A method for recycling and reusing waste graphite negative electrode material and an electrode sheet prepared thereby

Abstract

The application relates to the technical field of graphite recovery, and particularly discloses a recycling method of waste graphite negative material and an electrode sheet prepared by the method. The waste graphite negative material is sequentially washed by water and an organic solvent to obtain recycled graphite negative material A; the waste graphite negative material is sintered at 400 DEG C-1200 DEG C under an inert atmosphere to obtain recycled graphite negative material B; the recycled graphite negative material A and the recycled graphite negative material B are respectively mixed with a conductive agent, a binder and water to obtain viscous slurry A and viscous slurry B; the viscous slurry A and the viscous slurry B are coated on the surface of a current collector, and the current collector, the viscous slurry A and the viscous slurry B are sequentially arranged from bottom to top; and then, heat treatment is carried out under an inert atmosphere to obtain an electrode sheet. The electrode sheet prepared by the method can balance capacity, fast charging, volume energy density and cycle performance simultaneously.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of graphite recovery, in particular to a recycling method of waste graphite negative material and an electrode sheet prepared by the method. BACKGROUND

[0002] With the increasing installation capacity of lithium ion batteries year by year, the data of scrapped batteries also increases significantly, and the recycling of batteries, especially the recycling of high-energy consumption and high-carbon emission graphite negative material, has great potential. The recycled graphite negative material has significant advantages in many aspects. First, the recycled graphite resource is abundant and low in cost, and its price is more competitive than other negative materials. Second, the recycling of graphite negative material can effectively reduce the pollution of waste batteries to the environment and reduce resource waste, and has good environmental benefits. In addition, the recycled graphite can be reused for battery manufacturing after proper treatment, realizing the recycling of resources and reducing the dependence on new graphite resources.

[0003] Although recycled graphite has many advantages, it still faces many challenges in engineering. First, the source and composition of recycled graphite negative material are complex, and the graphite negative of different batteries is quite different and has many impurities, which is difficult to process uniformly. Second, the recycling process is complex and inefficient, and the existing methods can only achieve a single goal, and there are problems such as graphite loss, high energy consumption, and environmental pollution. Third, the comprehensive performance of recycled graphite is poor, and the cycle stability is poor, which is difficult to meet the application requirements of battery grade. In addition, there is currently a lack of unified recycling standards and specifications, resulting in uneven product quality, non-standard recycling process, and affecting the efficient recycling and reuse of graphite negative material. Therefore, there is an urgent need in the art to develop a recycling method of graphite negative material to further improve the recycling efficiency and improve the quality of the recycled product, and promote the sustainable development of new energy field. SUMMARY

[0004] In view of the above problems, the present application provides a recycling and reuse method of waste graphite negative material and an electrode sheet prepared by the method. The same kind of waste graphite negative material is recycled by two different treatment processes, and then used as the upper and lower layers of the electrode, which can ensure that the source of the graphite raw material in the same electrode sheet is controllable, and the unique double-layer structure of the electrode sheet can balance the capacity, fast charging, volume energy density and cycle performance at the same time, greatly improving the electrochemical performance of the battery.

[0005] To solve the above technical problems, the technical scheme provided by the present application is:

[0006] In a first aspect, the present application provides a recycling and reuse method of waste graphite negative material, comprising the following steps:

[0007] S100, the waste graphite negative material is washed with water and an organic solvent in sequence to obtain a recycled graphite negative material A;

[0008] sintering the waste graphite negative electrode material at 400-1200 DEG C under an inert atmosphere to obtain a recycled graphite negative electrode material B;

[0009] S200, mixing the recycled graphite negative electrode material A and the recycled graphite negative electrode material B respectively with a conductive agent, a binder and water to obtain viscous slurries A and B;

[0010] S300, coating the viscous slurries A and B on the surface of the current collector, sequentially from bottom to top as the current collector, the viscous slurry A and the viscous slurry B; and then performing heat treatment under an inert atmosphere to obtain an electrode sheet.

[0011] Compared with the prior art, the application provides a recycling method of waste graphite negative electrode material, which recycles the same kind of waste graphite negative electrode material through two different processing techniques, and then uses it as a double-layer structure on the surface of the current collector, so as to effectively guarantee that the source of the graphite material in the same electrode sheet is controllable, and further guarantee that the electrochemical performance of the same electrode sheet is at the same level. It should be noted that the same kind of graphite negative electrode material is used in the same battery, and the waste graphite negative electrode material is divided according to the battery cell batch, and the same batch is the same kind of waste graphite negative electrode material.

[0012] The application prepares the recycled graphite negative electrode material A by a liquid phase washing method, removes the binder in the waste graphite negative electrode material, and retains the graphite and the conductive agent in the waste graphite negative electrode material, wherein the conductive agent can still improve the conductivity of the material. The application prepares the recycled graphite negative electrode material B by a high-temperature sintering method, sinters all components in the waste graphite negative electrode material together, makes the conductive agent and the binder become carbon residues on the surface of the graphite, improves the carbon coating amount of the recycled graphite negative electrode material, and thus improves the conductivity and fast charging performance of the material.

[0013] The application forms the viscous slurry A and the viscous slurry B from the recycled graphite negative electrode material A and the recycled graphite negative electrode material B respectively, and then sequentially coats them on the surface of the current collector, takes the current collector as a substrate, and can form a structure with the upper layer being the material B (i.e. the upper layer material B formed by the viscous slurry B) and the lower layer being the material A (i.e. the lower layer material A formed by the viscous slurry A). In view of the characteristics of the recycled graphite negative electrode material B and the recycled graphite negative electrode material A in the upper layer material B and the lower layer material A, the double-layer structure can effectively improve the properties of the electrode sheet, significantly improves the volume energy density of the battery while not losing the fast charging performance, and also balances the capacity and improves the cycle performance.

[0014] Preferably, in S100, the waste graphite negative electrode material is derived from a power battery or an energy storage battery.

[0015] Preferably, in S100, the waste and old graphite negative electrode material comprises the following components in mass percentage: graphite 95%~97%, conductive agent 0.5%~1.5%, and binder 2.5%~3.5%.

[0016] The waste and old graphite negative electrode material of the present application further comprises some trace elements, with content in PPM level.

[0017] Further preferably, in S100 and S200, the conductive agent comprises carbon black type conductive agent, and the binder comprises carboxymethyl cellulose and styrene butadiene rubber.

[0018] For example, in S100 and S300, the carbon black type conductive agent comprises SP (Super-P).

[0019] The present application mainly recycles power batteries and energy storage batteries, and the conductive agent in the graphite negative electrode material thereof is mainly SP, and the binder is mainly carboxymethyl cellulose (CMC) and styrene butadiene rubber (SBR), and other types of conductive agent and binder are not mainstream products, which are not considered in the present application. In addition, the present application does not limit the mass ratio of CMC and SBR in the binder in S100, and is suitable for binders comprising CMC and SBR in any ratio.

[0020] Preferably, in S100, the preparation method of the recycled graphite negative electrode material A specifically comprises the following steps:

[0021] The waste and old graphite negative electrode material is added into water, washed for 4~5 times, filtered; the obtained filter is added into an organic solvent, washed for 2~3 times, filtered, dried, to obtain the recycled graphite negative electrode material A.

[0022] Further preferably, in S100, the mass ratio of the waste and old graphite negative electrode material to water is 1:9~4:6.

[0023] Further preferably, in S100, the mass ratio of the filter to the organic solvent is 2:8~4:6.

[0024] Further preferably, in S100, the organic solvent comprises at least one of ethanol, acetone, isopropyl alcohol, ethyl acetate, or propylene glycol.

[0025] Washing with an organic solvent can reduce the adhesion of the material in the subsequent drying process.

[0026] For example, in S100 and S300, the inert atmosphere comprises a nitrogen atmosphere.

[0027] Preferably, in S100, the sintering temperature is 800℃~1200℃, and the sintering time is 2h~8h.

[0028] Preferably, in S200, the mass ratio of the recovered graphite negative material A, the conductive agent and the binder in the viscous slurry A is (96-97):(0.4-0.6):(2.8-3.2).

[0029] Preferably, in S200, the binder in the viscous slurry A comprises carboxymethyl cellulose and butadiene-styrene rubber in a mass ratio of 1:(1.3-1.7).

[0030] Preferably, in S200, the solid content of the viscous slurry A is 35%-45%.

[0031] Preferably, in S200, the mass ratio of the recovered graphite negative material B, the conductive agent and the binder in the viscous slurry B is (96.5-97.5):(0.4-0.6):(2.3-2.7).

[0032] Preferably, in S200, the binder in the viscous slurry B comprises carboxymethyl cellulose and butadiene-styrene rubber in a mass ratio of 1:(1.8-2.2).

[0033] Preferably, in S200, the solid content of the viscous slurry B is 35%-45%.

[0034] Preferably, in S300, the current collector comprises a copper foil.

[0035] Preferably, in S300, the mass ratio of the viscous slurry A and the viscous slurry B is 3:7-6:4.

[0036] Preferably, in S300, the total coating area density of the viscous slurry A and the viscous slurry B is 5mg / cm 2 ~6mg / cm 2 .

[0037] Further preferably, in S300, the coating area density of the viscous slurry A is 1.5mg / cm 2 ~3.6mg / cm 2 , and the coating area density of the viscous slurry B is 2mg / cm 2 ~4mg / cm 2 .

[0038] The present application can use a double-layer slot-type extrusion coater to simultaneously coat the viscous slurry A and the viscous slurry B on the surface of the copper foil, which is more conducive to mass production; or the viscous slurry A can be coated on the surface of the copper foil first, and then the viscous slurry B is coated after drying.

[0039] Preferably, in S300, after the coating is completed, before the heat treatment, the method further comprises drying, rolling and cutting.

[0040] Further preferably, in S300, the drying temperature is 90-120℃.

[0041] For example, in S300, the electrode sheet can be cut into a disc with a diameter of 16mm.

[0042] Preferably, in S300, the heat treatment temperature is 250-600℃, and the heat treatment time is 8-12s.

[0043] Preferably, in S300, the heat treatment uses the Joule heat technology, and the heating rate is 50-500℃ / s (further preferably, 100-300℃ / s).

[0044] The present application improves the integrated properties of the electrode sheet through heat treatment, and improves the adhesion of the upper and lower layers and the binder and graphite particles. The obtained electrode sheet is subjected to short-time heat treatment using the Joule heat technology, so that the active material, conductive agent and binder are rearranged, the content of organic matter in the electrode sheet is reduced, the purpose of slightly carbonizing the electrode sheet is achieved, so that the electrode sheet has good electrochemical performance, and the initial coulomb efficiency, cycle stability and rate performance are improved.

[0045] In a second aspect, the present application provides an electrode sheet prepared by the recycling method of the waste graphite negative electrode material.

[0046] The present application has the following beneficial effects:

[0047] (1) Improving the properties of the electrode sheet. Since the capacity of the residual carbon after sintering is lower than that of graphite, the capacity of the recycled graphite negative electrode material B is lower than that of the recycled graphite negative electrode material A. The residual carbon content of the recycled graphite negative electrode material B is higher than that of the recycled graphite negative electrode material A, which is not easy to bond in the subsequent electrode sheet preparation process (slurry coating process), and more binder is needed, otherwise powder floating or material falling will occur. However, too high content of the binder will reduce the electrical conductivity of the electrode sheet, reduce the fast charging performance of the battery, and also reduce the proportion of the active material (recycled graphite negative electrode material B), thereby reducing the energy density of the electrode. The recycled graphite negative electrode material A is prepared by a liquid washing method, and the binder in the waste graphite negative electrode material is removed, so that the residual carbon content is low, and the amount of the binder used in the subsequent electrode sheet preparation process can be reduced. The present application adopts a double-layer structure with the upper layer being material B and the lower layer being material A, which can balance the amount of the binder, improve the floating of the binder in the coating and drying process, increase the residual amount of the binder in the upper material B, and improve the overall performance of the electrode sheet.

[0048] (2) Balance capacity, fast charging and volume energy density. The residual carbon content of the recycled graphite negative electrode material A is low, the fast charging performance is poor, the compaction density is also low (about 1.59 cc / g), but the capacity is higher (about 346 mAh / g); the residual carbon content of the recycled graphite negative electrode material B is higher, the fast charging performance is better, the capacity is about 352 mAh / g, and the compaction density is high (about 1.65 cc / g), which has a higher volume energy density. Using viscous slurry A or viscous slurry B alone cannot simultaneously satisfy the balance of high volume energy density and fast charging. The present application adopts a double-layer structure of material B in the upper layer and material A in the lower layer. Since the fast charging capacity is mainly provided by the upper layer material B, the overall compaction density can be significantly improved without losing the fast charging performance, thereby improving the volume energy density of the battery, while meeting the capacity balance.

[0049] (3) Improve the cycle performance. The decay of the lithium battery negative electrode cycle performance is mainly due to the consumption of active lithium, which mainly occurs in the first cycle to form the SEI film and in the subsequent cycle process. The continuously generated new SEI film will continuously consume active lithium. The residual fluorine, oxygen, lithium, sulfur and other elements in the recycled graphite help to form a more stable and thinner SEI film, thereby reducing the consumption of active lithium and improving the cycle performance. The present application adopts a double-layer structure of material B in the upper layer and material A in the lower layer. The upper layer material B can meet the rapid lithium intercalation of the negative electrode material in most of the fast charging process, and reduce the current when fully charged. The lower layer material A provides the main lithium intercalation capacity. Compared with the single-layer structure, the double-layer structure can better balance the capacity, fast charging, volume energy density and cycle performance. BRIEF DESCRIPTION OF DRAWINGS

[0050] Figure 1 FIG. 1 is a structural schematic diagram of the electrode sheet in the present application embodiment 1-5; in the figure, 1 represents copper foil, 2 represents the lower layer material A formed by viscous slurry A, and 3 represents the upper layer material B formed by viscous slurry B;

[0051] Figure 2 FIG. 2 is an SEM diagram of the recycled graphite negative electrode material A in the present application embodiment 3;

[0052] Figure 3 FIG. 3 is an SEM diagram of the recycled graphite negative electrode material B in the present application embodiment 3. DETAILED DESCRIPTION

[0053] In order to make the purpose, technical scheme and advantages of the present application more clear and explicit, the present application will be further described in detail below in combination with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and not to limit the present application.

[0054] In this invention, all materials except those specifically mentioned are commercially available products. The waste graphite anode material in the embodiments is derived from power batteries or energy storage batteries; the double-layer slit extrusion coating machine was purchased from Shenzhen Yinghe Technology Co., Ltd., model Super-E.

[0055] Example 1

[0056] This embodiment provides a method for recycling and reusing waste graphite anode materials, including the following steps:

[0057] S101. Add waste graphite anode material to water at a mass ratio of 1:9, wash 4 times (stir for 10 min) and filter by pressure; add the obtained filtrate to an organic solvent (propylene glycol) at a mass ratio of 2:8, wash 2 times and filter by pressure, and dry to obtain recovered graphite anode material A.

[0058] Waste graphite anode material comprises the following components by mass percentage: 95% graphite, 1.5% conductive agent (SP), and 3.5% binder (CMC and SBR) (trace elements are not included).

[0059] S102. Under a nitrogen atmosphere, the same type of waste graphite anode material is placed in a continuous roller furnace and sintered at 600°C for 8 hours. After cooling to room temperature, recycled graphite anode material B is obtained.

[0060] S201. Add the recycled graphite anode material A, conductive agent and binder to water. The mass ratio of the recycled graphite anode material A, SP, CMC and SBR is 96:0.4:1:1.8. Mix evenly to obtain a viscous slurry A with a solid content of 35%.

[0061] S202. Add the recycled graphite anode material B, conductive agent and binder to water. The mass ratio of the recycled graphite anode material B, SP, CMC and SBR is 96.5:0.4:1:1.3. Mix evenly to obtain a viscous slurry B with a solid content of 35%.

[0062] S300: A double-layer slit extrusion coating machine is used to simultaneously coat the copper foil surface with viscous slurry A and viscous slurry B. From bottom to top, the layers are current collector, viscous slurry A, and viscous slurry B. The surface density of viscous slurry A is 3 mg / cm³. 2 The coating surface density of the viscous slurry B is 3 mg / cm³. 2 The mass ratio of viscous slurry A to viscous slurry B is 5:5; then it is dried at 90℃, rolled, and cut into round sheets with a diameter of 16mm; under a nitrogen atmosphere, it is heat-treated at 300℃ using Joule heating technology, with a heating rate of 100℃ / s and a holding time of 12s. After cooling to room temperature, the electrode sheet is obtained. A schematic diagram of the electrode sheet structure is shown below. Figure 1As shown.

[0063] It should be noted that this embodiment does not limit the order of S101 and S102, nor does it limit the order of S201 and S202.

[0064] Example 2

[0065] This embodiment provides a method for recycling and reusing waste graphite anode materials, including the following steps:

[0066] S101. Add waste graphite anode material to water at a mass ratio of 2:8, wash 4 times (stirring for 10 min) and filter under pressure; add the obtained filtrate to an organic solvent (ethyl acetate) at a mass ratio of 3:7, wash 3 times and filter under pressure, and dry to obtain recovered graphite anode material A.

[0067] Waste graphite anode material comprises the following components by mass percentage: 97% graphite, 0.5% conductive agent (SP), and 2.5% binder (CMC and SBR) (trace elements are not included).

[0068] S102. Under a nitrogen atmosphere, the same type of waste graphite anode material is placed in a continuous roller furnace and sintered at 800°C for 6 hours. After cooling to room temperature, recycled graphite anode material B is obtained.

[0069] S201. Add the recycled graphite anode material A, conductive agent and binder to water. The mass ratio of the recycled graphite anode material A, SP, CMC and SBR is 96.5:0.5:1:2. Mix evenly to obtain a viscous slurry A with a solid content of 40%.

[0070] S202. Add the recycled graphite anode material B, conductive agent and binder to water. The mass ratio of the recycled graphite anode material B, SP, CMC and SBR is 97:0.5:1:1.5. Mix evenly to obtain a viscous slurry B with a solid content of 40%.

[0071] S300: A double-layer slit extrusion coating machine is used to simultaneously coat viscous slurry A and viscous slurry B onto the surface of copper foil. From bottom to top, the layers are current collector, viscous slurry A, and viscous slurry B. The surface density of viscous slurry A is 2.5 mg / cm³. 2 The coating surface density of the viscous slurry B is 2.5 mg / cm³. 2 The mass ratio of viscous slurry A to viscous slurry B is 5:5; then it is dried at 100℃, rolled, and cut into round sheets with a diameter of 16mm; under a nitrogen atmosphere, it is heat-treated at 400℃ using Joule heating technology, with a heating rate of 150℃ / s and a holding time of 10s. After cooling to room temperature, the electrode sheet is obtained. A schematic diagram of the electrode sheet structure is shown below. Figure 1As shown.

[0072] It should be noted that this embodiment does not limit the order of S101 and S102, nor does it limit the order of S201 and S202.

[0073] Example 3

[0074] This embodiment provides a method for recycling and reusing waste graphite anode materials, including the following steps:

[0075] S101. Add the waste graphite anode material to water, with a mass ratio of waste graphite anode material to water of 3:7, and wash 5 times (stirring for 10 min) and filter by pressure; add the obtained filter material to an organic solvent (ethanol), with a mass ratio of filter material to organic solvent of 3:7, and wash 3 times and filter by pressure, and dry to obtain recovered graphite anode material A.

[0076] Waste graphite anode material comprises the following components by mass percentage: 96% graphite, 1% conductive agent (SP) and 3% binder (CMC and SBR) (trace elements are not included).

[0077] S102. Under a nitrogen atmosphere, the same type of waste graphite anode material is placed in a continuous roller furnace and sintered at 1000℃ for 5 hours. After cooling to room temperature, recycled graphite anode material B is obtained.

[0078] S201. Add the recycled graphite anode material A, conductive agent and binder to water. The mass ratio of the recycled graphite anode material A, SP, CMC and SBR is 96.5:0.5:1:2. Mix evenly to obtain a viscous slurry A with a solid content of 40%.

[0079] S202. Add the recycled graphite anode material B, conductive agent and binder to water. The mass ratio of the recycled graphite anode material B, SP, CMC and SBR is 97:0.5:1:1.5. Mix evenly to obtain a viscous slurry B with a solid content of 40%.

[0080] S300: A double-layer slit extrusion coating machine is used to simultaneously coat the copper foil surface with viscous slurry A and viscous slurry B. From bottom to top, the layers are current collector, viscous slurry A, and viscous slurry B. The surface density of viscous slurry A is 2.8 mg / cm³. 2 The surface density of the viscous slurry B is 2.8 mg / cm³. 2 The mass ratio of viscous slurry A to viscous slurry B is 5:5; then it is dried at 105℃, rolled, and cut into round sheets with a diameter of 16mm; under a nitrogen atmosphere, it is heat-treated at 500℃ using Joule heating technology, with a heating rate of 180℃ / s and a holding time of 10s. After cooling to room temperature, the electrode sheet is obtained. A schematic diagram of the electrode sheet structure is shown below. Figure 1 As shown.

[0081] It should be noted that this embodiment does not limit the order of S101 and S102, nor does it limit the order of S201 and S202.

[0082] Electron microscopy was performed on the recycled graphite anode material A and recycled graphite anode material B prepared in this embodiment. The results are as follows: Figures 2-3 As shown. From Figure 2 As can be seen, a large number of SP nanoparticles are attached to the surface of the graphite particles, indicating that the liquid-phase washing method does not remove the SP nanoparticles from the graphite anode material. Figure 3 As can be seen, after sintering, some SP nanoparticles still remain on the surface of graphite particles, while some SP nanoparticles are embedded inside the binder. This indicates that sintering does not remove SP nanoparticles from waste graphite anode materials.

[0083] Example 4

[0084] This embodiment provides a method for recycling and reusing waste graphite anode materials, including the following steps:

[0085] S101. Add waste graphite anode material to water, with a mass ratio of waste graphite anode material to water of 4:6, and wash 5 times (stirring for 10 min) and filter by pressure; add the obtained filter material to an organic solvent (acetone), with a mass ratio of filter material to organic solvent of 4:6, and wash 3 times and filter by pressure, and dry to obtain recovered graphite anode material A.

[0086] Waste graphite anode material comprises the following components by mass percentage: graphite 96.5%, conductive agent (SP) 0.8%, and binder (CMC and SBR) 2.7% (trace elements are not included).

[0087] S102. Under a nitrogen atmosphere, the same type of waste graphite anode material is placed in a continuous roller furnace and sintered at 1200°C for 3 hours. After cooling to room temperature, recycled graphite anode material B is obtained.

[0088] S201. Add the recycled graphite anode material A, conductive agent and binder to water. The mass ratio of the recycled graphite anode material A, SP, CMC and SBR is 97:0.6:1:2.2. Mix evenly to obtain a viscous slurry A with a solid content of 45%.

[0089] S202. Add the recycled graphite anode material B, conductive agent and binder to water. The mass ratio of the recycled graphite anode material B, SP, CMC and SBR is 97.5:0.6:1:1.7. Mix evenly to obtain a viscous slurry B with a solid content of 45%.

[0090] S300: A double-layer slit extrusion coating machine is used to simultaneously coat the copper foil surface with viscous slurry A and viscous slurry B. From bottom to top, the layers are current collector, viscous slurry A, and viscous slurry B. The surface density of viscous slurry A is 3 mg / cm³. 2 The coating surface density of the viscous slurry B is 2 mg / cm³. 2 The mass ratio of viscous slurry A to viscous slurry B is 6:4; then it is dried at 120℃, rolled, and cut into circular pieces with a diameter of 16mm; under a nitrogen atmosphere, it is heat-treated at 600℃ using Joule heating technology, with a heating rate of 300℃ / s and a holding time of 9s. After cooling to room temperature, the electrode sheet is obtained. A schematic diagram of the electrode sheet structure is shown below. Figure 1 As shown.

[0091] It should be noted that this embodiment does not limit the order of S101 and S102, nor does it limit the order of S201 and S202.

[0092] Example 5

[0093] This embodiment provides a method for recycling and reusing waste graphite anode materials, including the following steps:

[0094] S101. Add the waste graphite anode material to water, with a mass ratio of waste graphite anode material to water of 3:7, and wash 5 times (stirring for 10 minutes) and filter by pressure; add the obtained filter material to an organic solvent (isopropanol), with a mass ratio of filter material to organic solvent of 3:7, and wash and filter by pressure 3 times, and dry to obtain recovered graphite anode material A.

[0095] Waste graphite anode material comprises the following components by mass percentage: 95.5% graphite, 1.3% conductive agent (SP), and 3.2% binder (CMC and SBR) (trace elements are not included).

[0096] S102. Under a nitrogen atmosphere, the same type of waste graphite anode material is placed in a continuous roller furnace and sintered at 1000°C for 4 hours. After cooling to room temperature, recycled graphite anode material B is obtained.

[0097] S201. Add the recycled graphite anode material A, conductive agent and binder to water. The mass ratio of the recycled graphite anode material A, SP, CMC and SBR is 96.5:0.5:1:2. Mix evenly to obtain a viscous slurry A with a solid content of 40%.

[0098] S202. Add the recycled graphite anode material B, conductive agent and binder to water. The mass ratio of the recycled graphite anode material B, SP, CMC and SBR is 97:0.5:1:1.5. Mix evenly to obtain a viscous slurry B with a solid content of 40%.

[0099] S300: A double-layer slit extrusion coating machine is used to simultaneously coat the copper foil surface with viscous slurry A and viscous slurry B. From bottom to top, the layers are current collector, viscous slurry A, and viscous slurry B. The surface density of viscous slurry A is 1.7 mg / cm³. 2 The coating surface density of the viscous slurry B is 4 mg / cm³. 2 The mass ratio of viscous slurry A to viscous slurry B is 3:7; then it is dried at 110℃, rolled, and cut into round sheets with a diameter of 16mm; under a nitrogen atmosphere, it is heat-treated at 500℃ using Joule heating technology, with a heating rate of 160℃ / s and a holding time of 10s. After cooling to room temperature, the electrode sheet is obtained. A schematic diagram of the electrode sheet structure is shown below. Figure 1 As shown.

[0100] It should be noted that this embodiment does not limit the order of S101 and S102, nor does it limit the order of S201 and S202.

[0101] Comparative Example 1

[0102] This comparative example provides a method for recycling and reusing waste graphite anode materials. The steps are similar to those in Example 3, except that in S300, only a viscous slurry A (with a coating surface density of 5.6 mg / cm³) is coated on the copper foil. 2 The remaining conditions are the same as in Example 3, and will not be repeated here.

[0103] Comparative Example 2

[0104] This comparative example provides a method for recycling and reusing waste graphite anode materials. The steps are similar to those in Example 3, except that in S300, only a viscous slurry B (with a coating surface density of 5.6 mg / cm³) is coated on the copper foil. 2 The remaining conditions are the same as in Example 3, and will not be repeated here.

[0105] Comparative Example 3

[0106] This comparative example provides a method for recycling and reusing waste graphite anode materials. The steps are similar to those in Example 3, except that heat treatment is omitted in step S300. Specifically, it includes the following steps:

[0107] S101~S202 are the same as in Example 3, and will not be described again.

[0108] S300: A double-layer slit extrusion coating machine is used to simultaneously coat the copper foil surface with viscous slurry A and viscous slurry B. From bottom to top, the layers are current collector, viscous slurry A, and viscous slurry B. The surface density of viscous slurry A is 2.8 mg / cm³. 2 The surface density of the viscous slurry B is 2.8 mg / cm³. 2The mass ratio of viscous slurry A to viscous slurry B is 5:5; then it is dried at 105℃, rolled, and cut into round pieces with a diameter of 16mm to obtain electrode sheets.

[0109] Comparative Example 4

[0110] This comparative example provides a method for recycling and reusing waste graphite anode materials. The steps are similar to those in Example 3, except that in S300, when coating the copper foil with viscous slurry B and viscous slurry A, the order from bottom to top is current collector, viscous slurry B, and viscous slurry A. The remaining conditions are the same as in Example 3 and will not be repeated.

[0111] Application examples

[0112] The electrode sheets provided in Examples 1-5 and Comparative Examples 1-4 were respectively made into button batteries, and the specific steps are as follows:

[0113] A 2430 type button cell was assembled using a lithium metal sheet with a diameter of 18 mm and a thickness of 0.5 mm as the counter electrode, a Celgard 2400 with a diameter of 20 mm and a thickness of 20 μm as the separator, a 16 mm negative electrode sheet provided in Examples 1-5 and Comparative Examples 1-4 as the working electrode, and a solution of 1.1 mol / L LiPF6 dissolved in ethylene carbonate and diethyl carbonate (volume ratio 1:1) as the electrolyte.

[0114] Verification test

[0115] Test method for electrode sheet compaction density: Cut the electrode sheets provided in Examples 1-5 and Comparative Examples 1-4 into 10cm × 15cm pieces respectively, and test the density of the electrode sheets in g / cc. Roll the electrode sheets under an initial pressure of 0.5 tons at 25°C. If the electrode sheet is not crushed, increase the pressure by 0.5 tons and continue rolling until the electrode sheet is crushed. Record the compaction density of the electrode sheet before it is crushed. Test each electrode sheet 5 times and take the average value.

[0116] Electrochemical performance tests were conducted on the button cells fabricated for the corresponding use cases. Ten cells were assembled for each type of electrode, and a total of 10 sets of data were tested. After removing the highest and lowest data, the average of the remaining 8 sets of data was taken as the performance data of the cell. The test results are shown in Table 1.

[0117] Specific test conditions for button cell battery performance:

[0118] At room temperature of 25℃, using a Blue Electricity Tester, the assembled button battery was discharged to 0.005V at 0.1C (1C corresponds to 350mAh / g), and the discharge program was ended. After standing for 5 minutes, it was charged to 2V at 0.1C. The cycle was repeated three times, and the average charging specific capacity was taken, which is the 0.1C charging capacity.

[0119] Furthermore, the battery is charged at 3C to 2V, left to stand for 5 minutes, and then discharged at 1C to 0.005V. This process is repeated 5 times, and the average charging capacity is taken as the 3C charging capacity. The ratio of the charging specific capacity after 100 cycles to the charging specific capacity of the first cycle is the 3C charging capacity retention rate.

[0120] Table 1. Performance test results of button batteries prepared using the application example.

[0121]

[0122] As shown in Table 1, the electrode sheet provided by this invention has a higher compaction density, resulting in a higher volumetric energy density of the battery cell, thus enhancing the application value of recycled graphite in lithium-ion batteries. The button battery made from the electrode sheet provided by this invention exhibits excellent electrochemical performance. In the electrode sheet of Comparative Example 4, the upper layer is material A and the lower layer is material B. Compared to the examples, Comparative Example 4 shows reduced fast charging and cycle performance. During the charging process, lithium ions travel from the positive electrode to the negative electrode, first contacting the upper layer material. Therefore, materials with good fast charging performance are located in the upper layer; if the upper layer has poor kinetics, the cycle performance will also deteriorate.

[0123] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for recycling and reusing waste graphite anode materials, characterized in that, Includes the following steps: S100. The waste graphite anode material is washed sequentially with water and organic solvent to obtain recycled graphite anode material A. Under an inert atmosphere, the waste graphite anode material is sintered at 400℃~1200℃ for 2h~8h to obtain recycled graphite anode material B. in, The waste graphite anode material comprises the following components by mass percentage: 95%~97% graphite, 0.5%~1.5% conductive agent, and 2.5%~3.5% binder; The mass ratio of the waste graphite anode material to water is 1:9 to 4:6; the mass ratio of the filter material obtained after washing and filtering the waste graphite anode material in water to the organic solvent is 2:8 to 4:

6. The organic solvent includes at least one of ethanol, acetone, isopropanol, ethyl acetate, or propylene glycol; S200. The recycled graphite anode material A and recycled graphite anode material B are mixed with a conductive agent, a binder and water respectively to obtain viscous slurry A and viscous slurry B. S300. The viscous slurry A and viscous slurry B are coated on the surface of the current collector, with the current collector, viscous slurry A and viscous slurry B arranged from bottom to top; then heat-treated under an inert atmosphere to obtain an electrode sheet. The heat treatment temperature is 250℃~600℃, and the heat treatment time is 8s~12s; the heat treatment adopts Joule heating technology, and the heating rate is 50℃ / s~500℃ / s.

2. The method for recycling and reusing waste graphite anode materials as described in claim 1, characterized in that, In S100 and S200, the conductive agent includes carbon black-based conductive agents, and the binder includes carboxymethyl cellulose and styrene-butadiene rubber.

3. The method for recycling and reusing waste graphite anode materials as described in claim 1, characterized in that, In S100, the preparation method of the recycled graphite anode material A specifically includes the following steps: The waste graphite anode material is added to water and washed 4 to 5 times, then filtered. The resulting filtrate is added to an organic solvent and washed 2 to 3 times, then filtered and dried to obtain the recycled graphite anode material A.

4. The method for recycling and reusing waste graphite anode materials as described in claim 1, characterized in that, In S100, the sintering temperature is 800℃~1200℃.

5. The method for recycling and reusing waste graphite anode materials as described in claim 1, characterized in that, In S200, the mass ratio of recycled graphite anode material A, conductive agent, and binder in the viscous slurry A is (96~97):(0.4~0.6):(2.8~3.2), and the solid content of the viscous slurry A is 35%~45%. In S200, the mass ratio of the recovered graphite anode material B, conductive agent and binder in the viscous slurry B is (96.5~97.5):(0.4~0.6):(2.3~2.7), and the solid content of the viscous slurry B is 35%~45%.

6. The method for recycling and reusing waste graphite anode materials as described in claim 1, characterized in that, In S300, the total coating surface density of the viscous slurry A and viscous slurry B is 5 mg / cm³. 2 ~6mg / cm 2 The mass ratio of the viscous slurry A to the viscous slurry B is 3:7 to 6:

4.

7. An electrode sheet, characterized in that, It is prepared by the recycling and reuse method of waste graphite anode material as described in any one of claims 1 to 6.

Images