Method for regenerating waste positive electrode material through oxalic acid surface modification

Abstract

The application relates to the technical field of lithium batteries and discloses a method for regenerating waste positive electrode materials through oxalic acid surface modification, which comprises the following steps: separating and drying modified materials obtained by ball milling of waste positive electrode materials and an oxalic acid solution; and calcining the modified materials mixed with a lithium source to obtain regenerated positive electrode materials. In the mechanical activation surface modification process, oxalic acid is introduced, the surface transition metal oxide structure of the waste NCM material is successfully modified into an oxalate structure, the broken polycrystalline particles are depolymerized and converted into uniform single crystal morphology, the surface LiF impurities are completely removed, and the influence of the impurities on the repair process and the regenerated materials is eliminated; the material repaired through the surface modification of the oxalic acid exhibits smaller structural degradation in the cycle process, a more stable CEI film is formed, the interface side reaction between the electrode and the electrolyte is effectively reduced, and therefore the cycle stability of the electrode is significantly improved.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, and in particular to a method for regenerating waste cathode materials through oxalic acid surface modification. Background Technology

[0002] The rapid global adoption of electric vehicles has spurred a surge in demand for lithium-ion batteries (LIBs), resulting in a large number of retired batteries and exacerbating resource and environmental pressures. Therefore, the recycling and disposal of spent LIBs has become crucial. This is especially true for LiNi batteries, which are rich in lithium, cobalt, nickel, and manganese. x Co y Mn 1-x-y O2 (NCM) ternary layered oxide cathode materials have demonstrated significant economic and environmental value in the field of battery recycling. In recent years, direct repair and regeneration technology for ternary cathode materials has gradually gained attention due to its advantages such as short process flow, low energy consumption, and high returns. However, as the nickel content in NCM materials increases, their failure rate significantly intensifies, and more LiF impurities and inactive NiO are generated during cycling. This not only increases the difficulty of material repair and regeneration but also limits the recovery of the performance of the regenerated electrode materials.

[0003] Therefore, how to provide a recycling method to achieve efficient restoration of the morphology and performance of spent lithium battery cathode materials is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0004] In view of this, the present invention provides a method for regenerating waste cathode materials through oxalic acid surface modification. This regeneration method can achieve efficient repair of the morphology and performance of waste cathode materials through mechanical activation surface modification and high-temperature calcination.

[0005] To achieve the above objectives, the present invention adopts the following solution:

[0006] On one hand, the present invention provides a method for regenerating waste cathode materials through oxalic acid surface modification, comprising the following steps:

[0007] (1) The waste cathode material and oxalic acid solution were separated by ball milling and then dried to obtain the modified material;

[0008] (2) The modified material and lithium source are mixed and calcined to obtain a recycled cathode material.

[0009] Preferably, the ball mill rotates at a speed of 450-500 rpm for a duration of 25-35 minutes.

[0010] Preferably, the ball-to-material ratio in the ball milling process is (18-28):1.

[0011] Preferably, the oxalic acid solution is prepared by mixing oxalic acid and water in a ratio of (0.1-0.75)g:(30-70)ml.

[0012] Preferably, the molar ratio of the waste cathode material to oxalic acid is (1.4-2.8):5.

[0013] Preferably, the modified material has an oxalate coating layer with a thickness of 1.2-2.8 nm on its surface, and the morphology is single crystal particles with a particle size of 0.5-2 μm.

[0014] Preferably, the molar ratio of lithium element in the lithium source to transition metal element in the waste cathode material is (1-1.1):1.

[0015] Preferably, the lithium source includes one or more of lithium hydroxide, lithium carbonate, and lithium nitrate.

[0016] Preferably, the calcination includes a first calcination and a second calcination performed sequentially, wherein the temperature of the first calcination is 450-550℃ and the time is 1.5-2.5h; and the temperature of the second calcination is 800-900℃ and the time is 13-17h.

[0017] Preferably, the waste cathode material comes from nickel-cobalt-manganese ternary lithium batteries.

[0018] Preferably, the separation and drying processes further include washing and centrifugation.

[0019] On the other hand, the present invention also provides a regenerated cathode material, which is prepared by the method described in any of the above-mentioned methods for regenerating waste cathode materials by surface modification with oxalic acid.

[0020] This invention provides a method for regenerating waste cathode materials through oxalic acid surface modification. Compared with existing technologies, its advantages are as follows:

[0021] This invention introduces oxalic acid during the mechanical activation surface modification process, successfully modifying the transition metal oxide structure on the surface of waste NCM materials into an oxalate structure. Simultaneously, the broken polycrystalline particles depolymerize and transform into a uniform single crystal morphology, completely removing LiF impurities from the surface and eliminating the influence of impurities on the repair process and regenerated materials. Materials repaired with oxalic acid surface modification exhibit less structural degradation during cycling and form a more stable CEI film, effectively reducing interfacial side reactions between the electrode and electrolyte, thereby significantly improving the cycling stability of the electrode.

[0022] The regeneration process of the waste cathode material of this invention mainly uses common and inexpensive industrial raw materials such as water and oxalic acid. The operation steps are simple and easy to implement, and it has high industrialization potential. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0024] Figure 1 The image is a SEM image of 622-S in Comparative Example 1;

[0025] Figure 2 The image shows the SEM image of 622-HCO-MA in Example 1.

[0026] Figure 3 Here is a SEM image of the modified material in Example 2;

[0027] Figure 4 Here is a SEM image of the modified material in Example 3;

[0028] Figure 5 Here is a SEM image of the modified material in Example 4;

[0029] Figure 6 Here is a SEM image of the modified material in Example 5;

[0030] Figure 7 The XRD patterns of the mechanically activated modified materials in Examples 1-5 are shown.

[0031] Figure 8 Thermogravimetric curves of the mechanically activated modified materials in Examples 1 and 3-5;

[0032] Figure 9 This is a TEM image of the mechanically activated 622-HCO-MA material in Example 1;

[0033] Figure 10 The O1s spectra of XPS for 622-S in Comparative Example 1 and 622-HCO-MA in Example 1 are shown.

[0034] Figure 11 The F1s spectra of XPS for 622-S in Comparative Example 1 and 622-HCO-MA in Example 1 are shown.

[0035] Figure 12 SEM image of the recycled 622-HCO-R material in Example 5;

[0036] Figure 13 The results are the cycle performance test results of the regenerated electrode materials in Examples 1-4;

[0037] Figure 14 The results are the cycle performance test results of the regenerated electrode materials in Examples 1, 5, and 6.

[0038] Figure 15 Cyclic performance test results of 622-S in Comparative Example 1, and the regenerated electrode materials in Comparative Example 2 and Example 5;

[0039] Figure 16 The F1s spectra of the regenerated electrode materials of Comparative Example 2 and Example 5 were obtained by XPS testing after cyclic testing. Detailed Implementation

[0040] The present invention will be described below through specific embodiments. Those skilled in the art will understand that the specific embodiments below are merely illustrative and do not limit the scope of the invention in any way. Furthermore, in the following embodiments, unless otherwise specified, the reagents and equipment used are commercially available. If specific processing conditions and methods are not explicitly described in the later embodiments, conditions and methods known in the art can be used for processing.

[0041] In one aspect of the present invention, a method for regenerating waste cathode materials through oxalic acid surface modification is provided, comprising the following steps:

[0042] S100. Dissolve oxalic acid in water to obtain an oxalic acid solution.

[0043] In this step, the oxalic acid solution is prepared by mixing oxalic acid and water in a ratio of (0.1-0.75)g:(30-70)ml, preferably in a ratio of (0.38-0.5)g:(45-55)ml.

[0044] S200. Waste cathode material and oxalic acid solution are ball-milled in a ball mill jar, then separated, washed, centrifuged and dried to obtain modified material.

[0045] In this step, the waste cathode material comes from nickel-cobalt-manganese ternary lithium batteries, and the ternary cathode material includes LiNi. 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2 or LiNi 0.8 Co 0.1 Mn 0.1 O2, preferably LiNi 0.6 Co 0.2 Mn 0.2 O2.

[0046] The molar ratio of the waste cathode material to oxalic acid is (1.4-2.8):5, preferably (2-2.5):5. When the amount of oxalic acid added increases, the surface content of the modified oxalate increases.

[0047] The ball milling speed is 450-500 rpm, and the duration is 25-35 min; preferably, the ball milling speed is 475-485 rpm, and the duration is 25-35 min; the ball-to-material ratio in the ball milling process is (18-28):1, preferably (24-26):1, and the faster the ball milling speed, the faster the particle deagglomeration rate.

[0048] During the separation, washing, centrifugation and drying process, deionized water is used for filtration, washing 5-10 times, centrifugation at 8000-12000 rpm, and drying in air at 70-90℃ for 10-15 hours. More preferably, the process involves washing 8 times, centrifugation at 9900-10500 rpm, and drying in air at 78-82℃ for 10-12 hours.

[0049] The modified material has an oxalate structure on its surface, the oxalate coating layer has a thickness of 1.2-2.8 nm, preferably 1.8-2.2 nm, and the morphology is single crystal particles with a particle size of 0.5-2 μm, preferably 0.8-1.2 μm.

[0050] This invention introduces oxalic acid during the mechanical activation process, successfully modifying the surface of waste NCM materials into an oxalate structure and transforming broken polycrystalline particles into uniform single-crystal morphology. At the same time, it completely removes LiF impurities from the surface, eliminating the impact of impurities on the repair process and the recycled materials.

[0051] S300. Add a lithium source to the modified material, and calcine the resulting mixture in an oxygen atmosphere to obtain a recycled cathode material.

[0052] In this step, the molar ratio of lithium element in the lithium source to transition metal element in the waste cathode material is (1-1.1):1, preferably 1.05:1; the lithium source includes one or more of lithium hydroxide, lithium carbonate, and lithium nitrate, preferably lithium hydroxide.

[0053] The calcination includes a first calcination and a second calcination performed sequentially. The temperature of the first calcination is 450-550℃, preferably 490-510℃, and the time is 1.5-2.5h, preferably 1.9-2.1h. The temperature of the second calcination is 800-900℃, preferably 845-855℃, and the time is 13-17h, preferably 15.5-16.5h.

[0054] In another aspect, the present invention also provides a regenerated cathode material, which is obtained by regenerating using the method described above. Thus, the regenerated cathode material has all the features and preferences of the method described above, which will not be repeated here.

[0055] To further illustrate the present invention, the technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0056] Example 1

[0057] Used ternary lithium batteries (with LiNi cathode material) whose capacity has been reduced to 75% of their original capacity. 0.6 Co 0.2 Mn 0.2 After the O2 is fully discharged by the discharge machine, it is disassembled in a glove box filled with inert argon gas. The positive and negative electrodes are separated by hand to obtain the positive electrode sheet. After calcination at 600℃ for 3 hours, the binder and conductive carbon are removed to obtain the positive electrode material powder to be repaired, which is named 622-S.

[0058] 0.4 g of oxalic acid was fully dissolved in 50 mL of water. 1 g of 622-S material was placed in a 100 mL ball mill jar, and the oxalic acid solution was added. The mixture was mechanically activated at 480 rpm for 30 min, with the molar ratio of oxalic acid to waste cathode material being 2.2:5. The powder was separated, washed and centrifuged multiple times, and dried at 80 °C for 12 h to obtain the oxalic acid-modified material, named 622-HCO-MA.

[0059] The elemental composition of the 622-HCO-MA material was tested by ICP-OES. LiOH·H2O was added according to the stoichiometric ratio of lithium to transition metal elements of 1.05:1. After the material was mixed evenly, it was calcined at high temperature in an oxygen atmosphere, calcined at 500℃ for 2 h, and then calcined at 800℃ for 16 h. The resulting recycled material was named 622-HCO-R.

[0060] Example 2

[0061] The only difference between this embodiment and Embodiment 1 is that the mechanical activation medium is 50 mL of distilled water and no oxalic acid is added; the other operating steps are the same as in Embodiment 1.

[0062] Example 3

[0063] The only difference between this embodiment and Embodiment 1 is that the ratio of oxalic acid to waste cathode material is 0.6:5, and the other operating steps are the same as in Embodiment 1.

[0064] Example 4

[0065] The only difference between this embodiment and Embodiment 1 is that the ratio of oxalic acid to waste cathode material is 1.4:5. The other operating steps are the same as in Embodiment 1.

[0066] Example 5

[0067] The only difference between this embodiment and Embodiment 1 is that the ratio of oxalic acid to waste cathode material is 2.8:5. The other operating steps are the same as in Embodiment 1.

[0068] Example 6

[0069] The only difference between this embodiment and Embodiment 1 is that the calcination conditions are: calcination at 500°C for 2 hours, followed by calcination at 850°C for 16 hours. The remaining operation steps are the same as in Embodiment 1.

[0070] Example 7

[0071] The only difference between this embodiment and Embodiment 1 is that the calcination conditions are: calcination at 500°C for 2 hours, followed by calcination at 900°C for 16 hours. The remaining operation steps are the same as in Embodiment 1.

[0072] Comparative Example 1

[0073] The only difference between this comparative example and Example 1 is that the molecular formula of the waste lithium battery cathode material 622-S is Li. 0.83 Ni 0.6 Co 0.2 Mn 0.2 O2.

[0074] Comparative Example 2

[0075] The only difference between this comparative example and Example 1 is that the waste lithium battery cathode material 622-S was not subjected to surface modification treatment by mechanical activation with oxalic acid, but was obtained directly through lithium replenishment and high-temperature calcination repair.

[0076] This invention conducted SEM tests on samples of waste lithium battery cathode materials from Comparative Example 1 and Examples 1-5 after mechanical activation, from... Figure 1 It can be seen that the morphology of the waste ternary cathode material 622-S in Comparative Example 1 is a broken secondary spherical shape, indicating fracture. Figures 2 to 6 It can be seen that: In Example 2, without the addition of oxalic acid, the morphology still retains the characteristics of 622-S particles, which are a large number of broken secondary particles with irregular shapes, indicating that the particle morphology changes little when oxalic acid is not added; However, after adding oxalic acid to the system, it can be observed that the secondary particles are deagglomerated, and the particles begin to become smaller and more uniform; Among them, the secondary particles of the 622-HCO-MA material in Example 1 have completely deagglomerated, and their morphology is more uniform primary particles.

[0077] This invention uses XRD characterization technology to compare the changes in the crystal structure of electrode materials before and after oxalic acid surface modification, obtaining the XRD patterns of the modified materials after mechanical activation in Examples 1-5. The results are shown in [Figure 1]. Figure 7 The results showed that the XRD patterns of the modified materials in Examples 1 and 5 showed characteristic peaks of transition metal oxalates at around 22.6° and 30.2°, respectively. The modified materials in Examples 2-4 did not show obvious characteristic peaks of oxalates. Furthermore, as the amount of oxalic acid added increased, the characteristic peaks of transition metal oxalates in the XRD patterns gradually became stronger, indicating that the amount of oxalic acid added directly affected the formation of the oxalate surface structure.

[0078] Based on this, the thermogravimetric (TG) curves of NCM622 materials prepared with different oxalic acid addition amounts were analyzed. Figure 8 As can be seen, samples prepared with different amounts of oxalic acid exhibited different mass losses during heating. The thermogravimetric curves showed two distinct weight loss phases starting at 100℃ and 200℃, representing water evaporation and oxalate decomposition, respectively, with the decomposition reaction continuing until approximately 500℃. Weight loss peaks clearly indicating oxalate decomposition were detected in Examples 1, 4, and 5, demonstrating the successful preparation of oxalate surfaces under these conditions. Comparing the percentage weight loss of different samples revealed that the mass loss during heating gradually increased with increasing oxalic acid content, indicating an increase in the oxalate content in the samples and further clarifying the influence of oxalic acid addition on the surface structure of the prepared NCM622 material.

[0079] The present invention used TEM detection technology to characterize the surface structure of the mechanically activated surface-modified material in Example 1. The detection results are shown in [Figure 1]. Figure 9 The TEM image shows a uniform coating layer with a thickness of approximately 2 nm formed on the surface of the 622-S material. This result indicates that a uniform and dense oxalate surface structure was successfully prepared on the surface of waste NCM material through mechanical activation assisted by oxalic acid.

[0080] This invention performed XPS tests on the materials before and after mechanical activation with oxalic acid, analyzing the changes in the elemental chemical states of the material surface before and after oxalate modification. The O 1s test results are shown below. Figure 10 The F1s test results are shown below. Figure 11 As can be seen from the figure, the O1s spectrum mainly contains two characteristic peaks on the surface of the oxalate-modified 622-HCO-MA material. ImpurityThe significantly increased peak ratio indicates an increase in surface oxalate structures, providing further evidence for the successful preparation of oxalate surface structures. In the F1s spectrum of 622-HCO-MA, the strong LiF peak (684.8 eV) that was originally present in the 622-S sample was completely removed, indicating that the oxalate surface modification process thoroughly removed the LiF impurities from the surface of the waste electrode material.

[0081] like Figure 12 The image shown is a SEM image of the regenerated 622-HCO-R material obtained in Example 5 of this invention. The present invention tested the charge-discharge cycle performance of the electrode materials obtained in Comparative Examples 1, 2, and Examples 1-7, cycling 100 times at 0.5C. The test results are shown below. Figure 13 , Figure 14 and Figure 15 .from Figure 13-15 It can be seen that the cycling performance of the regenerated electrode material was effectively restored after surface modification by adding oxalic acid during the mechanical activation process. Compared with Comparative Example 1, it was significantly improved and far exceeded that of Example 2 without the addition of oxalic acid. It also surpassed Comparative Example 2, which confirms the effectiveness of the oxalic acid surface modification and repair technology.

[0082] The present invention further disassembled the batteries of Example 5 and Comparative Example 2 after cycling, and analyzed the chemical composition of the CEI film on the electrode surface using XPS detection technology. The F 1s energy dispersive spectroscopy results are shown in […]. Figure 16 The F 1s energy spectrum includes Li-F and Li. x PO y F z Li is the main inorganic substance in the CEI film formed on the electrode surface during cycling; in addition, the peak near 688 eV is CF, which mainly comes from the polyvinylidene fluoride (PVDF) binder under the CEI film. By fitting the peak area, it was found that the Li on the electrode surface after cycling in Example 5 x PO y F z LiF content is dominant, accounting for approximately 71.9%, while in Comparative Example 2, the LiF peak reaches as high as 81.5% on the electrode surface. Excessive LiF content indicates more severe electrolyte decomposition, forming a high-resistivity layer that hinders lithium-ion migration in the CEI layer and negatively impacts the cycle stability of the cathode. Therefore, the surge in LiF content on the Comparative Example 2 electrode surface after cycling is also a key factor limiting its cycle performance. This result precisely illustrates the importance of removing the LiF impurity phase during the repair process.

[0083] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for regenerating waste cathode materials through oxalic acid surface modification, characterized in that, Includes the following steps: (1) The waste cathode material and oxalic acid solution were separated by ball milling and then dried to obtain the modified material; The molar ratio of the waste cathode material to oxalic acid is (1.4-2.8):5; (2) The modified material and lithium source are mixed and calcined to obtain a recycled cathode material; The waste cathode material comes from nickel-cobalt-manganese ternary lithium batteries, where the ternary cathode material includes LiNi. 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2 or LiNi 0.8 Co 0.1 Mn 0.1 O2; The modified material has an oxalate coating layer on its surface, and its morphology is single-crystal particles.

2. The method for regenerating waste cathode materials by surface modification with oxalic acid according to claim 1, characterized in that, The ball mill rotates at 450-500 rpm for 25-35 minutes. The ball-to-material ratio in the ball milling process is (18-28):

1.

3. The method for regenerating waste cathode materials by surface modification with oxalic acid according to claim 1, characterized in that, The oxalic acid solution is prepared by mixing oxalic acid and water in a ratio of (0.1-0.75)g:(30-70)ml.

4. The method for regenerating waste cathode materials by surface modification with oxalic acid according to claim 1, characterized in that, The thickness of the oxalate coating layer is 1.2-2.8 nm, and the particle size of the single crystal particles is 0.5-2 μm.

5. The method for regenerating waste cathode materials by surface modification with oxalic acid according to claim 1, characterized in that, The molar ratio of lithium in the lithium source to transition metal in the waste cathode material is (1-1.1):1; The lithium source includes one or more of lithium hydroxide, lithium carbonate, and lithium nitrate.

6. The method for regenerating waste cathode materials by surface modification with oxalic acid according to claim 1, characterized in that, The calcination includes a first calcination and a second calcination performed sequentially. The first calcination temperature is 450-550℃ and the time is 1.5-2.5h; the second calcination temperature is 800-900℃ and the time is 13-17h.

7. The method for regenerating waste cathode materials by surface modification with oxalic acid according to any one of claims 1-6, characterized in that, The separation and drying process also includes washing and centrifugation.

8. A regenerated cathode material, prepared by the method of surface modification of waste cathode material with oxalic acid as described in any one of claims 1-7.

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