Non-Aqueous Electrolyte Composition for Elastic SEI Film Stability
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Solution Overview
Problem
Lithium-ion secondary batteries face issues with increased impedance and reduced life due to the formation of an SEI film rich in organic components, which leads to lithium precipitation and deterioration of battery performance.
Innovation Solution
A non-aqueous electrolyte containing specific cyclic sulfate compounds and inorganic additives forms a highly elastic and stable SEI film on the negative electrode, incorporating inorganic components like Li2S, ROSOLi, carbonate, LiF, and borate, enhancing ion conductivity and electron blocking capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If electrolyte additives are added to form an SEI film on the negative electrode, then battery life is improved, but electrode impedance increases and power performance deteriorates
Solution Approach 1:
The patent uses a composite electrolyte additive system comprising cyclic sulfate compound (first additive) combined with fluoroethylene carbonate (second additive) or difluoroethylene carbonate (third additive). This composite approach creates an SEI film with balanced properties: the cyclic sulfate provides inorganic components for stability and life extension, while the fluorinated cyclic carbonate components control impedance and prevent excessive thickness, thus resolving the contradiction between battery life improvement and impedance increase.
2Reliability
If SEI film is formed to protect electrodes and inhibit lithium consumption, then battery stability is improved, but lithium precipitation occurs and power performance deteriorates
Solution Approach 1:
The patent modifies the chemical composition parameters of the SEI film by introducing fluorinated cyclic carbonate components (FEC or DFEC) alongside cyclic sulfate. This parameter change alters the SEI film's physical and chemical properties, making it more lithium-ion conductive while maintaining electron-blocking capability. The fluorinated components ensure the SEI film remains thin and flexible, preventing lithium precipitation while preserving battery stability.
3Quantity of substance
If inorganic components are added to the electrolyte, then ion conductivity is improved, but electron blocking capability may be compromised
Solution Approach 1:
The patent merges two distinct functional components into a unified SEI film structure: cyclic sulfate compound providing inorganic components (Li2S, ROSO2Li, LiF, borate, phosphate) for high ion conductivity, and fluorinated cyclic carbonate (FEC or DFEC) providing organic matrix for electron blocking. This merging creates a synergistic effect where the composite SEI film simultaneously achieves superior ion conductivity and electron blocking capability, resolving the contradiction between these two opposing requirements.
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 SEI film effectively blocks electrons, improving cycling and storage performance, and prolonging battery life by stabilizing the film against volume changes and mechanical stress.
Implementation Method 1
The cyclic sulfate additive in the non-aqueous electrolyte forms a highly elastic SEI film on a negative electrode side during first charging
Implementation Method 2
The SEI film is a good lithium ion conductor as well as a poor electron conductor, which inhibits continuation of a lithium consumption reaction and plays a role in protecting electrodes
Implementation Method 3
Compared with a single sulfide, the mixed inorganic components have more stable and higher ion conducting and electron blocking capabilities
Implementation Method 4
inorganic components such as Li 2 S, ROSO 2 Li, a carbonate, LiF, a borate, and a phosphate are generated on the negative electrode side during first charging
Data Source
Figure 1~3
Figure 4~6
AI summary
The present application provides a non-aqueous electrolyte solution, a secondary battery, and an electric device. The non-aqueous electrolyte solution comprises additives, wherein the additives comprise a first additive and a second additive, the first additive is any one or more cyclic sulfate compounds having a structure represented by general formula (I), and the second additive comprises one or more of lithium monofluorophosphate, lithium difluorophosphate, lithium tetrafluoroborate, a compound represented by general formula (III), and fluorosulfonates.