Lithium ion battery consistency difference detection method

Abstract

The invention belongs to the technical field of battery sorting, and particularly relates to a lithium ion battery consistency difference detection method which comprises the following steps: (1) preparing negative electrode slurry by taking a coal-based negative electrode material as a main raw material, coating the negative electrode slurry on a negative electrode current collector, and rolling to obtain a negative electrode piece; the interplanar spacing range of the coal-based negative electrode material is 0.337 to 0.339 nm; (2) preparing positive electrode slurry by taking the lithium iron phosphate powder material as a main raw material, coating the positive electrode slurry on a negative electrode current collector, and rolling to obtain a positive electrode piece; (3) assembling the prepared positive pole piece and the prepared negative pole piece, and injecting electrolyte; (4) for the assembled to-be-screened lithium ion batteries in the same batch, the batteries are fully charged at the rate of 1C firstly, then the batteries stand for 1-4 hours at the temperature of 0-20 DEG C, and then the batteries are discharged for 1 minute at the rate of 2C-3C; and recording the voltage change of the battery in the discharging process. According to the method disclosed by the invention, the screening efficiency of the consistency detection of the batteries is remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of battery sorting technology, and particularly relates to a method for detecting consistency differences in lithium-ion batteries. Background Technology

[0002] In recent years, lithium-ion batteries have developed exceptionally rapidly and have been widely used in 3C consumer electronics, electric vehicles, and energy storage products. However, with increasing demand for battery capabilities, especially in energy storage and electric vehicles, where the requirements for battery consistency are extremely high, the demand for these batteries is growing.

[0003] Chinese patent document (CN114200324A) discloses a method, apparatus, device and storage medium for sorting lithium iron phosphate batteries. The method involves sorting lithium iron phosphate batteries by discharging them twice and recording parameter changes. The method also involves standardizing the initial state of the batteries, resulting in good battery consistency. Multiple parameters are selected, leading to high sorting accuracy.

[0004] Chinese patent document (CN117706393A) provides a battery consistency difference detection method, electronic device, and storage medium. The battery consistency difference detection method includes: determining the charging data of each cell in a battery pack after it is fully charged and left to stand for a first preset time; determining the discharging data of each cell in the battery pack after it is fully discharged and left to stand for a second preset time; determining the electrical performance data of each cell based on the charging and discharging data; and detecting whether there are consistency differences in the battery pack based on the electrical performance data. This method achieves a comprehensive analysis of the cell charging and discharging processes, fully considers the impact of charging and discharging data on the electrical performance evaluation of the cells, improves the accuracy of the cell electrical performance data, and quantifies the electrical performance of the cells, thereby improving the accuracy and efficiency of consistency difference detection.

[0005] However, traditional battery screening methods are characterized by long screening times and high costs. Improving the efficiency of battery consistency screening is a worthwhile area of ​​research. Summary of the Invention

[0006] Traditional battery screening methods suffer from time-consuming and costly processes. The purpose of this invention is to provide a method for detecting consistency differences in lithium-ion batteries. By using low-temperature pulse technology, the screening efficiency for battery consistency detection is significantly improved. The method of this invention can screen batteries in 1 minute, which is an order of magnitude improvement compared to the original detection time.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A method for detecting consistency differences in lithium-ion batteries includes the following steps:

[0009] (I) Preparation of negative electrode sheet: A negative electrode slurry is prepared by using coal-based negative electrode material as the main raw material and coated onto the negative electrode current collector, and then rolled and pressed to obtain a negative electrode sheet; wherein, the interplanar spacing of the coal-based negative electrode material is 0.337-0.339nm (e.g., 0.338nm);

[0010] (II) Preparation of positive electrode sheet: The positive electrode slurry is prepared by using lithium iron phosphate powder as the main raw material and coated onto the negative electrode current collector. The positive electrode sheet is obtained by rolling and pressing.

[0011] (III) Battery assembly: The prepared positive and negative electrode sheets are assembled and injected with electrolyte;

[0012] (iv) Battery consistency difference detection: For the same batch of lithium-ion batteries to be screened after assembly, first fully charge the obtained lithium-ion batteries at a 1C rate, then let the batteries stand at 0℃ to -20℃ (e.g., -1℃, -5℃, -10℃, -15℃, -18℃) for 1-4 hours (e.g., 2 hours, 3 hours), and then discharge them at a 2C to 3C rate for 1 minute; record the voltage change of each lithium-ion cell during the discharge process, and simultaneously measure the internal resistance of the battery, and evaluate the battery consistency difference based on the characteristic parameters obtained during the discharge process.

[0013] According to the detection method provided by the present invention, in some embodiments, the preparation method of the coal-based anode material includes:

[0014] (1) Material selection and shaping: The raw coal is crushed and ground and then sieved through a 200-mesh sieve. The resulting powder is then shaped, and the size range of the shaped particles is as follows:

[0015] 2 micrometers <D 10 <5 micrometers, 10 micrometers <D 50 <11 micrometers, 24 micrometers <D 90 <27 micrometers;

[0016] (2) Primary granulation: The particle size obtained above is 10 micrometers. <D 50Particles <11 micrometers are placed in a reaction vessel, and the temperature inside the vessel is controlled at 100-150℃ (e.g., 105℃, 110℃, 120℃, 130℃, 140℃). Under closed conditions of 1-5 atmospheres, electric heating is carried out according to the following temperature curve: stirring at 200-300℃ (e.g., 220℃, 250℃, 280℃) for 2-4 hours (e.g., 2.5h, 3h, 3.5h), and then continuing to heat to 400-500℃ (e.g., 420℃, 450℃, 480℃) and stirring for 1-3 hours (e.g., 2 hours).

[0017] After the reaction was completed, the material was cooled and discharged. The particle size of the obtained particles is as follows:

[0018] 8 micrometers <D 10 <10 micrometers, 16 micrometers <D 50 <18 micrometers, 27 micrometers <D 90 <30 micrometers;

[0019] (3) Ball milling: Under vacuum conditions, the particle size of 16 micrometers obtained in step (2) is ball milled. <D 50 Ball milling particles smaller than 18 microns to a particle size of 12 microns <D 50 Powder with a particle size of less than 15 microns is then sieved using a screening machine.

[0020] (4) Graphitization: The powder obtained in step (3) is placed in a graphitization furnace for graphitization. First, the temperature is raised to 1000℃ and held for 2 hours; then the temperature is raised to 2250℃ and held for 3 hours; finally, the temperature is raised to 2800-2950℃ and held for 24 hours, and then the temperature is lowered to room temperature.

[0021] (5) Ball milling: The graphitized material obtained in step (4) is transported to a ball mill under vacuum for ball milling, and then sieved using a 200-mesh molecular sieve;

[0022] (6) Secondary granulation: The sieved material obtained in step (5) is placed in a reactor for secondary granulation. The secondary granulation is carried out according to the following process:

[0023] First, the temperature is raised from room temperature to 350℃ and held for 30 minutes, then raised to 550℃ for 60 minutes and held for 90 minutes; then raised to 650℃ and held for 60 minutes, and then lowered to below 200℃; during this process, the stirring speed of the reactor is 30-40 rpm (e.g., 32 rpm, 35 rpm, 38 rpm);

[0024] The resulting particles were ball-milled to a particle size of 14 micrometers using a shaping machine. <D 50 Powder with a particle size of <17 microns is then sieved and ball-milled to obtain particles with a particle size of 12 microns. <D 50Powder with a particle size of <14 microns;

[0025] (7) Carbonization: Place the powder obtained in step (6) in a carbonization furnace and sinter at 1400℃-1600℃ (e.g., 1450℃, 1500℃, 1550℃) for 12-24 hours, and then cool to room temperature;

[0026] (8) Demagnetization: The carbonized material obtained in step (7) is demagnetized to remove Fe, so that the Fe content is controlled at 30ppm or below, and then it is packaged to obtain powdered coal-based anode material.

[0027] In some implementation methods, the raw coal used in the preparation method of the coal-based anode material is Taixi anthracite.

[0028] According to the detection method provided by the present invention, in some embodiments, the preparation steps of the negative electrode sheet are as follows:

[0029] (1) First, mix the thickener CMC with deionized water, then add the conductive agent SP while stirring at a speed of 500-1000 rpm (e.g., 600 rpm, 800 rpm) for 1-2 hours; then, add the binder SBR while stirring for 30-60 minutes at a speed of 500-1000 rpm (e.g., 600 rpm, 800 rpm); finally, add the coal-based anode material and stir for 60-90 minutes (e.g., 45 minutes); adjust the viscosity of the resulting anode slurry to 3000-5000 cps (e.g., 3500 cps, 4000 cps, 4500 cps) by adding deionized water as a solvent;

[0030] (2) Place the negative electrode slurry prepared above onto a coating machine and use the coating machine to coat the negative electrode slurry onto the negative electrode current collector. The temperature of the coating machine is controlled at 90℃-110℃ (e.g., 100℃, 105℃).

[0031] (3) The electrode obtained after the above coating is rolled by a rolling mill so that the electrode thickness is 100-120 micrometers and the rolling pressure is 5-15MPa (e.g., 6MPa, 10MPa, 12MPa).

[0032] (4) Heat the rolled electrode sheet as described above at 100-110℃ (e.g., 105℃) for 10-12 hours to obtain the negative electrode sheet.

[0033] In some embodiments, in step (1) of preparing the negative electrode sheet, based on the total weight of all components as 100%, the amount of coal-based negative electrode material is 85-94 wt% (e.g., 86 wt%, 90 wt%, 92 wt%), the amount of thickener CMC is 0.5-6 wt% (e.g., 0.8 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%), and the amount of binder SBR is 0.5-8 wt% (e.g., 0.8 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%). The negative electrode slurry prepared by using deionized water as solvent has a solid content of 30-50 wt% (e.g., 32 wt%, 35 wt%, 38 wt%, 40 wt%, 45 wt%), with the amounts of conductive agent SP being 0.5-5 wt% (e.g., 0.8 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 4.5 wt%).

[0034] According to the detection method provided by the present invention, in some embodiments, the preparation steps of the positive electrode sheet are as follows:

[0035] (1) First, mix half of the lithium iron phosphate powder with the conductive agent SP powder at a stirring speed of 10-30 rpm. Then, add the solvent NMP and graphene conductive slurry while stirring at a stirring speed of 400-800 rpm (e.g., 500 rpm, 600 rpm) for 1-2 hours. After that, add the remaining half of the lithium iron phosphate powder while stirring at a stirring speed of 300-600 rpm (e.g., 400 rpm, 500 rpm) for 60-75 minutes. Finally, add the binder PVDF while stirring at a stirring speed of 200-400 rpm (e.g., 300 rpm) for 40-90 minutes to obtain the positive electrode slurry. Adjust the viscosity of the positive electrode slurry by adding the solvent NMP to achieve 6000-8000 cps (e.g., 6500 cps, 7000 cps, 7500 cps).

[0036] (2) Place the positive electrode slurry prepared above onto a coating machine and use the coating machine to coat the positive electrode slurry onto the positive electrode current collector. The temperature of the coating machine is controlled at 90℃-110℃ (e.g., 100℃, 105℃).

[0037] (3) The electrode obtained after the above coating is rolled by a rolling mill so that the electrode thickness is 150-170 micrometers and the rolling pressure is 5-15MPa (e.g., 6MPa, 10MPa, 12MPa).

[0038] (4) Heat the rolled electrode sheet as described above at 100-110℃ (e.g., 105℃) for 10-12 hours to obtain the positive electrode sheet.

[0039] In some embodiments, in step (1) of preparing the positive electrode sheet, based on the total weight of each component as 100%, the amount of lithium iron phosphate powder material is 85-94 wt% (e.g., 86 wt%, 90 wt%, 92 wt%), the amount of conductive agent SP is 0.5-5 wt% (e.g., 0.8 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 4.5 wt%), the amount of binder PVDF is 1-8 wt% (e.g., 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%), and the amount of graphene conductive paste is 0.5-5 wt% (e.g., 0.8 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 4.5 wt%); the solvent is NMP, and the solid content of the obtained positive electrode paste is 50-80 wt%.

[0040] In some implementation schemes, the battery assembly process in step (iii) includes the following steps:

[0041] (1) Stack the prepared positive and negative electrode sheets;

[0042] (2) Place the stacked battery electrode assembly into an aluminum-plastic shell for edge sealing (e.g., the temperature of the upper and lower sealing heads of the packaging equipment is 180°C and the time is 10s), and then bake (e.g., the baking temperature is 90°C and the baking time is 12 hours).

[0043] (3) Inject the electrolyte into the sealed battery box and perform the edge sealing process again to obtain a full cell.

[0044] According to the detection method provided by the present invention, in some embodiments, the positive electrode and the negative electrode are assembled in a five-positive-six-negative-electrode stacking manner.

[0045] In some implementations, the positive electrode and the negative electrode are stacked in the following manner: the electrodes are stacked in a "Z" shape, with the top and bottom surfaces being the negative electrodes, and the stacking is done in the form of "negative electrode-positive electrode-negative electrode-positive electrode-negative electrode-positive electrode-negative electrode-positive electrode-negative electrode-positive electrode-negative electrode-positive electrode-negative electrode".

[0046] According to the detection method provided by the present invention, in some embodiments, the electrolyte injected in the battery assembly comprises the following components in varying amounts:

[0047] LiTFSI, 5-20 wt% (e.g., 10 wt%, 15 wt%);

[0048] LiPF6, 5-20 wt% (e.g., 6 wt%, 10 wt%, 15 wt%, 18 wt%);

[0049] EP, 30-60wt% (e.g., 40wt%, 50wt%);

[0050] EC, 15-40wt% (e.g., 20wt%, 25wt%, 30wt%, 35wt%);

[0051] VC, 1-3wt% (e.g., 1wt%, 2wt%, 2.5wt%);

[0052] PS, 1-5wt% (e.g., 2wt%, 3wt%, 4wt%);

[0053] FEC, 2-10wt% (e.g., 4wt%, 5wt%, 6wt%, 8wt%);

[0054] LiODFB, 1-3 wt% (e.g., 2 wt%).

[0055] Compared with the prior art, the beneficial effects of the technical solution of the present invention are at least as follows:

[0056] 1) Fast detection speed: Utilizing the excellent low-temperature performance of coal-based anode materials, the consistency of batteries can be confirmed by the change in voltage drop under low temperature (such as 0℃ to -20℃) and 2C-3C rate pulse discharge conditions; and the battery screening time using this low-temperature pulse technology is 1 minute, which is an order of magnitude improvement over the detection time of existing technologies.

[0057] 2) High detection accuracy: The detection method of the present invention can classify batteries into more grades, which is beneficial for accurately assessing the consistency of batteries;

[0058] 3) Wide applicable temperature range: Based on the characteristics of different batteries, it can reduce the loss of battery cycle capacity by discharging at a high rate under different low temperature conditions to degrade the coal-based negative electrode material battery. Detailed Implementation

[0059] To provide a detailed understanding of the technical features and content of this invention, preferred embodiments will be described in more detail below. While preferred embodiments are described in the examples, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer shall apply.

[0060] In the following examples and comparative examples, the sources of some or all of the reagents or raw materials used, unless otherwise specified, are all conventional products that can be purchased commercially.

[0061] Interplanar spacing testing of coal-based anode materials:

[0062] The coal-based anode material powder was tested by XRD at an angle of 20° to 90°. The diffraction peak of the (002) crystal plane was obtained in the XRD with an angle between 26.1° and 26.4°, and marked as θ. Then, the interplanar spacing d was calculated according to the Scherrer formula: 2dsinθ=λ (λ is the wavelength of the X-ray, which is generally 0.154nm for Cu). The interplanar spacing d can be calculated by substituting the parameters obtained from the test into the formula.

[0063] Example 1

[0064] The method for detecting consistency differences in lithium-ion batteries includes the following steps:

[0065] 1. Preparation of coal-based anode materials

[0066] (1) Material selection and shaping: Taixi anthracite (preliminary analysis showed that its main components were: ash 2.5wt%, fixed carbon 89.49wt%, sulfides 6.77wt%, and moisture 1.24wt%) was crushed, ground, and sieved through a 200-mesh sieve. The sieved powder was then shaped. The size range of the shaped particles is as follows:

[0067] 2 micrometers <D 10 <5 micrometers, 10 micrometers <D 50 <11 micrometers, 24 micrometers <D 90 <27 micrometers;

[0068] (2) Primary granulation: The particle size obtained above is 10 micrometers. <D 50 Particles smaller than 11 micrometers were placed in a reactor, and the temperature inside the reactor was controlled at 150°C. Under a closed system of 5 atmospheres, electric heating was carried out according to the following temperature curve: stirring at 200-300°C for 4 hours, and then continuing to heat to 400-500°C and stirring for 1.5 hours.

[0069] After the reaction was completed, the material was cooled and discharged. The particle size of the obtained particles is as follows:

[0070] 8 micrometers <D 10 <10 micrometers, 16 micrometers <D 50 <18 micrometers, 27 micrometers <D 90 <30 micrometers;

[0071] The volatile gas in the reactor is drawn out by the blower, condensed in the condenser, and the resulting liquid phase condenses in the form of tar. The resulting gaseous waste gas is drawn out by the blower, filtered by activated carbon and then discharged into the air.

[0072] (3) Ball milling: Under vacuum conditions, the particle size of 16 micrometers obtained in step (2) is ball milled. <D 50 Ball milling particles smaller than 18 microns to a particle size of 12 microns <D 50Powder with a particle size of less than 15 microns is then sieved using a screening machine.

[0073] The screened material is metered and packaged using an automatic packaging and metering device to obtain the screened material; the remaining material is returned to the ball mill for ball milling again via vacuum pipeline, and the above process is repeated. The gas and material are separated by air jetting and vibration, and the dust-containing exhaust gas after gas-material separation is filtered through a filter cartridge before being discharged.

[0074] (4) Graphitization: The powder obtained in step (3) is placed in a graphitization furnace for graphitization. First, the temperature is raised to 1000℃ and kept for 2 hours; then the temperature is raised to 2250℃ and kept for 3 hours; finally, the temperature is raised to 2800-2950℃ and kept for 24 hours, and then slowly lowered to room temperature.

[0075] (5) Ball milling: The graphitized material obtained in step (4) is transported to a ball mill under vacuum for ball milling, and then sieved using a 200-mesh molecular sieve;

[0076] The undersize material is inspected, measured, packaged, and stored; the oversize material is further ball-milled to meet particle size requirements before being sieved.

[0077] (6) Secondary granulation: The sieved material obtained in step (5) is placed in a reactor for secondary granulation. The secondary granulation is carried out according to the following process:

[0078] First, the temperature is raised from room temperature to 350℃ and held for 30 minutes, then raised to 550℃ for 60 minutes and held for 90 minutes; then raised to 650℃ and held for 60 minutes, and then lowered to below 200℃; during this process, the stirring speed of the reactor is 31.2 rpm.

[0079] The resulting particles were ball-milled to a particle size of 14 micrometers using a shaping machine. <D 50 Powder with a particle size of <17 microns is then sieved and ball-milled to obtain particles with a particle size of 12 microns. <D 50 Powder with a particle size of <14 microns;

[0080] (7) Carbonization: The powder obtained after secondary granulation in step (6) is placed in a carbonization furnace and sintered at 1400℃-1600℃ for 24 hours, and then cooled to room temperature;

[0081] (8) Demagnetization: The carbonized material obtained in step (7) is demagnetized to remove Fe and the Fe content is controlled at 30ppm or below. Then it is packaged to obtain coal-based anode material-I in powder form with a crystal plane spacing of 0.338nm.

[0082] 2. Preparation of the negative electrode sheet:

[0083] (1) First, mix the thickener CMC (sodium carboxymethyl cellulose) with deionized water to a concentration of 1 wt%, and stir at 800 rpm. Then, add the conductive agent SP and continue stirring at 800 rpm for 1 hour. Next, add the binder SBR and stir for 45 minutes at 600 rpm. Finally, add the negative electrode powder material (coal-based negative electrode material-I) and stir for 90 minutes to obtain the negative electrode slurry. Adjust the viscosity of the obtained negative electrode slurry to 3000-5000 cps (e.g., 4300 cps) by adding deionized water.

[0084] Based on a total component weight of 100 wt%, the amount of negative electrode powder material (coal-based negative electrode material-I) is 94 wt%, the amount of thickener CMC (sodium carboxymethyl cellulose) is 2 wt%, the amount of binder SBR (styrene-butadiene rubber) is 2.5 wt%, the amount of conductive agent SP (conductive carbon black) is 1.5 wt%, and the solvent is deionized water. The solid content of the obtained negative electrode slurry is 42.32 wt%.

[0085] (2) Place the obtained negative electrode slurry onto a coating machine and use the coating machine to coat the negative electrode slurry onto the metal copper foil. The temperature of the coating machine is controlled at 105℃.

[0086] (3) The electrode sheet obtained after the above coating is rolled by a rolling mill, with a thickness of about 100-120 micrometers and a pressure of about 10 MPa.

[0087] (4) The above-rolled electrode sheet is heated at 110°C for 12 hours to obtain negative electrode sheet-I; the moisture content of the negative electrode sheet is 213ppm according to the moisture tester.

[0088] 3. Preparation of the positive electrode sheet:

[0089] (1) First, mix half of the lithium iron phosphate powder with the conductive agent SP powder and stir at a stirring speed of 30 rpm. Then, add graphene conductive slurry and a certain amount of solvent NMP and stir at a stirring speed of 800 rpm for 1 hour. Then, add the remaining half of the lithium iron phosphate powder and stir for 75 minutes at a stirring speed of 600 rpm. Finally, add the binder PVDF and stir for 90 minutes at a stirring speed of 400 rpm to obtain the positive electrode slurry. Adjust the viscosity of the obtained positive electrode slurry by adding solvent NMP to make it reach 6000-8000 cps (e.g., 7200 cps).

[0090] The positive electrode powder material is commercially available energy storage lithium iron phosphate powder. Based on a total component weight of 100wt%, the amount of lithium iron phosphate powder material is 94wt%, the amount of conductive agent SP (conductive carbon black) is 2wt%, the amount of binder PVDF is 3wt%, the amount of graphene conductive slurry is 1wt%, and the solvent is NMP (N-methylpyrrolidone). The solid content of the obtained positive electrode slurry is 72.3wt%.

[0091] (2) Place the obtained positive electrode slurry onto a coating machine and use the coating machine to coat the positive electrode slurry onto the metal aluminum foil. The temperature of the coating machine is controlled at 105℃.

[0092] (3) The electrode sheet obtained after the above coating is rolled by a rolling mill, with a thickness of about 150-170 micrometers and a pressure of about 12 MPa.

[0093] (4) The above-rolled electrode sheet is heated at 100°C for 12 hours to obtain the positive electrode sheet; the moisture content of the positive electrode sheet is 312ppm according to the moisture tester.

[0094] 4. Battery assembly:

[0095] (1) Cut the positive electrode sheet obtained above into 84mm*60mm and the negative electrode sheet obtained above into 88mm*64mm. The battery is packaged in a soft pack and uses a five positive electrode and six negative electrode stacking method, that is: stack the electrode sheets in a "Z" shape, with the top and bottom sides being negative electrodes, and stack them in the form of "negative electrode-positive electrode-negative electrode-positive electrode-negative electrode-positive electrode-negative electrode-positive electrode-negative electrode-positive electrode-negative electrode-positive electrode-negative electrode".

[0096] (2) Place the stacked battery electrode assembly into an aluminum-plastic shell for double-sided sealing process, that is: the temperature of the upper and lower sealing heads of the sealing equipment is 180℃ and the time is 10s;

[0097] (3) Place the packaged battery into a vacuum chamber for baking at a temperature of 90°C for 12 hours.

[0098] (4) In the glove box, the electrolyte is injected into the battery with an injection coefficient of 5; wherein the electrolyte comprises the following components in the following amounts:

[0099] LiTFSI, 15 wt%;

[0100] LiPF6, 20wt%;

[0101] EP, 35wt%;

[0102] EC, 20wt%;

[0103] Vitamin C, 2wt%;

[0104] PS, 3wt%;

[0105] FEC, 3wt%;

[0106] LiODFB, 2wt%;

[0107] The injection volume is 5 grams per hour;

[0108] The diaphragm is a 16-micron-thick polyethylene diaphragm;

[0109] (5) After the battery is filled with liquid, it is sealed by side sealing. The sealing temperature of the upper and lower sealing heads of the sealing equipment is 180°C and the sealing time is 10 seconds.

[0110] 5. Detection of consistency differences in all batteries

[0111] The assembled batch of lithium-ion batteries (with negative electrode sheets prepared using coal-based negative electrode material I) were screened. First, the lithium-ion batteries were fully charged at a 1C rate. Then, they were placed in a low-temperature chamber and left to stand at -20°C for 4 hours. Next, they were discharged at a 3C rate for 1 minute, and the voltage of the lithium-ion batteries during the discharge process was recorded, i.e., V. 1-1 V 1-2 ...V 1-n The internal resistance of the battery was measured, and the consistency differences of the batteries were evaluated based on the characteristic parameters obtained during the discharge process.

[0112] Example 2:

[0113] The method for detecting consistency differences in lithium-ion batteries is the same as in Example 1, except that in the full-cell consistency difference detection step, the lithium-ion battery is first fully charged at a 1C rate, then placed in a low-temperature chamber and left to stand at 0°C for 4 hours, and then discharged at a 3C rate for 1 minute. The voltage of the lithium-ion battery during the discharge process is recorded, i.e., V. 2-1 V 2-2 ...V 2-n The internal resistance of the battery was measured, and the consistency differences of the batteries were evaluated based on the characteristic parameters obtained during the discharge process.

[0114] Example 3:

[0115] The method for detecting consistency differences in lithium-ion batteries is the same as in Example 1, except that in the full-cell consistency difference detection step, the lithium-ion battery is first fully charged at a 1C rate, then placed in a low-temperature chamber and left to stand at -20°C for 4 hours, and then discharged at a 2C rate for 1 minute. The voltage of the lithium-ion battery during the discharge process is recorded, i.e., V. 3-1 V 3-2 ...V3-n The internal resistance of the battery was measured, and the consistency differences of the batteries were evaluated based on the characteristic parameters obtained during the discharge process.

[0116] Example 4:

[0117] The method for detecting consistency differences in lithium-ion batteries is the same as in Example 1, except that in step 1, the graphitization step (4) of the coal-based anode material preparation process, the temperature is first raised to 1000℃ and held for 2 hours; then raised to 2250℃ and held for 3 hours; finally raised to 2700-2750℃ and held for 24 hours, and then slowly lowered to room temperature; the resulting coal-based anode material-II has a crystal plane spacing of 0.339 nm; and the anode sheet is prepared using coal-based anode material-II in step 2; the remaining steps are the same as in Example 1. The voltage of the lithium-ion battery during discharge is recorded, i.e., V. 4-1 V 4-2 ...V 4-n The internal resistance of the battery was measured, and the consistency differences of the batteries were evaluated based on the characteristic parameters obtained during the discharge process.

[0118] Comparative Example 1:

[0119] The method for detecting consistency differences in lithium-ion batteries is the same as in Example 1, except that in the full-cell consistency difference detection step, the lithium-ion battery is first fully charged at a 1C rate, then placed in a low-temperature chamber and left to stand at room temperature (25°C) for 4 hours, and then discharged at a 3C rate for 1 minute. The voltage of the lithium-ion battery during the discharge process is recorded, i.e., V. 5-1 V 5-2 ...V 5-n The internal resistance of the battery was measured, and the consistency differences of the batteries were evaluated based on the characteristic parameters obtained during the discharge process.

[0120] Comparative Example 2:

[0121] The method for detecting consistency differences in lithium-ion batteries is the same as in Example 1, except that in the full-cell consistency difference detection step, the lithium-ion battery is first fully charged at a 1C rate, and then left to stand at room temperature for 28 days. The voltage of the lithium-ion battery during the standing period is recorded, i.e., V. 6-1 V 6-2 ...V 6-n The internal resistance of the battery was measured, and the consistency differences of the batteries were evaluated based on the characteristic parameters obtained during the discharge process.

[0122] Comparative Example 3:

[0123] The method for detecting consistency differences in lithium-ion batteries is the same as in Example 1, except that in the full-cell consistency difference detection step, the lithium-ion battery is first fully charged at a 1C rate, then placed in a low-temperature chamber and left to stand at -20°C for 4 hours, and then discharged at a 1C rate for 1 minute. The voltage of the lithium-ion battery during the discharge process is recorded, i.e., V. 7-1 V 7-2 ...V 7-n The internal resistance of the battery was measured, and the consistency differences of the batteries were evaluated based on the characteristic parameters obtained during the discharge process.

[0124] Comparative Example 4:

[0125] The method for detecting consistency differences in lithium-ion batteries is the same as in Example 1, except that a negative electrode sheet is prepared using commercially available conventional negative electrode material, and then a lithium-ion full cell is fabricated; the remaining steps are the same as in Example 1; the voltage of the lithium-ion battery during discharge is recorded, i.e., V. 8-1 V 8-2 ...V 8-n The internal resistance of the battery was measured, and the consistency differences of the batteries were evaluated based on the characteristic parameters obtained during the discharge process.

[0126] The characteristic parameters obtained for the discharge process of the obtained full battery in each embodiment and comparative example are shown in Tables 1-8.

[0127] Table 1. Characteristic parameters obtained during the full-cell discharge process in Example 1.

[0128] Example 1 V 1-1 ]]> V 1-2 ]]> V 1-3 ]]> V 1-4 ]]> V 1-5 ]]> V 1-6 ]]> V 1-7 ]]> V 1-8 ]]> V 1-9 ]]> V 1-10 ]]> Ave Voltage (mV) 3244 3221 3258 3230 3273 3247 3240 3245 3257 3269 3248.4 Internal resistance (mΩ) 14.63 15.13 14.83 15.02 14.93 16.01 15.27 15.03 14.28 14.98 15.011 Voltage deviation (mV) 4.4 27.4 9.6 18.4 24.6 1.4 8.4 3.4 8.6 20.6 <20 mV

[0129] Table 2. Characteristic parameters obtained during the full-cell discharge process in Example 2.

[0130] Example 2 V 2-1 ]]> V 2-2 ]]> V 2-3 ]]> V 2-4 ]]> <![CDATA[V 2-5 ]]> <![CDATA[V 2-6 ]]> <![CDATA[V 2-7 ]]> <![CDATA[V 2-8 ]]> <![CDATA[V 2-9 ]]> <![CDATA[V 2-10 ]]> Ave Voltage (mV) 3292 3279 3311 3288 3319 3300 3293 3299 3311 3321 3300.7 Internal resistance (mΩ) 13.52 14.02 13.72 13.91 13.82 14.9 14.16 13.92 13.17 13.87 13.901 Voltage deviation (mV) 8.7 21.7 10.3 12.7 18.3 0.7 7.7 1.7 10.3 20.3 <20mV

[0131] Table 3. Characteristic parameters obtained during the full-cell discharge process in Example 3.

[0132] Example 3 <![CDATA[V 3-1 ]]> <![CDATA[V 3-2 ]]> <![CDATA[V 3-3 ]]> <![CDATA[V 3-4 ]]> <![CDATA[V 3-5 ]]> <![CDATA[V 3-6 ]]> <![CDATA[V 3-7 ]]> <![CDATA[V 3-8 ]]> <![CDATA[V 3-9 ]]> <![CDATA[V 3-10 ]]> Ave Voltage (mV) 3278 3253 3291 3266 3310 3280 3272 3280 3296 3301 3282.7 Internal resistance (mΩ) 15.83 16.39 16.02 16.23 16.08 17.25 16.53 16.29 15.54 14.82 16.108 Voltage deviation (mV) 4.7 29.7 8.3 16.7 27.3 2.7 10.7 2.7 13.3 18.3 <20mV

[0133] Table 4. Characteristic parameters obtained during the full-cell discharge process in Example 4.

[0134]

[0135]

[0136] Table 5 shows the characteristic parameters obtained during the full-cell discharge process of Comparative Example 1.

[0137] Comparative Example 1 <![CDATA[V 5-1 ]]> <![CDATA[V 5-2 ]]> <![CDATA[V 5-3 ]]> <![CDATA[V 5-4 ]]> <![CDATA[V 5-5 ]]> <![CDATA[V 5-6 ]]> <![CDATA[V 5-7 ]]> <![CDATA[V 5-8 ]]> <![CDATA[V 5-9 ]]> <![CDATA[V 5-10 ]]> Ave Voltage (mV) 3311 3298 3324 3302 3321 3314 3307 3312 3324 3331 3314.4 Internal resistance (mΩ) 12.67 13.17 12.87 13.06 12.97 14.05 13.31 13.07 12.32 13.02 13.051 Voltage deviation (mV) 3.4 16.4 9.6 12.4 6.6 0.4 7.4 2.4 9.6 16.6 <20mV

[0138] Table 6 shows the characteristic parameters obtained during the full-cell discharge process of Comparative Example 2.

[0139] Comparative Example 2 <![CDATA[V 6-1 ]]> <![CDATA[V 6-2 ]]> <![CDATA[V 6-3 ]]> <![CDATA[V 6-4 ]]> <![CDATA[V 6-5 ]]> <![CDATA[V 6-6 ]]> <![CDATA[V 6-7 ]]> <![CDATA[V 6-8 ]]> <![CDATA[V 6-9 ]]> <![CDATA[V 6-10 ]]> Ave Voltage (mV) 3436 3421 3449 3432 3466 3439 3432 3437 3449 3428 3445.13 Internal resistance (mΩ) 12.89 13.39 13.09 13.28 13.19 14.26 13.53 13.29 12.53 13.24 13.269 Voltage deviation (mV) 9.1 24.1 3.9 13.1 20.9 6.1 13.1 8.1 3.9 17.1 <20mV

[0140] Table 7 shows the characteristic parameters obtained during the full-cell discharge process of Comparative Example 3.

[0141] Comparative Example 3 <![CDATA[V 7-1 ]]> <![CDATA[V 7-2 ]]> <![CDATA[V 7-3 ]]> <![CDATA[V 7-4 ]]> <![CDATA[V 7-5 ]]> <![CDATA[V 7-6 ]]> <![CDATA[V 7-7 ]]> <![CDATA[V 7-8 ]]> <![CDATA[V 7-9 ]]> <![CDATA[V 7-10 ]]> Ave Voltage (mV) 3268 3256 3257 3283 3289 3273 3276 3271 3283 3258 3274.4 Internal resistance (mΩ) 13.21 13.71 13.41 13.6 13.51 14.59 13.85 13.61 12.86 13.56 13.901 Voltage deviation (mV) 6.4 18.4 17.4 8.6 14.6 1.4 1.6 3.4 8.6 16.4 <20mV

[0142] Table 8 shows the characteristic parameters obtained during the full-cell discharge process of Comparative Example 4.

[0143] Comparative Example 4 <![CDATA[V 8-1 ]]> <![CDATA[V 8-2 ]]> <![CDATA[V 8-3 ]]> <![CDATA[V 8-4 ]]> <![CDATA[V 8-5 ]]> <![CDATA[V 8-6 ]]> <![CDATA[V 8-7 ]]> <![CDATA[V 8-8 ]]> <![CDATA[V 8-9 ]]> <![CDATA[V 8-10 ]]> Ave Voltage (mV) 3234 3247 3231 3221 3206 3236 3233 3242 3228 3220 3230.8 Internal resistance (mΩ) 17.3 17.8 17.5 17.69 17.4 18.68 17.32 16.3 17.93 14.98 17.274 Voltage deviation (mV) 3.2 16.2 0.2 9.8 24.8 5.2 2.2 11.2 7.2 10.8 <20mV

[0144] In each embodiment, the obtained full cells are tested using a low-temperature, high-rate method, which allows for rapid classification of the cells into multiple grades based on the obtained characteristic parameters. Furthermore, the discharge time is short under low-temperature conditions, meaning that characteristic parameters such as voltage difference of cells in different grades can be detected within one minute. The higher the dispersion of characteristic parameters such as voltage difference of the cells, the better the cell screening effect, which allows for greater flexibility in cell matching.

[0145] As can be seen from Examples 1-2 and Comparative Example 1, under the condition of high-rate 3C discharge, as the temperature decreases during the detection process, the differences between batteries increase. The lower the detection temperature, the greater the differences between batteries, the more obvious the dispersion, and the better the battery screening effect.

[0146] As can be seen from Example 1 and Comparative Example 2, after being left to stand under the same charging conditions, the characteristic parameters obtained by pulse discharge at -20°C for 1 minute in Example 1 are basically close to the full cell voltage difference and voltage dispersion after being left to stand at room temperature for 28 days in Comparative Example 2. However, the pulse discharge at low temperature for 1 minute in Example 1 takes a shorter time, which is much shorter than the time taken by conventional detection method in Comparative Example 2 (28 days).

[0147] As can be seen from Example 1 and Comparative Example 3, under the same detection temperature, the battery dispersion is higher when discharged at a 3C rate; that is, the battery dispersion is higher when discharged at a high rate.

[0148] As can be seen from Example 1 and Comparative Example 4, under the same testing conditions (minus 20°C, 3C rate discharge), the distribution dispersion of batteries made from coal-based anode materials increases, which is also beneficial for battery screening.

[0149] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the spirit of the invention.

Claims

1. A method of detecting inconsistencies in lithium-ion batteries, characterized by, It comprises the following steps: (I) Preparation of negative electrode sheet: coal-based negative electrode material is used as the main raw material to prepare negative electrode slurry which is coated on the negative electrode current collector, and the negative electrode sheet is prepared by rolling; (II) Preparation of positive electrode sheet: lithium iron phosphate powder material is used as the main raw material to prepare positive electrode slurry which is coated on the negative electrode current collector, and the positive electrode sheet is prepared by rolling; (III) Battery assembly: the prepared positive electrode sheet and negative electrode sheet are assembled and electrolyte is injected; (IV) Battery consistency difference detection: for the same batch of lithium ion batteries to be screened, first fully charge the obtained lithium ion battery at 1C rate, then place the battery at 0℃ to minus 20℃ for 1-4 hours, and then discharge at 2C to 3C rate for 1min; record the voltage change of each lithium ion single battery during discharging, and measure the internal resistance of the battery at the same time, and evaluate the consistency difference of the battery according to the characteristic parameters obtained during discharging.

2. The detection method according to claim 1, characterized in that, The preparation method of the coal-based negative electrode material comprises: (1) Selecting and shaping: the raw coal is crushed and ground and sieved to 200 mesh, and then the sieved powder is shaped, and the size of the obtained particles after shaping is as follows: 2 microns < D 10 <5 microns, 10 microns < D 50 <11 microns, 24 microns < D 90 <27 microns; (2) Primary granulation: The particle size of 10 microns < D 50 <11 microns of particles in the reactor, the temperature control in the kettle 100-150 ℃, in a closed condition of 1-5 atmosphere, according to the following temperature curve for electric heating: at 200-300 ℃ stirring 2-4 h, and then continue to heat to 400-500 ℃ stirring 1-3 hours; After the reaction is completed, the temperature is lowered to discharge the material, and the particle size of the obtained particles is as follows: 8 microns < D 10 <10 microns, 16 microns < D 50 <18 microns, 27 microns < D 90 <30 microns; (3) Ball milling: the particle size of 16 microns < D of the product of step (2) is reduced to 12 microns < D under vacuum 50 <18 microns of the particle ball milling is reduced to 12 microns < D 50 <15 microns of the powder is sieved by a sifter (4) Graphitization: the powder obtained in step (3) is placed in a graphitization furnace for graphitization, first heated to 1000℃, and kept for 2 hours; then heated to 2250℃, and kept for 3 hours, and finally heated to 2800-2950℃ and kept for 24 hours, and then lowered to room temperature; (5) Ball milling: the graphitized material obtained in step (4) is transported to a ball mill under vacuum for ball milling, and then sieved using a 200 mesh molecular sieve; (6) Second granulation: the sieved material obtained in step (5) is placed in a reaction kettle for second granulation, which is carried out according to the following process: First, the temperature is raised from room temperature to 350℃ and kept for 30 minutes, then raised to 550℃, the heating time is 60 minutes, and the holding time is 90 minutes; then heated to 650℃, the holding time is 60 minutes, and then lowered to below 200℃; during this process, the stirring speed of the reaction kettle is 30-40rpm; The obtained granules are ball milled to 14 micron <D by a sizer 50 <17 micron powder, which is then sieved and ball milled by a sizer to get 12 micron <D 50 <14 micron powder; (7) Carbonization: the powder obtained in step (6) is placed in a carbonization furnace and sintered at 1400℃-1600℃ for 12-24 hours, and then cooled to room temperature; (8) Demagnetization: the carbonized material obtained in step (7) is demagnetized to remove Fe, so that the Fe content is controlled to be 30ppm or less, and then packaged to obtain the powder coal-based negative electrode material.

3. The detection method according to claim 2, characterized in that, In the preparation method of the coal-based negative electrode material, the raw coal is Taixi anthracite.

4. The method of claim 1, wherein The preparation steps of the negative electrode sheet are as follows: (1) first mix thickening agent CMC with deionized water, then add conductive agent SP to the mixture under stirring, stirring speed is 500-1000 rpm, stirring time is 1-2 hours; then add binder SBR to the mixture under stirring, stirring time is 30-60 minutes, stirring speed is 500-1000 rpm; finally add the coal-based negative electrode material to the mixture, stirring time is 60-90 minutes; adjust the viscosity of the obtained negative electrode slurry by adding deionized water as solvent, so that the viscosity reaches 3000-5000 cps; (2) place the negative electrode slurry prepared above on a coating machine, use the coating machine to coat the negative electrode slurry on the negative electrode current collector, temperature of the coating machine is controlled at 90-110℃; (3) roll the electrode sheet obtained after coating as above by a rolling machine, so that the thickness of the electrode sheet is 100-120 microns, rolling pressure is 5-15 MPa; (4) heat the electrode sheet after rolling as above at 100-110℃ for 10-12 hours, to obtain a negative electrode sheet.

5. The detection method according to claim 4, characterized in that, In step (1) of the preparation of the negative electrode sheet, the amount of the coal-based negative electrode material is 85-94 wt%, the amount of thickening agent CMC is 0.5-6 wt%, the amount of binder SBR is 0.5-8 wt%, the amount of conductive agent SP is 0.5-5 wt%, and deionized water is used as solvent, the solid content of the obtained negative electrode slurry is 30-50 wt%, based on 100% of the total weight of the components.

6. The method of claim 1, wherein, The preparation steps of the positive electrode sheet are as follows: (1) first mix half of the amount of lithium iron phosphate powder material with conductive agent SP powder under stirring, stirring speed is 10-30 rpm, then add solvent NMP and graphene conductive slurry to the mixture under stirring, stirring speed is 400-800 rpm, stirring time is 1-2 hours; then add the remaining half of the amount of lithium iron phosphate powder material to the mixture under stirring, stirring time is 60-75 minutes, stirring speed is 300-600 rpm, finally add binder PVDF to the mixture, stirring time is 40-90 minutes, stirring speed is 200-400 rpm, to obtain a positive electrode slurry; adjust the viscosity of the positive electrode slurry by adding solvent NMP, so that the viscosity reaches 6000-8000 cps; (2) place the positive electrode slurry prepared above on a coating machine, use the coating machine to coat the positive electrode slurry on the positive electrode current collector, temperature of the coating machine is controlled at 90-110℃; (3) roll the electrode sheet obtained after coating as above by a rolling machine, so that the thickness of the electrode sheet is 150-170 microns, rolling pressure is 5-15 MPa; (4) heat the electrode sheet after rolling as above at 100-110℃ for 10-12 hours, to obtain a positive electrode sheet.

7. The detection method according to claim 6, characterized in that, In the preparation step (1) of the positive electrode sheet, the lithium iron phosphate powder material is used in an amount of 85-94wt% based on 100% of the total weight of the components, the conductive agent SP is used in an amount of 0.5-5wt%, the adhesive PVDF is used in an amount of 1-8wt%, and the graphene conductive paste is used in an amount of 0.5-5wt%; the solvent is NMP, and the solid content of the prepared positive electrode slurry is 50-80wt%.

8. The method of claim 1, wherein, In the process of assembling the positive electrode sheet and the negative electrode sheet, a five-positive-electrode and six-negative-electrode lamination method is adopted.

9. The detection method according to claim 8, characterized in that, The lamination method of the positive electrode sheet and the negative electrode sheet is that the electrode sheets are laminated in a "Z" shape, the upper and lower surfaces are negative electrodes, and the lamination is performed in the form of "negative electrode-positive electrode-negative electrode-positive electrode-negative electrode-positive electrode-negative electrode-positive electrode-negative electrode-positive electrode-negative electrode-positive electrode-negative electrode".

10. The method of claim 1, wherein, The electrolyte injected in the battery assembly comprises the following components: LiTFSI, 5-20wt%; LiPF6, 5-20wt%; EP, 30-60wt%; EC, 15-40wt%; VC, 1-3wt%; PS, 1-5wt%; FEC, 2-10wt%; LiODFB, 1-3wt%.

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