A gradient ternary cathode material, its preparation method and application

Abstract

This invention provides a gradient ternary cathode material, its preparation method, and its application. The preparation method includes the following steps: (1) mixing a nickel source and a manganese source with a solvent to obtain solution A, mixing a cobalt source with a solvent to obtain solution B, and simultaneously adding solution A, liquid alkali, and ammonia to the bottom liquid for reaction. After the particle D50 reaches 5-8 μm, solution A is replaced with solution B to continue the reaction and obtain a cobalt-coated nickel-manganese binary precursor; (2) mixing the cobalt-coated nickel-manganese binary precursor with a lithium source and then performing sintering treatment to obtain a core material. Using liquid organic matter as a carbon source, graphene is coated on the surface of the core material using atomic layer deposition to obtain the gradient ternary cathode material. The cobalt metal concentration in the gradient ternary cathode material gradually increases from the inside to the outside, improving the rate performance and structural stability of the material. The single-layer graphene coating maximizes the rate performance and cycle performance of the material.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion batteries and relates to a gradient ternary cathode material, its preparation method, and its application. Background Technology

[0002] With the development of new energy vehicles, lithium-ion power batteries have attracted much attention as the most popular power batteries for electric vehicles. High-nickel, low-cobalt ternary materials have high energy density, and the low cobalt content can reduce raw material costs, making them a popular material for commercial cathodes. However, as the nickel content increases, issues such as thermal stability and structural stability become particularly prominent.

[0003] The primary function of coating is to act as a protective layer, isolating the electrolyte from direct contact with the active electrode material. This significantly reduces a series of side reactions, such as decreasing transition metal deposition, forming a thinner SEI film, and reducing oxygen atom deposition, thereby improving electrochemical stability. Graphene, due to its ultra-high conductivity, large specific surface area, and strong mechanical properties, has been widely used in numerous fields, including lithium-ion batteries, sodium-ion batteries, and supercapacitors. As a coating material, graphene can effectively improve electronic conductivity, compensating for the negative impacts of low cobalt content, such as high battery impedance and rapid cycle failure.

[0004] CN110311136A discloses a graphene-coated ternary cathode material for lithium-ion batteries. The graphene is uniformly dispersed between the ternary cathode material particles, and the graphene on the surface of the ternary cathode plays a "fixing" role on the O atoms on the material surface, thereby stabilizing the material structure.

[0005] CN112002896A discloses a method for preparing a lithium-ion battery electrode containing graphene-coated single-crystal cathode material. The steps include mixing the graphene-coated single-crystal cathode material with a conductive agent and a binder, then adding N-methylpyrrolidone to adjust the solid content, and finally coating it onto a current collector to obtain the electrode.

[0006] The above-mentioned solution has limited controllability of graphene coating thickness and a high cobalt content, resulting in high cost and low capacity, which greatly limits the application of ternary cathode materials. Summary of the Invention

[0007] The purpose of this invention is to provide a gradient ternary cathode material, its preparation method, and its application. In the gradient ternary cathode material, the cobalt metal concentration gradually increases from the inside to the outside, thereby improving the rate performance and structural stability of the material. The single-layer graphene coating maximizes the rate performance and cycle performance of the material.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a method for preparing a gradient ternary cathode material, the method comprising the following steps:

[0010] (1) Mix the nickel source and manganese source with the solvent to obtain solution A, mix the cobalt source with the solvent to obtain solution B, add solution A, liquid alkali and ammonia water to the bottom liquid at the same time to react, and after the particle D50 reaches 5-8 μm, replace solution A with solution B to continue the reaction to obtain cobalt-coated nickel-manganese binary precursor.

[0011] (2) After mixing the cobalt-coated nickel-manganese binary precursor and the lithium source, the core material is obtained by sintering. Using liquid organic matter as the carbon source, graphene is coated on the surface of the core material by atomic layer deposition to obtain the gradient ternary cathode material.

[0012] This invention forms a ternary material with a cobalt element concentration gradient distribution through post-sintering diffusion, effectively solving the problem of poor consistency in gradient material production. Furthermore, the cobalt element gradient distribution is beneficial to improving the rate performance of the material. An atomic layer deposition method is used to coat the material surface with a layer of graphene. The atomic layer deposition method can achieve single-layer graphene coating, which greatly improves the conductivity, rate performance and cycle performance of the material.

[0013] In the preparation method of the gradient ternary cathode material of the present invention, graphene coating is performed immediately after sintering, eliminating the need for water washing and secondary sintering, thus reducing processing costs.

[0014] Preferably, the nickel source in step (1) includes any one or a combination of at least two of nickel sulfate, nickel chloride, or nickel nitrate.

[0015] Preferably, the manganese source includes any one or a combination of at least two of manganese sulfate, manganese chloride, or manganese nitrate.

[0016] Preferably, the cobalt source includes any one or a combination of at least two of cobalt sulfate, cobalt chloride, or cobalt nitrate.

[0017] Preferably, the molar ratio of nickel ions to manganese ions in solution A is (90-98):(2-10), for example: 90:10, 92:8, 95:5, 96:4 or 98:2, etc.

[0018] Preferably, the mass concentration of the liquid alkali in step (1) is 30-35%, for example: 30%, 31%, 32%, 33%, 34% or 35%, etc.

[0019] Preferably, the mass concentration of the ammonia water is 12-18%, for example: 12%, 14%, 16% or 18%, etc.

[0020] Preferably, the pH of the base solution in step (1) is 11 to 13, for example: 11, 11.5, 12, 12.5 or 13, and more preferably 11.6 to 11.8.

[0021] Preferably, the ammonia concentration of the base liquid is 5-20 g / L, for example: 5 g / L, 8 g / L, 10 g / L, 15 g / L or 20 g / L, and more preferably 10-12 g / L.

[0022] Preferably, the reaction temperature is 40 to 80°C, for example: 40°C, 50°C, 60°C, 70°C or 80°C.

[0023] Preferably, the reaction is carried out while stirring.

[0024] Preferably, the stirring speed is 100 to 500 rpm, for example: 100 rpm, 200 rpm, 300 rpm, 400 rpm or 500 rpm.

[0025] Preferably, the flow rate of solution A is 200-400 L / h, for example: 200 L / h, 250 L / h, 300 L / h, 350 L / h or 400 L / h, etc.

[0026] Preferably, the flow rate of the liquid alkali is 80-120 L / h, for example: 80 L / h, 90 L / h, 100 L / h, 110 L / h or 120 L / h, etc.

[0027] Preferably, the flow rate of the ammonia water is 50-80 L / h, for example: 50 L / h, 55 L / h, 60 L / h, 70 L / h or 80 L / h.

[0028] Preferably, the sintering temperature in step (2) is 600 to 1000°C, for example: 600°C, 700°C, 800°C, 900°C or 1000°C.

[0029] Preferably, the sintering treatment time is 10 to 20 hours, for example: 10 hours, 12 hours, 15 hours, 18 hours or 20 hours.

[0030] Preferably, the liquid organic matter in step (2) includes any one or a combination of at least two of nitrobenzene, bromobenzene, carbon tetrachloride, chloroform, bromohydrocarbons, ethylene glycol or glycerol.

[0031] In a second aspect, the present invention provides a gradient ternary cathode material, which is prepared by the method described in the first aspect.

[0032] Preferably, the gradient ternary cathode material includes a core and a single-layer graphene coating layer covering the surface of the core.

[0033] Preferably, the cobalt element in the core increases in a gradient from the inside to the outside.

[0034] In the gradient ternary cathode material described in this invention, the cobalt metal concentration gradually increases from the inside out, improving the rate performance and structural stability of the material. The single-layer graphene coating maximizes the rate performance and cycle performance of the material.

[0035] Thirdly, the present invention provides a positive electrode sheet comprising a gradient ternary positive electrode material as described in the second aspect.

[0036] Fourthly, the present invention provides a lithium-ion battery comprising a positive electrode as described in the first aspect.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] (1) The present invention forms a ternary material with a cobalt element concentration gradient distribution through post-sintering diffusion, which effectively solves the problem of poor consistency in gradient material production. Furthermore, the cobalt element gradient distribution is beneficial to improving the rate performance of the material. A layer of graphene is coated on the surface of the material using atomic layer deposition. The atomic layer deposition method can achieve single-layer graphene coating, which greatly improves the conductivity, rate performance and cycle performance of the material.

[0039] (2) The structural stability of the material after cobalt coating is improved. The electronic conductivity of the material after graphene coating is significantly improved, while the ionic conductivity is not reduced (compared to coating inert materials such as Al, Zr and Ti). At the same time, since there is no water washing to damage the surface structure, the NiO-type rock salt phase is thinner in the surface area, the side reaction is reduced, which is more conducive to the deintercalation and intercalation of lithium ions, thereby improving the cycle performance.

[0040] (3) The battery made of the ternary cathode material described in this invention has a charging specific capacity of more than 250 mAh / g, a discharge specific capacity of more than 229.4 mAh / g, an initial efficiency of more than 91.6%, a 1C rate performance of more than 218 mAh / g, a 5C rate performance of more than 180 mAh / g, and a capacity retention rate of more than 97%. Detailed Implementation

[0041] 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.

[0042] Example 1

[0043] This embodiment provides a gradient ternary cathode material, and the preparation method of the gradient ternary cathode material is as follows:

[0044] (1) Prepare a 2 mol / L aqueous solution A by mixing nickel sulfate and manganese sulfate in a molar ratio of 95:5, and prepare a 2 mol / L aqueous solution B by mixing cobalt sulfate. Use 32% industrial alkali as a precipitant and 16% ammonia as a complexing agent. Add 3000L of pure water to the reactor and introduce N2 as a protective gas. Add alkali to adjust the pH to 12.0, add ammonia to adjust the ammonia concentration to 10g / L, control the temperature at 80℃, and control the stirring speed at 450rpm. Combine solution A, alkali, and... Ammonia water was simultaneously added to the reactor at rates of 300 L / h, 100 L / h, and 60 L / h, maintaining the pH at 11.6-11.8, the ammonia concentration at 10-12 g / L, the temperature at 80℃, and the rotation speed at 450 rpm. After the D50 reached 6 μm, solution A was replaced with solution B, the reaction pH was adjusted to 11.0-11.2, and the reaction was continued for 2 hours before the feed was stopped. The resulting slurry was washed, dried, sieved, iron removed, and packaged to obtain the cobalt-coated NM95 / 5 nickel-manganese binary precursor.

[0045] (2) The cobalt-coated NM95 / 5 binary precursor was mixed with lithium hydroxide monohydrate and sintered at 680°C for 12 hours in an oxygen atmosphere to obtain a core material with a cobalt gradient distribution. Using ethylene glycol as the carbon source, a layer of graphene was coated on the surface of the core material by atomic layer deposition to obtain a graphene-coated gradient NCM90 / 5 / 5 ternary material.

[0046] Example 2

[0047] This embodiment provides a gradient ternary cathode material, and the preparation method of the gradient ternary cathode material is as follows:

[0048] (1) Prepare a 2 mol / L aqueous solution A by mixing nickel sulfate and manganese sulfate in a molar ratio of 96:4, and prepare a 2 mol / L aqueous solution B by mixing cobalt sulfate. Use 32% industrial alkali as a precipitant and 17% ammonia as a complexing agent. Add 3000L of pure water to the reactor and introduce N2 as a protective gas. Add alkali to adjust the pH to 12.2, add ammonia to adjust the ammonia concentration to 10g / L, control the temperature at 80℃, and control the stirring speed at 480rpm. Combine solution A, alkali, and... Ammonia water was simultaneously added to the reactor at rates of 300 L / h, 100 L / h, and 60 L / h, maintaining the pH at 12.0-12.2, the ammonia concentration at 10-12 g / L, the temperature at 80℃, and the rotation speed at 450 rpm. After the D50 reached 6 μm, solution A was replaced with solution B, the reaction pH was adjusted to 11.0-11.2, and the reaction was continued for 2 hours before the feed was stopped. The resulting slurry was washed, dried, sieved, iron removed, and packaged to obtain the cobalt-coated NM95 / 5 nickel-manganese binary precursor.

[0049] (2) The cobalt-coated NM95 / 5 binary precursor was mixed with lithium hydroxide monohydrate and sintered at 690°C for 12 hours in an oxygen atmosphere to obtain a core material with a cobalt gradient distribution. Using ethylene glycol as the carbon source, a layer of graphene was coated on the surface of the core material by atomic layer deposition to obtain a graphene-coated gradient NCM96 / 4 / 5 ternary material.

[0050] Example 3

[0051] The only difference between this embodiment and Example 1 is that the pH of the reaction in step (1) is 11.2-11.4, while the other conditions and parameters are exactly the same as in Example 1.

[0052] Example 4

[0053] The only difference between this embodiment and Example 1 is that the pH of the reaction in step (1) is 11.0-11.2, while the other conditions and parameters are exactly the same as in Example 1.

[0054] Example 5

[0055] The only difference between this embodiment and Example 1 is that the ammonia concentration in step (1) is 14-16 g / L, while the other conditions and parameters are exactly the same as in Example 1.

[0056] Example 6

[0057] The only difference between this embodiment and Embodiment 1 is that the ammonia concentration in step (1) is 6-8 g / L, while the other conditions and parameters are exactly the same as in Embodiment 1.

[0058] Comparative Example 1

[0059] The only difference between this comparative example and Example 1 is that solution B was added when the D50 reached 4 μm; all other conditions and parameters were exactly the same as in Example 1.

[0060] Comparative Example 2

[0061] The only difference between this comparative example and Example 1 is that solution B was added when the D50 reached 10 μm; all other conditions and parameters were exactly the same as in Example 1.

[0062] Comparative Example 3

[0063] The only difference between this comparative example and Example 1 is that conventional solid-state mixed sintering coating is used to coat graphene onto the core surface; all other conditions and parameters are exactly the same as in Example 1.

[0064] Performance testing:

[0065] The prepared positive electrode material was mixed uniformly with conductive agent acetylene black and binder PVDF in a mass ratio of 92:4:4. An appropriate amount of 1-methyl-2-pyrrolidone was added, and the mixture was ball-milled for 1 hour to form a slurry. This slurry was then uniformly coated onto an aluminum sheet, dried, and pressed to form the positive electrode sheet. A 2032 coin cell was assembled using a lithium metal sheet as the negative electrode. Electrical performance was tested using a Blue Electric testing system with a charge / discharge voltage of 2.5-4.25V. The first cycle was performed at 0.2 / 0.2C, followed by 50 cycles at 0.5C / 1C.

[0066] The test results are shown in Table 1:

[0067] Table 1

[0068]

[0069]

[0070] As shown in Table 1, and based on Examples 1-2, the battery made from the ternary cathode material of the present invention has a charge specific capacity of over 250 mAh / g, a discharge specific capacity of over 229.4 mAh / g, an initial efficiency of over 91.6%, a 1C rate performance of over 218 mAh / g, a 5C rate performance of over 180 mAh / g, a capacity retention rate of over 97%, a high precursor reaction pH, high discharge specific capacity, good rate performance, and excellent cycle performance.

[0071] A comparison of Examples 1 and 3-4 shows that during the preparation of the gradient ternary cathode material of the present invention, the pH of the precursor reaction affects the performance of the cathode material. Controlling the reaction pH at 11.6-11.8 results in a cathode material with better performance. If the pH is too high, a large amount of fine powder will be generated, and the cycle performance will deteriorate. If the pH is too low, the primary particles will be too coarse, and the reduced porosity will affect the lithium-ion insertion / extraction.

[0072] A comparison of Examples 1 and 5-6 shows that the concentration of ammonia in the precursor reaction process during the preparation of the gradient ternary cathode material of the present invention affects the performance of the cathode material. Controlling the ammonia concentration at 10-12 g / L results in a cathode material with better performance. If the ammonia concentration is too high, the metal precipitation will be incomplete; if the ammonia concentration is too low, it will affect the electrochemical performance of the finished product.

[0073] As can be seen from the comparison between Example 1 and Comparative Examples 1-2, the timing of adding solution B during the preparation of the gradient ternary cathode material of the present invention affects the performance of the cathode material. Adding solution B when the particle D50 reaches 5-8 μm results in a cathode material with better performance. If the addition time is too early, the cobalt coating layer is too thick, making it difficult for the cobalt to diffuse completely during subsequent sintering; if the addition time is too late, the cobalt coating layer is too thin, resulting in insufficient cobalt content. Neither of these conditions can achieve the optimal performance of the material.

[0074] As can be seen from the comparison between Example 1 and Comparative Example 3, the present invention uses atomic layer deposition to coat a layer of graphene on the surface of a material. The atomic layer deposition method can achieve single-layer graphene coating, which greatly improves the conductivity, rate performance and cycle performance of the material.

[0075] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing a gradient ternary cathode material, characterized in that, The preparation method includes the following steps: (1) Mix the nickel source and manganese source with the solvent to obtain solution A, and mix the cobalt source with the solvent to obtain solution B. Add solution A, liquid alkali and ammonia water to the bottom solution at the same time to carry out the reaction. Keep the pH at 11.6-11.8 and the ammonia concentration at 10-12 g / L. After the particle D50 reaches 5~8 μm, replace solution A with solution B, adjust the reaction pH to 11.0-11.2 and continue the reaction to obtain cobalt-coated nickel-manganese binary precursor; (2) After mixing the cobalt-coated nickel-manganese binary precursor and the lithium source, the mixture is sintered at 600~1000℃ to obtain a core material with a cobalt element gradient from the inside to the outside. Using liquid organic matter as the carbon source, a single layer of graphene is coated on the surface of the core material by atomic layer deposition to obtain the gradient ternary cathode material.

2. The preparation method according to claim 1, characterized in that, The nickel source in step (1) includes any one or a combination of at least two of nickel sulfate, nickel chloride, or nickel nitrate.

3. The preparation method according to claim 1, characterized in that, The manganese source includes any one or a combination of at least two of manganese sulfate, manganese chloride, or manganese nitrate.

4. The preparation method according to claim 1, characterized in that, The cobalt source includes any one or a combination of at least two of cobalt sulfate, cobalt chloride, or cobalt nitrate.

5. The preparation method according to claim 1, characterized in that, The molar ratio of nickel ions to manganese ions in solution A is (90~98):(2~10).

6. The preparation method according to claim 1, characterized in that, The molar concentration of solution B is 1.5~2.5 mol / L.

7. The preparation method according to claim 1, characterized in that, The mass concentration of the liquid alkali in step (1) is 30~35%.

8. The preparation method according to claim 1, characterized in that, The mass concentration of the ammonia water is 12-18%.

9. The preparation method according to claim 1, characterized in that, The reaction temperature is 40~80℃.

10. The preparation method according to claim 1, characterized in that, The reaction is carried out while stirring.

11. The preparation method according to claim 10, characterized in that, The stirring speed is 100~500 rpm.

12. The preparation method according to claim 1, characterized in that, The flow rate of solution A is 200~400 L / h.

13. The preparation method according to claim 1, characterized in that, The flow rate of the liquid alkali is 80~120 L / h.

14. The preparation method according to claim 1, characterized in that, The flow rate of the ammonia water is 50~80L / h.

15. The preparation method according to claim 1, characterized in that, The sintering process takes 10 to 20 hours.

16. The preparation method according to claim 1, characterized in that, The liquid organic matter in step (2) includes any one or a combination of at least two of nitrobenzene, bromobenzene, carbon tetrachloride, chloroform, bromohydrocarbons, ethylene glycol or glycerol.

17. A gradient ternary cathode material, characterized in that, The gradient ternary cathode material is prepared by the method described in any one of claims 1-16.

18. The gradient ternary cathode material as described in claim 17, characterized in that, The gradient ternary cathode material includes a core and a single-layer graphene coating layer covering the surface of the core.

19. The gradient ternary cathode material as described in claim 18, characterized in that, The amount of cobalt in the core increases in a gradient from the inside out.

20. A positive electrode sheet, characterized in that, The positive electrode comprises a gradient ternary positive electrode material as described in any one of claims 17-19.

21. A lithium-ion battery, characterized in that, The lithium-ion battery includes the positive electrode as described in claim 20.

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