Formation current and cut-off voltage setting method for lithium ion battery
By performing constant current charging of lithium-ion batteries at different magnifications, drawing dQ/dV curves, quantizing and determining the decomposition of the decomposition current and cutoff voltage in the prior art, the problem of lack of quantization confirmation standards for the determination of decomposition current and cutoff voltage in the prior art is solved, and the film formation quality of the SEI film and the cycling performance of the battery are improved.
Patent Information
- Application Number
- CN202411834760.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-13
- Publication Date
- 2025-04-11
AI Technical Summary
In the existing lithium-ion battery shaping process, there is a lack of quantitative confirmation standards for determining the formation current and cut-off voltage, which affects the film formation quality of the SEI film and the cycling performance of the battery.
By performing constant current charging of lithium-ion batteries at different magnifications, dQ/dV curves are drawn, the film formation end voltage and film impedance are determined, and the formation current and cut-off voltage are quantified.
It ensures high-quality film formation of SEI film, improves the cycle performance and chemical efficiency of the battery, and provides a scientific and reasonable method of determining the chemical current and cut-off voltage.
Smart Images
Figure CN119812534A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to the technical field of lithium ion battery formation, and in particular to a method for formulating a lithium ion battery formation current and a cut-off voltage. Background Art
[0002] Formation is the process of charging a lithium-ion battery for the first time. Its function is to activate the positive and negative electrode materials inside the lithium-ion battery and improve the comprehensive performance of the lithium-ion battery, such as charging and discharging, self-discharging, and storage. During the formation process of the lithium-ion battery, an electrochemical reaction will occur in the battery. At the interface between the carbon negative electrode and the electrolyte, the film-forming additive forms a passivation thin layer on the surface of the active material particles, namely the solid electrolyte interface film (SEI film). The SEI film has the properties of a solid electrolyte and is a good electronic insulator. It can effectively reduce the probability of short circuits inside the lithium-ion battery and improve the self-discharge of the lithium-ion battery. The SEI film will have a protective effect on the negative electrode material, prevent the co-embedding of solvent molecules, and increase the cycle life of the electrode.
[0003] The current and cut-off voltage of the formation process have a crucial impact on the quality of SEI formation in the battery cell. In the process of electrode material activation, when a large current is used, the negative electrode and the electrolyte surface are more likely to undergo a two-electron reaction, that is, it is easier to generate inorganic lithium salt components. At this time, the SEI film molecules formed are more likely to be randomly stacked, and its structure is looser, the corresponding thickness is also larger, and the interface impedance is also larger, which is not conducive to the cycle performance of the battery cell; when a small current is used for formation, a single electron reaction is more likely to occur, and it is also easier to generate organic lithium salt components. At this time, the SEI structure formed is more compact, the corresponding thickness is also smaller, and there are fewer irreversible reactions.
[0004] There are two technical solutions for the current formation process: one is to charge the battery to the cut-off voltage by step-by-step small-rate constant current charging, and the other is to charge the battery to the cut-off voltage by constant small-rate constant current charging. Since the charging current and cut-off voltage in the film formation stage have a significant impact on the quality of SEI film formation, such as uniformity and density, the current formation current in the industry is mostly determined by experience, and there is no quantitative confirmation standard. Summary of the invention
[0005] Based on this, the purpose of the present invention is to provide a method for formulating the formation current and cut-off voltage of a lithium-ion battery, which can determine the current size of the lithium-ion battery during the film formation and charging stage to ensure the quality of the film formation and the efficiency of the formation.
[0006] To achieve the above object, the present invention adopts the following technical solutions: The present invention first provides a method for formulating a formation current and a cut-off voltage of a lithium ion battery, which comprises the following steps: S1. Take the batteries after injection from the same batch and divide them into multiple groups. Charge the multiple groups of batteries to full power at different charging currents A0, and draw the dQ / dV curves of each group of batteries; S2. Obtain the film formation end voltage V1 of each group of batteries according to the dQ / dV curve of each group of batteries, compare the film formation end voltage V1 of each group of batteries, and formulate the formation cut-off voltage according to the maximum film formation end voltage V1; S3. Obtain the membrane impedance R formed after each group of batteries are formed SEI , compare the membrane impedance R of each group of batteries SEI , according to the minimum membrane resistance R SEI The corresponding battery charging current A0 is formulated as a conversion current.
[0007] As a further improvement of the above solution of the present invention, in step S1, the charging current A0 of the multiple battery groups increases in a gradient manner.
[0008] As a further improvement of the above solution of the present invention, in step S1, the range of the charging current A0 is: 0 <A0≤0.5C。
[0009] As a further improvement of the above solution of the present invention, in step S1, the batteries after injection in the same batch are divided into three groups.
[0010] As a further improvement of the above solution of the present invention, in step S2, the cut-off voltage = the maximum film-forming end voltage V1 + 0.3V.
[0011] As a further improvement of the above solution of the present invention, in step S3, the minimum membrane impedance R SEI The charging current A0 of the corresponding battery is set as the formation current.
[0012] As a further improvement of the above solution of the present invention, in step S3, the membrane impedance formed by the battery after formation is obtained by EIS measurement.
[0013] Compared with the prior art, the present invention has the following beneficial effects: The present invention determines whether the small rate current used for formation is appropriate by determining whether the reaction process of the negative electrode SEI produces polarization during the charging process of the battery cell at different rates by the position of the film-forming reaction peak of the dQ / dV differential tolerance curve under the constant current full charge of the small battery cell at different rates; the voltage at which the film-forming reaction ends is determined as the formation cut-off voltage, and due to the existence of polarization, the formation cut-off voltage is adjusted to 0.3V higher than the film-forming reaction cut-off voltage to ensure that the film-forming reaction of the film-forming additive is completed to ensure the quality of SEI film formation; and the charging current of the battery cell with the smallest film impedance is selected as the charging current during formation film formation to ensure the formation efficiency. The present invention provides a quantitative determination method for formation current and cut-off voltage, which can determine the current size in the formation film charging stage to ensure the quality of SEI film formation and the efficiency of formation. BRIEF DESCRIPTION OF THE DRAWINGS
[0014] Figure 1 A flow chart of a method for formulating formation current and cut-off voltage of a lithium-ion battery proposed in an embodiment of the present invention; Figure 2 is a charging curve diagram of a battery in an embodiment of the present invention; Figure 3 dQ / dV curve of the battery in the embodiment of the present invention. DETAILED DESCRIPTION
[0015] For ease of understanding of the present invention, the present invention will be described more fully below in conjunction with specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present invention more thoroughly understood.
[0016] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.
[0017] Reference Figure 1 This embodiment provides a method for formulating a formation current and a cut-off voltage of a lithium-ion battery, which comprises the following steps: S1. Take the batteries after injection from the same batch and divide them into multiple groups. Charge the multiple groups of batteries to full charge at different charging currents A0, and draw the dQ / dV curves of each group of batteries.
[0018] In this embodiment, the batteries after injection of the same batch are divided into three groups. Of course, in other embodiments, the batteries can also be divided into two groups, four groups, etc. The charging current A0 of multiple groups of batteries increases in a gradient, and the range of the charging current A0 is: 0 <A0≤0.5C。
[0019] S2. Obtain the film formation end voltage V1 of each group of batteries according to the dQ / dV curve of each group of batteries, compare the film formation end voltage V1 of each group of batteries, and determine the formation cut-off voltage according to the maximum film formation end voltage V1.
[0020] To ensure that the film-forming reaction of the film-forming additive is completed, the formation cut-off voltage is set at the voltage at the end of the film-forming reaction; and due to the influence of the polarization of the battery cell on the open circuit voltage as the rate increases, the formation cut-off voltage is selected to be larger than the maximum film-forming end voltage V1. Therefore, in this embodiment, the cut-off voltage = the maximum film-forming end voltage V1 + 0.3V.
[0021] S3. Obtain the membrane impedance R formed after each group of batteries are formed SEI , compare the membrane impedance R of each group of batteries SEI , according to the minimum membrane resistance R SEI The corresponding battery charging current A0 is formulated as a conversion current.
[0022] In this embodiment, the membrane impedance of the battery after formation is obtained by EIS measurement. For the battery cycle (capacity retention rate), the minimum membrane impedance R is selected. SEI The charging current A0 of the corresponding battery is set as the formation current.
[0023] Next, the present invention will be described with reference to specific examples.
[0024] Three batteries from the same batch that were not charged after injection and immersion were selected. The three batteries were charged at 0.01C, 0.03C, and 0.05C rates respectively until the batteries were fully charged. The full charge curves of the three batteries are as follows: Figure 2 shown.
[0025] Differentiate the fully charged battery data at different rates to obtain the differential tolerance curve of the battery, as shown in Figure 3 As shown. Due to the film-forming reaction of the film-forming additive, the dQ / dV curve shows a film-forming reaction peak at 2.7V, and the film-forming reactions of the three batteries end at L1=2.91V, L2=2.92V, and L3=3.1V. The peak values of the end of the reactions of L1 and L2 are similar. As the charging current rate increases, the polarization of the battery cell gradually increases, resulting in an increase in the cut-off potential of the film-forming reaction. To ensure that the film-forming reaction of the film-forming additive is completed, the formation cut-off voltage is set at the voltage at the end of the film-forming reaction. As the rate increases, the polarization of the battery cell affects the open-circuit voltage, and the formation cut-off voltage is selected to be larger than the voltages of L1, L2, and L3. Therefore, the cut-off voltage is set to: cut-off voltage = L3 + 0.3V = 3.4V.
[0026] The membrane impedance formed by the battery after formation is measured by EIS. For the battery cycle (capacity retention rate), the charging current of the cell with the smallest membrane impedance should be selected as the charging current during formation to ensure the quality of SEI film formation and formation efficiency.
[0027] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.
[0028] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.
Claims
1. A method for formulating formation current and cut-off voltage of a lithium-ion battery, characterized in that: It includes the following steps: S1. Take the batteries after injection from the same batch and divide them into multiple groups. Charge the multiple groups of batteries to full power at different charging currents A0, and draw the dQ / dV curves of each group of batteries; S2. Obtain the film formation end voltage V1 of each group of batteries according to the dQ / dV curve of each group of batteries, compare the film formation end voltage V1 of each group of batteries, and formulate the formation cut-off voltage according to the maximum film formation end voltage V1; S3. Obtain the membrane impedance R formed after each group of batteries are formed SEI , compare the membrane impedance R of each group of batteries SEI , according to the minimum membrane resistance R SEI The corresponding battery charging current A0 is formulated as a conversion current.
2. The method for formulating formation current and cut-off voltage of a lithium-ion battery according to claim 1, characterized in that: In step S1 , the charging current A0 of the multiple battery groups increases in a gradient manner.
3. The method for formulating formation current and cut-off voltage of a lithium-ion battery according to claim 2, characterized in that: In step S1, the range of the charging current A0 is: 0 <A0≤0.5C。 4. The method for formulating formation current and cut-off voltage of a lithium-ion battery according to claim 1, characterized in that: In step S1, the batteries after injection in the same batch are divided into three groups.
5. The method for formulating formation current and cut-off voltage of a lithium-ion battery according to claim 1, characterized in that: In step S2, the cut-off voltage = the maximum film formation end voltage V1 + 0.3V.
6. The method for formulating formation current and cut-off voltage of a lithium-ion battery according to claim 1, characterized in that: In step S3, the minimum membrane resistance R SEI The charging current A0 of the corresponding battery is set as the formation current.
7. The method for formulating formation current and cut-off voltage of a lithium-ion battery according to claim 1, characterized in that: In step S3, the membrane impedance formed by the battery after formation is obtained by EIS measurement.