A method for repairing and regenerating failed ternary cathode materials based on in-situ conversion of residual alkali into a LiF-Li3PO4-LiAlO2 coating, its preparation method, and its application.

Abstract

The application provides a kind of based on residual alkali in situ conversion LiF-Li3PO4-LiAlO2 coating layer repair regeneration failure ternary positive electrode material and its preparation method and application, preparation method includes the following steps: S1, failure ternary material is mixed with Li2CO3 Or LiOH.H2O, grinding, calcination obtains repair ternary material;S2, the repair ternary material is mixed with NH4F Or NH4H2PO4 Or Al2O3, grinding, calcination obtains LiF-Li3PO4-LiAlO2 In situ co-coated NCM positive electrode material.The prepared LiF-Li3PO4-LiAlO2 In situ co-coated LiNi x Co y Mn z O2(NCM) positive electrode material is used as lithium ion battery positive electrode material, can effectively improve the air stability of material, thermal stability and electrochemical stability, thereby realizing the high value recovery of failure LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523).And the method reduces the surface residual lithium salt of regenerated material, compared with ordinary recovery method, the interface stability is effectively improved.

Description

Technical Field

[0001] This invention relates to the field of waste battery recycling technology, and in particular to a method for repairing and regenerating failed ternary cathode materials based on in-situ conversion of residual alkali into a LiF-Li3PO4-LiAlO2 coating layer, its preparation method, and its application. Background Technology

[0002] In recent years, driven by the explosive growth of downstream applications such as electric vehicles and energy storage, the lithium-ion battery (LIB) industry, especially the power battery industry, has flourished. However, power batteries have a limited lifespan, and a large-scale retirement wave of lithium-ion power batteries is imminent. Properly handling spent power batteries is crucial for environmental protection and resource recycling. Currently, a large amount of spent LIBs, especially the cathode materials with high recycling value, have not been recycled in a green, sustainable, and efficient manner. Layered transition metal oxides (NCMs), as one of the most widely used cathode materials in LIBs, have high recycling value. However, traditional NCM cathode material recycling technologies suffer from high energy consumption and serious secondary pollution. Developing short-process, low-pollution, and highly efficient NCM recycling technologies is of great significance for both resource development and environmental protection.

[0003] Current NCM recycling strategies often involve adding excess lithium salts during the repair process to compensate for Li volatilization losses during high-temperature sintering, such as CN117594900A. This results in residual lithium salts like Li₂CO₃ and LiOH on the material surface. These surface alkali residues accelerate the reaction between the electrode and electrolyte at the interface during battery cycling, causing material structural degradation and capacity loss. Furthermore, the electrochemical performance of recycled materials repaired using a single lithium replenishment strategy is insufficient to reach the level of commercially available materials, necessitating downgraded use. Therefore, in addition to lithium replenishment repair, developing new recycling technologies to upgrade and utilize recycled materials and improve their electrochemical performance is crucial. Summary of the Invention

[0004] To address the issues of poor electrochemical performance and air stability of existing retired lithium-ion battery NCM cathode materials after direct regeneration, and interfacial side reactions caused by residual lithium impurities on the surface of the regenerated material during the repair process, this invention proposes a method for preparing and regenerating failed ternary cathode materials based on in-situ conversion of residual alkali into a LiF-Li3PO4-LiAlO2 coating layer, along with the prepared cathode material and its applications. This invention directly repairs failed NCM cathode materials obtained from the dismantling of retired lithium-ion batteries, and then coats them with LiF, Li3PO4, and LiAlO2 after repair, achieving a mixed coating that replenishes the lithium source and repairs the structure. When the LiF-Li3PO4-LiAlO2 in-situ co-coated NCM cathode material is used as a cathode material for lithium-ion batteries, it can effectively improve the material's air stability, thermal stability, and electrochemical stability, thereby achieving efficient repair and regeneration of failed NCM. Furthermore, this method reduces residual lithium salts on the surface of the regenerated material, and compared to ordinary recycling methods, the interfacial stability is effectively improved.

[0005] The technical solution of this invention is implemented as follows:

[0006] In a first aspect, the present invention provides a method for preparing a failed ternary cathode material based on in-situ conversion of residual alkali into a LiF-Li3PO4-LiAlO2 coating layer, comprising the following steps:

[0007] S1. Mix the failed ternary material with Li2CO3 or LiOH·H2O, grind, and calcine to obtain the repaired ternary material;

[0008] S2. The repaired ternary material is mixed with NH4F or NH4H2PO4 or Al2O3, ground, and calcined to obtain LiF-Li3PO4-LiAlO2 in-situ co-coated NCM cathode material.

[0009] NH4F, NH4H2PO4 and Al2O3 react with residual lithium impurities such as Li2CO3, LiOH and Li2O on the surface of RNCM, and are converted in situ on the surface of the cathode particles to form a LiF-Li3PO4-LiAlO2 coating layer.

[0010] The performance of regenerated ternary materials (RNCMs) was improved by co-coating the surface with LiF-Li3PO4-LiAlO2. LiF effectively enhances the electrochemical stability of the material, Li3PO4 improves its thermal stability, and LiAlO2 effectively reduces the air sensitivity of the regenerated material, minimizing reactions with H2O and CO2. Simultaneously, the formation of the LiF-Li3PO4-LiAlO2 co-coating layer consumes residual lithium salts on the RNCM surface, effectively improving the stability of the cathode-electrolyte interface.

[0011] The repaired ternary material is a sample of DNCM that has undergone solid-state sintering and lithium replenishment repair. It can be used as a positive electrode active material for lithium-ion batteries. It can be prepared into a positive electrode slurry with acetylene black, PVDF, NMP, etc., coated on aluminum foil to form a positive electrode sheet, and then assembled into a lithium-ion battery.

[0012] Based on the above technical solution, further, the molar percentage of lithium deficiency in the failed ternary material is x, and the ratio of the molar percentage of lithium deficiency in the failed ternary material to the molar percentage of lithium in Li2CO3 or LiOH·H2O is x:(x+0.05~x+0.1).

[0013] Based on the above technical solution, the coating amount of the in-situ co-coating is further 3% to 6%, wherein the coating amount is the ratio of the molar amount of fluoride ions, phosphate ions and aluminum ions to the molar amount of the repair ternary material.

[0014] For example, if the molar ratio of the ternary material to NH4F, NH4H2PO4 and Al2O3 is 1:0.01:0.02:0.01, then the coating amount is 5%.

[0015] Based on the above technical solution, furthermore, when the repair ternary material is mixed with NH4F, NH4H2PO4 and Al2O3, the molar ratio of the repair ternary material to NH4F, NH4H2PO4 and Al2O3 is 1:(0.01~0.02):(0.01~0.02):(0.005~0.01).

[0016] Based on the above technical solution, further, the calcination in step S1 is carried out in an oxygen atmosphere at a heating rate of 5℃ / min to 750~850℃ for 8~12h.

[0017] Based on the above technical solution, further, the calcination in step S2 is carried out in an air or oxygen atmosphere, with the temperature increased to 350-500°C at a heating rate of 5°C / min for 5-6 hours.

[0018] Based on the above technical solution, furthermore, the grinding in step S2 is performed at a rotation speed of 400-500 r / min for 2-4 hours.

[0019] Secondly, the present invention provides a LiF-Li3PO4-LiAlO2 in-situ co-coated NCM cathode material, which is prepared by the above method.

[0020] Thirdly, the present invention provides an application of the above-mentioned LiF-Li3PO4-LiAlO2 in-situ co-coated NCM cathode material in the preparation of cathode materials for lithium-ion batteries.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) In this invention, NH4F, NH4H2PO4 or Al2O3 react with residual lithium impurities such as Li2CO3, LiOH, and Li2O on the surface of RNCM. While forming an in-situ coating layer, the residual lithium impurities on the surface are consumed, reducing interfacial side reactions during the cycle.

[0023] (2) The LiF-Li3PO4-LiAlO2 in-situ co-coated NCM cathode material prepared by the present invention has better air stability, interface stability and lithium ion diffusion rate, and has better cycle stability after being made into electrode material.

[0024] (3) The LiF-Li3PO4-LiAlO2 in-situ co-coated NCM cathode material prepared by this invention has better thermal stability, especially under high voltage, which greatly improves the safety of the battery system.

[0025] (4) The present invention adopts a completely dry process, without the use of strong acids or alkalis, and without the generation of wastewater, which is environmentally friendly;

[0026] (5) The process of this invention is simple, easy to operate, requires low equipment, and is easy to mass-produce. Attached Figure Description

[0027] 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 some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 The images are scanning electron microscope (SEM) images of DNCM523 and RNCM523 in Comparative Examples 1 and 3 and RNCM523@LFPA-5c in Example 1.

[0029] Figure 2 The energy dispersive X-ray spectrum (EDS) of RNCM523@LFPA-5c in Example 1 is shown below.

[0030] Figure 3 X-ray diffraction (XRD) images of commercial NCM523, RNCM523, and RNCM523, RNCM523@LAO, and RNCM523@LFPA after 10 days of exposure to air;

[0031] Figure 4Differential scanning calorimetry (DSC) tests were performed on Example 1 RNCM523@LFPA-5c and Comparative Example 3 RNCM523 charged to 4.3V.

[0032] Figure 5 The first charge-discharge capacity-voltage curves of DNCM523, NCM523, and RNCM523 in Comparative Examples 1-3 and RNCM523@LFPA-5c in Example 1 are shown.

[0033] Figure 6 Comparative Example 2 NCM523 and Example 1 RNCM523@LFPA-5c were tested at 1C (1C = 180 mAg). -1 The energy density of the device is shown in the schematic diagram of its performance after 250 cycles at 3.0-4.3V. Detailed Implementation

[0034] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0035] The following specific embodiments use DNCM523 (LiNi), a failed ternary material with 10% lithium deficiency. 0.5 Co 0.2 Mn 0.3 O2 is a black powder obtained by peeling off the positive electrode sheet from a used power battery after heat treatment at 300℃. It does not contain the binder PVDF.

[0036] Example 1

[0037] This embodiment provides a method for preparing a regenerated ternary cathode material based on in-situ conversion of residual alkali into a LiF-Li3PO4-LiAlO2 coating layer, including the following steps:

[0038] S1. Mix 1g of failed ternary material DNCM523 with 0.0763g of lithium carbonate (Li2CO3, Aladdin) and grind for 20min. Place the resulting mixture in a tube furnace and calcine it at 850℃ for 10h under an oxygen atmosphere at a heating rate of 5℃ / min. After calcination, the repaired ternary material RNCM523 is obtained.

[0039] S2. The repaired ternary material RNCM523 obtained in step S1 is mixed with NH4F, NH4H2PO4 and Al2O3 in a molar ratio of 1:0.01:0.02:0.01 and ball-milled at 450 r / min for 2 h. The resulting mixture is placed in a tube furnace and calcined at 400 °C for 5 h in air atmosphere at a heating rate of 5 °C / min to obtain an upgraded NCM523 material co-coated with 5% LiF-Li3PO4-LiAlO2, denoted as RNCM523@LFPA-5c.

[0040] Example 2

[0041] This embodiment provides a method for preparing a regenerated ternary cathode material based on in-situ conversion of residual alkali into a LiF-Li3PO4-LiAlO2 coating layer, including the following steps:

[0042] S1. Mix 1g of failed ternary material DNCM523 with 0.0763g of lithium carbonate (Li2CO3, Aladdin) and grind for 20min. Place the resulting mixture in a tube furnace and calcine it at 750℃ for 12h under an oxygen atmosphere at a heating rate of 5℃ / min. After calcination, the repaired ternary material RNCM523 is obtained.

[0043] S2. The repaired ternary material RNCM523 obtained in step S1 is mixed with NH4F, NH4H2PO4 and Al2O3 in a molar ratio of 1:0.02:0.01:0.005 and ball-milled at 500 r / min for 3 h. The resulting mixture is placed in a tube furnace and calcined at 350 °C for 6 h in an air atmosphere at a heating rate of 5 °C / min to obtain an upgraded NCM523 material co-coated with 4% LiF-Li3PO4-LiAlO2, denoted as RNCM523@LFPA-4a.

[0044] Example 3

[0045] This embodiment provides a method for preparing a regenerated ternary cathode material based on in-situ conversion of residual alkali into a LiF-Li3PO4-LiAlO2 coating layer, including the following steps:

[0046] S1. Mix 1g of failed ternary material DNCM523 with 0.0763g of lithium carbonate (Li2CO3, Aladdin) and grind for 20min. Place the resulting mixture in a tube furnace and calcine it at 800℃ for 8h under an oxygen atmosphere at a heating rate of 5℃ / min. After calcination, the repaired ternary material RNCM523 is obtained.

[0047] S2. The repaired ternary material RNCM523 obtained in step S1 is mixed with NH4F, NH4H2PO4 and Al2O3 in a molar ratio of 1:0.015:0.015:0.005 and ball-milled at 400 r / min for 4 h. The resulting mixture is placed in a tube furnace and calcined at 500 °C for 5.5 h in air atmosphere at a heating rate of 5 °C / min to obtain an upgraded NCM523 material co-coated with 4% LiF-Li3PO4-LiAlO2, denoted as RNCM523@LFPA-4b.

[0048] Example 4

[0049] This embodiment provides a method for repairing and regenerating failed ternary cathode materials based on in-situ conversion of residual alkali into a LiF-Li3PO4-LiAlO2 coating layer. The remaining operations are the same as in Example 1, except that:

[0050] The repaired ternary material RNCM523 obtained in step S1 is mixed with NH4F, NH4H2PO4 and Al2O3 in a molar ratio of 1:0.01:0.01:0.01 to obtain an upgraded NCM523 material co-coated with 4% LiF-Li3PO4-LiAlO2, denoted as RNCM523@LFPA-4c.

[0051] Example 5

[0052] This embodiment provides a method for repairing and regenerating failed ternary cathode materials based on in-situ conversion of residual alkali into a LiF-Li3PO4-LiAlO2 coating layer. The remaining operations are the same as in Example 1, except that:

[0053] The repaired ternary material RNCM523 obtained in step S1 was mixed with NH4F, NH4H2PO4 and Al2O3 in a molar ratio of 1:0.02:0.02:0.005 to obtain an upgraded NCM523 material co-coated with 5% LiF-Li3PO4-LiAlO2, denoted as RNCM523@LFPA-5a.

[0054] Example 6

[0055] This embodiment provides a method for repairing and regenerating failed ternary cathode materials based on in-situ conversion of residual alkali into a LiF-Li3PO4-LiAlO2 coating layer. The remaining operations are the same as in Example 1, except that:

[0056] The repaired ternary material RNCM523 obtained in step S1 was mixed with NH4F, NH4H2PO4 and Al2O3 in a molar ratio of 1:0.02:0.01:0.01 to obtain an upgraded NCM523 material co-coated with 5% LiF-Li3PO4-LiAlO2, denoted as RNCM523@LFPA-5b.

[0057] Example 7

[0058] This embodiment provides a method for repairing and regenerating failed ternary cathode materials based on in-situ conversion of residual alkali into a LiF-Li3PO4-LiAlO2 coating layer. The remaining operations are the same as in Example 1, except that:

[0059] The repaired ternary material RNCM523 obtained in step S1 was mixed with NH4F, NH4H2PO4 and Al2O3 in a molar ratio of 1:0.01:0.01:0.005 to obtain an upgraded NCM523 material co-coated with 3% LiF-Li3PO4-LiAlO2, denoted as RNCM523@LFPA-3.

[0060] Example 8

[0061] This embodiment provides a method for repairing and regenerating failed ternary cathode materials based on in-situ conversion of residual alkali into a LiF-Li3PO4-LiAlO2 coating layer. The remaining operations are the same as in Example 1, except that:

[0062] The repaired ternary material RNCM523 obtained in step S1 was mixed with NH4F, NH4H2PO4 and Al2O3 in a molar ratio of 1:0.02:0.02:0.01 to obtain an upgraded NCM523 material co-coated with 6% LiF-Li3PO4-LiAlO2, denoted as RNCM523@LFPA-6.

[0063] Comparative Example 1

[0064] This comparative example provides a failed ternary material, LiNi, with a lithium deficiency of 10%. 0.5 Co 0.2 Mn 0.3 O2, denoted as DNCM523.

[0065] Comparative Example 2

[0066] This comparative example provides a ternary material, polycrystalline LiNi. 0.5 Co 0.2 Mn 0.3 O2 (purchased from Dongguan Kelude Experimental Equipment Technology Co., Ltd.), designated as NCM523.

[0067] Comparative Example 3

[0068] This comparative example provides a repaired ternary material, which differs from Example 1 in that it does not include step 2, and the resulting repaired ternary material LiNi 0.5 Co 0.2 Mn 0.3 O2, denoted as RNCM523.

[0069] Comparative Example 4

[0070] This comparative example provides a method for preparing an upgraded NCM523 material coated with LiAlO2. The remaining operations are the same as in Example 1. The difference from Example 1 is that in step S2, the repaired ternary material RNCM523 is mixed with Al2O3 at a molar ratio of 1:0.025 to finally obtain an upgraded NCM523 material coated with 5% LiAlO2, denoted as RNCM523@LAO-5.

[0071] Comparative Example 5

[0072] This comparative example provides a method for preparing an upgraded NCM523 material coated with LiF. The remaining operations are the same as in Example 1. The difference from Example 1 is that in step S2, the repaired ternary material RNCM523 is mixed with NH4F at a molar ratio of 1:0.05 to finally obtain an upgraded NCM523 material coated with 5% LiF, denoted as RNCM523@LF-5.

[0073] Comparative Example 6

[0074] This comparative example provides a method for preparing an upgraded NCM523 material coated with Li3PO4. The remaining operations are the same as in Example 1. The difference from Example 1 is that in step S2, the repaired ternary material RNCM523 and NH4H2PO4 are mixed at a molar ratio of 1:0.05 to finally obtain an upgraded NCM523 material coated with 5% Li3PO4, denoted as RNCM523@LP-5.

[0075] Comparative Example 7

[0076] This comparative example provides a method for preparing an upgraded NCM523 material co-coated with LiF-Li3PO4. The remaining operations are the same as in Example 1, except that in step S2, the repaired ternary material RNCM523 is mixed with NH4F and NH4H2PO4 in a molar ratio of 1:0.02:0.03. The final result is an upgraded NCM523 material co-coated with 5% LiF-Li3PO4, denoted as RNCM523@LFP-5.

[0077] Comparative Example 8

[0078] This comparative example provides a method for preparing an upgraded NCM523 material coated with LiAlO2. The remaining operations are the same as in Example 1, except that in step S2, the repaired ternary material RNCM523 is mixed with NH4F, NH4H2PO4, and Al2O3 in a molar ratio of 1:0.05:0.02:0.01. The final result is an upgraded NCM523 material coated with 9% LiF-Li3PO4-LiAlO2, denoted as RNCM523@LFPA-9.

[0079] Application examples

[0080] (1) The positive electrode materials obtained in the examples and comparative examples were mixed with conductive agent acetylene black and binder PVDF at a mass ratio of 8:1:1. After being added to a homogenizing tube, the mixture was ball-milled in a homogenizer for 3 minutes. The uniformly mixed slurry was coated onto carbon-coated aluminum foil in an argon-filled glove box and dried at 80°C for 2 hours on a heating table. The dried coated aluminum foil was then pressed into electrode sheets with a diameter of 10 mm using a tablet press and placed in an argon-filled glove box for later use.

[0081] (2) Using lithium metal sheet as negative electrode, Celgard2500 as separator, and 1M LiPF6 as electrolyte dissolved in a mixed solution of ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) in a volume ratio of 1:1:1, a CR2032 button cell was assembled in an argon glove box.

[0082] (3) The assembled CR2032 button cells were subjected to constant current charge-discharge tests and cycle stability tests using the battery test channel. The charge-discharge range was 3.0-4.3V (1C = 180mAh g). -1 The results are shown in Table 1 and... Figure 4-5 As shown.

[0083] Table 1 Comparison of Electrochemical Performance of NCM Cathode Materials

[0084]

[0085] As shown in Table 1, within the voltage window of 3.0–4.3V, the first-cycle discharge specific capacity at 0.1C for each embodiment is concentrated in the range of 161–167 mAh g. -1 Among them, the capacity retention rates after 250 cycles at 1C were similar, with RNCM523@LFPA-5c exhibiting the best electrochemical performance, with an initial discharge specific capacity of 166.6 mAh g⁻¹. -1The capacity retention rate was 80%, surpassing that of the commercial sample NCM523 in Comparative Example 2. The cycling performance of RNCM523@LFPA-3 with 3% coating was slightly worse than that of the sample with only 5% LiAlO2 coating, indicating that lower co-coating and LiAlO2 have less impact on stability improvement. The sample RNCM523@LF-5 with only 5% LiF coating had a lower first-cycle discharge capacity, indicating that increasing LiF coating has an adverse effect on discharge specific capacity. The sample with 6% coating had a slightly worse discharge specific capacity, while the sample with 9% coating in Comparative Example 8 showed a significant decrease in discharge capacity, indicating that excessive coating reduces the specific capacity of the material.

[0086] Scanning electron microscopy was performed on RNCM523@LFPA-5c, DNCM523, and RNCM523 prepared in Example 1, Comparative Example 1, and Comparative Example 3. The results are as follows: Figure 1 As shown. The DNCM523 prepared in Comparative Example 1 has carbon particles, planar slip and cracks, as well as dense micropores on its surface, indicating particle breakage. The RNCM523 material prepared in Comparative Example 3, after high-temperature solid-phase repair, shows that the surface cracks and micropores have disappeared, but a certain amount of residual Li2CO3 particles remain. The RNCM523@LFPA-5c prepared in Example 1 has no microcracks or pores on its surface and has a uniform coating layer.

[0087] Energy-dispersive X-ray spectroscopy (EDS mapping) was performed on RNCM523@LFPA-5c prepared in Example 1, and the results are as follows: Figure 2 As shown. From Figure 2 It can be seen that F, P and Al are evenly distributed on the surface of the secondary grains after repair, indicating that the material surface is uniformly coated with LiF, Li3PO4 and LiAlO2.

[0088] XRD images of commercially available NCM523 and RNCM523 from Comparative Examples 2 and 3, as well as RNCM523 exposed to air for 10 days, RNCM523@LAO-5 prepared in Comparative Example 4, and RNCM523@LFPA-9 prepared in Comparative Example 8 were observed. The results are as follows: Figure 3 As shown in the figure, the peaks marked with red pentagrams are characteristic peaks of the NCM hydration phase. From Figure 3 It can be seen that after 10 days of exposure to air with high humidity and CO2 content, only the remediated RNCM523 showed a clear hydrated phase, and the peak intensity ratio of (003) peak to (104) peak was I (003) / (104) The significant reduction indicates the presence of Li in the material. + / TM (TM represents transition metal ions) mixed arrangement. Compared with materials not exposed to air, RNCM523@LAO and RNCM523@LFPA coated with LiAlO2 and LiF-Li3PO4-LiAlO2 did not show obvious hydration phase characteristic peaks. (003) / (104) The values ​​are good. This indicates that both LiAlO2 and LiF-Li3PO4-LiAlO2 co-coating can reduce the air sensitivity of NCM materials.

[0089] Differential scanning calorimetry (DSC) tests were performed on the RNCM523@LFPA-5c prepared in Example 1 and the RNCM523 of Comparative Example 3, both charged to 4.3V. The results are as follows: Figure 4 As shown in the figure, the exothermic peaks of RNCM523@LFPA-5c and RNCM523 are 304.5℃ and 294.8℃, respectively, indicating that RNCM523@LFPA-5c has better thermal stability.

[0090] Figure 5 The first-cycle charge / discharge capacity-voltage curves are shown for Comparative Examples 1-3 (DNCM523, NCM523, RNCM523) and the RNCM523@LFPA-5c obtained in Example 1. The first-cycle discharge specific capacity of DNCM523, NCM523, RNCM523, and RNCM523@LFPA-5c in the 0.1C, 3.0-4.3V voltage range is 57 mAh g. -1 164mAh g -1 152mAh g -1 167mAh g -1 It is evident that the LiF-Li3PO4-LiAlO2 co-coating method employed in this invention significantly improves the recovery of electrochemical performance.

[0091] Figure 6 This diagram illustrates the performance of Comparative Example 2 NCM523 and Example 1 RNCM523@LFPA-5c at an energy density of 1C and 250 cycles at 3.0-4.3V. After 250 cycles at a current density of 1C, the capacity retention rates of NCM523 and RNCM523@LFPA-5c are 71% and 80%, respectively. This demonstrates that the LiF-Li3PO4-LiAlO2 co-coating employed in this invention significantly improves the cycling stability of the materials.

[0092] In summary, the LiF-Li3PO4-LiAlO2 in-situ co-coated NCM cathode material of the present invention showed no significant changes in XRD phase after being exposed to humid air for 10 days, indicating that the air stability of the coated sample was effectively improved.

[0093] When the LiF-Li3PO4-LiAlO2 in-situ co-coated NCM cathode material of the present invention is used as a cathode material for lithium-ion batteries, it exhibits excellent electrochemical performance in the voltage range of 3-4.3V, and can provide 166.6 mAh g at 0.1C rate. -1 The reversible discharge specific capacity.

[0094] The LiF-Li3PO4-LiAlO2 in-situ co-coated NCM cathode material of the present invention also exhibits excellent cycle stability, with an initial discharge specific capacity of 151.1 mAh g at 1C rate. -1 After 250 cycles, the capacity retention rate reached 80%, while the uncoated RNCM material only retained 71% under the same conditions. Furthermore, in the DSC test at 4.3V, the exothermic peak of the coated sample increased from 294.8℃ to 304.5℃, indicating that the LiF-Li3PO4-LiAlO2 co-coating layer improved the high-pressure stability of the material.

[0095] The material design and preparation technology of this invention is environmentally friendly, controllable, and practical, providing a completely new approach for the direct regeneration of NCM cathode materials from failed lithium-ion batteries.

[0096] 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, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a failed ternary cathode material based on in-situ conversion of residual alkali into a LiF-Li3PO4-LiAlO2 coating layer for repairing and regenerating the material, characterized in that, Includes the following steps: S1. Mix the failed ternary material with Li2CO3 or LiOH·H2O, grind, and calcine to obtain the repaired ternary material; S2. The repaired ternary material is mixed with NH4F, NH4H2PO4 and Al2O3, ground and calcined to obtain LiF-Li3PO4-LiAlO2 in-situ co-coated NCM cathode material; The molar percentage of lithium deficiency in the failed ternary material is x, and the ratio of the molar percentage of lithium deficiency in the failed ternary material to the molar percentage of lithium in Li2CO3 or LiOH·H2O is x:(x+0.05~x+0.1). The coating amount of the in-situ co-coating is 3% to 6%, wherein the coating amount is the ratio of the molar amount of fluoride ions, phosphate ions and aluminum ions to the molar amount of the repair ternary material. When the repair ternary material is mixed with NH4F, NH4H2PO4 and Al2O3, the molar ratio of the repair ternary material to NH4F, NH4H2PO4 and Al2O3 is 1:(0.01~0.02):(0.01~0.02):(0.005~0.01).

2. The preparation method of the failed ternary cathode material based on the in-situ conversion of residual alkali into a LiF-Li3PO4-LiAlO2 coating layer as described in claim 1, characterized in that, The calcination in step S1 is carried out in an air or oxygen atmosphere, with the temperature increased to 750~850℃ at a heating rate of 5℃ / min for 8~12 hours.

3. The preparation method of the failed ternary cathode material based on the in-situ conversion of residual alkali into a LiF-Li3PO4-LiAlO2 coating layer as described in claim 1, characterized in that, The calcination in step S2 is carried out in an air or oxygen atmosphere, with the temperature increased to 350~500℃ at a heating rate of 5℃ / min for 5~6 hours.

4. The preparation method of the failed ternary cathode material based on the in-situ conversion of residual alkali into a LiF-Li3PO4-LiAlO2 coating layer as described in claim 1, characterized in that, The grinding in step S2 is performed at a rotation speed of 400~500 r / min for 2~4 hours.

5. A LiF-Li3PO4-LiAlO2 in-situ co-coated NCM cathode material, characterized in that, The ternary cathode material was prepared by the method described in any one of claims 1 to 4, which is based on the in-situ conversion of residual alkali into a LiF-Li3PO4-LiAlO2 coating layer to repair and regenerate failed ternary cathode materials.

6. The application of the LiF-Li3PO4-LiAlO2 in-situ co-coated NCM cathode material as described in claim 5 in the preparation of cathode materials for lithium-ion batteries.

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