A method and system for determining a film formation reaction current in battery formation

Abstract

This invention discloses a method and system for determining the film-forming reaction current of a battery formation process. The method includes: forming the battery using a stepped-increasing current; obtaining the dQ / dV-V curves of the battery under different current formation conditions; and determining the film-forming reaction current based on the voltage corresponding to the peak of each dQ / dV-V curve using the formula ΔV. x =V x -V1 calculates the difference between each voltage and the voltage of the first reaction peak, X = 2, 3, 4, ..., n. Compare each difference; when the first difference exceeds the preset fluctuation difference compared to other differences, the voltage V... x The corresponding current is used as the formation current; the advantages of this invention are: it can determine the magnitude of the formation reaction current, improve the uniformity of the SEI film, and result in good cycle performance and other electrical properties of the battery.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and specifically to a method and system for determining the film-forming reaction current of a battery. Background Technology

[0002] Lithium-ion batteries are currently the world's most advanced commercially available rechargeable batteries. With the development of various electronic products, the demand for lithium-ion batteries is rapidly increasing, driven by expanding application areas and rising demand. Lithium-ion batteries possess outstanding advantages such as high energy density, environmental friendliness, no memory effect, long cycle life, and low self-discharge. They are ideal power sources for portable electronic products requiring small and lightweight designs, as well as for electric vehicles and military applications requiring lightweight, high-energy power. Therefore, lithium-ion batteries have become a hot research topic in the battery industry in recent years. The manufacturing of lithium-ion batteries is a complex process involving multiple different technological processes, each of which comprises numerous smaller steps, ultimately producing the finished individual battery cell.

[0003] Formation is a crucial step in lithium-ion battery production. During formation, a passivation layer, the SEI film, is formed on the surface of the negative electrode. The quality of the SEI film directly affects the battery's cycle life, stability, and other electrochemical performance characteristics. Different formation processes result in different SEI films, leading to significant variations in their impact on battery performance. Current formation processes, such as the lithium-ion battery formation method disclosed in CN102208685A, primarily involve initial low-current charging under negative pressure for a period, followed by charging with a higher current. The SEI film is formed during the low-current charging process, and the current magnitude is critical to the performance of the formed SEI. Higher currents result in greater polarization, uneven current distribution on the electrode, and an uneven SEI film, all of which negatively impact the battery's electrical performance. However, current technologies lack a method for determining the optimal formation reaction current, thus failing to specifically improve the uniformity and consistency of the SEI film. Summary of the Invention

[0004] The technical problem to be solved by this invention is how to determine the magnitude of the formation film-forming reaction current.

[0005] This invention solves the above-mentioned technical problems through the following technical means: a method for determining the film-forming reaction current of a battery formation, comprising the following steps:

[0006] Step 1: Form the battery using progressively increasing currents;

[0007] Step 2: Obtain the dQ / dV-V curves of the battery under different current formation conditions;

[0008] Step 3: Compare the voltages corresponding to the film formation reaction peaks of each dQ / dV-V curve, and use the formula ΔV x =Vx -V1 calculates the difference between each voltage and the voltage of the first reaction peak, X = 2, 3, 4, ..., n. The differences are compared, and the voltage V is set to increase when it first exceeds a preset fluctuation value compared to other differences. x The corresponding current is used as the formation current.

[0009] Further, step one includes:

[0010] Take n batteries that have been injected with electrolyte and, under negative pressure, apply progressively increasing currents I1, I2, I3, I4…I… n The battery undergoes formation.

[0011] Furthermore, the negative pressure is between -40 kPa and -95 kPa.

[0012] Furthermore, step two includes:

[0013] The formation data of each battery were analyzed for capacity Q and voltage V, and dQ / dV-V curves were plotted. The voltages corresponding to the film formation reaction peaks of each battery are V1, V2, V3, V4…V. n .

[0014] Furthermore, step three includes:

[0015] Based on the voltages V1, V2, V3, V4…V corresponding to the film formation reaction peaks n Calculate the voltage difference ΔV2 = V2 - V1; ΔV3 = V3 - V1; ΔV4 = V4 - V1; ΔV K-1 =V K-1 -V1;△V K =V K -V1; If △V1, △V2, △V3... are related to △V k-1 , △V k If there is a difference exceeding the preset fluctuation, then the voltage V at which the difference first appears will be taken. k-1 The corresponding current is taken as the formation current.

[0016] The present invention also provides a system for determining the film-forming reaction current of a battery formation, comprising the following steps:

[0017] A stepped formation module is used to form the battery using progressively increasing currents.

[0018] The dQ / dV-V curve acquisition module is used to acquire the dQ / dV-V curves of the battery under different current formation conditions.

[0019] The film formation reaction current acquisition module is used to compare the voltage corresponding to the film formation reaction peak of each dQ / dV-V curve, and to obtain the voltage using the formula ΔV. x =V x-V1 calculates the difference between each voltage and the voltage of the first reaction peak, X = 2, 3, 4, ..., n. The differences are compared, and the voltage V is set to increase when it first exceeds a preset fluctuation value compared to other differences. x The corresponding current is used as the formation current.

[0020] Furthermore, the step-forming module is also used for:

[0021] Take n batteries that have been injected with electrolyte and, under negative pressure, apply progressively increasing currents I1, I2, I3, I4…I… n The battery undergoes formation.

[0022] Furthermore, the negative pressure is between -40 kPa and -95 kPa.

[0023] Furthermore, the dQ / dV-V curve acquisition module is also used for:

[0024] The formation data of each battery were analyzed for capacity Q and voltage V, and dQ / dV-V curves were plotted. The voltages corresponding to the film formation reaction peaks of each battery are V1, V2, V3, V4…V. n .

[0025] Furthermore, the film-forming reaction current acquisition module is also used for:

[0026] Based on the voltages V1, V2, V3, V4…V corresponding to the film formation reaction peaks n Calculate the voltage difference ΔV2 = V2 - V1; ΔV3 = V3 - V1; ΔV4 = V4 - V1; ΔV K-1 =V K-1 -V1;△V K =V K -V1; If △V1, △V2, △V3... are related to △V k-1 , △V k If there is a difference exceeding the preset fluctuation, then the voltage V at which the difference first appears will be taken. k-1 The corresponding current is taken as the formation current.

[0027] The advantages of this invention are as follows: This invention creatively compares the magnitude of the voltage corresponding to the film formation reaction peak when different currents are formed, calculates the difference between each voltage and the voltage of the first reaction peak, compares each difference, and when the first difference exceeds the preset fluctuation difference compared with other differences, the voltage corresponding to the current is taken as the formation current, thereby simply and quickly determining the magnitude of the formation film formation reaction current. Under this current, the formation polarization is minimized, making the SEI film formed during formation uniform, consistent and dense, and the battery has good cycle performance and other electrical properties. Attached Figure Description

[0028] Figure 1This is a flowchart of a method for determining the film-forming reaction current of a battery according to an embodiment of the present invention;

[0029] Figure 2 This is a schematic diagram of the dQ / dV-V curves when the currents are I1, I2, and I3 in a method for determining the film-forming reaction current of a battery formation disclosed in an embodiment of the present invention.

[0030] Figure 3 The dQ / dV-V curves are shown in the battery formation film formation reaction current determination method disclosed in the embodiments of the present invention when the current is 0.02C, 0.04C, and 0.06C.

[0031] Figure 4 The cycling curves of battery A and battery B are shown in the battery formation film formation reaction current determination method disclosed in the embodiments of the present invention. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] Example 1

[0034] like Figure 1 and Figure 2 As shown, a method for determining the film-forming reaction current of a battery includes the following steps:

[0035] S1: The battery is formed using a stepped-increasing current; the specific process is as follows:

[0036] Take n batteries that have been injected with electrolyte and, under negative pressure, apply progressively increasing currents I1, I2, I3, I4…I… n The battery is formed. The negative pressure is from -40 kPa to -95 kPa.

[0037] S2: Obtain the dQ / dV-V curves of the battery under different current formation conditions; the specific process is as follows:

[0038] The formation data of each battery were analyzed for capacity Q and voltage V, and dQ / dV-V curves were plotted. The voltages corresponding to the film formation reaction peaks of each battery are V1, V2, V3, V4…V. n .

[0039] S3: Based on the voltage corresponding to the film formation reaction peak of each dQ / dV-V curve, use the formula ΔVx =V x -V1 calculates the difference between each voltage and the voltage of the first reaction peak, X = 2, 3, 4, ..., n. The differences are compared, and the voltage V is set to increase when it first exceeds a preset fluctuation value compared to other differences. x The corresponding current is used as the formation current; the specific process is as follows:

[0040] Based on the voltages V1, V2, V3, V4…V corresponding to the film formation reaction peaks n Calculate the voltage difference ΔV2 = V2 - V1; ΔV3 = V3 - V1; ΔV4 = V4 - V1; ΔV K-1 =V K-1 -V1;△V K =V K -V1; If △V1, △V2, △V3... are related to △V k-1 , △V k If there is a difference exceeding the preset fluctuation (judged manually or using the software minitab), then the current corresponding to the voltage Vk-1 where the difference first appears is taken as the formation current. (V1 is the voltage corresponding to a current of 0.02C).

[0041] To more clearly illustrate the method of the present invention, a simulation example is given below.

[0042] A certain type of square lithium-ion power battery (using lithium iron phosphate for the positive electrode and artificial graphite for the negative electrode), after being filled with electrolyte and allowed to stand, was charged at a constant current of 0.02C, 0.04C, and 0.06C until fully charged (3.65V). The battery capacity change (i.e., the dQ / dV value) within a constant voltage interval was calculated, and the dQ / dV-V curve is shown below. Figure 3 The voltages corresponding to the reaction peaks are V1 = 2.48V, V2 = 2.50V, and V3 = 2.58V, respectively. Comparing the three voltages, V1 and V2 are relatively close, while V3 differs significantly from both V1 and V2. Therefore, I2 = 0.04C is chosen as the formation reaction current. From the above results, it can be seen that when forming with a current of 0.02C and 0.04C, the peak positions of the film formation reaction are basically overlapping and will not have a significant impact on film formation. However, when forming with 0.06C, the peak position shifts significantly to the right, and the polarization increases, which will affect the formation effect. Therefore, from the perspective of obtaining a high-performance cell, selecting a current of 0.04C is the optimal result.

[0043] Batteries A and B of the same model were manufactured using the formation processes shown in Table 1, and then manufactured into batteries according to the normal process. The cycle curves are shown in [Table 1]. Figure 4 .

[0044] Table 1 Comparison of Formation Processes for Battery A and Battery B

[0045]

[0046] from Figure 4 It can be seen that the capacity retention rate of battery B is higher than that of battery A. Under the same conditions, battery B is formed by constant current charging at a current of 0.04C, while battery A is formed by constant current charging at a current of 0.06C. In comparison, the formation result of battery B is better, which further illustrates the reliability of the formation film reaction current determination method of the present invention.

[0047] Through the above technical solutions, this invention creatively compares the magnitudes of the voltages corresponding to the film formation reaction peaks under different current formation times, and uses the formula ΔV x =V x -V1 calculates the difference between each voltage and the voltage of the first reaction peak, X = 2, 3, 4, ..., n. The differences are compared, and the voltage V is set to increase when it first exceeds a preset fluctuation value compared to other differences. x The corresponding current is used as the formation current, so that the magnitude of the formation film formation reaction current can be determined simply and quickly. Under this current, the formation polarization is minimized, so that the SEI film formed during formation is uniform, dense, and the battery has good cycle performance and other electrical properties.

[0048] Example 2

[0049] Based on Example 1, Example 2 of the present invention also provides a system for determining the film-forming reaction current of a battery formation, comprising the following steps:

[0050] A stepped formation module is used to form the battery using progressively increasing currents.

[0051] The dQ / dV-V curve acquisition module is used to acquire the dQ / dV-V curves of the battery under different current formation conditions.

[0052] The film formation reaction current acquisition module is used to obtain the film formation reaction current based on the voltage corresponding to the film formation reaction peak of each dQ / dV-V curve, using the formula ΔV. x =V x -V1 calculates the difference between each voltage and the voltage of the first reaction peak, X = 2, 3, 4, ..., n. The differences are compared, and the voltage V is set to increase when it first exceeds a preset fluctuation value compared to other differences. x The corresponding current is used as the formation current.

[0053] Specifically, the step-forming module is also used for:

[0054] Take n batteries that have been injected with electrolyte and form them under negative pressure conditions using currents I1, I2, I3, I4...In respectively.

[0055] More specifically, the negative pressure is from -40 kPa to -95 kPa.

[0056] Specifically, the dQ / dV-V curve acquisition module is also used for:

[0057] The formation data of each battery were analyzed for capacity Q and voltage V, and dQ / dV-V curves were plotted. The voltages corresponding to the film formation reaction peaks of each battery are V1, V2, V3, V4…V. n .

[0058] Specifically, the film-forming reaction current acquisition module is also used for:

[0059] Based on the voltages V1, V2, V3, V4…V corresponding to the film formation reaction peaks n Calculate the voltage difference ΔV2 = V2 - V1; ΔV3 = V3 - V1; ΔV4 = V4 - V1; ΔV K-1 =V K-1 -V1;△V K =V K -V1; If △V1, △V2, △V3... are related to △V k-1 , △V k If there is a difference exceeding the preset fluctuation, then the voltage V at which the difference first appears will be taken. k-1 The corresponding current is taken as the formation current.

[0060] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for determining the film-forming reaction current in battery formation, characterized in that, Includes the following steps: Step 1: Form the battery using progressively increasing currents; Step 2: Obtain the dQ / dV-V curves of the battery under different current formation conditions; Step 3: Based on the voltage corresponding to the film formation reaction peak of each dQ / dV-V curve, calculate the voltage using the formula ΔV. x =V x -V1 calculates the difference between each voltage and the voltage of the first reaction peak, X=2, 3, 4, ..., n. The differences are compared, and the voltage V is set to increase when the first difference exceeds the preset fluctuation value compared to other differences. x The corresponding current is used as the formation current; Step three includes: Based on the voltages V1, V2, V3, V4…V corresponding to the film formation reaction peaks n Calculate the voltage differences: ΔV2 = V2 - V1; ΔV3 = V3 - V1; ΔV4 = V4 - V1; ΔV K-1 =V K-1 -V1;△V K =V K -V1; If △V1, △V2, △V3... are related to △V k-1 , △V k If there are differences exceeding the preset fluctuation, then the earliest occurrence of the difference △V is taken. k The corresponding voltage V k-1 The corresponding current is taken as the formation current.

2. The method for determining the film-forming reaction current of a battery according to claim 1, characterized in that, Step one includes: Take n batteries that have been injected with electrolyte and form them under negative pressure using currents I1, I2, I3, I4...In respectively.

3. The method for determining the film-forming reaction current of a battery according to claim 2, characterized in that, The negative pressure is from -40 kPa to -95 kPa.

4. The method for determining the film-forming reaction current of a battery according to claim 1, characterized in that, Step two includes: The formation data of each battery were analyzed for capacity Q and voltage V, and dQ / dV-V curves were plotted. The voltages corresponding to the film formation reaction peaks of each battery are V1, V2, V3, V4…V. n .

5. A system for determining the film-forming reaction current of a battery formation, characterized in that, Includes the following steps: A stepped formation module is used to form the battery using progressively increasing currents. The dQ / dV-V curve acquisition module is used to acquire the dQ / dV-V curves of the battery under different current formation conditions. The film formation reaction current acquisition module is used to obtain the film formation reaction current based on the voltage corresponding to the film formation reaction peak of each dQ / dV-V curve, using the formula ΔV. x =V x -V1 calculates the difference between each voltage and the voltage of the first reaction peak, X=2, 3, 4, ..., n. The differences are compared, and the voltage V is set to increase when the first difference exceeds the preset fluctuation value compared to other differences. x The corresponding current is used as the formation current; the film formation reaction current acquisition module is also used for: Based on the voltages V1, V2, V3, V4…V corresponding to the film formation reaction peaks n Calculate the voltage differences: ΔV2 = V2 - V1; ΔV3 = V3 - V1; ΔV4 = V4 - V1; ΔV K-1 =V K-1 -V1;△V K =V K -V1; If △V1, △V2, △V3... are related to △V k-1 , △V k If there are differences exceeding the preset fluctuation, then the earliest occurrence of the difference △V is taken. k The corresponding voltage V k-1 The corresponding current is taken as the formation current.

6. The battery formation film-forming reaction current determination system according to claim 5, characterized in that, The step-forming module is also used for: Take n batteries that have been injected with electrolyte and form them under negative pressure using currents I1, I2, I3, I4...In respectively.

7. The battery formation film-forming reaction current determination system according to claim 6, characterized in that, The negative pressure is from -40 kPa to -95 kPa.

8. A battery formation film-forming reaction current determination system according to claim 5, characterized in that, The dQ / dV-V curve acquisition module is also used for: The formation data of each battery were analyzed for capacity Q and voltage V, and dQ / dV-V curves were plotted. The voltages corresponding to the film formation reaction peaks of each battery are V1, V2, V3, V4…V. n .

Images