Composite cathode material, preparation method thereof and secondary battery

Abstract

The application provides a composite positive electrode material, a preparation method thereof and a secondary battery. The composite positive electrode material comprises a lithium nickel manganese oxide positive electrode material core and a polymer coating layer coated on the surface of the lithium nickel manganese oxide positive electrode material core; and the material of the polymer coating layer comprises cyanuric chloride. The composite positive electrode material provided by the application can not only reduce the dissolution of manganese ions, but also avoid the corrosion of hydrogen fluoride on the positive electrode material.

Description

Technical Field

[0001] This invention belongs to the field of cathode material technology, specifically relating to a composite cathode material, its preparation method, and a secondary battery. Background Technology

[0002] Since the 1990s, lithium-ion batteries have been successfully commercialized. With rapid technological advancements and increasing market demand, the energy density and cycle performance of electrode materials need further improvement. Spinel lithium nickel manganese oxide (LiMO) materials have attracted widespread attention due to their advantages of low cost and high voltage. However, on the one hand, under high voltage, LiMO materials are prone to the Jan Taylor effect, resulting in lattice distortion and reduced material symmetry. This hinders the rapid diffusion of lithium ions, leading to poorer electrochemical performance of the assembled battery. On the other hand, the decomposition reaction of the electrolyte is more severe under high voltage. Trace amounts of water can react with the electrolyte to generate hydrogen fluoride, which attacks the cathode material and accelerates the dissolution of manganese ions, causing material failure.

[0003] In summary, the continuous decomposition of the electrolyte and interfacial contact cause the SEI film to continuously decompose and form, gradually thickening and leading to rapid loss of active lithium ions. Simultaneously, the continuous deposition of manganese ions on the negative electrode side increases the battery's impedance, further affecting its capacity.

[0004] Therefore, there is an urgent need in this field to develop a cathode material that not only avoids the leaching of manganese ions but also mitigates the destructive effect of hydrogen fluoride on the cathode material structure. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a composite cathode material, its preparation method, and a secondary battery. The composite cathode material provided by this invention not only reduces the dissolution of manganese ions but also avoids the corrosive effect of hydrogen fluoride on the cathode material.

[0006] To achieve this objective, the present invention employs the following technical solution:

[0007] In a first aspect, the present invention provides a composite cathode material, the composite cathode material comprising a lithium nickel manganese oxide cathode material core and a polymer coating layer covering the surface of the lithium nickel manganese oxide cathode material core;

[0008] The polymer coating material includes cyanochlorotricyanurate.

[0009] This invention employs a cyanochlorotrioxide coating layer to fully coat the surface of lithium nickel manganese oxide cathode material. The cyanochlorotrioxide coating layer carries a positive charge, and through electrostatic repulsion, it can selectively separate monovalent cations (lithium ions) and divalent cations (manganese ions), thereby trapping divalent manganese ions. Other related positively charged organic compounds, due to their excessively large or small charges, have been tested and found unable to effectively selectively separate monovalent and divalent cations, thus failing to prevent manganese ions from attacking the material surface. Furthermore, many organic polymers are highly toxic and difficult to dissolve, resulting in poor coating effects and hindering their effectiveness in coating the cathode material surface. This invention, by coating the cathode material surface with cyanochlorotrioxide, effectively prevents manganese ions from attacking the cathode material surface, thereby reducing manganese ion dissolution. Furthermore, as a coating layer, it also reduces the contact area between the electrolyte and the cathode material, thus mitigating the corrosive effect of the electrolyte on the material.

[0010] Preferably, the chemical formula of the lithium nickel manganese oxide cathode material is LiNi. 0.5 Mn 1.5 O4.

[0011] Preferably, the average particle size of the lithium nickel manganese oxide cathode material is 4-12 μm, for example, it can be 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, etc.

[0012] Preferably, the monomer of the cyanochlorotricyanurate has the structural formula shown in Formula 1:

[0013]

[0014] The value of n is in the range of 0 < n < 6, preferably 3, and can be 1, 2, 3, 4, or 5.

[0015] In this invention, by adjusting the range of n, the adsorption of manganese ions is improved; if the value of n is too large, the selective adsorption of manganese ions will be poor.

[0016] Preferably, based on the total mass of the composite cathode material as 100%, the mass percentage of the lithium nickel manganese oxide cathode material core is 95%-99.9%, preferably 99.2%, and can be, for example, 95%, 96%, 97%, 98%, 99%, 99.2%, 99.5%, 99.9%, etc.

[0017] In this invention, the cycle performance of the battery is improved by adjusting the mass percentage content of the lithium nickel manganese oxide cathode material core. If the content is too low, the specific capacity will be low, and vice versa.

[0018] Preferably, based on the total mass of the composite cathode material as 100%, the mass percentage of the polymer coating layer is 0.5%-5%, preferably 0.8%, for example, it can be 0.5%, 0.8%, 1%, 1.5%, 2%, 3%, 4%, 5%, etc.

[0019] In this invention, the optimal cycling performance of the material is achieved by adjusting the mass percentage content of the polymer coating layer. If the content is too low, there will be no significant effect, while if it is too high, the battery internal resistance will increase and the rate performance will decrease.

[0020] Preferably, the mass ratio of the lithium nickel manganese oxide cathode material core to the polymer coating layer is (90-130):1, more preferably 124:1, and for example, it can be 90:1, 100:1, 110:1, 115:1, 120:1, 124:1, 130:1, etc.

[0021] In this invention, the battery cycle performance is optimized by adjusting the mass ratio of the lithium nickel manganese oxide cathode material core to the polymer coating layer. If the mass ratio is too low, the improvement effect will be insignificant, while if it is too high, the internal resistance of the material will increase.

[0022] Preferably, the pore size of the polymer coating layer is 10-100nm, for example, it can be 10nm, 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, etc.; the thickness is 5-20nm, for example, it can be 5nm, 7nm, 10nm, 15nm, 18nm, 20nm, etc.

[0023] In this invention, by adjusting the pore size and thickness of the polymer coating layer, the coating can be uniformly coated on the material surface without affecting the extraction and insertion of lithium ions.

[0024] In a second aspect, the present invention provides a method for preparing the composite cathode material according to the first aspect, the method comprising the following steps:

[0025] An organic solution containing cyanuric chloride is mixed with lithium nickel manganese oxide cathode material, and the solvent is removed to obtain the composite cathode material.

[0026] In this invention, the structural formula of the monomer of cyanochlorotricyanurate is shown in Formula 1:

[0027]

[0028] The value of n is in the range of 0 < n < 6, preferably 3, and can be 1, 2, 3, 4, or 5.

[0029] Preferably, the mass concentration of the cyanochlorotricyanurate is 1-10%, more preferably 1-5%, for example, it can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, etc.

[0030] Preferably, the solvent in the organic solution containing cyanochlorotricyanurate includes any one or a combination of at least two of N-methylpyrrolidone, anhydrous ethanol, cyclohexane, or acetone, for example, cyclohexane.

[0031] Preferably, the mass ratio of cyanochlorotricyanurate to lithium nickel manganese oxide cathode material is (0.005-0.02):1, more preferably (0.008-0.015):1, and for example, it can be 0.005:1, 0.008:1, 0.01:1, 0.011:1, 0.012:1, 0.013:1, 0.014:1, 0.015:1, 0.018:1, 0.02:1, etc.

[0032] Preferably, the mixing temperature is 60°C.

[0033] In this invention, the method for removing the solvent includes, but is not limited to, evaporation, with the evaporation temperature being 40-80°C, for example, 40°C, 50°C, 60°C, 70°C, 80°C, etc.; by further limiting the evaporation temperature, this invention achieves the best coating effect of cyanuric chloride.

[0034] Preferably, the solvent removal process further includes a grinding process.

[0035] Thirdly, the present invention provides a secondary battery comprising a positive electrode, a negative electrode, an electrolyte, and a separator, wherein the positive electrode comprises a composite positive electrode material according to the first aspect.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] This invention provides a composite cathode material in which a cyanochloride coating layer is used to fully coat the surface of a lithium nickel manganese oxide cathode material. The cyanochloride coating layer carries a positive charge, and through electrostatic repulsion, it can selectively separate monovalent cations (lithium ions) and divalent cations (manganese ions), thereby retaining divalent manganese ions. By coating the cathode material surface with cyanochloride, this invention effectively prevents manganese ions from attacking the cathode material surface, thus reducing manganese ion dissolution. Furthermore, as a coating layer, it also reduces the contact area between the electrolyte and the cathode material, thereby mitigating the corrosive effect of the electrolyte on the material. Detailed Implementation

[0038] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0039] Example 1

[0040] This embodiment provides a composite cathode material, comprising a lithium nickel manganese oxide cathode material core (average particle size of 6 μm) and a cyanochloride coating layer (thickness of 7 nm, pore size of 30 nm) covering the surface of the lithium nickel manganese oxide cathode material core; the mass ratio of the lithium nickel manganese oxide cathode material core to the cyanochloride coating layer is 124:1. Based on the total mass of the composite cathode material as 100%, the mass percentage of the lithium nickel manganese oxide cathode material core is 99.2%, and the mass percentage of the cyanochloride coating layer is 0.8%.

[0041] This embodiment also provides a method for preparing the above-mentioned composite cathode material, which includes the following steps:

[0042] (1) Add cyanuric chloride powder (purchased from Shanghai Xianding Biotechnology Co., Ltd.) to a beaker, and add an appropriate amount of cyclohexane organic solvent to the beaker while stirring to dissolve the powder completely;

[0043] (2) Add lithium nickel manganese oxide material to the beaker containing dissolved cyanuric chloride powder, place the beaker in a constant temperature water bath and stir to evaporate the solution;

[0044] (3) The evaporated materials are mixed and ground to obtain composite cathode materials.

[0045] Example 2

[0046] This embodiment provides a composite cathode material, comprising a lithium nickel manganese oxide cathode material core (average particle size of 10 μm) and a cyanochloride coating layer (thickness of 10 nm, pore size of 15 nm) covering the surface of the lithium nickel manganese oxide cathode material core; the mass ratio of the lithium nickel manganese oxide cathode material core to the cyanochloride coating layer is 99:1. Based on the total mass of the composite cathode material as 100%, the mass percentage of the lithium nickel manganese oxide cathode material core is 99%, and the mass percentage of the cyanochloride coating layer is 1%.

[0047] This embodiment also provides a method for preparing the above-mentioned composite cathode material, which includes the following steps:

[0048] (1) Add cyanuric chloride powder (purchased from Shanghai Xianding Biotechnology Co., Ltd.) to a beaker, and add an appropriate amount of anhydrous ethanol organic solvent to the beaker while stirring to dissolve the powder completely;

[0049] (2) Add lithium nickel manganese oxide material to the beaker containing dissolved cyanuric chloride powder, place the beaker in a constant temperature water bath and stir to evaporate the solution;

[0050] (3) The evaporated materials are mixed and ground to obtain composite cathode materials.

[0051] Example 3

[0052] This embodiment provides a composite cathode material, comprising a lithium nickel manganese oxide cathode material core (average particle size of 4 μm) and a cyanochloride coating layer (thickness of 15 nm, pore size of 50 nm) covering the surface of the lithium nickel manganese oxide cathode material core; the mass ratio of the lithium nickel manganese oxide cathode material core to the cyanochloride coating layer is 124:1. Based on the total mass of the composite cathode material as 100%, the mass percentage of the lithium nickel manganese oxide cathode material core is 99.2%, and the mass percentage of the cyanochloride coating layer is 0.8%.

[0053] This embodiment also provides a method for preparing the above-mentioned composite cathode material, which includes the following steps:

[0054] (1) Add cyanuric chloride powder (purchased from Shanghai Xianding Biotechnology Co., Ltd.) to a beaker, and add an appropriate amount of acetone organic solvent to the beaker while stirring to dissolve the powder completely;

[0055] (2) Add lithium nickel manganese oxide material to the beaker containing dissolved cyanuric chloride powder, place the beaker in a constant temperature water bath and stir to evaporate the solution;

[0056] (3) The evaporated materials are mixed and ground to obtain composite cathode materials.

[0057] Example 4

[0058] The difference between this embodiment and Embodiment 1 is that, taking the total mass of the composite cathode material as 100%, the mass percentage of the polymer coating layer is 0.2%, while all other aspects are the same as in Embodiment 1.

[0059] Example 5

[0060] The difference between this embodiment and Embodiment 1 is that, taking the total mass of the composite cathode material as 100%, the mass percentage of the polymer coating layer is 10%, while everything else is the same as in Embodiment 1.

[0061] Example 6

[0062] The difference between this embodiment and Embodiment 1 is that the mass ratio of the lithium nickel manganese oxide cathode material core to the polymer coating layer is 80:1, while all other aspects are the same as in Embodiment 1.

[0063] Example 7

[0064] The difference between this embodiment and Embodiment 1 is that the mass ratio of the lithium nickel manganese oxide cathode material core to the polymer coating layer is 140:1, while all other aspects are the same as in Embodiment 1.

[0065] Comparative Example 1

[0066] The difference between this comparative example and Example 1 is that the cyanuric chloride polymer coating layer is replaced with a carbon coating layer, while all other aspects are the same as in Example 1.

[0067] Comparative Example 2

[0068] The difference between this comparative example and Example 1 is that the cyanuric chloride polymer coating layer is replaced with a polyaniline coating layer; otherwise, they are the same as in Example 1.

[0069] Application Examples 1 to 7 and Comparative Application Examples 1 to 2

[0070] Lithium-ion batteries were prepared using the composite cathode materials provided in Examples 1 to 7 and Comparative Examples 1 to 2, and the preparation methods are as follows:

[0071] The above-mentioned composite cathode material, conductive carbon black, polyvinylidene fluoride binder, and a small amount of N-methylpyrrolidone are thoroughly mixed to form a uniform slurry, which is then coated onto an aluminum foil substrate as a test electrode. The treated separator is cut into a circle with a diameter of 19 mm for the assembly of lithium nickel manganese oxide / graphite coin cells.

[0072] Test conditions

[0073] The lithium-ion batteries provided in Application Examples 1 to 7 and Comparative Application Examples 1 to 2 were tested using the following methods:

[0074] Button assembly:

[0075] 1. The treated powder is thoroughly mixed with conductive carbon black (conductive agent) and polyvinylidene fluoride (PVDF binder) in a ratio of 94:3:3, along with a small amount of N-methylpyrrolidone, to form a uniform slurry. This slurry is then coated onto an aluminum foil substrate, vacuumed, and dried.

[0076] 2. Cut the dried sheet into circular electrode sheets with a diameter of 12mm, and roll them to a certain compaction density for later use.

[0077] 3. Cut the prepared diaphragm into circles with a diameter of 19mm and set aside.

[0078] 4. In a vacuum glove box, assemble the negative electrode shell, spring, gasket, lithium sheet, separator and positive electrode in a certain order, and add an appropriate amount of electrolyte to form a button cell.

[0079] Test conditions:

[0080] The assembled button cells were then subjected to the following tests:

[0081] 1. Under constant temperature of 25℃, with a starting and ending voltage of 3.5V-4.6V and a charging and discharging current of 0.1C, perform 3 cycles and record the charging and discharging capacity of the first cycle.

[0082] 2. After the cycle in step 1, under the conditions of constant temperature of 25℃, start and stop voltage of 3.5V-4.6V, and charge and discharge current of 1C, cycle 100 times, record the charge and discharge capacity, and calculate the capacity retention rate.

[0083] The test results are shown in Table 1:

[0084] Table 1

[0085] Application Example 1 89.4 Application Example 2 88.5 Application Example 3 88.1 Application Example 4 87.2 Application Example 5 84.2 Application Example 6 83.9 Application Example 7 82.7 Comparative Application Example 1 85.7 Comparative Application Example 2 79.2

[0086] As shown in Table 1, this invention uses a cyanoacrylate polymer coating layer and adjusts the appropriate amounts of both the cyanoacrylate and lithium nickel manganese oxide cathode materials to affect the LiNi... 0.5 Mn 1.5 Coating with O4 material can effectively improve the capacity retention rate of the material, thereby improving its electrochemical performance.

[0087] Compared with Application Example 1, Application Examples 4-5 show that insufficient content of cyanuric chloride polymer coating layer cannot effectively improve cycle performance, while excessive coating amount will increase the internal resistance of the material and deteriorate the cycle performance of the material.

[0088] Compared to Application Example 1, Application Examples 6-7 demonstrate that by adjusting the mass ratio of the lithium nickel manganese oxide cathode material core to the polymer coating layer, the cycle performance of the battery is optimized.

[0089] Comparative application examples 1-2 demonstrate that selecting unsuitable materials to coat LiNi is inappropriate. 0.5 Mn 1.5 O4 materials not only fail to improve the cycling performance of materials, but also increase the internal resistance of materials due to the introduction of impurities, thereby reducing the cycling performance and rate performance of materials and causing them to fail rapidly.

[0090] The applicant declares that the present invention is illustrated by the above embodiments, but the present invention is not limited to the above process steps, that is, it does not mean that the present invention must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials used in the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A composite cathode material, characterized in that, The composite cathode material includes a lithium nickel manganese oxide cathode material core and a polymer coating layer covering the surface of the lithium nickel manganese oxide cathode material core; The polymer coating material includes cyanochlorotricyanurate.

2. The composite cathode material according to claim 1, characterized in that, The chemical formula of the lithium nickel manganese oxide cathode material is LiNi 0.5 Mn 1.5 O4.

3. The composite cathode material according to claim 1, characterized in that, The average particle size of the lithium nickel manganese oxide cathode material is 4-12 μm.

4. The composite cathode material according to claim 1, characterized in that, Based on the total mass of the composite cathode material being 100%, the mass percentage of the lithium nickel manganese oxide cathode material core is 95%-99.9%.

5. The composite cathode material according to claim 4, characterized in that, Based on the total mass of the composite cathode material being 100%, the mass percentage of the lithium nickel manganese oxide cathode material core is 99.2%.

6. The composite cathode material according to claim 1, characterized in that, Based on the total mass of the composite cathode material being 100%, the mass percentage of the polymer coating layer is 0.5%-5%.

7. The composite cathode material according to claim 6, characterized in that, Based on the total mass of the composite cathode material being 100%, the polymer coating layer has a mass percentage content of 0.8%.

8. The composite cathode material according to claim 1, characterized in that, The mass ratio of the lithium nickel manganese oxide cathode material core to the polymer coating layer is (90-130):

1.

9. The composite cathode material according to claim 8, characterized in that, The mass ratio of the lithium nickel manganese oxide cathode material core to the polymer coating layer is 124:

1.

10. The composite cathode material according to claim 1, characterized in that, The polymer coating has a pore size of 10-100 nm and a thickness of 5-20 nm.

11. A method for preparing a composite cathode material according to any one of claims 1-10, characterized in that, The method includes the following steps: An organic solution containing cyanuric chloride is mixed with lithium nickel manganese oxide cathode material, and the solvent is removed to obtain the composite cathode material.

12. The method according to claim 11, characterized in that, The mass concentration of the cyanochlorotrichloride is 1-10%.

13. The method according to claim 12, characterized in that, The mass concentration of the cyanochlorotrichloride is 1-5%.

14. The method according to claim 11, characterized in that, The solvent in the organic solution containing cyanuric chloride includes any one or a combination of at least two of N-methylpyrrolidone, anhydrous ethanol, cyclohexane, or acetone.

15. The method according to claim 11, characterized in that, The mass ratio of cyanochlorotricyanurate to lithium nickel manganese oxide cathode material is (0.005-0.02):

1.

16. The method according to claim 15, characterized in that, The mass ratio of cyanochlorotricyanurate to lithium nickel manganese oxide cathode material is (0.008-0.015):

1.

17. The method according to claim 11, characterized in that, The mixing temperature is 60°C.

18. The method according to claim 11, characterized in that, The process after solvent removal also includes grinding.

19. A secondary battery, characterized in that, The secondary battery includes a positive electrode, a negative electrode, an electrolyte, and a separator, wherein the positive electrode includes a composite positive electrode material according to any one of claims 1-10.

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