Battery Electrolyte Sequencing for Stable SEI and CEI Films
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Solution Overview
Problem
Existing electrochemical apparatuses, such as lithium-ion batteries, face challenges in achieving stable cycle performance due to the instability of the solid electrolyte interphase (SEI) and cathode electrolyte interphase (CEI) films, particularly when sulfur-containing compounds are used.
Innovation Solution
The electrochemical apparatus incorporates a method of pre-lithiating the negative electrode and using a multi-step electrolyte injection process. The first electrolyte contains a fluorine-containing compound but no sulfur-containing compound, forming a stable SEI film on the negative electrode. The second electrolyte, containing both fluorine- and sulfur-containing compounds, forms a stable CEI film on the positive electrode, optimizing the mass ratios of fluorine to sulfur in the surface layers of the electrodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If sulfur-containing compounds are used in the electrolyte to form CEI film on the positive electrode, then the cycle performance is improved, but the SEI film on the negative electrode deteriorates due to reduction of sulfur-containing compounds
Solution Approach 1:
The electrolyte is divided into two separate electrolytes: a first electrolyte containing fluorine-containing compounds for forming stable SEI film on the negative electrode, and a second electrolyte containing sulfur-containing compounds for forming stable CEI film on the positive electrode. This segmentation prevents the harmful interaction between sulfur-containing compounds and the negative electrode while maintaining the benefits of both additives.
Solution Approach 2:
The first electrolyte containing fluorine-containing compounds is added before the second electrolyte containing sulfur-containing compounds. This preliminary action ensures that the SEI film on the negative electrode is formed and stabilized first, preventing subsequent deterioration by sulfur-containing compounds, while still allowing the sulfur-containing compounds to form the desired CEI film on the positive electrode.
2Stability of the object's composition
If fluorine-containing compounds are used to form stable SEI film on the negative electrode, then the SEI film stability is improved, but the CEI film on the positive electrode becomes unstable
Solution Approach 1:
The electrolyte system is segmented into two distinct electrolytes with different functional compositions. The first electrolyte focuses on stabilizing the negative electrode interface with fluorine-containing compounds, while the second electrolyte addresses the positive electrode interface stability with sulfur-containing compounds, ensuring both interfaces are optimized without compromise.
Solution Approach 2:
The fluorine-containing compounds are introduced first to establish a stable SEI film on the negative electrode, creating a protective foundation. Subsequently, sulfur-containing compounds are added to form the CEI film on the positive electrode, ensuring both films are formed in an optimal sequence for maximum stability.
3Device complexity
If a single electrolyte containing both fluorine-containing and sulfur-containing compounds is used, then the process is simplified, but the mass ratio control of fluorine to sulfur in surface layers becomes difficult
Solution Approach 1:
The electrolyte is segmented into two separate formulations with distinct compositional ratios. The first electrolyte contains fluorine-containing compounds at a first mass ratio, and the second electrolyte contains sulfur-containing compounds at a second mass ratio. This segmentation enables precise control of the final fluorine-to-sulfur mass ratio in the electrode surface layers by adjusting the relative amounts of the two electrolytes added.
Solution Approach 2:
The mass ratios of fluorine to sulfur in the electrolyte are changed between the two electrolytes. The first electrolyte has a first mass ratio of fluorine to sulfur, and the second electrolyte has a second mass ratio of fluorine to sulfur, allowing flexible adjustment of the final surface layer composition to achieve the desired 5:1 to 20:1 mass ratio range.
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 approach ensures the formation of stable SEI and CEI films, reducing the risk of film deterioration and enhancing the cycle performance of the electrochemical apparatus by maintaining balanced stability and performance of both electrodes.
Implementation Method 1
adding a first electrolyte to the electrochemical apparatus to perform a first formation step, where the first electrolyte includes a first fluorine-containing compound... forming a stable SEI film on the negative electrode
Implementation Method 2
adding a second electrolyte to the electrochemical apparatus to perform a second formation step, where the second electrolyte includes a second fluorine-containing compound and a sulfur-containing compound... forms a stable CEI film on the positive electrode
Data Source
AI summary
An electrochemical apparatus includes a positive electrode plate including a positive electrode active material layer; a negative electrode plate including a negative electrode active material layer; and a separator disposed between the positive electrode plate and the negative electrode plate. A mass ratio of fluorine to sulfur in a surface layer of the positive electrode active material layer is A, and a mass ratio of fluorine to sulfur in a surface layer of the negative electrode active material layer is B, where 30≤A≤300, and 5≤B≤50.