Natural graphite waste-based repair material, repair method thereof and application of repair material in lithium ion battery

Abstract

The invention belongs to the field of waste battery recovery, and particularly relates to a natural graphite waste-based repair material and a repair method and application thereof, the repair method comprises the following steps: carrying out first-stage modification treatment on a waste graphite material in a solution of formula 1 (R1-COOH), and then carrying out second-stage modification treatment on the waste graphite material in a modification solution containing inorganic acid and an additive, a second-stage material is prepared; carrying out spray granulation treatment on the second-stage material, a titanium-based component, a transition metal source, a hard carbon precursor material and an organic binder to obtain a precursor 1; the precursor 1 is heated to the temperature T1 in the CO-containing atmosphere, then introduction of the CO-containing atmosphere is stopped, heat preservation heat treatment is carried out under negative pressure, and a precursor 2 is prepared; the temperature T1 is 750 to 1200 DEG C; and compounding the precursor 2, a lithium compound and a carbon source, and roasting to obtain the natural graphite waste-based repair material. The method provided by the invention can adapt to the physicochemical characteristics of the natural graphite waste, and can be regenerated to obtain a material with excellent multiplying power, fast charge and long circulation.

Description

Technical Field

[0001] The invention belongs to the field of recycling and regenerating natural graphite negative electrode materials of waste lithium-ion batteries. Background Art

[0002] The graphite negative electrode materials of lithium-ion batteries mainly include natural graphite and artificial graphite. As the volume of retired batteries increases, recycling and repairing natural graphite from waste batteries can effectively make up for the shortage of natural graphite resources and has great recycling value.

[0003] Regarding the recycling of waste natural graphite, there are relatively few repair methods in the prior art that are adapted to the physical and chemical characteristics of natural graphite. For example, the Chinese patent document with publication number CN115432699A discloses a method for regenerating graphite materials based on waste negative electrodes, specifically recording a method of subjecting waste negative electrode materials to gas-solid modification in a nitric acid vapor atmosphere, followed by mixing with modified graphite raw materials, carbon sources, and catalytic graphitization aids and thermally modifying in an atmosphere containing gaseous water. The Chinese patent document with publication number CN114583315A discloses a method for recycling and reusing carbon negative electrode materials from waste lithium-ion batteries, specifically recording a regeneration process of negative electrode materials in organic solvents, dilute acid, water washing, organic solvent washing, and calcining. For another example, the Chinese patent document with publication number CN101944644A discloses a method for recycling negative electrode materials for lithium-ion batteries, specifically recording a scheme of baking the pole piece at high temperature and sieving to obtain negative electrode powder.

[0004] It can be seen that although there have been an endless stream of regeneration methods for graphite negative electrodes in recent years, there are still few exclusive repair solutions that are suitable for the physical and chemical characteristics of waste natural graphite. Although the existing conventional waste graphite regeneration process can be transferred to the treatment of waste natural graphite to a certain extent, certain effects can also be achieved. However, compared with other graphite materials, waste natural graphite negative electrode materials have a relatively stable intrinsic structure. It is difficult to effectively repair and reconstruct the short-range network of ion conduction based on existing means, and it is difficult to obtain recycled materials that meet the requirements of super-fast charging. In addition, the existing process is not conducive to the recovery rate of waste natural graphite. In summary, it is necessary to develop new technologies that are suitable for the recovery and high-value utilization of waste natural graphite negative electrode materials. Summary of the invention

[0005] In view of the problem that the prior art lacks exclusive repair means suitable for waste natural graphite, the first purpose of the present invention is to provide a repair method for natural graphite waste-based repair materials, aiming to provide a graphite repair material that is suitable for the physical and chemical characteristics of waste natural graphite and can be repaired to obtain excellent fast charging and yield.

[0006] The second purpose of the present invention is to provide a natural graphite waste-based repair material obtained by the repair method and its application.

[0007] The third object of the present invention is to provide a lithium-ion battery including the natural graphite waste-based repair material, as well as its negative electrode and negative electrode material.

[0008] Different from materials such as waste artificial graphite materials, waste natural graphite has a more stable intrinsic structure, characteristics such as smaller interlayer spacing, etc., but there are obvious edge structure damages, significant embedding of metal and organic matter impurities, etc., and it has a greater difficulty in homogenization repair. Aiming at the repair problem of waste natural graphite, based on the existing conventional graphite repair schemes, it is difficult to highly adapt to the physical and chemical characteristics of waste graphite, and it is difficult to repair a repair material that takes into account fast charging performance. To solve this problem, the present invention provides the following improvement scheme:

[0009] A repair method for a natural graphite waste-based repair material, the steps include:

[0010] Step 1:

[0011] Recover the natural graphite waste to be treated from waste lithium-ion batteries;

[0012] Perform the first-stage modification treatment on the waste graphite material in the solution of Formula 1 to obtain a first-stage material;

[0013] Then place the first-stage material in a modification solution containing inorganic acid and an additive for the second-stage modification treatment; obtain a second-stage material; the additive is an oxidizing component;

[0014] R 1 -COOH

[0015] Formula 1

[0016] In the said Formula 1, the said R 1 is at least one of an alkyl group, a substituted alkyl group, a phenyl group, and a substituted phenyl group of C 1 ~C 6 ;

[0017] Step 2:

[0018] Perform spray granulation treatment on the second-stage material, a titanium-based component, a transition metal source, a hard carbon precursor material, and an organic binder to obtain a precursor 1;

[0019] Step 3:

[0020] Heat the precursor 1 to a temperature T1 in a CO-containing atmosphere, then stop introducing the CO-containing atmosphere and perform heat treatment under negative pressure to obtain a precursor 2; the temperature T1 is 750-1200 °C;

[0021] Step 4:

[0022] Compound the precursor 2 with a lithium compound and a carbon source and then perform roasting treatment to obtain the natural graphite waste-based repair material.

[0023] Regarding the repair problem caused by the physical and chemical characteristics of natural graphite waste, the present invention innovatively subjects waste natural graphite to two-stage modification treatment in Formula 1 and the modified liquid described above, and further combines it with Ti-based materials, transition metal sources, spray granulation, CO-containing atmosphere, negative pressure heat preservation treatment, and subsequent lithiation roasting. In this way, the physical and chemical characteristics of natural graphite waste can be repaired, its short-range battery and ion transport network can be reconstructed, and the fast charging performance of the recycled material can be improved. In addition, the yield, first Coulomb efficiency, fast charging, and long cycle performance can be further improved.

[0024] In the present invention, the natural graphite waste to be treated is a material peeled from the negative electrode of a waste lithium-ion battery using natural graphite as the negative electrode active material.

[0025] Preferably, the content of natural graphite in the natural graphite waste to be treated is above 80 wt.%.

[0026] In the present invention, in Formula 1, the R 1 is at least one of methyl, ethyl, phenylpropyl, and phenylpropylamino.

[0027] Preferably, in the system of the first-stage modification treatment, a component of Formula 2 is further added;

[0028]

[0029] The R 2 is a fluorine-substituted group, preferably a fluoroalkyl or fluorophenyl group of C 1 to C 6

[0030] Research in the present invention shows that using the combined components of Formula 1 and Formula 2 to modify natural graphite waste helps to further optimize the damaged edge structure of natural graphite waste, equalize the physical and chemical differences between the edge and the bulk phase, and thus is beneficial to improving the performance of the prepared material.

[0031] Preferably, Formula 2 is 2 to 5% of the weight of natural graphite waste.

[0032] In the present invention, the temperature of the first-stage modification treatment is below 100 °C, further can be 15 to 80 °C, and still further can be 70 to 80 °C.

[0033] The time of the first-stage modification can be, for example, 0.5 to 5 h. Further can be 3 to 4 h.

[0034] In the present invention, during the second-stage modification process, the inorganic acid can be any inorganic acid, for example, it can include one or several of hydrochloric acid, sulfuric acid, and nitric acid.

[0035] ​Preferably, the additive can be any component with certain oxidizing property, such as at least one of hydrogen peroxide and iron chloride.

[0036] Preferably, in the modifying solution, the concentration of the inorganic acid is 0.02 - 0.5 M; the concentration of the additive is 0.01 - 0.5 mM. For example, when the additive is saturated hydrogen peroxide, its volume can be 0.1 - 0.5% of the volume of the modifying solution.

[0037] The second-stage modification process is carried out in a closed container, where the preferred treatment temperature is 80 - 150 °C, and further can be 80 - 90 °C.

[0038] The time of the second-stage modification can be, for example, 0.5 - 5 h, and can be 2 - 3 h.

[0039] In the present invention, in step 2, the titanium-based component includes inorganic and / or organic substances of titanium; preferably one or several of titanium propoxide, titanium tetrachloride, titanium tetrafluoride, titanium boride, tetrabutyl titanate, lithium titanate, metatitanic acid, sodium titanate, lithium titanate, potassium fluorotitanate; preferably containing titanium tetrachloride and Li with a weight ratio of 1:0.5 - 2 4 Ti 5 O 12 . Research shows that the preferred titanium-based component, combined with the process, helps to further synergistically optimize the homogenization repair effect and repair adaptability of natural graphite waste, and can further improve the rate performance, capacity, long cycle performance and fast charging performance of the repaired materials.

[0040] Preferably, the transition metal source is one or several of nitrates, chlorides, oxalates of iron, cobalt, and nickel.

[0041] Preferably, the hard carbon precursor material includes one or several of glucose, sucrose, organic polymers, starch, etc.

[0042] Preferably, the organic binder includes one or several of sodium alginate, polyacrylic acid, polyvinylidene fluoride, carboxymethyl cellulose, gum arabic, etc.

[0043] Preferably, the mass ratio of precursor 1, titanium-based component, transition metal source, hard carbon precursor material, and organic binder is 100:0.001 - 0.2:0.005 - 0.2:3 - 8:0.5 - 2; further can be 100:0.05 - 0.1:0.01 - 0.05:4 - 6:1 - 1.5.

[0044] In the present invention, after the components are mixed in liquid phase, such as mechanical-assisted liquid phase mixing, spray treatment can be carried out to obtain precursor 1. The spray means can be conventional.

[0045] In the present invention, the content of CO in the CO-containing atmosphere is 1-10 v%, and further can be 4-6 v%.

[0046] Preferably, the rate of heating up to temperature T1 is 1-10 °C / min.

[0047] In the present invention, the temperature T1 in step 3 can be 800-900 °C.

[0048] The negative pressure can be the pressure of a conventional vacuum environment. For example, the pressure can be below 250 Pa.

[0049] Preferably, the time for holding under negative pressure is 2-6 h, and further can be 3-4 h.

[0050] In the present invention, in step 4, the lithium compound includes at least one of lithium halides, carboxylic acid compounds, phosphoric acid compounds, alcoholates, alkylates, hydrides, niobates, and aluminum hydride salts; preferably niobates of lithium. Research in the present invention shows that using niobates of lithium for subsequent calcination treatment, in combination with the process of the present invention, can further synergistically enhance the repair performance of the material.

[0051] Preferably, the carbon source includes at least one of pitch, resin, polypropylene, polyethylene, polyvinyl chloride, and polyamide;

[0052] Preferably, the mass ratio of precursor 2, lithium compound, and carbon source is 100:0.05-0.2:3-8; further can be 100:0.1-0.15:4-6.

[0053] Preferably, the calcination temperature is 950-1250 °C, and further can be 1000-1100 °C.

[0054] Preferably, the calcination time is 2-8 h, and further can be 2-3 h.

[0055] In the present invention, before the said calcination, a pre-calcination heat preservation process is further included, wherein the temperature of the pre-calcination process is 300-500 °C.

[0056] Preferably, the time for the pre-calcination heat preservation process is 1-3 h.

[0057] Preferably, the pre-calcination heat preservation process is carried out under normal pressure, preferably under high pressure. The said high pressure refers to 2-4 standard atmospheres.

[0058] Research in the present invention shows that adopting a two-stage heat preservation process of pre-calcination and calcination, especially the treatment of high-pressure pre-calcination, can further improve the homogenization and repair effect of natural graphite waste, and contribute to further enhancing the capacity, rate performance, and long-cycle performance of the prepared repair material.

[0059] The present invention also provides a natural graphite waste-based repair material prepared by the described repair method.

[0060] The present invention also provides a negative electrode of a lithium-ion battery, which includes a current collector and a negative electrode material compounded on its surface. The negative electrode material includes a negative electrode active material, a conductive agent, and a binder. The negative electrode active material includes the natural graphite waste-based repair material prepared by the described repair method.

[0061] The present invention also provides a lithium-ion battery including the described negative electrode.

[0062] For the lithium-ion battery and its negative electrode of the present invention, except for including the repair material of the present invention, other components, contents, and structures can all be known.

[0063] Beneficial effects

[0064] Aiming at the repair problems caused by the physical and chemical characteristics of natural graphite waste, the present invention innovatively conducts two-stage modification treatment on waste natural graphite in Formula 1 and the described modification liquid, and further combines with Ti-based materials, transition metal sources, spray granulation, CO-containing atmosphere, negative pressure heat preservation, and subsequent lithiation roasting. In this way, the physical and chemical characteristics of natural graphite waste can be repaired, its short-range battery and ion transport network can be reconstructed, and further, the fast charging performance of the recycled material can be improved. In addition, its yield, first Coulomb efficiency, fast charging, and long cycle performance are further improved.

[0065] In addition, research also shows that by using Formula 2 to assist in the first-stage modification treatment and / or conducting two-stage controlled-pressure roasting treatment, a better homogenization repair effect of natural graphite waste can be obtained, which helps to further improve the performance of the repaired material in half-cells and full-cells. Description of the drawings

[0066] Figure 1 SEM image of natural graphite waste in Example 1;

[0067] Figure 2 SEM image of the repaired natural graphite repair material in Example 1. Detailed implementation manners

[0068] The regeneration of the waste natural graphite negative electrode material includes the following steps in its treatment method:

[0069] 1. Crush the natural graphite waste recycled from waste batteries to obtain particles with a median particle size of 5 - 8 μm;

[0070] 2. Treatment with Formula 1: Place the above powder in Formula 1 for stirring reaction, and after the reaction ends, perform solid-liquid separation, filter cake washing, and drying.

[0071] The concentration of Formula 1 is 0.01 - 0.2 M; the liquid-solid ratio (volume ratio) is 20:3 - 8; the reaction time is 0.5 - 5 h, and the reaction temperature is 15 - 80 °C.

[0072] 3. Inorganic acid treatment: The obtained powder is placed in an inorganic acid and an additive for stirring reaction. After the reaction ends, solid-liquid separation, filter cake washing, and drying are carried out.

[0073] The inorganic acid mentioned refers to one or several of hydrochloric acid, sulfuric acid, and nitric acid; the acid concentration is 0.02 - 0.5 M; the additive is, for example, hydrogen peroxide, the reaction time is 0.5 - 5 h, the reaction temperature is 80 - 150 °C, preferably a mixed system of hydrochloric acid and hydrogen peroxide; the liquid-solid ratio (volume ratio) is 10:3 - 8.

[0074] 4. Surface modification: The obtained powder is mixed evenly with a titanium-based material, a transition metal source, a hard carbon precursor, an organic binder, and a solvent, and then spray-dried to obtain a powder.

[0075] The titanium-based material mentioned is one or several of titanium n-propoxide, titanium tetrachloride, titanium tetrafluoride, titanium boride, tetrabutyl titanate, lithium titanate, metatitanic acid, sodium titanate, lithium titanate, potassium fluotitanate, etc.; the transition metal source is one or several of nitrates, chlorides, and oxalates of iron, cobalt, and nickel; the hard carbon precursor is one or several of glucose, sucrose, organic polymers, starch, etc.; the organic binder is one or several of sodium alginate, polyacrylic acid, polyvinylidene fluoride, carboxymethyl cellulose, gum arabic, etc.; the solvent is one or several of water, methanol, ethanol, etc. The mass ratio of graphite powder to the titanium-based material, the transition metal source, the hard carbon precursor, and the organic binder is 100:0.001 - 0.2:0.005 - 0.2:3 - 8:0.5 - 2.

[0076] 5. The obtained powder is subjected to a one-stage heat treatment.

[0077] The obtained powder is placed in an atmosphere furnace. First, under an atmosphere of 2 - 10% CO + inert protective gas, it is heated to 600 - 900 °C, then evacuated (such as 20 - 200 Pa), held for 2 - 6 h, and cooled naturally.

[0078] 6. The obtained powder is mixed evenly with a lithium compound and a carbon source and then calcined.

[0079] The lithium compound mentioned is one or several of lithium chloride, lithium formate, lithium benzoate, lithium oxalate, lithium phosphate, lithium isopropoxide, lithium methoxide, n-butyllithium, lithium hexafluorophosphate, lithium aluminum hydride, lithium niobate, etc., preferably lithium aluminum hydride and lithium niobate; the carbon source refers to pitch; the mass ratio of the powder to the lithium source is 100:0.05 - 0.2; the mass ratio of the powder to the carbon source is 100:3 - 8; the heat treatment temperature is 950 - 1250 °C, and the treatment time is 2 - 8 h.

[0080] The natural graphite waste described in the present invention is the natural graphite waste recovered from waste batteries with natural graphite as the negative electrode active material. The carbon content of the natural graphite therein is, for example, 85% or more, and its median particle size can be 5-10 μm.

[0081] Example 1

[0082] (1) The natural graphite waste of the waste battery (natural graphite content is 85-87 wt%) is crushed to obtain particles with a median particle size of 5.8 μm.

[0083] (2) The above powder is placed in a 0.02 M of Formula 1 (in this case, Formula 1A, specifically ) and stirred for 4 h. The reaction temperature is 70-80 °C, and the reaction system is a closed reaction system. After the reaction, solid-liquid separation, filter cake washing and drying are carried out.

[0084] (3) The obtained powder is placed in a mixed system of 0.2 M hydrochloric acid and an additive (saturated hydrogen peroxide, and its dosage is 0.2% vol of hydrochloric acid) and stirred for 2 h. The reaction temperature is 85-90 °C. After the reaction, solid-liquid separation, filter cake washing and drying are carried out.

[0085] (4) The obtained powder is dissolved and dispersed in water with a titanium source (titanium tetrachloride), a metal source (nickel oxalate), a carbon source (glucose), and a binder (polyacrylic acid) in a mass ratio of 100:0.1:0.01:5:1.5, and spray-dried to obtain a powder (precursor 1, particle D50 = 11.5 μm).

[0086] (5) The obtained powder (precursor 1) is placed in an atmosphere furnace. First, it is heated to 800 °C in an atmosphere of 6% CO + inert protective gas (Ar), and then evacuated and kept warm under vacuum for 3 h, and cooled with the furnace (precursor 2).

[0087] (6) The obtained powder (precursor 2) is mixed evenly with lithium niobate and pitch in a mass ratio of 100:0.1:5, and calcined at 1000 °C under Ar (atmospheric pressure) for 4 h to obtain the described natural graphite waste.

[0088] Example 2

[0089] Compared with Example 1, the difference is only that in the starting treatment system of step 2, Formula 2 (in this case, Formula 2A, and its structure is ) is also added, and the dosage of Formula 2A is 3% of the graphite powder in step 1. Other operations and parameters are the same as in Example 1.

[0090] Example 3

[0091] Compared with Example 1, the only difference is that the conditions in Steps 4 and 5 are changed. The experimental groups are as follows:

[0092] Group A: In Step 4, the titanium source is an equal amount of Li 4 Ti 5 O 12 .

[0093] Group B: In Step 4, the titanium source is a mixture of titanium tetrachloride and Li 4 Ti 5 O 12 , with a mass ratio of 1:1.

[0094] Group C: In Step 4, the powder obtained in Step 3 is mixed with titanium tetrachloride, nickel oxalate, glucose, and polyacrylic acid in a mass ratio of 100:0.05:0.05:6:1; the content of CO in Step 5 is 5 v%; the temperature is 900 °C, and the vacuum holding time is 4 h.

[0095] All other operations and parameters are the same as in Example 1.

[0096] Example 4

[0097] Compared with Example 1, the only difference is that the conditions in Step 6 are changed. The experimental groups are as follows:

[0098] Group A: The temperature of the system is preheated to T1 (400 ± 20 °C) and held at this temperature for 2 hours, then heated to T2 (1000 °C) and held for another 2 h. The pressure during the calcination process is normal pressure, and the material is prepared. All other operations and parameters are the same as in Example 1.

[0099] Group B: Compared with Group A, the only difference is that during the holding process at temperature T1, Ar is used for pressure treatment, and the pressure is 2 - 3 atm. All other operations are the same as in Group A.

[0100] Example 5

[0101] Compared with Example 1, the only difference is that in Step 6, after mixing the powder obtained in Step 5 with lithium acetate and pitch in a mass ratio of 100:0.15:6, it is calcined in Ar at 1100 °C for 3 h to prepare the material.

[0102] Comparative Example 1

[0103] Compared with Example 1, the only difference is that in Step 2, the powder obtained in Step 1 is directly processed in Step 3, and the processing time of the missing Step 2 is extended by an equal amount by extending the processing time of Step 3, and the total time is the same. All other operations and parameters are the same as in Example 1.

[0104] Comparative Example 2

[0105] Compared with Example 1, the only difference is that step 3 is not carried out, but the hydrochloric acid and additive in step 3 are added to the starting solution system in step 2 for the treatment of step 2, and then the product is directly subjected to step 4 and subsequent treatments. Other operations and parameters are the same as those in Example 1.

[0106] Comparative Example 3

[0107] Compared with Example 1, the only difference is that in step 4, titanium tetrachloride is not added, and the missing part is supplemented with nickel oxalate in equal weight. Other operations and parameters are the same as those in Example 1.

[0108] Comparative Example 4

[0109] Compared with Example 1, the only difference is that in step 4, nickel oxalate is not added, and the missing weight is supplemented with titanium tetrachloride in equal weight. Other operations and parameters are the same as those in Example 1.

[0110] Comparative Example 5

[0111] Compared with Example 1, the only difference is that in step 4, spray treatment is not carried out, but physical mixing is carried out to obtain a mixed material. Other operations and parameters are the same as those in Example 1.

[0112] Comparative Example 6

[0113] Compared with Example 1, the only difference is that in step 5, the sintering atmosphere is 6% H2 + inert protective gas. Other operations and parameters are the same as those in Example 1.

[0114] Comparative Example 7

[0115] Compared with Example 1, the only difference is that in step 5, negative pressure heat preservation treatment is not carried out, but normal pressure heat preservation is carried out in an Ar atmosphere after the temperature rises to 800°C. Other operations and parameters are the same as those in Example 1.

[0116] Comparative Example 8

[0117] Compared with Example 1, the only difference is that in step 6, lithium niobate is not added. Other operations and parameters are the same as those in Example 1.

[0118] Comparative Example 9

[0119] Compared with Example 1, the only difference is that step 6 is not carried out, but the lithium niobate and asphalt in step 6 are mixed with other components during the process of step 4, and the treatment of step 5 is carried out to obtain the recycled material. Other operations and parameters are the same as those in Example 1.

[0120] 1. The 0.2C test is a half-cell test

[0121] Using the graphite prepared in the example as the negative electrode, the steps are as follows: Graphite, Super P, and LA133 are dispersed in deionized water at a mass ratio of 96:2:2 to form a slurry, which is coated on a copper foil. After drying, it becomes the negative electrode sheet; the separator is a Celgard 2400 membrane; the electrolyte is 1M LiPF6 / EC+DEC+DMC (1:1:1); the counter electrode is a lithium sheet. Assemble it into a lithium half-cell in a glove box for testing.

[0122] 2. The 10C fast charge test is a full cell test

[0123] Using the graphite prepared in the example as the negative electrode (the same negative electrode as above), LiNi1 / 3Co1 / 3Mn1 / 3O2 as the positive electrode material (the weight ratio of the active material, conductive carbon black, and PVDF binder is 9:0.5:0.5), the separator is a Celgard 2400 membrane, and the electrolyte is 1M LiPF6 / EC+DEC+DMC (1:1:1) to prepare a 2Ah soft pack battery, which is charged at 10C and discharged at 2C to test its constant current ratio.

[0124] The results are shown in Table 2 and Table 3

[0125] Table 2

[0126]

[0127] Table 3

[0128]

[0129]

[0130] It can be seen from the examples and comparative examples that the waste natural graphite is innovatively subjected to two-stage modification treatment in Formula 1 and the modified liquid described above, and further combined with Ti-based materials, transition metal sources, spray granulation, CO-containing atmosphere, negative pressure heat preservation, and subsequent lithiumation roasting. In this way, the physical and chemical characteristics of the natural graphite waste can be repaired, its short-range battery and ion transport network can be reconstructed, and the fast charge performance of the recycled material can be improved. In addition, the yield, initial Coulomb efficiency, fast charge, and long cycle performance can be further improved.

[0131] In addition, it can be seen from Examples 1 and 2 that using Formula 2 to assist in the first-stage modification treatment helps to further optimize the repair effect of the natural graphite waste and helps to further strengthen the performance of the repaired material. It can be seen from Examples 1 and 3 that using the preferred titanate can achieve synergy to a certain extent and optimize the performance. In addition, it can be seen from Examples 1 and 4 that using the two-stage roasting process described above, especially the process of controlling pressure and heat preservation during the first-stage roasting, can obtain a better synergy effect and help to further improve the performance of the repaired material in half-cells and full cells.

Claims

1. A method for repairing a natural graphite waste-based repair material, characterized in that the steps include: Step 1: Recovering natural graphite waste from spent lithium-ion batteries for processing; The waste graphite material is subjected to a first stage modification treatment in a solution of Formula 1 to obtain a first stage material; Then, the first-stage material is placed in a modification liquid containing an inorganic acid and an additive to carry out a second-stage modification treatment; The second stage material is obtained; the additive is an oxidizing component; R1-COOH Formula 1 In the formula 1, R1 is at least one of a C1-C6 alkyl group, a substituted alkyl group, a phenyl group, and a substituted phenyl group; Step 2: The second-stage material, the titanium-based component, the transition metal source, the hard carbon precursor material, and the organic binder are subjected to spray granulation treatment to obtain a precursor 1; Step 3: The precursor 1 is heated to a temperature T1 in a CO-containing atmosphere, and then the CO-containing atmosphere is stopped and heat-treated under negative pressure to obtain a precursor 2; the temperature T1 is 750-1200°C; Step 4: The precursor 2 is compounded with a lithium compound and a carbon source and then calcined to obtain the natural graphite waste-based repair material.

2. The repair method of the natural graphite waste-based repair material according to claim 1, characterized in that: The natural graphite waste to be treated is a material obtained by stripping the negative electrode of a waste lithium-ion battery using natural graphite as the negative electrode active material; Preferably, the content of natural graphite in the natural graphite waste to be processed is above 80 wt.%.

3. The repair method of the natural graphite waste-based repair material according to claim 1, characterized in that: In the formula 1, R1 is at least one of methyl, ethyl, phenylpropyl, and phenylpropylamino; Preferably, the first stage modification treatment system further includes a component of formula 2; The R2 is a fluorine-substituted group, preferably a C1-C6 fluorinated alkyl or fluorinated phenyl group; Preferably, the formula 2 is 2-5% of the weight of natural graphite waste.

4. The repair method of the natural graphite waste-based repair material according to claim 1, characterized in that: In the second modification process, the inorganic acid includes one or more of hydrochloric acid, sulfuric acid, and nitric acid; Preferably, the additive includes at least one of hydrogen peroxide and ferric chloride; Preferably, in the modified solution, the concentration of the inorganic acid is 0.02 to 0.5 M; the concentration of the additive is 0.01 to 0.5 mM; Preferably, the second modification process is carried out in a closed container, wherein the preferred treatment temperature is 80-150°C.

5. The repair method of the natural graphite waste-based repair material according to claim 1, characterized in that: In step 2, the titanium-based component includes inorganic and / or organic titanium; preferably one or more of titanium n-propoxide, titanium tetrachloride, titanium tetrafluoride, titanium boride, tetrabutyl titanate, lithium titanate, metatitanic acid, sodium titanate, lithium titanate, and potassium fluorotitanate; Preferably, the transition metal source is one or more of nitrates, chlorides and oxalates of iron, cobalt and nickel; Preferably, the hard carbon precursor material includes one or more of glucose, sucrose, organic polymers, and starch; Preferably, the organic binder includes one or more of sodium alginate, polyacrylic acid, polyvinylidene fluoride, carboxymethyl cellulose, and arabic gum; Preferably, the mass ratio of the precursor 1, the titanium-based component, the transition metal source, the hard carbon precursor material, and the organic binder is 100:0.001-0.2:0.005-0.2:3-8:0.5-2.

6. The repair method of the natural graphite waste-based repair material according to claim 1, characterized in that: The content of CO in the CO-containing atmosphere is 1 to 10 v%; Preferably, the rate of heating to temperature T1 is 1 to 10°C / min; Preferably, the negative pressure is below 250 Pa; Preferably, the negative pressure insulation time is 2 to 6 hours.

7. The repair method of the natural graphite waste-based repair material according to claim 1, characterized in that: In step 4, the lithium compound includes at least one of lithium halides, carboxylic acid compounds, phosphoric acid compounds, alcoholates, alkylates, hydrides, niobates, and aluminum hydride salts; Preferably, the carbon source comprises at least one of asphalt, resin, polypropylene, polyethylene, polyvinyl chloride, and polyamide; Preferably, the mass ratio of the precursor 2, the lithium compound, and the carbon source is 100:0.05-0.2:3-8; Preferably, the calcination temperature is 950-1250°C; Preferably, the calcination time is 2 to 8 hours; Preferably, before the roasting, a pre-roasting and heat preservation process is also included, wherein the temperature of the pre-roasting process is 300-500°C; Preferably, the pre-baking and heat-insulating process lasts for 1 to 3 hours; Preferably, the pre-calcination and heat preservation process is carried out at normal pressure, preferably at high pressure; Preferably, the high pressure refers to 2 to 4 standard atmospheric pressures.

8. A natural graphite waste-based repair material obtained by the repair method according to any one of claims 1 to 7.

9. A negative electrode of a lithium ion battery, comprising a current collector and a negative electrode material composited on the surface of the current collector, wherein the negative electrode material comprises a negative electrode active material, a conductive agent and a binder, characterized in that: The negative electrode active material comprises a natural graphite waste-based repair material obtained by the repair method described in any one of claims 1 to 7.

10. A lithium ion battery, characterized in that: The negative electrode according to claim 9 is included.

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