Recycling method of waste graphite negative electrode material and prepared electrode plate

Abstract

The invention relates to the technical field of graphite recovery, and particularly discloses a recycling method of a waste graphite negative electrode material and a prepared electrode plate. The method comprises the following steps: washing a waste graphite negative electrode material with water and an organic solvent in sequence to obtain a recycled graphite negative electrode material A; in an inert atmosphere, sintering the waste graphite negative electrode material at 400-1200 DEG C to obtain a recycled graphite negative electrode material B; uniformly mixing the recycled graphite negative electrode material A and the recycled graphite negative electrode material B with a conductive agent, a binder and water respectively to correspondingly obtain viscous slurry A and viscous slurry B; coating the viscous slurry A and the viscous slurry B on the surface of a current collector, wherein the current collector, the viscous slurry A and the viscous slurry B are sequentially arranged from bottom to top; and carrying out heat treatment in an inert atmosphere to obtain the electrode plate. The electrode plate prepared by the method can balance capacity, fast charge, volume energy density and cycle performance at the same time.

Description

Technical Field

[0001] The present invention relates to the technical field of graphite recovery, and in particular to a method for recycling waste graphite negative electrode materials and an electrode sheet prepared therefrom. Background Art

[0002] With the annual increase in installed capacity of lithium-ion batteries, the number of scrapped batteries has also increased significantly. Battery recycling, especially the recycling of graphite anode materials, which are energy-intensive and have high carbon emissions, holds enormous potential. Recycling graphite anode materials offers significant advantages in many ways. First, recycled graphite is abundant and relatively cost-effective, making it more competitively priced than other anode materials. Second, recycling graphite anode materials can effectively reduce environmental pollution from used batteries, minimize resource waste, and offer significant environmental benefits. Furthermore, after proper processing, recycled graphite can be reused in battery manufacturing, achieving resource recycling and reducing reliance on new graphite resources.

[0003] Although recycling graphite has many advantages, it currently faces many challenges in engineering. First, the source and composition of recycled graphite negative electrode materials are complex, the graphite negative electrodes of different batteries vary greatly, there are many impurities, and it is difficult to treat them uniformly. Secondly, the recycling process is complicated and inefficient. Most existing methods can only achieve a single goal, and there are problems such as graphite loss, high energy consumption, and environmental pollution. Thirdly, the comprehensive performance of recycled graphite is poor, and the cycle stability is poor, which is difficult to meet battery-level application requirements. In addition, there is currently a lack of unified recycling standards and specifications, resulting in uneven product quality and non-standard recycling processes, which affects the efficient recovery and reuse of graphite negative electrode materials. Therefore, there is an urgent need in this field to develop a method for recycling graphite negative electrode materials, while further improving the recycling efficiency, improving the quality of recycled products, and promoting its sustainable development in the field of new energy. Summary of the Invention

[0004] In response to the above problems, the present invention provides a method for recycling and reusing waste graphite negative electrode materials and the resulting electrode sheet. The same type of waste graphite negative electrode material is recycled through two different treatment processes and then used as the upper and lower layers of the electrode, respectively. This can ensure that the source of graphite raw materials in the same electrode sheet is controllable, and the unique double-layer structure of the electrode sheet can simultaneously balance capacity, fast charging, volume energy density and cycle performance, thereby greatly improving the electrochemical performance of the battery.

[0005] In order to solve the above technical problems, the technical solution provided by the present invention is: In a first aspect, the present invention provides a method for recycling and reusing waste graphite negative electrode materials, comprising the following steps: S100, washing the waste graphite negative electrode material with water and an organic solvent in sequence to obtain a recovered graphite negative electrode material A; Under an inert atmosphere, sintering the waste graphite negative electrode material at 400° C. to 1200° C. to obtain a recovered graphite negative electrode material B; S200, mixing the recycled graphite negative electrode material A and the recycled graphite negative electrode material B with a conductive agent, a binder, and water, respectively, to obtain viscous slurry A and viscous slurry B; S300, coating the viscous slurry A and the viscous slurry B on the surface of the current collector, which is the current collector, the viscous slurry A and the viscous slurry B from bottom to top; and then performing heat treatment under an inert atmosphere to obtain an electrode sheet.

[0006] Compared to the prior art, the present invention provides a method for recycling and reusing waste graphite anode materials. The same waste graphite anode material is recycled through two different treatment processes and then used as a double-layer structure on the current collector surface. This effectively ensures that the source of graphite material in the same electrode sheet is controllable, thereby ensuring that the electrochemical performance of the same electrode sheet remains at the same level. It should be noted that when recycling graphite, the same type of graphite anode material is used in the same battery model. The waste graphite anode material is differentiated by battery cell batch, and the same batch refers to the same type of waste graphite anode material.

[0007] The present invention prepares recycled graphite negative electrode material A through a liquid-phase washing method, removing the binder from the waste graphite negative electrode material while retaining the graphite and conductive agent in the waste graphite negative electrode material, wherein the conductive agent can still improve the material's conductivity. The present invention uses a high-temperature sintering method to prepare recycled graphite negative electrode material B. The components of the waste graphite negative electrode material are sintered together, converting the conductive agent and binder into carbon residue on the graphite surface. This increases the carbon coating of the recycled graphite negative electrode material, thereby improving the material's conductivity and fast-charging performance.

[0008] The present invention prepares recycled graphite negative electrode material A and recycled graphite negative electrode material B into viscous slurries A and B, respectively. These are then sequentially applied to the surface of a current collector, with the current collector serving as a substrate. This creates a structure with an upper layer of material B (i.e., upper layer material B formed from viscous slurry B) and a lower layer of material A (i.e., lower layer material A formed from viscous slurry A). Given the properties of the recycled graphite negative electrode material B and recycled graphite negative electrode material A in the upper and lower layers, this dual-layer structure effectively improves the properties of the electrode sheet, significantly increasing the battery's volumetric energy density without sacrificing fast-charging performance. It also balances capacity and improves cycling performance.

[0009] Preferably, in S100, the waste graphite negative electrode material comes from a power battery or an energy storage battery.

[0010] Preferably, in S100, the waste graphite negative electrode material includes the following components in percentage by mass: 95% to 97% graphite, 0.5% to 1.5% conductive agent, and 2.5% to 3.5% binder.

[0011] The waste graphite negative electrode material of the present invention also contains some trace elements, the content of which is at PPM level.

[0012] Further preferably, in S100 and S200, the conductive agent includes a carbon black conductive agent, and the binder includes carboxymethyl cellulose and styrene-butadiene rubber.

[0013] For example, in S100 and S300, the carbon black conductive agent includes SP (Super-P).

[0014] This invention primarily recycles power batteries and energy storage batteries, whose graphite anode materials primarily contain SP as the conductive agent and carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) as the binder. Other types of conductive agents and binders are not mainstream products and are not currently considered in this invention. Furthermore, this invention does not impose a limit on the mass ratio of CMC to SBR in the binder used in S100 and is applicable to binders containing any ratio of CMC to SBR.

[0015] Preferably, in S100, the preparation method for recycling graphite negative electrode material A specifically comprises the following steps: The waste graphite negative electrode material is added to water, washed 4 to 5 times, and filtered; the obtained filtrate is added to an organic solvent, washed 2 to 3 times, filtered, and dried to obtain the recycled graphite negative electrode material A.

[0016] Further preferably, in S100, the mass ratio of the waste graphite negative electrode material to water is 1:9 to 4:6.

[0017] Further preferably, in S100, the mass ratio of the filtrate to the organic solvent is 2:8 to 4:6.

[0018] Further preferably, in S100, the organic solvent includes at least one of ethanol, acetone, isopropanol, ethyl acetate or propylene glycol.

[0019] Using organic solvents for washing can reduce the sticking of materials during the subsequent drying process.

[0020] Illustratively, in S100 and S300 , the inert atmosphere includes a nitrogen atmosphere.

[0021] Preferably, in S100, the sintering temperature is 800° C. to 1200° C., and the sintering time is 2 h to 8 h.

[0022] Preferably, in S200, the mass ratio of the recovered graphite negative electrode material A, the conductive agent and the binder in the viscous slurry A is (96~97):(0.4~0.6):(2.8~3.2).

[0023] Preferably, in S200, the binder in the viscous slurry A includes carboxymethyl cellulose and styrene-butadiene rubber in a mass ratio of 1: (1.3-1.7).

[0024] Preferably, in S200, the solid content of the viscous slurry A is 35% to 45%.

[0025] Preferably, in S200, the mass ratio of the graphite negative electrode material B, the conductive agent and the binder recovered in the viscous slurry B is (96.5~97.5):(0.4~0.6):(2.3~2.7).

[0026] Preferably, in S200, the binder in the viscous slurry B includes carboxymethyl cellulose and styrene-butadiene rubber in a mass ratio of 1:(1.8-2.2).

[0027] Preferably, in S200, the solid content of the viscous slurry B is 35% to 45%.

[0028] Preferably, in S300, the current collector includes copper foil.

[0029] Preferably, in S300, the mass ratio of the viscous slurry A to the viscous slurry B is 3:7 to 6:4.

[0030] Preferably, in S300, the total coating surface density of the viscous slurry A and the viscous slurry B is 5 mg / cm 2 ~6mg / cm 2 .

[0031] Further preferably, in S300, the coating surface density of the viscous slurry A is 1.5 mg / cm 2 ~3.6mg / cm 2 The coating surface density of the viscous slurry B is 2 mg / cm 2 ~4mg / cm 2 .

[0032] The present invention can use a double-layer slit extrusion coater to simultaneously apply viscous slurry A and viscous slurry B to the surface of the copper foil, which is more conducive to mass production; or the viscous slurry A can be applied to the surface of the copper foil first, and then the viscous slurry B is applied after drying.

[0033] Preferably, in S300 , after the coating is completed and before the heat treatment, the process further includes: drying, rolling, and cutting.

[0034] More preferably, in S300, the drying temperature is 90°C to 120°C.

[0035] For example, in S300 , the wafer may be cut into discs with a diameter of 16 mm.

[0036] Preferably, in S300, the heat treatment temperature is 250° C. to 600° C., and the heat treatment time is 8 s to 12 s.

[0037] Preferably, in S300, the heat treatment adopts Joule heating technology, and the heating rate is 50°C / s to 500°C / s (more preferably 100°C / s to 300°C / s).

[0038] The present invention uses heat treatment to enhance the integrated properties of the electrode sheet, improving the adhesion between the upper and lower layers, as well as the binder and graphite particles. Using Joule heating technology, the resulting electrode sheet is subjected to a short-term heat treatment to rearrange the active material, conductive agent, and binder, reducing the organic content in the electrode sheet and achieving a slight carbonization of the electrode sheet. This results in improved electrochemical performance, particularly in terms of initial coulombic efficiency, cycle stability, and rate capability.

[0039] In a second aspect, the present invention provides an electrode sheet, which is produced by the above-mentioned method for recycling and reusing waste graphite negative electrode materials.

[0040] The present invention has the following beneficial effects: (1) Improve the properties of the electrode. 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 amount of residual carbon in the recycled graphite negative electrode material B is greater than that in the recycled graphite negative electrode material A. It is not easy to bond in the subsequent preparation process of the electrode sheet (the slurry coating process) and requires more binder, otherwise floating powder or material falling will occur. However, if the binder content is too high, the conductivity of the electrode sheet will be reduced, the fast charging performance of the battery will be reduced, and the proportion of active material (recycled graphite negative electrode material B) will be reduced, which will reduce the energy density of the electrode. The recycled graphite negative electrode material A is prepared by a liquid phase washing method, which removes the binder in the waste graphite negative electrode material. The residual carbon content is low, and the amount of binder used in the subsequent preparation process of the electrode sheet can be reduced. The present invention 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 binder used, improve the floating of the binder during the coating and drying process, and increase the residual amount of binder in the upper layer material B, thereby improving the overall performance of the electrode sheet.

[0041] (2) Balancing capacity, fast charging, and volume energy density. The recycled graphite negative electrode material A has a low carbon residue, poor fast charging performance, and a low compaction density (about 1.59cc / g), but a high capacity (about 346mAh / g). The recycled graphite negative electrode material B has a high carbon residue, good fast charging performance, a capacity of about 352mAh / g, a high compaction density (about 1.65cc / g), and a higher volume energy density. Using either viscous slurry A or viscous slurry B alone cannot simultaneously meet the balance between high volume energy density and fast charging. The present invention adopts a double-layer structure with material B as the upper layer and material A as the lower layer. Since the fast charging capability is mainly provided by the upper layer material B, the overall compaction density can be significantly improved without sacrificing fast charging performance, thereby improving the volume energy density of the battery and meeting the capacity balance.

[0042] (3) Improved cycle performance. The attenuation of the negative electrode cycle performance of lithium batteries is mainly due to the consumption of active lithium, which mainly occurs in the formation of the SEI film in the first cycle and in the subsequent cycles. The continuously generated new SEI film will continue to consume active lithium. Recycling the residual fluorine, oxygen, lithium, sulfur and other elements in the graphite helps to form a more stable and thinner SEI film, thereby reducing the consumption of active lithium and improving the cycle performance. The present invention adopts a double-layer structure with the upper layer being material B and the lower layer being material A. The upper layer material B can meet the rapid lithium insertion of the negative electrode material in most of the fast charging early and middle stages, reducing the current when the battery is almost fully charged, and the lower layer material A provides the main lithium insertion capacity. Compared with the single-layer structure, it can better balance the capacity, fast charging, volume energy density and cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 Schematic diagram of the structure of the electrode sheet in Examples 1 to 5 of the present invention; in the figure, 1 represents copper foil, 2 represents lower layer material A formed by viscous slurry A, and 3 represents upper layer material B formed by viscous slurry B; Figure 2 This is a SEM image of the recycled graphite negative electrode material A in Example 3 of the present invention; Figure 3 This is an SEM image of the recycled graphite negative electrode material B in Example 3 of the present invention. DETAILED DESCRIPTION

[0044] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0045] In the present invention, materials not otherwise specified are all commercially available products. The waste graphite negative electrode material in the examples is derived from power batteries or energy storage batteries; the double-layer slot extrusion coating machine is purchased from Shenzhen Yinghe Technology Co., Ltd., model number Super-E.

[0046] Example 1 This embodiment provides a method for recycling and reusing waste graphite negative electrode materials, comprising the following steps: S101. Add the waste graphite negative electrode material to water at a mass ratio of 1:9, wash it four times (stirring for 10 minutes) and filter press it; add the obtained filtrate to an organic solvent (propylene glycol) at a mass ratio of 2:8, wash it twice and filter press it, and dry it to obtain recovered graphite negative electrode material A.

[0047] The waste graphite negative electrode material includes the following components in percentage by mass: graphite 95%, conductive agent (SP) 1.5% and binder (CMC and SBR) 3.5% (trace elements are not included).

[0048] S102. Under a nitrogen atmosphere, the same waste graphite negative electrode material is placed in a continuous roller furnace, sintered at 600° C. for 8 hours, and then cooled to room temperature to obtain a recovered graphite negative electrode material B.

[0049] S201. Add the recycled graphite negative electrode material A, the conductive agent and the binder into water, wherein the mass ratio of the recycled graphite negative electrode material A, SP, CMC and SBR is 96:0.4:1:1.8, and mix them evenly to obtain a viscous slurry A with a solid content of 35%.

[0050] S202. Add the recycled graphite negative electrode material B, the conductive agent and the binder into water, wherein the mass ratio of the recycled graphite negative electrode material B, SP, CMC and SBR is 96.5:0.4:1:1.3, and mix them evenly to obtain a viscous slurry B with a solid content of 35%.

[0051] S300: Use a double-layer slot extrusion coater to simultaneously coat viscous slurry A and viscous slurry B on the surface of the copper foil. From bottom to top, the order is current collector, viscous slurry A, and viscous slurry B. The coating surface density of viscous slurry A is 3 mg / cm 2 The coating surface density of the viscous slurry B is 3 mg / cm 2 The mass ratio of viscous slurry A to viscous slurry B is 5:5; then dried at 90℃, rolled, and cut into discs with a diameter of 16mm; in a nitrogen atmosphere, 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. The structural diagram of the electrode sheet is shown in the figure. Figure 1 shown.

[0052] 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 .

[0053] Example 2 This embodiment provides a method for recycling and reusing waste graphite negative electrode materials, comprising the following steps: S101. Add the waste graphite negative electrode material to water at a mass ratio of 2:8, wash it four times (stirring for 10 minutes) and filter press it; add the obtained filtrate to an organic solvent (ethyl acetate) at a mass ratio of 3:7, wash it three times and filter press it, and dry it to obtain recovered graphite negative electrode material A.

[0054] The waste graphite negative electrode material includes the following components in percentage by mass: graphite 97%, conductive agent (SP) 0.5% and binder (CMC and SBR) 2.5% (trace elements are not included).

[0055] S102. Under a nitrogen atmosphere, the same waste graphite negative electrode material is placed in a continuous roller furnace, sintered at 800° C. for 6 hours, and then cooled to room temperature to obtain a recovered graphite negative electrode material B.

[0056] S201. Add the recycled graphite negative electrode material A, the conductive agent and the binder into water, wherein the mass ratio of the recycled graphite negative electrode material A, SP, CMC and SBR is 96.5:0.5:1:2, and mix them evenly to obtain a viscous slurry A with a solid content of 40%.

[0057] S202. Add the recycled graphite negative electrode material B, the conductive agent and the binder into water, wherein the mass ratio of the recycled graphite negative electrode material B, SP, CMC and SBR is 97:0.5:1:1.5, and mix them evenly to obtain a viscous slurry B with a solid content of 40%.

[0058] S300: Use a double-layer slot extrusion coater to simultaneously coat viscous slurry A and viscous slurry B on the surface of the copper foil. From bottom to top, the order is current collector, viscous slurry A, and viscous slurry B. The coating surface density of viscous slurry A is 2.5 mg / cm 2 The coating surface density of the viscous slurry B is 2.5 mg / cm 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 discs with a diameter of 16mm; in 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. The structural diagram of the electrode sheet is shown in the figure. Figure 1 shown.

[0059] 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 .

[0060] Example 3 This embodiment provides a method for recycling and reusing waste graphite negative electrode materials, comprising the following steps: S101. Add the waste graphite negative electrode material to water at a mass ratio of 3:7, wash it five times (stirring for 10 minutes), and filter press it. Add the obtained filtrate to an organic solvent (ethanol) at a mass ratio of 3:7, wash it three times, filter press it, and dry it to obtain recovered graphite negative electrode material A.

[0061] The waste graphite negative electrode material includes the following components in percentage by mass: graphite 96%, conductive agent (SP) 1% and binder (CMC and SBR) 3% (trace elements are not included).

[0062] S102. Under a nitrogen atmosphere, the same waste graphite negative electrode material is placed in a continuous roller furnace, sintered at 1000° C. for 5 hours, and then cooled to room temperature to obtain a recovered graphite negative electrode material B.

[0063] S201. Add the recycled graphite negative electrode material A, the conductive agent and the binder into water, wherein the mass ratio of the recycled graphite negative electrode material A, SP, CMC and SBR is 96.5:0.5:1:2, and mix them evenly to obtain a viscous slurry A with a solid content of 40%.

[0064] S202. Add the recycled graphite negative electrode material B, the conductive agent and the binder into water, wherein the mass ratio of the recycled graphite negative electrode material B, SP, CMC and SBR is 97:0.5:1:1.5, and mix them evenly to obtain a viscous slurry B with a solid content of 40%.

[0065] S300: Use a double-layer slot extrusion coater to simultaneously coat viscous slurry A and viscous slurry B on the surface of the copper foil. From bottom to top, the order is current collector, viscous slurry A, and viscous slurry B. The coating surface density of viscous slurry A is 2.8 mg / cm 2 The coating surface density of the viscous slurry B is 2.8 mg / cm 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 discs with a diameter of 16mm; in 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. The structural diagram of the electrode sheet is shown in the figure. Figure 1 shown.

[0066] 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 .

[0067] The recovered graphite negative electrode material A and the recovered graphite negative electrode material B prepared in this embodiment were scanned by electron microscope, and the results were as follows: Figure 2~Figure 3 As shown. Figure 2 It can be seen that a large number of SP nanoparticles are attached to the surface of graphite particles, which shows that the liquid phase washing method will not remove the SP nanoparticles in the graphite negative electrode material. Figure 3 It can be seen from the figure that after sintering, some SP nanoparticles still exist on the surface of graphite particles, and some SP nanoparticles are embedded in the binder, which shows that sintering will not remove the SP nanoparticles in the waste graphite negative electrode material.

[0068] Example 4 This embodiment provides a method for recycling and reusing waste graphite negative electrode materials, comprising the following steps: S101. Add waste graphite negative electrode material to water at a mass ratio of 4:6, wash the waste graphite negative electrode material five times (stirring for 10 minutes) and filter press; add the obtained filtrate to an organic solvent (acetone) at a mass ratio of 4:6, wash the filtrate three times and filter press, and dry to obtain recovered graphite negative electrode material A.

[0069] The waste graphite negative electrode material includes the following components in percentage by mass: graphite 96.5%, conductive agent (SP) 0.8% and binder (CMC and SBR) 2.7% (trace elements are not included).

[0070] S102. Under a nitrogen atmosphere, the same waste graphite negative electrode material is placed in a continuous roller furnace, sintered at 1200° C. for 3 hours, and then cooled to room temperature to obtain a recovered graphite negative electrode material B.

[0071] S201. Add the recycled graphite negative electrode material A, the conductive agent and the binder into water, wherein the mass ratio of the recycled graphite negative electrode material A, SP, CMC and SBR is 97:0.6:1:2.2, and mix them evenly to obtain a viscous slurry A with a solid content of 45%.

[0072] S202. Add the recycled graphite negative electrode material B, the conductive agent and the binder into water, wherein the mass ratio of the recycled graphite negative electrode material B, SP, CMC and SBR is 97.5:0.6:1:1.7, and mix them evenly to obtain a viscous slurry B with a solid content of 45%.

[0073] S300: Use a double-layer slot extrusion coater to simultaneously coat viscous slurry A and viscous slurry B on the surface of the copper foil. From bottom to top, the order is current collector, viscous slurry A, and viscous slurry B. The coating surface density of viscous slurry A is 3 mg / cm 2 The coating surface density of the viscous slurry B is 2 mg / cm 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 discs with a diameter of 16mm; in 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. The structural diagram of the electrode sheet is shown in the figure. Figure 1 shown.

[0074] 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 .

[0075] Example 5 This embodiment provides a method for recycling and reusing waste graphite negative electrode materials, comprising the following steps: S101. Add waste graphite negative electrode material to water at a mass ratio of 3:7, wash the waste graphite negative electrode material five times (stirring for 10 minutes) and filter press; add the obtained filtrate to an organic solvent (isopropyl alcohol) at a mass ratio of 3:7, wash the filtrate three times and filter press, and dry to obtain recovered graphite negative electrode material A.

[0076] The waste graphite negative electrode material includes the following components in percentage by mass: graphite 95.5%, conductive agent (SP) 1.3% and binder (CMC and SBR) 3.2% (trace elements are not included).

[0077] S102. Under a nitrogen atmosphere, the same waste graphite negative electrode material is placed in a continuous roller furnace, sintered at 1000° C. for 4 hours, and then cooled to room temperature to obtain a recovered graphite negative electrode material B.

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

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

[0080] S300: Use a double-layer slot extrusion coater to simultaneously coat viscous slurry A and viscous slurry B on the surface of the copper foil. From bottom to top, the order is current collector, viscous slurry A, and viscous slurry B. The coating surface density of viscous slurry A is 1.7 mg / cm 2 The coating surface density of the viscous slurry B is 4 mg / cm 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 discs with a diameter of 16mm; in 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. The structural diagram of the electrode sheet is shown in the figure. Figure 1 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] Comparative Example 1 This comparative example provides a method for recycling and reusing waste graphite negative electrode materials. The steps are similar to those in Example 3, except that in S300, only viscous slurry A (coating surface density of 5.6 mg / cm2) is coated on the copper foil. 2 ). The remaining conditions are the same as those in Example 3 and will not be repeated here.

[0083] Comparative Example 2 This comparative example provides a method for recycling and reusing waste graphite negative electrode materials. The steps are similar to those in Example 3, except that in S300, only viscous slurry B (with a coating surface density of 5.6 mg / cm2) is coated on the copper foil. 2 ). The remaining conditions are the same as those in Example 3 and will not be repeated here.

[0084] Comparative Example 3 This comparative example provides a method for recycling and reusing waste graphite negative electrode materials. The steps are similar to those in Example 3, except that the heat treatment is omitted in S300. Specifically, the method includes the following steps: S101 to S202 are the same as those in Example 3 and will not be described in detail.

[0085] S300: Use a double-layer slot extrusion coater to simultaneously coat viscous slurry A and viscous slurry B on the surface of the copper foil. From bottom to top, the order is current collector, viscous slurry A, and viscous slurry B. The coating surface density of viscous slurry A is 2.8 mg / cm 2 The coating surface density of the viscous slurry B is 2.8 mg / cm 2 The mass ratio of viscous slurry A to viscous slurry B is 5:5; then the mixture is dried at 105°C, rolled, and cut into discs with a diameter of 16 mm to obtain electrode sheets.

[0086] Comparative Example 4 This comparative example provides a method for recycling and reusing waste graphite negative electrode materials. The steps are similar to those in Example 3, except that, in S300, when viscous slurry B and viscous slurry A are coated on the copper foil, the current collector, viscous slurry B, and viscous slurry A are coated on the copper foil from bottom to top. The remaining conditions are the same as those in Example 3 and are not further described.

[0087] Application Examples The electrode sheets provided in Examples 1 to 5 and Comparative Examples 1 to 4 were respectively made into button batteries, and the specific steps were as follows: 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, the 16 mm negative electrode sheets provided in Examples 1 to 5 and Comparative Examples 1 to 4 as the working electrodes, and a solution of 1.1 mol / L LiPF6 dissolved in ethylene carbonate and diethyl carbonate (volume ratio of 1:1) as the electrolyte.

[0088] Verification test Electrode sheet compaction density testing method: Cut the electrode sheets provided in Examples 1-5 and Comparative Examples 1-4 into 10 cm x 15 cm pieces and measure the density of the electrode sheets in g / cc. Roll the electrode sheets at 25°C with an initial pressure of 0.5 tons. If the electrode sheet is not crushed, increase the pressure by 0.5 tons and continue rolling until it is crushed. Record the compaction density of the electrode sheet before crushing. Test each electrode sheet five times and take the average value.

[0089] Electrochemical performance tests were conducted on button cells produced for the corresponding use cases. Ten cells were assembled from each electrode sheet, resulting in 10 sets of data. After removing the highest and lowest values, the average of the remaining eight sets was used as the battery performance data. The test results are shown in Table 1.

[0090] Specific test conditions for button battery performance: At room temperature of 25°C, use a blue battery tester to discharge the assembled button battery at 0.1C (1C corresponds to 350mAh / g) to 0.005V and then end the discharge procedure. After standing for 5 minutes, charge it at 0.1C to 2V. Repeat three cycles and take the average value of the charge capacity, i.e., the 0.1C charge capacity.

[0091] The battery was then charged to 2V at 3C, left to rest for 5 minutes, and then discharged to 0.005V at 1C. This cycle was repeated five times, and the average charge capacity was calculated as the 3C charge capacity. The ratio of the charge capacity after 100 cycles to the first charge capacity is the 3C charge capacity retention rate.

[0092] Table 1 Performance test results of button batteries prepared in application examples

[0093] As can be seen from Table 1, the electrode sheet provided by the present invention has a high compaction density, and the corresponding battery cell volume energy density will be higher, thereby improving the application value of recycled graphite in lithium-ion batteries; the button battery made from the electrode sheet provided by the present invention has excellent electrochemical properties. In the electrode sheet of Comparative Example 4, the upper layer is material A and the lower layer is material B. Compared with the embodiment, the fast charging and cycle performance of Comparative Example 4 are reduced. During the charging process, lithium ions run from the positive electrode to the negative electrode and first contact the upper layer material, so the fast charging performance should be good in the upper layer; if the upper layer dynamics is not good, the cycle performance will also deteriorate.

[0094] 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 in the scope of protection of the present invention.

Claims

1. A method for recycling and reusing waste graphite negative electrode materials, characterized in that: The following steps are involved: S100, washing the waste graphite negative electrode material with water and an organic solvent in sequence to obtain a recovered graphite negative electrode material A; Under an inert atmosphere, sintering the waste graphite negative electrode material at 400° C. to 1200° C. to obtain a recovered graphite negative electrode material B; S200, mixing the recycled graphite negative electrode material A and the recycled graphite negative electrode material B with a conductive agent, a binder, and water, respectively, to obtain viscous slurry A and viscous slurry B; S300, coating the viscous slurry A and the viscous slurry B on the surface of the current collector, which is the current collector, the viscous slurry A and the viscous slurry B from bottom to top; and then performing heat treatment under an inert atmosphere to obtain an electrode sheet.

2. The method for recycling waste graphite negative electrode materials according to claim 1, wherein: In S100, the waste graphite negative electrode material includes the following components in percentage by mass: 95% to 97% graphite, 0.5% to 1.5% conductive agent, and 2.5% to 3.5% binder.

3. The method for recycling waste graphite negative electrode materials according to claim 2, wherein: In S100 and S200, the conductive agent includes a carbon black conductive agent, and the binder includes carboxymethyl cellulose and styrene-butadiene rubber.

4. The method for recycling waste graphite negative electrode materials according to claim 1, wherein: In S100, the preparation method for recycling graphite negative electrode material A specifically includes the following steps: The waste graphite negative electrode material is added to water, washed 4 to 5 times, and filtered; the obtained filtrate is added to an organic solvent, washed 2 to 3 times, filtered, and dried to obtain the recycled graphite negative electrode material A.

5. The method for recycling waste graphite negative electrode materials according to claim 4, wherein: In S100, the mass ratio of the waste graphite negative electrode material to water is 1:9 to 4:6; In S100, the mass ratio of the filtrate to the organic solvent is 2:8 to 4:6; In S100, the organic solvent includes at least one of ethanol, acetone, isopropyl alcohol, ethyl acetate or propylene glycol.

6. The method for recycling waste graphite negative electrode materials according to claim 1, wherein: In S100, the sintering temperature is 800° C. to 1200° C., and the sintering time is 2 h to 8 h.

7. The method for recycling waste graphite negative electrode materials according to claim 1, wherein: In S200, the mass ratio of the recovered graphite negative electrode material A, the conductive agent, and the 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 negative electrode 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), and the solid content of the viscous slurry B is 35%~45%.

8. The method for recycling waste graphite negative electrode materials according to claim 1, wherein: In S300, the total coating surface density of the viscous slurry A and the viscous slurry B is 5 mg / cm 2 ~6mg / cm 2 The mass ratio of the viscous slurry A to the viscous slurry B is 3:7~6:

4.

9. The method for recycling waste graphite negative electrode materials according to claim 1, wherein: In S300 , the heat treatment temperature is 250° C. to 600° C., and the heat treatment time is 8 s to 12 s. The heat treatment adopts Joule heating technology, and the heating rate is 50° C. / s to 500° C. / s.

10. An electrode sheet, characterized in that: The invention is prepared by the method for recycling and reusing waste graphite negative electrode materials according to any one of claims 1 to 9.

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