Method for measuring effective discharge specific capacity of negative electrode active material in full cell
By combining half-cell testing and conversion coefficient prediction with full-cell charging cutoff voltage gradient testing and disassembly, the problem of difficulty in determining the effective discharge specific capacity of the negative electrode active material in a full cell is solved, achieving rapid and accurate capacity determination, applicable to sodium-ion and lithium-ion batteries.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- HUNAN DESAY BATTERY CO LTD
- Filing Date
- 2026-04-08
- Publication Date
- 2026-07-14
Smart Images
Figure CN121995257B_ABST
Abstract
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:
[0006] 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 discharge specific capacity C0 of the negative electrode active material in the half cell is tested.
[0007] S2: The first conversion coefficient is preset to P1, and the estimated charge specific capacity C of the negative electrode active material in the full cell is calculated. 预估充电比容量 C 预估充电比容量 =C0×P1, P1=0.7~0.9;
[0008] S3: The second conversion coefficient is preset to P2, and the estimated discharge specific capacity C of the negative electrode active material in the full cell is calculated. 预估放电比容量 C 预估放电比容量 =C 预估充电比容量 ×P2, P2 = 0.8~0.9;
[0009] S4: A second negative electrode is prepared using a negative electrode active material, with a preset N / P value of <1. A first positive electrode is prepared using a positive electrode active material based on the N / P value. A first full cell is made using the first positive electrode and the second negative electrode.
[0010] S5: Preset the relationship between the preset charging specific capacity and the charging cutoff voltage, based on the estimated charging specific capacity C of the negative electrode active material in the full battery. 预估充电比容量 The charging cutoff voltage gradient sequence is determined from the relationship between charging specific capacity and charging cutoff voltage.
[0011] S6: Perform discharge tests on the first full cell respectively, calculate the actual discharge specific capacity of the negative electrode active material in each first full cell, and use the voltage in the charging cutoff voltage gradient series as the charging cutoff voltage to perform a full charge test on the first full cell.
[0012] S7: Disassemble the first full cell separately, and determine the effective discharge specific capacity of the negative electrode active material in the full cell from the actual discharge specific capacity of the negative electrode active material in the corresponding first full cell based on the metal precipitation at the negative electrode interface of each first full cell.
[0013] Preferably, step S1 includes the following sub-steps:
[0014] 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 ;
[0015] The first negative electrode sheet was prepared using a negative electrode active material;
[0016] Obtain the mass of the negative electrode active material layer in the first negative electrode plate;
[0017] 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.
[0018] A half-cell is made using the first negative electrode plate;
[0019] Perform a discharge test on the half-cell and record the discharge capacity of the half-cell;
[0020] According to the formula: Discharge specific capacity of negative electrode active material = Discharge capacity ÷ Mass of negative electrode active material, the discharge specific capacity C0 of the negative electrode active material in the half cell can be calculated.
[0021] Preferably, after the step of making a half-cell using the first negative electrode, the following steps are also included:
[0022] The half-cell was left to stand in a high-temperature environment.
[0023] Preferably, the step of performing a discharge test on the half-cell and recording the discharge capacity of the half-cell includes the following sub-steps:
[0024] After discharging the half-cell to 0V at a constant current with the first discharge rate, it is left to stand.
[0025] After discharging the half-cell to 0V at a constant current using the second discharge rate, it is left to stand.
[0026] After discharging the half-cell to 0V at a constant current rate of the third discharge rate, it is left to stand.
[0027] 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.
[0028] After repeating the above steps multiple times, record the sum of the discharge capacities of the three constant current discharges in the last cycle;
[0029] Among them, the first discharge rate > the second discharge rate > the third discharge rate, and the first charge rate ≤ the first discharge rate.
[0030] Preferably, step S4 includes the following sub-steps:
[0031] 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 ;
[0032] The second negative electrode sheet was prepared using a negative electrode active material;
[0033] The surface density of the coating on the second negative electrode was measured to be ρ. 负1 ;
[0034] 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 ;
[0035] The discharge specific capacity of the positive electrode active material in the full cell is C. 正 ;
[0036] The default N / P value is <1. According to the formula N / P = The coating surface density ρ of the first positive electrode was calculated. 正1 ;
[0037] According to B 正1 and ρ 正1 The first positive electrode sheet was prepared using a positive electrode active material;
[0038] A first full cell was made using the first positive electrode and the second negative electrode.
[0039] 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:
[0040] 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 ;
[0041] The second positive electrode sheet was prepared using a positive electrode active material;
[0042] Obtain the mass of the positive electrode active material layer in the second positive electrode plate;
[0043] 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.
[0044] A second full cell with an N / P value > 1 is made using a second positive electrode and a third negative electrode.
[0045] The second full cell was subjected to a discharge test, and its discharge capacity was recorded.
[0046] 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 .
[0047] Preferably, after the step of fabricating a first full cell using the first positive electrode and the second negative electrode, the process further includes a step of performing high-temperature formation and charging on the first full cells respectively:
[0048] The first full battery is charged at a constant current rate of the second charging rate and then left to stand.
[0049] The first full battery was charged at a constant current rate of the third charging rate and then left to stand.
[0050] The first full battery was charged at a constant current rate of the fourth charging rate and then left to stand.
[0051] Among them, the second charging rate < the third charging rate < the fourth charging rate.
[0052] Preferably, step S5 includes the following sub-steps:
[0053] A preset reference charging specific capacity gradient series and a reference charging cutoff voltage gradient series are provided, with the charging specific capacity reference value in the reference charging specific capacity gradient series and the charging cutoff voltage reference value in the reference charging cutoff voltage gradient series set to correspond one-to-one.
[0054] When the estimated charge specific capacity C of the negative electrode active material in the full battery 预估充电比容量When the reference charging specific capacity gradient is located between two adjacent charging specific capacity reference values, two charging cut-off voltage reference values in the reference charging cut-off voltage gradient sequence corresponding to the two adjacent charging specific capacity reference values, and N charging cut-off voltage reference values adjacent to the two charging cut-off voltage reference values are selected as the charging cut-off voltage gradient sequence.
[0055] Preferably, the step of performing a discharge test on the first full cell includes the following sub-steps:
[0056] The voltage in the charging cutoff voltage gradient sequence is used as the charging cutoff voltage. The first full cell is charged at a constant current of the fifth charging rate to the charging cutoff voltage and then left to stand.
[0057] 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.
[0058] Repeat the above steps multiple times.
[0059] 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 ;
[0060] 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.
[0061] 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.
[0062] The steps for calculating the actual discharge specific capacity of the negative electrode active material in each first full cell include the following sub-steps:
[0063] When the first full cell is discharged, the discharge capacity of the first full cell is recorded.
[0064] According to the formula: Discharge specific capacity of negative electrode active material = Discharge capacity ÷ Mass of negative electrode active material, the actual discharge specific capacity of the negative electrode active material in the first full cell can be calculated.
[0065] Preferably, the step of determining the effective discharge specific capacity of the negative electrode active material in the full cell from the actual 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:
[0066] 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.
[0067] Among all the first full cells without metal deposition, the one with the largest actual 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.
[0068] The beneficial effects of this application are as follows: First, the discharge specific capacity C0 of the negative electrode active material under ideal conditions is obtained through half-cell testing. Then, by introducing a first conversion coefficient P1 and a second conversion coefficient P2, the estimated charge specific capacity and the estimated discharge specific capacity of the negative electrode active material in the full battery system are obtained by successively reducing the values. Based on the preset N / P value < 1, a set of first full batteries with negative electrode capacity as the limiting factor are designed and prepared. Next, based on the estimated charge specific capacity of the negative electrode active material, a small number of charge cutoff voltage gradient sequences are determined from the preset correspondence between charge specific capacity and charge cutoff voltage. Then, discharge tests are performed on the first full batteries respectively, and the actual discharge specific capacity of the negative electrode active material in each first full battery is calculated. Finally, the voltages in the charge cutoff voltage gradient sequence are used as the charge cutoff voltages, and the first full batteries are fully charged and disassembled to directly observe the metal deposition at the negative electrode interface. From the actual discharge specific capacity of the negative electrode active material in the corresponding first full battery, the effective discharge specific capacity of the negative electrode active material in the full battery is determined. This reduces the number of measurements, generally less than three full-charge tests and disassemblies of the first full cell, which is sufficient to determine the effective discharge specific capacity of the negative electrode active material in the full cell. It is simple, quick, and saves on experimental costs.
[0069] 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 not only applicable to hard carbon anode active materials, but also has no special requirements for the selection of materials such as cathode, anode, separator and electrolyte, and has a wide range of applications. Attached Figure Description
[0070] 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:
[0071] 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, as shown in the examples. Detailed Implementation
[0072] 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.
[0073] 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.
[0074] 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.
[0075] 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:
[0076] 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 discharge specific capacity C0 of the negative electrode active material in the half cell is tested.
[0077] Preferably, step S1 includes the following sub-steps:
[0078] 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%.
[0079] 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.
[0080] 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.
[0081] 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.
[0082] 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.
[0083] S16: Place the half-cell in a high-temperature environment. In specific applications, place the half-cell obtained in step S15 at 45°C for 8 hours to accelerate the internal chemical stability of the half-cell after assembly.
[0084] S17: Perform a discharge test on the half-cell and record its discharge capacity. In practical applications, the half-cell that has been subjected to high-temperature storage in step S16 is then subjected to a discharge test at 25°C.
[0085] Specifically, step S17 includes the following sub-steps:
[0086] S171: After discharging the half-cell to 0V at a constant current using the first discharge rate, it is then left to rest.
[0087] S172: After discharging the half-cell to 0V at a constant current using the second discharge rate, it is then left to rest.
[0088] S173: After discharging the half-cell to 0V at a constant current rate using the third discharge rate, it is then left to rest.
[0089] 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.
[0090] S175: After repeating steps S171 to S174 multiple times, record the sum of the discharge capacities of the three constant current discharges in steps S171 to S173 in the last cycle, and record it as the first discharge capacity.
[0091] 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. 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 the number of cycles in steps S171 to S174 is 3. Discharging to 0V at different rates and cycling 3 times can eliminate the internal polarization of the half-cell and fully activate the ion channels of the half-cell.
[0092] S18: According to the formula: Discharge specific capacity of negative electrode active material = First discharge capacity ÷ Mass of negative electrode active material, the discharge specific capacity C0 of the negative electrode active material in the half-cell is calculated. Specifically, in this embodiment, C0 = 337.2 mAh / g.
[0093] S2: The first conversion coefficient is preset to P1, and the estimated charge specific capacity C of the negative electrode active material in the full cell is calculated. 预估充电比容量 C 预估充电比容量 =C0×P1, P1=0.7~0.9. In practical applications, since the first negative electrode in the half-cell obtained in step S15 faces the sodium metal plate, sodium ions are embedded in the negative electrode active material during half-cell discharge, and sodium ions are embedded in the negative electrode active material during full-cell charging. Therefore, the discharge specific capacity C0 of the negative electrode active material in the half-cell numerically corresponds to the estimated charging specific capacity of the negative electrode active material in the full-cell. Moreover, the discharge specific capacity C0 of the negative electrode active material obtained from the half-cell discharge test 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 first conversion coefficient P1 to reduce the discharge specific capacity C0 of the negative electrode active material in the half-cell, the estimated charging 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. 预估充电比容量 In this embodiment, the first conversion coefficient P1 is 0.9, and C 预估充电比容量 =337.2mAh / g × 0.9 = 303.5mAh / g. Of course, the first conversion coefficient P1 can also be adjusted to other values.
[0094] S3: The second conversion coefficient is preset to P2, and the estimated discharge specific capacity C of the negative electrode active material in the full cell is calculated. 预估放电比容量 C 预估放电比容量 =C 预估充电比容量 ×P2, P2=0.8~0.9. The estimated specific charge capacity C of the negative electrode active material in the full cell obtained in step S2. 预估充电比容量Multiplying by the second conversion factor P2, we obtain the estimated discharge specific capacity C of the negative electrode active material in the full cell. 预估放电比容量 C 预估放电比容量 =303.5mAh / g × 0.9 = 273.15mAh / g. It is understandable that in a full battery, the sodium ions inserted into the negative electrode active material during charging are not all reversibly released during subsequent discharge, and its discharge capacity is usually slightly lower than its charging capacity. Therefore, by presetting a second conversion coefficient P2 and making it less than 1, the C... 预估充电比容量 Further reductions are made to obtain the estimated discharge specific capacity of the negative electrode active material in a full battery that is closer to the actual application scenario of a full battery.
[0095] S4: A second negative electrode is prepared using negative electrode active material, with a preset N / P value < 1. A first positive electrode is prepared using 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.
[0096] Preferably, step S4 includes the following sub-steps:
[0097] S41: 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%.
[0098] S42: 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.
[0099] S43: 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1The 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.
[0100] S44: 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 In 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 active material in the positive electrode slurry by mass of all solid components (positive electrode active material, conductive agent, binder). In this embodiment, B... 正1 =95%.
[0101] S45: 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.
[0102] Preferably, step S45 includes the following sub-steps:
[0103] S451: 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 S44, B 正2 With B 正1 The figures are the same, both at 95%.
[0104] S452: A second positive electrode sheet is prepared using a positive electrode active material. In specific applications, the positive electrode active material (B) is used... 正2 =95%), conductive agent, binder and solvent are mixed to form a positive electrode slurry, and the positive electrode sheet is prepared by coating, rolling and baking. Finally, a second positive electrode sheet of a specified area is cut from the positive electrode sheet.
[0105] S453: Obtain the mass of the positive electrode active material layer in the second positive electrode sheet. In specific 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.
[0106] S454: 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 S453 and the mass percentage B of the positive electrode active material in step S451 are used. 正2 The mass of the positive active material of the second positive electrode can then be calculated.
[0107] S455: 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 S452 is paired with a third negative electrode of known sufficient capacity to assemble a second full cell, ensuring that the N / P value of the second full cell 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.
[0108] S456: Perform a discharge test on the second full cell and record its discharge capacity. In specific applications, the second full cell assembled in step S455 is subjected to constant current discharge at a rate of 0.5C to the cutoff voltage at 25°C. The total capacity released during the discharge process is recorded as the second discharge capacity.
[0109] S457: 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 In practical applications, the second discharge capacity recorded in step S456 is divided by the mass of the positive electrode active material calculated in step S454 to obtain the discharge specific capacity C of the positive electrode active material in the full cell. 正 In this embodiment, C 正 =92mAh / g.
[0110] S46: Preset N / P value < 1, according to the formula N / P value = 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 S3, 预估放电比容量 (273.15mAh / g), the mass percentage of the negative electrode active material in the second negative electrode sheet preset in step S41, B 负1 (95%), the coating surface density ρ of the second negative electrode sheet determined in step S43. 负1 The discharge specific capacity C of the positive electrode active material obtained in step S457 正 (92mAh / g) and the mass percentage of the positive active material of the first positive electrode sheet preset in step S44 B 正1(95%), according to the formula N / P value = The coating surface density ρ of the first positive electrode was derived and calculated. 正1 .
[0111] S47: 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 S44. 正1 (95%), and the coating surface density ρ calculated in step S46. 正1 The 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.
[0112] S48: 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 S42 and the first positive electrode prepared in step S47 are combined with electrolyte, separator, and other materials to fabricate a first full cell. In this embodiment, the number of first full cells is 4, and the design capacity C of the first full cell is 1 Ah.
[0113] S49: Perform high-temperature formation and charging on the first full cell separately. In specific applications, the first full cells obtained in step S48 are subjected to high-temperature charging and formation at 45°C to ensure that the first full cells have good SEI film formation effect.
[0114] Specifically, step S49 includes the following sub-steps:
[0115] S491: After charging the first full battery at a constant current rate using the second charging rate, allow it to rest. In specific applications, charge the first full battery at a constant current of 0.02C for 30 minutes and then allow it to rest for 5 minutes.
[0116] S492: After charging the first full battery at a constant current rate of the third charging rate, it is left to rest. In specific applications, the first full battery is charged at a constant current of 0.05C for 30 minutes and then left to rest for 5 minutes.
[0117] S493: After charging the first full battery at a constant current rate of the fourth charging rate, it is left to rest. In specific applications, the first full battery is charged at a constant current of 0.1C for 60 minutes and then left to rest for 8 hours.
[0118] S5: Preset the relationship between the preset charging specific capacity and the charging cutoff voltage, based on the estimated charging specific capacity C of the negative electrode active material in the full battery. 预估充电比容量 The charging cutoff voltage gradient sequence is determined from the relationship between charging specific capacity and charging cutoff voltage.
[0119] Preferably, step S5 includes the following sub-steps:
[0120] S51: A preset reference charging specific capacity gradient series and a preset reference charging cutoff voltage gradient series are established. The reference charging specific capacity reference value in the reference charging specific capacity gradient series corresponds one-to-one with the reference charging cutoff voltage reference value in the reference charging cutoff voltage gradient series. In specific applications, the preset reference charging specific capacity gradient series in this embodiment is an arithmetic sequence with 295mAh / g as the arithmetic mean and 5mAh / g as the common difference. The corresponding reference charging cutoff voltage gradient series is an arithmetic sequence with 3.70V as the arithmetic mean and 0.05V as the common difference, as shown in Table 1.
[0121] Table 1
[0122]
[0123] S52: When the estimated charge specific capacity C of the negative electrode active material in the full battery... 预估充电比容量 When the value lies between two adjacent reference values of charge specific capacity in the reference charge specific capacity gradient sequence, two reference values of charge cutoff voltage are selected from the reference charge cutoff voltage gradient sequence corresponding to the two adjacent reference values of charge specific capacity, and N reference values of charge cutoff voltage adjacent to the two reference values of charge cutoff voltage are used as the charge cutoff voltage gradient sequence. In specific applications, C obtained in step S2... 预估充电比容量 The specific capacity is 303.5 mAh / g, which falls between the charging specific capacity reference values of 300 mAh / g and 305 mAh / g, corresponding to charging cutoff voltage reference values of 3.75V and 3.80V, respectively. These two voltages are selected, and each is extended to an adjacent charging cutoff voltage reference value (N=1) to both ends, resulting in a charging cutoff voltage gradient series including 3.70V, 3.75V, 3.80V, and 3.85V.
[0124] S6: Perform discharge tests on the first full cell respectively, calculate the actual discharge specific capacity of the negative electrode active material in each first full cell, and use the voltage in the charging cutoff voltage gradient series as the charging cutoff voltage to perform a full charge test on the first full cell.
[0125] Preferably, step S6 includes the following sub-steps:
[0126] S61: Perform a discharge test on the first full cell. In specific applications, step S61 includes the following sub-steps:
[0127] S611: Using the voltage in the charging cutoff voltage gradient series as the charging cutoff voltage, the first full cell is charged at a constant current at the fifth charging rate until the charging cutoff voltage is reached, and then left to rest. In specific applications, in a set of first full cells prepared in step S48 and formed in step S49, the voltage in the charging cutoff voltage gradient series determined in step S52 is used as the charging cutoff voltage. At 25°C, the first full cell is charged at a constant current at the fifth charging rate (0.5C in this embodiment) until the voltage reaches its corresponding charging cutoff voltage, then stopped and left to rest for 5 minutes.
[0128] S612: The first full cell is discharged at a constant current at the fourth discharge rate until the second cutoff voltage is reached, and then left to rest. In specific applications, the first full cell is discharged at a constant current at the fourth discharge rate (0.5C in this embodiment) at 25°C until the voltage reaches the second cutoff voltage (1.5V in this embodiment), and then left to rest for 5 minutes.
[0129] S613: The above steps are repeated multiple times. In specific applications, steps S611 and S612 are repeated three times. 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, 4, or other numbers, which is not limited here.
[0130] S62: Calculate the actual discharge specific capacity of the negative electrode active material in each first full cell. In practical applications, step S62 includes the following sub-steps:
[0131] S621: When performing a discharge test on the first full cell, record the discharge capacity of the first full cell. In specific applications, after completing multiple cycles of step S613, record the discharge capacity of step S612 in the last cycle as the discharge capacity of the first full cell.
[0132] S622: Calculate the actual discharge specific capacity of the negative electrode active material in the first full cell using the formula: Discharge specific capacity of negative electrode active material = Discharge capacity ÷ Mass of negative electrode active material. In practical application, divide the discharge capacity of the first full cell recorded in step S621 by the mass of the negative electrode active material of the second negative electrode sheet calculated in step S43 to obtain the actual discharge specific capacity of the negative electrode active material in the first full cell.
[0133] S63: Using the voltages in the charging cutoff voltage gradient series as the charging cutoff voltages, perform a full-charge test on the first full cell. In specific applications, after completing steps S61 and S62, charge a group of first full cells at a constant current rate of 0.5C to their corresponding charging cutoff voltages (from the charging cutoff voltage gradient series determined in step S52) at 25°C, and let them rest for 5 minutes. It is understandable that if the charging cutoff voltage of the first full cell is set too high, the amount of sodium ions released from the positive electrode active material may exceed the actual capacity of the negative electrode active material in the full cell system, resulting in excess sodium ions being deposited in metallic form at the negative electrode interface.
[0134] S7: Disassemble the first full cell separately, and determine the effective discharge specific capacity of the negative electrode active material in the full cell from the actual discharge specific capacity of the negative electrode active material in the corresponding first full cell based on the metal precipitation at the negative electrode interface of each first full cell.
[0135] Preferably, step S7 includes the following sub-steps:
[0136] S71: Disassemble each first full cell and 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 without metal deposition. In specific applications, disassemble a group of first full cells after the full charge test in step S63, and observe the surface of the negative electrode active material layer of each first full cell to determine whether sodium metal has been deposited at the negative electrode interface under different charging cutoff voltages, and screen out the first full cells without sodium metal deposition.
[0137] S72: Among all the first full cells without metal deposition, select the one with the largest actual discharge specific capacity of the negative electrode active material as the effective discharge specific capacity of the negative electrode active material in the full cell. In specific applications, if no sodium deposition is observed at the negative electrode interface of a first full cell after disassembly, it indicates that the charging cutoff voltage is still within a safe range, and the actual discharge specific capacity of the corresponding negative electrode active material has not 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 of a first full cell after disassembly, it indicates that the actual discharge specific capacity of the negative electrode active material has exceeded the effective discharge specific capacity of the negative electrode active material in the full cell. Based on this, by comparing the state of the negative electrode interface after disassembly of each first full cell with the actual discharge specific capacity calculated in step S622, the maximum value of the actual discharge specific capacity of the negative electrode active material is selected among all the first full cells without sodium deposition, which is the effective discharge specific capacity of the negative electrode active material in the full cell system.
[0138] Based on the disassembly observation and calculation results (refer to Table 2), the actual discharge specific capacities in the first full cell without sodium precipitation are 268.4 mAh / g and 272.6 mAh / g, respectively. Therefore, the larger one, 272.6 mAh / g, should be selected as the effective discharge specific capacity. It should be noted that, to improve measurement accuracy, this can be achieved in other embodiments by setting a reference charge specific capacity gradient series with more terms and a smaller tolerance.
[0139] Table 2
[0140]
[0141] In summary, this embodiment first obtains the discharge specific capacity C0 of the negative electrode active material under ideal conditions through half-cell testing. Then, by introducing a first conversion coefficient P1 and a second conversion coefficient P2, the estimated charge specific capacity and the estimated discharge specific capacity of the negative electrode active material in the full battery system are obtained by successively reducing the values. Based on the preset N / P value < 1, a set of first full batteries with negative electrode capacity as the limiting factor are designed and prepared. Next, based on the estimated charge specific capacity of the negative electrode active material, a small number of charge cutoff voltage gradient sequences are determined from the preset correspondence between charge specific capacity and charge cutoff voltage. Then, discharge tests are performed on the first full batteries respectively to calculate the actual discharge specific capacity of the negative electrode active material in each first full battery. Finally, the voltages in the charge cutoff voltage gradient sequence are used as the charge cutoff voltages to perform full charge tests and disassembly on the first full batteries to directly observe the metal deposition at the negative electrode interface. From the actual discharge specific capacity of the negative electrode active material in the corresponding first full battery, the effective discharge specific capacity of the negative electrode active material in the full battery is determined. This reduces the number of measurements, generally less than three full-charge tests and disassemblies of the first full cell, which is sufficient to determine the effective discharge specific capacity of the negative electrode active material in the full cell. It is simple, quick, and saves on experimental costs.
[0142] This embodiment is not only applicable to sodium-ion full batteries of different systems, but its principle can also be applied to other alkali metal ion batteries such as lithium-ion batteries. In addition, it is not only applicable to hard carbon negative electrode active materials, but also has no special requirements for the selection of materials such as positive electrode, negative electrode, separator and electrolyte, and has a wide range of application scenarios.
[0143] 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 discharge specific capacity C0 of the negative electrode active material in the half cell is tested. S2: The first conversion coefficient is preset to P1, and the estimated charge specific capacity C of the negative electrode active material in the full battery is calculated. 预估充电比容量 C 预估充电比容量 =C0×P1, P1=0.7~0.9; S3: The second conversion coefficient is preset to P2, and the estimated discharge specific capacity C of the negative electrode active material in the full cell is calculated. 预估放电比容量 C 预估放电比容量 =C 预估充电比容量 ×P2, P2 = 0.8~0.9; S4: A second negative electrode sheet is prepared using a negative electrode active material, with a preset N / P value of <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. S5: Preset the relationship between the preset charging specific capacity and the charging cutoff voltage, based on the estimated charging specific capacity C of the negative electrode active material in the full battery. 预估充电比容量 The charging cutoff voltage gradient sequence is determined from the relationship between charging specific capacity and charging cutoff voltage. S6: Perform discharge tests on the first full battery respectively, calculate the actual discharge specific capacity of the negative electrode active material in each of the first full batteries, and use the voltage in the charging cutoff voltage gradient sequence as the charging cutoff voltage to perform a full charge test on the first full battery. S7: Disassemble the first full cell separately; 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 actual discharge specific capacity of the negative electrode active material in the corresponding first full cell. Specifically, this includes the following sub-steps: 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, screen the first full cells without metal deposition, and select the one with the largest actual 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.
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; The half-cell was subjected to a discharge test, and the discharge capacity of the half-cell was recorded. According to the formula: Discharge specific capacity of negative electrode active material = Discharge capacity ÷ Mass of negative electrode active material, the discharge specific 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 a high-temperature environment.
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 discharge test on the half-cell and recording the discharge 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 sum of the discharge capacities of the three constant current discharges in the last cycle; 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 S4 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 N / P = 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 performing high-temperature formation and charging on 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, Step S5 includes the following sub-steps: A preset reference charging specific capacity gradient sequence and a reference charging cutoff voltage gradient sequence are provided, wherein the charging specific capacity reference value in the reference charging specific capacity gradient sequence and the charging cutoff voltage reference value in the reference charging cutoff voltage gradient sequence are set to correspond one-to-one; When the estimated charge specific capacity C of the negative electrode active material in the full battery 预估充电比容量 When located between two adjacent charging specific capacity reference values in the reference charging specific capacity gradient sequence, two charging cutoff voltage reference values in the reference charging cutoff voltage gradient sequence corresponding to the two adjacent charging specific capacity reference values, and N charging cutoff voltage reference values adjacent to the two charging cutoff voltage reference values are selected as the charging cutoff voltage gradient sequence.
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, The steps for performing a discharge test on the first full cell include the following sub-steps: The voltage in the charging cutoff voltage gradient sequence is used as the charging cutoff voltage. The first full cell is charged at a constant current of the fifth charging rate to the charging cutoff voltage 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, 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. The steps for calculating the actual discharge specific capacity of the negative electrode active material in each of the first full cells include the following sub-steps: When the first full cell is discharged, the discharge capacity of the first full cell is recorded. According to the formula: Discharge specific capacity of negative electrode active material = Discharge capacity ÷ Mass of negative electrode active material, the actual discharge specific capacity of the negative electrode active material in the first full cell can be calculated.