Ternary positive electrode material for repairing and regenerating failure based on residual alkali in-situ conversion of LiF-Li3PO4-LiAlO2 coating layer as well as preparation method and application of ternary positive electrode material

Abstract

The invention provides a residual alkali in-situ conversion LiF-Li3PO4-LiAlO2 coating layer-based repaired and regenerated ineffective ternary positive electrode material and a preparation method and application thereof. The preparation method comprises the following steps: S1, mixing, grinding and calcining an ineffective ternary material and Li2CO3 or LiOH.H2O to obtain a repaired ternary material; and S2, mixing the repairing ternary material with NH4F or NH4H2PO4 or Al2O3, grinding, and calcining, so as to obtain the LiF-Li3PO4-LiAlO2 in-situ co-coated NCM positive electrode material. When the prepared LiF-Li3PO4-LiAlO2 in-situ co-coated LiNi < x > Co < y > Mn < z > O < 2 > (NCM) positive electrode material is used as a positive electrode material of a lithium ion battery, the air stability, the thermal stability and the electrochemical stability of the material can be effectively improved, so that the high-value recovery of invalid LiNi < 0.5 > Co < 0.2 > Mn < 0.3 > O < 2 > (NCM < 523 >) is realized. And the method reduces the residual lithium salt on the surface of the regenerated material, and compared with a common recovery method, the interface stability is effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of waste battery recycling, and particularly to a method for repairing and regenerating a failed ternary cathode material with a LiF-Li3PO4-LiAlO2 coating layer based on in-situ conversion of residual alkali, and a preparation method and application thereof. Background Art

[0002] In recent years, driven by the explosive growth of downstream application scenarios such as electric vehicles and energy storage, the lithium-ion battery (LIBs) industry, especially the power battery industry, has developed vigorously. However, the service life of power batteries is limited, and a large-scale retirement wave of lithium-ion power batteries is coming soon. Proper treatment of waste power batteries will be crucial for environmental protection and resource recycling and reuse. At present, a large number of waste LIBs, especially the cathode materials with high recycling value among them, have not been recycled and disposed of in a green, sustainable and efficient manner. As one of the most widely used cathode materials in LIBs, the layered transition metal oxide NCM has high recycling value. However, traditional NCM cathode material recycling technologies have many problems such as high energy consumption and serious secondary pollution. Developing a short-process, low-pollution, low-cost and high-efficiency NCM recycling technology is of great significance for resource development and environmental protection.

[0003] Most current NCM recycling strategies add excessive lithium salts during the repair process to cope with the loss of Li during high-temperature sintering, such as CN117594900A, etc. This results in residual lithium salts such as Li2CO3 and LiOH on the material surface. These surface residual alkalis will accelerate the reaction between the electrode and the electrolyte at the interface during battery cycling, causing material structure degradation and capacity loss. In addition, the electrochemical performance of the regenerated materials repaired by a single lithium supplementation strategy is difficult to reach the level of commercial materials and can only be used at a degraded level. Therefore, on the basis of lithium supplementation repair, it is particularly important to develop new recycling technologies to achieve the upgraded utilization of regenerated materials and improve the electrochemical performance of regenerated materials. Summary of the Invention

[0004] In view of the problems that the electrochemical performance and air stability of the existing recycled lithium-ion battery NCM cathode materials are poor after direct regeneration, and the interfacial side reactions caused by the residual lithium impurities on the surface of the recycled materials during the repair process, the present invention proposes a preparation method for repairing and regenerating a failed ternary cathode material based on an in-situ conversion LiF-Li3PO4-LiAlO2 coating layer of residual alkali, the cathode material prepared thereby, and its application. The present invention directly repairs the failed NCM cathode material obtained by disassembling the retired lithium-ion battery, and performs LiF, Li3PO4, and LiAlO2 coating after the repair to achieve a mixed coating on the basis of lithium source supplementation and structure repair. When the LiF-Li3PO4-LiAlO2 in-situ co-coated NCM cathode material is used as the cathode material of a lithium-ion battery, it can effectively improve the air stability, thermal stability, and electrochemical stability of the material, thereby realizing the efficient repair and regeneration of the failed NCM. And this method reduces the residual lithium salt on the surface of the recycled material, and effectively improves the interfacial stability compared with the ordinary recycling method.

[0005] The technical solution of the present invention is realized as follows:

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

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

[0008] S2. Mix the repaired ternary material with NH4F or NH4H2PO4 or Al2O3, grind, and calcine to obtain a LiF-Li3PO4-LiAlO2 in-situ co-coated NCM cathode material.

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

[0010] By performing LiF-Li3PO4-LiAlO2 co-coating on the surface of the repaired ternary material RNCM, the performance of the repaired ternary material is improved. Among them, LiF can effectively improve the electrochemical stability of the material, Li3PO4 can improve the thermal stability of the material, and LiAlO2 can effectively reduce the air sensitivity of the recycled material and reduce the reaction of the sample with H2O and CO2. At the same time, the formation of the LiF-Li3PO4-LiAlO2 co-coating layer consumes the residual lithium salt on the surface of RNCM, which will effectively improve the interfacial stability between the cathode and the electrolyte.

[0011] The sample of the repaired ternary material DNCM repaired by solid-phase sintering with lithium supplementation can be used as the positive electrode active material of a lithium-ion battery, and is prepared into a positive electrode slurry with acetylene black, PVDF, NMP, etc., coated on an aluminum foil to make a positive electrode sheet, and a lithium-ion battery is assembled.

[0012] On the basis of the above technical solutions, 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 to x + 0.1).

[0013] On the basis of the above technical solutions, further, the coating amount of the in-situ co-coating is 3% to 6%, where the coating amount is the ratio of the molar amounts of fluoride ions, phosphate ions, and aluminum ions to the molar amount of the repaired ternary material.

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

[0015] On the basis of the above technical solutions, further, when the repaired ternary material is mixed with NH4F, NH4H2PO4, and Al2O3, the molar ratio of the repaired ternary material to NH4F, NH4H2PO4, and Al2O3 is 1:(0.01 to 0.02):(0.01 to 0.02):(0.005 to 0.01).

[0016] On the basis of the above technical solutions, further, the calcination in step S1 is carried out in an oxygen atmosphere at a heating rate of 5°C / min to 750 - 850°C and calcined for 8 - 12 hours.

[0017] On the basis of the above technical solutions, further, the calcination in step S2 is carried out in an air or oxygen atmosphere at a heating rate of 5°C / min to 350 - 500°C and calcined for 5 - 6 hours.

[0018] On the basis of the above technical solutions, further, the grinding in step S2 is carried out at a rotation speed of 400 - 500 r / min for 2 - 4 hours.

[0019] In a second aspect, the present invention provides a LiF-Li3PO4-LiAlO2 in-situ co-coated NCM positive electrode material, which is prepared by the above method.

[0020] In a third aspect, the present invention provides an application of the above LiF-Li3PO4-LiAlO2 in-situ co-coated NCM positive electrode material in the preparation of a positive electrode material for a lithium-ion battery.

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

[0022] (1) The present invention utilizes the reaction of NH4F, NH4H2PO4 or Al2O3 with residual lithium impurities such as Li2CO3, LiOH, and Li2O on the surface of RNCM. While forming an in-situ coating layer, it will consume the residual lithium impurities on the surface, reducing the interfacial side reactions during the cycling process;

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

[0024] (3) The LiF-Li3PO4-LiAlO2 in-situ co-coated NCM cathode material prepared by the present invention has better thermal stability, especially at high voltages, which significantly improves the safety of the battery system;

[0025] (4) The present invention adopts a fully dry process, without the use of strong acids and strong bases, and no waste water is generated, which is environmentally friendly;

[0026] (5) The process of the present invention is short, the operation is simple, the equipment requirements are low, and it is convenient for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0028] Figure 1 Scanning electron microscope (SEM) images of DNCM523, RNCM523 of Comparative Examples 1 and 3, and RNCM523@LFPA-5c of Example 1;

[0029] Figure 2 Energy dispersive X-ray spectroscopy (EDS) image of RNCM523@LFPA-5c of Example 1;

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

[0031] Figure 4This is a differential scanning calorimetry (DSC) test of RNCM523@LFPA-5c of Example 1 and RNCM523 of Comparative Example 3 when charged to 4.3V;

[0032] Figure 5 The first charge and discharge capacity-voltage curves of DNCM523, NCM523, RNCM523 of comparative examples 1-3 and RNCM523@LFPA-5c of example 1;

[0033] Figure 6 Comparative Example 2 NCM523 and Example 1 NCM523@LFPA-5c at 1C (1C = 180mAg -1 ) energy density, and performance diagram of 250 cycles at 3.0-4.3V. DETAILED DESCRIPTION

[0034] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0035] The following specific embodiments use a failed ternary material DNCM523 (LiNi 0.5 Co 0.2 Mn 0.3 O2) is the black powder obtained by peeling off the positive electrode sheets disassembled from waste power batteries after heat treatment at 300℃, and does not contain the binder PVDF.

[0036] Example 1

[0037] This embodiment provides a preparation method for repairing and regenerating a failed ternary positive electrode material based on in-situ conversion of a LiF-Li3PO4-LiAlO2 coating layer with residual alkali, comprising the following steps:

[0038] S1. Mix 1g of failed ternary material DNCM523 and 0.0763g of lithium carbonate (Li2CO3, Aladdin) and grind them for 20 minutes. Put the resulting mixture into a tubular furnace, heat it to 850°C at a heating rate of 5°C / min in an oxygen atmosphere and calcine it for 10 hours. After calcination, the repaired ternary material RNCM523 is obtained.

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

[0040] Example 2

[0041] This embodiment provides a preparation method for repairing and regenerating a failed ternary positive electrode material based on in-situ conversion of a LiF-Li3PO4-LiAlO2 coating layer with residual alkali, comprising the following steps:

[0042] S1. Mix 1g of failed ternary material DNCM523 and 0.0763g of lithium carbonate (Li2CO3, Aladdin) and grind them for 20 minutes. Put the resulting mixture into a tubular furnace, heat it to 750°C at a heating rate of 5°C / min in an oxygen atmosphere and calcine it for 12 hours. After calcination, the repaired ternary material RNCM523 is obtained.

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

[0044] Example 3

[0045] This embodiment provides a preparation method for repairing and regenerating a failed ternary positive electrode material based on in-situ conversion of a LiF-Li3PO4-LiAlO2 coating layer with residual alkali, comprising the following steps:

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

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

[0048] Example 4

[0049] This example provides a preparation method for repairing and regenerating a failed ternary cathode material based on in-situ conversion of residual alkali into a LiF-Li3PO4-LiAlO2 coating layer. The remaining operations are the same as those in Example 1. The difference from Example 1 is as follows:

[0050] Mix the repaired ternary material RNCM523 obtained in step S1 with NH4F, NH4H2PO4, and Al2O3 at 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 example provides a preparation method for repairing and regenerating a failed ternary cathode material based on in-situ conversion of residual alkali into a LiF-Li3PO4-LiAlO2 coating layer. The remaining operations are the same as those in Example 1. The difference from Example 1 is as follows:

[0053] Mix the repaired ternary material RNCM523 obtained in step S1 with NH4F, NH4H2PO4, and Al2O3 at 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 example provides a preparation method for repairing and regenerating a failed ternary cathode material based on in-situ conversion of residual alkali into a LiF-Li3PO4-LiAlO2 coating layer. The remaining operations are the same as those in Example 1. The difference from Example 1 is as follows:

[0056] Mix the repaired ternary material RNCM523 obtained in step S1 with NH4F, NH4H2PO4, and Al2O3 at 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 example provides a preparation method for repairing and regenerating a failed ternary cathode material based on in-situ conversion of residual alkali to a LiF-Li3PO4-LiAlO2 coating layer. The remaining operations are the same as in Example 1. The difference from Example 1 is as follows:

[0059] Mix the repaired ternary material RNCM523 obtained in step S1 with NH4F, NH4H2PO4, and Al2O3 at 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 example provides a preparation method for repairing and regenerating a failed ternary cathode material based on in-situ conversion of residual alkali to a LiF-Li3PO4-LiAlO2 coating layer. The remaining operations are the same as in Example 1. The difference from Example 1 is as follows:

[0062] Mix the repaired ternary material RNCM523 obtained in step S1 with NH4F, NH4H2PO4, and Al2O3 at 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 10% lithium deficiency 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.), denoted as NCM523.

[0067] Comparative Example 3

[0068] This comparative example provides a repaired ternary material, which is different from Example 1 in that: step 2 is not included, and the obtained 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 preparation method of an upgraded NCM523 material coated with LiAlO2, and the remaining operations are the same as those in Example 1. The difference from Example 1 is that: in step S2, the repaired ternary material RNCM523 and Al2O3 are mixed at a molar ratio of 1:0.025, and finally an upgraded NCM523 material coated with 5% LiAlO2 is obtained, denoted as RNCM523@LAO-5.

[0071] Comparative Example 5

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

[0073] Comparative Example 6

[0074] This comparative example provides a preparation method of an upgraded NCM523 material coated with Li3PO4, and the remaining operations are the same as those 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, and finally an upgraded NCM523 material coated with 5% Li3PO4 is obtained, denoted as RNCM523@LP-5.

[0075] Comparative Example 7

[0076] This comparative example provides a preparation method of an upgraded NCM523 material co-coated with LiF-Li3PO4, and the remaining operations are the same as those in Example 1. The difference from Example 1 is that: in step S2, the repaired ternary material RNCM523 and NH4F and NH4H2PO4 are mixed at a molar ratio of 1:0.02:0.03. Finally, an upgraded NCM523 material co-coated with 5% LiF-Li3PO4 is obtained, 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 those in Example 1. The difference from Example 1 is that in step S2, the ternary material RNCM523 is repaired and mixed with NH4F, NH4H2PO4, and Al2O3 in a molar ratio of 1:0.05:0.02:0.01. Finally, an upgraded NCM523 material coated with 9% LiF-Li3PO4-LiAlO2 is obtained, denoted as RNCM523@LFPA-9.

[0079] Application example

[0080] (1) The positive electrode materials obtained in the examples and comparative examples were respectively sampled and mixed with the conductive agent acetylene black and the binder PVDF at a mass ratio of 8:1:1, added to a homogenization tube, and then ball-milled in a homogenizer for 3 min. The uniformly mixed slurry was coated on carbon-coated aluminum foil in a glove box filled with argon and dried on a heating table at 80 °C for 2 h. A tablet press was used to punch the dried coated aluminum foil into an electrode sheet with a diameter of 10 mm, which was then placed in a glove box filled with argon for use.

[0081] (2) A metal lithium sheet was used as the negative electrode, Celgard 2500 was used as the separator, and the electrolyte was a mixed solution of 1 M LiPF6 dissolved in ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) with a volume ratio of 1:1:1. A CR2032 button battery was assembled in a glove box filled with argon.

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

[0083] Table 1 Comparison of electrochemical properties of NCM positive electrode materials

[0084]

[0085] As shown in Table 1, in the voltage window of 3.0 - 4.3 V, the initial discharge specific capacities of the examples at 0.1C are concentrated between 161 - 167 mAh g -1 . After 250 cycles at 1C rate, the capacity retention rates are similar. Among them, RNCM523@LFPA-5c has the best electrochemical performance, and the initial discharge specific capacity is 166.6 mAh g -1, the capacity retention rate is 80%, exceeding that of the commercial sample NCM523 in Comparative Example 2. The cycling performance of RNCM523@LFPA-3 with a coating amount of 3% is slightly worse than that of the sample coated with only 5% LiAlO2, indicating that the lower co - coating amount and LiAlO2 have a relatively low improvement in stability. The first - cycle discharge capacity of the sample RNCM523@LF-5 coated with only 5% LiF is relatively low, indicating that an increase in the LiF coating amount has an adverse effect on the discharge specific capacity. The discharge specific capacity of the sample with a coating amount of 6% is slightly worse, while the discharge capacity of the sample with a coating amount of 9% in Comparative Example 8 drops significantly, indicating that an excessive coating amount will reduce the specific capacity of the material.

[0086] Scanning electron microscopy observations were carried out on RNCM523@LFPA-5c, DNCM523, and RNCM523 prepared in Example 1, Comparative Example 1, and Comparative Example 3. The results are as Figure 1 shown. The surface of DNCM523 prepared in Comparative Example 1 has carbon particles, planar slip and cracks, as well as dense micropores, and there is particle fragmentation. For the RNCM523 material prepared in Comparative Example 3 after high - temperature solid - state repair, the surface cracks and micropores disappear, and there are a certain amount of residual Li2CO3 small particles. The surface of RNCM523@LFPA-5c prepared in Example 1 has no micro - cracks and holes, and there is a uniform coating layer.

[0087] Energy - dispersive X - ray spectroscopy (EDS mapping) observations were carried out on RNCM523@LFPA-5c prepared in Example 1. The results are as Figure 2 shown. From Figure 2 it can be seen that on the surface of the secondary grains after repair, F, P, and Al are evenly distributed, indicating that there is a uniform coating of LiF, Li3PO4, and LiAlO2 on the material surface.

[0088] XRD image observations were carried out on the commercial NCM523, RNCM523 in Comparative Example 2 and Comparative Example 3, RNCM523 exposed to air for 10 days, RNCM523@LAO-5 prepared in Comparative Example 4, and RNCM523@LFPA-9 prepared in Comparative Example 8. The results are as Figure 3 shown. The peak positions marked by red pentagrams in the figure are the characteristic peaks of the NCM hydrated phase. From Figure 3 it can be seen that after being exposed to air with a relatively high humidity and CO2 content for 10 days, only the repaired RNCM523 has an obvious hydrated phase, and the peak intensity ratio I of the (003) peak and the (104) peak (003) / (104) significantly decreases, indicating that the material has Li + / TM (TM represents transition metal ions) mixed arrangement. Compared with the materials not exposed to air, no obvious characteristic peaks of the hydrated phase appeared in RNCM523@LAO and RNCM523@LFPA coated with LiAlO2 and LiF-Li3PO4-LiAlO2, and the I (003) / (104) value is good. This indicates that the co-coating of LiAlO2 and LiF-Li3PO4-LiAlO2 can reduce the air sensitivity of NCM materials.

[0089] The RNCM523@LFPA-5c prepared in Example 1 and the RNCM523 of Comparative Example 3 were charged to 4.3V for differential scanning calorimetry (DSC) test, and the results are as Figure 4 shown. As shown in the figure, the exothermic peaks of RNCM523@LFPA-5c and RNCM523 are 304.5 °C and 294.8 °C respectively, indicating that RNCM523@LFPA-5c has better thermal stability.

[0090] Figure 5 is the first-cycle charge-discharge capacity-voltage curve diagram of DNCM523, NCM523, RNCM523 of Comparative Examples 1-3 and RNCM523@LFPA-5c obtained in Example 1. The first-cycle discharge specific capacities of DNCM523, NCM523, RNCM523 and RNCM523@LFPA-5c in the voltage range of 0.1C, 3.0 - 4.3V are 57 mAh g -1 ,164 mAh g -1 ,152 mAh g -1 ,167 mAh g -1 respectively. It can be seen that the co-coating of LiF-Li3PO4-LiAlO2 adopted in the present invention has a significant effect on the recovery of electrochemical performance.

[0091] Figure 6 is the performance schematic diagram of the energy density of NCM523 of Comparative Example 2 and RNCM523@LFPA-5c of Example 1 at 1C and cycling 250 times at 3.0 - 4.3V. After cycling 250 times at a current density of 1C, the capacity retention rates of NCM523 and RNCM523@LFPA-5c are 71% and 80% respectively. It can be seen that the co-coating of LiF-Li3PO4-LiAlO2 adopted in the present invention can significantly improve the cycling stability of the material.

[0092] In summary, after the LiF-Li3PO4-LiAlO2 in-situ co-coated NCM cathode material of the present invention was exposed to wet air for 10 days, no obvious change was observed in the XRD phase, 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 the cathode material of a lithium-ion battery, it exhibits excellent electrochemical performance in the voltage range of 3-4.3V and can provide a reversible discharge specific capacity of 166.6 mAh g -1 -1 at a rate of 0.1C.

[0094] The LiF-Li3PO4-LiAlO2 in-situ co-coated NCM cathode material of the present invention also has excellent cycle stability. The initial discharge specific capacity at a rate of 1C is 151.1 mAh g -1 -1, and the capacity retention rate reaches 80% after 250 cycles, while the capacity retention rate of the uncoated RNCM material under the same conditions is only 71%. In addition, in the DSC test at a voltage of 4.3V, the exothermic peak of the coated sample is increased from 294.8°C to 304.5°C, indicating that the LiF-Li3PO4-LiAlO2 co-coating layer improves the high-voltage stability of the material.

[0095] The material design and preparation technology of the present invention are environmentally friendly, controllable and practical, providing a new idea for the direct regeneration of the NCM cathode material of failed lithium-ion batteries.

[0096] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A preparation method for repairing and regenerating a failed ternary cathode material based on in-situ conversion of residual alkali to form a LiF-Li3PO4-LiAlO2 coating layer, characterized in that, It 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. Mix the repaired ternary material with NH4F or NH4H2PO4 or Al2O3, grind, and calcine to obtain the LiF-Li3PO4-LiAlO2 in-situ co-coated NCM cathode material.

2. The preparation method of repairing and regenerating the failed ternary cathode material based on the in-situ conversion of residual alkali to form a LiF-Li3PO4-LiAlO2 coating layer as claimed in claim 1, wherein 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).

3. The preparation method of repairing and regenerating the failed ternary cathode material based on the in-situ conversion of residual alkali to form a LiF-Li3PO4-LiAlO2 coating layer as claimed in claim 1, wherein, The coating amount of the in-situ co-coating is 3%~6%, where the coating amount is the ratio of the molar amounts of fluoride ions, phosphate ions, and aluminum ions to the molar amount of the repaired ternary material.

4. The preparation method of repairing and regenerating the failed ternary cathode material based on the in-situ conversion of residual alkali to form a LiF-Li3PO4-LiAlO2 coating layer as claimed in claim 1, characterized in that, When the repaired ternary material is mixed with NH4F, NH4H2PO4, and Al2O3, the molar ratio of the repaired ternary material to NH4F, NH4H2PO4, and Al2O3 is 1:(0.01~0.02):(0.01~0.02):(0.005~0.01).

5. The preparation method of repairing and regenerating the failed ternary cathode material based on the in-situ conversion of residual alkali to form a LiF-Li3PO4-LiAlO2 coating layer as claimed in claim 1, wherein The calcination in step S1 is carried out in an air or oxygen atmosphere at a heating rate of 5°C / min to 750~850°C and calcined for 8~12 h.

6. The preparation method of repairing and regenerating the failed ternary cathode material based on the in-situ conversion of residual alkali to the LiF-Li3PO4-LiAlO2 coating layer as described in claim 1, wherein, The calcination in step S2 is carried out in an air or oxygen atmosphere at a heating rate of 5°C / min to 350~500°C and calcined for 5~6 h.

7. The preparation method of repairing and regenerating the failed ternary cathode material based on the in-situ conversion of residual alkali to form a LiF-Li3PO4-LiAlO2 coating layer as described in claim 1, characterized in that, The grinding in step S2 is carried out at a rotation speed of 400~500 r / min for 2~4 h.

8. An in-situ co-coated NCM cathode material of LiF-Li3PO4-LiAlO2, characterized in that, It is prepared by using the preparation method of repairing and regenerating the failed ternary cathode material by in-situ conversion of LiF-Li3PO4-LiAlO2 coating layer based on residual alkali as described in any one of claims 1~7.

9. The application of the LiF-Li3PO4-LiAlO2 in-situ co-coated NCM cathode material as described in claim 8 in the preparation of the cathode material of a lithium-ion battery.

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