A cobalt-free positive electrode material and its preparation method and application

Abstract

The present invention belongs to the technical field of battery materials, and specifically relates to a cobalt-free positive electrode material and a preparation method and application thereof. The present invention coats and modifies the basic cobalt-free layered positive electrode material, and coats a type of MAX phase carbonized nanomaterial and superconducting low-temperature nanomaterial on the surface of the basic cobalt-free positive electrode material, thereby significantly improving the material conductivity and reducing the low-temperature DCR. Specifically, the MAX phase carbonized nanomaterial provides excellent conductivity, but poor low-temperature performance, while the superconducting low-temperature nanomaterial improves the performance of the cobalt-free positive electrode material at low temperatures. The two coating materials play a synergistic role and jointly reduce the low-temperature DCR of the cobalt-free positive electrode material.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery materials, and in particular relates to a cobalt-free positive electrode material and a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries are widely used in various fields such as electronic products, automobiles, and aerospace due to their high energy density and good cycle performance. As people have higher and higher requirements for the environmental protection, battery life, and life of lithium-ion batteries, battery design and optimization are becoming more and more important. As the core of lithium-ion batteries, the quality of the positive electrode material directly determines the performance of the battery.

[0003] At present, the ternary cathode materials widely used in lithium-ion batteries all include three metal elements: Ni, Co, and Mn. Among these three metal elements, Co has the highest price and the most scarce resources. Therefore, cobalt-free cathode materials are more attractive in the field of lithium-ion batteries. Among them, nickel-manganese layered materials have the advantages of high energy density, low cost, and excellent cycle performance, and have always been the focus of research. However, studies have shown that nickel-manganese layered cathode materials with high nickel content (more than 80% by mole) will cause poor conductivity of the cathode material due to the lack of cobalt, and its low-temperature DCR is high, which in turn affects the charging of electric vehicles at low temperatures and their range.

[0004] In view of this, how to reduce the low-temperature DCR of cobalt-free cathode materials has become a technical problem that needs to be solved urgently in this field. Summary of the invention

[0005] Therefore, the technical problem to be solved by the present invention is to overcome the defects of the cobalt-free positive electrode material in the prior art, such as high low-temperature DCR, thereby providing a cobalt-free positive electrode material and a preparation method and application thereof.

[0006] To this end, the present invention provides the following technical solutions:

[0007] The present invention provides a cobalt-free positive electrode material, comprising a basic cobalt-free positive electrode material and a coating layer, wherein the coating layer comprises a MAX phase carbonized nanomaterial and a low-temperature superconducting nanomaterial, wherein the low-temperature superconducting nanomaterial is at least one of NbN and Nb3Sn.

[0008] Optionally, the low-temperature superconducting nanomaterial accounts for 0.1-2% of the mass of the basic cobalt-free positive electrode material.

[0009] Optionally, the MAX phase carbonized nanomaterial accounts for 0.5-10% of the mass of the basic cobalt-free positive electrode material.

[0010] Optionally, the general formula of the MAX phase carbonized nanomaterial is N+1 AX N, wherein M is one or two of Ti, Nb, Mo, V; A is one of Al, Sn, Si; X is C; N=1 or 2 or 3;

[0011] Optional: Ti3AlC2, Nb2AlC, Ti2SnC, V2AlC, Ti3SiC2, Mo2Ti2AlC3, Mo2TiAlC2 nanomaterials.

[0012] Optionally, the general formula of the basic cobalt-free cathode material is Li a Ni x Mn y O2, where 1≤a≤1.2, 0.5<x<1, x+y=1.

[0013] The present invention also provides a method for preparing the above-mentioned cobalt-free positive electrode material, comprising the following steps:

[0014] S1, mixing a basic cobalt-free positive electrode material, a MAX phase carbonized nanomaterial and a low-temperature superconducting nanomaterial to obtain a mixed material;

[0015] S2, calcining the obtained mixed material in a protective atmosphere to obtain the cobalt-free positive electrode material.

[0016] Optionally, the calcination temperature in step S2 is 500-700° C., and the calcination time is 4-8 hours.

[0017] Optionally, the method for preparing the cobalt-free positive electrode material satisfies at least one of the following (1)-(4):

[0018] (1) The mixing in step S1 is performed at a rotation speed of 2000-4000 rpm for 10-20 min;

[0019] (2) The basic cobalt-free positive electrode material is a single crystal material, wherein the median particle size D50 is between 2.5-3.5 μm and the specific surface area is between 0.6-0.9 m 2 / g;

[0020] (3) The median particle size D50 of the MAX phase carbonized nanomaterial is between 50-200 nm;

[0021] (4) The median particle size D50 of the low-temperature superconducting nanomaterial is between 300-500 nm.

[0022] The present invention can further improve the coating effect and enhance the electrical properties of the material by limiting the median particle size D50 of the material. For example, the D50 of the positive electrode material will affect the material's cycle and safety performance. If it is too small, the cycle will be poor, the electrolyte side reaction will be serious, and more gas will be produced, affecting the safety performance; if it is too large, agglomeration will occur and the coating effect will deteriorate. If the D50 of the coating material is too large, agglomeration will occur, the primary particle size of the obtained material will also be large, and the coating effect will deteriorate.

[0023] The present invention also provides a positive electrode plate, comprising the above-mentioned cobalt-free positive electrode material or the cobalt-free positive electrode material prepared by the above-mentioned preparation method.

[0024] The present invention also provides a secondary battery, comprising the above-mentioned positive electrode plate.

[0025] The secondary battery in the present invention may be a lithium ion battery.

[0026] The composition and preparation method of the positive electrode plate and the secondary battery provided in the present invention are well known in the art. Typically, but not limitingly, the composition of the positive electrode plate is a positive electrode material, conductive carbon black (SP) and polyvinylidene fluoride (PVDF); the preparation method is to make PVDF glue from PVDF, the solvent is N-methylpyrrolidone (NMP), the positive electrode material, SP, PVDF glue, and NMP are stirred in a mass ratio of 92:4:4:46, and then coated, dried, and cut into pieces to prepare the positive electrode plate.

[0027] The secondary battery may include a negative electrode shell, a spring, a gasket, a lithium sheet, a diaphragm, an electrolyte, a positive electrode sheet, and a positive electrode shell; and the preparation method is to assemble and seal the negative electrode shell, the spring, the gasket, the lithium sheet, the diaphragm, the electrolyte, the positive electrode sheet, and the positive electrode shell in sequence.

[0028] The technical solution of the present invention has the following advantages:

[0029] The cobalt-free positive electrode material provided by the present invention is modified by coating the basic cobalt-free layered positive electrode material, and a type of MAX phase carbonized nanomaterial and superconducting low-temperature nanomaterial are coated on the surface of the basic cobalt-free positive electrode material, thereby significantly improving the material conductivity and reducing the low-temperature DCR. Specifically, the MAX phase carbonized nanomaterial provides excellent conductivity, but poor low-temperature performance, while the superconducting low-temperature nanomaterial improves the performance of the cobalt-free positive electrode material at low temperatures. The two coating materials play a synergistic role and jointly reduce the low-temperature DCR of the cobalt-free positive electrode material.

[0030] The cobalt-free positive electrode material provided by the present invention can further improve the coating effect and reduce the low-temperature DCR of the cobalt-free positive electrode material by limiting the material.

[0031] The method for preparing the cobalt-free positive electrode material provided by the present invention does not require complicated preparation steps and process equipment, is simple to operate, and is easy to promote and apply. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0033] Figure 1 It is a comparison chart of DCR of the assembled batteries of Examples 1-3 of the present invention and Comparative Example 1 at different SOCs at -20°C;

[0034] Figure 2 It is a SEM electron microscope image of the finished product in Example 1 of the present invention. DETAILED DESCRIPTION

[0035] The following examples are provided for a better understanding of the present invention, but are not intended to limit the best mode of implementation, nor to limit the content and protection scope of the present invention. Any product identical or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other prior arts shall fall within the protection scope of the present invention.

[0036] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in the field can be used. If no manufacturer is specified for the reagents or instruments used, they are all conventional reagent products that can be obtained commercially.

[0037] Example 1

[0038] This embodiment provides a cobalt-free positive electrode material, and its preparation method and specific parameters are as follows:

[0039] The basic layered single crystal cobalt-free cathode material is Li 1.05 Ni 0.55 Mn 0.45 O2, median particle size D50 is 3.2um, specific surface area is 0.74m 2 / g, Mo2Ti2AlC3, NbN and basic layered single crystal lithium nickel manganese oxide are mixed at a high speed in a mass ratio of 5:0.5:100, and stirred at 2000rpm for 10min. The median particle size D50 of the Mo2Ti2AlC3 is 88nm, and the median particle size D50 of the NbN is 376nm. The mixed materials are calcined at 500℃ for 4h in a nitrogen atmosphere to obtain a finished cobalt-free positive electrode material.

[0040] Figure 2 This is a SEM electron microscope image of the finished product in Example 1 of the present invention. It can be seen from the image that the two types of coating agents are evenly coated on the surface of the positive electrode material to form a dense coating layer.

[0041] Example 2

[0042] This embodiment provides a cobalt-free positive electrode material. Compared with Embodiment 1, the difference is that the MAX phase carbonized nanomaterial is Nb2AlC, and the median particle size D50 is 122 nm.

[0043] Example 3

[0044] This embodiment provides a cobalt-free positive electrode material. Compared with Embodiment 1, the difference is that the mass ratio of Mo2Ti2AlC3, NbN and basic layered single crystal lithium nickel manganese oxide is 2:0.2:100.

[0045] Example 4

[0046] This embodiment provides a cobalt-free positive electrode material. Compared with Embodiment 1, the difference is that the low-temperature superconducting nanomaterial is Nb3Sn, and the median particle size D50 is 469 nm.

[0047] Example 5

[0048] This embodiment provides a cobalt-free positive electrode material. Compared with Embodiment 1, the difference is that the material is calcined at 700° C. for 8 h in a nitrogen atmosphere.

[0049] Example 6

[0050] This embodiment provides a cobalt-free positive electrode material. Compared with Embodiment 1, the difference is that the material is calcined at 600° C. for 6 hours in a nitrogen atmosphere.

[0051] Example 7

[0052] This embodiment provides a cobalt-free positive electrode material. Compared with Embodiment 1, the difference is that the mass ratio of Mo2Ti2AlC3, NbN and basic layered single crystal lithium nickel manganese oxide is 9:1.5:100.

[0053] Example 8

[0054] This embodiment provides a cobalt-free positive electrode material. Compared with the embodiment 1, the difference is that the basic layered single crystal cobalt-free positive electrode material is Li 1.08 Ni 0.8 Mn 0.2 O2, median particle size D50 is 2.7um, specific surface area is 0.83m 2 / g.

[0055] Comparative Example 1

[0056] This comparative example provides a cobalt-free positive electrode material. Compared with Example 1, the difference is that no Mo2Ti2AlC3 and NbN coating modification is performed.

[0057] Comparative Example 2

[0058] This comparative example provides a cobalt-free positive electrode material. Compared with Example 1, the difference is that NbN is used instead of Mo2Ti2AlC3 for coating modification.

[0059] Comparative Example 3

[0060] This comparative example provides a cobalt-free positive electrode material. Compared with Example 1, the difference is that Mo2Ti2AlC3 is used instead of NbN for coating modification.

[0061] Test Case

[0062] 1. Use a powder resistivity tester to test the conductivity of the positive electrode material 12KN.

[0063] 2. Electrical performance test

[0064] Power-off preparation and DCR test under different SOC:

[0065] The cobalt-free positive electrode material obtained in each embodiment and comparative example, carbon black (SP), and polyvinylidene fluoride (PVDF, manufacturer Shenzhen Taineng New Materials Co., Ltd., model France 5130) were added to N-methylpyrrolidone (NMP) at a mass ratio of 92:4:4, mixed evenly, and coated on a 20um thick aluminum foil, dried at 100°C for 4h, cut into a positive electrode sheet with a diameter of 12mm, and then rolled. The surface density of the electrode sheet is 9g / cm 2 , compacted density is 3.3g / cm 3 , the negative electrode uses a lithium sheet (lithium sheet diameter is 16cm), assembled into a button half-cell, the electrolyte uses the product name LBC3401A60 produced by Shenzhen Xinzhoubang Technology Co., Ltd., model U718041806, and the injection volume is 60uL. The diaphragm uses an Al2O3 coated diaphragm. Let it stand for 12 hours, charge at a rate of 0.1C in a 25℃ oven until the voltage reaches 4.5V, record every 10s; charge at a constant voltage of 4.5V until the rate reaches 0.02C, record every 10s; let it stand for 5 minutes, then discharge at 0.1C until the voltage reaches 3V, record every 10s, let it stand for 10 minutes, and the capacity of the button is A.

[0066] Continue to charge at 0.1C rate at 25℃ until the voltage reaches 4.5V, record every 10s; charge at 4.5V constant voltage until the rate reaches 0.02C, record every 10s; adjust the oven to -20℃, let it stand for 180 minutes, record every 10s, record the cut-off voltage V1, then discharge at 0.5C for 10s, record every 0.1s, and record the voltage V2 at the end of 10s; adjust the oven temperature to 25℃, let it stand for 180 minutes, then discharge at 0.1C, the cut-off capacity reaches 0.5A, record every 10s, adjust the temperature to -20℃, let it stand for 180 minutes, record every 10s, record the cut-off voltage V3, then discharge at 0.5C for 10s, record every 0.1s, and record Record the voltage V4 at the end of 10s; adjust the oven temperature to 25℃, let it stand for 180 minutes, discharge at 0.1C, the cut-off capacity reaches 0.7A, record every 10s, adjust the temperature to -20℃, let it stand for 180 minutes, record every 10s, record the cut-off voltage V5, then discharge at 0.5C for 10s, record every 0.1s, and record the voltage V6 at the end of 10s; adjust the oven temperature to 25℃, let it stand for 180 minutes, finally discharge at 0.1C, the cut-off capacity reaches 0.9A, record every 10s, adjust the temperature to -20℃, let it stand for 180 minutes, record every 10s, record the cut-off voltage V7, then discharge at 0.5C for 10s, record every 0.1s, and record the voltage V8 at the end of 10s.

[0067] DCR at 100% SOC = (V1-V2) / I 0.5C ;

[0068] DCR at 50% SOC = (V3-V4) / I 0.5C ;

[0069] DCR at 30% SOC = (V5-V6) / I 0.5C ;

[0070] DCR at 10% SOC = (V7-V8) / I 0.5C .

[0071] The specific test results are shown in the table below:

[0072] Table 1

[0073]

[0074] From the data in the above table, it can be seen that the embodiment of the present invention coats a type of MAX phase carbonized nanomaterial and superconducting low-temperature nanomaterial on the surface of the basic cobalt-free positive electrode material, which can significantly improve the material conductivity and reduce the low-temperature DCR of the battery. Specifically, the conductivity of the embodiment is significantly greater than that of the comparative example, and comparative example 1 is significantly smaller than comparative examples 2 and 3, indicating that the conductivity of simultaneously coating MAX phase carbonized nanomaterials and superconducting low-temperature nanomaterials is higher than that of coating one of the nanomaterials, and the conductivity of the positive electrode material without coating is the lowest. The same is true for the DCR law under different SOCs at low temperatures. The DCR of the embodiment is significantly smaller than that of the comparative example, and comparative example 1 is significantly greater than comparative examples 2 and 3. Figure 1 This is a comparison chart of the DCR of the buckled battery prepared with the cobalt-free positive electrode material provided in each embodiment and comparative example at -20°C. It can be intuitively seen that the difference is greater at low temperature, especially at low SOC.

[0075] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the scope of protection of the invention.

Claims

1. A cobalt-free positive electrode material, characterized in that: It comprises a basic cobalt-free positive electrode material and a coating layer, wherein the coating layer comprises a MAX phase carbonized nanomaterial and a low-temperature superconducting nanomaterial, wherein the low-temperature superconducting nanomaterial is at least one of NbN and Nb3Sn; The general formula of the MAX phase carbonized nanomaterial is M N+1 AX N , wherein M is one or two of Ti, Nb, Mo, V; A is one of Al, Sn, Si; X is C; N=1 or 2 or 3; The general formula of the basic cobalt-free cathode material is Li a Ni x Mn y O2, where 1≤a≤1.2, 0.5<x<1, x+y=1.

2. The cobalt-free positive electrode material according to claim 1, characterized in that The low-temperature superconducting nanomaterial accounts for 0.1-2% of the mass of the basic cobalt-free positive electrode material.

3. The cobalt-free positive electrode material according to claim 1, characterized in that The MAX phase carbonized nanomaterial accounts for 0.5-10% of the mass of the basic cobalt-free positive electrode material.

4. The cobalt-free positive electrode material according to any one of claims 1 to 3, characterized in that: The MAX phase carbonized nanomaterial includes Ti3AlC2, Nb2AlC, Ti2SnC, V2AlC, Ti3SiC2, Mo2Ti2AlC3 or Mo2TiAlC2 nanomaterial.

5. A method for preparing the cobalt-free positive electrode material according to any one of claims 1 to 4, characterized in that: The steps include: S1, mixing a basic cobalt-free positive electrode material, a MAX phase carbonized nanomaterial and a low-temperature superconducting nanomaterial to obtain a mixed material; S2, calcining the obtained mixed material in a protective atmosphere to obtain the cobalt-free positive electrode material.

6. The method for preparing a cobalt-free positive electrode material according to claim 5, characterized in that: The calcination temperature in step S2 is 500-700° C., and the calcination time is 4-8 hours.

7. The method for preparing a cobalt-free positive electrode material according to claim 5 or 6, characterized in that: Satisfy at least one of the following (1)-(4): (1) The mixing in step S1 is performed at a rotation speed of 2000-4000 rpm for 10-20 min; (2) The basic cobalt-free positive electrode material is a single crystal material, wherein the median particle size D50 is between 2.5-3.5 μm and the specific surface area is between 0.6-0.9 m 2 / g; (3) The median particle size D50 of the MAX phase carbonized nanomaterial is between 50-200 nm; (4) The median particle size D50 of the low-temperature superconducting nanomaterial is between 300-500 nm.

8. A positive electrode sheet, characterized in that: The invention comprises the cobalt-free positive electrode material according to any one of claims 1 to 4 or the cobalt-free positive electrode material prepared by the preparation method according to any one of claims 5 to 7.

9. A secondary battery, characterized in that: Including the positive electrode sheet as described in claim 8.

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