Lithium iron phosphate battery cell capacity prediction method
By using Raman spectroscopy to detect and calculate the relationship to predict the capacity of lithium iron phosphate battery cells, the problem of lag in cell capacity detection in existing technologies has been solved, enabling material selection and cost control.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-31
- Publication Date
- 2026-04-03
AI Technical Summary
In existing technologies, capacity testing of lithium iron phosphate battery cells can only be carried out in the later stages of production, resulting in delays, increased production costs, and waste of resources.
By detecting the characteristic peak intensity of carbonate and phosphate, pH value, median particle size, and powder resistivity of lithium iron phosphate cathode materials using Raman spectroscopy, the relationship is calculated to predict the cell capacity and screen out materials that may have low capacity.
This technology enables the prediction of cell capacity before materials are assembled into cells, avoiding the assembly of low-quality materials, reducing production costs, and improving production efficiency.
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Figure CN121784584A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of lithium-ion battery technology, and more specifically to a method for predicting the capacity of lithium iron phosphate battery cells. Background Technology
[0002] Cell capacity is a core indicator for evaluating the performance of rechargeable batteries. If the cell capacity is low, devices using that cell will experience problems such as abnormal battery life and deteriorated system consistency, severely impacting normal device operation. Current technologies typically test cell capacity after the finished cells are manufactured using capacity grading tests. However, this step requires assembling the materials into a finished cell, meaning additional assembly costs are incurred for cells with lower capacity, resulting in resource waste. Summary of the Invention
[0003] This invention provides a method for predicting the capacity of lithium iron phosphate battery cells, which solves the problem that the existing technology can only detect the cell capacity in the later stage of cell production, resulting in a lag and hindering production cost control.
[0004] In a first aspect, the present invention provides a method for predicting the capacity of a lithium iron phosphate battery cell, comprising the following steps: The lithium iron phosphate cathode material used in the lithium iron phosphate battery cell to be tested was subjected to Raman spectroscopy to measure the characteristic peak intensity of carbonate and phosphate in the lithium iron phosphate cathode material; the pH value of the lithium iron phosphate cathode material was measured; the median particle size of the lithium iron phosphate cathode material was measured; and the powder resistivity of the lithium iron phosphate cathode material was measured. Calculate the following relationship: , Among them, l c This represents the numerical value of the characteristic peak intensity of carbonate ions; l p This represents the numerical value of the characteristic peak intensity of phosphate. pH refers to the pH value of the lithium iron phosphate cathode material. D 50 The median particle size of the lithium iron phosphate cathode material is expressed in μm. k is the numerical value of the powder resistivity of the lithium iron phosphate cathode material, and the unit of powder resistivity is Ω·cm; when When F ≥ 0.95 and F ≥ 0.95, the capacity of the lithium iron phosphate battery cell under test is ≤ 85% of the design capacity; it is determined that the lithium iron phosphate battery cell under test has low capacity.
[0005] In this application, typically and non-limitingly, the pH value of the lithium iron phosphate cathode material is determined by acid-base titration; the median particle size of the lithium iron phosphate cathode material is determined by laser particle size analyzer; and the powder resistivity of the lithium iron phosphate cathode material is determined by a four-probe method or a two-probe method.
[0006] In one optional embodiment, the measured carbonate characteristic peak intensity of the lithium iron phosphate cathode material is 1040–1055 cm⁻¹ in the Raman spectrum. -1 The intensity of the carbonate characteristic peak at a certain point. The carbonate ions in lithium iron phosphate typically exhibit three characteristic vibrational regions in Raman spectra: the symmetric stretching vibration (ν1) ranges from 1040 to 1055 cm⁻¹. - ¹ is a strong peak with relatively little interference; the out-of-plane bending vibration (ν2) range is approximately 600 cm. - ¹ is a weak peak that is easily masked by the phosphate peak; the asymmetric stretching vibration (ν3) ranges from 1400 to 1450 cm⁻¹. - ¹, this peak easily overlaps with the graphite peak. Therefore, firstly, select the ν1 range that can overlap with the peak of phosphate (approximately 950 cm⁻¹). - ¹) Clear separation avoids spectral overlap and interference; secondly, the intensity of ν1 peak has a strong linear correlation with carbonate concentration, making it more suitable for quantitative analysis.
[0007] In one optional embodiment, the intensity of the carbonate characteristic peak is 800~2000.
[0008] In one optional embodiment, the measured intensity of the phosphate characteristic peak of the lithium iron phosphate cathode material is 985–1005 cm⁻¹ in the Raman spectrum. -1 The intensity of the characteristic peak of phosphate at the location.
[0009] In one optional embodiment, the intensity of the phosphate characteristic peak is 800~1600.
[0010] In one alternative embodiment, the resistivity of the lithium iron phosphate cathode material powder is 0.1~0.9 Ω·cm.
[0011] In one optional embodiment, when testing the powder resistivity of the lithium iron phosphate cathode material, a pressure of 10~50 MPa is applied.
[0012] In one alternative implementation, 8 ≤ pH ≤ 11.
[0013] In one optional embodiment, the median particle size of the lithium iron phosphate cathode material is 0.3~5.0 μm.
[0014] In one optional embodiment, the lithium iron phosphate cathode material includes lithium iron phosphate cathode material with a storage time of 0 to 12 months.
[0015] In the preparation method provided by this invention, typically and non-limitingly, the preparation method of the lithium iron phosphate battery cell is as follows: For the preparation of the positive electrode sheet, lithium iron phosphate positive electrode material, conductive agent, and binder are mixed in a mass ratio of 90~99:5~0.5:5~0.5, and a solvent is added to prepare a positive electrode slurry with a solid content of 50%~80%. This slurry is then coated onto the positive electrode current collector, with a coating surface density of 50~500 g / m². 3 The material is dried at 80-120℃ for 0.5-3 hours and rolled to a thickness of 80-160 μm to obtain the positive electrode sheet. The conductive agent includes at least one of carbon black and carbon nanotubes, the binder includes at least one of PVDF, the solvent includes N-methylpyrrolidone, and the positive electrode current collector includes at least one of aluminum foil and carbon-coated aluminum foil. For the negative electrode sheet preparation, the negative electrode active material, conductive agent, and binder are mixed in a mass ratio of 90-99:5-0.5:5-0.5, and a solvent is added to prepare a negative electrode slurry with a solid content of 40%-60%. This slurry is then coated onto the negative electrode current collector, with a coating surface density of 50-200 g / m². 3 The material is dried at 80-120℃ for 0.5-3 hours and rolled to a thickness of 30-70 μm to obtain the negative electrode sheet. The negative electrode active material includes at least one of carbon-based and silicon-based materials; the conductive agent includes at least one of carbon black and carbon nanotubes; the binder includes at least one of PAA (polyacrylic acid), CMC (carboxymethyl cellulose), and SBR (styrene-butadiene rubber); the solvent includes water; and the negative electrode current collector includes at least one of copper foil and carbon-coated copper foil. The separator includes at least one of polyethylene separator and polypropylene separator. The electrolyte includes lithium hexafluorophosphate electrolyte, with a lithium hexafluorophosphate concentration of 0.8-1.5 mol / L. The solvent of the electrolyte is EC (ethylene carbonate), EMC (ethyl methyl carbonate), and DEC (diethyl carbonate) in a mass ratio of 0.8-1.2: 0.8-1.2: 0.8-1.2. The positive electrode, negative electrode, and separator are assembled, wound, and injected with electrolyte to obtain a lithium iron phosphate battery cell.
[0016] The technical solution of this invention has the following advantages: 1. The method for predicting the capacity of a lithium iron phosphate battery cell provided by the present invention includes the following steps: taking the lithium iron phosphate cathode material used in the lithium iron phosphate battery cell to be tested, performing Raman spectroscopy to detect the characteristic peak intensity of carbonate and phosphate of the lithium iron phosphate cathode material; detecting the pH value of the lithium iron phosphate cathode material; detecting the median particle size of the lithium iron phosphate cathode material; detecting the powder resistivity of the lithium iron phosphate cathode material; and calculating the following relationship: , where l c The numerical value represents the intensity of the characteristic peak of carbonate; l p The value represents the intensity of the characteristic peak of phosphate; pH represents the pH value of the lithium iron phosphate cathode material; D50 is the median particle size of the lithium iron phosphate cathode material, with the unit being μm; k is the powder resistivity of the lithium iron phosphate cathode material, with the unit being Ω·cm; when When F ≥ 0.95 and F ≥ 0.95, the capacity of the lithium iron phosphate battery cell under test is ≤ 85% of the design capacity; this indicates that the lithium iron phosphate battery cell under test exhibits low capacity. This method can predict whether a lithium iron phosphate battery cell will exhibit low capacity after assembly, even before the lithium iron phosphate material is assembled into a cell. It can effectively screen low-quality lithium iron phosphate materials and reduce the cost of assembling lithium iron phosphate materials into cells before testing. In lithium iron phosphate materials, lithium ions on the material surface easily react with water and carbon dioxide to form lithium carbonate, leading to increased internal resistance and low cell capacity. Simultaneously, the particle size and pH value of the lithium iron phosphate material also have a certain impact on the cell capacity. Therefore, in this application, by constructing the Raman spectrum characteristic peak intensity ratio of carbonate and phosphate groups in lithium iron phosphate materials, and a reasonable relationship between pH value, median particle size, and powder resistivity, the capacity prediction of lithium iron phosphate materials is achieved. Attached Figure Description
[0017] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.
[0018] Figure 1 This is the Raman spectrum image measured in Example 6 of the present invention; Figure 2 This is the Raman spectrum image measured in Comparative Example 2 of this invention. Detailed Implementation
[0019] The following embodiments are provided to better understand the present invention, but the following embodiments do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the scope of protection of the present invention.
[0020] Unless otherwise specified, all experimental steps or conditions in the examples were performed according to conventional experimental procedures and conditions in the art. Reagents or instruments whose manufacturers are not specified are all commercially available products.
[0021] The following five lithium iron phosphate materials are used in this invention: Lithium iron phosphate material No. 1: Dissolve 280g of ferrous sulfate in deoxygenated water, and add dropwise a 5% sodium hydroxide aqueous solution until the pH reaches 8. At this point, the amount of sodium hydroxide in the sodium hydroxide aqueous solution is approximately 80g. Filter to obtain ferrous hydroxide. Mix ferrous hydroxide with 27g of lithium carbonate, 58g of ammonium dihydrogen phosphate, and 30g of sucrose, and ball mill for 10 hours. Then, calcine it in a N2 atmosphere at 350℃ for 4 hours for the first stage of calcineation, and continue to raise the temperature to 700℃ and hold for 10 hours for the second stage of calcineation. After calcineation, cool to room temperature, grind, and sieve to obtain lithium iron phosphate particles within the target particle size range, which is used as lithium iron phosphate material No. 1.
[0022] Lithium iron phosphate material No. 2: The difference in preparation from lithium iron phosphate material No. 1 is that the sucrose content is 20g.
[0023] Lithium iron phosphate material No. 3: The difference in preparation from lithium iron phosphate material No. 1 is that the sucrose content is 10g.
[0024] Lithium iron phosphate material No. 4: The difference in preparation from lithium iron phosphate material No. 1 is that the sodium hydroxide solution content is 100g.
[0025] Lithium iron phosphate material No. 5: The difference in preparation between this material and lithium iron phosphate material No. 1 is that the sodium hydroxide solution content is 120g.
[0026] Raman spectroscopy detection equipment and methods: The XploRA PLUS Raman spectrometer was used for testing. The sample was irradiated with a 532nm laser, and the weak Raman scattering signal in the scattered light was collected. The frequency shift (wavenumber, in cm) was analyzed. -1 ) and intensity.
[0027] Particle size analysis equipment and methods: A laser particle size analyzer was used for testing. 0.5g of lithium iron phosphate sample was dissolved in 100mL of pure water, stirred, and sonicated for 10min to obtain a sample solution. The sample solution was then irradiated with a laser, and the intensity of the scattered light generated by the particles was collected. The particle size distribution was then calculated using software.
[0028] The pH value test method is as follows: The acid-base titration method is used. 10g of lithium iron phosphate material is dissolved in 90g of NMP (N-methylpyrrolidone). A standard acid (or base) solution of known concentration is gradually added to the test solution. The pH change of the solution is monitored in real time using a pH meter. When the titration reaches the stoichiometric point, the original pH value of the test solution is calculated based on the volume of standard solution consumed.
[0029] Powder resistivity testing equipment and methods: The powder resistivity of lithium iron phosphate material was tested using a four-probe instrument at a test pressure of 20 MPa.
[0030] Example 1 This embodiment provides a method for predicting the capacity of lithium iron phosphate battery cells, including the following steps: (1) Take the No. 1 lithium iron phosphate material that has been stored for 4 months and perform Raman spectroscopy detection using the above-mentioned Raman spectroscopy detection equipment. The Raman spectroscopy results were obtained from 1040 to 1055 cm⁻¹. -1 The characteristic peak intensity of carbonate at this location is 1023; its 985~1005 cm⁻¹ -1 The characteristic peak intensity of phosphate at that location is 1052; calculation =1023 / 1052=0.97.
[0031] (2) The pH value of the No. 1 lithium iron phosphate material, which had been stored for 4 months, was 10.0.
[0032] (3) The median particle size D50 of the No. 1 lithium iron phosphate material, which had been stored for 4 months, was 2.3 μm.
[0033] (4) The powder resistivity of the corresponding positive electrode sheet of the No. 1 lithium iron phosphate material, which has been stored for 4 months, is 0.5 Ω·cm.
[0034] (5) Calculation =0.97×(0.5×(|10.0-7|) / 2.3)=0.63.
[0035] Lithium iron phosphate material No. 1 that has been stored for 4 months If F < 0.95, it is determined that the battery cell made using it as the positive electrode material has an actual capacity greater than 85% of the designed capacity, and it is determined that the battery cell using this lithium iron phosphate material will not exhibit low capacity phenomenon.
[0036] Example 2 This embodiment provides a method for predicting the capacity of lithium iron phosphate battery cells, including the following steps: (1) Take the freshly prepared No. 1 lithium iron phosphate material and perform Raman spectroscopy detection using the above-mentioned Raman spectroscopy detection equipment. The Raman spectroscopy results were obtained from 1040 to 1055 cm⁻¹. -1 The characteristic peak intensity of carbonate at this location is 854; its 985~1005 cm⁻¹ -1 The characteristic peak intensity of phosphate at that location is 1058; calculation =854 / 1058=0.81.
[0037] (2) The pH value of the freshly prepared No. 1 lithium iron phosphate material was 8.0.
[0038] (3) The median particle size D50 of the freshly prepared No. 1 lithium iron phosphate material was found to be 2.0 μm.
[0039] (4) The powder resistivity of the corresponding positive electrode of the freshly prepared No. 1 lithium iron phosphate material was found to be 0.4 Ω·cm.
[0040] (5) Calculation =0.81×(0.4×(|8.0-7|) / 2.0)=0.16.
[0041] Freshly produced No. 1 lithium iron phosphate material If F < 0.95, it is determined that the battery cell made using it as the positive electrode material has an actual capacity greater than 85% of the designed capacity, and it is determined that the battery cell using this lithium iron phosphate material will not exhibit low capacity phenomenon.
[0042] Example 3 This embodiment provides a method for predicting the capacity of lithium iron phosphate battery cells, including the following steps: (1) Take the No. 1 lithium iron phosphate material that has been stored for 12 months and perform Raman spectroscopy detection using the above-mentioned Raman spectroscopy detection equipment. The Raman spectroscopy results were obtained from 1040 to 1055 cm⁻¹. -1 The characteristic peak intensity of carbonate at this location is 1035; its 985~1005 cm⁻¹ value is... -1 The characteristic peak intensity of phosphate at that location is 1068; calculation =1035 / 1068=0.97.
[0043] (2) The pH value of the No. 1 lithium iron phosphate material, which had been stored for 12 months, was 11.0.
[0044] (3) The median particle size D50 of the No. 1 lithium iron phosphate material, which had been stored for 12 months, was 2.4 μm.
[0045] (4) The powder resistivity of the corresponding positive electrode sheet of the No. 1 lithium iron phosphate material, which has been stored for 12 months, is 0.8 Ω·cm.
[0046] (5) Calculation =0.97×(0.4×(|11.0-7|) / 2.4)=0.65.
[0047] Lithium iron phosphate material No. 1 stored for 12 months If F > 0.95 and F < 0.95, it is determined that the actual capacity of the battery cell made using it as the positive electrode material is greater than 85% of the designed capacity, and it is determined that the battery cell using this lithium iron phosphate material will not have low capacity.
[0048] Example 4 This embodiment provides a method for predicting the capacity of lithium iron phosphate battery cells, including the following steps: (1) Take the No. 2 lithium iron phosphate material that has been stored for 4 months and perform Raman spectroscopy detection using the above-mentioned Raman spectroscopy detection equipment. The Raman spectroscopy results were obtained from 1040 to 1055 cm⁻¹. -1The characteristic peak intensity of carbonate at this location is 875; its range is 985~1005 cm⁻¹. -1 The characteristic peak intensity of phosphate at that location is 1008; calculation =875 / 1008=0.87.
[0049] (2) The pH value of the No. 2 lithium iron phosphate material, which had been stored for 4 months, was 9.8.
[0050] (3) The median particle size D50 of the No. 2 lithium iron phosphate material, which had been stored for 4 months, was found to be 0.3 μm.
[0051] (4) The powder resistivity of the corresponding positive electrode sheet of the No. 2 lithium iron phosphate material, which has been stored for 4 months, is 0.3 Ω·cm.
[0052] (5) Calculation =0.87×(0.3×(|9.8-7|) / 0.3)=2.43.
[0053] Lithium iron phosphate material No. 2 that has been stored for 4 months <0.95, F>0.95, indicating that the battery cell made using it as the positive electrode material has an actual capacity greater than 85% of the designed capacity, and that the battery cell using this lithium iron phosphate material will not exhibit low capacity phenomenon.
[0054] Example 5 This embodiment provides a method for predicting the capacity of lithium iron phosphate battery cells, including the following steps: (1) Take the No. 3 lithium iron phosphate material that has been stored for 4 months and perform Raman spectroscopy detection using the above-mentioned Raman spectroscopy detection equipment. The Raman spectroscopy results were obtained from 1040 to 1055 cm⁻¹. -1 The characteristic peak intensity of carbonate at this location is 990; its range is 985–1005 cm⁻¹. -1 The characteristic peak intensity of phosphate at that location is 1025; calculation =990 / 1025=0.97.
[0055] (2) The pH value of the No. 3 lithium iron phosphate material, which had been stored for 4 months, was 9.7.
[0056] (3) The median particle size D50 of the No. 3 lithium iron phosphate material, which had been stored for 4 months, was found to be 5.0 μm.
[0057] (4) The powder resistivity of the corresponding positive electrode sheet of the No. 3 lithium iron phosphate material, which has been stored for 4 months, is 0.3 Ω·cm.
[0058] (5) Calculation =0.97×(0.3×(|9.7-7|) / 5.0)=0.16.
[0059] Lithium iron phosphate material No. 3 that has been stored for 4 months If F > 0.95 and F < 0.95, it is determined that the actual capacity of the battery cell made using it as the positive electrode material is greater than 85% of the designed capacity, and it is determined that the battery cell using this lithium iron phosphate material will not have low capacity.
[0060] Example 6 This embodiment provides a method for predicting the capacity of lithium iron phosphate battery cells, including the following steps: (1) Take the No. 3 lithium iron phosphate material that has been stored for 2 months and perform Raman spectroscopy detection using the above-mentioned Raman spectroscopy detection equipment. The obtained Raman spectrum is shown in the figure. Figure 1 Its dimensions were measured to be 1040~1055 cm. -1 The characteristic peak intensity of carbonate at this location is 921; its range is 985–1005 cm⁻¹. -1 The characteristic peak intensity of phosphate at that location is 1004; calculation =921 / 1004=0.92.
[0061] (2) The pH value of the No. 3 lithium iron phosphate material, which had been stored for 2 months, was 8.7.
[0062] (3) The median particle size D50 of the No. 3 lithium iron phosphate material, which had been stored for 2 months, was 3.4 μm.
[0063] (4) The powder resistivity of the corresponding positive electrode sheet of the No. 3 lithium iron phosphate material, which has been stored for 2 months, is 0.1 Ω·cm.
[0064] (5) Calculation =0.92×(0.3×(|8.7-7|) / 3.4)=0.05.
[0065] Lithium iron phosphate material No. 3 that has been stored for 2 months If F < 0.95, it is determined that the battery cell made using it as the positive electrode material has an actual capacity greater than 85% of the designed capacity, and it is determined that the battery cell using this lithium iron phosphate material will not exhibit low capacity phenomenon.
[0066] Example 7 This embodiment provides a method for predicting the capacity of lithium iron phosphate battery cells, including the following steps: (1) Take the No. 4 lithium iron phosphate material that has been stored for 4 months and perform Raman spectroscopy detection using the above-mentioned Raman spectroscopy detection equipment. The Raman spectroscopy results were obtained from 1040 to 1055 cm⁻¹. -1 The characteristic peak intensity of carbonate at this location is 1082; its 985~1005 cm⁻¹ value is... -1 The characteristic peak intensity of phosphate at that location is 1035; calculation =1082 / 1035=1.05.
[0067] (2) The pH value of the No. 4 lithium iron phosphate material, which had been stored for 4 months, was 10.5.
[0068] (3) The median particle size D50 of the No. 4 lithium iron phosphate material, which had been stored for 4 months, was 1.2 μm.
[0069] (4) The powder resistivity of the corresponding positive electrode sheet of the No. 4 lithium iron phosphate material, which has been stored for 4 months, is 0.5 Ω·cm.
[0070] (5) Calculation =1.05×(0.5×(|10.5-7|) / 1.2)=1.52.
[0071] Lithium iron phosphate material No. 4 that has been stored for 4 months If F > 0.95, it is determined that the actual capacity of the battery cell made using it as the positive electrode material is ≤ 85% of the designed capacity, and the battery cell using this lithium iron phosphate material will exhibit low capacity.
[0072] Example 8 This embodiment provides a method for predicting the capacity of lithium iron phosphate battery cells, including the following steps: (1) Take the No. 5 lithium iron phosphate material that has been stored for 4 months and perform Raman spectroscopy detection using the above-mentioned Raman spectroscopy detection equipment. The Raman spectroscopy results were obtained from 1040 to 1055 cm⁻¹. -1 The characteristic peak intensity of carbonate at this location is 1205; its 985~1005 cm⁻¹ -1 The characteristic peak intensity of phosphate at that location is 1024; calculation =1205 / 1024=1.18.
[0073] (2) The pH value of the No. 5 lithium iron phosphate material, which had been stored for 4 months, was 10.6.
[0074] (3) The median particle size D50 of the No. 5 lithium iron phosphate material, which had been stored for 4 months, was 1.3 μm.
[0075] (4) The powder resistivity of the corresponding positive electrode sheet of the No. 5 lithium iron phosphate material, which has been stored for 4 months, is 0.8 Ω·cm.
[0076] (5) Calculation =1.18×(0.8×(|10.6-7|) / 1.3)=2.61.
[0077] Lithium iron phosphate material No. 5 that has been stored for 4 months If F > 0.95, it is determined that the actual capacity of the battery cell made using it as the positive electrode material is ≤ 85% of the designed capacity, and the battery cell using this lithium iron phosphate material will exhibit low capacity.
[0078] Comparative Example 1 This comparative example provides a method for predicting the capacity of a lithium iron phosphate battery cell, including the following steps: (1) Take the No. 4 lithium iron phosphate material that has been stored for 4 months and perform Raman spectroscopy detection using the above-mentioned Raman spectroscopy detection equipment. The Raman spectroscopy results were obtained from 1400 to 1450 cm⁻¹. -1 The characteristic peak intensity of carbonate at this location is 724; its 985~1005 cm⁻¹ -1 The characteristic peak intensity of phosphate at that location is 1035; calculation =724 / 1035=0.70.
[0079] (2) The pH value of the No. 4 lithium iron phosphate material, which had been stored for 4 months, was 10.5.
[0080] (3) The median particle size D50 of the No. 4 lithium iron phosphate material, which had been stored for 4 months, was 1.2 μm.
[0081] (4) The powder resistivity of the corresponding positive electrode sheet of the No. 4 lithium iron phosphate material, which has been stored for 4 months, is 0.5 Ω·cm.
[0082] (5) Calculation =0.70×(0.5×(|10.5-7|) / 1.2)=1.02.
[0083] Lithium iron phosphate material No. 4 that has been stored for 4 months 0.95, F > 0.95, indicating that the battery cell made using it as the positive electrode material has an actual capacity > 85% of the designed capacity, and that the battery cell using this lithium iron phosphate material will not exhibit low capacity.
[0084] Comparative Example 2 This comparative example provides a method for predicting the capacity of a lithium iron phosphate battery cell, including the following steps: (1) Take the No. 4 lithium iron phosphate material that has been stored for 4 months and perform Raman spectroscopy detection using the above-mentioned Raman spectroscopy detection equipment. The obtained spectrum is shown in the figure. Figure 2 Its dimensions were measured to be 1040~1055 cm. -1 The characteristic peak intensity of carbonate at this location is 1082; its 985~1005 cm⁻¹ value is... -1 The characteristic peak intensity of phosphate at that location is 1035; calculation =1082 / 1035=1.05.
[0085] (2) The pH value of the No. 4 lithium iron phosphate material, which had been stored for 4 months, was 10.5.
[0086] (3) The particle size D90 of the No. 4 lithium iron phosphate material, which has been stored for 4 months, is 12.3 μm and the particle size D10 is 0.5 μm. The calculated D90-D10=11.8 μm.
[0087] (4) The powder resistivity of the corresponding positive electrode sheet of the No. 4 lithium iron phosphate material, which has been stored for 4 months, is 0.5 Ω·cm.
[0088] (5) Calculation =1.05×(0.5×(|10.5-7|) / 11.8)=0.16.
[0089] Lithium iron phosphate material No. 4 that has been stored for 4 months If F > 0.95 and F < 0.95, it is determined that the actual capacity of the battery cell made using it as the positive electrode material is greater than 85% of the designed capacity, and it is determined that the battery cell using this lithium iron phosphate material will not have low capacity.
[0090] Test Example 1 This test case verifies the capacity prediction results provided in the examples and comparative examples.
[0091] The lithium iron phosphate material tested in the examples and comparative examples was used to prepare battery cells. The specific preparation method is as follows: Lithium iron phosphate cathode material, carbon black conductive agent, and polyvinylidene fluoride binder were mixed in a mass ratio of 99:0.5:0.5, and NMP was added for homogenization for 4 hours. The resulting cathode slurry had a solid content of 60%. The cathode slurry was then coated onto aluminum foil with a coating surface density of 100 g / m². 3 The material was dried at 100℃ for 1 hour and rolled to a thickness of 100 μm to obtain the positive electrode sheet. Graphite negative electrode material, carbon black conductive agent, and binder (CMC, SBR mass ratio 3:4) were mixed at a mass ratio of 90:5:5, and water was added for homogenization for 4 hours. The resulting negative electrode slurry had a solid content of 60%. The negative electrode slurry was then coated onto copper foil with a coating surface density of 50 g / m². 3 The negative electrode is dried at 80℃ for 1 hour and rolled to a thickness of 50μm. A polyethylene diaphragm is used as the separator. A 1mol / L lithium hexafluorophosphate electrolyte is used, with EC, EMC, and DEC in a mass ratio of 1:1:1. The positive electrode, negative electrode, and separator are then slit, die-cut, wound, injected with electrolyte, and subjected to composition and capacity testing to obtain the final battery cell.
[0092] The theoretical capacity of each of the cells prepared above is 20Ah.
[0093] The cells were placed in the Blue Electricity Test System and tested for their actual capacity at a cutoff voltage of 2.5~3.7V and a current of 1C. The data obtained are shown in Table 1. The criterion for judging whether there is low capacity is that the percentage of actual capacity to design capacity is ≤85%.
[0094] Table 1
[0095] As can be seen from Table 1, the prediction method provided in this application used in the embodiments can accurately predict whether the capacity of lithium iron phosphate battery cells will be low; while the method used in the comparative examples cannot predict whether lithium iron phosphate materials will be low in capacity.
[0096] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.
Claims
1. A method for predicting the capacity of a lithium iron phosphate battery cell, characterized in that, Includes the following steps: The lithium iron phosphate cathode material used in the lithium iron phosphate battery cell to be tested was subjected to Raman spectroscopy to measure the characteristic peak intensity of carbonate and phosphate in the lithium iron phosphate cathode material; the pH value of the lithium iron phosphate cathode material was measured; the median particle size of the lithium iron phosphate cathode material was measured; and the powder resistivity of the lithium iron phosphate cathode material was measured. Calculate the following relationship: ， Among them, l c This represents the numerical value of the characteristic peak intensity of carbonate ions; l p This represents the numerical value of the characteristic peak intensity of phosphate. pH refers to the pH value of the lithium iron phosphate cathode material; D 50 The median particle size of the lithium iron phosphate cathode material is expressed in μm. k is the numerical value of the powder resistivity of the lithium iron phosphate cathode material, and the unit of powder resistivity is Ω·cm; when When F ≥ 0.95 and F ≥ 0.95, the capacity of the lithium iron phosphate battery cell under test is ≤ 85% of the design capacity; it is determined that the lithium iron phosphate battery cell under test has low capacity.
2. The method for predicting the capacity of lithium iron phosphate battery cells according to claim 1, characterized in that, The measured intensity of the carbonate characteristic peak of the lithium iron phosphate cathode material was 1040–1055 cm⁻¹ in the Raman spectrum. -1 The intensity of the carbonate characteristic peak at the location.
3. The method for predicting the capacity of lithium iron phosphate battery cells according to claim 2, characterized in that, The characteristic peak intensity of the carbonate ion is 800~2000.
4. The method for predicting the capacity of a lithium iron phosphate battery cell according to claim 1, characterized in that, The measured intensity of the phosphate characteristic peak of the lithium iron phosphate cathode material was 985–1005 cm⁻¹ in the Raman spectrum. -1 The intensity of the characteristic peak of phosphate at the location.
5. The method for predicting the capacity of a lithium iron phosphate battery cell according to claim 4, characterized in that, The characteristic peak intensity of the phosphate group is 800~1600.
6. The method for predicting the capacity of a lithium iron phosphate battery cell according to any one of claims 1 to 5, characterized in that, The powder resistivity of lithium iron phosphate cathode material is 0.1~0.9Ω·cm.
7. The method for predicting the capacity of a lithium iron phosphate battery cell according to claim 6, characterized in that, When testing the powder resistivity of the lithium iron phosphate cathode material, the applied pressure is 10~50MPa.
8. The method for predicting the capacity of a lithium iron phosphate battery cell according to any one of claims 1 to 5, characterized in that, 8≤pH≤11.
9. The method for predicting the capacity of a lithium iron phosphate battery cell according to any one of claims 1 to 5, characterized in that, The median particle size of the lithium iron phosphate cathode material is 0.3~5.0 μm.
10. The method for predicting the capacity of a lithium iron phosphate battery cell according to any one of claims 1 to 5, characterized in that, The lithium iron phosphate cathode material includes lithium iron phosphate cathode materials with a storage time of 0 to 12 months.