Test method and application for quantifying silicon-carbon and graphite capacity in hybrid electrodes

Abstract

The application provides a test method and application for quantifying silicon-carbon and graphite capacity in a mixed electrode, and relates to the technical field of batteries. The test method uses XRD technology to obtain diffraction peak intensity of each phase of graphite in a pure graphite negative electrode sheet, calculates specific capacity constants corresponding to each phase of graphite according to the relationship between the diffraction peak intensity of each phase of graphite and the relative specific capacity of each voltage platform of the pure graphite negative electrode sheet, then obtains the diffraction peak intensity of each phase of graphite in a silicon-carbon / graphite mixed negative electrode sheet through XRD, combines the calculated specific capacity constants corresponding to each phase of graphite, measures the real specific capacity contribution of silicon-carbon and graphite under each SOC condition in the mixed negative electrode sheet, and calculates the lithium intercalation amount of the negative electrode material according to theoretical calculation. The test method can be applied to the determination of the silicon-carbon and graphite capacity in silicon-carbon / graphite mixed electrodes with different silicon doping ratios, the test result is real and reliable, continuous and stable, and the test time can be saved.

Description

Technical Field

[0001] This invention belongs to the field of battery technology and relates to a test method and application for quantifying the capacity of silicon-carbon and graphite in a hybrid electrode. Background Technology

[0002] In existing hybrid electrodes, the specific capacity is calculated based on a pre-designed silicon doping ratio. For example, in a 500 mAh / g silicon-carbon / graphite hybrid electrode, the specific capacity is calculated based on 12% silicon-carbon with a 0.8V coin cell capacity of 1500 mAh / g under 0.1C conditions and 88% artificial graphite (350 mAh / g).

[0003] Current technologies cannot account for the capacity contributions of silicon-carbon and artificial graphite in actual hybrid electrodes. Furthermore, considering the competitive lithiation in silicon-carbon / graphite hybrid electrodes, during the initial lithiation stage, due to the alloying lithiation in silicon-carbon, lithiation preferentially occurs in the silicon-carbon material, and only later, at a potential of 0.2V vsLi, does lithiation begin in the graphite. Therefore, a method is needed to quantify the capacity contributions of silicon-carbon and graphite in hybrid electrodes.

[0004] In view of this, the present invention is hereby proposed. Summary of the Invention

[0005] In view of the shortcomings and defects of the existing technology, the present invention aims to provide a test method and application for quantifying the capacity of silicon-carbon and graphite in a hybrid electrode.

[0006] To achieve the above objectives, the following technical solution is adopted:

[0007] The primary objective of this invention is to provide a method for quantifying the capacity of silicon-carbon and graphite in a hybrid electrode, comprising the following steps:

[0008] S1. Provides a coin cell A containing a pure graphite negative electrode sheet, and a coin cell B containing a silicon-carbon / graphite hybrid negative electrode sheet;

[0009] Activate button cell A and button cell B separately;

[0010] S2. Charge and discharge the activated coin cell A in step S1 at a certain rate to obtain the charge and discharge curve and the specific capacity of coin cell A. Calculate the relative specific capacity of each voltage plateau of the pure graphite negative electrode in coin cell A based on the dV / dQ curve of the pure graphite negative electrode.

[0011] S3. Disassemble the coin cell A and perform XRD testing on the pure graphite negative electrode obtained from the disassembly. Based on the obtained XRD pattern, obtain the diffraction peak intensities of each phase of graphite stage4L, stage3L, stage2, stage2L and stage1 in the pure graphite negative electrode. Based on the relationship between the diffraction peak intensities of each phase of graphite and the relative specific capacity of each voltage plateau of the pure graphite negative electrode in the coin cell A obtained in step S2, calculate the specific capacity constants corresponding to each phase of graphite stage4L, stage3L, stage2, stage2L and stage1.

[0012] S4. Charge the coin cell B activated in step S1 to a certain SOC at a certain rate, then disassemble the coin cell B and perform XRD testing on the disassembled silicon-carbon / graphite hybrid negative electrode. Based on the obtained XRD pattern, obtain the diffraction peak intensities of graphite stage4L, stage3L, stage2, stage2L and stage1 in the silicon-carbon / graphite hybrid negative electrode, as well as the specific capacity constants corresponding to graphite stage4L, stage3L, stage2, stage2L and stage1 obtained in step S3. Use the following formula (1) to calculate the specific capacity of graphite and the specific capacity of silicon-carbon in the silicon-carbon / graphite hybrid negative electrode at a certain SOC:

[0013]

[0014] In formula (1), A i B i C i D i E i The XRD diffraction peak intensities of the graphite stage4L, stage3L, stage2, stage2L and stage1 phases in a silicon-carbon / graphite hybrid negative electrode at a certain SOC are shown.

[0015] α, β, γ, δ and ε are the specific capacity constants corresponding to each phase of graphite stage4L, stage3L, stage2, stage2L and stage1, respectively;

[0016] This corresponds to the specific capacity of silicon-carbon in the silicon-carbon / graphite hybrid negative electrode at SOC.

[0017] η i This corresponds to the specific capacity of graphite in the silicon-carbon / graphite hybrid negative electrode at SOC.

[0018] Capacity i This represents the specific capacity of the silicon-carbon / graphite hybrid negative electrode at the corresponding SOC.

[0019] Furthermore, based on the above-mentioned technical solution of the present invention, in step S1, activation includes standing at room temperature for 24±2 hours.

[0020] Furthermore, based on the above-mentioned technical solution of the present invention, in step S2, the coin cell A activated in step S1 is charged and discharged at a rate of 0.1C.

[0021] Furthermore, based on the above-mentioned technical solution of the present invention, in step S3, the pure graphite negative electrode sheet obtained after disassembling the coin cell A is first soaked in solvent, vacuum dried, punched, weighed, and then subjected to XRD testing.

[0022] Furthermore, based on the above-mentioned technical solution of the present invention, in step S3, the relationship between the diffraction peak intensities of each phase of graphite stage4L, stage3L, stage2, stage2L and stage1 in the pure graphite negative electrode sheet and the relative specific capacity of each voltage plateau of the pure graphite negative electrode sheet in the coin cell A obtained in step S2 follows the following formula (2):

[0023] a i × а + b i × β + c i × γ + d i × δ + e i × ε = Capacity g (2);

[0024] In equation (2), a i b i c i d i e i The XRD diffraction peak intensities of the graphite stage4L, stage3L, stage2, stage2L and stage1 phases in a pure graphite anode sheet at 100% SOC are respectively.

[0025] α, β, γ, δ and ε are the specific capacity constants corresponding to each phase of graphite stage4L, stage3L, stage2, stage2L and stage1, respectively;

[0026] Capacity g The specific capacity of a pure graphite anode at 100% SOC.

[0027] Furthermore, based on the above technical solution of the present invention, in step S4, the button cell B activated in step S1 is charged to a certain SOC at a rate of 0.1.

[0028] Furthermore, based on the above-mentioned technical solution of the present invention, in step S4, the silicon-carbon / graphite hybrid negative electrode sheet obtained by disassembling the coin cell B is first soaked in solvent, vacuum dried, punched, weighed, and then subjected to XRD testing.

[0029] Furthermore, based on the above technical solution of the present invention, in steps S2 and S4, the solvent used for soaking includes at least one of dimethyl carbonate, ethylene carbonate, diethyl carbonate, ethylene glycol dimethyl ether or N-methylpyrrolidone.

[0030] And / or, the soaking time is 10-20 minutes.

[0031] Furthermore, based on the above-mentioned technical solution of the present invention, in steps S2 and S4, the temperature of vacuum drying is 85±2℃.

[0032] The second objective of this invention is to provide the application of the above-mentioned method for testing the capacity of silicon-carbon and graphite in a quantified hybrid electrode in the fields of failure analysis or performance testing.

[0033] Compared with the prior art, the technical solution of the present invention has at least the following technical effects:

[0034] (1) This invention provides a method for quantifying the capacity of silicon-carbon and graphite in a hybrid electrode. The method first uses XRD to obtain the diffraction peak intensities of each graphite phase in a pure graphite anode. Based on the relationship between the diffraction peak intensities of each graphite phase and the relative specific capacity of each voltage plateau of the pure graphite anode, the specific capacity constant corresponding to each graphite phase is calculated. Then, the diffraction peak intensities of each graphite phase in the silicon-carbon / graphite hybrid anode are obtained using XRD. Combined with the previously calculated specific capacity constants corresponding to each graphite phase, the actual specific capacity contribution of silicon-carbon and graphite under each SOC condition in the hybrid anode is measured. Based on theoretical calculations, the lithium intercalation amount of the anode material is calculated. This method is applicable to the determination of the specific capacity of silicon-carbon and graphite in silicon-carbon / graphite hybrid electrodes with different silicon doping ratios. The test results are reliable, continuous, and stable, saving testing time.

[0035] (2) The present invention provides the application of the above-mentioned method for testing the capacity of silicon-carbon and graphite in the quantitative hybrid electrode. Given the advantages of the above-mentioned method for testing the capacity of silicon-carbon and graphite in the quantitative hybrid electrode, it has good application prospects in the field of lithium-ion battery failure analysis or performance testing. Attached Figure Description

[0036] Figure 1 The dV / dQ curve of the pure graphite negative electrode sheet in Example 1 of this invention;

[0037] Figure 2This is a diffraction image of graphite in the pure graphite negative electrode sheet of Embodiment 1 of the present invention. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Those skilled in the art should understand that the embodiments described are merely illustrative of the invention and should not be considered as specific limitations thereof. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention. Process parameters not specifically specified in the following embodiments are generally performed under conventional conditions.

[0039] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0040] According to a first aspect of the present invention, a method for testing the capacity of silicon-carbon and graphite in a hybrid electrode is provided, comprising the following steps:

[0041] S1. Provides a coin cell A containing a pure graphite negative electrode sheet, and a coin cell B containing a silicon-carbon / graphite hybrid negative electrode sheet;

[0042] Activate button cell A and button cell B separately;

[0043] S2. Charge and discharge the activated coin cell A in step S1 at a certain rate to obtain the charge and discharge curve and the specific capacity of coin cell A. Calculate the relative specific capacity of each voltage plateau of the pure graphite negative electrode in coin cell A based on the dV / dQ curve of the pure graphite negative electrode in coin cell A.

[0044] S3. Disassemble the coin cell A and perform XRD testing on the obtained pure graphite negative electrode sheet. Based on the obtained XRD pattern, obtain the diffraction peak intensities of each phase of graphite stage4L, stage3L, stage2, stage2L and stage1 in the pure graphite negative electrode sheet. Based on the relationship between the diffraction peak intensities of each phase of graphite and the relative specific capacity of each voltage plateau of the pure graphite negative electrode sheet in the coin cell A obtained in step S2, calculate the specific capacity constants corresponding to each phase of graphite stage4L, stage3L, stage2, stage2L and stage1.

[0045] S4. Charge the coin cell B activated in step S1 to a certain SOC at a certain rate, then disassemble the coin cell B and perform XRD testing on the disassembled silicon-carbon / graphite hybrid negative electrode. Based on the obtained XRD pattern, obtain the diffraction peak intensities of graphite stage4L, stage3L, stage2, stage2L and stage1 in the silicon-carbon / graphite hybrid negative electrode, as well as the specific capacity constants corresponding to graphite stage4L, stage3L, stage2, stage2L and stage1 obtained in step S3. Use the following formula (1) to calculate the specific capacity of graphite and the specific capacity of silicon-carbon in the silicon-carbon / graphite hybrid negative electrode at a certain SOC:

[0046]

[0047] In equation (1), A i B i C i D i E i The XRD diffraction peak intensities are respectively the XRD diffraction peak intensities of the corresponding graphite phases stage4L, stage3L, stage2, stage2L, and stage1 in a silicon-carbon / graphite hybrid negative electrode at a certain SOC.

[0048] α, β, γ, δ and ε are the specific capacity constants corresponding to each phase of graphite stage4L, stage3L, stage2, stage2L and stage1, respectively;

[0049] This corresponds to the specific capacity of silicon-carbon in the silicon-carbon / graphite hybrid negative electrode at SOC.

[0050] η i This corresponds to the specific capacity of graphite in the silicon-carbon / graphite hybrid negative electrode at SOC.

[0051] Capacity i This represents the specific capacity of the silicon-carbon / graphite hybrid negative electrode at the corresponding SOC.

[0052] That is, the specific capacity η of graphite in the silicon-carbon / graphite hybrid negative electrode (hybrid electrode) at a certain SOC. i =A i ×а+B i ×β+C i ×γ+D i ×δ+E i ×ε, the specific capacity of silicon-carbon

[0053] Specifically, in step S1, in order to test the specific capacity of silicon-carbon and graphite in the silicon-carbon / graphite hybrid electrode, the silicon-carbon / graphite hybrid electrode is used as the negative electrode, i.e., a silicon-carbon / graphite hybrid negative electrode sheet, and assembled with the counter electrode lithium sheet to form a coin cell B. At the same time, a pure graphite electrode is used as the negative electrode, i.e., a pure graphite negative electrode sheet, and assembled with the counter electrode lithium sheet to form a coin cell A.

[0054] The activation of coin cells A and B under the same conditions is mainly because in the lithium-ion coin cell manufacturing process, it is necessary to ensure sufficient wetting between the lithium sheet and the negative electrode to guarantee subsequent electrical performance testing.

[0055] In step S2, the coin cell A activated in step S1 is charged and discharged at a certain rate (0.1C). Based on the obtained charge and discharge test curve, the specific capacity (actual specific capacity) of the pure graphite negative electrode of coin cell A can be obtained. The dV / dQ curve of the pure graphite negative electrode of coin cell A is then constructed (specifically, the SOC-OCV curve is constructed based on the negative electrode half-cell of coin cell A, and then the SOC-OCV curve is differentiated to obtain the dV / dQ curve). For a pure graphite negative electrode, there are multiple voltage plateaus. Within the voltage plateau range, the battery specific capacity changes relatively little, which is represented by a characteristic peak on the dV / dQ curve. Based on peak smoothing and curve fitting, the peak spacing (difference) in the dV / dQ curve is calculated. The peak spacing is the relative capacity of the pure graphite negative electrode corresponding to the voltage plateau. Furthermore, based on the fitting of the plateau peak of the dV / dQ curve, in the process of calculating the difference between the two peaks during peak finding, the function fitting method is used to find the difference corresponding to the two peaks. If the result of the function fitting is more accurate and the R value is closer to 1, the fitting result between the peaks is more accurate, and the relative capacity of the corresponding voltage plateau is also more accurate.

[0056] It should be noted that the specific methods for fabricating the SOC-OCV curve and the dV / dQ curve are well known to those skilled in the art and can be fabricated using commonly used methods in the field. For example, the SOC-OCV curve is obtained through the coin cell charge-discharge curve, where the horizontal axis SOC represents the charging capacity / total capacity within the corresponding time period, and OCV represents the voltage value within the corresponding time period; the dV / dQ curve is obtained by differentiating the SOC-OCV curve.

[0057] After graphitization, graphite materials form an ordered layered structure. In the negative electrode material, lithium ions are embedded between the graphite layers to form Li. X C6 (0≤x≤1, theoretical specific capacity can reach 372mAh / g(x=1)). The specific capacity of graphite materials can directly reflect the degree of graphitization of the material. XRD test can reflect the degree of graphitization of graphite materials. Specifically, it reflects the degree of graphitization based on the intensity of the diffraction peaks of stage4L, stage3L, stage2, stage2L and stage1 corresponding to different diffraction angles of XRD.

[0058] Therefore, in step S3, the XRD diffraction peak intensities of each phase of graphite stage4L, stage3L, stage2, stage2L and stage1 in the pure graphite negative electrode sheet are correlated with the relative specific capacity of each voltage plateau of the pure graphite negative electrode sheet of coin cell A obtained in step S2. Using the positive proportional relationship between the two, the specific capacity constants of each phase of graphite stage4L, stage3L, stage2, stage2L and stage1 are calculated.

[0059] In step S4, formula (1) establishes a direct proportional relationship between the specific capacity of silicon-carbon and graphite at a certain SOC and the actual specific capacity of the measured silicon-carbon / graphite hybrid negative electrode.

[0060] The following explains formula (1). When the silicon-carbon / graphite hybrid negative electrode is at different SOCs, for example, when the silicon-carbon / graphite hybrid negative electrode is at 50% SOC and when it is at a non-50% SOC (e.g., 70% SOC), the XRD peak intensities of the graphite phases stage4L, stage3L, stage2, stage2L and stage1 in formula (1) are different. However, the specific capacity constants corresponding to each phase of graphite (calculated from pure graphite negative electrode) remain unchanged. Therefore, the specific capacity of graphite in the silicon-carbon / graphite hybrid negative electrode can be calculated by summing the products of the XRD peak intensities of each phase of graphite and the specific capacity constants. The specific capacity of silicon-carbon in the silicon-carbon / graphite hybrid negative electrode can be calculated by the difference between the actual specific capacity of the silicon-carbon / graphite hybrid negative electrode and the specific capacity of graphite.

[0061] This invention provides a method for quantifying the capacity of silicon-carbon and graphite in a hybrid electrode. The method first uses XRD to obtain the diffraction peak intensities of each graphite phase in a pure graphite anode. Based on the relationship between the diffraction peak intensities of each graphite phase and the relative specific capacity of each voltage plateau of the pure graphite anode, the specific capacity constant corresponding to each graphite phase is calculated. Then, the diffraction peak intensities of each graphite phase in the silicon-carbon / graphite hybrid anode are obtained using XRD. Combined with the previously calculated specific capacity constants corresponding to each graphite phase, the actual specific capacity contribution of silicon-carbon and graphite under each state of charge (SOC) condition in the hybrid anode is calculated. Finally, based on theoretical calculations, the lithium intercalation capacity of the anode material is calculated. This method is applicable to the determination of the capacity of silicon-carbon and graphite in silicon-carbon / graphite hybrid electrodes with different silicon doping ratios. The test results are reliable, continuous, and stable, saving testing time.

[0062] As an optional embodiment of the technical solution of the present invention, in step S1, the silicon-carbon / graphite hybrid electrode includes a current collector and an active material layer located on the surface of the current collector. The active material layer is mainly made of silicon-carbon + graphite, polyacrylic acid (PAA), carbon nanotubes (CNT), Super P (SP) and styrene-butadiene rubber emulsion (SBR) in a certain ratio. The specific ratio can be set according to actual needs. The specific preparation method is no different from the conventional negative electrode material preparation method, except that silicon-carbon material and graphite are mixed during the mixing process.

[0063] As an optional embodiment of the technical solution of the present invention, in step S1, activation includes standing at room temperature for 24±2h, for example, 22h, 23h, 24h, 25h or 26h.

[0064] As an optional embodiment of the technical solution of the present invention, in step S2, the coin cell A activated in step S1 is charged and discharged at a rate of 0.1C, mainly considering that the capacity calculation standard of the coin cell is calculated based on the 0.1C charge and discharge rate of the coin cell.

[0065] As an optional embodiment of the technical solution of the present invention, in step S3, the pure graphite negative electrode sheet obtained after disassembling the coin cell A is first soaked in solvent, vacuum dried, punched, weighed, and then subjected to XRD testing.

[0066] The pure graphite negative electrode obtained from disassembly is soaked in solvent, mainly to remove the electrolyte on the negative electrode and prevent the presence of electrolyte from having an adverse effect on subsequent XRD tests.

[0067] As an optional embodiment of the technical solution of the present invention, in step S3, the relationship between the diffraction peak intensity of each phase of graphite stage4L, stage3L, stage2, stage2L and stage1 in the pure graphite negative electrode sheet and the relative specific capacity of each voltage plateau of the pure graphite negative electrode sheet in the coin cell A obtained in step S2 follows the following formula (2):

[0068] a i × а + b i × β + c i × γ + d i × δ + e i × ε = Capacity g (2)

[0069] In formula (2), a i b i c i d i e iThe XRD diffraction peak intensities of the graphite stage4L, stage3L, stage2, stage2L and stage1 phases in a pure graphite anode sheet at 100% SOC are respectively.

[0070] α, β, γ, δ and ε are the specific capacity constants corresponding to each phase of graphite stage4L, stage3L, stage2, stage2L and stage1, respectively;

[0071] Capacity g The specific capacity of a pure graphite anode at 100% SOC.

[0072] It should be noted that a i ×а、b i ×β、c i ×γ、d i ×δ、e i ×ε respectively correspond to the relative specific capacity of each voltage plateau of the pure graphite negative electrode in coin cell A, and the relative specific capacity of each voltage plateau is obtained through step S2.

[0073] As an optional embodiment of the technical solution of the present invention, in step S4, the button cell B activated in step S1 is charged to a certain SOC at a rate of 0.1C.

[0074] As an optional embodiment of the technical solution of the present invention, in step S4, the silicon-carbon / graphite hybrid negative electrode sheet obtained by disassembling the coin cell B is first soaked in solvent, vacuum dried, punched, weighed, and then subjected to XRD testing.

[0075] Similarly, the purpose of soaking the disassembled silicon-carbon / graphite hybrid negative electrode sheet in solvent in step S4 is the same as in step S2, which is to remove the electrolyte on the negative electrode sheet and prevent the residual electrolyte from having an adverse effect on subsequent XRD tests.

[0076] As an optional embodiment of the technical solution of the present invention, in steps S2 and S4, the solvent used for soaking includes at least one of dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), ethylene glycol dimethyl ether (DME) or N-methylpyrrolidone (NMP), preferably DMC, and the soaking time is 10-20 min, for example, 10 min, 15 min or 20 min.

[0077] As an optional embodiment of the technical solution of the present invention, in steps S2 and S4, the temperature of vacuum drying is 85℃±2℃.

[0078] During the XRD testing in steps S2 and S4, excessively fast scanning speed and excessively low scanning intensity can lead to noise peaks. It is necessary to ensure low-speed scanning across the entire angle. Furthermore, after acquiring the XRD data, fine-tuning is required to ensure a smooth XRD curve. Therefore, the scanning speed range is 0.001°-8° / min, for example, 0.01° / min, 0.1° / min, 0.5° / min, 1° / min, 2° / min, 4° / min, 5° / min, 6° / min, or 8° / min, with 0.1° / min being the preferred speed.

[0079] According to a second aspect of the present invention, a method for quantifying the capacity of silicon-carbon and graphite in a hybrid electrode is also provided for application in the field of battery failure analysis or battery performance testing.

[0080] Given the advantages of the method for testing the capacity of silicon-carbon and graphite in a quantitative hybrid electrode provided by this invention, it has good application prospects in the fields of battery failure analysis or battery performance testing.

[0081] The present invention will now be described in further detail with reference to specific embodiments.

[0082] Example 1

[0083] This embodiment provides a method for testing the capacity of silicon-carbon and graphite in a hybrid electrode, including the following steps:

[0084] S1. Provides a coin cell A with a pure graphite electrode as the negative electrode, and a coin cell B with a silicon-carbon / graphite hybrid electrode as the negative electrode;

[0085] Making button cell A:

[0086] Negative electrode sheet: Artificial graphite, PAA, CNT, SP and SBR are mixed in a mass ratio of 95:3:0.05:0.95:1, and water is added to make a negative electrode slurry. The negative electrode slurry is then coated on both sides of the copper foil surface. The rolled electrode sheet is wiped on one side (since the double-coated electrode sheet is used in the experiment, but only the single-coated electrode sheet is needed in the subsequent test, the negative electrode material layer on one side needs to be wiped off and dried here) to obtain a single-coated negative electrode sheet.

[0087] Counter electrode: Lithium sheet;

[0088] The negative electrode and the counter electrode lithium sheet are assembled in a glove box to obtain coin cell A.

[0089] Making button cell B:

[0090] Except for replacing the artificial graphite in the negative electrode sheet with an equal mass of 5% silicon-doped mixed negative electrode powder (i.e., the mass ratio of artificial graphite to silicon-carbon powder is 95:5), the remaining steps are the same as those for coin cell A.

[0091] Activate button cell A and button cell B by leaving them to stand at room temperature for 24 hours.

[0092] S2. Charge and discharge the activated coin cell A in step S1 at 0.1C to obtain the charge and discharge curve and the capacity of coin cell A (the specific capacity of the pure graphite negative electrode was measured to be 332 mAh / g).

[0093] For pure graphite anodes, there are multiple voltage plateaus. Within these plateaus, the battery capacity changes relatively little, which is represented by a characteristic peak on the dV / dQ curve. Based on the dV / dQ curve of the pure graphite anode in coin cell A, the peaks are smoothed and the curve is fitted. The spacing (difference) between each peak (①, ②, ③, ④) in the dV / dQ curve is calculated. The spacing (difference) between each peak represents the capacity corresponding to each voltage plateau of the pure graphite anode, as shown in Table 1 and... Figure 1 As shown.

[0094] Table 1

[0095]

[0096] Note: Qa represents the total capacity of the negative electrode.

[0097] From Table 1, the capacities of the plateau peaks for pure graphite anode sheets stage4L, stage3L, stage2, stage2L, and stage1 can be calculated to be 0.4620 Ah, 0.1491 Ah, 0.2760 Ah, 1.1502 Ah, and 1.4372 Ah, respectively. Using a coin cell active material mass of 9.93 g, the specific capacity of each plateau peak is obtained by dividing the capacity of each plateau peak by the mass of the active material. (The text then abruptly shifts to a different topic: "Each voltage plateau (based on Li...") + The different stages of graphite embedding and their corresponding relative specific capacities are shown below:

[0098] (C6→LiC36 stage4L)46.53mAh / g;

[0099] (LiC36→LiC27 stage3L)15.02mAh / g;

[0100] (LiC27→LiC18 stage2)27.79mAh / g;

[0101] (LiC18→LiC12 stage2L)115.83mAh / g;

[0102] (LiC12→LiC6 stage1)144.73mAh / g;

[0103] Based on the specific capacity corresponding to each voltage platform, the calculated total specific capacity of the negative electrode is 349.9 mAh / g, which is not much different from the specific capacity of the pure graphite negative electrode of 332 mAh / g obtained above, and is within the acceptable error range.

[0104] S3. Disassemble the button cell A obtained in step S2, soak the pure graphite negative electrode sheet obtained from disassembly in DMC for 15 minutes, dry it under vacuum at 85°C, punch the sheet, and weigh it.

[0105] XRD tests were performed on the pure graphite negative electrode sheet of the disassembled coin cell A. The diffraction peak intensities of each phase of artificial graphite (stage4L, stage3L, stage2, stage2L and stage1) were obtained based on the obtained XRD pattern. Based on the relationship between the diffraction peak intensities of each phase of artificial graphite and the relative specific capacity of each voltage of the pure graphite negative electrode sheet in the coin cell A obtained in step S2, the specific capacity constants (i.e. a, β, γ, δ and ε) corresponding to each phase of artificial graphite were calculated according to formula (2).

[0106] a i × а + b i × β + c i × γ + d i × δ + e i × ε = Capacity g (2);

[0107] Among them, a i b i c i d i e i The peak intensities of the XRD diffraction peaks of each phase of artificial graphite stage4L, stage3L, stage2, stage2L and stage1 in a pure graphite anode sheet at 100% SOC are shown.

[0108] α, β, γ, δ and ε are the specific capacity constants corresponding to each phase of graphite stage4L, stage3L, stage2, stage2L and stage1, respectively;

[0109] Capacity g The specific capacity of a pure graphite anode at 100% SOC can be measured.

[0110] Specifically, with a specific capacity of 332 mAh / g for the pure graphite anode sheet, the peak intensity (height) of its diffraction peaks was calculated by fitting the actual XRD peaks and normalizing them. The XRD peak intensities of each phase (stage4L, stage3L, stage2, stage2L, and stage1) of the artificial graphite in the pure graphite anode sheet at 100% SOC were then calculated: a i =1.312, b i =0.161, c i =4.02, d i =1.14, e i =0.216. Based on the relationship between the relative specific capacities of each voltage plateau of the pure graphite anode sheet (46.53 mAh / g, 15.02 mAh / g, 27.79 mAh / g, 115.83 mAh / g, and 144.73 mAh / g) and the XRD peak intensities of each phase of artificial graphite, the specific capacity constants corresponding to each phase of artificial graphite stage4L, stage3L, stage2, stage2L, and stage1 are calculated as follows: α = 35.4649, β = 93.2919, γ = 6.9129, δ = 101.6052, ε = 531.0185. The diffraction patterns are shown in [reference needed]. Figure 1 .

[0111] S4. Charge the coin cell B activated in step S1 at a rate of 0.1C for 5 hours to 50% SOC. Then disassemble the coin cell B, soak the silicon-carbon / graphite hybrid negative electrode sheet obtained from the disassembly in DMC for 15 minutes, vacuum dry it at 85°C, punch the sheet, and weigh it.

[0112] The obtained silicon-carbon / graphite hybrid negative electrode was subjected to XRD testing. The specific capacity of silicon and carbon in the silicon-carbon / graphite hybrid negative electrode was obtained according to the following formula (1). Specific capacity η of graphite i ;

[0113]

[0114] In equation (1), A i B i C i D i E i The XRD peak intensities are those of each phase of artificial graphite in the silicon-carbon / graphite hybrid negative electrode at 50% SOC: stage4L, stage3L, stage2, stage2L, and stage1.

[0115] α, β, γ, δ and ε are the specific capacity constants corresponding to each phase of artificial graphite stage4L, stage3L, stage2, stage2L and stage1, respectively, and are calculated by step S3;

[0116] The specific capacity of silicon-carbon in a silicon-carbon / graphite hybrid negative electrode at 50% SOC;

[0117] Capacity i The specific capacity of the silicon-carbon / graphite hybrid negative electrode at 50% SOC.

[0118] Specifically, at 50% SOC, the specific capacity of the silicon-carbon / graphite hybrid negative electrode (with 5% silicon doping) is... i The concentration was 380.12 mAh / g. Based on the actual XRD peaks, the peak intensity (height) of the diffraction peaks was calculated by fitting the actual XRD peaks and normalizing them. The XRD peak intensities of each phase of graphite at 50% SOC, namely stage4L, stage3L, stage2, stage2L, and stage1, were then calculated: a i =2.412, b i =0.356, c i =7.81, d i =0.048, e i =0.014, and the specific capacity constants of graphite phases stage4L, stage3L, stage2, stage2L and stage1 calculated according to step S3 are a = 35.4649, β = 93.2919, γ = 6.9129, δ = 101.6052, ε = 531.0185, respectively. The specific capacity η of graphite in the mixed electrode is then calculated. i The specific capacity of silicon-carbon is 184.53 mAh / g. It is 195.59mAh / g.

[0119] The specific capacities of silicon-carbon and graphite in the pure graphite anode sheet and the silicon-carbon / graphite hybrid anode sheet in the examples were compared, and the specific results are shown in Table 2.

[0120] Table 2

[0121]

[0122] Using conventional specific capacity calculation methods, under 5% silicon doping conditions, with a silicon anode specific capacity of 1500 mAh / g at 0.8V and a graphite anode specific capacity of 332 mAh / g, the specific capacity of the hybrid electrode at 100% SOC is 1500×0.05+332×0.95=390.4 mAh / g. The specific capacity of the hybrid electrode at the same 50% SOC is calculated to be 390.4×0.5=195.2 mAh / g.

[0123] According to the data in Table 2, the specific capacity of the hybrid electrode under 5% silicon doping and 50% SOC is calculated to be 195.59×0.05+184.53×0.95=185.083mAh / g using the test method of this invention.

[0124] The testing method provided by this invention is applicable to the determination of the capacity of silicon-carbon and graphite in silicon-carbon / graphite hybrid electrodes with different silicon doping ratios. It can quantify the capacity contribution of silicon-carbon and graphite in the hybrid electrode, providing a good foundation for battery failure analysis or performance testing.

[0125] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention shall be within the scope of protection of the pending claims of the present invention.

Claims

1. A method for testing the capacity of silicon-carbon and graphite in a quantified hybrid electrode, characterized in that, Includes the following steps: S1. Provide a coin cell A containing a pure graphite negative electrode sheet, and a coin cell B containing a silicon-carbon / graphite hybrid negative electrode sheet; Activate button cell A and button cell B separately; S2. Charge and discharge the activated coin cell A in step S1 at a certain rate to obtain the charge and discharge curve and the capacity of coin cell A. Calculate the relative specific capacity of each voltage plateau of the pure graphite negative electrode in coin cell A based on the dV / dQ curve of the pure graphite negative electrode. S3. Disassemble the coin cell A and perform XRD testing on the obtained pure graphite negative electrode sheet. Based on the obtained XRD pattern, obtain the diffraction peak intensities of each phase of graphite stage4L, stage3L, stage2, stage2L and stage1 in the pure graphite negative electrode sheet. Based on the relationship between the diffraction peak intensities of each phase of graphite and the relative specific capacity of each voltage plateau of the pure graphite negative electrode sheet in the coin cell A obtained in step S2, calculate the specific capacity constants corresponding to each phase of graphite stage4L, stage3L, stage2, stage2L and stage1. S4. Charge the coin cell B activated in step S1 to a certain SOC at a certain rate, then disassemble the coin cell B and perform XRD testing on the disassembled silicon-carbon / graphite hybrid negative electrode. Based on the obtained XRD pattern, obtain the diffraction peak intensities of graphite stage4L, stage3L, stage2, stage2L and stage1 in the silicon-carbon / graphite hybrid negative electrode, as well as the specific capacity constants corresponding to graphite stage4L, stage3L, stage2, stage2L and stage1 obtained in step S3. Use the following formula (1) to calculate the specific capacity of graphite and the specific capacity of silicon-carbon in the silicon-carbon / graphite hybrid negative electrode at a certain SOC: A i × a + B i × β + C i × γ + D i × δ + E i × ε + φ i = η i +φ i = Capacity i (1) In formula (1), A i , B i , C i , D i , E i The XRD diffraction peak intensities of the graphite stage4L, stage3L, stage2, stage2L and stage1 phases in a silicon-carbon / graphite hybrid negative electrode at a certain SOC are shown. a , β , γ , δ and ε These are the specific capacity constants corresponding to each phase of graphite stage4L, stage3L, stage2, stage2L, and stage1, respectively. φ i This corresponds to the specific capacity of silicon-carbon in the silicon-carbon / graphite hybrid negative electrode at SOC. η i This corresponds to the specific capacity of graphite in the silicon-carbon / graphite hybrid negative electrode at SOC. Capacity i This corresponds to the specific capacity of the silicon-carbon / graphite hybrid negative electrode at SOC. In step S3, the relationship between the diffraction peak intensities of each phase (stage4L, stage3L, stage2, stage2L, and stage1) of the graphite anode sheet and the relative specific capacity of each voltage plateau of the pure graphite anode sheet in the coin cell A obtained in step S2 follows the following formula (2): a i × a + b i × β + c i × γ + d i × δ + e i × ε = Capacity g （2）； In formula (2), a i , b i , c i , d i , e i The XRD diffraction peak intensities of the graphite stage4L, stage3L, stage2, stage2L and stage1 phases in a pure graphite anode sheet at 100% SOC are respectively. a , β , γ , δ and ε These are the specific capacity constants corresponding to each phase of graphite stage4L, stage3L, stage2, stage2L, and stage1, respectively. Capacity g This represents the specific capacity of a pure graphite anode at 100% SOC.

2. The test method according to claim 1, characterized in that, In step S1, activation includes standing at room temperature for 24±2 hours.

3. The test method according to claim 1, characterized in that, In step S2, the coin cell A activated in step S1 is charged and discharged at a rate of 0.1C.

4. The test method according to claim 1, characterized in that, In step S3, the pure graphite negative electrode sheet obtained after disassembling the coin cell A is first soaked in solvent, vacuum dried, punched, weighed, and then subjected to XRD testing.

5. The test method according to claim 1, characterized in that, In step S4, the coin cell B activated in step S1 is charged to a certain SOC at a rate of 0.

1.

6. The test method according to claim 1, characterized in that, In step S4, the silicon-carbon / graphite hybrid negative electrode sheet obtained from disassembling the coin cell B is first soaked in solvent, vacuum dried, punched, weighed, and then subjected to XRD testing.

7. The test method according to claim 4 or 6, characterized in that, In steps S2 and S4, the solvent used for soaking includes at least one of dimethyl carbonate, ethylene carbonate, diethyl carbonate, ethylene glycol dimethyl ether, or N-methylpyrrolidone. And / or, the soaking time is 10-20 minutes.

8. The test method according to claim 4 or 6, characterized in that, In steps S2 and S4, the vacuum drying temperature is 85±2℃. 。 9. The application of the method for testing the capacity of silicon-carbon and graphite in a quantitative hybrid electrode according to any one of claims 1-8 in the field of battery failure analysis or battery performance testing.

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