A calculation method for the liquid retention amount required by a battery

Abstract

The present invention belongs to the technical field of lithium-ion batteries, and particularly relates to a calculation method for the liquid retention amount required by a battery, including obtaining the minimum liquid retention amount x of the battery, calculating the chemical consumption amount y of the electrolyte during the cycle through the cycle diving point and the liquid retention coefficient, obtaining the increment z of the electrolyte filling demand caused by the expansion of the battery core during the cycle through the density of the electrolyte, the cycle expansion coefficient of the battery, and the volume of the bare battery core, and obtaining the liquid retention amount d required by the battery according to the cycle requirement, where d = x + y + z. The present invention ensures the accurate calculation of the target liquid retention amount of the battery, effectively promotes the battery to have a longer service life, and enables the battery to have better operation stability.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium - ion batteries, and particularly relates to a method for calculating the required liquid - retaining amount of a battery. Background Art

[0002] At present, after a lithium - ion battery is filled with liquid, the liquid electrolyte can fill each space in the lithium - ion battery under the action of diffusion. During the cycling process, due to various chemical side reactions and volume changes of the battery, the lithium - ion electrolyte will be continuously consumed. When the electrolyte inside the battery is scarce, the battery impedance increases, resulting in a sharp drop in the charge - discharge efficiency, and ultimately leading to a drop in the cycling capacity and the end of the battery life.

[0003] Meanwhile, in the prior art, the electrolyte is continuously consumed during the cycling process of the lithium - ion battery. When the electrolyte is insufficient, the battery capacity drops, resulting in a poor user experience. In the actual battery manufacturing process, due to limitations in energy density and manufacturing requirements, the electrolyte of a soft - pack lithium - ion battery cannot be too much. Moreover, when the amount of the electrolyte is too low or insufficient, it will cause the situation of electrolyte depletion in the later stage of cycling, making it impossible for the prior art to solve the problem of accurately obtaining the target required liquid - retaining amount of the battery. Therefore, a new technical solution is urgently needed to solve the above problems. Summary of the Invention

[0004] The purpose of the present invention is: aiming at the deficiencies of the prior art, to provide a method for calculating the required liquid - retaining amount of a battery, which ensures accurate calculation of the target liquid - retaining amount of the battery, effectively promotes the battery to have a longer service life, and enables the battery to have better operating stability.

[0005] To achieve the above purpose, the present invention adopts the following technical solutions:

[0006] A method for calculating the required liquid - retaining amount of a battery, comprising the following steps:

[0007] S1. According to the space inside the battery that contains the electrolyte, calculate the electrolyte amount a1 in the pores of the cathode electrode sheet, the electrolyte amount a2 in the pores of the anode electrode sheet, and the electrolyte amount a3 in the pores of the separator through the cell design parameters, and calculate the volume v inside the battery excluding the cathode electrode sheet, anode electrode sheet, separator, insulating glue, and tab. Obtain the minimum liquid - retaining amount x of the battery through a1, a2, a3, and v;

[0008] S2. Through the cycle life test of the battery and the set required number of cycles, obtain the cell cycle life curve based on the capacity retention rate and the number of cycles, and then calculate the chemical consumption amount y of the electrolyte during the cycling process through the cycle drop point and the liquid - retaining coefficient;

[0009] S3. Obtain the cycle expansion coefficient of the battery based on the average expansion rate after the full life cycle of the battery. Obtain the increment z of the electrolyte filling demand caused by the expansion of the battery cell during the cycle through the density of the electrolyte, the cycle expansion coefficient of the battery, and the volume of the bare battery cell. Obtain the liquid retention amount d required for the battery according to the cycle requirement, where d = x + y + z.

[0010] As an improvement of the calculation method for the liquid retention amount required for the battery described in the present invention, the S2 further includes: taking the capacity retention rate as the ordinate and the number of cycles as the abscissa to construct a rectangular coordinate system, recording the battery cell cycle life curve in the rectangular coordinate system, obtaining the cycle diving point by making an auxiliary tangent to the battery cell cycle life curve, and obtaining the chemical consumption amount y of the electrolyte during the cycle based on the number of cycles corresponding to the cycle diving point, the liquid retention coefficient of the battery, the number of cycles required for the battery cycle life, and the designed capacity of the battery.

[0011] As an improvement of the calculation method for the liquid retention amount required for the battery described in the present invention, the S2 further includes: performing cycle life tests on two batteries using the same electrolyte but with different liquid retention coefficients to obtain two different cycle diving points c1 and c2, obtaining the number of cycles t1 corresponding to c1 and the number of cycles t2 corresponding to c2 from the cycle life curve, and calculating the chemical consumption rate h of the electrolyte from the liquid retention coefficient k1 of the battery with the cycle diving point c1 and the liquid retention coefficient k2 of the battery with the cycle diving point c2. Obtain the chemical consumption amount y of the electrolyte during the cycle through the chemical consumption rate h, the number of cycles e required for the battery cycle life, and the designed capacity L of the battery, where y = h × e × L.

[0012] As an improvement of the calculation method for the liquid retention amount required for the battery described in the present invention, the chemical consumption rate h of the electrolyte = |k1 - k2| / |t1 - t2|.

[0013] As an improvement of the calculation method for the liquid retention amount required for the battery described in the present invention, the S2 further includes: performing cycle life tests on several batteries with different liquid retention coefficients using the same electrolyte, calculating the average chemical consumption rate of the electrolyte, and calculating the chemical consumption amount of the electrolyte based on the average chemical consumption rate, the number of cycles required for the battery cycle life, and the designed capacity of the battery.

[0014] As an improvement of the calculation method for the liquid retention amount required for the battery described in the present invention, the S3 further includes: obtaining the cycle expansion coefficient of the battery through the number of cycles required for the battery cycle life and the average expansion rate corresponding thereto.

[0015] As an improvement of the calculation method for the liquid retention amount required for the battery described in the present invention, the volume of the bare battery cell is obtained through the battery cell design parameters, and the increment z of the electrolyte filling demand = the density ρ of the electrolyte × the cycle expansion coefficient of the battery × the volume of the bare battery cell.

[0016] As an improvement to the method for calculating the liquid retention amount required for the battery described in the present invention, the S1 further includes: in the cell design parameters, the pore space volume of the cathode electrode = the apparent volume of the cathode electrode - the true volume of the cathode electrode, the pore space volume of the anode electrode = the apparent volume of the anode electrode - the true volume of the anode electrode, and the pore space volume of the separator = the pore volume of the separator substrate - the pore volume of the separator coating. Among them, the electrolyte amount a1 is obtained by converting through the pore space volume of the cathode electrode, the electrolyte amount a2 is obtained by converting through the pore space volume of the anode electrode, and the electrolyte amount a3 is obtained by converting through the pore space volume of the separator.

[0017] As an improvement to the method for calculating the liquid retention amount required for the battery described in the present invention, in the S1, the true volume of the cathode electrode = the weight of the cathode electrode / the true density of the cathode electrode, and the true volume of the anode electrode = the weight of the anode electrode / the true density of the anode electrode.

[0018] As an improvement to the method for calculating the liquid retention amount required for the battery described in the present invention, the minimum liquid retention amount x = a1 + a2 + a3 + v.

[0019] The beneficial effects of the present invention are as follows: The present invention combines the three-dimensional size structure of the battery and the electrolyte consumption speed and volume change during the cycling process. Under the condition of a clear cycling life requirement, an accurate designed value of the liquid retention amount is calculated. Since the present invention conducts actual cycling life tests on the battery, as the cycling data becomes richer, the calculation model can be gradually corrected during the calculation process, thereby ensuring the accuracy of the target liquid retention amount calculation of the battery. Therefore, the present invention not only changes and optimizes the current "empirical design of liquid retention amount" and "trial-and-error design of liquid retention amount", but also effectively enables the battery to have a longer service life, significantly improves the battery cycling life and consistency, and enables the battery to have better operation stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a flowchart of the present invention.

[0021] Figure 2 is a schematic diagram of the flow of the electrolyte inside the battery of the present invention.

[0022] Figure 3 is an explanatory diagram of the existence space of the electrolyte of the present invention.

[0023] Figure 4 is a schematic diagram of the model of the cycle capacity retention rate of the present invention.

[0024] Figure 5 is a schematic diagram of the cycle diving point of the present invention.

[0025] Figure 6 Schematic diagram of the chemical consumption rate of the electrolyte of the present invention.

[0026] Figure 7 Schematic diagram of the cyclic expansion coefficient of the present invention. Detailed implementation manners

[0027] As used in the specification and claims, certain terms are used to refer to specific components. Those skilled in the art should understand that manufacturers may use different terms to refer to the same component. The specification and claims do not use the difference in names as a way to distinguish components, but use the difference in functions of components as the criterion for distinction. As mentioned throughout the specification and claims, "comprising" is an open-ended term and should be interpreted as "including but not limited to". "Substantially" means within an acceptable error range. Those skilled in the art can solve technical problems within a certain error range and basically achieve the technical effect.

[0028] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "upper", "lower", "front", "rear", "left", "right", "horizontal", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus cannot be understood as a limitation to the present invention.

[0029] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed", etc. should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0030] The following further describes the present invention in detail in conjunction with the attached Figures 1 to 7 drawings and specific embodiments, but it is not a limitation to the present invention.

[0031] Embodiment 1

[0032] A calculation method for the liquid retention amount required by a battery, as Figure 1 shown, includes the following steps:

[0033] S1. Based on the space inside the battery that contains the electrolyte, calculate the electrolyte volume a1 in the pores of the cathode electrode sheet, the electrolyte volume a2 in the pores of the anode electrode sheet, and the electrolyte volume a3 in the pores of the separator through the cell design parameters, and calculate the volume v inside the battery excluding the cathode electrode sheet, anode electrode sheet, separator, insulating glue, and tab. Obtain the minimum liquid retention amount x of the battery through a1, a2, a3, and v, where the minimum liquid retention amount x = a1 + a2 + a3 + v;

[0034] S2. Through the cycle life test of the battery and setting the required number of cycles, obtain the cell cycle life curve based on the capacity retention rate and the number of cycles, and then calculate the chemical consumption amount y of the electrolyte during the cycle through the cycle dive point and the liquid retention coefficient;

[0035] S3. Obtain the cycle expansion coefficient of the battery based on the average expansion rate after the full life cycle of the battery. Obtain the incremental demand for electrolyte filling caused by cell expansion during the cycle z through the density of the electrolyte, the cycle expansion coefficient of the battery, and the volume of the bare cell. According to the cycle requirements, obtain the required liquid retention amount d of the battery = x + y + z.

[0036] Among them, step S1 also includes: in the cell design parameters, the pore space volume of the cathode electrode sheet = the apparent volume of the cathode electrode sheet - the true volume of the cathode electrode sheet, the true volume of the cathode electrode sheet = the weight of the cathode electrode sheet / the true density of the cathode electrode sheet, the pore space volume of the anode electrode sheet = the apparent volume of the anode electrode sheet - the true volume of the anode electrode sheet, the true volume of the anode electrode sheet = the weight of the anode electrode sheet / the true density of the anode electrode sheet, the pore space volume of the separator = the pore volume of the separator substrate - the pore volume of the separator coating, the electrolyte volume a1 is obtained by converting the pore space volume of the cathode electrode sheet, the electrolyte volume a2 is obtained by converting the pore space volume of the anode electrode sheet, and the electrolyte volume a3 is obtained by converting the pore space volume of the separator.

[0037] During the calculation process, step S2 also includes: taking the capacity retention rate as the ordinate and the number of cycles as the abscissa to construct a rectangular coordinate system, recording the cell cycle life curve in the rectangular coordinate system, obtaining the cycle dive point by making an auxiliary tangent to the cell cycle life curve, and obtaining the chemical consumption amount y of the electrolyte during the cycle based on the number of cycles corresponding to the cycle dive point, the liquid retention coefficient of the battery, the number of cycle weeks required for the battery cycle life, and the design capacity of the battery.

[0038] As shown in the Figure 5 attachment, in the cell cycle life curve, the number of cycle weeks corresponding to the cycle dive point is 400 weeks, which corresponds to the moment when the liquid retention amount is insufficient.

[0039] Moreover, the step S2 further includes: performing a cycle life test on two batteries that use the same electrolyte but have different liquid retention coefficients, obtaining two different cycle dive points c1 and c2, obtaining the number of cycles t1 corresponding to c1 and the number of cycles t2 corresponding to c2 from the cycle life curve, and calculating the chemical consumption rate h of the electrolyte from the liquid retention coefficient k1 of the battery with the cycle dive point c1 and the liquid retention coefficient k2 of the battery with the cycle dive point c2. Among them, dividing the difference in liquid retention amount by the difference in dive points will obtain the amount of electrolyte consumed per cycle. Then, the chemical consumption rate h of the electrolyte = |k1 - k2| / |t1 - t2|. Through the chemical consumption rate h, the number of cycles e required for the battery cycle life, and the designed capacity L of the battery, the chemical consumption amount y of the electrolyte during the cycle is obtained, where y = h × e × L.

[0040] As shown in the Figure 6 attachment, tangents are drawn to the two cycle curves obtained in the step S2 to find the corresponding cycle dive points. Among them, the number of cycles corresponding to the cycle dive points of the two cycle curves are 610 weeks and 670 weeks respectively. At the same time, since the liquid retention coefficients of the two selected batteries are 1.38 g / Ah and 1.42 g / Ah respectively, it is understood that the dive point of the battery with a liquid retention coefficient of 1.42 is delayed by 60 weeks compared to the battery with a liquid retention coefficient of 1.38. Then, the calculation formula for the chemical consumption rate h of the electrolyte during the cycle is (1.42 - 1.38) / (670 - 610) = 0.53 mg / Ah / week; if the number of cycles e required for the battery cycle life is 800 weeks and the designed capacity L of the battery is 4 Ah, then the chemical consumption amount y of the electrolyte = 0.53 × 800 × 4 = 1.7 g, so that the chemical consumption amount y of the electrolyte during the cycle can be accurately calculated. And when the cycle life requirement is clear, not only can the accurate designed value of the liquid retention amount be obtained, but also the model algorithm can be corrected accordingly through the historical cycle retention rate curve, making the theoretical calculation of the target liquid retention amount more and more accurate.

[0041] During the calculation process, the step S3 further includes: obtaining the cycle expansion coefficient of the battery through the number of cycles required for the battery cycle life and the average value of the corresponding expansion rate.

[0042] Moreover, the volume of the bare cell is obtained through the cell design parameters, and the increment z of the electrolyte filling requirement = the density ρ of the electrolyte × the cycle expansion coefficient of the battery × the volume of the bare cell.

[0043] As shown in the Figure 7 attachment, if the cycle life requirement is 700 weeks and the average value of the corresponding expansion rate is 6.07%, it is considered that the cycle expansion coefficient of the battery within the life cycle is 6.07%. Then, the increment z of the electrolyte filling requirement during the 700 - week cycle = the volume of the bare cell × 6.07% × the density ρ of the electrolyte.

[0044] Example 2

[0045] Different from Example 1, in step S2 of this example, it further includes: by performing cyclic life tests on several batteries with different liquid retention coefficients using the same electrolyte, calculating the average chemical consumption rate of the electrolyte, and calculating the chemical consumption of the electrolyte based on the average chemical consumption rate, the number of cycles required for the battery cyclic life, and the designed capacity of the battery, so as to further improve the accuracy of the liquid retention amount design. And with the enrichment of cyclic data, the model can be gradually corrected to improve its accuracy step by step.

[0046] Other steps of this example are the same as those of Example 1 and will not be elaborated here.

[0047] Obviously, the theoretical liquid retention amount of the target cyclic life calculated by the present invention through the three-dimensional size structure of the battery and the chemical consumption of the electrolyte and the volume expansion of the battery during the cycle can ensure the "natural death" of the battery without injecting too much electrolyte, and improve the battery cyclic life.

[0048] According to the disclosure and teachings of the above specification, those skilled in the art to which the present invention pertains can also make changes and modifications to the above embodiments. Therefore, the present invention is not limited to the above specific embodiments, and any obvious improvements, substitutions or variations made by those skilled in the art on the basis of the present invention all belong to the protection scope of the present invention. In addition, although some specific terms are used in this specification, these terms are only for convenience of description and do not constitute any limitation to the present invention.

Claims

1. A calculation method for the liquid retention amount required by a battery, characterized in that, It includes the following steps: S1. According to the space inside the battery that contains the electrolyte, calculate the electrolyte volume a1 in the pores of the cathode electrode sheet, the electrolyte volume a2 in the pores of the anode electrode sheet, and the electrolyte volume a3 in the pores of the separator through the cell design parameters, and calculate the volume v inside the battery excluding the cathode electrode sheet, anode electrode sheet, separator, insulating glue, and electrode tab. Obtain the minimum liquid retention amount x of the battery through a1, a2, a3, and v; S2. Through the cycle life test of the battery and setting the required number of cycles, obtain the cell cycle life curve based on the capacity retention rate and the number of cycles. Then calculate the chemical consumption amount y of the electrolyte during the cycle through the cycle diving point and the liquid retention coefficient; S3. Obtain the cycle expansion coefficient of the battery based on the average expansion rate after the full life cycle of the battery. Obtain the increment z of the electrolyte filling demand caused by the expansion of the cell during the cycle through the density of the electrolyte, the cycle expansion coefficient of the battery, and the volume of the bare cell. According to the cycle requirements, obtain the required liquid retention amount d of the battery = x + y + z.

2. The calculation method of the liquid retention amount required for the battery according to claim 1, characterized in that, In S2, it also includes: taking the capacity retention rate as the ordinate and the number of cycles as the abscissa to construct a rectangular coordinate system, recording the cell cycle life curve in the rectangular coordinate system, obtaining the cycle diving point by making an auxiliary tangent to the cell cycle life curve, and obtaining the chemical consumption amount y of the electrolyte during the cycle based on the number of cycles corresponding to the cycle diving point, the liquid retention coefficient of the battery, the number of cycle weeks required for the battery cycle life, and the design capacity of the battery.

3. The calculation method of the liquid retention amount required for the battery according to claim 2, characterized in that, In S2, it also includes: conducting cycle life tests on two batteries using the same electrolyte but with different liquid retention coefficients, obtaining two different cycle diving points c1 and c2, obtaining the number of cycles t1 corresponding to c1 and the number of cycles t2 corresponding to c2 from the cycle life curve, and calculating the chemical consumption rate h of the electrolyte from the liquid retention coefficient k1 of the battery with the cycle diving point c1 and the liquid retention coefficient k2 of the battery with the cycle diving point c2. Obtain the chemical consumption amount y of the electrolyte during the cycle through the chemical consumption rate h, the number of cycle weeks e required for the battery cycle life, and the design capacity L of the battery, where y = h × e × L.

4. The method for calculating the liquid retention amount required for the battery according to claim 3, wherein: The chemical consumption rate h of the electrolyte = |k1 - k2| / |t1 - t2|.

5. The method for calculating the required battery liquid storage volume according to claim 3, wherein: In S2, it also includes: conducting cycle life tests on several batteries with different liquid retention coefficients using the same electrolyte, calculating the average chemical consumption rate of the electrolyte, and calculating the chemical consumption amount of the electrolyte based on the average chemical consumption rate, the number of cycle weeks required for the battery cycle life, and the design capacity of the battery.

6. The method for calculating the liquid retention amount required for the battery according to any one of claims 1 to 3, characterized in that, In S3, it also includes: obtaining the cycle expansion coefficient of the battery through the number of cycle weeks required for the battery cycle life and the average value of the corresponding expansion rate.

7. The method for calculating the liquid retention amount required for the battery according to claim 1, wherein: The volume of the bare cell is obtained through the cell design parameters, and the increment z of the electrolyte filling demand = the density ρ of the electrolyte × the cycle expansion coefficient of the battery × the volume of the bare cell.

8. The calculation method of the liquid retention amount required for the battery according to claim 1, wherein, The content in S1 also includes: in the cell design parameters, the pore space volume of the cathode electrode = the apparent volume of the cathode electrode - the true volume of the cathode electrode, the pore space volume of the anode electrode = the apparent volume of the anode electrode - the true volume of the anode electrode, and the pore space volume of the separator = the pore volume of the separator substrate - the pore volume of the separator coating.

9. The method for calculating the liquid retention amount required for the battery according to claim 8, wherein: The true volume of the cathode electrode = the weight of the cathode electrode / the true density of the cathode electrode, and the true volume of the anode electrode = the weight of the anode electrode / the true density of the anode electrode.

10. The calculation method of the liquid retention amount required for the battery according to claim 1, characterized in that: The minimum liquid retention amount x = a1 + a2 + a3 + v.

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