining high capacity.
3Ease of operation
If conventional electrolyte composition is used, then basic electrochemical function is achieved, but cycling performance and safety performance deteriorate
Solution Approach 1:
The patent systematically modifies the electrolyte composition parameters by controlling the concentrations of metal cations (D1 ppm) and tetrafluoroborate anions (D2 ppm) within specific ranges (D1 = 0.1 to 1250 ppm, D1/D2 = 0.02 to 2). These parameter changes optimize the formation of protective SEI films while maintaining good ionic conductivity, thereby simultaneously improving cycling performance and safety performance without compromising basic electrochemical function.
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 improves capacity retention rate, reduces volume swelling, and maintains good kinetic performance by reducing irreversible lithium ion consumption and forming a stable SEI film, while increasing thermal stability and reducing impedance.
Implementation Method 1
a difference between a standard reduction potential of Men+ and a standard reduction potential of Li+ is 1.0 V or more... Men+ is reduced before the lithium ions, thereby better reducing irreversible consumption of active lithium ions during SEI film formation
Implementation Method 2
non-aqueous electrolyte containing a non-aqueous solvent and lithium ions, first cations, and first anions dissolved therein... mass concentration of the first cations in the non-aqueous electrolyte is D1 ppm, and mass concentration of the first anions in the non-aqueous electrolyte is D2 ppm
Data Source
AI summary
This application provides a non-aqueous electrolyte and a preparation method thereof, and a secondary battery and an electric apparatus containing the same. The non-aqueous electrolyte contains the non-aqueous solvent and lithium ions, first cations, and first anions dissolved therein, where the first cation is a metal cation Men+ other than the lithium ion, n representing a chemical valence of the metal cation; the first anion is a tetrafluoroborate anion BF4−; mass concentration of the first cations in the non-aqueous electrolyte is D1 ppm, and mass concentration of the first anions in the non-aqueous electrolyte is D2 ppm, both based on total mass of the non-aqueous electrolyte; and the non-aqueous electrolyte satisfies that D1 is 0.1 to 1250 and that D1/D2 is 0.02 to 2. The non-aqueous electrolyte in this application enables the secondary battery to have good cycling performance, safety performance, and kinetic performance.