Method for evaluating tortuosity of electrode

Abstract

The present invention relates to a method for measuring the curvature of an electrode by impregnating the electrode with resin. According to the present invention, the correlation between curvature and the wettability of the electrolyte is enhanced, thereby enabling the actual operating performance of a battery cell to be determined with high precision from the curvature. Furthermore, the time and cost required for the analysis of the electrode's curvature can be reduced.

Description

Technology Field

[0001] The present invention relates to a method for measuring the curvature of an electrode by impregnating the electrode with resin. Background Technology

[0002] If the electrode tortuosity is low, Li in the electrolyte + Electron movement is faster, and efficient diffusion is possible. Consequently, electrode resistance can be directly reduced, and delays in degradation and power loss can be expected, which helps improve battery performance. Additionally, since curvature affects the wettability of the electrolyte filling the cell during electrode manufacturing, electrodes with high curvature increase the time required depending on the electrolyte's wettability, thereby becoming a factor that raises process costs.

[0003] Generally, electrospray ionization (EIS) measurement is applied to determine the curvature of an electrode. This method can be calculated through the restricted diffusion method and the symmetric cell method. However, the curvature measured by the electrospray ionization method varies significantly depending on the model's fit, pore structure, experimental environment, and data fitting accuracy, resulting in poor correlation with the wettability of the electrolyte and the actual operating performance of the cell.

[0004] In addition, there is a method to calculate porosity and curvature by scanning the interior of the actual cell with computed tomography (CT) and using a focused ion beam (FIB) for three-dimensional space (3D) modeling, but it is difficult to perform magnified analysis on all samples because it is very time-consuming and expensive to analyze.

[0005] Therefore, a method is needed to improve the correlation between the wettability of the actual electrolyte at the electrode and the driving performance of the cell. The problem to be solved

[0006] The objective of the present invention is to provide a method for measuring the curvature of an electrode to improve the correlation between the curvature of the electrode and the wettability of the electrolyte. means of solving the problem

[0007] In order to solve the above problem, the present invention,

[0008] A bending factor determination step comprising the following steps: and

[0009] S1-1) A step of measuring the curvature of a reference electrode using a 3D analysis method;

[0010] S1-2) A step of contacting a guide on a reference electrode;

[0011] S1-3) A step of injecting resin into the above guide and curing it;

[0012] S1-4) A step of fabricating cross-sections of the impregnated area and the non-impregnated area;

[0013] S1-5) A step of distinguishing pores by metal coating the cross-section; and

[0014] S1-6) A step for determining a tortuosity factor comprising the step of extracting pores by area ratio to obtain the tortuosity factor of Equation 1.

[0015] [Mathematical Formula 1]

[0016]

[0017] Curvature calculation steps including the following steps:

[0018] S2-1) A step of performing the same method as S1-2) to S1-5) on the electrode to be analyzed; and

[0019] S2-2) A step of calculating the curvature by substituting the measured value into Equation 2 from the result of S2-1) above.

[0020] [Mathematical Formula 2]

[0021]

[0022] A method for measuring the curvature of an electrode including is provided.

[0023] According to one embodiment, the guide may include one or more of polypropylene, polystyrene, polycarbonate, and polyethylene terephthalate.

[0024] According to one embodiment, the resin may include a silicone-based, fluorine-based, or carbon-based resin.

[0025] According to one embodiment, the curvature factor may be 0 to 10.

[0026] According to another embodiment of the present invention, a system for evaluating the curvature of an electrode is provided, comprising: a system module for determining a curvature factor according to Equation 1; and a system module for calculating the curvature according to Equation 2.

[0027] Specific details of other embodiments of the present invention are included in the following detailed description. Effects of the invention

[0028] According to the present invention, since the curvature measurement environment is applied in a manner similar to the actual manufacturing process of a battery cell, the correlation between curvature and the wettability of the electrolyte can be enhanced. Consequently, the actual operating performance of the battery cell can be determined with high precision from the curvature. Furthermore, the time and cost required for the analysis of electrode curvature can be reduced. Brief explanation of the drawing

[0029] Figure 1 illustrates the reference electrode measurement process. Figure 2 illustrates the process of measuring the electrode to be analyzed. Specific details for implementing the invention

[0030] The present invention is capable of various modifications and may have various embodiments, and specific embodiments are illustrated in the drawings and described in detail in the detailed description. However, this is not intended to limit the present invention to specific embodiments, and it should be understood that it includes all modifications, equivalents, and substitutions that fall within the spirit and scope of the invention.

[0031] Hereinafter, a method for measuring the curvature of an electrode according to an embodiment of the present invention will be described in more detail.

[0032] The present invention improves the correlation between curvature and electrolyte wettability by applying a curvature measurement environment similar to the actual battery cell manufacturing process in order to overcome the problem of a significant discrepancy between the wettability of the electrolyte identified by conventional curvature measurement methods such as electrospray ionization (EIS) and computed tomography scan (CT) and the operating performance of the actual battery cell, as well as the limitations of high time and cost required for analysis. In addition, the time and cost required for electrode curvature analysis have been reduced.

[0033] According to one embodiment, the present invention includes a step of determining a curvature factor and a step of calculating a curvature.

[0034] The step of determining the curvature factor includes the following steps.

[0035] S1-1) A step of measuring the curvature of a reference electrode using a 3D analysis method;

[0036] S1-2) A step of contacting a guide on a reference electrode;

[0037] S1-3) A step of injecting resin into the above guide and curing it;

[0038] S1-4) A step of fabricating cross-sections of the impregnated area and the non-impregnated area;

[0039] S1-5) A step of distinguishing pores by metal coating the cross-section; and

[0040] S1-6) A step for determining a tortuosity factor comprising the step of extracting pores by area ratio to obtain the tortuosity factor of Equation 1.

[0041] [Mathematical Formula 1]

[0042]

[0043] The curvature calculation step includes the following steps.

[0044] S2-1) A step of performing the same method as S1-2) to S1-5) on the electrode to be analyzed; and

[0045] S2-2) A step of calculating the curvature by substituting the measured value into Equation 2 from the result of S2-1) above.

[0046] [Mathematical Formula 2]

[0047]

[0048] According to one embodiment, the metal coating in step S1-5) can specifically use common metallic elements such as gold (Au), silver (Ag), palladium (Pd), aluminum (Al), nickel (Ni), chromium (Cr), and tungsten (W). The metallic elements used for the metal coating are not limited to those described above, and are not limited to any coating material that can be used to impart conductivity to a non-conductive material during SEM measurement.

[0049] As mentioned above, the tortuosity factor can be calculated from the reference electrode by measuring its curvature using a 3D analysis method. The tortuosity factor of the reference electrode is always fixed at a similar value when performed under constant experimental conditions such as temperature and humidity. Theoretically, the electrode's performance is best when its tortuosity (T) is 1; however, since this implies the absence of active material, it is difficult to measure the tortuosity of an electrode applied to an actual battery cell as 1. The impregnation of the electrolyte is related to tortuosity, and the higher the tortuosity, the lower the impregnation of the electrolyte. When the electrode has low tortuosity and excellent electrolyte impregnation, it is advantageous for rapid charging and discharging.

[0050] According to one embodiment, in the step of measuring curvature of the reference electrode using a 3D analysis method, the size of the reference electrode may be 50 to 500 µm in width, for example, 70 µm or more, 100 µm or more, or 400 µm or less, 300 µm or less, 200 µm or less, and also 10 to 200 µm in height, for example, 20 µm or more, 30 µm or more, or 150 µm or less, 100 µm or less, 80 µm or less, 50 µm or less, and 10 to 300 µm in height, for example, 20 µm or more, 30 µm or more, 40 µm or more, 50 µm or more, or 250 µm or less, 200 µm or less, 150 µm or less, 100 µm or less.

[0051] According to one embodiment, the guide may be made of polypropylene (PP), polystyrene (PS), polycarbonate, polyethylene terephthalate (PET), etc. The shape of the guide is not particularly limited, but it may be a rectangular or circular column shape to facilitate the calculation of the area. For example, if the guide is circular, it may have a circular area with a radius (r) of 0.5 to 10 cm, 0.5 cm or more and 1 cm or more, or 9 cm or less, 8 cm or less, 7 cm or less, 6 cm or less, and 5 cm or less.

[0052] According to one embodiment, the resin may include silicone-based, fluorine-based, or carbon-based resins. Specifically, for example, silicone-based resins may include one or more of methylsilsesquioxane, silicone acrylate, silicone urethane, phenyl silicone, and polydimethylsiloxane. For example, fluorine-based resins may include one or more of polytetrafluoroethylene, polyvinylidene fluoride, fluorinated ethylene propylene, perfluoroalkoxy alkanes, and ethylene tetrafluoroethylene. For example, carbon-based materials may include one or more of phenolic resin, polyurethane resin, vinyl ester resin, polyimide resin, polycarbonate resin, and polyepoxide resin.

[0053] According to one embodiment, the step of injecting and curing resin into the guide may include the step of positioning the guide on the electrode plane and then injecting the resin into the guide to naturally impregnate it by gravity. According to the present invention, when impregnating the electrode with resin, only gravity is used without applying pressure, so it is similar to the actual impregnation process of the electrolyte, and the correlation between the wettability and flexibility values ​​of the electrolyte can be improved. For example, the impregnation and curing time may be 1 to 2 days or 10 to 50 hours.

[0054] The amount of resin injected may be 0.05 to 3g, for example, 0.1 or more, 0.2 or more, or 2g or less, or 1.5g or less. Alternatively, the amount of resin injected may be 50 to 3000ul, for example, 100ul or more, 200ul or more, or 2000ul or less, or 1500ul or less.

[0055] According to one embodiment, the curvature factor may be 0 to 10, for example, greater than 0, 1 or more, 5 or less, 4 or less, 3 or less, or 2 or less.

[0056] According to one embodiment, the measurement range of curvature is theoretically not limited to an upper limit value, but can be, for example, 1 to 20.

[0057] According to another embodiment of the present invention, a system for evaluating the curvature of an electrode is provided, comprising: a system module for determining a curvature factor according to Equation 1; and a system module for calculating the curvature according to Equation 2.

[0058] According to the present invention, statistical data can be obtained through an increase in large area and parameters. Specifically, when measuring multiple target electrode samples of the same type as a reference electrode, 3D analysis of all samples is unnecessary, and the curvature of each can be analyzed by applying the same guide size and resin amount to multiple target electrode samples based on a single curvature value for the reference electrode. Since the degree of spreading, i.e., wettability, varies depending on the electrode, the type of electrode, guide size, and resin amount are applied identically. In addition, since the curvature varies depending on the guide size and resin amount, these are fixed and applied. Both positive and negative electrodes can be applied, and their types are not particularly limited.

[0059] Hereinafter, embodiments of the present invention are described in detail so that those skilled in the art can easily implement the invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein.

[0061] Examples

[0062] Reference electrode measurement

[0063] 1. The curvature of the reference electrode was measured using 3D analysis (FID (Thermofisher) 3D reconstruction tool). An NCM-based anode (thickness 110 µm, loading amount: 500 mg / 25 cm²) was used as the reference electrode. 2 ) was used. The curvature of the reference electrode measured according to the guidelines of the 3D measuring instrument is 4.9. The guidelines are 150 µm (W) * 42 µm (T) * 50 µm (H), silcing distance 200 nm, and number of slices 210 ea.

[0064] 2. A cylindrical polypropylene (PP) guide with a radius (r) of 2 cm was placed on the plane of the reference electrode. At this time, the size of the reference electrode is approximately 2 cm in width and length or larger. The size of the reference electrode can be appropriately selected to be larger than the guide.

[0065] 3. 100 µl (0.11 g) of resin was injected into the guide using a micropipette or balance. It was left for one day to allow the resin to impregnate the inner surface of the guide by gravity.

[0066] 4. Cross-sections of the impregnated and non-impregnated regions were fabricated. The impregnated region corresponds to the inner area of ​​the guide, and the non-impregnated region corresponds to the outer area of ​​the guide.

[0067] 5. The pores were separated by coating the impregnated area and the non-impregnated area with platinum (Pt), respectively. Platinum was coated on the non-impregnated area.

[0068] 6. The pores were extracted by area ratio to calculate the curvature factor. The formula for calculating the curvature factor is Equation 1.

[0069] [Mathematical Formula 1]

[0070]

[0071] The pore area ratio of the non-impregnated region is 12.6%, and

[0072] The pore area ratio of the impregnated region is 8.2%, and

[0073] The curvature factor calculated according to mathematical formula 1 is 1.71.

[0074] The reference electrode measurement process is illustrated in Figure 1.

[0076] Measurement of electrodes subject to analysis

[0077] 1. The curvature factor was determined from the measurement of the above reference electrode. The curvature factor of the reference electrode is 1.71.

[0078] 2. The procedure was performed on the electrode under analysis in the same manner as steps 2 to 5 of the reference electrode measurement above. The electrode under analysis was an NCM-based anode (thickness 110 µm, loading amount: 500 mg / 25 cm²). 2 ) was used.

[0079] 3. The pores were extracted by area ratio to calculate the curvature factor. The curvature was calculated according to Equation 2.

[0080] [Mathematical Formula 2]

[0081]

[0082] The curvature factor is 1.71, and

[0083] The pore area ratio of the non-impregnated region is 12.5%, and

[0084] The porosity of the impregnated area is 5.8%, and

[0085] The curvature of the electrode under analysis calculated according to mathematical formula 2 is 3.19.

[0086] The measurement process of the electrode to be analyzed is illustrated in Figure 2.

[0088] Experimental example

[0089] An evaluation was performed to compare the electrode's flexibility and electrolyte wettability. The electrode was cut to a uniform size, its dry weight was measured, and it was immersed in Dimethyl Carbonate (DMC), one of the solvents used in electrolytes. As DMC permeated into the electrode over time, the point at which there was no change in weight was defined as the endpoint and determined as the electrolyte wettability time.

[0090] In addition, the charge transfer resistance was measured by preparing a coin half cell with the same cathode and using the reference electrode and comparison electrode as positive electrodes and measuring the EIS. The electrolyte composition was EC / DMC 2:8, and the additive was 1M LiPF6, consisting of 0.25% VC (Vinylene Carbonate) and 0.25% FEC (Fluoroethylene Carbonate).

[0091] curvature Electrolyte wettability (wetting time) Charge transfer resistance (Charge transfer R) reference electrode 4.90 10 hours 8.55 Ω comparison electrode 3.19 4 hours 7.98 Ω

[0092] As shown in Table 1, it can be confirmed that the curvature and electrolyte wettability measured by the method according to the present invention are in a proportional relationship. From this, it was confirmed that electrolyte wettability improves as curvature decreases, and it can be seen that the battery curvature and battery performance are inversely proportional as the charge transfer resistance decreases.

[0094] The present invention can improve the correlation between the curvature and the wettability of the electrolyte by measuring the curvature of the electrode in the manner described above. Consequently, the actual operating performance of the battery cell can be determined with high precision from the curvature. Furthermore, the time and cost required for the analysis of the electrode curvature can be reduced.

[0096] The foregoing description is merely an illustrative explanation of the technical concept of the present invention, and those skilled in the art to which the present invention pertains may make various modifications and variations within the scope of the essential characteristics of the present invention. Furthermore, the embodiments disclosed in the present invention are intended to explain, not limit, the technical concept of the present invention, and the scope of the technical concept of the present invention is not limited by such embodiments. The scope of protection of the present invention shall be interpreted by the claims below, and all technical concepts within an equivalent scope shall be interpreted as being included within the scope of rights of the present invention.

Claims

Claim 1 A step for determining a tortuosity factor comprising the following steps: and S1-1) a step of measuring tortuosity with respect to a reference electrode using a 3D analysis method; S1-2) a step of contacting a guide onto the reference electrode; S1-3) a step of injecting resin into the guide and curing it; S1-4) a step of fabricating cross-sections of an impregnated region and a non-impregnated region; S1-5) a step of distinguishing pores by metal coating the cross-section; and S1-6) a step of obtaining a tortuosity factor of Equation 1 by extracting pores by area ratio [Equation 1] Curvature calculation step comprising the following steps: S2-1) a step of performing the same method as S1-2) to S1-5) on the electrode to be analyzed; and S2-2) a step of calculating curvature by substituting the measured value into Equation 2 from the result of S2-1) [Equation 2] A method for measuring the curvature of an electrode including Claim 2 A method for measuring the curvature of an electrode according to claim 1, wherein the guide comprises one or more of polypropylene, polystyrene, polycarbonate and polyethylene terephthalate. Claim 3 A method for measuring the curvature of an electrode according to claim 1, wherein the resin comprises a silicone-based, fluorine-based, or carbon-based resin. Claim 4 A method for measuring the curvature of an electrode according to claim 1, wherein the curvature factor is 0 to 10. Claim 5 An electrode curvature evaluation system comprising: a system module for determining a curvature factor according to mathematical formula 1; and a system module for calculating curvature according to mathematical formula 2: [Mathematical Formula 1] [Mathematical Formula 2]

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