Lithium-ion Battery Formation Process Using dQ/dV Analysis
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Solution Overview
Problem
The existing formation processes for lithium-ion batteries are time-consuming and require extensive testing to determine optimal charging parameters for each type of cell, limiting the efficiency and scalability of the initial charging process.
Innovation Solution
A method involving the addition of specific additives to the electrolyte, which calculates and utilizes the first derivative of charge capacity relative to voltage (dQ/dV) to determine key voltage values for charging and discharging cycles, allowing for reduced formation time without the need for extensive testing, by identifying peak voltage values and threshold voltages to control the formation of the solid electrolyte interface (SEI) on the anode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the battery is charged at a small C-rate to form SEI layer, then the SEI formation quality is improved, but the formation process duration is extended
Solution Approach 1:
The patent applies preliminary action by performing initial charging at a small C-rate only up to a threshold voltage (e.g., 3.0V or 3.1V) rather than charging to the full battery voltage. This preliminary charging stage is sufficient to initiate SEI layer formation on the anode, after which the battery can be charged at higher C-rates without compromising SEI quality. This approach separates the SEI formation function from the complete charging process, reducing overall formation time while maintaining reliability.
2Loss of time
If dynamic forming process is used with large C-rate charging, then the formation time is reduced, but the voltage threshold determination requires extensive testing for each cell type
Solution Approach 1:
The patent applies parameter changes by using dQ/dV (derivative of charge capacity with respect to voltage) as a universal parameter to determine the threshold voltage for SEI formation. Instead of requiring extensive testing for each cell type, the method identifies the threshold voltage as the point where the dQ/dV curve shows a maximum value during charging. This parameter-based approach provides a consistent, measurable criterion that can be applied across different cell types without requiring type-specific testing, thereby reducing device complexity while maintaining the time-saving benefits of dynamic forming.
3Quantity of substance
If the battery is charged to full voltage at small C-rate, then complete charging is achieved, but the formation process becomes time-consuming
Solution Approach 1:
The patent applies segmentation by dividing the charging process into two distinct stages: (1) an initial charging stage at small C-rate up to a threshold voltage to form the SEI layer, and (2) a subsequent charging stage at large C-rate to complete the charging to full voltage. This segmentation allows each stage to be optimized independently - the first stage ensures proper SEI formation while the second stage rapidly completes charging, thereby reducing total charging time while achieving complete charge capacity.
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 method significantly reduces the duration of the formation process while maintaining high retention capacity, allowing for efficient SEI formation and improved battery performance, with the ability to apply the process to various cell types without prior testing.
Implementation Method 1
During the formation process, a solid electrolyte interface (SEI) is formed on the anode. The SEI formation is important for the lifetime of the lithium-ion battery or cell.
Implementation Method 2
Additives have also been added to the electrolyte to improve the formation of the SEI and therefore enhancing the anode stability.
Implementation Method 3
lithium ions move from the negative electrode to the positive electrode during discharge and from the positive electrode to the negative electrode when charging
Data Source
AI summary
A method of performing a formation process for a lithium-ion cell having an anode, a cathode, an electrolyte and a separator, the formation process including adding an additive to the electrolyte for improving a solid electrolyte interface build-up on the anode, performing a first charge of the cell at a first predetermined rate, performing a cycle of discharging/charging the cell at the first predetermined rate, repeating the cycle until a cycle maximum dQ/dV peak value is smaller than or equal to a predetermined dQ/dV value during charging of the cell and charging the cell to a fully charged capacity at a second predetermine rate, the second predetermined rate being greater than the first predetermined rate.