Method for preparing high-rate single crystal cathode material from gel mixture and its application

Abstract

The present invention discloses a method for preparing a high-rate single-crystal positive electrode material from a gel mixture and its application. In the present invention, a precursor is crushed, mixed with a lithium source, and sintered at low temperature for a short time to allow the lithium to enter the internal structure of the precursor. At this time, the particle size of the material is small. By evaporating the sol liquid, a gel is formed and uniformly attached to the surface of the material. The gel is first sintered at low temperature and then at high temperature to form yttrium barium copper oxide with a superconducting-like structure. At the same time, the positive electrode material is completely crystallized. The present method can avoid grain boundary fusion between particles while coating the positive electrode material, forming small-particle single crystals with high electrical conductivity.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium ion battery positive electrode materials, and particularly relates to a method for preparing a high-rate single crystal positive electrode material from a gel mixture and application thereof. Background Art

[0002] With the rapid development of green energy, the use of high-rate power tools has become widespread, especially with the popularity of 20C, 40C, and even higher-rate power tools. This has led to increasingly stringent requirements for the rate performance of cathode materials. Furthermore, with the gradual promotion of new energy vehicles, hybrid electric vehicles (HEVs), as a new energy branch, are gradually gaining acceptance and trust from consumers. Cathode materials for HEV batteries must possess advantages such as high instantaneous discharge rate, long cycle life, and excellent power performance. Both power tools and new energy vehicles require cathode materials that combine ultra-high rate performance with long cycle life.

[0003] Currently, the mainstream positive electrode material products on the market are mainly secondary spheres formed by the agglomeration of primary particles. Due to the wide particle size distribution of secondary spherical NCA / NCM materials, this type of material is prone to secondary spherical morphology rupture caused by uneven force during the electrode rolling process, affecting the compaction density of the electrode. The electrolyte has difficulty in completely infiltrating the positive electrode material with secondary spherical morphology, resulting in an increase in the internal resistance of the electrode. At the same time, the broken morphology of the secondary particles leads to a larger contact area between the material and the electrolyte, causing more intense side reactions, resulting in an increase in the internal resistance of the battery cell and limiting its application in the high-end market. In addition, due to the wide particle size distribution, uneven gaps, and easy breakage of the secondary spheres, it is difficult to achieve uniform coating of the material.

[0004] Compared with traditional secondary spherical positive electrode materials, single crystal or quasi-single crystal products have higher compaction and tap density, which effectively avoids phenomena such as particle breakage during the electrode rolling process, reduces side reactions between the electrolyte and the material, and improves the cycle performance of single cells and their performance under high-rate conditions.

[0005] In the existing technology, single crystal positive electrode materials have poor rate performance and poor cycle stability, making it difficult to achieve ultra-high rate stable charge and discharge cycles; moreover, single crystal positive electrode materials prepared by high-temperature sintering and additive methods have uneven particle size distribution, large particle size (micrometer level), and poor mechanical integrity.

[0006] On the other hand, existing technologies mostly use coating to improve the performance of positive electrode materials. However, as the type and amount of coating increase, the powder resistivity of the positive electrode material increases linearly, which restricts the cycle performance of the positive electrode material.

[0007] How to achieve fast charging performance of positive electrode materials and achieve stable ultra-high rate charge and discharge cycles is a technical problem that needs to be solved urgently. Summary of the Invention

[0008] The present invention aims to address at least one of the technical problems existing in the aforementioned prior art. To this end, the present invention provides a method for producing a high-rate single-crystal positive electrode material from a gel mixture and its application. This method can coat the positive electrode material while preventing grain boundary fusion between particles, resulting in small single crystal particles with high electrical conductivity.

[0009] According to one aspect of the present invention, a method for preparing a high-rate single crystal cathode material from a gel mixture is provided, comprising the following steps:

[0010] S1: The cathode material precursor is crushed, the crushed material is mixed with a lithium source, and the temperature is raised to 500-550°C in an oxygen atmosphere to react to obtain a sintered material;

[0011] S2: mixing yttrium salt, barium salt, copper salt, organic solvent and complexing agent to obtain a sol solution, adding the first sintered material to the sol solution, heating and evaporating to dryness to obtain a solid gel mixture;

[0012] S3: The solid gel mixture is first heated to 400-450°C for reaction under an oxygen atmosphere, then heated to 850-900°C for reaction, and then cooled to 450-550°C for reaction. The obtained reaction product is crushed to obtain the high-rate single crystal positive electrode material.

[0013] In some embodiments of the present invention, in step S1, the positive electrode material precursor is a hydroxide of nickel, cobalt and manganese. a Co b Mn c (OH)2, nickel cobalt manganese oxide Ni a Co b Mn c O or nickel-cobalt-manganese carbonate Ni a Co b Mn c CO3, where 0≤a≤0.6, 0≤b≤0.6, 0≤c≤0.4, a+b+c=1.

[0014] In some embodiments of the present invention, in step S1, the particle size D50 of the crushed material is 500-1000 nm.

[0015] In some embodiments of the present invention, in step S1, the crushed material is mixed with the lithium source according to a molar ratio of the sum of nickel, cobalt and manganese elements to lithium element of 1:(1.0-1.2).

[0016] In some embodiments of the present invention, in step S1, the lithium source is at least one of lithium hydroxide, lithium carbonate, lithium nitrate or lithium oxalate.

[0017] In some embodiments of the present invention, in step S1, the heating rate is 5-10°C / min.

[0018] In some embodiments of the present invention, in step S1, the reaction time is 3-5 hours.

[0019] In some embodiments of the present invention, in step S1, the oxygen atmosphere is air or oxygen atmosphere.

[0020] In some embodiments of the present invention, in step S2, the molar ratio of the yttrium salt, the barium salt, the copper salt, the organic solvent and the complexing agent is 1:2:3:(400-800):(1-5).

[0021] In some embodiments of the present invention, in step S2, the solid-to-liquid ratio of the first sintered material to the sol liquid is 20-30 g / 100 mL.

[0022] In some embodiments of the present invention, in step S2, the yttrium salt, barium salt, and copper salt are at least one of nitrates and acetates.

[0023] In some embodiments of the present invention, in step S2, the organic solvent is at least one of methanol, ethanol or dimethyl ether.

[0024] In some embodiments of the present invention, in step S2, the complexing agent is at least one of ethylene glycol, ethanolamine or diethylenetriamine.

[0025] In some embodiments of the present invention, in step S2, the temperature of the heating and evaporation is 150-250°C.

[0026] In some embodiments of the present invention, in step S3, the reaction time when the temperature is raised to 400-450°C is 20-30 minutes; the reaction time when the temperature is raised to 850-900°C is 12-24 hours; and the reaction time when the temperature is lowered to 450-550°C is 1-2 hours.

[0027] In some embodiments of the present invention, in step S3, the heating rate is 5-10°C / min.

[0028] In some embodiments of the present invention, in step S3, the cooling rate is 5-10°C / min.

[0029] In some embodiments of the present invention, the particle size D50 of the high-rate single crystal cathode material is 0.8-2 μm.

[0030] The present invention also provides application of the method in preparing lithium ion batteries.

[0031] According to a preferred embodiment of the present invention, there are at least the following beneficial effects:

[0032] 1. The present invention first crushes and pulverizes the cathode material precursor, then mixes it with a lithium source, and sintered it at low temperature for a short time to allow the lithium to enter the internal structure of the precursor. At the same time, no fusion of grain boundaries occurs, and the particle size of the material remains small.

[0033] 2. By evaporating the sol and volatilizing the organic solvent, the resulting gel can evenly adhere to the surface of the material. It is first sintered at low temperature in an oxygen atmosphere to initially solidify the material into a yttrium barium copper oxide complex that coats the surface of the crushed material. It is then sintered at high temperature to form a yttrium barium copper oxide with a superconducting structure. At the same time, the positive electrode material reaches complete crystallization. Finally, low-temperature sintering further stabilizes the structure of the yttrium barium copper oxide, which helps improve the material's conductivity. During the sintering process of the solid gel mixture, the material begins to fuse at the grain boundaries. However, due to the obstruction of the coating, its fusion capacity is limited, reducing the pressure on the subsequent single crystal material to break. The resulting single crystal particles have a smaller particle size. At the same time, due to the presence of the superconducting structure of yttrium barium copper oxide on the surface, the electronic conductivity of the positive electrode material is greatly improved.

[0034] 3. Since the lithium infiltrated into the immature positive electrode material is still unstable and can easily be released, the nickel content in the high-nickel positive electrode material is relatively high, and the immature positive electrode material has extremely serious lithium-nickel mixing. Even if an organic solvent is used to prepare the sol solution, a large amount of lithium is easily lost, resulting in a decrease in the material's gram capacity. The dissolved lithium may react with the coating material, affecting the formation of the yttrium barium copper oxide superconducting structure, thereby reducing the conductivity of the coating layer. Therefore, this scheme preferably uses a precursor with a lower nickel content. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The present invention will be further described below with reference to the accompanying drawings and embodiments, in which:

[0036] Figure 1 This is the SEM image of the high-rate single crystal positive electrode material prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0037] The following will clearly and completely describe the concept and technical effects of the present invention in conjunction with the embodiments to fully understand the purpose, features and effects of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative work are all within the scope of protection of the present invention.

[0038] Example 1

[0039] This embodiment prepares a high-rate single crystal cathode material, and the specific process is as follows:

[0040] Step 1: The cathode material precursor nickel cobalt manganese hydroxide (chemical formula is Ni 0.6 Co 0.2 Mn 0.2 (OH)2) was crushed by air flow mill, and the particle size D50 of the crushed material was 850nm;

[0041] Step 2: mixing the crushed precursor with lithium carbonate at a molar ratio of the sum of nickel, cobalt, and manganese elements to lithium element of 1:1.1, heating the mixture in an oxygen atmosphere at a heating rate of 8°C / min, with a temperature gradient from room temperature to 530°C and holding for 4 hours. After the reaction is completed, the mixture is cooled to room temperature to obtain a sinter;

[0042] Step 3, according to the molar ratio of yttrium salt, barium salt, copper salt, methanol and diethylenetriamine being 1:2:3:600:3, yttrium nitrate, barium nitrate and copper nitrate are added to methanol, and diethylenetriamine is added, and stirred to mix to obtain a sol solution;

[0043] Step 4: Add the sintered material obtained in step 2 to the sol solution at a solid-liquid ratio of 25 g / 100 mL, and heat and evaporate to dryness at 200° C. to obtain a solid gel mixture;

[0044] Step 5: Heat the solid gel mixture to 430°C at a rate of 8°C / min in an oxygen atmosphere and keep it warm for 25 minutes. Then heat it to 880°C at the same rate and keep it warm for 18 hours. Then cool it to 500°C at a cooling rate of 8°C / min and keep it warm for 1.5 hours. After crushing, screening and iron removal, a high-rate single crystal positive electrode material with a D50 of 1.5μm is obtained.

[0045] Example 2

[0046] This embodiment prepares a high-rate single crystal cathode material, and the specific process is as follows:

[0047] Step 1: nickel-cobalt-manganese oxide (chemical formula: Ni 0.6 Co 0.2 Mn 0.2 O) using a jet mill to grind the material, and the particle size D50 after grinding is 720nm;

[0048] Step 2: mixing the crushed precursor with lithium nitrate at a molar ratio of the sum of nickel, cobalt, and manganese elements to lithium element of 1:1.0, heating the mixture in an air atmosphere at a heating rate of 5°C / min, with a temperature gradient from room temperature to 500°C and holding for 5 hours. After the reaction is completed, cooling the mixture to room temperature to obtain a sinter;

[0049] Step 3, according to the molar ratio of yttrium salt, barium salt, copper salt, ethanol and ethanolamine being 1:2:3:400:1, yttrium, barium and copper acetate are added to ethanol, and ethanolamine is added, and stirring is performed to obtain a sol solution;

[0050] Step 4: Add the sintered material obtained in step 2 to the sol solution at a solid-liquid ratio of 20 g / 100 mL, and heat and evaporate to dryness at 150° C. to obtain a solid gel mixture;

[0051] Step 5: Heat the solid gel mixture to 400°C at a rate of 5°C / min in an oxygen atmosphere and keep it warm for 20 minutes. Then heat it to 850°C at the same rate and keep it warm for 12 hours. Then cool it to 450°C at a cooling rate of 5°C / min and keep it warm for 2 hours. After crushing, screening and iron removal, a high-rate small-particle single-crystal positive electrode material with a D50 of 1.2μm is obtained.

[0052] Example 3

[0053] This embodiment prepares a high-rate single crystal cathode material, and the specific process is as follows:

[0054] Step 1: The positive electrode material precursor nickel cobalt manganese carbonate (chemical formula is Ni 0.6 Co 0.2 Mn 0.2 CO3) was crushed by air flow mill, and the particle size D50 of the crushed material was 600nm;

[0055] Step 2: mixing the crushed precursor with lithium hydroxide at a molar ratio of the sum of nickel, cobalt, and manganese elements to lithium element of 1:1.2, heating the mixture in an oxygen atmosphere at a heating rate of 10°C / min, with a temperature gradient from room temperature to 550°C and holding for 3 hours. After the reaction is completed, cooling the mixture to room temperature to obtain a sinter;

[0056] Step 3, adding yttrium, barium, and copper nitrates to methyl ether according to a molar ratio of yttrium salt, barium salt, copper salt, methyl ether, and ethylene glycol of 1:2:3:800:5, and adding ethylene glycol, stirring and mixing to obtain a sol solution;

[0057] Step 4: Add the sintered material obtained in step 2 to the sol solution at a solid-liquid ratio of 30 g / 100 mL, and heat and evaporate to dryness at 250° C. to obtain a solid gel mixture;

[0058] Step 5: Heat the solid gel mixture to 450°C at a rate of 10°C / min in an oxygen atmosphere and keep it warm for 30 minutes. Then heat it to 900°C at the same rate and keep it warm for 24 hours. Then cool it to 550°C at a cooling rate of 10°C / min and keep it warm for 1 hour. After crushing, screening and iron removal, a high-rate small-particle single-crystal positive electrode material with a D50 of 0.9 μm is obtained.

[0059] Comparative Example 1

[0060] This comparative example prepared a single crystal positive electrode material. The difference from Example 1 is that no solid gel mixture was prepared. The specific process is as follows:

[0061] Step 1: The cathode material precursor nickel cobalt manganese hydroxide (chemical formula is Ni 0.6 Co 0.2 Mn 0.2 (OH)2) was crushed by air flow mill, and the particle size D50 of the crushed material was 850nm;

[0062] Step 2: Mix the crushed precursor with lithium carbonate at a molar ratio of 1:1.1 between the sum of nickel, cobalt, and manganese elements and lithium element, and heat the mixture in an oxygen atmosphere at a heating rate of 8°C / min with a heating gradient from room temperature to 530°C for 4 hours.

[0063] In step 3, the temperature was raised to 880°C at the same rate and kept at this temperature for 18 hours. The temperature was then lowered to 500°C at a cooling rate of 8°C / min and kept at this temperature for 1.5 hours. After crushing, screening and iron removal, a single crystal positive electrode material with a D50 of 3.5 μm was obtained.

[0064] Comparative Example 2

[0065] This comparative example prepares a single crystal positive electrode material. The difference from Example 2 is that no solid gel mixture is prepared. The specific process is as follows:

[0066] Step 1: nickel-cobalt-manganese oxide (chemical formula: Ni 0.6 Co 0.2 Mn 0.2 O) using a jet mill to grind the material, and the particle size D50 after grinding is 720nm;

[0067] Step 2: Mix the crushed precursor with lithium nitrate in a molar ratio of 1:1.0 between the sum of nickel, cobalt, and manganese elements and lithium element, and heat the mixture in an air atmosphere at a heating rate of 5°C / min, with a heating gradient from room temperature to 500°C and holding for 5 hours.

[0068] In step 3, the temperature is raised to 850°C at the same rate and kept at this temperature for 12 hours. The temperature is then lowered to 450°C at a cooling rate of 5°C / min and kept at this temperature for 2 hours. After crushing, screening and iron removal, a single crystal positive electrode material with a D50 of 2.8 μm is obtained.

[0069] Comparative Example 3

[0070] This comparative example prepared a single crystal positive electrode material. The difference from Example 3 is that no solid gel mixture was prepared. The specific process is as follows:

[0071] Step 1: The positive electrode material precursor nickel cobalt manganese carbonate (chemical formula is Ni 0.6 Co 0.2 Mn 0.2 CO3) was crushed by air flow mill, and the particle size D50 of the crushed material was 600nm;

[0072] Step 2: Mix the crushed precursor with lithium hydroxide in a molar ratio of 1:1.2 between the sum of nickel, cobalt, and manganese elements and lithium element, and heat the mixture in an oxygen atmosphere at a heating rate of 10°C / min with a heating gradient from room temperature to 550°C and holding for 3 hours.

[0073] In step 3, the temperature was raised to 900°C at the same rate and kept at this temperature for 24 hours. The temperature was then lowered to 550°C at a cooling rate of 10°C / min and kept at this temperature for 1 hour. After crushing, screening and iron removal, a high-rate small-particle single crystal positive electrode material with a D50 of 4.2 μm was obtained.

[0074] Comparative Example 4

[0075] This comparative example prepared a single crystal positive electrode material, and the specific process was as follows:

[0076] Step 1: adding yttrium nitrate, barium nitrate, and copper nitrate to methanol at a molar ratio of yttrium salt, barium salt, copper salt, methanol, and diethylenetriamine of 1:2:3:600:3, and adding diethylenetriamine, stirring and mixing to obtain a sol solution;

[0077] Step 2: adding the cathode material obtained in Comparative Example 1 to the sol solution at a solid-liquid ratio of 25 g / 100 mL, heating and evaporating the mixture at 200° C. to obtain a solid gel mixture;

[0078] Step 3: Heat the solid gel mixture to 430°C at a rate of 8°C / min in an oxygen atmosphere and keep it warm for 25 minutes. Then heat it to 880°C at the same rate and keep it warm for 18 hours. Then cool it to 500°C at a rate of 8°C / min and keep it warm for 1.5 hours. After screening and iron removal, a single crystal positive electrode material with a D50 of 3.5μm is obtained.

[0079] Comparative Example 5

[0080] This comparative example prepared a single crystal positive electrode material, and the specific process was as follows:

[0081] Step 1, according to the molar ratio of yttrium salt, barium salt, copper salt, ethanol and ethanolamine being 1:2:3:400:1, yttrium, barium and copper acetate are added to ethanol, and ethanolamine is added, and stirring is performed to obtain a sol solution;

[0082] Step 2: adding the cathode material obtained in Comparative Example 2 to the sol solution at a solid-liquid ratio of 20 g / 100 mL, heating and evaporating the mixture at 150° C. to obtain a solid gel mixture;

[0083] Step 3: Heat the solid gel mixture to 400°C at a rate of 5°C / min in an oxygen atmosphere and keep it warm for 20 minutes. Then heat it to 850°C at the same rate and keep it warm for 12 hours. Then cool it to 450°C at a cooling rate of 5°C / min and keep it warm for 2 hours. After screening and iron removal, a high-rate small-particle single-crystal positive electrode material with a D50 of 2.8μm is obtained.

[0084] Comparative Example 6

[0085] This comparative example prepared a single crystal positive electrode material, and the specific process was as follows:

[0086] Step 1: adding yttrium, barium, and copper nitrates to methyl ether in a molar ratio of yttrium salt, barium salt, copper salt, methyl ether, and ethylene glycol of 1:2:3:800:5, and adding ethylene glycol, stirring and mixing to obtain a sol solution;

[0087] Step 2: adding the cathode material obtained in Comparative Example 3 to the sol solution at a solid-liquid ratio of 30 g / 100 mL, heating and evaporating the mixture at 250° C. to obtain a solid gel mixture;

[0088] Step 3: Heat the solid gel mixture to 450°C at a rate of 10°C / min in an oxygen atmosphere and keep it warm for 30 minutes. Then heat it to 900°C at the same rate and keep it warm for 24 hours. Then cool it to 550°C at a rate of 10°C / min and keep it warm for 1 hour. After screening and iron removal, a high-rate small-particle single-crystal positive electrode material with a D50 of 4.2μm is obtained.

[0089] Test example

[0090] The resistivity of the positive electrode materials obtained in the embodiment and the comparative example was tested by a four-probe method at 12 MPa;

[0091] The positive electrode sheet was prepared using the positive electrode material obtained in the embodiment and the comparative example: binder (PVDF): conductive agent (acetylene black) = 90:5:5, and metallic lithium was used as the counter electrode in an argon-filled glove box to assemble a CR2025 button cell. The electrolyte was 1 M LiPF6 / EC:DMC:FEC (the volume ratio of EC, DMC and FEC was 1:1:1), and the separator was a Celgard2400 microporous separator. The initial discharge specific capacity was tested under the conditions of 0.2C / 0.2C in the voltage range of 3-4.3V. The rate performance of 0.5C / 0.2C, 1C / 0.2C, 2C / 0.2C, 4C / 0.2C and 8C / 0.2C was investigated. The capacity retention rate after 500 cycles was tested under the conditions of 1.2C / 1C. The results are shown in Table 1.

[0092] Table 1

[0093]

[0094] As shown in Table 1, the resistivity of Comparative Examples 1-3 is significantly higher than that of the Examples. This is because Comparative Examples 1-3 lack yttrium barium copper oxide coating, resulting in inferior conductivity and consequently lower rate and cycle performance. While the resistivity of Comparative Examples 4-6 is comparable to that of the Examples, the sol solution contains fully sintered positive electrode material. This leads to larger grain sizes in the final single-crystal positive electrode material, which in turn reduces rate performance.

[0095] While the embodiments of the present invention have been described in detail above with reference to the accompanying drawings, the present invention is not limited to the embodiments described above. Various modifications may be made within the scope of knowledge possessed by a person skilled in the art without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof may be combined with one another unless there is a conflict.

Claims

1. A method for preparing a high-rate single crystal cathode material from a gel mixture, characterized in that: The following steps are involved: S1: The cathode material precursor is crushed, the crushed material is mixed with a lithium source, and the temperature is raised to 500-550°C in an oxygen atmosphere to react to obtain a sintered material; S2: mixing yttrium salt, barium salt, copper salt, organic solvent and complexing agent to obtain a sol solution, adding the first sintered material to the sol solution, heating and evaporating to dryness to obtain a solid gel mixture; S3: heating the solid gel mixture to 400-450° C. for reaction in an oxygen atmosphere, then heating it to 850-900° C. for reaction, and then cooling it to 450-550° C. for reaction, and crushing the obtained reaction product to obtain the high-rate single crystal positive electrode material; In step S1, the cathode material precursor is nickel-cobalt-manganese hydroxide Ni a Co b Mn c (OH)2, nickel cobalt manganese oxide Ni a Co b Mn c O or nickel-cobalt-manganese carbonate Ni a Co b Mn c CO3, wherein 0<a≤0.6, 0<b≤0.6, 0<c≤0.4, a+b+c=1; the particle size D50 of the crushed material is 500-1000nm.

2. The method according to claim 1, characterized in that In step S2, the molar ratio of the yttrium salt, the barium salt, the copper salt, the organic solvent and the complexing agent is 1:2:3:(400-800):(1-5).

3. The method according to claim 1, characterized in that In step S2, the yttrium salt, barium salt, and copper salt are at least one of nitrate and acetate.

4. The method according to claim 1, wherein In step S2, the organic solvent is at least one of methanol, ethanol or dimethyl ether.

5. The method according to claim 1, characterized in that In step S2, the complexing agent is at least one of ethylene glycol, ethanolamine or diethylenetriamine.

6. The method according to claim 1, wherein In step S2, the temperature of heating and evaporating to dryness is 150-250°C.

7. The method according to claim 1, characterized in that In step S3, the reaction time when the temperature is raised to 400-450°C is 20-30 minutes; the reaction time when the temperature is raised to 850-900°C is 12-24 hours; and the reaction time when the temperature is lowered to 450-550°C is 1-2 hours.

8. Use of the method according to any one of claims 1 to 7 in the preparation of lithium-ion batteries.

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