Electrochemical Cell Electrolyte Staging for Stable SEI and CEI Films
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Solution Overview
Problem
Existing methods for improving the cycling performance of electrochemical apparatuses, such as lithium-ion batteries, are not completely satisfactory, particularly due to the instability of the anode and cathode films caused by the reduction of nitrile compounds on the negative electrode surface, leading to deterioration of the SEI film and poor performance.
Innovation Solution
A two-stage electrolyte injection process is employed, where a first electrolyte containing a fluorine-containing compound forms a stable SEI film on the negative electrode without nitrile compounds, followed by a second electrolyte with both fluorine-containing and nitrile compounds to form a stable CEI film on the positive electrode, maintaining optimal mass ratios of fluorine to nitrogen on the surface layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If fluorine-containing compounds are used to form SEI film on the negative electrode, then the SEI film stability is improved, but the cycling performance is limited without proper CEI film formation on the positive electrode
Solution Approach 1:
The electrolyte injection is segmented into two stages: the first injection uses fluorine-containing compounds to form stable SEI film on the negative electrode, and the second injection adds nitrile compounds to form stable CEI film on the positive electrode. This ensures both films are properly formed for optimal cycling performance.
Solution Approach 2:
The composition of the electrolyte is changed between two injection stages: the first electrolyte contains only fluorine-containing compounds (5-40% by mass), while the second electrolyte contains both fluorine-containing compounds (5-40% by mass) and nitrile compounds (1-6% by mass). This parameter change enables sequential film formation on different electrodes.
2Device complexity
If the mass ratio of fluorine to nitrogen is not controlled on the surface layers, then the film formation process is simpler, but the cycling retention rate decreases
Solution Approach 1:
The electrolyte injection process incorporates feedback control by monitoring and controlling the mass ratios of fluorine and nitrogen on the surface layers of both electrodes. The first electrolyte injection is controlled to achieve fluorine mass ratio of 3≤A≤50 on the positive electrode and 30≤B≤300 on the negative electrode, and the second injection adjusts these ratios to 20≤A≤50 and 70≤B≤300, ensuring optimal cycling retention rate of 90% or above after 300 cycles.
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 results in a stable SEI and CEI film formation, enhancing the cycling performance of the electrochemical apparatus, with a cycling retention rate of 90% or above after 300 cycles at 25°C, and maintaining high performance even at elevated temperatures.
Implementation Method 1
a first electrolyte containing a fluorine-containing compound forms a stable SEI film on the negative electrode
Implementation Method 2
a second electrolyte with both fluorine-containing and nitrile compounds to form a stable CEI film on the positive electrode
Data Source
AI summary
An electrochemical apparatus includes a positive electrode sheet including a positive electrode active material layer; a negative electrode sheet including a negative electrode active material layer; and a separator disposed between the positive electrode sheet and the negative electrode sheet. A mass ratio of fluorine to nitrogen on a surface layer of the positive electrode active material layer is A, a mass ratio of fluorine to nitrogen on a surface layer of the negative electrode active material layer is B, 3≤A≤50, and 30≤B≤300.