Recycling methods for negative electrode graphite in spent lithium batteries and the application of recycled graphite.
By forming CSP bonds and Li3P-based SEI layers in spent lithium batteries, the problem of graphite impurity removal was solved, the performance and environmental friendliness of lithium battery anode materials were improved, and efficient recycling of graphite was achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- HEFEI UNIV OF TECH
- Filing Date
- 2026-03-05
- Publication Date
- 2026-05-26
Smart Images
Figure CN122079147A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of lithium battery recycling technology, specifically a method for reusing negative electrode graphite in waste lithium batteries and the application of recycled graphite. Background Technology
[0002] Lithium-ion batteries (LIBs) are widely used in electronic products, electric vehicles, and various energy storage devices due to their high energy density, low self-discharge rate, and lack of memory effect. As the lifespan of electric vehicle batteries gradually reaches its end (5 to 8 years), the number of spent power batteries is increasing. However, because the positive electrode contains a large number of metal elements, the focus is mainly on the recycling of the positive electrode, while less attention is paid to the recycling of graphite, which has lower added value. Graphite has many advantages, including a unique layered structure, high specific capacity, good conductivity, stable chemical properties, abundant resources, and mature processing methods. Although its structure is damaged and its electrical performance degrades due to the repeated insertion and extraction of lithium ions from the SEI film during battery operation, SG still has significant reuse value.
[0003] Existing recycling methods include physical dismantling, pyrometallurgy, hydrometallurgy, and extraction to recover graphite from used batteries, but they all have some drawbacks, such as: Direct physical recycling: contains many impurities, and the purity is difficult to meet the requirements of commercial graphite anode materials; Heat treatment: High energy consumption; excessively high temperatures burn off the graphite, releasing large amounts of greenhouse gases. Hydrometallurgy: Waste acid / alkali leachates pollute the environment and endanger human health; Electrochemical recovery and extraction methods: Extraction reduces the crystallinity of graphite, which is detrimental to performance, and the mass fraction recovered by electrochemical methods is relatively low.
[0004] Therefore, there is an urgent need to design an environmentally friendly, green production method that is simple in process, lower in cost, and has good recyclability of graphite anodes. Summary of the Invention
[0005] In view of the above problems, the present invention is proposed to provide solutions that overcome or at least partially solve the above problems.
[0006] According to one aspect of the present invention, a method for reusing negative electrode graphite from spent lithium-ion batteries, as well as the recycled graphite and its applications, are provided. The recycled graphite obtained by the method has a P-coating layer with S as an intermediate bridge formed on its surface. During cycling, this coating layer forms an in-situ Li3P-based SEI layer with high ionic conductivity, while simultaneously generating FeS and Li3PO4 nanoparticles to form a conductive network. This not only restores the electrical properties of spent graphite but also further improves its initial coulombic efficiency, cycling stability under high current, and rate performance, thereby realizing the reuse of graphite as a negative electrode material for lithium-ion batteries.
[0007] In a first aspect, the present invention proposes a method for reusing negative electrode graphite in waste lithium batteries, comprising the following steps: S1. Graphite in waste lithium battery negative electrode material is stripped from the current collector to obtain waste graphite (SG). S2. The waste graphite (SG), sublimed sulfur (S) and red phosphorus (P) are mixed and ground in a certain proportion to obtain a mixed powder.
[0008] S3. The mixed powder is placed in an inert gas atmosphere and burned in a fast-burning device for a period of time, and then cooled to obtain recycled graphite.
[0009] This invention essentially proposes a new "one-step" strategy for recycling and modifying graphite from waste lithium-ion battery anodes. Specifically, waste graphite is obtained from waste anode materials through a cleaning solution (DMC). Then, the waste graphite is mixed with sublimed sulfur and red phosphorus in a certain proportion, ground evenly, and then rapidly sintered in an ultra-fast high-temperature sintering equipment to obtain CSP-bonded recycled graphite (RG).
[0010] In this invention, the cleaning and stripping of waste graphite can remove the current collector and partially remove residual metal ions (such as Fe, Al, Cu, Li, etc.), reducing the impact of metal elements on recycled graphite (RG). After the waste graphite is mixed and ground with sublimed sulfur and red phosphorus, it is subjected to ultra-fast high-temperature sintering. Since S decomposes into S2-S4 molecules at the melting point, S acts as an intermediate bridge, promoting the vaporization of P into P4 molecules and their deposition. The resulting CSP bonds can generate a continuous crystal line Li3P-based SEI layer (Li3P has high ionic conductivity) in situ during battery cycling, which helps to effectively desolvate Li+ and migrate Li+ across the SEI layer. Finally, this invention yields a graphite anode that combines high initial coulombic efficiency and high current charge-discharge capability. Its reuse in lithium batteries can effectively improve the cycle stability and rate performance of the battery.
[0011] Preferably, in step S1, the stripping of waste graphite is achieved by soaking the waste negative electrode in a dimethyl carbonate (DMC) solution and then drying it. Preferably, the solid-liquid ratio of the waste negative electrode material to DMC is 1:50; Preferably, the ultrasonic dispersion power is 500-1000 W; Preferably, the soaking temperature is 20-30 ℃ and the soaking time is 0.5-1 h; Preferably, step S1 further includes soaking the waste graphite a second time; Preferably, the secondary soaking is achieved by soaking the waste graphite in alcohol.
[0012] Preferably, the alcohol is anhydrous ethanol; Preferably, the soaking temperature is 20-40 ℃ and the soaking time is 0.5-2 h.
[0013] Preferably, the re-drying temperature is 50-100 ℃ and the time is 16-24 h.
[0014] Preferably, in step S2, the mass ratio of the waste graphite to red phosphorus and sublimated sulfur is 1:0.05-0.06:0.0005-0.01; Preferably, the grinding is carried out in a mortar for 1 hour, or it can be carried out by mixing and grinding in a ball mill for 0.5 hours; Preferably, the mass ratio of the waste graphite to red phosphorus and elemental sulfur is 1:0.05-0.06:0.0005-0.01; In this invention, the waste graphite surface has a certain amount of defects. These defects promote the deposition of S2 molecules on the waste graphite surface to form CS bonds, which can activate the basic unit P4 molecules of red phosphorus, further promoting the deposition of red phosphorus on the graphite surface, thus making it more conducive to obtaining CSP-bonded recycled graphite (RG).
[0015] Preferably, in step S3, the fast-firing equipment is an ultra-fast high-temperature sintering equipment (Joule heating device, UHS), wherein the inert gas atmosphere is nitrogen, vacuum environment, argon atmosphere, etc.
[0016] Preferably, in step S3, the calcination of the uniformly mixed powder includes: first passing a current of 500A through the mixed powder to heat it to 1200 ℃ for a short time and then calcining it for a period of time, followed by natural cooling to room temperature.
[0017] Secondly, the present invention also proposes a recycled graphite obtained by the above-described reuse method.
[0018] Thirdly, the present invention also proposes an application of the above-mentioned recycled graphite in lithium batteries.
[0019] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are: In this invention, rapid heating effectively removes impurities from the negative electrode graphite in spent lithium batteries, helping to reduce the negative impact of these impurities on the graphite's performance. Subsequently, through a grinding reaction with sublimated sulfur and red phosphorus, CSP bonds are formed, which can generate a continuous crystalline Li3P-based SEI layer in situ during cycling. Furthermore, FeS and Li3PO4 nanoparticles are generated to form a conductive network, improving the graphite's conductivity. This repairs graphite surface defects, increases lithium-ion migration channels, and thus enhances the capacity and cycle performance of the resulting recycled graphite. This preparation method is more environmentally friendly, promotes green production, is simple in process, low in cost, and yields graphite with good reusability.
[0020] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, and in order to make the above and other objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described below. Attached Figure Description
[0021] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0022] Figure 1 This is a schematic diagram of the reuse method described in Embodiment 1 of the present invention; Figure 2 The image shows an electron microscopy characterization image of recycled graphite obtained by the recycling method described in Embodiment 1 of the present invention; wherein, Figure 2 (a) and Figure 2 (b) are scanning electron microscope (SEM) images of waste graphite (SG) at different magnifications; Figure 2 (c) is a high-resolution transmission electron microscope (HRTEM) image of waste graphite (SG); Figure 2 (d) is Figure 2 (c) The inverse Fourier transform image of the marked region; Figure 2 (e) and Figure 2 (f) are scanning electron microscope (SEM) images of regenerated graphite (RG-20s) at different magnifications; Figure 2 (g) is a high-resolution transmission electron microscope (HRTEM) image of recycled graphite (RG-20s), showing the graphite lattice. Figure 2 (h) is a high-resolution transmission electron microscope (HRTEM) image of recycled graphite (RG-20s), showing the lattice space (114) of FeS nanoparticles. Figure 2 (i) is an energy dispersive X-ray spectroscopy (EDX) image of recycled graphite (RG-20s); Figure 3 Advanced spectroscopic analysis of recycled graphite and waste graphite obtained by the recycling method described in Embodiment 1 of the present invention; wherein, Figure 3 (a) XRD patterns of recycled graphite (RG-20s) and waste graphite (SG); Figure 3 (b) RG, SG, and CG at 150-3500 cm -1 Raman shift spectra within the range; Figure 3 (c) RG, SG, and CG in 100-600 cm -1 Raman shift spectra within the range; Figure 3 (d)- Figure 3 (i) are the XPS spectra of RG-20s and SG, including C1s, P2p and S2p peaks.
[0023] Figure 4 This is a performance analysis of the recycled graphite obtained by the reuse method described in Embodiment 1 of the present invention; wherein, Figure 4 (a) The discharge capacity of CG and RG series battery cells was tested at different current densities (the specific capacity was 372 mAh / g at 1 C current density). Figure 4 (b) Testing the long-term cycle performance of CG and RG series battery cells at high current density (3 C); Figure 5 This refers to a series of characterizations of batteries made from recycled graphite obtained by the recycling method described in Embodiment 1 of the present invention after cycling; wherein, Figure 5 (a) Transmission electron microscopy image of the RG-20s sample after cycling in the battery, showing the SEI layer; Figure 5 (b) High-resolution transmission electron microscopy images of the corresponding surfaces, showing the presence of the LiP(103) lattice; Figure 5 (c) First charge-discharge curves of half-cells assembled using RG series and CG; Figure 5 (d) CV curves of the RG-20s lithium half-cell under the first three cycles at a current density of 0.1 mV s⁻¹; Figure 5 (e) XPS spectrum of RG-20s after half-cell cycling; Figure 5 (f) XPS spectrum of CG lithium half-cell after cycling. Detailed Implementation
[0024] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.
[0025] The terms "comprising" and "having," and any variations thereof, in the specification, embodiments, claims, and drawings of this invention are intended to cover non-exclusive inclusion, such as including a series of steps or units.
[0026] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.
[0027] Example 1 Methods for reusing graphite anodes in spent lithium batteries, such as... Figure 1 As shown, it includes the following steps: (1) Place the waste lithium-ion battery negative electrode material into a stripping vessel, add dimethyl carbonate (DMC) at a solid-liquid ratio of 1:50, then place the stripping vessel into an ultrasonic device and soak it at room temperature for 0.5 h with a power of 200 W. The waste powder was successfully stripped from the negative electrode material. Then, add a certain amount of alcohol (anhydrous ethanol) to the waste graphite, soak it at room temperature for 1 h, centrifuge to remove the cleaned waste powder, and dry it in a forced-air drying oven at 80°C for 20 h to obtain waste graphite powder (SG).
[0028] (2) Add 4 g SG and 1.2 mg sulfur (S) powder and 118.8 mg red phosphorus (P) powder to a mortar and grind them thoroughly for 1 hour to make them evenly mixed. At this time, the mass ratio of each substance satisfies S / (S+P)=1 / 100 and (S+P) / N-PG=3 / 100.
[0029] (3) The obtained mixed powder was placed in an ultra-fast high-temperature sintering equipment, argon gas was slowly introduced, and a current of 500 A was introduced in an inert gas atmosphere to rapidly heat the mixed powder to 1200 ℃, hold it at the temperature for 20 s, and then cool it naturally to room temperature. The obtained sintered powder was washed with CS2 and alcohol, centrifuged three times, and dried to obtain recycled graphite (RG-20S).
[0030] like Figure 2As shown, the scanning electron microscope (SEM) image, high-resolution transmission electron microscope (HRTEM) image, and EDS image of the recycled graphite obtained by the recycling method are presented. The SEM image reveals that after ultra-rapid high-temperature sintering, the graphite surface becomes significantly smoother, and large cracks disappear. This is mainly because some impurities in the SEI layer on the surface of the waste graphite are burned off at high temperatures, and the high temperature promotes the shrinkage of the graphite layer, which was originally increased in spacing due to repeated lithium ion insertion and extraction. The HRTEM image shows that S and P are uniformly distributed on the graphite surface, forming a coating layer, and the previously present Fe-containing impurity particles are transformed into FeS nanoparticles.
[0031] like Figure 3 The XRD pattern, Raman pattern, and X-ray photoelectron spectrum of the recycled graphite obtained by the reuse method are shown in the figure. Figure 3 CSP bonds and FeS nanoparticles can be clearly observed on the graphite surface. The formation of CSP bonds can generate a continuous crystal line Li3P-based SEI layer (Li3P has high ionic conductivity) in situ during battery cycling. FeS nanoparticles form a conductive network, which improves the conductivity and rate performance of graphite and helps to facilitate the effective Li+ desolvation process and Li+ migration across the SEI layer.
[0032] Example 2 A method for reusing negative electrode graphite in waste lithium batteries, the specific steps of which are as described in Example 1, the difference being that in step (3), “heat preservation and firing for 20 s” is changed to “heat preservation and firing for 40 s”.
[0033] Example 3 A method for reusing negative electrode graphite in waste lithium batteries, the specific steps of which are as described in Example 1, the difference being that in step (3), “heat preservation and firing for 20 s” is changed to “heat preservation and firing for 60 s”.
[0034] Example 4 A method for reusing negative electrode graphite in waste lithium batteries, the specific steps of which are the same as those in Example 1, the difference being that in step (3), “rapidly heating the mixed powder to 1200 ℃” is changed to “rapidly heating the mixed powder to 800 ℃”.
[0035] Example 5 A method for reusing negative electrode graphite in waste lithium batteries, the specific steps of which are the same as those in Example 1, the difference being that in step (3), “rapidly heating the mixed powder to 1200 ℃” is changed to “rapidly heating the mixed powder to 1600 ℃”.
[0036] Example 6 A method for reusing negative electrode graphite in waste lithium batteries, the specific steps of which are as described in Example 1, the difference being that in step (2), 4 g SG is kept constant, and the mass ratio of each substance is changed to S / (S+P)=10 / 100 and (S+P) / N-PG=3 / 100.
[0037] Example 7 A method for reusing negative electrode graphite in waste lithium batteries, the specific steps of which are as described in Example 1, the difference being that in step (2), 4 g SG is kept constant, and the mass ratio of each substance is changed to S / (S+P)=1 / 100 and (S+P) / N-PG=10 / 100.
[0038] Comparative Example 1 A method for reusing negative electrode graphite from waste lithium batteries, the specific steps of which are the same as in Example 1, the difference being that step (2) is changed to: adding 4 g SG and 1.2 mg sulfur (S) powder into a mortar and grinding thoroughly for 1 h to make them evenly mixed, placing the resulting mixed powder in an ultra-fast high-temperature sintering device, slowly introducing argon gas, and introducing a current of 500 A in an inert gas atmosphere to rapidly heat the mixed powder to 1200 ℃, holding it at that temperature for 20 s, and then naturally cooling it to room temperature, then adding the powder at this time and 118.8 mg red phosphorus (P) powder into the mortar and grinding thoroughly for 1 h to make them evenly mixed, repeating the sintering operation, at which time the mass ratio of each substance satisfies S / (S+P)=1 / 100 and (S+P) / N-PG=3 / 100. The resulting sintered powder is washed with CS2 and alcohol, centrifuged three times, and dried to obtain recycled graphite (RG-20S).
[0039] Comparative Example 2 A method for reusing negative electrode graphite from waste lithium batteries, the specific steps of which are the same as in Example 1, the difference being that steps (1) and (2) are omitted, and only waste graphite is used without any processing.
[0040] This invention also proposes a lithium battery, which is specifically prepared by the following method: In a glove box where the water and oxygen content are both less than 0.1 ppm, lithium sheets are used as the counter electrode, and the recycled graphite (RG) described in the above embodiments or comparative examples is used as the negative electrode. Together with the electrolyte and the separator, they are assembled into a half cell. The electrolyte was obtained by mixing ethylene carbonate (EC) and diethyl carbonate (DEC) at a mass ratio of 1:1 in a glove box with a water and oxygen content of less than 0.1 ppm at room temperature, adding 1 mol / L LiPF6, mixing thoroughly, and letting stand for 24 h. The diaphragm was obtained by punching a polypropylene membrane into a disc with a diameter of 16 mm and then vacuum drying it in a vacuum drying oven at 55°C for 24 h.
[0041] The lithium batteries were tested using an Arbin BT2000 testing system with a charge / discharge voltage range of 0.01-3V and 3 cycles at 0.1 C (30℃) to obtain the initial coulombic efficiency. Additionally, the high-rate performance of the lithium batteries was tested using the Arbin BT2000 system with a voltage range of 0.01-3V, a current density of 3C, and 3000 cycles. The test results are shown in Table 1 below. Figure 4 The table above shows the discharge specific capacity curves of recycled graphite and commercial graphite obtained by the reuse methods described in Examples 1, 2, and 3 of this invention at a 3C rate. Figure 4 The results show that the formation of CSP bonds in the recycled graphite of this invention can generate a continuous crystal line Li3P-based SEI layer (Li3P has high ionic conductivity) in situ during the first charge and discharge of a lithium battery. This facilitates an effective Li+ desolvation process and Li+ migration across the SEI layer, enabling the recycled graphite to maintain a specific capacity of over 100 mAh / g at a 3C current density (in contrast, commercial graphite has a specific capacity of only about 40 mAh / g at a 3C current density, and waste graphite has a specific capacity of only about 30 mAh / g at a 3C current density, and even fails after a short cycle time). Furthermore, the recycled graphite exhibits excellent cycle stability. Therefore, with an external high ionic conductivity coating, recycled graphite can simultaneously possess advantages such as high initial efficiency, excellent cycle stability, and rate performance. This is achieved by cleverly utilizing the transformation of CSP bonds during the cycling process, which allows the in-situ reaction to generate a coating layer with excellent physicochemical properties. At the same time, Fe-containing impurity particles are transformed into FeS nanoparticles to form a conductive network. The synergistic effect of these two processes improves the conductivity and rate performance of graphite, thereby enhancing the performance of the secondary battery.
[0042] Figure 5 These are HRTEM images, first-cycle charge / discharge capacity and voltage curves, first-cycle CV curves, and XPS analysis of the recycled graphite obtained by the recycling method described in Embodiment 1 of this invention after half-cell cycling. The data clearly show the formation of Li3P and its impact on the structure; the presence of CSP bonds and Li3P reduces graphite degradation.
[0043] The above specific embodiments further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above are merely specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.
Claims
1. A method for reusing negative electrode graphite from waste lithium batteries, characterized in that, Includes the following steps: S1. Remove graphite from the current collector to obtain waste graphite from the negative electrode material of waste lithium batteries; S2. Mix and grind waste graphite, sublimed sulfur and red phosphorus to obtain mixed powder; S3. Place the mixed powder in an inert gas atmosphere and burn it in a fast-burning device for a period of time, then cool it to obtain recycled graphite.
2. The method for reusing negative electrode graphite in waste lithium batteries as described in claim 1, characterized in that: In step S1, the stripping is achieved by soaking the waste lithium battery negative electrode material in a cleaning solution and then drying it. The cleaning solution is dimethyl carbonate, the soaking temperature is 20-30 ℃, the soaking time is 0.5-1 h, and the solid-liquid ratio of the waste lithium battery negative electrode material to the cleaning solution is 1:
50.
3. The method for reusing negative electrode graphite in waste lithium batteries as described in claim 2, characterized in that: In step S1, ultrasonic dispersion is performed during soaking, and the ultrasonic dispersion power is 500-1000 W.
4. The method for reusing negative electrode graphite in waste lithium batteries as described in claim 2, characterized in that: Step S1 further includes adding waste graphite to alcohol until the alcohol completely covers the waste graphite, soaking it a second time, and then drying it. The second soaking temperature is 20-40 ℃ and the time is 0.5-2 h. The drying temperature is 50-100 ℃ and the time is 16-24 h.
5. The method for reusing negative electrode graphite in waste lithium batteries as described in claim 1, characterized in that: In step S2, the mass ratio of waste graphite to red phosphorus and sublimated sulfur is 1:0.05-0.06:0.0005-0.
01.
6. The method for reusing negative electrode graphite in waste lithium batteries as described in claim 1, characterized in that: In step S2, the grinding is carried out in a mortar or a ball mill, wherein grinding is performed in a mortar for 1 hour and mixed grinding is performed in a ball mill for 0.5 hours.
7. The method for reusing negative electrode graphite in waste lithium batteries as described in claim 1, characterized in that: In step S3, the fast-firing equipment is an ultra-fast high-temperature sintering equipment, including a Joule heating device or UHS, and the inert gas atmosphere is a nitrogen atmosphere, a vacuum environment, or an argon atmosphere.
8. The method for reusing negative electrode graphite in waste lithium batteries as described in claim 1, characterized in that: In step S3, during rapid heating, the temperature is first increased to 800-1500 ℃ at a rate of 800-2000 ℃ / s, held for 20-60s, and then allowed to cool naturally to room temperature.
9. Regenerated graphite prepared by the method for reusing negative electrode graphite in waste lithium batteries as described in any one of claims 1-8.
10. The application of recycled graphite in lithium batteries as described in claim 9.