A method for calculating the liquid injection amount of an aluminum shell lithium battery

Abstract

The application discloses a kind of aluminum shell lithium battery injection quantity calculation method, the application comprehensively considers the influence of the thickness rebound of the core suction capacity, free state electrolyte volume and process pole piece on injection volume to determine total injection volume and primary / secondary injection volume, can be applied to aluminum shell and soft package core simultaneously, with high accuracy of calculation result, beneficial to defining the best injection volume, can improve product quality, reduce waste, reduce production cost.The application uses the total volume Va inside the aluminum shell core design, the solid volume Vb and solid pore volume Vc inside the core, considering the porosity of pole piece and the porosity of diaphragm, combined with the density of electrolyte, to calculate the theoretical total injection volume of the core.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery technology and relates to the calculation of lithium battery electrolyte volume, particularly to a method for calculating the electrolyte volume of aluminum-cased lithium batteries that can efficiently and accurately determine the appropriate electrolyte volume and primary / secondary electrolyte volume. Background Technology

[0002] Lithium-ion batteries are widely used in mobile electronic devices, electric vehicles, and energy storage and communication fields due to their numerous advantages, including high energy density, long cycle life, and environmental friendliness. Electrolyte, as one of the main materials in lithium-ion batteries, primarily functions to conduct ions between the positive and negative electrodes, ensuring the high cycle life and high capacity of lithium-ion batteries. Therefore, the amount of electrolyte used is a crucial design parameter.

[0003] During the production process, excessive electrolyte filling can cause excessive internal pressure in pouch batteries, leading to issues such as seal bursting, leakage, surface corrosion, and battery softening, severely affecting the battery's appearance or even causing direct battery failure. For aluminum-cased cells, it can cause excessive electrolyte overflow and excessive liquid loss during negative pressure formation. Insufficient electrolyte filling prevents the positive and negative electrodes and separator from being adequately wetted, affecting battery capacity and internal resistance, thus impacting electrical performance and cycle life. Due to insufficient electrolyte, lithium ions cannot smoothly intercalate and deintercalate between the positive and negative electrodes during charging and discharging, forming lithium dendrites. These dendrites can pierce the separator, causing a short circuit between the positive and negative electrodes, severely impacting battery safety.

[0004] In existing technologies, there are roughly the following methods for determining the optimal injection volume:

[0005] 1) A common calculation method involves estimating the electrolyte volume based on battery capacity or empirical values, then using a gradient of electrolyte injection volume to test gas production, free electrolyte volume, cycle performance, and dissection experiments to determine the correct injection volume. The drawback of this method is that it doesn't fully consider the impact of the compaction density of the positive and negative electrode materials and the separator thickness on the actual electrolyte injection volume. While empirical values ​​are usable for conventional battery systems, they are likely inaccurate for batteries made from new materials, differing significantly from actual values. This is because some new materials have completely different characteristics from existing materials, such as silicon carbon and graphene, which have large specific surface areas and highly variable pore volumes. Furthermore, on established factory production lines, processes are limited by factory space and equipment, restricting significant adjustments. Therefore, the electrolyte volume obtained using the above method cannot be achieved with existing processes, limiting its practical guidance. This can easily lead to excessive or insufficient electrolyte, severely impacting product quality and causing substantial cost losses.

[0006] 2) The electrolyte injection mass is calculated by combining the porosity of the electrode and the separator with the electrolyte density, and then a certain proportional coefficient is used to obtain the actual injection volume. However, this method has the drawback of ignoring the microscopic changes in the expansion of the negative electrode during the actual process. The actual calculated injection volume may not be able to support actual battery cycles. In addition, aluminum-cased cells include primary and secondary electrolyte injection, and the above method can only obtain the total injection volume, which cannot guide the allocation of primary and secondary electrolyte injection volumes. Summary of the Invention

[0007] To address the aforementioned problems, this invention provides a method for calculating the electrolyte injection volume of aluminum-cased lithium batteries. This invention can efficiently and accurately determine the appropriate electrolyte injection volume and the primary / secondary electrolyte injection volume.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] This invention provides a method for calculating the electrolyte filling volume of an aluminum-cased lithium battery, the calculation method comprising:

[0010] Calculate the total internal design volume Va of the aluminum-cased battery cell, the internal solid volume Vb and solid pore volume Vc of the cell, and the theoretical electrolyte injection volume m = (Va-Vb+Vc) * electrolyte density ρ.

[0011] During the liquid injection process, the volume change of the positive and negative electrode plates corresponding to the rebound thickness of the roller pressing thickness is Vd. Then, the total adsorbed electrolyte after one liquid injection is M1=(Vc+Vd)*electrolyte densityρ, and the total liquid injection volume is m1=M1 / K1.

[0012] After formation, the volume change of the positive and negative electrode plates corresponding to the rebound thickness of the rolling thickness is Ve. Then, the total adsorbed electrolyte after the second liquid injection is M2=(Vc+Ve)*electrolyte densityρ, and the total secondary liquid injection volume is m2=M2 / K2-m1.

[0013] Total injection volume m0 = m1 + m2;

[0014] Injection difficulty coefficient K = m0 / m;

[0015] Where K1 is 0.8, K2 is 0.78-0.83, and 80%≤K≤95%.

[0016] As a preferred embodiment of the present invention, the internal solid volume Vb of the battery cell includes the cover plate support volume V1, the cover plate terminal volume V2, the positive electrode plate volume V3, the negative electrode plate volume V4, the separator volume V5, the positive electrode connecting plate volume V6, the negative electrode connecting plate volume V7, the positive electrode tab volume V8, the negative electrode tab volume V9, the Mylar membrane volume V10, the bottom plate volume V11, the tape volume V12, and the volume V13 of other possible components, i.e., Vb = (V1 + V2 + ... V13).

[0017] As a preferred embodiment of the present invention, the solid pore volume Vc includes the pore volume of the positive electrode, the pore volume of the negative electrode, and the pore volume of the separator.

[0018] As a preferred embodiment of the present invention, the pore volume of the positive electrode sheet = (positive electrode sheet volume - foil volume) * theoretical porosity; the pore volume of the negative electrode sheet = (negative electrode sheet volume - foil volume) * theoretical porosity;

[0019] The volume of the positive electrode and the volume of the negative electrode are calculated based on the roll-pressed thickness, length, width and number of layers. The theoretical porosity is calculated from the true density of the various raw materials used in lithium-ion batteries.

[0020] As a preferred embodiment of the present invention, the pore volume of the diaphragm = diaphragm volume * porosity.

[0021] As a preferred embodiment of the present invention, the volume change Vd during the liquid injection process and the volume change Ve during the formation process are calculated based on the rebound thickness, length, width and number of layers of the positive and negative electrode sheets.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1) This invention comprehensively considers the liquid absorption capacity of the core, the amount of free electrolyte, and the influence of electrode thickness rebound on the liquid injection amount during the process to determine the total liquid injection amount and the primary / secondary liquid injection amount. It can be applied to both aluminum shell and soft-pack cells. It has high calculation accuracy, which is helpful in defining the optimal liquid injection amount, improving product quality, reducing waste, and reducing production costs.

[0024] 2) This invention utilizes the total internal design volume Va, the internal solid volume Vb, and the solid pore volume Vc of the aluminum-cased battery cell, taking into account the porosity of the electrode and the diaphragm, and combining the electrolyte density, to calculate the theoretical total electrolyte injection volume (maximum injectable volume) of the battery cell.

[0025] 3) This invention considers the porosity of the electrode, the porosity of the separator, and the volume change of electrode rebound during the cell manufacturing process. This allows for the determination of the amount of adsorbed electrolyte in the cell under different conditions. The ratio of adsorbed electrolyte to free electrolyte is then used to obtain the actual primary and secondary electrolyte injection amounts. The sum of the primary and secondary electrolyte injection amounts is the actual total electrolyte injection amount. By comparing the actual total electrolyte injection amount with the theoretical total electrolyte injection ratio, the ease or difficulty of electrolyte injection can be determined, thus guiding the adjustment of existing process parameters.

[0026] 4) The calculation method of the present invention has the advantages of high efficiency and accuracy. The actual calculated liquid injection volume can support the actual battery cycle, which can improve product quality and reduce cost losses. Detailed Implementation

[0027] To facilitate understanding of the technical means, creative features, objectives, and effects of this invention, the invention is further described below with reference to specific embodiments. However, the following embodiments are merely preferred embodiments of this invention and not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments described herein without creative effort are all within the scope of protection of this invention. Unless otherwise specified, the experimental methods in the following embodiments are conventional methods, and the materials and reagents used in the following embodiments are commercially available unless otherwise specified.

[0028] This invention provides a method for calculating the electrolyte filling volume of an aluminum-cased lithium battery, the calculation method comprising:

[0029] Calculate the total internal design volume Va of the aluminum-cased battery cell, the internal solid volume Vb and solid pore volume Vc of the cell, and the theoretical electrolyte injection volume m = (Va-Vb+Vc) * electrolyte density ρ.

[0030] During the liquid injection process, the volume change of the positive and negative electrode plates corresponding to the rebound thickness of the roller pressing thickness is Vd. Then, the total adsorbed electrolyte after one liquid injection is M1=(Vc+Vd)*electrolyte densityρ, and the total liquid injection volume is m1=M1 / K1.

[0031] After formation, the volume change of the positive and negative electrode plates corresponding to the rebound thickness of the rolling thickness is Ve. Then, the total adsorbed electrolyte after the second liquid injection is M2=(Vc+Ve)*electrolyte densityρ, and the total secondary liquid injection volume is m2=M2 / K2-m1.

[0032] Total injection volume m0 = m1 + m2;

[0033] Injection difficulty coefficient K = m0 / m;

[0034] Where K1 is 0.8, K2 is 0.78-0.83, and 80%≤K≤95%.

[0035] Using the calculation method of this invention, the theoretical total liquid injection volume (maximum injectable liquid injection volume) of the battery cell can be obtained simply by knowing the cell size, materials used, compaction density, number of layers, and electrolyte density.

[0036] By employing the calculation method of this invention, and considering the compaction density, the rebound of the positive and negative electrodes after electrolyte injection and formation, the amount of adsorbed electrolyte in the cell under different conditions can be accurately obtained. Then, the ratio coefficient of adsorbed electrolyte to free electrolyte is used to obtain the actual primary and secondary electrolyte injection amounts. The primary and secondary electrolyte injection amounts obtained by this method accurately reflect the actual internal conditions of the cell, avoiding excessive or insufficient electrolyte due to large differences in empirical parameters caused by material variations and changes in compaction density.

[0037] Using the calculation method of this invention, the actual total liquid injection volume is obtained by summing the primary and secondary liquid injection volumes. The actual total liquid injection volume also reflects the liquid retention requirements to ensure the performance of the battery cell. The ratio of the actual total liquid injection volume to the theoretical total liquid injection volume reflects the difficulty of liquid injection into the battery cell. The larger the ratio, the higher the difficulty of liquid injection. In actual production, the liquid injection parameters can be adjusted in advance based on this value to ensure the liquid injection effect.

[0038] Example 1

[0039] This embodiment uses a 36130235-125Ah lithium-ion battery as an example to further illustrate the technical solution of the present invention. The specific steps are as follows:

[0040] (1) The total internal volume Va of the aluminum-cased battery cell is shown in Table 1.

[0041] Table 1. Total internal design volume Va of aluminum-cased battery cells

[0042]

[0043] (2) The solid volume Vb inside the cell is shown in Table 2.

[0044] Table 2. Solid volume Vb inside the battery cell

[0045]

[0046]

[0047] (3) Solid pore volume Vc, see Table 3 and Table 4.

[0048] Electrode porosity (%) = (True density of mixture - Compacted density of electrode) / True density of mixture * 100%;

[0049] Positive electrode pore volume = electrode height * width * (positive electrode thickness - foil thickness) * number of layers * porosity;

[0050] Negative electrode pore volume = electrode height * width * (negative electrode thickness - foil thickness) * number of layers * porosity;

[0051] Diaphragm pore volume = total diaphragm length * width * thickness * porosity.

[0052] Table 3. Pore Volume of Positive Electrode

[0053]

[0054] Table 4. Porous Volume of Negative Electrode

[0055]

[0056] Diaphragm pore volume = 3.812E-05m 3 Vc = 0.00025m 3 .

[0057] (4) The rebound rate of the positive electrode thickness after liquid injection is calculated as 2%, and the rebound rate of the negative electrode thickness is calculated as 6%. The volume change Vd during liquid injection is calculated as follows: electrode height * width * thickness * number of layers * rebound rate = 2.80988E-05m 3 The rebound rate of the positive electrode thickness after formation is calculated as 3%, and the rebound rate of the negative electrode thickness is calculated as 14%. The volume change Ve during liquid injection is calculated as: electrode height * width * thickness * number of layers * rebound rate = 5.82413E-05m 3 .

[0058] (5) Total adsorbed electrolyte after one injection

[0059] M1=(0.00025+2.80988E-05)*100*100*100*1.22=339.28,

[0060] m1 = 339.28 / 0.8 = 424.1 g;

[0061] Total adsorbed electrolyte after secondary injection

[0062] M2=(0.00025+5.82413E-05)*100*100*100*1.22=376g;

[0063] The total volume of fluid injected twice, m2 = 376 / 0.82 - 424.1g = 34.5g;

[0064] Total injection volume m0 = 425 + 35 = 460g;

[0065] Theoretical total injection volume = (0.0010439 - 8.71E-04 + 0.00025) * 100 * 100 * 100 * 1.22 = 515.9g;

[0066] Difficulty coefficient of injection = 460g / 515.9g = 89.1%.

[0067] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any form or substance. It should be noted that those skilled in the art can make various improvements and additions without departing from the method of the present invention, and these improvements and additions should also be considered within the scope of protection of the present invention. Any modifications, alterations, and equivalent changes made by those skilled in the art based on the above-disclosed technical content without departing from the spirit and scope of the present invention are equivalent embodiments of the present invention. Furthermore, any modifications, alterations, and evolutions made to the above embodiments based on the essential technology of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A method for calculating the amount of electrolyte to be injected into an aluminum can lithium battery, characterized by, The calculation method includes: Calculate the total internal design volume Va of the aluminum-cased battery cell, the internal solid volume Vb, and the solid pore volume Vc. The theoretical electrolyte injection volume m = (Va - Vb + Vc) * electrolyte density ρ. During the electrolyte injection process, the volume change of the positive and negative electrode plates corresponding to the rebound thickness relative to the rolling thickness is Vd. Therefore, the total adsorbed electrolyte after the first injection is M1 = (Vc + Vd) * electrolyte density ρ, and the total first injection volume m1 = M1 / K1. After formation, the volume change of the positive and negative electrode plates corresponding to the rebound thickness relative to the rolling thickness is Ve. Therefore, the total adsorbed electrolyte after the second injection is M2 = (Vc + Ve) * electrolyte density ρ, and the total second injection volume m2 = M2 / K2 - m1. The total injection volume m0 = m1 + m2. The electrolyte injection difficulty coefficient K = m0 / m. Where K1 is taken as 0.8, and K2 is taken as 0.78-0. 0.83, 80% ≤ K ≤ 95%; The volume change Vd during liquid injection and the volume change Ve during formation are calculated based on the rebound thickness, length, width and number of layers of the positive and negative electrode sheets. Volume change Vd = Electrode height * Width * Thickness * Number of layers * Rebound rate = 2.80988E-05m 3 Volume change Ve = electrode height * width * thickness * number of layers * rebound rate = 5.82413E-05m 3 . 2.The method of claim 1, wherein, The solid volume Vb inside the battery cell includes the volume of the cover plate support V1, the volume of the cover plate terminal V2, the volume of the positive electrode plate V3, the volume of the negative electrode plate V4, the volume of the separator V5, the volume of the positive electrode connecting piece V6, the volume of the negative electrode connecting piece V7, the volume of the positive electrode tab V8, the volume of the negative electrode tab V9, the volume of the Mylar membrane V10, the volume of the bottom plate V11, the volume of the tape V12, and the volume of other components V13, i.e., Vb = (V1 + V2 + ... V13).

3. The method for calculating the electrolyte volume of an aluminum-cased lithium battery according to claim 1, characterized in that, Solid pore volume Vc includes the pore volume of the positive electrode, the pore volume of the negative electrode, and the pore volume of the separator.

4. The method for calculating the electrolyte volume of an aluminum-cased lithium battery according to claim 3, characterized in that, The pore volume of the positive electrode sheet = (positive electrode sheet volume - foil volume) * theoretical porosity; the pore volume of the negative electrode sheet = (negative electrode sheet volume - foil volume) * theoretical porosity; the positive electrode sheet volume and negative electrode sheet volume are calculated based on the roll-pressed thickness, length, width and number of layers, and the theoretical porosity is calculated from the true density of various raw materials used in lithium-ion batteries.

5. The method for calculating the electrolyte volume of an aluminum-cased lithium battery according to claim 3, characterized in that, The pore volume of the diaphragm = diaphragm volume * porosity.

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