Method for measuring effective discharge specific capacity of negative active material in total battery

Abstract

The invention provides a method for determining the effective discharge specific capacity of a negative electrode active material in a full battery. The method comprises the following steps: testing to obtain the charge specific capacity C0 of the negative electrode active material in a half battery; the conversion coefficient is preset to be P, and the estimated specific discharge capacity C estimated 0 of the negative electrode active material in the whole battery is obtained; when the preset N / P value is less than 1, manufacturing a first total battery by using the positive pole piece and the negative pole piece; presetting a pre-estimated discharge specific capacity gradient sequence of the negative active material in the first total battery by taking the C pre-estimated 0 as a central value, and calculating a corresponding pre-estimated discharge specific capacity gradient sequence of the negative active material in the first total battery; taking the estimated discharge capacity in the estimated discharge capacity gradient sequence of the negative electrode active material in the first total battery as the charging cut-off capacity, and carrying out a full charge test on the first total battery; and determining the effective specific discharge capacity of the negative electrode active material in the total battery from the estimated specific discharge capacity of the negative electrode active material in the first total battery according to the metal precipitation condition of the negative electrode interface.

Description

Technical Field

[0001] This invention relates to the field of full-cell active material specific capacity measurement technology, specifically, to a method for measuring the effective discharge specific capacity of the negative electrode active material in a full cell. Background Technology

[0002] Lithium-ion batteries, as advanced rechargeable secondary batteries, have been widely used in various fields of new energy. However, lithium-ion batteries still face problems such as safety hazards, large fluctuations in the price of raw material lithium carbonate, and a global shortage of lithium resources. In the era of "beyond lithium-ion batteries," rechargeable sodium-ion batteries have become an important energy storage technology due to their advantages such as high sodium abundance, wide distribution of sodium resources, and low raw material costs. Moreover, sodium-ion batteries have better rate capability and low-temperature discharge performance than lithium-ion batteries, giving them a greater competitive advantage in high-latitude regions and special applications.

[0003] Currently, hard carbon is the commonly used negative electrode active material in sodium-ion batteries. Hard carbon has a disordered internal crystal arrangement and abundant porosity; its interlayer spaces, closed micropores, and surface defect sites can all provide storage space for sodium ions, thus making it a highly promising negative electrode active material for sodium-ion batteries. However, the effective specific capacity of hard carbon is limited by various factors, including sodium insertion / extraction mechanisms. In traditional coin cells, it is difficult to accurately measure the effective specific capacity of the negative electrode active material in the entire cell. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this application provides a method for determining the effective discharge specific capacity of the negative electrode active material in a full battery.

[0005] This application discloses a method for determining the effective discharge specific capacity of the negative electrode active material in a full battery, comprising the following steps: S1: The first negative electrode sheet is prepared using the negative electrode active material, a half cell is made using the first negative electrode sheet, and the charge specific capacity C0 of the negative electrode active material in the half cell is tested. S2: Set the conversion coefficient to P and obtain the estimated discharge specific capacity C of the negative electrode active material in the full cell. 预估0 , P = 0.8~1.0; S3: A second negative electrode is prepared using a negative electrode active material, with a preset N / P value < 1. A first positive electrode is prepared using a positive electrode active material according to the N / P value. A first full cell is made using the first positive electrode and the second negative electrode. S4: With C 预估0 The estimated discharge specific capacity gradient sequence of the negative electrode active material in the first full cell is preset with the center value, and the corresponding estimated discharge capacity gradient sequence of the negative electrode active material in the first full cell is calculated. S5: Take the estimated discharge capacity in the estimated discharge capacity gradient sequence of the negative electrode active material in the first full cell as the charging cutoff capacity, and perform a full charge test on the first full cell. S6: Disassemble the first full cell separately, and based on the metal precipitation at the negative electrode interface of each first full cell, determine the effective discharge specific capacity of the negative electrode active material in the full cell from the estimated discharge specific capacity of the negative electrode active material in the corresponding first full cell.

[0006] Preferably, step S1 includes the following sub-steps: The mass percentage of negative active material in the negative active material layer of the first negative electrode is preset to be B. 负0 ; The first negative electrode sheet was prepared using a negative electrode active material; Obtain the mass of the negative electrode active material layer in the first negative electrode plate; According to the formula: Mass of negative electrode active material = Mass of negative electrode active material layer × Mass ratio of negative electrode active material, the mass of negative electrode active material of the first negative electrode sheet can be calculated. A half-cell is made using the first negative electrode plate; Perform a charging test on the half-cell and record the charging capacity of the half-cell. According to the formula: specific charge capacity of negative electrode active material = charge capacity ÷ mass of negative electrode active material, the specific charge capacity C0 of the negative electrode active material in the half cell can be calculated.

[0007] Preferably, after the step of making a half-cell using the first negative electrode, the following steps are also included: The half-cell was placed in an environment of 40℃~50℃.

[0008] Preferably, the step of performing a charging test on the half-cell and recording the charging capacity of the half-cell includes the following sub-steps: After discharging the half-cell to 0V at a constant current with the first discharge rate, it is left to stand. After discharging the half-cell to 0V at a constant current using the second discharge rate, it is left to stand. After discharging the half-cell to 0V at a constant current rate of the third discharge rate, it is left to stand. After the half-cell is charged at a constant current at a first charging rate to the first cutoff voltage, it is left to stand. After repeating the above steps multiple times, record the charging capacity of the last constant current charge. Among them, the first discharge rate > the second discharge rate > the third discharge rate, and the first charge rate ≤ the first discharge rate.

[0009] Preferably, step S3 includes the following sub-steps: The mass percentage of negative electrode active material in the negative electrode active material layer of the second negative electrode is preset to be B.负1 ; The second negative electrode sheet was prepared using a negative electrode active material; The surface density of the coating on the second negative electrode was measured to be ρ. 负1 ; The mass percentage of the positive active material in the positive active material layer of the first positive electrode is preset to be B. 正1 ; The discharge specific capacity of the positive electrode active material in the full cell is C. 正 ; The default N / P value is <1, according to the formula The coating surface density ρ of the first positive electrode was calculated. 正1 ; According to B 正1 and ρ 正1 The first positive electrode sheet was prepared using a positive electrode active material; A first full cell was made using the first positive electrode and the second negative electrode.

[0010] Preferably, the discharge specific capacity of the positive electrode active material in the full cell is C. 正 The steps include the following sub-steps: The mass percentage of the positive active material in the positive active material layer of the second positive electrode is preset to be B. 正2 ; The second positive electrode sheet was prepared using a positive electrode active material; Obtain the mass of the positive electrode active material layer in the second positive electrode plate; According to the formula: Mass of positive electrode active material = Mass of positive electrode active material layer × Mass ratio of positive electrode active material, the mass of positive electrode active material of the second positive electrode sheet can be calculated. A second full cell with an N / P value > 1 is made using a second positive electrode and a third negative electrode. The second full cell was subjected to a discharge test, and its discharge capacity was recorded. Based on the formula: Discharge specific capacity of positive electrode active material = Discharge capacity ÷ Mass of positive electrode active material, the discharge specific capacity C of the positive electrode active material in the full cell can be calculated. 正 .

[0011] Preferably, after the step of fabricating a first full cell using the first positive electrode and the second negative electrode, the method further includes the step of forming and charging the first full cell separately: The first full battery is charged at a constant current rate of the second charging rate and then left to stand. The first full battery was charged at a constant current rate of the third charging rate and then left to stand. The first full battery was charged at a constant current rate of the fourth charging rate and then left to stand. Among them, the second charging rate < the third charging rate < the fourth charging rate.

[0012] Preferably, before the step of preparing the second negative electrode sheet using the negative electrode active material, the mass percentage of the negative electrode active material in the negative electrode active material layer of the second negative electrode sheet is preset to be B. 负1 ; After the step of preparing the second negative electrode sheet using the negative electrode active material, the mass of the negative electrode active material layer in the second negative electrode sheet is obtained. According to the formula: Mass of negative electrode active material = Mass of negative electrode active material layer × Mass ratio of negative electrode active material, the mass of negative electrode active material of the second negative electrode sheet can be calculated. Step S4 includes the following sub-steps: With C 预估0 An arithmetic sequence with odd-numbered terms is pre-defined for the arithmetic mean, and is used as the estimated discharge specific capacity gradient sequence for the negative electrode active material in the first full cell; According to the formula: Estimated discharge capacity of negative electrode active material in the first full cell = Estimated discharge specific capacity of negative electrode active material in the first full cell × Mass of negative electrode active material of the second negative electrode, the corresponding gradient series of estimated discharge capacity of negative electrode active material in the first full cell can be calculated.

[0013] Preferably, before step S5, the process further includes a step of cycling the first full battery through charge and discharge cycles: The estimated discharge capacity in the gradient series of the estimated discharge capacity of the negative electrode active material in the first full cell is used as the charging cutoff capacity. The first full cell is charged at a constant current of the fifth charging rate to the charging cutoff capacity and then left to stand. The first full cell was discharged at a constant current at the fourth discharge rate to the second cutoff voltage and then left to stand. Repeat the above steps multiple times.

[0014] Preferably, the step of determining the effective discharge specific capacity of the negative electrode active material in the full cell from the estimated discharge specific capacity of the negative electrode active material in the corresponding first full cell, based on the metal deposition at the negative electrode interface of each first full cell, includes the following sub-steps: Observe the surface of the negative electrode active material layer of each first full cell to determine whether metal has been deposited at the negative electrode interface of each first full cell, and screen out the first full cells that have not been deposited with metal. Among all the first full cells without metal deposition, the one with the largest estimated discharge specific capacity of the negative electrode active material in the corresponding first full cell is selected as the effective discharge specific capacity of the negative electrode active material in the full cell.

[0015] The beneficial effects of this application are as follows: This application first obtains the charge specific capacity C0 of the negative electrode active material under ideal conditions through half-cell testing, and then reduces it to the estimated discharge specific capacity C more closely related to the actual application scenario of a full battery through the conversion factor P. 预估0 Using this as the center value, a gradient sequence of the estimated discharge specific capacity of the negative electrode active material in a small number of first full cells is set, and the corresponding estimated discharge capacity gradient sequence of the negative electrode active material in the first full cell is calculated. At the same time, by pre-designing and manufacturing a first full cell with an N / P value of less than 1, the negative electrode capacity is ensured to be the limiting factor. Combined with a charging strategy that uses the estimated discharge capacity as the charging cutoff capacity, only a small number of first full cells need to be fully charged and disassembled. By visually observing the metal precipitation state at the negative electrode interface, the effective discharge specific capacity of the negative electrode active material in the full cell system can be accurately and quickly determined from the estimated discharge specific capacity of the negative electrode active material in the corresponding first full cell.

[0016] This application is applicable not only to sodium-ion full batteries of different systems, but also to other alkali metal-ion batteries such as lithium-ion batteries. Furthermore, it is applicable not only to hard carbon anode active materials, but also to the selection of materials such as cathode, anode, separator, and electrolyte, making it suitable for a wide range of applications. This application significantly reduces the number of experiments required; the effective discharge specific capacity of the anode active material in the full battery can be determined in less than five full-charge tests and disassemblies of the first full battery, making it simple, quick, and cost-effective. Attached Figure Description

[0017] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings: Figure 1 This is a flowchart illustrating the method for determining the effective discharge specific capacity of the negative electrode active material in the full cell in the examples; Figure 2 The estimated discharge specific capacity of the negative electrode active material in the example is C. 预估-6 A diagram showing sodium deposition after the first full cell was disassembled; Figure 3 The estimated discharge specific capacity of the negative electrode active material in the example is C. 预估-3 A diagram showing sodium deposition after the first full cell was disassembled; Figure 4 The estimated discharge specific capacity of the negative electrode active material in the example is C. 预估0 A diagram showing sodium deposition after the first full cell was disassembled; Figure 5 The estimated discharge specific capacity of the negative electrode active material in the example is C. 预估+3 A diagram showing sodium deposition after the first full cell was disassembled; Figure 6 The estimated discharge specific capacity of the negative electrode active material in the example is C. 预估+6 The sodium deposition situation after the first full cell was disassembled. Detailed Implementation

[0018] The following drawings disclose several embodiments of this application. For clarity, many practical details will be described in the following description. However, it should be understood that these practical details should not be used to limit this application. That is, in some embodiments of this application, these practical details are not essential.

[0019] Furthermore, the use of terms such as "first" and "second" in this application is for descriptive purposes only and does not specifically refer to any order or sequence, nor is it intended to limit this application. They are merely used to distinguish components or operations described using the same technical terms and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the technical solutions of various embodiments can be combined with each other, but only if they are feasible for those skilled in the art. If a combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed in this application.

[0020] To further understand the content, features, and effects of this application, the following embodiments are provided, and detailed descriptions are given in conjunction with the accompanying drawings.

[0021] Reference Figure 1 , Figure 1 This is a flowchart illustrating the method for determining the effective discharge specific capacity of the negative electrode active material in a full cell in this embodiment. The method for determining the effective discharge specific capacity of the negative electrode active material in a full cell in this embodiment includes the following steps: S1: The first negative electrode is prepared using the negative electrode active material. A half-cell is made using the first negative electrode, and the charge specific capacity C0 of the negative electrode active material in the half-cell is tested.

[0022] Preferably, step S1 includes the following sub-steps: S11: The mass percentage of negative active material in the negative active material layer of the first negative electrode sheet is preset to be B. 负0 In this specific application, the negative electrode active material is hard carbon. The negative electrode active material layer is formed on the surface of the negative electrode foil by coating, rolling, and baking of the negative electrode slurry. The negative electrode slurry is made by uniformly stirring hard carbon, conductive agent, and binder in N-methylpyrrolidone solvent. The mass percentage of hard carbon in the negative electrode slurry (i.e., hard carbon, conductive agent, and binder) is B.负0 =95%.

[0023] S12: The first negative electrode sheet is prepared using a negative electrode active material. In specific applications, hard carbon (B) is used. 负0 =95%), conductive agent and binder are uniformly stirred with N-methylpyrrolidone solvent to prepare negative electrode slurry. Then, the negative electrode slurry is prepared into negative electrode sheet through steps such as coating, rolling and baking. Finally, the first negative electrode sheet for assembling coin cell is cut from the negative electrode sheet.

[0024] S13: Obtain the mass of the negative electrode active material layer in the first negative electrode sheet. In specific applications, weigh the total mass of the first negative electrode sheet, and subtract the mass of the negative electrode foil material corresponding to the area of ​​the first negative electrode sheet. The difference obtained is the mass of the negative electrode active material layer in the first negative electrode sheet.

[0025] S14: Calculate the mass of the negative electrode active material in the first negative electrode sheet according to the formula: Mass of negative electrode active material = Mass of negative electrode active material layer × Mass percentage of negative electrode active material. In specific applications, the mass of the negative electrode active material layer in the first negative electrode sheet obtained through step S13 and the mass percentage of negative electrode active material B obtained through step S11 are used. 负0 The mass of the negative electrode active material of the first negative electrode sheet can then be calculated.

[0026] S15: Fabricate a half-cell using the first negative electrode sheet. In specific applications, the first negative electrode sheet obtained in step S12 is assembled and sealed with a glass fiber separator, nickel foam, electrolyte, and sodium sheet to form a button cell. Specifically, in this embodiment, the first negative electrode sheet is a hard carbon negative electrode sheet, and the half-cell is a sodium-ion button cell. Of course, in other embodiments, other materials can be used for the first negative electrode sheet or a lithium-ion button cell can be fabricated; this is not limited here.

[0027] S16: Place the half-cell at 40℃~50℃. In specific applications, place the half-cell obtained in step S15 at 45℃ for 8 hours to accelerate the internal chemical stability of the half-cell after assembly.

[0028] S17: Perform a charging test on the half-cell and record its charging capacity. In practical applications, the half-cell, after being left to rest in step S16, is charged at 25°C.

[0029] Specifically, step S17 includes the following sub-steps: S171: After discharging the half-cell to 0V at a constant current using the first discharge rate, it is then left to rest.

[0030] S172: After discharging the half-cell to 0V at a constant current using the second discharge rate, it is then left to rest.

[0031] S173: After discharging the half-cell to 0V at a constant current using the third discharge rate, it is then left to rest.

[0032] S174: After the half-cell is charged at a constant current at the first charging rate to the first cutoff voltage, it is placed aside.

[0033] S175: After repeating steps S171 to S174 multiple times, record the charging capacity of constant current charging in the last step S174.

[0034] In this embodiment, the first discharge rate is greater than the second discharge rate, the second discharge rate is greater than the third discharge rate, and the first charge rate is less than or equal to the first discharge rate. The half-cell exhibits significant polarization during charging, thus requiring a smaller charging current. Specifically, in this application, the first discharge rate is 0.1C, the second discharge rate is 0.01C, the third discharge rate is 0.002C, the first charge rate is 0.1C, the first cutoff voltage is 2V, the resting time is 10 minutes, C is the design capacity of the half-cell, and steps S171 to S174 are repeated three times. Discharging to 0V at different rates and repeating three times eliminates internal polarization of the half-cell and fully activates its ion channels.

[0035] S18: According to the formula: specific charge capacity of negative electrode active material = charge capacity ÷ mass of negative electrode active material, the specific charge capacity C0 of the negative electrode active material in the half-cell is calculated. Specifically, in this embodiment, the specific charge capacity C0 of the negative electrode active material in the half-cell is 322.5 mAh / g.

[0036] S2: Set the conversion coefficient to P and obtain the estimated discharge specific capacity C of the negative electrode active material in the full cell. 预估0 , P = 0.8~1.0. In practical applications, since the first negative electrode in the half-cell obtained in step S15 faces the sodium metal plate, the negative electrode active material desodiums during charging of the half-cell, while in the full cell, the negative electrode active material desodiums during discharging. Therefore, the charging specific capacity of the negative electrode active material in the half-cell numerically corresponds to the estimated discharging specific capacity of the negative electrode active material in the full cell. Moreover, the charging specific capacity C0 of the negative electrode active material obtained from the charging test of the half-cell is measured under the condition that the first negative electrode is facing the sodium plate, which is close to the theoretical upper limit of the specific capacity of the negative electrode active material. However, in the full cell, the effective specific capacity of the negative electrode active material is lower than this upper limit. Therefore, by setting the conversion coefficient P to reduce the charging specific capacity C0 of the negative electrode active material in the half-cell, the estimated discharging specific capacity C of the negative electrode active material in the full cell, which is closer to the actual application scenario of the full cell, is obtained. 预估0 In this embodiment, the conversion coefficient P is set to 0.8, and C... 预估0=322.5mAh / g × 0.8 = 258mAh / g. Of course, the conversion factor P can also be adjusted to other values.

[0037] S3: A second negative electrode is prepared using a negative electrode active material, with a preset N / P value < 1. A first positive electrode is prepared using a positive electrode active material based on the N / P value. A first full cell is then constructed using the first positive electrode and the second negative electrode. In specific applications, the N / P value is the ratio of the negative electrode capacity to the positive electrode capacity. Setting the N / P value to less than 1 ensures that the usable capacity of the negative electrode active material in the first full cell is less than the available capacity of the positive electrode active material. After a full-charge test of the first full cell, if metal is deposited at the negative electrode interface, it can be directly attributed to insufficient effective capacity of the negative electrode active material, eliminating interference from positive electrode capacity limitations, thus fully verifying the effective capacity of the negative electrode active material. In this embodiment, the preset N / P value is 0.8.

[0038] Preferably, step S3 includes the following sub-steps: S31: The mass percentage of negative active material in the negative active material layer of the second negative electrode is preset to be B. 负1 In specific applications, this embodiment uses the same negative electrode slurry formulation as in step S11, with the mass of hard carbon accounting for B% of the total mass of all solid components (i.e., hard carbon, conductive agent, and binder) in the negative electrode slurry. 负1 =95%.

[0039] S32: Prepare a second negative electrode sheet using the negative electrode active material. In specific applications, a second negative electrode sheet of a specified area is cut from the negative electrode sheet obtained in step S12.

[0040] S33: Obtain the mass of the negative electrode active material layer in the second negative electrode sheet, and determine the coating surface density of the second negative electrode sheet as ρ. 负1 The mass of the negative electrode active material in the second negative electrode sheet is obtained. In practical applications, the total mass of the second negative electrode sheet is weighed and the mass of the corresponding area of ​​the negative electrode foil is subtracted to obtain the mass of the negative electrode active material layer in the second negative electrode sheet. The mass of the negative electrode active material layer in the second negative electrode sheet is divided by the area of ​​the second negative electrode sheet to calculate the mass of the negative electrode active material layer per unit area, which is the coating surface density ρ. 负1 According to the formula: Mass of negative electrode active material = Mass of negative electrode active material layer × Mass ratio of negative electrode active material, the mass of negative electrode active material of the second negative electrode sheet can be calculated.

[0041] S34: The mass percentage of the positive active material in the positive active material layer of the first positive electrode is preset to be B. 正1In practical applications, the positive electrode active material layer is formed on the surface of the positive electrode foil through steps such as coating, rolling, and baking of the positive electrode slurry. The positive electrode slurry is made by uniformly stirring the positive electrode active material, conductive agent, and binder with a solvent. The mass percentage of the positive electrode active material is B. 正1 This refers to the percentage of the positive electrode active material in the positive electrode slurry by the total mass of all solid components (positive electrode active material, conductive agent, binder). In this embodiment, B... 正1 It is 95%.

[0042] S35: Obtain the discharge specific capacity of the positive electrode active material in the full cell as C. 正 In practical applications, the discharge specific capacity C of the positive electrode active material in a full battery... 正 It is determined by the positive electrode active material used.

[0043] Preferably, step S35 includes the following sub-steps: S351: The mass percentage of the positive active material in the positive active material layer of the second positive electrode is preset to be B. 正2 In specific applications, this embodiment uses the same positive electrode slurry ratio as in step S34, B 正2 With B 正1 The figures are the same, both at 95%.

[0044] S352: A second positive electrode sheet is prepared using a positive active material. In specific applications, the positive active material, conductive agent, binder and solvent are mixed to form a positive slurry, and a positive electrode sheet is prepared through steps such as coating, rolling and baking. Finally, a second positive electrode sheet of a specified area is cut from the positive electrode sheet.

[0045] S353: Obtain the mass of the positive electrode active material layer in the second positive electrode sheet. In practical applications, weigh the total mass of the second positive electrode sheet and subtract the mass of the corresponding area of ​​the positive electrode foil; the difference is the mass of the positive electrode active material layer.

[0046] S354: Calculate the mass of the positive electrode active material in the second positive electrode sheet according to the formula: Mass of positive electrode active material = Mass of positive electrode active material layer × Mass percentage of positive electrode active material. In specific applications, the mass of the positive electrode active material layer obtained through step S353 and the mass percentage B of the positive electrode active material in step S351 are used. 正2 The mass of the positive active material of the second positive electrode can then be calculated.

[0047] S355: Construct a second full cell with an N / P value > 1 using a second positive electrode and a third negative electrode. In practical applications, the second positive electrode prepared in step S352 is paired with a third negative electrode of known sufficient capacity to assemble a second full cell, ensuring that the N / P value is greater than 1. The purpose is to make the positive electrode capacity the only capacity limiting factor of the second full cell, so as to test the effective discharge capacity of the positive electrode active material.

[0048] S356: Perform a discharge test on the second full cell and record its discharge capacity. In specific applications, the second full cell assembled in step S355 is subjected to constant current discharge at a rate of 0.5C to the cutoff voltage at 25°C, and the total capacity released during the discharge process is recorded.

[0049] S357: Based on the formula: Discharge specific capacity of positive electrode active material = Discharge capacity ÷ Mass of positive electrode active material, the discharge specific capacity C of the positive electrode active material in the full cell can be calculated. 正 Specifically, in this embodiment, C 正 =92mAh / g.

[0050] S36: Preset N / P value < 1, according to the formula The coating surface density ρ of the first positive electrode was calculated. 正1 In practical applications, based on the preset N / P value (0.8) and the estimated discharge specific capacity C of the negative electrode active material in the full cell obtained in step S2, 预估0 (258mAh / g), the mass percentage of negative electrode active material in the second negative electrode sheet preset in step S31, B 负1 (95%), the coating surface density ρ of the second negative electrode sheet determined in step S33. 负1 The discharge specific capacity C of the positive electrode active material obtained in step S35 正 (92mAh / g) and the mass percentage B of the positive active material of the first positive electrode sheet preset in step S34. 正1 (95%), according to the formula The coating surface density ρ of the first positive electrode was derived and calculated. 正1 .

[0051] S37: According to B 正1 and ρ 正1 The first positive electrode sheet is prepared using a positive electrode active material. In specific applications, the mass ratio B of the positive electrode active material is preset according to step S34. 正1 (95%), and the coating surface density ρ calculated in step S36. 正1The positive electrode active material, conductive agent, binder and solvent are mixed to form a positive electrode slurry. Then, positive electrode sheets that meet the design requirements are prepared through steps such as coating, rolling and baking. Finally, the first positive electrode sheet of a specified area is cut from the positive electrode sheet.

[0052] S38: A first full cell is fabricated using the first positive electrode and the second negative electrode. In specific applications, the second negative electrode prepared in step S32 and the first positive electrode prepared in step S37 are combined with electrolyte, separator, and other materials to form a first full cell. In this embodiment, the number of first full cells is 5, and the design capacity C of the first full cell is 1 Ah.

[0053] S39: Form and charge the first full cell separately. In specific applications, the first full cells obtained in step S38 are charged and formed separately at 25℃~45℃ to ensure that the first full cells have good SEI film formation effect.

[0054] Preferably, step S39 includes the following sub-steps: S391: After charging the first full battery at a constant current rate with the second charging rate, it is placed aside.

[0055] S392: After charging the first full battery at a constant current rate of the third charging rate, it is placed on standby.

[0056] S393: After charging the first full cell at a constant current rate of the fourth charging rate, it is placed on standby.

[0057] Wherein, the second charging rate < the third charging rate < the fourth charging rate. In specific applications, in this embodiment, the second charging rate is 0.02C, the third charging rate is 0.05C, and the fourth charging rate is 0.1C, with corresponding constant current charging times of 30min, 30min, and 60min, and corresponding resting times of 5min, 5min, and 8h, respectively.

[0058] S4: With C 预估0 The estimated discharge specific capacity gradient sequence of the negative electrode active material in the first full cell is preset with the center value, and the corresponding estimated discharge capacity gradient sequence of the negative electrode active material in the first full cell is calculated.

[0059] Preferably, step S4 includes the following sub-steps: S41: With C 预估0 An arithmetic progression with an odd number of terms is pre-defined for the arithmetic mean, and this progression serves as the estimated discharge specific capacity gradient sequence for the negative electrode active material in the first full cell. In practical application, the estimated discharge specific capacity gradient sequence for the negative electrode active material in the first full cell is defined by C... 预估0 Let C be an arithmetic sequence with n as the arithmetic mean, n as the common difference, and 2x+1 terms. Let C be the first set of full cells. 预估-xn..., C 预估-2n C 预估-n C 预估0 C 预估+n C 预估+2n ..., C 预估+xn In this embodiment, the number of first full cells is five, that is, 2x+1=5, n=3. Therefore, the estimated discharge specific capacity gradient sequence of the negative electrode active material in the first full cell of this embodiment is C. 预估-6 C 预估-3 C 预估0 C 预估+3 C 预估+6 These correspond to 252mAh / g, 255mAh / g, 258mAh / g, 261mAh / g, and 264mAh / g, respectively. Of course, in other embodiments, the number of the first full-cell batteries can be set according to actual needs.

[0060] S42: According to the formula: Estimated discharge capacity of the negative electrode active material in the first full cell = Estimated discharge specific capacity of the negative electrode active material in the first full cell × Mass of the negative electrode active material of the second negative electrode, the corresponding gradient sequence of the estimated discharge capacity of the negative electrode active material in the first full cell can be calculated. In specific applications, the gradient sequence of the estimated discharge capacity of the negative electrode active material in the first full cell is recorded as Q. 预估-xn ... Q 预估-2n Q 预估-n Q 预估0 Q 预估+n Q 预估+2n ... Q 预估+xn Specifically, in this embodiment, the estimated discharge capacity gradient sequence of the negative electrode active material in the first full cell is recorded as Q. 预估-6 Q 预估-3 Q 预估0 Q 预估+3 Q 预估+6 .

[0061] Preferably, step S4a further includes a step of cyclically charging and discharging the first full battery before step S5, wherein step S4a includes the following sub-steps: S4a1: The estimated discharge capacity in the estimated discharge capacity gradient series of the negative electrode active material in the first full cell is used as the charging cutoff capacity. The first full cell is charged at a constant current rate of the fifth charging rate to the charging cutoff capacity and then left to rest. In this specific application, the fifth charging rate is 0.5C. During charging, the estimated discharge capacity in the estimated discharge capacity gradient series of the negative electrode active material in the first full cell calculated in step S42 is used as the charging cutoff capacity for constant current charging of the first full cell. After charging is completed, the cell is left to rest for 5 minutes.

[0062] S4a2: The first full cell is discharged at a constant current rate of the fourth discharge rate to the second cutoff voltage and then left to stand. In this specific application, the fourth discharge rate is 0.5C, the second cutoff voltage is 1.5V, the first full cell is discharged at a constant current rate of 0.5C to 1.5V and then stopped, and left to stand for 5 minutes.

[0063] S4a3: The above steps are repeated multiple times. In specific applications, steps S4a1 and S4a2 are sequentially repeated 4 times at 25°C. The purpose of multiple charge-discharge cycles is to fully verify the ability of the negative electrode active material to accept sodium ions, increase reliability, eliminate the influence of previous SEI film repair and reforming, eliminate internal electrochemical side reactions, and increase charge-discharge stability. Of course, in other embodiments, the number of cycles can be 2, 3, or other times, which is not limited here.

[0064] S5: Using the estimated discharge capacity from the gradient series of estimated discharge capacity of the negative electrode active material in the first full cell as the charging cutoff capacity, a full charge test is performed on the first full cell. In specific applications, after completing multiple charge-discharge cycles in step S4a3, a full charge test is performed on the first full cell in step S5. The charging steps are consistent with those in step S4a1, i.e., constant current charging at a rate of 0.5C. The charging cutoff capacity is also the estimated discharge capacity from the gradient series of estimated discharge capacity of the corresponding negative electrode active material in the first full cell. After charging, the cell is left to stand for 5 minutes to allow it to stabilize. It is understandable that when the charging capacity of the first full cell exceeds the effective capacity of the negative electrode active material, excess sodium ions will be extracted from the first positive electrode. Since the second negative electrode is not designed to accommodate these excess sodium ions, sodium deposition will occur at the negative electrode interface of the second negative electrode.

[0065] S6: Disassemble each of the first full cells and, based on the metal deposition at the negative electrode interface of each first full cell, determine the effective discharge specific capacity of the negative electrode active material in the full cell from the estimated discharge specific capacity of the negative electrode active material in the corresponding first full cell. In specific applications, disassemble a group of first full cells after the test in step S5, and observe the negative electrode surface of each first full cell to determine whether there is sodium metal deposition at the negative electrode interface under the estimated discharge specific capacity of the negative electrode active material in different first full cells. When charging the first full cell, if the set charging cutoff capacity (i.e., the estimated discharge capacity) exceeds the effective capacity of the negative electrode active material in the first full cell, the excess sodium ions released from the positive electrode active material cannot be effectively accommodated by the negative electrode active material, thus causing sodium metal deposition at the negative electrode interface. After disassembly, if no sodium deposition is observed at the negative electrode interface of a certain first full cell, it indicates that its corresponding estimated discharge specific capacity has not yet exceeded the effective discharge specific capacity of the negative electrode active material in the full cell; if sodium deposition is observed at the negative electrode interface, it indicates that its corresponding estimated discharge specific capacity has exceeded the effective discharge specific capacity of the negative electrode active material in the full cell.

[0066] Reference Figures 2-6 , Figure 2 The estimated discharge specific capacity of the negative electrode active material in the example is C. 预估-6 The sodium deposition situation after the first full cell was disassembled. Figure 3 The estimated discharge specific capacity of the negative electrode active material in the example is C. 预估-3 The sodium deposition situation after the first full cell was disassembled. Figure 4 The estimated discharge specific capacity of the negative electrode active material in the example is C. 预估0 The sodium deposition situation after the first full cell was disassembled. Figure 5 The estimated discharge specific capacity of the negative electrode active material in the example is C. 预估+3 The sodium deposition situation after the first full cell was disassembled. Figure 6 The estimated discharge specific capacity of the negative electrode active material in the example is C. 预估+6 The sodium deposition situation after the first full cell was disassembled.

[0067] Preferably, the step of determining the effective discharge specific capacity of the negative electrode active material in the full cell from the estimated discharge specific capacity of the negative electrode active material in the corresponding first full cell, based on the metal deposition at the negative electrode interface of each first full cell, includes the following sub-steps: S6a: Observe the surface of the negative electrode active material layer of each first full cell, determine whether metal has been deposited at the negative electrode interface of each first full cell, and screen the first full cells that have not been deposited with metal.

[0068] S6b: Among all the first full cells without metal deposition, select the one with the largest estimated discharge specific capacity of the negative electrode active material in the corresponding first full cell as the effective discharge specific capacity of the negative electrode active material in the full cell. For specific applications, see the table below, C 预估-3 The negative electrode interface with a value of 255 mAh / g corresponds to the largest value among the first full cells without sodium deposition. Therefore, 255 mAh / g is determined to be the effective discharge specific capacity of this negative electrode active material in the full cell system. It should be noted that, to improve the measurement accuracy, in other embodiments, this can be achieved by setting a predicted discharge specific capacity gradient series with more terms and a smaller tolerance n.

[0069]

[0070] In summary, this embodiment first obtains the charge specific capacity C0 of the negative electrode active material under ideal conditions through half-cell testing, and then reduces it to the estimated discharge specific capacity C that is closer to the actual application scenario of a full battery through the conversion factor P. 预估0 Using this as the center value, a gradient sequence of the estimated discharge specific capacity of the negative electrode active material in a small number of first full cells is set, and the corresponding estimated discharge capacity gradient sequence of the negative electrode active material in the first full cell is calculated. At the same time, by pre-designing and manufacturing a first full cell with an N / P value of less than 1, the negative electrode capacity is ensured to be the limiting factor. Combined with a charging strategy that uses the estimated discharge capacity as the charging cutoff capacity, only a small number of first full cells need to be fully charged and disassembled. By visually observing the metal precipitation state at the negative electrode interface, the effective discharge specific capacity of the negative electrode active material in the full cell system can be accurately and quickly determined from the estimated discharge specific capacity of the negative electrode active material in the corresponding first full cell.

[0071] This embodiment is applicable not only to sodium-ion full batteries of different systems, but also to other alkali metal-ion batteries such as lithium-ion batteries. Furthermore, it is suitable not only for hard carbon anode active materials, but also for the selection of materials such as cathode, anode, separator, and electrolyte, making it applicable to a wide range of scenarios. This embodiment significantly reduces the number of experiments; the effective discharge specific capacity of the anode active material in the full battery can be determined in less than 5 full-charge tests and disassemblies of the first full battery, making it simple, quick, and cost-effective.

[0072] The above description is merely an embodiment of this application and is not intended to limit the scope of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of the claims of this application.

Claims

1. A method for determining the effective discharge specific capacity of the negative electrode active material in a full battery, characterized in that, Includes the following steps: S1: A first negative electrode sheet is prepared using a negative electrode active material, a half cell is made using the first negative electrode sheet, and the charge specific capacity C0 of the negative electrode active material in the half cell is tested. S2: Set the conversion coefficient to P and obtain the estimated discharge specific capacity C of the negative electrode active material in the full cell. 预估0 , P = 0.8~1.0; S3: A second negative electrode sheet is prepared using a negative electrode active material, with a preset N / P value < 1. A first positive electrode sheet is prepared using a positive electrode active material according to the N / P value. A first full cell is made using the first positive electrode sheet and the second negative electrode sheet. S4: With C 预估0 The estimated discharge specific capacity gradient sequence of the negative electrode active material in the first full cell is preset with the center value, and the corresponding estimated discharge capacity gradient sequence of the negative electrode active material in the first full cell is calculated. S5: Take the estimated discharge capacity in the estimated discharge capacity gradient sequence of the negative electrode active material in the first full battery as the charging cutoff capacity, and perform a full charge test on the first full battery. S6: Disassemble the first full cell separately, and based on the metal deposition at the negative electrode interface of each first full cell, determine the effective discharge specific capacity of the negative electrode active material in the full cell from the estimated discharge specific capacity of the negative electrode active material in the corresponding first full cell.

2. The method for determining the effective discharge specific capacity of the negative electrode active material in a full battery according to claim 1, characterized in that, Step S1 includes the following sub-steps: The mass percentage of negative active material in the negative active material layer of the first negative electrode is preset to be B. 负0 ; The first negative electrode sheet was prepared using a negative electrode active material; Obtain the mass of the negative electrode active material layer in the first negative electrode sheet; According to the formula: Mass of negative electrode active material = Mass of negative electrode active material layer × Mass ratio of negative electrode active material, the mass of negative electrode active material of the first negative electrode sheet can be calculated. A half-cell is made using the first negative electrode sheet; Perform a charging test on the half-cell and record the charging capacity of the half-cell; According to the formula: specific charge capacity of negative electrode active material = charge capacity ÷ mass of negative electrode active material, the specific charge capacity C0 of the negative electrode active material in the half cell can be calculated.

3. The method for determining the effective discharge specific capacity of the negative electrode active material in a full battery according to claim 1 or 2, characterized in that, Following the step of fabricating a half-cell using the first negative electrode, the following steps are also included: The half-cell was placed in an environment of 40℃~50℃.

4. The method for determining the effective discharge specific capacity of the negative electrode active material in a full battery according to claim 2, characterized in that, The step of performing a charging test on the half-cell and recording the charging capacity of the half-cell includes the following sub-steps: The half-cell is discharged at a constant current rate to 0V at the first discharge rate and then left to stand. The half-cell is discharged to 0V at a constant current at a second discharge rate and then left to stand. The half-cell is discharged at a constant current rate to 0V at the third discharge rate and then left to stand. The half-cell is charged at a constant current at a first charging rate to a first cutoff voltage and then left to stand. After repeating the above steps multiple times, record the charging capacity of the last constant current charge. Wherein, the first discharge rate > the second discharge rate > the third discharge rate, and the first charging rate ≤ the first discharge rate.

5. The method for determining the effective discharge specific capacity of the negative electrode active material in a full battery according to claim 1, characterized in that, Step S3 includes the following sub-steps: The mass percentage of negative electrode active material in the negative electrode active material layer of the second negative electrode is preset to be B. 负1 ; The second negative electrode sheet was prepared using a negative electrode active material; The surface density of the coating on the second negative electrode was measured to be ρ. 负1 ; The mass percentage of the positive active material in the positive active material layer of the first positive electrode is preset to be B. 正1 ; The discharge specific capacity of the positive electrode active material in the full cell is C. 正 ; The default N / P value is <1, according to the formula The coating surface density ρ of the first positive electrode was calculated. 正1 ; According to B 正1 and ρ 正1 The first positive electrode sheet was prepared using a positive electrode active material; A first full cell is made using the first positive electrode and the second negative electrode.

6. The method for determining the effective discharge specific capacity of the negative electrode active material in a full battery according to claim 5, characterized in that, The discharge specific capacity of the positive electrode active material in the full cell is C. 正 The steps include the following sub-steps: The mass percentage of the positive active material in the positive active material layer of the second positive electrode is preset to be B. 正2 ; The second positive electrode sheet was prepared using a positive electrode active material; Obtain the mass of the positive electrode active material layer in the second positive electrode sheet; According to the formula: Mass of positive electrode active material = Mass of positive electrode active material layer × Mass ratio of positive electrode active material, the mass of positive electrode active material of the second positive electrode sheet can be calculated. A second full cell with an N / P value > 1 is made using the second positive electrode and the third negative electrode. The second full cell was subjected to a discharge test, and the discharge capacity of the second full cell was recorded. Based on the formula: Discharge specific capacity of positive electrode active material = Discharge capacity ÷ Mass of positive electrode active material, the discharge specific capacity C of the positive electrode active material in the full cell can be calculated. 正 .

7. The method for determining the effective discharge specific capacity of the negative electrode active material in a full battery according to claim 1 or 5, characterized in that, After the step of fabricating a first full cell using the first positive electrode and the second negative electrode, the method further includes the step of forming and charging the first full cell respectively: The first full battery is charged at a constant current rate at the second charging rate and then left to stand. The first full battery is charged at a constant current rate of the third charging rate and then left to stand. The first full battery is charged at a constant current rate of the fourth charging rate and then left to stand. Wherein, the second charging rate < the third charging rate < the fourth charging rate.

8. The method for determining the effective discharge specific capacity of the negative electrode active material in a full battery according to claim 1, characterized in that, Before the step of preparing the second negative electrode sheet using the negative electrode active material, the mass percentage of the negative electrode active material in the negative electrode active material layer of the second negative electrode sheet is preset to be B. 负1 ; After the step of preparing the second negative electrode sheet using the negative electrode active material, the mass of the negative electrode active material layer in the second negative electrode sheet is obtained. According to the formula: Mass of negative electrode active material = Mass of negative electrode active material layer × Mass ratio of negative electrode active material, the mass of negative electrode active material of the second negative electrode sheet can be calculated. Step S4 includes the following sub-steps: With C 预估0 An arithmetic sequence with odd-numbered terms is pre-defined for the arithmetic mean, and is used as the estimated discharge specific capacity gradient sequence for the negative electrode active material in the first full cell; According to the formula: Estimated discharge capacity of negative electrode active material in the first full cell = Estimated discharge specific capacity of negative electrode active material in the first full cell × Mass of negative electrode active material of the second negative electrode, the corresponding gradient series of estimated discharge capacity of negative electrode active material in the first full cell can be calculated.

9. The method for determining the effective discharge specific capacity of the negative electrode active material in a full battery according to claim 1 or 8, characterized in that, Before step S5, there is also a step of cyclically charging and discharging the first full battery: The estimated discharge capacity in the estimated discharge capacity gradient sequence of the negative electrode active material in the first full cell is used as the charging cutoff capacity. The first full cell is charged at a constant current of the fifth charging rate to the charging cutoff capacity and then left to stand. The first full cell is discharged at a constant current at a fourth discharge rate to the second cutoff voltage and then left to stand. Repeat the above steps multiple times.

10. The method for determining the effective discharge specific capacity of the negative electrode active material in a full battery according to claim 1, characterized in that, Based on the metal deposition at the negative electrode interface of each of the first full cells, the step of determining the effective discharge specific capacity of the negative electrode active material in the full cell from the estimated discharge specific capacity of the negative electrode active material in the corresponding first full cell includes the following sub-steps: Observe the surface of the negative electrode active material layer of each first full cell to determine whether metal is deposited at the negative electrode interface of each first full cell, and screen out the first full cells that have not deposited metal. Among all the first full cells without metal deposition, the one with the largest estimated discharge specific capacity of the negative electrode active material in the corresponding first full cell is selected as the effective discharge specific capacity of the negative electrode active material in the full cell.

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