A high-nickel cobalt-free positive electrode material and a preparation method thereof

Abstract

This invention discloses a high-nickel cobalt-free cathode material and its preparation method. The preparation method includes the following steps: preparing zirconium-doped high-nickel cobalt-free nickel-manganese hydroxide; adding zirconium-doped high-nickel cobalt-free nickel-manganese hydroxide, lithium hydroxide, magnesium titanate, and zirconium aluminate to water, mixing evenly, and drying to obtain a mixture; placing the mixture in a pure oxygen atmosphere and holding it at 300℃-800℃ for 6-12 hours to obtain high-nickel cobalt-free nickel-manganese lithium oxide; mixing high-nickel cobalt-free nickel-manganese lithium oxide, borosilicate, and tungsten oxide evenly, drying, and sintering to obtain the target product. In this invention, the addition of magnesium titanate and zirconium aluminate during the preparation process makes the material's crystal structure more complete; the synergistic coating of borosilicate and tungsten oxide effectively improves the specific capacity of the material, better stabilizes the crystal structure, and significantly enhances the overall performance of the material.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion cathode material technology, specifically relating to a high-nickel, cobalt-free cathode material and its preparation method. Background Technology

[0002] With the accelerated development of new energy vehicles, nickel-cobalt-manganese / aluminum ternary cathode materials, especially high-nickel ternary materials, have shown significantly better discharge capacity and cost compared to other materials. In recent years, due to the increasing cost of cobalt, high-nickel cobalt-free materials have become a research hotspot. While also being a relatively green and environmentally friendly material, its industrial mass production requires stringent conditions and has high production costs, attracting widespread attention from academia and industry. Ternary cathode materials are solid solutions of lithium nickelate and lithium manganese oxide. Their ionic radii are roughly the same, allowing them to substitute positions without altering the crystal structure. While the capacity increases with increasing nickel content, their rate capability and high-temperature cycling performance decrease significantly. Summary of the Invention

[0003] The purpose of this invention is to provide a high-nickel cobalt-free cathode material and its preparation method, so as to solve the problem of reduced material rate capability and high-temperature cycling performance caused by the increase of nickel content in existing high-nickel cobalt-free materials.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0005] A method for preparing a high-nickel, cobalt-free cathode material includes the following steps:

[0006] (1) Preparation of zirconium-doped high-nickel cobalt-free nickel-manganese hydroxide

[0007] Zirconium salt, a complexing agent, and a precipitant are added to a mixed salt solution containing nickel and manganese salts. The pH of the solution is adjusted to 8-12, and the reaction is carried out under stirring. The resulting precipitate is washed and dried to obtain zirconium-doped high-nickel, cobalt-free nickel-manganese hydroxide. Preferably, the nickel salt is nickel sulfate, the manganese salt is manganese sulfate, the complexing agent is ammonia, and the precipitant is sodium hydroxide.

[0008] (2) Preparation of high-nickel cobalt-free lithium nickel manganese oxide

[0009] Zirconium-doped high-nickel cobalt-free nickel-manganese hydroxide is premixed with a certain amount of lithium hydroxide, followed by the addition of nano-sized 300-800nm ​​magnesium titanate and zirconium aluminate, and then a certain amount of deionized water. The mixture is then wet-mixed in a plow-type mixer. After uniform mixing, it is dried using a spray drying method to obtain a final mixture. The mass fraction of magnesium titanate in the mixture is 0.1-1.5 wt%, and the mass fraction of zirconium aluminate is 0.03-1 wt%. The ratio of cobalt-free nickel-manganese hydroxide to lithium hydroxide is not particularly limited and can be adjusted according to the final product requirements. Preferably, the molar ratio of cobalt-free nickel-manganese hydroxide to lithium hydroxide is between 1:(1.01-1.8), and the particle size of lithium hydroxide should be ≤6 micrometers, which allows for a lower reaction temperature. The mixture was sintered in a pure oxygen atmosphere with an oxygen intake rate of 1-30 L / min. The oxygen atmosphere allowed the sample to react more fully. The sintering temperature was 300℃-800℃ and the holding time was 6-12 h, thus preparing high-nickel cobalt-free lithium nickel manganese oxide.

[0010] In the above preparation process, the use of a plow-type mixer for wet mixing ensures uniform material mixing, good product consistency, and the production of cobalt-free Li cathode material. + / Ni 2+ The reduction of mixing phenomena increases the migration rate of lithium ions, thus improving rate performance. Because the crystal structure of high-nickel cobalt-free materials is prone to change during charge and discharge, especially under high voltage conditions, oxygen loss can easily lead to a transformation from a layered structure to a spinel to a rock salt phase. Doping with magnesium titanate and zirconium aluminate can suppress the formation of oxygen vacancies, thereby reducing phase transitions. Simultaneously, the addition of magnesium titanate, with magnesium doping playing a stabilizing role, and the synergistic effect of magnesium and zirconium, further improves the structural stability of the material. Furthermore, most of the titanium in magnesium titanate is enriched on the material surface, which can improve the interfacial contact between material particles, thereby enhancing the rate performance. This results in a significant improvement in the overall performance of the material.

[0011] (3) High-nickel cobalt-free cathode material was prepared by coating.

[0012] High-nickel cobalt-free lithium nickel manganese oxide is wet-mixed with nano-sized borosilicate in a certain proportion, while tungsten oxide is added simultaneously. After uniform mixing, the mixture is spray-dried and then transferred to a muffle furnace for sintering at 200℃-600℃ for 6-10 hours to obtain the target product. Preferably, the amount of borosilicate used is 0.4-2 wt% of the high-nickel cobalt-free lithium nickel manganese oxide, and the amount of tungsten oxide used is 0.2-2 wt% of the high-nickel cobalt-free lithium nickel manganese oxide.

[0013] High-nickel, cobalt-free nickel-manganese lithium oxide (LiNOA) coated with borosilicate and tungsten oxide offers several advantages. High-nickel, cobalt-free LiNOA has a higher residual lithium content, while borosilicate has lower residual moisture, a lower coefficient of thermal expansion, lower thermal conductivity, and higher chemical and dielectric properties. Borosilicate coating can repair surface damage to crystal particles, reduce surface residual lithium, and minimize surface side reactions. Furthermore, the co-coating with borosilicate and tungsten oxide reduces the migration of some trivalent nickel ions to divalent nickel ions from the particle surface into the lithium layer. During charge and discharge, this better stabilizes the layered structure, improving the material's discharge specific capacity and thus its efficiency.

[0014] Compared with existing technologies, the beneficial effects of this invention are reflected in:

[0015] (1) The present invention uses liquid phase method for mixing and spray drying method for drying, resulting in products with good consistency.

[0016] (2) In this invention, magnesium titanate and zirconium aluminate are added. The synergistic effect of elements such as titanium and zirconium can make the crystal structure more complete. During the charging and discharging process, under the condition of oxygen loss, the crystal is not easy to transform from spinel to rock salt phase.

[0017] (3) The present invention utilizes pure oxygen conditions for reaction, which can reduce the generation of divalent nickel ions and prevent lithium ions from migrating to the nickel ion position, thereby improving the specific capacity of the material.

[0018] (4) The present invention utilizes borosilicate coating, which can reduce residual lithium on the material surface and improve the material's cycle performance. Tungsten oxide synergistic coating effectively improves the material's specific capacity and better stabilizes the material's crystal structure.

[0019] (5) The preparation process of the present invention is simple, energy consumption is low, and it is suitable for industrial production. Attached Figure Description

[0020] Figure 1 This is a 3000x SEM image of the high-nickel, cobalt-free nickel-manganese hydroxide obtained in step (1) of Example 1 of the present invention.

[0021] Figure 2 This is a 3000x SEM image of the modified high-nickel cobalt-free lithium nickel manganese oxide obtained in step (3) of Example 1 of the present invention. Detailed Implementation

[0022] The present invention will be further described below with reference to embodiments, so that those skilled in the art can better understand and implement the present invention, but the embodiments are not intended to limit the present invention.

[0023] In addition, unless otherwise specified, the preparation processes in the following embodiments are all conventional methods in the prior art, and therefore will not be described in detail; the raw materials used in the following embodiments are all commercially available products.

[0024] Example 1

[0025] (1) Add 50L of pure water to a 100L reactor, and add NiSO4 and Mn(SO4)2 to the water in a molar ratio of Ni:Mn = 90:10 to obtain a mixed salt solution. Based on the total amount of NiSO4 and Mn(SO4)2, add 0.05wt% zirconium sulfate, 15L of 2mol / L ammonia water as a complexing agent and 25L of 3mol / L sodium hydroxide as a precipitant to the reactor. Adjust the pH to 10 and carry out the reaction under stirring. The resulting precipitate is washed, dried, and then dried at 120℃ to obtain zirconium-doped high-nickel cobalt-free nickel-manganese hydroxide.

[0026] (2) Zirconium-doped high-nickel cobalt-free nickel-manganese hydroxide and lithium hydroxide were mixed at a molar ratio of 1:1.03. Based on the mass of the high-nickel cobalt-free nickel-manganese hydroxide, 1.2 wt% nano-sized magnesium titanate and 0.1 wt% zirconium aluminate were added, along with deionized water. The mixture was then mixed in a plow-type mixer until homogeneous, and then spray-dried to obtain the final mixture. The mixture was sintered at 500°C for 10 hours in an oxygen atmosphere. The sintered material was then pulverized using an air jet mill. The pulverized sample was sieved and demagnetized to obtain high-nickel cobalt-free nickel-manganese lithium oxide.

[0027] (3) The above-mentioned high-nickel cobalt-free nickel-manganese oxide lithium oxide was wet-coated by means of: wet mixing high-nickel cobalt-free nickel-manganese oxide lithium oxide with nano-sized lithium borosilicate, while adding tungsten oxide, mixing evenly and then spray-drying, and then transferring to a muffle furnace for sintering at 400℃ for 8 hours to obtain the target product. The amount of lithium borosilicate used was 0.5 wt% of the high-nickel cobalt-free nickel-manganese oxide lithium oxide, and the amount of tungsten oxide used was 1.5 wt% of the high-nickel cobalt-free nickel-manganese oxide lithium oxide.

[0028] Figure 1 This is a 3000x SEM image of the high-nickel, cobalt-free nickel-manganese hydroxide obtained in step (1) of Example 1 of the present invention. Figure 2 This is a 3000x SEM image of the modified high-nickel cobalt-free lithium nickel manganese oxide obtained in step (3) of Example 1 of the present invention. Figure 2 Analysis shows that the particles have a single crystal morphology with a small number of grain boundaries between them. The crystal structure is relatively complete and without defects, thus optimizing the crystal structure. Furthermore, the coated material has a coating layer attached to its surface to prevent electrolyte erosion and can improve the capacity retention rate of the material, thereby improving the material's cycle performance and capacity retention rate.

[0029] Example 2

[0030] S1. Add 50L of pure water to a 100L reactor. Add NiSO4 and Mn(SO4)2 to the water in a molar ratio of Ni:Mn = 95:5 to obtain a mixed salt solution. Based on the total amount of NiSO4 and Mn(SO4)2, add 1.5wt% zirconium sulfate, 15L of 2mol / L ammonia water as a complexing agent, and 25L of 3mol / L sodium hydroxide as a precipitant to the reactor. Adjust the pH to 10 and react under stirring. The resulting precipitate is washed, dried, and then dried at 120℃ to obtain zirconium-doped high-nickel cobalt-free nickel-manganese hydroxide.

[0031] S2. Zirconium-doped high-nickel cobalt-free nickel-manganese hydroxide and lithium hydroxide were mixed at a molar ratio of 1:1.03. Based on the mass of the high-nickel cobalt-free nickel-manganese hydroxide, 0.4 wt% nano-sized magnesium titanate and 1 wt% zirconium aluminate were added, along with deionized water. The mixture was then mixed in a plow-type mixer until homogeneous, followed by spray drying to obtain the final mixture. The mixture was sintered at 500℃ for 10 hours in an oxygen atmosphere. The sintered material was then pulverized using an air jet mill. The pulverized sample was sieved and demagnetized to obtain high-nickel cobalt-free nickel-manganese lithium oxide.

[0032] S3. The above-mentioned high-nickel cobalt-free nickel-manganese oxide lithium oxide is subjected to wet coating. The method is as follows: high-nickel cobalt-free nickel-manganese oxide lithium oxide is wet-mixed with nano-sized lithium borosilicate, and tungsten oxide is added simultaneously. After mixing evenly, it is spray-dried and then transferred to a muffle furnace for sintering at 400°C for 8 hours to obtain the target product. The amount of lithium borosilicate is 0.5 wt% of the high-nickel cobalt-free nickel-manganese oxide lithium oxide, and the amount of tungsten oxide is 1 wt% of the high-nickel cobalt-free nickel-manganese oxide lithium oxide.

[0033] Comparative Example 1

[0034] The difference between this comparative example and Example 1 is that zirconium sulfate was not added in step S1, and a high-nickel, cobalt-free nickel-manganese hydroxide without zirconium sulfate was prepared. The other steps are the same as in Example 1.

[0035] Comparative Example 2

[0036] The difference between this comparative example and Example 1 is that magnesium titanate and zirconium aluminate were not added in step S2, and high-nickel cobalt-free lithium nickel manganese oxide without magnesium titanate and zirconium aluminate was prepared.

[0037] Comparative Example 3

[0038] The difference between this comparative example and Example 1 is that magnesium titanate was not added in step S2, while the other steps were the same as in Example 1. The resulting product is high-nickel, cobalt-free lithium nickel manganese oxide without magnesium titanate doping.

[0039] Comparative Example 4

[0040] The difference between this comparative example and Example 1 is that zirconium aluminate was not added in step S2, while the other steps were the same as in Example 1. The product obtained in step S2 is high-nickel, cobalt-free lithium nickel manganese oxide without zirconium aluminate doping.

[0041] Comparative Example 5

[0042] The difference between this comparative example and Example 1 is that lithium borosilicate and tungsten oxide were not added in step S3, while the other steps were the same as in Example 1, resulting in high-nickel, cobalt-free nickel-manganese lithium oxide without borosilicate and tungsten oxide coating.

[0043] Comparative Example 6

[0044] The difference between this comparative example and Example 1 is that lithium borosilicate was not added in step S3, while the other steps were the same as in Example 1, and the resulting product was high-nickel, cobalt-free nickel-manganese lithium oxide without borosilicate coating.

[0045] Comparative Example 7

[0046] The difference between this comparative example and Example 1 is that tungsten oxide was not added in step S3, while the other steps were the same as in Example 1, and the resulting product was high-nickel, cobalt-free lithium nickel manganese oxide without tungsten oxide coating.

[0047] Performance testing

[0048] The products prepared in the above embodiments and comparative examples are used as positive electrode active materials. Positive electrode slurry is prepared by mixing positive electrode active material, conductive agent SP and binder PVDF in a mass ratio of 90:5:5. After the positive electrode slurry is prepared, it is coated on the positive electrode current collector to form a positive electrode sheet.

[0049] Battery assembly: The battery is assembled in the following order: negative electrode shell, spring, 1mm pad + lithium sheet electrolyte, separator electrolyte, positive electrode sheet, and positive electrode shell; after assembly, the sheet is pressed.

[0050] After assembly, the battery can be charged and discharged. The positive electrode case is connected to the positive electrode, and the negative electrode case is connected to the negative electrode. The negative electrode is a lithium sheet. The test conditions are 25℃, 3.0-4.45V, and a 0.2C charge / discharge capacity for the first cycle.

[0051] Table 1. Residual lithium analysis results of materials prepared in each embodiment and comparative example.

[0052] serial number Residual lithium (ppm) Example 1 300 Example 2 320 Comparative Example 1 350 Comparative Example 2 700 Comparative Example 3 600 Comparative Example 4 650 Comparative Example 5 2000 Comparative Example 6 1080 Comparative Example 7 1153

[0053] Table 2. Battery performance test results of materials prepared in each embodiment and comparative example.

[0054]

[0055] As shown in Table 1, the residual lithium in the materials prepared in Examples 1 and 2 was significantly lower than that in the comparative examples. The residual lithium in the products prepared in Comparative Examples 5 to 7 was significantly increased due to the lack of coating of lithium borosilicate and / or tungsten oxide. In particular, the residual lithium in Comparative Example 5 was significantly increased, indicating that lithium borosilicate and tungsten oxide have a synergistic effect and can reduce the residual alkali on the surface of the material.

[0056] As shown in Table 2, the initial discharge capacity, 1C discharge capacity, and capacity retention rate after 50 cycles at 45℃ in Comparative Example 2 are significantly lower than those in Comparative Examples 3 and 4, indicating that the doping of magnesium titanate and zirconium aluminate has a synergistic effect. The capacity retention rate after 50 cycles at 45℃ in Comparative Example 5 is significantly lower than that in Comparative Examples 6 and 7, indicating that borosilicate and tungsten oxide have a synergistic promoting effect that can improve the material's performance.

[0057] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a high-nickel, cobalt-free cathode material, characterized in that: Includes the following steps: To prepare zirconium-doped high-nickel cobalt-free nickel-manganese hydroxide, zirconium-doped high-nickel cobalt-free nickel-manganese hydroxide, lithium hydroxide, magnesium titanate, and zirconium aluminate were added to water, mixed evenly, and dried to obtain a mixture. The mixture was then placed in a pure oxygen atmosphere and kept at a temperature of 300℃-800℃ for 6-12 hours to obtain high-nickel cobalt-free nickel-manganese lithium oxide. After mixing high-nickel cobalt-free nickel-manganese lithium oxide, borosilicate, and tungsten oxide evenly, the mixture was dried and sintered to obtain the target product, namely the high-nickel cobalt-free cathode material.

2. The method for preparing the high-nickel cobalt-free cathode material according to claim 1, characterized in that: The method for preparing zirconium-doped high-nickel cobalt-free nickel-manganese hydroxide is as follows: Zirconium salt, complexing agent, and precipitant are added to a mixed salt solution containing nickel and manganese salts. The pH of the solution is adjusted to 8-12, and the reaction is carried out under stirring. The resulting precipitate is washed and dried to obtain zirconium-doped high-nickel cobalt-free nickel-manganese hydroxide.

3. The method for preparing the high-nickel cobalt-free cathode material according to claim 2, characterized in that: The complexing agent is ammonia, and the precipitant is sodium hydroxide.

4. The method for preparing the high-nickel cobalt-free cathode material according to claim 1, characterized in that: The lithium hydroxide has a particle size of ≤6 micrometers.

5. The method for preparing the high-nickel cobalt-free cathode material according to claim 1, characterized in that: The molar ratio of zirconium-doped high-nickel cobalt-free nickel-manganese hydroxide to lithium hydroxide is 1:(1.01-1.8).

6. The method for preparing the high-nickel cobalt-free cathode material according to claim 1, characterized in that: The mixture contains 0.1-1.5 wt% magnesium titanate and 0.03-1 wt% zirconium aluminate.

7. The method for preparing the high-nickel cobalt-free cathode material according to claim 1, characterized in that: The amount of borosilicate used is 0.4-2 wt% of high-nickel cobalt-free lithium nickel manganese oxide, and the amount of tungsten oxide used is 0.2-2 wt% of high-nickel cobalt-free lithium nickel manganese oxide.

8. The method for preparing the high-nickel cobalt-free cathode material according to claim 1, characterized in that: The sintering temperature is 200℃-600℃, and the time is 6-10h.

9. The high-nickel cobalt-free cathode material prepared by any one of claims 1 to 8.

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