Graphite negative electrode active material and preparation method thereof, negative electrode material, secondary battery, battery pack and electric device

Abstract

The invention provides a graphite negative electrode active material and a preparation method thereof, a negative electrode material, a secondary battery, a battery pack and an electric device. A thermogravimetric analysis curve of the graphite negative electrode active material shows that the initial weight loss temperature T0 is 610-715 DEG C; the initial weight loss temperature T0 is the temperature corresponding to the intersection point of the tangent line at the horizontal position in front of the step of the thermogravimetric analysis curve and the tangent line at the maximum weight loss rate. When the graphite negative electrode active material is used for a battery negative electrode, consumption of active ions in SEI film forming can be reduced, consumption of the active ions in the battery storage process can be reduced, and the battery has high first coulombic efficiency and good storage resistance.

Description

Technical Field

[0001] The present application relates to the technical field of battery materials, and in particular to a graphite negative electrode active material, a preparation method thereof, a negative electrode material, a secondary battery, a battery pack, and an electrical device composed of the same. Background Art

[0002] With the progress of society and the development of science and technology, the performance of current lithium-ion batteries can gradually no longer meet people's needs. The negative electrode material plays a crucial role in the cycle performance and safety performance of lithium-ion batteries. Therefore, it is of great significance to improve the performance of the negative electrode material.

[0003] For this reason, the present application is proposed. Summary of the Invention

[0004] The present application is made in view of the above problems, and its purpose is to provide a graphite negative electrode active material, a preparation method thereof, a negative electrode material, a secondary battery, a battery pack, and an electrical device composed of the same. When the graphite negative electrode active material is used for the battery negative electrode, it can reduce the consumption of active ions during the formation of the SEI film and the consumption of active ions during the storage of the battery, enabling the battery to have both a high first Coulomb efficiency and good storage resistance performance.

[0005] To achieve the above object, the present application provides the following technical solutions.

[0006] In a first aspect of the present application, a graphite negative electrode active material is provided. The thermogravimetric analysis curve of the graphite negative electrode active material shows that the initial weight loss temperature T0 is 610 °C to 715 °C; the initial weight loss temperature T0 is the temperature corresponding to the intersection point of the tangent line at the horizontal position before the step of the thermogravimetric analysis curve and the tangent line at the maximum weight loss rate.

[0007] Thus, the present application has a larger initial weight loss temperature compared to the conventionally recycled graphite negative electrode active material, and thus has fewer surface defects and / or bulk defects. Furthermore, when used for the battery negative electrode, it can reduce the consumption of active ions during the formation of the SEI film and the consumption of active ions during the storage of the battery, enabling the battery to have both a high first Coulomb efficiency and good storage resistance performance.

[0008] In any embodiment, the initial weight loss temperature T0 is 620 °C to 710 °C.

[0009] In any embodiment, the maximum weight loss rate in the thermogravimetric analysis curve ≤ 6.5% / min, preferably 0.5% / min - 6.0% / min, more preferably 0.8% / min - 5.0% / min;

[0010] and / or, the temperature T corresponding to the maximum weight loss rate in the thermogravimetric analysis curve max≥710 °C, preferably 710 °C - 810 °C.

[0011] In any embodiment, the thermogravimetric analysis curve of the graphite negative electrode active material shows that the weight loss rate between 35 °C and 700 °C is ≤60%.

[0012] A reasonable maximum weight loss rate, maximum weight loss temperature, and weight loss rate can enable the graphite negative electrode active material to exhibit better stability and fewer microdefects, thereby further improving the first Coulombic efficiency and storage stability when used as the negative electrode of a battery.

[0013] In any embodiment, the specific surface area SSA of the graphite negative electrode active material is 0.7 - 2.0 m 2 / g, preferably 0.8 - 1.8 m 2 / g. When the specific surface area of the graphite negative electrode active material is within the above range, it has good thermal stability.

[0014] In any embodiment, the volume average particle size of the graphite negative electrode active material satisfies at least one of the following conditions:

[0015] Dv1 is 1.0 - 5.0 μm, preferably 2.0 - 3.5 μm,

[0016] Or, Dv50 is 10.0 - 22.0 μm, preferably 12.0 - 18.0 μm,

[0017] Or, Dv10 is 4.0 - 12.0 μm, preferably 6.0 - 10.0 μm,

[0018] Or, Dv90 is 25.0 - 40.0 μm, preferably 28.0 - 35.0 μm.

[0019] When the volume particle sizes Dv1, Dv10, Dv50, and / or Dv90 of the graphite negative electrode active material are within the above ranges, it has good thermal stability.

[0020] In any embodiment, the powder resistivity of the graphite negative electrode active material at 8 MPa is 0.005 - 0.025 Ω / cm, preferably 0.005 - 0.020 Ω / cm.

[0021] When the resistivity of the graphite negative electrode active material is within the above range, its application in a battery will improve point contact and enhance electrokinetic performance.

[0022] In any embodiment, when the graphite negative electrode active material of the battery is used as the negative electrode of a CR2430 type button cell, the first discharge efficiency of the cell is 92% - 96%, preferably 93% - 95%;

[0023] And / or, the specific capacity of the graphite negative electrode active material is 345-365 mAh / g, preferably 345-360 mAh / g. The test method for the specific capacity is as follows: Mix the graphite negative electrode active material, conductive agent Super P, and binder (PVDF) of the present application in a mass ratio of 91.6:1.8:6.6 with the solvent NMP (N-methylpyrrolidone) to make a slurry; coat the prepared slurry on a copper foil current collector, dry it in an oven and set aside; use a lithium metal sheet as the counter electrode; use a polyethylene (PE) film as the separator; mix ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of 1:1:1, and then uniformly dissolve LiPF6 in the above solution to obtain an electrolyte, where the concentration of LiPF6 is 1 mol / L; assemble the above components into a CR2430 type button cell in a glove box under argon protection. After standing the obtained button cell for 12 hours, perform constant current discharge at a current of 0.05C until 0.005V, stand for 10 minutes, perform constant current discharge at a current of 50 μA until 0.005V, stand for 10 minutes, and perform constant current discharge at a current of 10 μA until 0.005V; then perform constant current charge at a current of 0.1C until 2V, and record the charge capacity. The ratio of the charge capacity to the mass of the regenerated negative electrode material is the specific capacity of the prepared regenerated negative electrode material.

[0024] When the first discharge efficiency of the graphite negative electrode active material in the button cell is within the above range, it is beneficial to obtain a higher first Coulomb efficiency of the full battery. At the same time, when the specific capacity of the graphite negative electrode active material is within this range, the kinetics and energy density can be better balanced.

[0025] In any embodiment, the true density of the graphite negative electrode active material is 2.18-2.25 g / cm 3 , preferably 2.20-2.23 g / cm 3 ;

[0026] And / or, the tap density of the graphite negative electrode active material is 0.95-1.45 g / cm 3 , preferably 1.0-1.25 g / cm 3 ;

[0027] And / or, the powder compaction density of the graphite negative electrode active material under 20000 N is 1.50 g / cc - 1.90 g / cc, preferably 1.55 g / cc - 1.85 g / cc.

[0028] When the true density, tap density, and powder compaction density of the graphite are within the above ranges, it is beneficial to improve the energy density, electrokinetics, slurry stability, etc. of the material.

[0029] In any embodiment, the mass percentage of carbon in the graphite negative electrode active material ≥ 99%;

[0030] Preferably, the content of Na element in the graphite negative electrode active material is 10 - 200 ppm, preferably 20 - 100 ppm.

[0031] The second aspect of the present application provides a recovery method for the graphite negative electrode active material of the first aspect, which includes:

[0032] Recover the negative electrode sheet of the graphite system, separate the active material from the negative electrode sheet to obtain graphite negative electrode active material 1;

[0033] Perform heat treatment on the graphite negative electrode active material 1 under an inert atmosphere to obtain graphite negative electrode active material 2, and the temperature of the heat treatment is 300 °C - 600 °C;

[0034] Perform oxidation treatment and pickling on the graphite negative electrode active material 2 to obtain graphite negative electrode active material 3; wherein, the oxidation treatment includes: introducing an oxidation gas into the reaction furnace and heating to 200 °C - 600 °C for oxidation reaction;

[0035] Perform coating treatment on the graphite negative electrode active material 3, and the coating treatment includes: mixing the graphite negative electrode active material 3 with a carbon source and performing carbonization under an inert atmosphere at 1100 - 1400 °C to obtain the final graphite negative electrode active material.

[0036] Thus, after the negative electrode sheet is recovered in the present application, the active material is separated, and then heat treated under an inert atmosphere, so that small molecule organic substances can volatilize and / or decompose into small molecule volatiles, thereby removing small molecule organic impurities; then through oxidation treatment and pickling at a lower temperature, the remaining organic impurities, metal impurities, etc. in the graphite are removed, and finally the graphite negative electrode active material is obtained through coating treatment. The graphite negative electrode active material obtained by this method has a higher initial weight loss temperature compared to conventional recycled graphite, thus having fewer surface defects and / or bulk defects, and further being able to reduce the consumption of active ions during the formation of the SEI film when used as the battery negative electrode, as well as reduce the consumption of active ions during the storage of the battery, enabling the battery to have both a high first Coulomb efficiency and good storage performance.

[0037] In addition, the present application realizes resource reuse by recovering and preparing the negative electrode material, which is more environmentally friendly and reduces the raw material cost at the same time.

[0038] In any embodiment, the heating to 200 °C - 600 °C for oxidation reaction includes:

[0039] First, heat up to 200°C to 450°C, keep warm for the first time for 0.5 h to 2.5 h, then continue to heat up to 450°C to 600°C, and keep warm for the second time for 0.5 h to 1.5 h; wherein, the flow rate of the oxidation gas introduced during the first heat preservation is greater than the flow rate of the oxidation gas introduced during the second heat preservation.

[0040] Except for the small molecule organic substances removed by heat treatment, there are many other types of organic impurities in the graphite anode active material, and the oxidation reaction temperatures of different impurities vary. Controlling the heating process in the above two stages can play the following roles: First, oxidize as many organic impurities as possible; second, oxidize some conductive agents to improve the electrical properties of graphite. In addition, maintaining the condition that the flow rate of the oxidation gas is first large and then small can achieve the following effects: (1) The oxidation of organic impurities mainly occurs in the low temperature section. By increasing the gas flow rate in the low temperature section, the reactants can be quickly supplied and the products can be carried away, promoting the reaction and improving the treatment efficiency; (2) Reducing the gas flow rate in the high temperature section. First, the residual amount of organic impurities is small, and the amount of oxidizing gas required for the decomposition reaction is reduced; second, the oxidation ablation of graphite in the high temperature section is reduced, improving the yield.

[0041] In any embodiment, the mass ratio of the graphite anode active material 3 to the carbon source is 100:1 to 10.

[0042] When the dosage of the carbon source is within this range, the carbon formed during the subsequent carbonization process can effectively repair the defects on the surface of the purified graphite, reducing the consumption of active lithium during the first charge and discharge process.

[0043] In any embodiment, the carbon source includes one or more of coal tar pitch, petroleum pitch, high molecular compounds, and resins, preferably petroleum pitch; the softening point temperature of the petroleum pitch is preferably 80°C to 250°C. Petroleum pitch with a softening point of 80°C to 250°C is more effective for surface repair of recycled graphite.

[0044] In any embodiment, the carbonization in an inert atmosphere at 1100°C to 1400°C includes: first heating up to 225°C, keeping warm for 1 h to 2 h, then heating up to 1100°C to 1400°C, and keeping warm for 2.5 h to 3.5 h.

[0045] In the above-mentioned staged heating process, first heat up to 225°C to make the carbon source melt and soften, and uniformly coat the surface of the recycled graphite; then heat up to 1100°C to 1400°C to make the carbon source undergo a carbonization reaction. At this time, after keeping warm for 2.5 h to 3.5 h, the graphitization degree is high, and the formed graphite anode active material has good thermal stability and a high weight loss temperature T0.

[0046] In any embodiment, the following method can be used to separate the active material from the negative electrode plate:

[0047] The negative electrode sheet to be recycled is crushed and then classified by air separation;

[0048] Alternatively, the negative electrode sheet to be recycled is crushed, then washed with water, filtered, and collected.

[0049] Thus, when used in secondary batteries such as lithium batteries, this negative electrode material has a high first discharge efficiency and better storage stability.

[0050] The third aspect of this application provides a secondary battery, which includes a positive electrode sheet and a negative electrode sheet, and a separator disposed between the positive electrode sheet and the negative electrode sheet. The negative electrode sheet includes the negative electrode material described in the second aspect.

[0051] The fourth aspect of this application provides a battery pack, which includes the secondary battery of the third aspect of this application.

[0052] The fifth aspect of this application provides an electrical device, which includes at least one selected from the secondary battery of the third aspect of this application and the battery pack of the fourth aspect of this application. Description of the Drawings

[0053] Figure 1 is a schematic diagram of a secondary battery according to an embodiment of this application.

[0054] Figure 2 is Figure 5 an exploded view of the secondary battery according to an embodiment of this application shown in

[0055] Figure 3 is a schematic diagram of a battery module according to an embodiment of this application.

[0056] Figure 4 is a schematic diagram of a battery pack according to an embodiment of this application.

[0057] Figure 5 is Figure 4 an exploded view of the battery pack according to an embodiment of this application shown in

[0058] Figure 6 is a schematic diagram of an electrical device using the secondary battery according to an embodiment of this application as a power source;

[0059] Figure 7 is a thermogravimetric analysis curve of the graphite negative electrode active material according to an embodiment of this application;

[0060] Figure 8 is a surface morphology diagram (5000x) of the graphite negative electrode active material obtained in Example 2 of this application.

[0061] Description of the Reference Numerals:

[0062] 1 - Battery pack; 2 - Upper box body; 3 - Lower box body; 4 - Battery module; 5 - Secondary battery; 51 - Housing; 52 - Electrode assembly; 53 - Cover plate. Detailed implementation manners

[0063] Hereinafter, implementation manners of the negative electrode material recovery method, negative electrode material, secondary battery, battery module, battery pack, and electrical device of the present application will be specifically disclosed in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually identical structures are omitted. This is to prevent the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the accompanying drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter recited in the claims.

[0064] The "range" disclosed in the present application is defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a particular range. The ranges defined in this way can include the end values or not include the end values, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 - 120 and 80 - 110 are listed for a specific parameter, it is understood that ranges of 60 - 110 and 80 - 120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all contemplated: 1 - 3, 1 - 4, 1 - 5, 2 - 3, 2 - 4, and 2 - 5. In the present application, unless otherwise specified, the numerical range "a - b" represents an abbreviated representation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0 - 5" represents that all real numbers between "0 - 5" have been fully listed herein, and "0 - 5" is only an abbreviated representation of these numerical combinations. Additionally, when it is stated that a certain parameter is an integer ≥2, it is equivalent to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0065] If there is no special instruction, all implementation manners and optional implementation manners of the present application can be combined with each other to form a new technical solution.

[0066] If there is no special instruction, all technical features and optional technical features of the present application can be combined with each other to form a new technical solution.

[0067] Unless otherwise specified, all steps of this application can be carried out sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) carried out sequentially, or may also include steps (b) and (a) carried out sequentially. For example, when it is mentioned that the method may further include step (c), it means that step (c) can be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may also include steps (c), (a) and (b), etc.

[0068] Unless otherwise specified, the terms "comprising" and "including" mentioned in this application mean open-ended, and can also be closed-ended. For example, the "comprising" and "including" may mean that other components not listed may also be included or contained, or may only include or contain the listed components.

[0069] Unless otherwise specified, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) while B is true (or exists); or both A and B are true (or exist).

[0070] Graphite is commonly used as the negative electrode of secondary batteries such as lithium-ion batteries, and its initial weight loss temperature can reflect the chemical stability of carbon materials. Considering environmental protection and cost, etc., recycling the negative electrode sheet is increasingly widely used as one of the sources of graphite. However, the initial weight loss temperature of conventionally recycled graphite is relatively low, which reflects serious surface defects and / or bulk phase defects of the material, resulting in a significant increase in the consumption of active ions during the formation of the SEI film when it is used as the negative electrode of the battery, as well as an increase in the consumption of active ions during the storage process of the battery, thereby reducing the first Coulombic efficiency and deteriorating the storage performance.

[0071] Therefore, this application proposes a graphite negative electrode active material with a high initial weight loss temperature T0. Its thermogravimetric analysis curve shows that the initial weight loss temperature T0 is 610 °C to 715 °C.

[0072] In this application, the initial weight loss temperature T0 is the temperature corresponding to the intersection point of the tangent line at the horizontal position before the step of the thermogravimetric analysis curve and the tangent line at the maximum weight loss rate. Taking Figure 7 the thermogravimetric analysis curve of a graphite negative electrode active material shown as an example, T0 is 677.5 °C.

[0073] The test method of the thermogravimetric analysis curve is usually as follows: Weigh the active material of the graphite negative electrode and place it in a flat-bottom crucible. Shake it evenly, keep it open, use air as the purge gas, with an air flow rate of 60 mL / min and a heating rate of 5 °C / min. Perform differential scanning thermogravimetric analysis in the range of 35 °C - 950 °C to obtain the thermogravimetric (TG) analysis curve and the derivative thermogravimetric (DTG) curve of the active material of the graphite negative electrode.

[0074] Therefore, the active material of the graphite negative electrode in this application has a higher initial weight loss temperature compared to the conventionally recycled one, thus having fewer surface defects and / or bulk defects. Furthermore, when used as the battery negative electrode, it can reduce the consumption of active ions during the formation of the SEI film and during battery storage, enabling the battery to have both a high initial Coulombic efficiency and good storage performance.

[0075] The above initial weight loss temperature T0 within the range of 610 °C to 715 °C means that T0 can be any value within this range, including but not limited to the following: 610 °C, 615 °C, 620 °C, 625 °C, 630 °C, 635 °C, 640 °C, 645 °C, 650 °C, 655 °C, 660 °C, 665 °C, 670 °C, 675 °C, 680 °C, 685 °C, 690 °C, 695 °C, 700 °C, 705 °C, 710 °C, 715 °C, etc.

[0076] For the active material of the graphite negative electrode in this application, reasonable maximum weight loss rate, maximum weight loss temperature, and weight loss percentage can make the active material of the graphite negative electrode exhibit better stability and fewer micro-defects, thus further improving the initial Coulombic efficiency and storage stability when used as the battery negative electrode.

[0077] In some embodiments, the initial weight loss temperature T0 is 620 °C to 710 °C.

[0078] In some embodiments, the maximum weight loss rate in the thermogravimetric analysis curve ≤ 6.5% / min, preferably 0.5% / min - 6.0% / min, more preferably 0.8% / min - 5.0% / min.

[0079] The maximum weight loss rate refers to the temperature at which the weight drops fastest in the thermogravimetric analysis curve, which is manifested as the peak in the DTG curve.

[0080] In some embodiments, the temperature T corresponding to the maximum weight loss rate in the thermogravimetric analysis curve max ≥ 710 °C, preferably 710 °C - 810 °C.

[0081] In some embodiments, the thermogravimetric analysis curve of the active material of the graphite negative electrode shows that the weight loss percentage between 35 °C and 700 °C is ≤ 60%.

[0082] The weight loss rate between 35°C and 700°C refers to the cumulative amount of the weight loss rate of the graphite anode active material in this temperature range starting from 30°C and ending at 700°C. In some embodiments, the specific surface area SSA of the graphite anode active material is 0.7 to 2.0 m 2 / g, preferably 0.8 to 1.8 m 2 / g. When the specific surface area of the graphite anode active material is within the above range, it has good thermal stability.

[0083] In some embodiments, the volume average particle size of the graphite anode active material satisfies at least one of the following conditions:

[0084] Dv1 is 1.0 to 5.0 μm, preferably 2.0 to 3.5 μm,

[0085] Or, Dv50 is 10.0 to 22.0 μm, preferably 12.0 to 18.0 μm,

[0086] Or, Dv10 is 4.0 to 12.0 μm, preferably 6.0 to 10.0 μm,

[0087] Or, Dv90 is 25.0 to 40.0 μm, preferably 28.0 to 35.0 μm.

[0088] When the volume particle sizes Dv1, Dv10, Dv50 and / or Dv90 of the graphite anode active material are within the above ranges, it has good thermal stability.

[0089] In this application, the meanings of Dv1, Dv10, Dv50, and Dv90 respectively refer to the particle sizes at which the volume cumulative is 1%, 10%, 50%, and 90% when measured from the small particle size in the particle size distribution based on volume.

[0090] In some embodiments, the powder resistivity of the graphite anode active material at 8 MPa is 0.005 to 0.025 Ω / cm, preferably 0.005 to 0.020 Ω / cm.

[0091] When the resistivity of the graphite anode active material is within the above range, applying it to the battery will improve the electrical contact between particles and enhance the electrokinetic performance. Here, "8 MPa" refers to the powder resistivity of the graphite anode active material when the external pressure is 8 MPa. Generally, the powder resistivity is used to illustrate the current-carrying ability of powder particles; the lower the powder resistivity, the better the rate performance and current-carrying ability.

[0092] In some embodiments, the first discharge efficiency of the battery is 92 to 96%, preferably 93% to 95%.

[0093] The battery is a CR2430 button cell. The specific assembly process is as follows: The graphite negative electrode active material, conductive agent Super P, and binder (PVDF) of the present application are mixed evenly with the solvent NMP (N-methylpyrrolidone) in a mass ratio of 91.6:1.8:6.6 to form a slurry; the prepared slurry is coated on a copper foil current collector and dried in an oven for later use; a lithium metal sheet is used as the counter electrode; a polyethylene (PE) film is used as the separator; ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1, and then LiPF6 is uniformly dissolved in the above solution to obtain an electrolyte, where the concentration of LiPF6 is 1 mol / L; the above components are assembled into a CR2430 button cell in a glove box under argon protection.

[0094] The test method for the first Coulomb efficiency of the button cell is as follows: At 25 °C, first, the button cell prepared above is discharged at a constant current of 0.15 mA to 0.005 V, allowed to stand for 5 minutes, and then discharged at a constant current of 10 μA to 0.005 V, and the first-cycle discharge capacity of the button cell is recorded; then, it is charged at a constant current of 0.3 mA to 2.0 V, and the first-cycle charge capacity of the button cell is recorded. The first Coulomb efficiency (%) of the carbon material = the first-cycle charge capacity of the button cell / the first-cycle discharge capacity of the button cell × 100%.

[0095] In some embodiments, the specific capacity of the graphite negative electrode active material is 345 - 365 mAh / g, preferably 345 - 360 mAh / g. The test method for the specific capacity is as follows: The graphite negative electrode active material, conductive agent Super P, and binder (PVDF) of the present application are mixed evenly with the solvent NMP (N-methylpyrrolidone) in a mass ratio of 91.6:1.8:6.6 to form a slurry; the prepared slurry is coated on a copper foil current collector and dried in an oven for later use; a lithium metal sheet is used as the counter electrode; a polyethylene (PE) film is used as the separator; ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1, and then LiPF6 is uniformly dissolved in the above solution to obtain an electrolyte, where the concentration of LiPF6 is 1 mol / L; the above components are assembled into a CR2430 button cell in a glove box under argon protection. After the obtained button cell is allowed to stand for 12 hours, it is discharged at a constant current of 0.05C to 0.005 V, allowed to stand for 10 minutes, discharged at a constant current of 50 μA to 0.005 V, allowed to stand for 10 minutes, and discharged at a constant current of 10 μA to 0.005 V; then, it is charged at a constant current of 0.1C to 2 V, and the charge capacity is recorded. The ratio of the charge capacity to the mass of the regenerated negative electrode material is the specific capacity of the prepared regenerated negative electrode material.

[0096] When the first discharge efficiency of the graphite negative electrode active material is within the above range, it is beneficial to obtain a higher first Coulomb efficiency of the full cell. At the same time, when the specific capacity of the graphite negative electrode active material is within this range, the kinetics and energy density can be better balanced.

[0097] In some embodiments, the true density of the graphite negative electrode active material is 2.18 - 2.25 g / cm 3 , preferably 2.20 - 2.23 g / cm 3 .

[0098] In some embodiments, the tapped density of the graphite negative electrode active material is 0.95 - 1.45 g / cm 3 , preferably 1.0 - 1.25 g / cm 3 .

[0099] In some embodiments, the powder compaction density of the graphite negative electrode active material under 20000 N is 1.65 g / cc - 2.00 g / cc, preferably 1.68 g / cc - 1.98 g / cc.

[0100] When the true density, tapped density and powder compaction density of the graphite are within the above ranges, it is beneficial to improve the energy density, electrokinetics, slurry stability, etc. of the material.

[0101] Among them, the test method for true density is: referring to the standard GB / T 24586 - 2009; taking a certain mass of the sample, placing it in a true density tester, introducing a certain amount of helium gas, measuring the pressure in the current chamber, and then connecting to another chamber with known pressure and volume, and the true volume can be calculated according to Boyle's law (PV = nRT), so as to calculate the true density.

[0102] The test method for tapped density is: referring to the standard GB / T 5162 - 2006, placing a certain amount of powder in a container, vibrating it through a vibrating device until the volume of the powder no longer decreases, reading the volume of the powder after tapping, and calculating the tapped density.

[0103] The powder compaction density under 20000 N refers to: referring to the standard GB / T 24533 - 2009, placing a certain amount of powder in a mold with a known cross-sectional area, during the external force compression process, as the powder moves and deforms, the voids are filled, the contact area between particles increases, the atomic attraction is generated and the mechanical fitting effect between particles is enhanced, thus forming a green compact with a certain density; after removing the external force, measuring the volume of the green compact, and then calculating the compaction density.

[0104] In some embodiments, the mass percentage of carbon in the graphite negative electrode active material is ≥99%, preferably ≥99.5%.

[0105] In some embodiments, the content of Na element in the graphite negative electrode active material is 10 to 200 ppm, preferably 20 to 100 ppm.

[0106] The second aspect of the present application provides a method for recycling the graphite negative electrode active material of the first aspect, which includes:

[0107] Recycling the negative electrode sheet of the graphite system, separating the active material from the negative electrode sheet to obtain graphite negative electrode active material 1;

[0108] Performing heat treatment on the graphite negative electrode active material 1 under an inert atmosphere to obtain graphite negative electrode active material 2, and the temperature of the heat treatment is 300 to 600 °C;

[0109] Performing oxidation treatment and pickling on the heat-treated graphite negative electrode active material 2 to obtain graphite negative electrode active material 3; wherein, the oxidation treatment includes: introducing an oxidation gas into the reaction furnace and heating to 200 to 600 °C for an oxidation reaction;

[0110] Performing a coating treatment on the graphite negative electrode active material 3, and the coating treatment includes: mixing the purified graphite with a carbon source and performing carbonization under an inert atmosphere at 1100 to 1400 °C to obtain the graphite negative electrode active material.

[0111] Thus, after the negative electrode sheet is recycled in the present application, the active material is separated, and then heat-treated under an inert atmosphere, so that small molecule organic substances can volatilize and / or decompose into small molecule volatiles, thereby removing small molecule organic impurities; then, through oxidation treatment and pickling at a lower temperature, other organic impurities, metal impurities, etc. in the graphite are removed, and finally, the graphite negative electrode active material is obtained through a coating treatment. The graphite negative electrode active material obtained by this method has a higher initial weight loss temperature compared to conventional recycled graphite, thus having fewer surface defects and / or bulk defects, and further reducing the consumption of active ions for SEI film formation and the consumption of active ions during battery storage when used as a battery negative electrode, enabling the battery to have both high first Coulomb efficiency and good storage performance.

[0112] In addition, by recycling and preparing the negative electrode material in the present application, resource reuse is achieved, which is more environmentally friendly and reduces the raw material cost at the same time.

[0113] In the present application, the active material separated from the negative electrode sheet usually includes components such as graphite, conductive agent, thickening agent, binder, etc. and impurities such as metals embedded during the use of the negative electrode. Some negative electrodes may also include auxiliary materials such as dispersants. The separation means include but are not limited to at least one or a combination of means such as solvent immersion, crushing, air separation, water washing, filtration, etc.

[0114] The heat treatment is carried out in an inert atmosphere, including but not limited to atmospheres such as argon and helium. The temperature of the heat treatment is usually: after heating to a certain temperature value within the range of 300 - 600 °C, hold for a certain period of time, and the holding time can be 1 - 3 h.

[0115] Oxidation treatment and pickling are two steps. It can be oxidation treatment first followed by pickling, or pickling first followed by oxidation treatment. The main purpose of oxidation treatment is to remove the remaining organic impurities in the graphite anode active material, and the main purpose of pickling is to remove metal impurities. However, the types of impurities removed in these two steps are not limited to the above types. For example, pickling may also remove some organic impurities that are easily acid-hydrolyzed.

[0116] The temperature in the oxidation treatment needs to be controlled within 200 - 600 °C. This temperature is lower than the oxidation temperature of conventional recovery methods. However, since some impurities have been removed by the prior heat treatment, the temperature in this step is sufficient to remove the remaining impurities. "Controlled within 200 - 600 °C" includes but not limited to controlling at temperatures such as 200 °C, 300 °C, 400 °C, 500 °C, 600 °C, etc., or controlling within a range with a small fluctuation around the average value of the above-mentioned values, such as ±10 °C, ±20 °C, ±30 °C, etc., or using stepped heating, such as first heating to a relatively low temperature level, holding for a period of time, and then continuing to heat to a higher temperature and holding. The oxidation treatment needs to be carried out in an oxidation atmosphere, and the oxidation gas can be air, oxygen, water vapor, etc.

[0117] In some embodiments, heating to 200 - 600 °C for the oxidation reaction includes:

[0118] First heat to 200 - 450 °C, hold for the first time for 0.5 - 2.5 h, continue to heat to 450 - 600 °C, and hold for the second time for 0.5 - 1.5 h; wherein, the flow rate of the oxidation gas introduced during the first holding process is greater than the flow rate of the oxidation gas introduced during the second holding process.

[0119] Pickling refers to immersing the graphite anode active material in an acid solution for reaction, and appropriate heating and / or stirring can be carried out. The acid solution includes but not limited to sulfuric acid, hydrochloric acid, hydrofluoric acid, nitric acid, phosphoric acid, etc.

[0120] In some embodiments, the mass ratio of the graphite anode active material 3 to the carbon source is 100:1 - 10, preferably 100:2 - 10.

[0121] When the dosage of the carbon source is within this range, the carbon formed during the subsequent carbonization process can effectively repair the defects on the surface of the impurity-removed graphite and reduce the consumption of active lithium during the first charge and discharge process.

[0122] In some embodiments, the carbon source includes one or more of coal tar pitch, petroleum pitch, high molecular compounds, and resins, preferably petroleum pitch; the softening point temperature of the petroleum pitch is preferably 80 to 250 °C. Petroleum pitch with a softening point of 80 to 250 °C is more effective for surface repair of the recycled graphite surface.

[0123] In some embodiments, the carbonization in an inert atmosphere at 1100 to 1400 °C includes: first heating to 225 °C and holding for 1 to 2 h, then heating to 1100 to 1400 °C and holding for 2.5 to 3.5 h.

[0124] In the above-mentioned staged heating process, first heating to 225 °C causes the carbon source to melt and soften, uniformly coating the surface of the recycled graphite; then heating to 1100 to 1400 °C causes the carbon source to undergo a carbonization reaction. At this time, after holding for 2.5 to 3.5 h, the graphitization degree is high, the thermal stability of the formed graphite anode active material is good, and the weight loss temperature T0 is high.

[0125] In some embodiments, the following method can be used to separate the active material from the negative electrode sheet:

[0126] Crush the negative electrode sheet to be recycled, and then perform air classification;

[0127] Alternatively, crush the negative electrode sheet to be recycled, then wash, filter, and collect.

[0128] In addition, the secondary battery, battery module, battery pack, and electrical device of the present application will be described below with reference to the accompanying drawings as appropriate.

[0129] In one embodiment of the present application, a secondary battery is provided.

[0130] Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During the charge and discharge process of the battery, active ions are embedded and extracted back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is disposed between the positive electrode sheet and the negative electrode sheet, mainly to prevent short circuit between the positive and negative electrodes, and at the same time allows ions to pass through.

[0131] [Positive electrode sheet]

[0132] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector.

[0133] As an example, the positive electrode current collector has two surfaces opposite to each other in its own thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

[0134] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, as the metal foil, aluminum foil may be used. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0135] In some embodiments, when the secondary battery is a lithium-ion battery, the positive electrode active material in the positive electrode film layer may be a positive electrode active material known in the art for lithium-ion batteries. As an example, the positive electrode active material may include at least one of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Among them, examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (which may also be abbreviated as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (which may also be abbreviated as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (which may also be abbreviated as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (which may also be abbreviated as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (which may also be abbreviated as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05at least one of O2) and its modified compounds, etc. Examples of the lithium-containing phosphate with olivine structure may include, but are not limited to, lithium iron phosphate (such as LiFePO4 (which can also be abbreviated as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and a composite material of lithium manganese iron phosphate and carbon.

[0136] In some embodiments, when the secondary battery is a sodium-ion battery, the positive electrode active material can adopt the positive electrode active material for sodium-ion batteries well-known in the art. As an example, the positive electrode active material can be used alone, or two or more of them can be combined. Among them, the positive electrode active substance can be selected from sodium iron composite oxide (NaFeO2), sodium cobalt composite oxide (NaCoO2), sodium chromium composite oxide (NaCrO2), sodium manganese composite oxide (NaMnO2), sodium nickel composite oxide (NaNiO2), sodium nickel titanium composite oxide (NaNi 1 / 2 Ti 1 / 2 O2), sodium nickel manganese composite oxide (NaNi 1 / 2 Mn 1 / 2 O2), sodium iron manganese composite oxide (Na 2 / 3 Fe 1 / 3 Mn 2 / 3 O2), sodium nickel cobalt manganese composite oxide (NaNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2), sodium iron phosphate compound (NaFePO4), sodium manganese phosphate compound (NaMn P O4), sodium cobalt phosphate compound (NaCoPO4), Prussian blue-based materials, polyanion materials (phosphates, fluorophosphates, pyrophosphates, sulfates), etc. However, the present application is not limited to these materials, and other conventionally well-known materials that can be used as the positive electrode active substance of sodium-ion batteries can also be used in the present application.

[0137] In some embodiments, the positive electrode film layer may also optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0138] In some embodiments, the positive electrode film layer may also optionally include a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0139] In some embodiments, the positive electrode plate can be prepared in the following manner: the components for preparing the positive electrode plate described above, such as the positive electrode active material, the conductive agent, the binder, and any other components, are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after processes such as drying and cold pressing, the positive electrode plate can be obtained.

[0140] [Negative electrode plate]

[0141] The negative electrode plate includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector. The negative electrode film layer may include using the graphite negative electrode active material of the present application as the negative electrode active material.

[0142] As an example, the negative electrode current collector has two surfaces opposite to each other in its own thickness direction, and the negative electrode film layer is provided on any one or both of the two opposite surfaces of the negative electrode current collector.

[0143] In some embodiments, the negative electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, copper foil can be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (such as copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0144] In some embodiments, the negative electrode film layer may also optionally include a binder. The binder can be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0145] In some embodiments, the negative electrode film layer may also optionally include a conductive agent. The conductive agent can be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0146] In some embodiments, the negative electrode film layer may also optionally include other additives, such as a thickener (such as sodium carboxymethyl cellulose (CMC-Na)), etc.

[0147] In some embodiments, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet described above, such as the negative electrode active material, the conductive agent, the binder, and any other components, are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after processes such as drying and cold pressing, the negative electrode sheet can be obtained.

[0148] [Electrolyte]

[0149] The electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet. There is no specific limitation on the type of electrolyte in this application, and it can be selected according to requirements. For example, the electrolyte can be liquid, gel-like, or all-solid-state.

[0150] In some embodiments, the electrolyte uses an electrolytic solution. The electrolytic solution includes an electrolyte salt and a solvent.

[0151] In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluoro(oxalato)borate, lithium bis(oxalato)borate, lithium difluoro bis(oxalato)phosphate, and lithium tetrafluoro(oxalato)phosphate.

[0152] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0153] In some embodiments, the electrolytic solution may further optionally include additives. For example, the additives can include negative electrode film-forming additives, positive electrode film-forming additives, and can also include additives that can improve certain battery performance, such as additives that improve the overcharge performance of the battery, additives that improve the high-temperature or low-temperature performance of the battery, etc.

[0154] [Separator]

[0155] In some embodiments, the secondary battery further includes a separator. There is no particular limitation on the type of separator in this application, and any well-known porous structure separator with good chemical stability and mechanical stability can be selected.

[0156] In some embodiments, the material of the separator membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator membrane can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator membrane is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0157] In some embodiments, the positive electrode plate, the negative electrode plate, and the separator membrane can be made into an electrode assembly by a winding process or a stacking process.

[0158] In some embodiments, the secondary battery can include an outer package. The outer package can be used to encapsulate the above-mentioned electrode assembly and electrolyte.

[0159] In some embodiments, the outer package of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the secondary battery can also be a soft package, such as a pouch-type soft package. The material of the soft package can be plastic. As plastics, polypropylene, polybutylene terephthalate, and polybutylene succinate can be listed, etc.

[0160] This application has no particular limitation on the shape of the secondary battery, and it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 is a secondary battery 5 with a square structure as an example.

[0161] In some embodiments, referring to Figure 2 , the outer package can include a housing 51 and a cover plate 53. Among them, the housing 51 can include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose to form a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode plate, the negative electrode plate, and the separator membrane can form an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. The number of electrode assemblies 52 included in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0162] In some embodiments, secondary batteries can be assembled into a battery module. The number of secondary batteries included in the battery module can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0163] Figure 3 is a battery module 4 as an example. Referring to Figure 3 , in the battery module 4, multiple secondary batteries 5 can be arranged in sequence along the length direction of the battery module 4. Of course, they can also be arranged in any other arbitrary manner. Further, the multiple secondary batteries 5 can be fixed by fasteners.

[0164] Optionally, the battery module 4 may further include a housing having an accommodation space, and a plurality of secondary batteries 5 are accommodated in the accommodation space.

[0165] In some embodiments, the above battery module may also be assembled into a battery pack. The number of battery modules included in the battery pack may be one or more. Those skilled in the art can select the specific number according to the application and capacity of the battery pack.

[0166] Figure 4 and Figure 5 is a battery pack 1 as an example. Refer to Figure 4 and Figure 5 , in the battery pack 1, a battery box and a plurality of battery modules 4 disposed in the battery box may be included. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can cover the lower box body 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0167] In addition, the present application also provides an electrical device, and the electrical device includes at least one of the secondary battery, battery module, or battery pack provided by the present application. The secondary battery, battery module, or battery pack can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device may include mobile devices (such as mobile phones, laptop computers, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, energy storage systems, etc., but is not limited thereto.

[0168] As the electrical device, the secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0169] Figure 6 is an electrical device as an example. The electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the high power and high energy density requirements of the electrical device for the secondary battery, a battery pack or a battery module can be adopted.

[0170] Another example of the device can be a mobile phone, a tablet computer, a laptop computer, etc. This device usually requires thin and light, and a secondary battery can be used as the power source.

[0171] Embodiment

[0172] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If no specific techniques or conditions are indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. If the manufacturer is not indicated in the reagents or instruments used, they are all conventional products that can be obtained commercially.

[0173] Example

[0174] The steps for recycling and processing the negative electrode sheets of the intermediate products (i.e., the sheets after cold pressing) in the production process of ternary lithium batteries are as follows.

[0175] The first step is preprocessing

[0176] The recovered negative electrode sheets were coarsely crushed by a hammer crusher, and then the crushed mixture was sent to the next hammer crusher for fine crushing, and then subjected to air separation, classification and vibration screening to obtain negative electrode material I with a Dv50 of 16μm.

[0177] Step 2: Heat treatment

[0178] The negative electrode material I is placed in a reaction furnace and heat treated under an inert atmosphere. The heat treatment process is shown in Table 1.

[0179] The third step is oxidation treatment

[0180] The material after the second step treatment was subjected to the oxidation treatment described in Table 1. The oxidizing gas used was air, and the "V" in the gas flow rate refers to the effective volume of the reaction equipment.

[0181] Step 4: Pickling

[0182] In the pickling tank, the material from the third step and the acid solution are fed simultaneously and fully stirred. The material undergoes two pickling steps in sequence. The acid solution composition of the first pickling step is a mixed solution of HF:HNO3:HCl=13:6:14 (molar ratio), and the composition of the second pickling step is a mixed solution of HNO3:HCl=5:2 (molar ratio). The above two pickling steps can be heated appropriately to accelerate the reaction. After the pickling step, the material is filtered, washed with water, and dried to obtain the impurity-free graphite.

[0183] Step 4: Coating

[0184] The decontaminated graphite is mixed with the carbon source in Table 1 and carbonized using the process in Table 1 to obtain a regenerated graphite negative electrode active material.

[0185] Comparative Example

[0186] The graphite was recovered in a manner different from that in the embodiment, and the properties of the obtained graphite were different from those in the embodiment, as follows.

[0187] Comparative Example 1: T0 is lower than that of the present application, and the recovery method is as follows.

[0188] The steps for recycling and processing the negative electrode sheets of the intermediate products (i.e., the sheets after cold pressing) in the production process of ternary lithium batteries are as follows.

[0189] The first step is preprocessing

[0190] The recovered negative electrode sheets were coarsely crushed by a hammer crusher, and then the crushed mixture was sent to the next hammer crusher for fine crushing, and then subjected to air separation, classification and vibration screening to obtain negative electrode material I with a Dv50 of 16μm.

[0191] Step 2: Heat treatment

[0192] The negative electrode material I is placed in a reaction furnace and heat treated under an inert atmosphere. The heat treatment process is shown in Table 1, specifically: keeping warm at 400°C for 2 hours.

[0193] Comparative Example 2: The powder resistivity is higher than that of the present application, and the specific recovery method is as follows.

[0194] The steps for recycling and processing the negative electrode sheets of the intermediate products (i.e., the sheets after cold pressing) in the production process of ternary lithium batteries are as follows.

[0195] The first step is preprocessing

[0196] The recovered negative electrode sheets were coarsely crushed by a hammer crusher, and then the crushed mixture was sent to the next hammer crusher for fine crushing, and then subjected to air separation, classification and vibration screening to obtain negative electrode material I with a Dv50 of 16μm.

[0197] The second step is oxidation treatment

[0198] The negative electrode material I after the first step treatment was subjected to the oxidation treatment described in Table 1. The oxidizing gas used was air, and the "V" in the gas flow rate refers to the effective volume of the reaction equipment.

[0199] Step 3: Pickling

[0200] In the pickling tank, the material from the third step and the acid solution are fed simultaneously and fully stirred. The material undergoes two pickling steps in sequence. The acid solution composition of the first pickling step is a mixed solution of HF:HNO3:HCl=13:6:14 (molar ratio), and the composition of the second pickling step is a mixed solution of HNO3:HCl=5:2 (molar ratio). The above two pickling steps can be heated appropriately to accelerate the reaction. After the pickling step, the material is filtered, washed with water, and dried to obtain the impurity-free graphite.

[0201] Step 4: Coating

[0202] Mix the purified graphite with the carbon source in Table 1 and perform carbonization treatment using the process in Table 1 to obtain the regenerated graphite anode active material.

[0203] The relevant parameters of the recovery methods in the above examples and comparative examples are shown in Table 1 below.

[0204] Table 1 Process conditions for recovering graphite in examples and comparative examples

[0205]

[0206]

[0207] The test method for the number of storage days is as follows:

[0208] At 25 °C, charge the CR2430 coin cell prepared above at a constant current of 1C to the upper cut-off voltage (corresponding to 100% SOC), then charge it at a constant voltage until the current is 0.05C. After standing for 5 minutes, discharge the secondary battery at a constant current of 1C to the lower cut-off voltage (corresponding to 0% SOC), and record the discharge capacity at this time, which is the discharge capacity before storage.

[0209] At 25 °C, charge the secondary battery prepared above at a constant current of 1C to the upper cut-off voltage (corresponding to 100% SOC), and then charge it at a constant voltage until the current is 0.05C. Then place the secondary battery in a constant temperature oven at 60 °C for storage until the discharge capacity of the secondary battery after storage decays to 80% of the discharge capacity before storage, stop the test, and record the storage days of the secondary battery.

[0210] The performance of the graphite anode active materials obtained in the above examples and comparative examples and the performance after assembling into batteries are shown in Table 2. For the determination of the remaining parameters in Table 2, refer to the foregoing description. The test methods for the same parameters in this application are the same.

[0211] Table 2

[0212]

[0213] It can be seen from the data in Table 2 that the weight loss characteristics (including the initial weight loss temperature and weight loss rate) of the graphite anode active material have a significant impact on the electrical properties such as the first discharge efficiency and storage performance of the battery. Generally, when the initial weight loss temperature T0 is in the range of 610 - 715 °C, the higher T0 is, the higher the first discharge efficiency of the graphite used as the anode of the battery and the more excellent the storage performance. At the same time, the powder resistivity of the graphite also has an obvious impact on the electrical properties. If it is too high, the electrical properties will deteriorate significantly. The experiment also found that the heat treatment conditions, oxidation treatment conditions, and coating conditions during recovery have a significant impact on the weight loss characteristics and powder resistivity of the graphite. Therefore, in the actual application process, graphite with the required performance can be obtained by adjusting the recovery process conditions.

[0214] It should be noted that this application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and embodiments having the same constitution and achieving the same effects as the technical idea within the scope of the technical solution of this application are all included in the technical scope of this application. In addition, within the scope of not departing from the gist of this application, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways constructed by combining some constituent elements in the embodiments are also included in the scope of this application.

Claims

1. A graphite anode active material, characterized in that, The initial weight loss temperature T0 of the graphite negative electrode active material is 610°C to 715°C; the initial weight loss temperature T0 is the temperature corresponding to the intersection point of the tangent line at the horizontal part before the step of the thermogravimetric analysis curve and the tangent line at the maximum weight loss rate.

2. The graphite anode active material according to claim 1, wherein The initial weight loss temperature T0 is 620°C to 710°C.

3. The graphite anode active material according to claim 1, wherein The maximum weight loss rate in the thermogravimetric analysis curve ≤ 6.5% / min; And / or, the temperature T corresponding to the maximum weight loss rate in the thermogravimetric analysis curve max is 710°C to 810°C.

4. The graphite negative electrode active material according to any one of claims 1-3, characterized in that, The thermogravimetric analysis curve of the graphite negative electrode active material shows that the weight loss rate between 35°C and 700°C is ≤ 60%.

5. The graphite negative electrode active material according to claim 1, wherein, The specific surface area SSA of the graphite negative electrode active material is 0.7 to 2.0 m 2 / g.

6. The graphite negative electrode active material according to claim 1 or 5, characterized in that The volume average particle size of the graphite negative electrode active material satisfies at least one of the following conditions: Dv1 is 1.0 to 5.0 μm, or, Dv50 is 10.0 to 22.0 μm, or, Dv10 is 4.0 to 12.0 μm, or, Dv90 is 25.0 to 40.0 μm.

7. The graphite negative electrode active material according to claim 1, characterized in that, The powder resistivity of the graphite negative electrode active material at 8 MPa is 0.005 to 0.025 Ω / cm.

8. The graphite negative electrode active material according to claim 1, characterized in that, When the graphite negative electrode active material is used as the negative electrode of a CR2430 type button cell, the first discharge efficiency of the cell is 92% to 96%; and / or, the specific capacity of the graphite negative electrode active material is 345 to 365 mAh / g.

9. The graphite negative electrode active material according to any one of claims 1 to 3, or claim 7 or 8, characterized in that, The true density of the graphite negative electrode active material is 2.18 to 2.25 g / cm 3 ; And / or, the tap density of the graphite negative electrode active material is 0.95 to 1.45 g / cm 3 ; and / or, the powder compaction density of the graphite negative electrode active material under 20000 N is 1.50 g / cc to 1.90 g / cc.

10. The graphite negative electrode active material according to any one of claims 1 to 3 or claim 7 or 8, characterized in that, The mass percentage of carbon in the graphite negative electrode active material ≥ 99%; and / or, the content of Na element in the graphite negative electrode active material is 10 to 200 ppm.

11. A method for recycling a graphite anode active material, characterized in that, Including: Recycling the negative electrode plate in the secondary battery, separating the negative electrode active material from the negative electrode plate to obtain graphite negative electrode active material 1; Performing heat treatment on the graphite negative electrode active material 1 in an inert atmosphere to obtain graphite negative electrode active material 2, and the temperature of the heat treatment is 300°C to 600°C; Performing oxidation treatment and pickling on the graphite negative electrode active material 2 to obtain graphite negative electrode active material 3; wherein, the oxidation treatment includes: introducing an oxidation gas into the reaction furnace and heating to 200°C to 600°C for oxidation reaction; Performing coating treatment on the graphite negative electrode active material 3, and the coating treatment includes: mixing the purified graphite negative electrode active material 3 with a carbon source and performing carbonization in an inert atmosphere at 1100°C to 1400°C to obtain the final graphite negative electrode active material.

12. The recovery method according to claim 11, wherein, The heating to 200°C to 600°C for oxidation reaction includes: First heating to 200°C to 450°C, holding for the first time for 0.5 h to 2.5 h, then continuing to heat to 450°C to 600°C and holding for the second time for 0.5 h to 1.5 h; wherein, the flow rate of the oxidation gas introduced during the first holding process is greater than the flow rate of the oxidation gas introduced during the second holding process.

13. The recovery method according to claim 11, wherein The mass ratio of the graphite negative electrode active material 3 to the carbon source is 100:1 to 10; Optionally, the carbon source includes one or more of coal tar pitch, petroleum pitch, high molecular compounds and resins; Optionally, the softening point temperature of the petroleum pitch is 80°C to 250°C.

14. A secondary battery, comprising a negative electrode sheet, wherein the negative electrode sheet comprises the graphite negative electrode active material according to any one of claims 1-10 or the graphite negative electrode active material obtained by the recovery method according to any one of claims 11-13.

15. An electrical device, characterized in that, Comprising the secondary battery according to claim 14.

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