A ternary positive electrode active material, a preparation method thereof, and a lithium ion battery containing the material

Abstract

The application belongs to the technical field of lithium ion battery cathode material, and particularly relates to a ternary cathode active material, a preparation method thereof and a lithium ion battery containing the material, wherein the ternary cathode active material comprises a ternary material and a coating layer coated on the surface of the ternary material; the coating layer comprises sulfidized polyacrylonitrile and polyacrylonitrile. The preparation method comprises the following steps in sequence: step one: mixing sulfur, polyacrylonitrile and lithium nickel cobalt manganese oxide as three raw materials, carrying out wet ball milling and then drying to obtain a mixed powder; step two: sintering the mixed powder obtained in step one under a protective atmosphere to obtain the ternary cathode active material. The ternary cathode active material prepared by the application is suitable for various types of electrolyte, has a more stable structure in the cycle process and has a high capacity retention rate.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery cathode material technology, specifically relating to a ternary cathode active material, its preparation method, and a lithium-ion battery containing the material. Background Technology

[0002] Ternary cathode materials are widely used in automotive power systems due to their high energy density, and their market share is increasing year by year. However, ternary cathode materials suffer from poor cycle life and low initial coulombic efficiency. During long-term cycling, microcracks, transition metal ion dissolution, and irreversible phase transition structural collapse on the material surface lead to battery capacity decay and reduced lifespan, affecting usability. Surface coating modification methods can effectively improve the electrical performance of cathode materials. The coating modifiers for ternary cathode materials are mostly oxides, fluorides, and phosphoric acid compounds, such as MgO, ZrO2, LiAlF3, LiF, and Li3PO4. These substances are either inert materials, acting as a physical barrier to inhibit HF corrosion, or they consume residual alkali on the surface of the ternary cathode material to suppress side reactions, or they are good conductors of electrons / ions, improving the material's conductivity and rate performance.

[0003] Although existing coating materials have significantly improved the electrochemical performance of ternary cathode materials, most of these materials are electrochemically inert. For example, the patent document CN111162249A discloses "A cathode material for improving the first discharge capacity and its preparation method," which uses boric acid, lithium borate, aluminum borate, sodium borate, potassium borate, aluminum oxide, titanium oxide, zirconium oxide, yttrium oxide, etc. After coating with the above-mentioned coating agents, the specific capacity and first-effect specific capacity of the ternary cathode material are still low, and the stability of the material needs to be further improved. Moreover, most of the existing technologies use dry mixing and sintering to coat the cathode active material, which is prone to problems such as uneven coating and weak coating. Summary of the Invention

[0004] This invention addresses the technical problems of conventional ternary materials in the prior art, such as low initial specific capacity, easy occurrence of side reactions at the interface during cycling, dissolution of transition metal ions, and structural instability. It provides a ternary positive electrode active material, its preparation method, and a lithium-ion battery containing the material.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] In a first aspect, the present invention provides a ternary cathode active material, the ternary cathode active material comprising a ternary material and a coating layer covering its surface; the coating layer comprising vulcanized polyacrylonitrile and polyacrylonitrile; preferably, the coating layer is composed of vulcanized polyacrylonitrile and polyacrylonitrile.

[0007] In the above ternary cathode active material, as a preferred embodiment, the ternary material is lithium nickel cobalt manganese oxide, preferably LiNi x Co y Mn z M 1-x-y-z O2, where 0.8 ≤ x < 1, 0 < y < 0.2, 0 < z < 0.2, x + y + z ≤ 1, and M is one or a combination of Al, Zr, W, and Mg.

[0008] Second, the present invention provides a method for preparing a ternary cathode active material, and the method sequentially includes the following steps:

[0009] Step 1: Mix three raw materials of sulfur (S), polyacrylonitrile (PAN), and lithium nickel cobalt manganese oxide, perform wet ball milling and then drying to obtain a mixed powder;

[0010] Step 2: Sinter the mixed powder obtained in Step 1 under a protective atmosphere to obtain a ternary cathode active material with double coating.

[0011] In the above preparation method, as a preferred embodiment, the lithium nickel cobalt manganese oxide (NCM) is LiNi x Co y Mn z M 1-x-y-z O2, where 0.8 ≤ x < 1, 0 < y < 0.2, 0 < z < 0.2, x + y + z ≤ 1, and M is one or a combination of Al, Zr, W, and Mg; preferably, the microstructure of the lithium nickel cobalt manganese oxide is: primary particles and / or secondary particles, where the secondary particles are spherical secondary particles composed of primary particles; preferably, the particle size distribution D 50 is in the range of 1 - 20 μm (such as 2 μm, 4 μm, 6 μm, 8 μm, 10 μm, 12.5 μm, 15 μm, 17.5 μm).

[0012] The spherical particles described in the present invention include spherical shapes and also include particles similar to spherical shapes.

[0013] In the above preparation method, as a preferred embodiment, the sulfur is elemental sulfur; preferably, the specification of the elemental sulfur is chemically pure.

[0014] In the above preparation method, as a preferred embodiment, the mass ratio of sulfur (S) to polyacrylonitrile (PAN) is 1-8:1; preferably, the sum of the masses of sulfur and polyacrylonitrile accounts for 0.1wt%-11wt% (e.g., 0.5wt%, 1wt%, 2.5wt%, 5wt%, 7.5wt%, 10wt%) of the total mass of the three raw materials (the sum of the masses of sulfur, polyacrylonitrile, and lithium nickel cobalt manganese oxide). This amount can make the coating more uniform and is more conducive to improving the electrochemical performance of the battery; preferably, the relative molecular mass of polyacrylonitrile (PAN) is 50,000-250,000 (e.g., 100,000, 150,000, 200,000).

[0015] In the above preparation method, as a preferred embodiment, in the wet ball milling of step one, the raw materials are mixed, a solvent is added, and then ball milling is performed; preferably, the solvent is one or more of ethanol, ethylene glycol, toluene, or acetone; preferably, the solvent is added to the raw materials according to a solid-liquid ratio: the ratio of the total weight of the raw materials (g) to the volume of the solvent (mL) is 13:1-4:1 (e.g., 12:1, 10:1, 8:1, 7:1, 6:1, 5:1); preferably, the ball milling speed is 30-100 rpm (e.g., 40 rpm, 50 rpm, 60 rpm, 70 rpm, 80 rpm, 90 rpm); preferably, the ball milling time is 1-3 hours; preferably, the drying is vacuum drying at 50-100℃ (e.g., 60℃, 70℃, 80℃, 90℃) for 1-3 hours.

[0016] In the above preparation method, as a preferred embodiment, the sintering in step two is carried out in a muffle furnace or a tube furnace.

[0017] In the above preparation method, as a preferred embodiment, the sintering process in step two is as follows: heating to 200-400℃ (e.g., 225℃, 250℃, 275℃, 300℃, 325℃, 350℃) at a heating rate of 3-10℃ / min (e.g., 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 7℃ / min, 8℃ / min, 8℃ / min, 9 ...

[0018] Thirdly, the present invention provides the application of the ternary cathode active material described in the first aspect above, or the preparation method described in the second aspect above, in lithium battery cathode materials.

[0019] Fourthly, the present invention provides a ternary cathode material, wherein the cathode material comprises the ternary cathode active material, conductive agent, and binder described in the first aspect above.

[0020] The conductive agent can be a conventional conductive agent in the art, such as SuperP, and the binder can be a conventional binder in the art, such as PVDF.

[0021] Fifthly, the present invention provides a lithium-ion battery, the battery comprising the ternary cathode active material described in the first aspect or the ternary cathode material described in the fourth aspect.

[0022] In the aforementioned lithium-ion battery, the battery further includes a battery casing and a positive electrode, a separator, and a negative electrode located within the battery casing. The positive electrode includes a positive electrode current collector and a positive electrode material located on the positive electrode current collector.

[0023] In a preferred embodiment of the present invention, the holding temperature during sintering is controlled at 200-400℃, which allows the reaction between sulfur and polyacrylonitrile to be more complete, reducing the probability of insufficient reaction between sulfur and polyacrylonitrile, sulfur sublimation, or polyacrylonitrile decomposition, thereby resulting in better conductivity of the prepared active material.

[0024] In a preferred embodiment of the present invention, the three materials, elemental sulfur, polyacrylonitrile, and ternary positive electrode active material, are mixed more uniformly by wet grinding, so that elemental sulfur and polyacrylonitrile are in uniform contact, and some polyacrylonitrile is coated on the surface of the ternary material.

[0025] This invention involves sintering a mixture of elemental sulfur, polyacrylonitrile (PAN), and a ternary cathode active material. Excess PAN is added, and the sintering temperature is controlled to induce cyclization of the PAN, which then reacts with elemental sulfur to obtain sulfurized PAN. Simultaneously, excess unreacted PAN is adsorbed onto the material surface, resulting in a ternary cathode active material with a double coating of sulfurized PAN (SPAN) and PAN. Preferably, the mass ratio of sulfur (S) to PAN is 1-8:1, and the sintering temperature is preferably controlled at 200-400℃ to ensure sufficient sulfurized PAN is produced, along with sufficient residual PAN. This achieves a superior coating ratio of sulfurized PAN and PAN on the surface of the lithium nickel cobalt manganese oxide active material, resulting in better performance in improving battery capacity and cycle performance.

[0026] This invention improves the electrochemical performance of materials by coating vulcanized polyacrylonitrile and polyacrylonitrile. Vulcanized polyacrylonitrile can increase the capacity of the material and improve cycling performance, while polyacrylonitrile can suppress interfacial side reactions, stabilize the surface structure of the material, and increase the compactness between particles.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] (1) The present invention uses a wet mechanical stirring and heating sintering method to uniformly coat the material surface with polyacrylonitrile (PAN) and vulcanized polyacrylonitrile (SPAN). In this process, an excess of polyacrylonitrile is added to ensure the complete reaction of elemental sulfur, and any unreacted sulfur that may remain is removed by heating and sintering at a certain temperature. At the same time, the temperature and holding time are reasonably controlled to ensure that the reaction between polyacrylonitrile and elemental sulfur proceeds while ensuring the stable existence of the remaining polyacrylonitrile.

[0029] (2) The specific capacity of the ternary positive electrode active material coated with SPAN in this invention is significantly improved, the cycle performance is better, and the organic carbon skeleton in the material has high conductivity, which reduces the material impedance.

[0030] (3) In the PAN-coated ternary cathode active material of the present invention, the carbon-nitrogen triple bond can form coordination bonds with transition metal ions, inhibiting the migration of transition metal ions to lithium vacancies, improving the structural stability of the material and improving cycle life. Furthermore, the presence of polyacrylonitrile (PAN) enables the cathode active material particles, the cathode active material and the conductive agent, and the cathode active material and the current collector to be tightly bonded together, thereby improving electrochemical performance.

[0031] (4) The SPAN and PAN of the present invention are coated on the surface of the ternary positive electrode active material as a protective shell, which reduces the erosion of the ternary positive electrode active material by the electrolyte, inhibits the occurrence of interfacial side reactions, and improves the stability of the material interface structure. Attached Figure Description

[0032] Figure 1 These are charge-discharge curves of coin cells prepared using the ternary cathode active materials of Examples 1-5 and Comparative Examples 1-5.

[0033] Figure 2 (a) is an SEM image of the uncoated ternary cathode active material in Comparative Example 1; (b) is an SEM image of the uncoated ternary cathode active material in Comparative Example 2; (c) is an SEM image of the double-coated ternary cathode active material prepared in Example 1; and (d) is an SEM image of the double-coated ternary cathode active material prepared in Example 5. Detailed Implementation

[0034] The preparation of the ternary cathode active material of the present invention will be further described in detail below with reference to specific embodiments. The examples given are only for illustrating the present invention and are not intended to limit the scope of the present invention. The examples provided below can serve as a basis for further improvements or applications by those skilled in the art and do not constitute a specific limitation on the present invention in any way.

[0035] Example 1

[0036] Preparation of organically double-coated ternary cathode active material LiNi 0.8 Co 0.1 Mn 0.1 O2, the steps are as follows:

[0037] (1) 4g of elemental sulfur, 2g of polyacrylonitrile (molecular weight 90000) and 300g of ternary positive electrode active material LiNi 0.8 Co 0.1 Mn 0.1 O2 (secondary spherical particles, particle size distribution D) 50 =9.62μm) was added to a ball mill jar, 50mL of ethanol solution was added, and the mixture was ground at 60rpm for 1h. Then it was taken out and placed in a vacuum drying oven at 60℃ for 2h.

[0038] (2) Take the above-mentioned uniformly mixed powder and sinter it in a tube furnace filled with nitrogen. Set the heating rate to 5℃ / min, heat it to 250℃ and keep it at that temperature for 8 hours. Finally, let it cool naturally to room temperature and take it out to obtain the SPAN / PAN double-coated ternary positive electrode active material.

[0039] Example 2

[0040] This embodiment is basically the same as that of embodiment 1. The only difference is that in step (1), the amount of elemental sulfur is 30g, the amount of polyacrylonitrile is 10g, the amount of ternary positive electrode active material is 350g, and the amount of ethanol solution added is 30mL.

[0041] Example 3

[0042] This embodiment is basically the same as that of Embodiment 1, except that the molecular weight of the polyacrylonitrile used in step (1) is 155,000.

[0043] Example 4

[0044] This embodiment is basically the same as embodiment 1. The only difference from embodiment 1 is that in step (2), the temperature is raised to 280°C and kept constant for 6 hours.

[0045] Example 5

[0046] This embodiment is basically the same as Embodiment 1, except that the ternary positive electrode active material LiNi used in step (2) is different. 0.8 Co 0.1 Mn 0.1 The microstructure of O2 is a single-crystal primary particle, with a particle size distribution of D. 50 =4.12μm.

[0047] Comparative Example 1

[0048] The LiNi from Example 1 was used directly. 0.8 Co 0.1 Mn 0.1 O2 (secondary spherical polycrystalline, particle size distribution D) 50 =9.62μm) as the positive electrode active material, that is, it is not coated with any substance.

[0049] Comparative Example 2

[0050] The LiNi from Example 5 was used directly. 0.8 Co 0.1 Mn 0.1 O2 (single-crystal particles, particle size distribution D) 50 =4.12μm) is used as the positive electrode active material, that is, it is not coated with any substance.

[0051] Comparative Example 3

[0052] This comparative example is basically the same as Example 1, except that the raw materials in this comparative example do not include elemental sulfur, and only 6g of polyacrylonitrile (molecular weight of 90,000) and 300g of ternary cathode active material LiNi are used. 0.8 Co 0.1 Mn 0.1 O2 (secondary spherical polycrystalline, particle size distribution D) 50 =9.62μm) were mixed and wet ball milled.

[0053] Comparative Example 4

[0054] This comparative example is basically the same as Example 1, except that the raw materials in this comparative example are 6g of vulcanized polyacrylonitrile (molecular weight 90000) and 300g of ternary positive electrode active material LiNi. 0.8 Co 0.1 Mn 0.1 O2 (secondary spherical polycrystalline, particle size distribution D) 50 =9.62μm) were mixed and wet ball milled.

[0055] Comparative Example 5

[0056] This comparative example is basically the same as Example 1, except that the sintering temperature is 600℃.

[0057] The ternary positive electrode active material (96.5 wt%), SuperP (1.5 wt%), and PVDF (2 wt%) obtained from Comparative Examples 1-5 and Examples 1-5 were uniformly mixed, and then coated on aluminum foil, dried, and rolled to form the positive electrode sheet. A lithium sheet was used as the negative electrode, and 1.1 M LiPF6 (solvent: volume ratio EC / DMC / EMC = 1:1:1) was used as the electrolyte. CR2032 coin cells were fabricated and tested in a battery cabinet. The voltage range was 3.0-4.3 V, and the charge / discharge cycle was 50 cycles at 0.2C. The charge / discharge data and curves are shown in Table 1 and below. Figure 1 .

[0058] Table 1 Charge / Discharge Data

[0059]

[0060]

[0061] From Table 1 and Figure 1 As can be seen, the discharge capacity, first-cycle efficiency, and capacity retention of the ternary cathode active materials with SPAN / PAN double coating in Examples 1-5 are all superior to the uncoated conventional ternary cathode active materials in Comparative Examples 1-2, showing significant performance improvement. Comparative Example 3, using only polyacrylonitrile coating, while stabilizing the layered structure of the ternary cathode material during cycling and suppressing the migration of transition metal ions, resulted in a lower material capacity. Comparative Example 4, using only sulfurized polyacrylonitrile coating, improved the first-cycle discharge specific capacity, but the capacity retention after 50 cycles was low. In Comparative Example 5, the sintering temperature was too high, leading to sulfur sublimation and high-temperature decomposition and carbonization of polyacrylonitrile, resulting in poor coating effect. The SPAN / PAN double coating significantly improved both secondary spherical polycrystalline lithium nickel cobalt manganese oxide and primary granular single-crystal lithium nickel cobalt manganese oxide. Figure 2 As can be seen, there is no significant difference in morphology between coated and uncoated lithium nickel cobalt manganese oxide.

[0062] The ternary cathode active material prepared by this invention, with SPAN / PAN double coating, has a ternary cathode material as both the main matrix and active material, coated with a small amount of sulfurized polyacrylonitrile and polyacrylonitrile. It is suitable for various types of electrolytes, exhibits greater structural stability during cycling, and demonstrates high capacity retention. No loss of active material, reduced cycling performance, decreased capacity retention, or severe capacity decay was observed in various electrolyte types, including ether-based and carbonate-based electrolytes.

[0063] Coating polyacrylonitrile (PA) can enhance the potential barrier by coordinating with transition metal ions through nitrogen-carbon triple bonds, inhibiting transition metal ion migration and improving the stability of the material during cycling. Coating with sulfurized PA can improve the conductivity of the material surface and reduce impedance through the presence of carbon chains, and the presence of trace amounts of sulfides can provide capacity. This invention optimizes the process steps and improves the uniformity of coating by mixing sulfur, PA, and ternary cathode materials, and concentrating the reaction of sulfur and PA to form sulfurized PA, the coating of excess PA on the surface of the ternary cathode material, and the coating of sulfurized PA on the surface of the ternary cathode material into a single sintering step. This makes it suitable for large-scale application and has significant industrial value.

[0064] Finally, it should be noted that the above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. However, any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A ternary cathode active material, characterized in that, The ternary cathode active material includes a ternary material and a coating layer covering its surface; The coating layer comprises vulcanized polyacrylonitrile and polyacrylonitrile. The preparation method of the ternary cathode active material includes the following steps in sequence: Step 1: Mix sulfur, polyacrylonitrile, and lithium nickel cobalt manganese oxide, wet ball mill, and then dry to obtain a mixed powder. The mass ratio of sulfur to polyacrylonitrile is 1-8:1, and the sum of the masses of sulfur and polyacrylonitrile accounts for 0.1wt%-11wt% of the total mass of the three raw materials. Step 2: Sinter the mixed powder obtained in Step 1 under a protective atmosphere to obtain a double-coated ternary cathode active material.

2. The ternary cathode active material as described in claim 1, characterized in that, The ternary material is lithium nickel cobalt manganese oxide.

3. The ternary cathode active material as described in claim 2, characterized in that, The lithium nickel cobalt manganese oxide is LiNi x Co y Mn z M 1-x-y-z O2, where 0.8 ≤ x < 1, 0 < y < 0.2, 0 < z < 0.2, x + y + z ≤ 1, and M is one or a combination of more than one of Al, Zr, W, and Mg.

4. The method for preparing the ternary positive electrode active material according to any one of claims 1 to 3, characterized in that, The method includes the following steps in sequence: Step 1: Mix sulfur, polyacrylonitrile, and lithium nickel cobalt manganese oxide, wet ball mill, and then dry to obtain a mixed powder. The mass ratio of sulfur to polyacrylonitrile is 1-8:1, and the sum of the masses of sulfur and polyacrylonitrile accounts for 0.1wt%-11wt% of the total mass of the three raw materials. Step 2: Sinter the mixed powder obtained in Step 1 under a protective atmosphere to obtain a double-coated ternary cathode active material.

5. The preparation method according to claim 4, characterized in that, The lithium nickel cobalt manganese oxide is LiNi x Co y Mn z M 1-x-y-z O2, where 0.8 ≤ x < 1, 0 < y < 0.2, 0 < z < 0.2, x + y + z ≤ 1, and M is one or a combination of more than one of Al, Zr, W, and Mg; And / or, the microstructure of the lithium nickel cobalt manganese oxide is: primary particles and / or secondary particles, wherein the secondary particles are spherical secondary particles composed of primary particles; And / or, the particle size distribution D of the lithium nickel cobalt manganese oxide 50 Within 1-20 μm; And / or, the sulfur is elemental sulfur; And / or, the relative molecular mass of the polyacrylonitrile is 50,000-250,000.

6. The preparation method according to claim 5, characterized in that, The elemental sulfur is chemically pure.

7. The preparation method according to claim 4 or 5, characterized in that, In the wet ball milling of step one, the raw materials are mixed, a solvent is added, and then ball milling is performed. And / or, the ball mill rotates at a speed of 30-100 rpm; And / or, the ball milling time is 1-3 hours; And / or, the drying is vacuum drying at 50-100°C for 1-3 hours.

8. The preparation method according to claim 7, characterized in that, The solvent is one or more selected from ethanol, ethylene glycol, toluene, or acetone; And / or, the solvent is added to the raw materials according to a solid-liquid ratio: the ratio of the total weight of the raw materials (g) to the volume of the solvent (mL) is 13:1-4:1; And / or, the sintering in step two is carried out in a muffle furnace or a tube furnace.

9. The preparation method according to any one of claims 4 to 6, characterized in that, The sintering process in step two is as follows: heating to 200-400℃ at a heating rate of 3-10℃ / min and holding at that temperature for 4-20 hours; And / or, the protective atmosphere is one or more of nitrogen, argon or helium; And / or, the cooling method after sintering is natural cooling to room temperature.

10. The application of the ternary cathode active material according to any one of claims 1 to 3, or the cathode active material prepared by the preparation method according to any one of claims 4 to 9, in the cathode material of lithium batteries.

11. A ternary cathode material, the cathode material comprising the ternary cathode active material according to any one of claims 1 to 3, or the cathode active material prepared by the preparation method according to any one of claims 4 to 9, as well as a conductive agent and a binder.

12. A lithium-ion battery, the battery comprising the ternary cathode material of claim 11.

13. The lithium-ion battery of claim 12, further comprising a battery casing and a positive electrode, a separator, and a negative electrode located within the battery casing, wherein the positive electrode comprises a positive electrode current collector and a positive electrode material located on the positive electrode current collector.

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