Low-temperature formation method of lithium ion battery based on coal-based negative electrode material

Abstract

The invention belongs to the technical field of lithium ion batteries, and particularly relates to a low-temperature formation method of a lithium ion battery based on a coal-based negative electrode material, which comprises the following steps of: (1) preparing negative electrode slurry by taking the 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 plate; wherein the range of the interplanar spacing 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) charging the whole battery at-20 DEG C, and then discharging the battery at normal temperature; and (5) aging the formed battery at the temperature of 40-45 DEG C. According to the method disclosed by the invention, the capacity loss of the total battery in the cycle process can be reduced, so that the total battery has excellent cycle performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion batteries, and particularly relates to a low-temperature formation method of a lithium ion battery based on a coal-based negative electrode material. BACKGROUND

[0002] In recent years, the development of lithium ion batteries is very fast, and the application fields thereof are expanded from consumer products to electric vehicles and energy storage fields. However, it is difficult to avoid some defects existing at present, such as the stability of the full battery in the energy storage process. In the root, this depends on the compactness and stability of the SEI film of the full battery. For this, some improvements are made in the field.

[0003] A low-temperature formation high-nickel ternary lithium battery processing method is disclosed in Chinese patent document (CN108666640A), propylene carbonate is frozen and solidified, and then added into electrolyte A composed of electrolyte lithium salt and solvent methyl acetate to obtain electrolyte B; the high-nickel ternary lithium battery to be injected with liquid is vacuumized, the solidified propylene carbonate in electrolyte B is kept, electrolyte B is injected into the battery, and the battery injected with liquid is obtained after standing. The patent prevents the co-intercalation material from contacting the graphite electrode with lithium ions before the passivation film is formed by the method of low-temperature formation.

[0004] A preparation method of an ultralow-temperature type lithium iron phosphate power battery is disclosed in Chinese patent document (CN102110805A), including the following steps: S1, dissolving iron source, phosphorus source and lithium source in a mixed solvent of polyhydric alcohol and water, mixing the wet solid combination after liquid-solid separation with low-membered sugar, calcining under a protective gas atmosphere to obtain a positive electrode material; S2, crushing and screening the needle-shaped coke raw material, high-temperature graphitizing after low-temperature heat treatment, liquid phase coating, selecting and screening after carbonization treatment to obtain a negative electrode material; S3, adding lithium salt in a multi-component solvent to prepare an electrolyte; S4, coating the positive electrode slurry on the positive electrode current collector to prepare a positive electrode sheet; S5, coating the negative electrode slurry on the negative electrode current collector to prepare a negative electrode sheet; S6, winding the positive electrode sheet, the negative electrode sheet and the separator, and then injecting the electrolyte into the shell to prepare the ultralow-temperature type lithium iron phosphate power battery. The patent can improve the electrochemical performance of the power battery in the ultralow-temperature environment, and realize the application of the power battery in the ultralow-temperature environment.

[0005] The Chinese patent document (CN113594450A) discloses a preparation method of a coal-based artificial graphite negative electrode material for lithium ion batteries, comprising the following steps: 1) sequentially drying, crushing and classifying the fine coke powder raw material; 2) purifying the fine coke powder obtained in step 1) with hydrofluoric acid; 3) roller pressing and shaping the purified fine coke powder; 4) graphitizing the shaped fine coke powder; 5) sequentially removing the magnetic field, screening and mixing the material obtained by graphitization in step 4), to obtain the coal-based artificial graphite negative electrode material. The present application uses hydrofluoric acid purification and graphitization process to remove key impurities such as Si, Al, Ca, Mg and Fe in the artificial graphite raw material in batches, solves the problem of deep removal of these impurities, and thus obtains high-purity artificial graphite; the prepared negative electrode material also has excellent electrochemical performance, and also provides a new production process for artificial graphite negative electrode material.

[0006] At present, the high-temperature formation (45 DEG C) treatment method is adopted for the conventional full battery. Although from the perspective of the reconstruction of the SEI film at high temperature, this method can also improve the storage performance of the battery, but a problem brought about by this is the capacity loss at high temperature. SUMMARY

[0007] The present application aims to solve the problem of stability improvement of full batteries during energy storage, and provides a low-temperature formation method of lithium ion batteries based on coal-based negative electrode material, which aims to improve the storage performance of coal-based negative electrode-lithium iron phosphate full battery; due to the good low-temperature performance of the selected coal-based negative electrode material, the capacity loss of the battery during the aging process can be reduced by formation at minus 20 DEG C, and the storage performance of the battery will be excellent due to the compactness of the SEI film, the method of the present application can reduce the capacity loss of the full battery during the cycle process, and the full battery has excellent cycle performance.

[0008] In order to achieve the above-mentioned purpose, the present application provides the following technical scheme:

[0009] A low-temperature formation method of lithium ion batteries based on coal-based negative electrode material, comprising the following steps:

[0010] (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; wherein the interplanar spacing of the coal-based negative electrode material is 0.337-0.339 nm (for example, 0.3375 nm, 0.338 nm, 0.3385 nm);

[0011] (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;

[0012] (III) battery assembly: the prepared positive electrode sheet, negative electrode sheet are assembled and injected with electrolyte;

[0013] (IV) low-temperature formation treatment: the assembled full battery is formed, and the formation process is as follows: the full battery is placed at minus 20℃, and the full battery is charged under this condition, the charge rate is 0.05C, the charge cutoff current is 0.05C, and the charge cutoff voltage is 3.6V; then the battery is discharged at room temperature, the discharge rate is 0.2C, and the discharge cutoff voltage is 2.0V;

[0014] (V) aging treatment: the battery after formation is charged at room temperature, the charge rate is 0.2C, the charge cutoff voltage is 3.6V, and the charge cutoff current is 0.05C; then the full battery fully charged is aged at 40-45℃ (such as 41℃, 42℃, 43℃, 44℃).

[0015] The full battery after aging can be tested by the cycle capacity retention rate of discharge-charge-discharge-charge cycle capacity calibration, and the capacity calibration rate can be 0.5C.

[0016] According to the low-temperature formation method provided by the application, in some embodiments, the energy density of the full battery prepared by taking lithium iron phosphate as the main raw material as the positive electrode and taking the coal-based negative electrode material as the main raw material as the negative electrode is ≤140Wh / Kg, for example, 30Wh / Kg, 50Wh / Kg, 80Wh / Kg, 100Wh / Kg, 110Wh / Kg, 115Wh / Kg, 120Wh / Kg, 125Wh / Kg, 130Wh / Kg, 135Wh / Kg.

[0017] According to the low-temperature formation method provided by the application, in some embodiments, the preparation method of the coal-based negative electrode material in step (I) comprises:

[0018] (1) material selection and shaping: crushing and grinding the raw material coal and sieving through 200 meshes, and then shaping the powder obtained by sieving, and the size range of the particles obtained after shaping is as follows:

[0019] 2 microns 10 <5 microns, 10 microns 50 <11 microns, 24 microns 90 <27 microns

[0020] (2) primary granulation: the particle size of 10 microns obtained as above 50<11 microns of particles are placed in a reactor, optionally with 2-5% by mass of the contents of the reactor of pitch; the temperature in the reactor is controlled at 100-150°C (e.g., 110°C, 120°C, 140°C), and the reactor is heated under a closed condition (e.g., 5 atmospheres) according to the following temperature profile: stirring at 200-300°C for 2-4 hours (e.g., 2.5 hours, 3 hours), and then heating to 400-500°C for 1-3 hours (e.g., 1.5 hours, 2 hours, 2.5 hours);

[0021] After the reaction is complete, the temperature is lowered and the contents are removed, and the resulting particles have the following size:

[0022] 8 microns < D 10 <10 microns, 16 microns < D 50 <18 microns, 27 microns < D 90 <30 microns;

[0023] (3) Ball milling: the 16 microns < D 50 <18 microns of particles are ball milled to 12 microns < D 50 <15 microns of powder, which is then sieved;

[0024] (4) Graphitization: the powder from step (3) is placed in a graphitization furnace and graphitized, first by heating to 1000°C for 2 hours, then to 2250°C for 3 hours, and finally to 2800-2950°C for 24 hours, and then to room temperature;

[0025] (5) Ball milling: the graphitized material from step (4) is transported under vacuum to a ball mill and ball milled, and then sieved using 200 mesh;

[0026] (6) Second granulation: the sieved material from step (5) is placed in a reactor and subjected to a second granulation, according to the following process:

[0027] first from room temperature to 350°C for 30 minutes, then to 550°C for 60 minutes, and then to 650°C for 60 minutes, and then to below 200°C; during this process, the stirring speed of the reactor is 30-40 rpm (e.g., 32 rpm, 35 rpm, 38 rpm);

[0028] The resulting particles are ball milled to 14 microns < D 50 <17 microns of powder, which is then sieved and ball milled, to give 12 microns < D 50 <14 microns of powder;

[0029] (7) Carbonization: Place the powder obtained in step (6) in a carbonization furnace and sinter at 1400℃-1600℃ for 12-24 hours (e.g., 15 hours, 18 hours, 20 hours), and then cool to room temperature;

[0030] (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.

[0031] In some implementation schemes, in the preparation method of the coal-based negative electrode material in step (i), the raw coal is Taixi anthracite.

[0032] In some implementation schemes, the preparation steps of the negative electrode sheet in step (i) are as follows:

[0033] (1) First, mix the thickener CMC with deionized water, then add the conductive agent SP while stirring at a speed of 500-1000 rpm for 1-2 hours; then, add the binder SBR while stirring for 30-60 minutes at a speed of 500-1000 rpm; finally, add the coal-based anode material and stir for 60-90 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;

[0034] Based on the total weight of all components (100%), the amount of coal-based anode 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., 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%), the amount of binder SBR is 0.5-8 wt% (e.g., 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%), the amount of conductive agent SP is 0.5-5 wt% (e.g., 1 wt%, 2 wt%, 3 wt%, 4 wt%, 4.5 wt%), and deionized water is used as solvent. The solid content of the resulting anode slurry is 30-50 wt% (e.g., 35 wt%, 40 wt%, 45 wt%).

[0035] (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., 95℃, 100℃, 105℃).

[0036] (3) The electrode obtained after the above coating is rolled by a rolling mill so that the electrode thickness is 100-120 micrometers (e.g., 105 micrometers, 110 micrometers, 115 micrometers) and the rolling pressure is 5-15 MPa (e.g., 6 MPa, 10 MPa, 12 MPa, 14 MPa).

[0037] (4) Heat the above-rolled electrode sheet at 100-110℃ (e.g., 105℃) for 10-12 hours to obtain the negative electrode sheet.

[0038] According to the low-temperature formation method provided by the present invention, in some embodiments, the preparation step of the positive electrode sheet in step (ii) is as follows:

[0039] (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 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 for 60-75 minutes. Finally, add the binder PVDF while stirring at a stirring speed of 200-400 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).

[0040] Based on the total weight of all components (100%), the amount of lithium iron phosphate powder 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., 1 wt%, 2 wt%, 3 wt%, 4 wt%, 4.5 wt%), the amount of binder PVDF is 1-8 wt% (e.g., 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%), and the amount of graphene conductive paste is 0.5-5 wt% (e.g., 1 wt%, 2 wt%, 3 wt%, 4 wt%, 4.5 wt%); the solvent is NMP, and the solid content of the resulting positive electrode paste is 50-80 wt% (e.g., 60 wt%, 70 wt%, 75 wt%).

[0041] (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., 95℃, 100℃, 105℃).

[0042] (3) The electrode obtained after the above coating is rolled by a rolling mill so that the electrode thickness is 150-170 micrometers (e.g., 155 micrometers, 160 micrometers, 165 micrometers) and the rolling pressure is 5-15 MPa (e.g., 6 MPa, 8 MPa, 10 MPa, 12 MPa).

[0043] (4) Heat the rolled electrode sheet as described above at 100-110℃ (e.g., 105℃, 108℃) for 10-12 hours (e.g., 11 hours) to obtain the positive electrode sheet.

[0044] In some implementation schemes, step (iii) of battery assembly includes the following steps:

[0045] (1) Stack the prepared positive and negative electrode sheets;

[0046] (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).

[0047] (3) Inject the electrolyte into the sealed battery box and perform the edge sealing process again to obtain a full cell.

[0048] According to the low-temperature formation method provided by the present invention, in some embodiments, during the assembly of the positive electrode and the negative electrode in step (iii), a six-positive-seven-negative-electrode stack is adopted.

[0049] In some implementation schemes, the positive electrode and the negative electrode in step (iii) 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 carried out 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-positive electrode-negative electrode-positive electrode-negative electrode”.

[0050] In some implementation schemes, based on the total weight of all components in the electrolyte, the electrolyte formulation in step (iii) is as follows:

[0051] EC (ethylene carbonate), 15-40 wt% (e.g., 20 wt%, 25.55 wt%, 30 wt%),

[0052] EMC (ethyl methyl carbonate), 10-50 wt% (e.g., 15 wt%, 20 wt%, 25 wt%, 30 wt%, 34.07 wt%, 35 wt%, 40 wt%),

[0053] PC (propylene carbonate), 10-20 wt% (e.g., 12 wt%, 15 wt%, 17.04 wt%, 18 wt%),

[0054] DMC, 3-10 wt% (e.g., 4 wt%, 5 wt%, 8.52 wt%, 9 wt%),

[0055] LiPF6, 5-15 wt% (e.g., 6 wt%, 10.65 wt%, 14 wt%),

[0056] VC (vinylene carbonate), 1-5 wt% (e.g., 1.5 wt%, 2.56 wt%, 3 wt%, 4 wt%), FEC (fluorovinyl carbonate), 0.1-1 wt% (e.g., 0.2 wt%, 0.4 wt%, 0.51 wt%, 0.6 wt%, 0.8 wt%).

[0057] ES (vinyl sulfite), 0.1-0.6 wt% (e.g., 0.2 wt%, 0.4 wt%, 0.43 wt%, 0.5 wt%),

[0058] TSMP, 0.1-0.5 wt% (e.g., 0.15 wt%, 0.2 wt%, 0.26 wt%, 0.4 wt%), DTD (vinyl sulfate), 0.1-0.6 wt% (e.g., 0.2 wt%, 0.4 wt%, 0.43 wt%, 0.5 wt%).

[0059] In some implementation schemes, in step (iv) low-temperature formation process, the full cell is placed at -20°C for 1-10 hours, for example, 2 hours, 4 hours, 5 hours, 6 hours, or 8 hours.

[0060] In some implementation schemes, in step (v) aging process, the full battery is aged for 5-7 days, for example, 6 days.

[0061] This invention, based on the principle of SEI film formation and the excellent low-temperature performance of coal-based anode materials, employs low-temperature formation technology to ensure the density of the SEI film. Simultaneously, solvents such as PC (propylene carbonate), VC (ethylene carbonate), and ES (ethylene sulfite) are added to the electrolyte formulation to further improve the battery's low-temperature performance. The full cell prepared based on the coal-based anode achieves excellent low-temperature performance, capable of discharging at temperatures ranging from -20°C to -30°C while maintaining a high capacity retention (>60%).

[0062] Compared with the prior art, the superior effects of the technical solution of the present invention are at least as follows:

[0063] (1) The full cell with negative electrode sheet prepared by the coal-based negative electrode material selected in this invention is aged after being formed at a low temperature of -20 degrees Celsius. The capacity loss of the cell is low and can be controlled between 0.45% and 0.8%. However, the capacity loss rate of the cell after being formed at room temperature and then aged at high temperature is usually between 1% and 2%.

[0064] (2) Compared with the negative electrode made of conventional negative electrode materials, the full cell made of the negative electrode sheet prepared by the coal-based negative electrode material selected in this invention has a performance advantage in cycle performance after low-temperature formation; the method of this invention can reduce the capacity loss of the full cell during the cycle process and achieve excellent cycle performance of the full cell. Detailed Implementation

[0065] 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.

[0066] 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.

[0067] Test method:

[0068] 1. Interplanar spacing test of coal-based anode materials:

[0069] 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.

[0070] 2. Energy density test of the full cell: Record the discharge capacity of the full cell after formation at full charge as C0, in Ah; then set its voltage plateau at 3.2V, measure its weight and record it as W0 (in kg), and record the energy density of the cell as E0, E0 = 3.2 * C0 / W0.

[0071] Example 1

[0072] The specific steps of the low-temperature formation method for lithium-ion batteries based on coal-based anodes are as follows:

[0073] 1. The preparation process of coal-based anode materials is as follows:

[0074] (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:

[0075] 2 micrometers <D 10 <5 micrometers, 10 micrometers <D 50 <11 micrometers, 24 micrometers <D 90 <27 micrometers;

[0076] (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.

[0077] After the reaction was completed, the material was cooled and discharged. The particle size of the obtained particles is as follows:

[0078] 8 micrometers <D 10 <10 micrometers, 16 micrometers <D 50 <18 micrometers, 27 micrometers <D 90 <30 micrometers;

[0079] 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.

[0080] (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.

[0081] 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.

[0082] (4) Graphitization: The powder obtained after ball milling 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 slowly lowered to room temperature.

[0083] (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;

[0084] The undersize material is inspected, measured, packaged, and stored; the oversize material is further ball-milled to meet particle size requirements before being sieved.

[0085] (6) Secondary granulation: The sieved material obtained after ball milling in step (5) is placed in a reaction vessel for secondary granulation. The secondary granulation is carried out according to the following process:

[0086] 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.

[0087] 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;

[0088] (7) Carbonization: Place the powder obtained in step (6) in a carbonization furnace and sinter at 1400℃-1600℃ for 24 hours, and then cool to room temperature;

[0089] (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.

[0090] A full cell was fabricated using this coal-based anode material-I, with an energy density of 114.3 Wh / Kg.

[0091] 2. Preparation of the negative electrode sheet:

[0092] (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.

[0093] 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%.

[0094] (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℃.

[0095] (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 12 MPa.

[0096] (4) The above-rolled electrode sheet is heated at 110°C for 12 hours to obtain negative electrode sheet-I; the moisture content of negative electrode sheet-I is 213ppm according to the moisture tester.

[0097] After testing, the thickness of the negative electrode sheet dried at 110℃ expanded from the original 102 micrometers to 106 micrometers (i.e., the Δ expansion value is 4 micrometers), and the adhesion force of the negative electrode sheet was 0.43N.

[0098] 3. Preparation of the positive electrode sheet:

[0099] (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).

[0100] 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%.

[0101] (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℃.

[0102] (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.

[0103] (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.

[0104] 4. Battery assembly:

[0105] (1) Cut the positive electrode sheet obtained above into a size of 84mm*60mm, and cut the negative electrode sheet obtained above into a size of 88mm*64mm. The battery is packaged in a soft pack and uses a six-positive-seven-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-positive electrode-negative electrode”.

[0106] (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;

[0107] (3) Place the packaged battery into a vacuum chamber for baking at a temperature of 90°C for 12 hours.

[0108] (4) In the glove box, the electrolyte is injected into the battery, with an injection volume of 3 grams; among which,

[0109] The electrolyte formula is as follows:

[0110] EC (ethylene carbonate), 25.55 wt%;

[0111] EMC (ethyl methyl carbonate), 34.07 wt%;

[0112] PC (propylene carbonate), 17.04 wt%;

[0113] DMC: 8.52 wt%;

[0114] LiPF6: 10.65 wt%;

[0115] VC (ethylene carbonate), 2.56 wt%;

[0116] FEC (fluoroethylene carbonate), 0.51 wt%;

[0117] ES (ethylene sulfite), 0.43 wt%;

[0118] TSMP, 0.26 wt%;

[0119] DTD (vinyl sulfate), 0.41 wt%;

[0120] The diaphragm is a 16-micron-thick polyethylene diaphragm;

[0121] (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.

[0122] 5. Formation of a full cell:

[0123] (1) Place the packaged battery in a low temperature chamber and let it stand at -20°C for 4 hours, and then connect it to a charging and discharging device; charge it at a rate of 0.05C, with a charging cut-off current of 0.05C and a charging cut-off voltage of 3.6V.

[0124] (2) After removing the battery from the low temperature chamber, let it stand at room temperature for 2 hours, and then discharge it at a discharge rate of 0.2C at room temperature. The discharge cutoff voltage is 2.0V, and the capacity is recorded as V1.

[0125] 6. Aging of the entire battery:

[0126] After formation, the battery was charged to 3.6V at room temperature with a charging rate of 0.2C and a charging cutoff current of 0.05C. Then, the fully charged battery was left to stand at 45°C for seven days.

[0127] 7. Charge-discharge cycle test:

[0128] After aging, the battery was calibrated at room temperature by performing a discharge-charge-discharge-charge cycle according to the operation steps and process conditions (charging: constant current charging to 3.6V at 0.5C, charging cut-off current is 0.05C; discharging: constant current discharging to 2.0V, current is 0.5C). The capacity after the second discharge was recorded as V2.

[0129] The loss of full cell capacity is studied by comparing the V2 value with the V1 value. That is, the capacity retention rate is calculated as V2 / V1×100%.

[0130] Example 2

[0131] The low-temperature formation method for lithium-ion batteries is the same as in Example 1, except that in step 5, the battery formation process, the packaged battery is placed in a low-temperature chamber and left to stand at -20°C for 1 hour, and then connected to a charging / discharging device. The remaining steps are the same as in Example 1.

[0132] Example 3

[0133] The low-temperature formation method for lithium-ion batteries is the same as in Example 1, except that in step 5, the battery formation process, the packaged battery is placed in a low-temperature chamber and left to stand at -20°C for 8 hours, and then connected to a charging and discharging device. The remaining steps are the same as in Example 1.

[0134] Comparative Example 1

[0135] The low-temperature formation method for lithium-ion batteries is the same as in Example 1, except that in step 5, the battery formation process involves placing the packaged battery in a low-temperature chamber, allowing it to stand at 45°C for 4 hours, and then connecting it to a charging / discharging device. The remaining steps are the same as in Example 1.

[0136] Comparative Example 2

[0137] The low-temperature formation method for lithium-ion batteries is the same as in Example 1, except that in step 5, the battery formation process involves placing the packaged battery in a low-temperature chamber, allowing it to stand at 25°C for 4 hours, and then connecting it to a charging / discharging device. The remaining steps are the same as in Example 1.

[0138] Comparative Example 3

[0139] The low-temperature formation method for lithium-ion batteries is the same as in Example 1, except that:

[0140] 1. Preparation of the negative electrode sheet:

[0141] The preparation process is the same as that of negative electrode sheet-I, except that the coal-based negative electrode material-I is replaced with commercially available conventional graphite to obtain negative electrode sheet-I'.

[0142] 2. Preparation of the positive electrode sheet: Same as in Example 1.

[0143] 3. Battery assembly: Same as in Example 1.

[0144] 4. Battery formation: Same as in Example 1.

[0145] 5. Battery aging: Same as in Example 1.

[0146] 6. Charge-discharge cycle test: Same as in Example 1.

[0147] Example 4

[0148] The low-temperature formation method for lithium-ion batteries is the same as in Example 1, except that:

[0149] 1. Preparation of coal-based anode materials:

[0150] In the first granulation process of step (2), 5% of the mass of the material in the reactor is added to the reactor; the remaining steps are the same as the preparation steps of coal-based anode material-I; coal-based anode material-II is obtained with a crystal plane spacing of 0.339 nm.

[0151] A full cell was fabricated using this coal-based anode material-II, with an energy density of 127.8 Wh / Kg.

[0152] 2. Preparation of the negative electrode sheet:

[0153] The preparation process is the same as that of negative electrode plate-I, except that coal-based negative electrode material-I is replaced with coal-based negative electrode material-II to obtain negative electrode plate-II.

[0154] After testing, the thickness of the negative electrode sheet dried at 110℃ expanded from the original 102 micrometers to 105 micrometers (i.e., the Δ expansion value is 3 micrometers), and the adhesion force of the rolled electrode sheet was 0.32N.

[0155] 3. Preparation of the positive electrode sheet: Same as in Example 1.

[0156] 4. Battery assembly: Same as in Example 1.

[0157] 5. Battery formation: Same as in Example 1.

[0158] 6. Battery aging: Same as in Example 1.

[0159] 7. Charge-discharge cycle test: Same as in Example 1.

[0160] Example 5

[0161] The low-temperature formation method for lithium-ion batteries is the same as in Example 4, except that in step 5, the battery formation process, the packaged battery is placed in a low-temperature chamber and left to stand at -20°C for 1 hour, and then connected to a charging and discharging device. The remaining steps are the same as in Example 4.

[0162] Example 6

[0163] The low-temperature formation method for lithium-ion batteries is the same as in Example 4, except that in step 5, the battery formation process, the packaged battery is placed in a low-temperature chamber and left to stand at -20°C for 8 hours, and then connected to a charging and discharging device. The remaining steps are the same as in Example 4.

[0164] Comparative Example 4

[0165] The low-temperature formation method for lithium-ion batteries is the same as in Example 4, except that in step 5, the battery formation process involves placing the packaged battery in a low-temperature chamber, allowing it to stand at 45°C for 4 hours, and then connecting it to a charging / discharging device. The remaining steps are the same as in Example 4.

[0166] Comparative Example 5

[0167] The low-temperature formation method for lithium-ion batteries is the same as in Example 4, except that in step 5, the battery formation process involves placing the packaged battery in a low-temperature chamber, allowing it to stand at 25°C for 4 hours, and then connecting it to a charging / discharging device. The remaining steps are the same as in Example 4.

[0168] Comparative Example 6

[0169] The low-temperature formation method for lithium-ion batteries is the same as in Example 4, except that:

[0170] 1. Preparation of the negative electrode sheet:

[0171] The preparation process is the same as that for negative electrode plate-II, except that the coal-based negative electrode material-I is replaced with commercially available conventional graphite to obtain negative electrode plate-II'.

[0172] 2. Preparation of the positive electrode sheet: Same as in Example 4.

[0173] 3. Battery assembly: Same as in Example 4.

[0174] 4. Battery formation: Same as in Example 4.

[0175] 5. Battery aging: Same as in Example 4.

[0176] 6. Charge-discharge cycle test: Same as in Example 4.

[0177] Table 1. Capacity retention rate of the full cell obtained from the negative electrode - I.

[0178]

[0179] Table 2 Capacity retention of the full cell

[0180]

[0181] Table 3 Capacity retention of full cells

[0182]

[0183] Table 4. Capacity retention of the full cell obtained from negative electrode plate-II

[0184]

[0185] Table 5 Capacity retention of the full cell

[0186]

[0187] Table 6 Capacity retention of full cells

[0188]

[0189] The experimental results show that all embodiments selected coal-based anode materials with a crystal plane spacing range of 0.337-0.339 nm and good low-temperature performance. At the same time, a formation process at -20℃ was adopted, which can reduce the capacity loss of the full cell during aging. In addition, the increased density of the SEI film will ensure the excellent storage performance of the battery and reduce the capacity loss of the full cell during cycling, so that the full cell has excellent cycle performance.

[0190] 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 low-temperature formation method of a lithium ion battery based on a coal-based negative electrode material, characterized by, Comprising 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) Low-temperature formation treatment: the assembled full battery is formed, and the formation process is as follows: the full battery is placed at -20℃, and the full battery is charged under this condition, the charge rate is 0.05C, the charge cutoff current is 0.05C, and the charge cutoff voltage is 3.6V; then the battery is discharged at room temperature, the discharge rate is 0.2C, and the discharge cutoff voltage is 2.0V; (V) Aging treatment: the battery after formation is charged at room temperature, the charge rate is 0.2C, the charge cutoff voltage is 3.6V, and the charge cutoff current is 0.05C; then the full battery fully charged is aged at 40-45℃.

2. The low temperature formation process of claim 1, wherein, The energy density of the full battery prepared by taking lithium iron phosphate as the main raw material as the positive electrode and the coal-based negative electrode material as the negative electrode is ≤140Wh / Kg.

3. The low temperature formation process of claim 1 wherein, The preparation method of the coal-based negative electrode material in step (I) comprises: (1) Selecting and shaping: the raw material 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, optional in the reactor to add 2-5% of the mass of the material in the kettle pitch; kettle temperature control in 100-150 ℃, in a closed condition, according to the following temperature curve for electric heating: at 200-300 ℃ for 2-4 hours, and then continue to heat to 400-500 ℃ for 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 after ball milling obtained in step (3) is placed in a graphitization furnace for graphitization, first heated to 1000℃, kept for 2 hours; then heated to 2250℃, kept for 3 hours, finally heated to 2800-2950℃ and kept for 24 hours, and then reduced to room temperature; (5) Ball milling: the material after graphitization obtained in step (4) is transported to a ball mill under vacuum for ball milling, and then sieved with 200 mesh molecular sieve; (6) Second granulation: the sieved material obtained in step (5) is placed in a reaction kettle for second granulation, and the second granulation 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 reduced to below 200℃; in 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 therein, so that the Fe content is controlled to be 30ppm or less, and then packaged to obtain the powder coal-based negative electrode material; In the preparation method of the coal-based negative electrode material in step (1), the raw coal is Taixi anthracite.

4. The cryogenic formation process of claim 1 wherein, The preparation steps of the negative electrode tab in step (1) are as follows: (1) first, the thickening agent CMC is mixed with deionized water, then the conductive agent SP is added thereto under stirring, the stirring speed is 500-1000 rpm, and the stirring time is 1-2 hours; thereafter, the binder SBR is added thereto under stirring, the stirring time is 30-60 minutes, and the stirring speed is 500-1000 rpm; finally, the coal-based negative electrode material is added thereto, the stirring time is 60-90 minutes; the obtained negative electrode slurry viscosity is adjusted to 3000-5000 cps by adding deionized water as a solvent; the coal-based negative electrode material is used in an amount of 85-94 wt%, the thickening agent CMC is used in an amount of 0.5-6 wt%, the binder SBR is used in an amount of 0.5-8 wt%, the conductive agent SP is used in an amount of 0.5-5 wt%, and deionized water is used as a solvent, based on the total weight of all components being 100%; the solid content of the prepared negative electrode slurry is 30-50 wt%; (2) the negative electrode slurry prepared above is placed on a coating machine, and the negative electrode slurry is coated onto the negative electrode current collector by using the coating machine, and the temperature of the coating machine is controlled at 90-110°C; (3) the electrode tab obtained after the coating is completed above is rolled by a rolling machine, so that the thickness of the electrode tab is 100-120 microns, and the rolling pressure is 5-15 MPa; (4) the electrode tab after rolling above is heated at 100-110°C for 10-12 hours to obtain a negative electrode tab.

5. The cryogenic formation process of claim 1 wherein, The preparation steps of the positive electrode tab in step (2) are as follows: (1) first, half of the amount of lithium iron phosphate powder material is mixed with the conductive agent SP powder under stirring, the stirring speed is 10-30 rpm, then the solvent NMP and the graphene conductive slurry are added thereto under stirring, the stirring speed is 400-800 rpm, and the stirring time is 1-2 hours; thereafter, the remaining half of the amount of lithium iron phosphate powder material is added thereto under stirring, the stirring time is 60-75 minutes, and the stirring speed is 300-600 rpm, finally the binder PVDF is added thereto, the stirring time is 40-90 minutes, and the stirring speed is 200-400 rpm, to obtain a positive electrode slurry; the viscosity of the positive electrode slurry is adjusted to 6000-8000 cps by adding the solvent NMP; the lithium iron phosphate powder material is used in an amount of 85-94 wt%, the conductive agent SP is used in an amount of 0.5-5 wt%, the binder PVDF is used in an amount of 1-8 wt%, and the graphene conductive slurry is used in an amount of 0.5-5 wt%, based on the total weight of all components being 100%; the solvent is NMP, and the solid content of the prepared positive electrode slurry is 50-80 wt%; (2) the positive electrode slurry prepared above is placed on a coating machine, and the positive electrode slurry is coated onto the positive electrode current collector by using the coating machine, and the temperature of the coating machine is controlled at 90-110°C; (3) the electrode tab obtained after the coating is completed above is rolled by a rolling machine, so that the thickness of the electrode tab is 150-170 microns, and the rolling pressure is 5-15 MPa; (4) The electrode sheet after rolling as above is heated at 100-110°C for 10-12 hours to obtain a positive electrode sheet.

6. The low temperature formation process of claim 1 wherein, In the process of assembling the positive electrode sheet and the negative electrode sheet in step (three), a six-positive-electrode-seven-negative-electrode stacking method is used.

7. The cryogenic formation process of claim 6, wherein, The stacking method of the positive electrode sheet and the negative electrode sheet in step (three) is that the electrode sheets are stacked in a "Z" shape, the upper and lower surfaces are negative electrodes, and the stacking 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-positive electrode-negative electrode".

8. The cryogenic formation process of claim 1 wherein, The formula of the electrolyte in step (three) is as follows, based on the total weight of each component in the electrolyte: EC, 15-40 wt%, EMC, 10-50 wt%, PC, 10-20 wt%, DMC, 3-10 wt%, LiPF6, 5-15 wt%, VC, 1-5 wt%, FEC, 0.1-1 wt%, ES, 0.1-0.6 wt%, TSMP, 0.1-0.5 wt%, DTD, 0.1-0.6 wt%.

9. The cryopoisoning method according to any one of claims 1 to 8, wherein In the low-temperature formation process in step (four), the full battery is placed at minus 20°C for 1-10 hours.

10. The cryopoisoning method of any one of claims 1-8, wherein, In the aging treatment process in step (five), the full battery is aged for 5-7 days.

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