A single crystal ternary cathode material and its preparation method

Abstract

The present invention discloses a single-crystal ternary positive electrode material and a preparation method thereof. The preparation method of the single-crystal ternary positive electrode material of the present invention comprises the following steps: 1) preparing single-crystal nickel-cobalt-manganese hydroxide ternary precursor solid particles; 2) preparing polycrystalline nickel-cobalt-manganese basic composite carbonate ternary precursor solid particles; 3) mixing the solid particles of step 1), lithium salt and additives to obtain a first mixture; 4) mixing the solid particles of step 2) and lithium salt to obtain a second mixture; 5) filling a container with a sealed gas-generating substance, the second mixture and the first mixture in sequence from bottom to top; 6) sintering in an oxygen-containing atmosphere after cutting; 7) collecting the upper solid particle agglomerates and crushing them. The present invention can improve the strong agglomeration force between particles during the sintering process, reduce the strong external force used for crushing, protect the mechanical strength of individual single-crystal ternary positive electrode material particles, and improve the electrochemical performance and cycle life of the single-crystal ternary positive electrode material.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and in particular to a single crystal ternary positive electrode material and a preparation method thereof. Background Art

[0002] Single-crystal ternary cathode materials are widely used in lithium-ion batteries due to their high energy density, excellent cycle performance, and safety. However, in actual production, due to the severe agglomeration of particles during sintering, a more aggressive crushing and separation method is used to obtain the powder material to ensure the processability of the subsequent electrode. However, this method not only separates the particles but also easily damages them due to the high external force, resulting in a decrease in material performance.

[0003] Therefore, for the preparation of single-crystal ternary positive electrode materials, a new preparation method is urgently needed to improve the strong agglomeration force between particles in the sintering process without introducing new impurities, thereby reducing the strong external force used in the crushing link, protecting the mechanical strength of single particles, and thus improving the service life and cycle performance of single-crystal ternary positive electrode materials.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] In order to reduce the strong agglomeration hardness between particles during the sintering preparation process of single-crystal ternary positive electrode materials, avoid using strong external forces to break the particles, and effectively protect the mechanical strength of single particles, thereby improving the rate and cycle performance of the material, the purpose of the present invention is to provide a ternary positive electrode material and a preparation method thereof, which is a low-agglomeration-hardness single-crystal ternary positive electrode material.

[0006] In a first aspect, the present invention provides a method for preparing a single-crystal ternary cathode material, comprising the following steps:

[0007] 1) subjecting an aqueous solution of a first metal salt comprising nickel, cobalt, and manganese, a first precipitant, and a first complexing agent to a first coprecipitation reaction to obtain single-crystalline nickel-cobalt-manganese hydroxide ternary precursor solid particles;

[0008] 2) subjecting an aqueous solution of a second metal salt comprising nickel, cobalt, and manganese, a second precipitant, and a second complexing agent to a second coprecipitation reaction to obtain polycrystalline nickel-cobalt-manganese basic composite carbonate ternary precursor solid particles;

[0009] 3) mixing the single crystal nickel-cobalt-manganese hydroxide ternary precursor solid particles, lithium salt and additives to obtain a first mixture;

[0010] 4) mixing the polycrystalline nickel-cobalt-manganese basic composite carbonate ternary precursor solid particles and a lithium salt to obtain a second mixture;

[0011] 5) filling the container with the sealed gas-generating material, the second mixture, and the first mixture in order from bottom to top to form a gas-generating layer, a polycrystalline layer, and a single crystal layer from bottom to top;

[0012] 6) cutting the single crystal layer into blocks from top to bottom, and then sintering the container in an oxygen-containing atmosphere to obtain solid particle agglomerates having upper, middle, and lower layers;

[0013] 7) Collecting the solid particle agglomerates in the upper layer and crushing them to obtain the single crystal ternary cathode material.

[0014] Based on the above technical solution, the present invention uses a mixture of single-crystal nickel-cobalt-manganese hydroxide ternary precursor solid particles, lithium salt and additives as a single-crystal layer, and a mixture of polycrystalline nickel-cobalt-manganese basic composite carbonate ternary precursor solid particles and lithium salt as a polycrystalline layer. The gas-producing layer, polycrystalline layer and single-crystal layer are filled in the container from bottom to top in sequence. Pore channels are generated during the agglomeration of single-crystal particles. The porous structure generated by the gas filling can improve the strong agglomeration force between the particles during the sintering process, protect the mechanical strength of the single-crystal ternary positive electrode material particles, and improve the electrochemical properties of the material.

[0015] In the above-mentioned method for preparing a single-crystal ternary positive electrode material, the nickel-cobalt-manganese hydroxide ternary precursor solid particles have a specific surface area of ​​6 to 18 m2 / g; a tap density of 1.6 to 2.2 g / cm³, and an average particle size D50 of 2.5 to 6.0 μm; as an example, D50 is 3.57 μm, the specific surface area is 10.23 m2 / g, and the tap density is 1.93 g / cm³; or, D50 is 3 μm, the specific surface area is 6.12 m2 / g, and the tap density is 2.15 g / cm³; or, D50 is 5.85 μm, the specific surface area is 17 m2 / g, and the tap density is 1.66 g / cm³;

[0016] The molar ratio of nickel, cobalt and manganese in the nickel-cobalt-manganese hydroxide ternary precursor solid particles can be adjusted according to the molar ratio of nickel, cobalt and manganese in the desired ternary positive electrode material, such as 50:20:30 or 60:20:20.

[0017] The first coprecipitation reaction comprises the following steps: under the protection of an inert atmosphere, continuously adding the aqueous solution of the first metal salt, the first precipitant and the first complexing agent to a reaction kettle containing a first base liquid to react;

[0018] The first base liquid is an aqueous solution of sodium hydroxide and ammonia, with a pH value of 12.0-13.0 (e.g., 12.5-12.8, 12.8-13.0, 12.0-12.3), and an ammonia concentration of 0.3-1.5 g / L (e.g., 1.2 g / L, 0.5 g / L, or 1.0 g / L);

[0019] The total molar concentration of the metal salt in the first metal salt solution is 1.0 to 3.0 mol / L, such as 2.1 mol / L or 1.5 mol / L;

[0020] The first precipitant is a metal hydroxide, preferably one or a mixture of sodium hydroxide, potassium hydroxide, and lithium hydroxide;

[0021] The amount of the first precipitant added is controlled to maintain the pH value of the reaction solution at 11.50 to 12.50, such as 12.0-12.3, 11.3-11.7, or 12.2-12.5;

[0022] The first precipitant can be added in the form of an aqueous solution with a mass concentration of 20 to 50%, such as a 40% sodium hydroxide solution;

[0023] The first complexing agent is ammonia water;

[0024] The amount of the first complexing agent added is controlled to maintain the concentration of ammonia in the reaction solution at 0.6-2.5 g / L, such as 1.8-2.0 g / L, 1.5-1.7 g / L or 0.6-0.8 g / L;

[0025] The first complexing agent can be added in the form of an aqueous solution with a concentration of 8 to 20 mol / L, such as a 14 mol / L ammonia aqueous solution;

[0026] The temperature of the first coprecipitation reaction is 40-80°C, such as 40°C, 50°C or 60°C.

[0027] In the above-mentioned method for preparing a single-crystal ternary positive electrode material, the specific surface area of ​​the nickel-cobalt-manganese basic composite carbonate ternary precursor solid particles is 20 to 80 m2 / g, the tap density is 0.9 to 1.8 g / cm³, and the average particle size D50 is 8.0 to 17.0 μm; as an example, the specific surface area is 30.26 m2 / g, the tap density is 1.55 g / cm³, and the average particle size D50 is 8.23 ​​μm; or, the specific surface area is 20.56 m2 / g, the tap density is 1.79 g / cm³, and the average particle size D50 is 14.2 μm; or, the specific surface area is 70.34 m2 / g, the tap density is 1.23 g / cm³, and the average particle size D50 is 16.3 μm.

[0028] The molar ratio of nickel, cobalt and manganese in the nickel-cobalt-manganese basic composite carbonate ternary precursor solid particles can be any, such as the same as the molar ratio of nickel, cobalt and manganese in the nickel-cobalt-manganese hydroxide ternary precursor solid particles;

[0029] The second coprecipitation reaction comprises the following steps: under the protection of an inert atmosphere, continuously adding the aqueous solution of the second metal salt, the second precipitant and the second complexing agent to a reaction kettle containing a second base liquid to react;

[0030] The second base solution is composed of sodium carbonate, ammonia water and water, with a pH of 7.5-8.5 (e.g., 8.0-8.3, 7.7-8.0 or 7.5-7.8), and an ammonia concentration of 1-5 g / L (e.g., 2.4 g / L, 3.2 g / L or 5 g / L);

[0031] The aqueous solution of the second metal salt is the same as the aqueous solution of the first metal salt;

[0032] The second precipitant is a metal carbonate, preferably one or a mixture of sodium carbonate and potassium carbonate;

[0033] The second precipitant is added in the form of an aqueous solution with a concentration of 3 to 6 g / L, such as 3 g / L, 4 g / L or 6 g / L;

[0034] The amount of the second precipitant added is controlled so that the pH value of the reaction solution is 6.5 to 7.5, such as 7.0 to 7.3, 7.2 to 7.5 or 6.5 to 6.8;

[0035] The second complexing agent is ammonia water;

[0036] The amount of the second complexing agent added is controlled to maintain the concentration of ammonia in the reaction solution at 2-10 g / L, such as 5-5.5 g / L, 6-6.5 g / L or 2.0-2.5 g / L;

[0037] The second complexing agent is added in the form of an aqueous solution with a concentration of 8 to 20 mol / L, such as an aqueous solution of 14 mol / L ammonia;

[0038] The temperature of the second coprecipitation reaction is 40-80°C, such as 60°C, 40°C or 70°C.

[0039] In the above-mentioned method for preparing the single crystal ternary cathode material, in the first mixture, the molar ratio of lithium: (nickel + cobalt + manganese) is (1.0-1.20):1, such as 1.01:1, 1.1:1 or 1.18:1;

[0040] The lithium salt in the first mixture is one or a mixture of lithium hydroxide and lithium carbonate;

[0041] The additive is one or a mixture of strontium carbonate, zirconium oxide, aluminum oxide, niobium oxide, and tungsten oxide;

[0042] The mass of the additive is 0.05% to 0.8% of the nickel-cobalt-manganese hydroxide ternary precursor solid particles, such as 0.2%, 0.8% or 0.05%.

[0043] In the above-mentioned method for preparing the single crystal ternary cathode material, in the second mixture, the molar ratio of lithium: (nickel + cobalt + manganese) is (1.0-1.20):1, such as 1.04:1, 1.14:1 or 1.2:1;

[0044] The lithium salt in the second mixture is the same as the lithium salt in the first mixture. Impurities are isolated by controlling the components in the polycrystalline layer to be consistent with the single crystal layer.

[0045] In the above-mentioned method for preparing the single crystal ternary cathode material, the gas generating substance is one or a mixture of calcium carbonate, magnesium carbonate, strontium carbonate, and coking pitch;

[0046] The sealing is performed using aluminum foil, and the thickness of the aluminum foil is preferably 8 to 30 μm (such as 14 μm, 8 μm or 30 μm). By using aluminum foil, on the one hand, it can be sealed when heated, and on the other hand, since the decomposition temperature of aluminum foil is 650-700°C, which is close to the temperature of single crystal growth, gas production can be controlled to start during the single crystal growth stage. The generated gas causes pore channels to form during the agglomeration of single crystal particles.

[0047] The thickness of the gas production layer is 1 to 2 cm, such as 1 cm, 1.5 cm or 2 cm;

[0048] When forming the polycrystalline layer, a solution is sprayed on the surface of the second mixture to solidify the surface, wherein the solution is preferably a mixture of ethanol and starch, the mass ratio of ethanol to starch is 1:(5-10) (such as 1:6, 1:8 or 1:10), and the mass of the solution is 20-50% (such as 20%, 30% or 50%) of the mass of the second mixture;

[0049] The thickness of the polycrystalline layer is 0.7 to 2.5 cm, such as 0.7 cm, 2 cm or 2.5 cm;

[0050] The thickness of the single crystal layer is 3 to 6 cm, such as 3 cm, 5 cm or 6 cm;

[0051] The container is a sagger made of alumina.

[0052] In the above-mentioned method for preparing a single-crystal ternary positive electrode material, in the step of cutting into blocks, the upper surface of each block after cutting is a square with a length × width of (0.5 to 8) cm * (0.5 to 8) cm, preferably a square with a size of (2 to 4) cm * (2 to 4) cm, such as 2 cm * 2 cm, 3 cm * 3 cm or 4 cm * 4 cm, and the thickness of each block is the same as the thickness of the single crystal layer; the spacing between two adjacent blocks is 0.2 to 0.5 cm, such as 0.2 cm, 0.3 cm or 0.5 cm; on the one hand, the cutting of the single crystal layer can leave gaps in the single crystal layer, so that the material can fully contact with the gas and heat exchange, and the reaction is more complete; on the other hand, the material will agglomerate and compact after sintering, and the small blocks after cutting are more convenient for subsequent rough crushing of the material;

[0053] The oxygen-containing atmosphere is air, oxygen or a mixture thereof;

[0054] The sintering temperature is 800-1000° C. (such as 800° C., 850° C. or 900° C.), and the holding time is 8-17 hours (such as 8 hours, 10 hours or 17 hours).

[0055] In the above-mentioned method for preparing the single crystal ternary cathode material, the Rockwell hardness of the single crystal layer solid particle agglomerate obtained after the sintering step is 10 to 40 HRC, such as 20 HRC, 30 HRC or 15 HRC;

[0056] The crushing is first coarse crushing and then mechanical grinding, and the coarse crushing is roller crushing, crocodile crushing or rotary grinding;

[0057] The average particle size of the single-crystal ternary positive electrode material is 1.0 to 3.0 μm (such as 1.7 μm, 2.2 μm or 3 μm), and the particle size distribution (D90-D10) / D50 value is 0.7 to 1.5 (such as 0.8, 1 or 1.2).

[0058] In a second aspect, the present invention provides a single-crystal ternary positive electrode material obtained by any of the preparation methods described above.

[0059] In a third aspect, the present invention provides a lithium-ion battery comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the positive electrode sheet comprises the single crystal ternary positive electrode material.

[0060] In the embodiments of the present invention, a 2016-type button cell was tested. The mass ratio of the ternary positive electrode material, the conductive agent, and the binder in the positive electrode sheet was 90:5:5. The conductive agent was acetylene black, the binder was polyvinylidene fluoride, the solvent was N-methylpyrrolidone, the current collector was aluminum foil, the lithium sheet was used as the negative electrode, and the electrolyte composition was as follows: ethylene carbonate:ethyl methyl carbonate = 3:7, the lithium salt was 1M lithium hexafluorophosphate, the additive was 2.0% vinylene carbonate, and the separator was polypropylene.

[0061] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0062] (1) The present invention provides a preparation method of a single crystal ternary positive electrode material with low agglomeration hardness, wherein a gas-generating coating is lined on the bottom of a sagger, and is matched with a middle layer of a polycrystalline carbonate precursor with low tap density to generate pore channels during the agglomeration of single crystal particles. The porous structure generated by the gas filling can improve the strong agglomeration force between particles in the sintering process, thereby reducing the strong external force used in the crushing link, protecting the mechanical strength of individual single crystal ternary positive electrode material particles, and improving the service life and cycle performance of the single crystal ternary positive electrode material. The middle layer of the material with the same nickel, cobalt and manganese ratio can also prevent the introduction of exogenous impurities while reducing the hardness.

[0063] (2) The single-crystal ternary cathode material prepared by the method of the present invention has excellent physical and chemical properties and can meet the battery industry's requirements for high energy density, long life, and fast charging. At the same time, the method improves the strong agglomeration between particles during the sintering process without introducing new impurities, thereby reducing the strong external force used in the crushing process, protecting the mechanical strength of individual single-crystal ternary cathode material particles, and improving the service life and cycle performance of the single-crystal ternary cathode material. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] Figure 1 This is a SEM image of the solid particle morphology of the nickel-cobalt-manganese hydroxide precursor prepared in Example 1;

[0065] Figure 2 This is a SEM image of the morphology of the nickel-cobalt-manganese basic composite carbonate precursor prepared in Example 1;

[0066] Figure 3 The diagram of the gas-producing layer, polycrystalline layer, and single crystal layer in the sagger from bottom to top is as follows: 1-single crystal layer; 2-polycrystalline layer; 3-gas-producing layer;

[0067] Figure 4 Schematic diagram of single crystal layer cutting in sagger;

[0068] Figure 5 This is a SEM image of the morphology of the ternary cathode material prepared in Example 1;

[0069] Figure 6 This is a SEM image of the morphology of the ternary cathode material prepared in Comparative Example 1;

[0070] Figure 7 This is a comparison chart of the cycling trends of the ternary positive electrode materials of Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0071] The present invention will be further described in detail below in conjunction with specific embodiments. The examples provided 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 guide for further improvements by those skilled in the art and are not intended to limit the present invention in any way.

[0072] Unless otherwise specified, the methods used in the following examples are all conventional methods and are performed according to the techniques or conditions described in the literature in the field or according to the product instructions. The materials, reagents, etc. used in the following examples are all commercially available unless otherwise specified.

[0073] Example 1

[0074] The single crystal ternary cathode material was prepared according to the following steps:

[0075] Step 1: Nickel sulfate, cobalt sulfate, and manganese sulfate were prepared into a solution at a molar ratio of 2.1 mol / L and 50:20:30. Deionized water, 40% sodium hydroxide solution, and 14 mol / L ammonia water were added to a 100 L reactor. The pH was adjusted to 12.5-12.8, and the bottom liquid ammonia concentration was adjusted to 1.2 g / L. The reaction mixture was maintained at 60°C and the rotation speed was controlled at 1500 rpm.

[0076] Then, under an inert atmosphere, a metal salt solution, a sodium hydroxide solution with a mass fraction of 40% as a precipitant, and 14 mol / L ammonia water as a complexing agent were continuously added to the reactor. The pH was gradually reduced to 12.0-12.3 within 4 hours, and the ammonia concentration was controlled within the range of 1.8-2.0 g / L. After the solid particles D50 grew to 2.0 μm, the rotation speed was reduced to 1000 r / min, and the coprecipitation reaction was continued until the solid particles D50 grew to 3.4-3.6 μm, at which time the reaction was stopped.

[0077] The obtained slurry was aged, filtered, washed and dried to obtain nickel-cobalt-manganese hydroxide precursor. The solid particles D50 was 3.57 μm, the specific surface area was 10.23 m2 / g, and the tap density was 1.93 g / cm³. The morphology is shown in the attached figure. Figure 1 As shown;

[0078] Step 2: In a 100L reactor, add deionized water, 3.0 g / L sodium carbonate solution, and 14 mol / L ammonia solution. Adjust the pH to 8.0-8.3 and the bottom liquid ammonia concentration to 2.4 g / L. Maintain the reactor temperature at 60°C and the speed at 1500 rpm.

[0079] Then, in an inert atmosphere, the metal salt solution prepared in step 1, a precipitant 3.0 g / L sodium carbonate solution, and a complexing agent 14 mol / L ammonia solution were continuously added to the reactor to adjust the pH of the reaction solution to 7.0-7.3 and the concentration of ammonia solution to 5.0-5.5 g / L. The reaction was stopped when the solid particles D50 grew to 8.0-8.5 μm.

[0080] The obtained slurry was aged, filtered, washed and dried to obtain nickel-cobalt-manganese basic composite carbonate precursor. The solid particles D50 was 8.23 ​​μm, the specific surface area was 30.26 m2 / g, and the tap density was 1.55 g / cm³. Its morphology is shown in the attached figure. Figure 2 As shown;

[0081] Step 3: lithium carbonate and nickel cobalt manganese hydroxide precursor were added to a high-pressure mixer at a molar ratio of lithium carbonate to nickel cobalt manganese hydroxide precursor = 1.01:1. Strontium carbonate and zirconium oxide were also added at a mass ratio of 0.2% based on the mass of the nickel cobalt manganese hydroxide precursor. After thorough mixing, a mixture 1 was obtained.

[0082] Step 4: lithium carbonate and nickel-cobalt-manganese basic composite carbonate precursor were added to a high-speed mixer at a molar ratio of lithium carbonate to nickel-cobalt-manganese basic composite carbonate of 1.04:1, and mixed thoroughly to obtain a mixture 2;

[0083] Step 5: First, a 14 μm thick aluminum foil is lined on the bottom of the alumina crucible, and then a 2 cm thick calcium carbonate is placed. The aluminum foil is then degassing and heat-sealed to form a gas-generating layer. Then, a 2 cm thick mixture 2 is placed as a polycrystalline layer. A mixture of ethanol and starch in a mass ratio of 1:6 is evenly sprayed on the surface at 20% of the mass of the mixture 2 to solidify the surface of the mixture 2.

[0084] Step 6: Then put 5cm single crystal layer into the above sagger, and each layer is as shown in the attached Figure 3 As shown, and as Figure 4 As shown, the single crystal layer is cut into squares with an upper surface of 2 cm*2 cm using a mold, and the distance between two adjacent blocks, i.e., the block gap, is 0.3 cm. Then, the single crystal layer is placed in an atmosphere furnace and sintered at 850°C in an oxygen atmosphere and kept warm for 10 hours.

[0085] Step 7: After sintering, the single crystal layer in the sagger was taken out and its hardness was tested to be 20HRC. After being coarsely crushed by two rollers with an upper gap of 7mm and a lower gap of 2mm, it was then mechanically ground with a grinding disc gap of 20μm to obtain the ternary positive electrode material. The morphology is shown in the attached figure. Figure 5 As shown, the average particle size is 1.7 μm and the particle size distribution (D90-D10) / D50 value is 1.2.

[0086] Example 2

[0087] The single crystal ternary cathode material was prepared according to the following steps:

[0088] Step 1: Nickel sulfate, cobalt sulfate, and manganese sulfate were prepared into a solution at a molar ratio of 2.1 mol / L and 60:20:20. Deionized water, 40% sodium hydroxide solution, and 14 mol / L ammonia were added to a 100 L reactor. The pH was adjusted to 12.8-13.0, and the bottom liquid ammonia concentration was 1.0 g / L. The reaction mixture was maintained at 50°C and the speed was controlled at 1500 rpm.

[0089] Then, under an inert atmosphere, a metal salt solution, a precipitant sodium hydroxide solution with a mass fraction of 40%, and a complexing agent 14 mol / L ammonia water were continuously added to the reactor. The pH was gradually reduced to 11.3-11.7 within 4 hours, and the ammonia concentration was within the range of 1.5-1.7 g / L. After the solid particles D50 grew to 2.0 μm, the rotation speed was reduced to 1000 r / min, and the co-precipitation reaction was continued until the solid particles D50 grew to 3.0-3.2 μm, at which time the reaction was stopped.

[0090] The obtained slurry was aged, filtered, washed, and dried to obtain a nickel-cobalt-manganese hydroxide precursor. The solid particles had a D50 of 3.0 μm, a specific surface area of ​​6.12 m2 / g, and a tap density of 2.15 g / cm³.

[0091] Step 2: Add sodium carbonate solution and ammonia water as the base liquid to a reactor containing deionized water, adjust the pH to 7.7-8.0, the ammonia concentration to 3.2g / L, maintain the reactor temperature at 40°C, and the speed at 1500r / min;

[0092] Then, in an inert atmosphere, the metal salt solution prepared in step 1, a precipitant 4g / L sodium carbonate solution, and a complexing agent 14mol / L ammonia solution were continuously added to the reactor, the pH value was adjusted to 7.2-7.5, and the ammonia concentration was maintained in the range of 6.0-6.5g / L. The reaction was stopped when the solid particles D50 grew to 14.0-14.20μm;

[0093] The obtained slurry was aged, filtered, washed, and dried to obtain a nickel-cobalt-manganese basic composite carbonate precursor. The solid particles had a D50 of 14.20 μm, a specific surface area of ​​20.56 m2 / g, and a tap density of 1.79 g / cm³.

[0094] Step 3: lithium hydroxide and nickel cobalt manganese hydroxide were added to a high-pressure mixer in a molar ratio of lithium carbonate to nickel cobalt manganese hydroxide precursor = 1.1:1. Alumina was also added at a mass ratio of 0.8% of the nickel cobalt manganese hydroxide, and the mixture was thoroughly mixed to obtain a mixture 1.

[0095] Step 4: adding lithium hydroxide and nickel-cobalt-manganese basic composite carbonate precursor to a high-speed mixer in a molar ratio of lithium carbonate to nickel-cobalt-manganese basic composite carbonate = 1.14:1, and mixing thoroughly to obtain a mixture 2;

[0096] Step 5: First, an 8-μm-thick aluminum foil is lined at the bottom of the alumina crucible, and then a 1.5-cm-thick strontium carbonate is placed. The aluminum foil is then degassing and heat-sealed to form a gas-generating layer. Then, a 0.7-cm-thick mixture 2 is placed as a polycrystalline layer. A mixture of ethanol and starch in a mass ratio of 1:8 is evenly sprayed on the surface at 30% by mass of the mixture 2 to solidify the surface of the mixture 2.

[0097] Step 6: Then, place a 3cm single crystal layer in the above sagger and cut it into 3cm*3cm sizes using a mold. The distance between two adjacent blocks, i.e. the block gap, is 0.2cm. Place it in an atmosphere kiln and sinter it at 900℃ in an oxygen atmosphere for 8 hours.

[0098] Step 7: After sintering, the single crystal layer in the sagger is taken out and its hardness is tested to be 30HRC. It is then coarsely crushed by two rollers with an upper gap of 7mm and a lower gap of 2mm, and then mechanically ground with a grinding disc gap of 20μm to obtain a ternary positive electrode material with an average particle size of 2.2μm and a particle size distribution (D90-D10) / D50 value of 1.0.

[0099] Example 3

[0100] The single crystal ternary cathode material was prepared according to the following steps:

[0101] Step 1: Nickel sulfate, cobalt sulfate, and manganese sulfate were prepared into a solution at a molar ratio of 1.5 mol / L and 80:10:10. Deionized water, 40% sodium hydroxide solution, and 14 mol / L ammonia water were added to a 100 L reactor. The pH was controlled at 12.0-12.3, and the bottom liquid ammonia concentration was adjusted to 0.5 g / L. The reaction mixture was maintained at 40°C and the rotation speed was controlled at 1500 rpm.

[0102] Then, under an inert atmosphere, a metal salt solution, a precipitant sodium hydroxide solution with a mass fraction of 40%, and a complexing agent 14 mol / L ammonia water were continuously added to the reactor. The pH was gradually reduced to 12.2-12.5 within 4 hours, and the ammonia concentration was within the range of 0.6-0.8 g / L. After the solid particles D50 grew to 2.0 μm, the rotation speed was reduced to 1000 r / min, and the co-precipitation reaction was continued until the solid particles D50 grew to 5.8-6.0 μm, and the reaction was stopped.

[0103] The obtained slurry was aged, filtered, washed, and dried to obtain a nickel-cobalt-manganese hydroxide precursor. The solid particles had a D50 of 5.85 μm, a specific surface area of ​​17.00 m2 / g, and a tap density of 1.66 g / cm³.

[0104] Step 2: Add sodium carbonate solution and ammonia water as the base liquid to the reactor containing deionized water, adjust the pH to 7.5-7.8, the ammonia concentration to 5.0g / L, maintain the reactor temperature at 70°C, and maintain the speed at 1500r / min;

[0105] Then, in an inert atmosphere, the metal salt solution prepared in step 1, a precipitant 6 g / L sodium carbonate solution, and a complexing agent 14 mol / L ammonia solution were continuously added to the reactor, the pH value was adjusted to 6.5-6.8, and the ammonia concentration was maintained in the range of 2.0-2.5 g / L. The reaction was stopped when the solid particles D50 grew to 16-17 μm.

[0106] The obtained slurry was aged, filtered, washed, and dried to obtain a nickel-cobalt-manganese basic composite carbonate precursor. The solid particles had a D50 of 16.3 μm, a specific surface area of ​​70.34 m2 / g, and a tap density of 1.23 g / cm³.

[0107] Step 3: Lithium hydroxide and nickel cobalt manganese hydroxide were added to a high-pressure mixer at a molar ratio of lithium hydroxide to nickel cobalt manganese hydroxide precursor = 1.18:1. Niobium oxide and tungsten oxide were also added at a mass ratio of 0.05% of the mass of the nickel cobalt manganese hydroxide, respectively. After thorough mixing, a mixture 1 was obtained.

[0108] Step 4: adding lithium hydroxide and nickel-cobalt-manganese basic composite carbonate precursor to a high-speed mixer in a molar ratio of lithium hydroxide to nickel-cobalt-manganese basic composite carbonate = 1.2:1, and mixing thoroughly to obtain a mixture 2;

[0109] Step 5: First, a 30 μm thick aluminum foil is lined at the bottom of the alumina crucible, and then a 1 cm thick calcium carbonate is placed. The aluminum foil is then degassing and heat-sealed to form a gas-generating layer. Then, a 2.5 cm thick mixture 2 is placed as a polycrystalline layer. A mixture of ethanol and starch in a mass ratio of 1:10 is evenly sprayed on the surface at 50% of the mass of the mixture 2 to solidify the surface of the mixture 2.

[0110] Step 6: Then, place a 6cm single crystal layer in the above sagger and cut it into 4cm*4cm size using a mold. The distance between two adjacent blocks, i.e. the block gap, is 0.5cm. Then, place it in an atmosphere kiln and sinter it at 800℃ in an oxygen atmosphere and keep it warm for 17 hours.

[0111] Step 7: After sintering, the single crystal layer in the sagger is taken out and its hardness is tested to be 15HRC. It is then coarsely crushed by two rollers with an upper gap of 7mm and a lower gap of 2mm, and then mechanically ground with a grinding disc gap of 20μm to obtain a ternary positive electrode material with an average particle size of 3.0μm and a particle size distribution (D90-D10) / D50 value of 0.8.

[0112] Comparative Example 1 (only single crystal layer is provided)

[0113] Nickel sulfate, cobalt sulfate, and manganese sulfate were prepared into a solution at a molar ratio of 2.1 mol / L and 50:20:30. Deionized water, 40% sodium hydroxide solution, and 14 mol / L ammonia were added to a 100 L reactor. The pH was adjusted to 12.5-12.8, and the bottom liquid ammonia concentration was 1.2 g / L. The reactor was maintained at 60°C and the rotation speed was controlled at 1500 r / min.

[0114] Then, under an inert atmosphere, a metal salt solution, a sodium hydroxide solution with a precipitant mass fraction of 40%, and a complexing agent 14 mol / L ammonia water were continuously added to the reactor, and the pH was gradually reduced to 12.0-12.3 within 4 hours, and the ammonia concentration was controlled within the range of 1.8-2.0 g / L. After the solid particles D50 grew to 2.0 μm, the rotation speed was reduced to 1000 r / min, and the coprecipitation reaction was continued until the solid particles D50 grew to 3.4-3.6 μm. The reaction was stopped until the solid particles D50 grew to 3.4-3.6 μm.

[0115] The obtained slurry was aged, filtered, washed, and dried to obtain a nickel-cobalt-manganese hydroxide precursor. The solid particles had a D50 of 3.42 μm, a specific surface area of ​​9.89 m2 / g, and a tap density of 1.89 g / cm³.

[0116] Lithium carbonate and nickel cobalt manganese hydroxide were added to a high-pressure mixer at a molar ratio of lithium carbonate to nickel cobalt manganese hydroxide precursor of 1.01:1. Strontium carbonate and zirconium oxide were added at a mass ratio of 0.2% of the nickel cobalt manganese hydroxide, respectively. After thorough mixing, the mixture was placed in a sagger to form a 5 cm high material layer. The material layer was cut into squares with an upper surface of 2 cm*2 cm using a mold. The distance between two adjacent blocks, i.e., the block gap, was 0.3 cm. The mixture was then placed in an atmosphere kiln and sintered at 850°C in an oxygen atmosphere for 10 hours.

[0117] After sintering, the obtained single crystal layer agglomerate was taken out and its hardness was tested to be 50HRC. After being crushed by two-stage rollers with an upper gap of 7mm and a lower gap of 2mm, it was air flow crushed and the particle size D50 was controlled to be 3.0-4.0μm to obtain the ternary positive electrode material. Its average particle size was measured to be 1.74μm, and the particle size distribution (D90-D10) / D50 value was 1.18. The morphology is shown in the attached figure. Figure 6 shown.

[0118] Comparative Example 2 (Single Crystal Layer + Polycrystalline Layer)

[0119] Step 1: Nickel sulfate, cobalt sulfate, and manganese sulfate were prepared into a solution at a molar ratio of 2.1 mol / L and 50:20:30. Deionized water, 40% sodium hydroxide solution, and 14 mol / L ammonia water were added to a 100 L reactor. The pH was adjusted to 12.5-12.8, and the bottom liquid ammonia concentration was adjusted to 1.2 g / L. The reaction mixture was maintained at 60°C and the rotation speed was controlled at 1500 rpm.

[0120] Then, under an inert atmosphere, a metal salt solution, a sodium hydroxide solution with a mass fraction of 40% as a precipitant, and 14 mol / L ammonia water as a complexing agent were continuously added to the reactor. The pH was gradually reduced to 12.0-12.3 within 4 hours, and the ammonia concentration was controlled within the range of 1.8-2.0 g / L. After the solid particles D50 grew to 2.0 μm, the rotation speed was reduced to 1000 r / min, and the coprecipitation reaction was continued until the solid particles D50 grew to 3.4-3.6 μm, at which time the reaction was stopped.

[0121] The obtained slurry was aged, filtered, washed, and dried to obtain a nickel-cobalt-manganese hydroxide precursor. The solid particles had a D50 of 3.48 μm, a specific surface area of ​​10.56 m2 / g, and a tap density of 1.89 g / cm³.

[0122] Step 2: In a 100L reactor, add deionized water, 3.0 g / L sodium carbonate solution, and 14 mol / L ammonia solution. Adjust the pH to 8.0-8.3 and the bottom liquid ammonia concentration to 2.4 g / L. Maintain the reactor temperature at 60°C and the speed at 1500 rpm.

[0123] Then, in an inert atmosphere, the metal salt solution prepared in step 1, a precipitant 3.0 g / L sodium carbonate solution, and a complexing agent 14 mol / L ammonia solution were continuously added to the reactor to adjust the pH of the reaction solution to 7.0-7.3 and the concentration of ammonia solution to 5.0-5.5 g / L. The reaction was stopped when the solid particles D50 grew to 8.0-8.5 μm.

[0124] The obtained slurry was aged, filtered, washed, and dried to obtain a nickel-cobalt-manganese basic composite carbonate precursor. The solid particles had a D50 of 9.14 μm, a specific surface area of ​​28.36 m2 / g, and a tap density of 1.59 g / cm³.

[0125] Step 3: lithium carbonate and nickel cobalt manganese hydroxide precursor were added to a high-pressure mixer at a molar ratio of lithium carbonate to nickel cobalt manganese hydroxide precursor = 1.01:1. Strontium carbonate and zirconium oxide were also added at a mass ratio of 0.2% based on the mass of the nickel cobalt manganese hydroxide precursor. After thorough mixing, a mixture 1 was obtained.

[0126] Step 4: lithium carbonate and nickel-cobalt-manganese basic composite carbonate precursor were added to a high-speed mixer at a molar ratio of lithium carbonate to nickel-cobalt-manganese basic composite carbonate of 1.04:1, and mixed thoroughly to obtain a mixture 2;

[0127] Step 5: Place a 2 cm thick layer of mixture 2 at the bottom of the alumina crucible as a polycrystalline layer, and evenly spray a mixture of ethanol and starch in a mass ratio of 1:6 on the surface according to 20% of the mass of mixture 2 to solidify the surface of mixture 2;

[0128] Step 6: Then, place a 5cm single crystal layer in the above sagger, and use a mold to cut the single crystal layer into squares with an upper surface of 2cm*2cm. The distance between two adjacent blocks, i.e. the block gap, is 0.3cm. Then, place it in an atmosphere kiln and sinter it at 850℃ in an oxygen atmosphere and keep it warm for 10 hours.

[0129] Step 7: After sintering, the obtained agglomerates were taken out and tested for hardness of 45HRC. The obtained agglomerates were then crushed by two-stage rollers with an upper gap of 7mm and a lower gap of 2mm, and then air flow crushed to control the particle size D50 to 3.0-4.0μm to obtain the ternary positive electrode material. The average particle size was measured to be 1.81μm, and the particle size distribution (D90-D10) / D50 value was 1.25.

[0130] Depend on Figure 5 and Figure 6 From the comparison results, it can be seen that, relative to Comparative Example 1, during the sintering process of Example 1, a gas-producing layer is set at the bottom of the crucible, and a submicron high-surface-weight basic composite carbonate precursor of the same molar ratio is used as a buffer layer. This not only forms a loose structure during the sintering process of the material, but also reduces the degree of compaction of the material. Therefore, only a weak crushing method is required to open the agglomeration bonding force, rather than using a stronger force such as air flow crushing, thereby protecting the degree of completion and mechanical strength of the particles, thereby protecting the electrical properties of the material, and isolating the impurities such as aluminum foil in the gas-producing layer from being introduced into the single crystal particles.

[0131] Effect Examples

[0132] The ternary positive electrode materials obtained in the above embodiments and comparative examples were prepared into electrode plates. In the preparation of the plates, the mass ratio of the ternary positive electrode material, the conductive agent and the binder was 90:5:5, wherein the conductive agent was acetylene black, the binder was polyvinylidene fluoride, the solvent was N-methylpyrrolidone, the current collector was aluminum foil, and the lithium plate was used as the negative electrode. The electrolyte composition was as follows: ethylene carbonate: ethyl methyl carbonate = 3:7, the lithium salt was lithium hexafluorophosphate 1M, the additive was 2.0% vinylene carbonate, and the separator was polypropylene. The plates were assembled into 2016-type button batteries, and then the electrochemical properties of the batteries were tested. The test temperature was a constant temperature cabinet at 25°C, and the rate test scheme was 0.2C charge / 0.2C discharge, 0.33C charge / 0.33C discharge, 1C charge / 1C discharge, followed by 0.5C charge / 1C discharge cycles. The test voltage range was 2.8-4.45V. The test results are shown in Table 1 below. The cycle trend graphs of Example 1 and Comparative Example 1 are shown in the attached Figure 7 shown.

[0133] The performance comparison results of Examples 1-3 and Comparative Examples 1-2 are shown in Table 1.

[0134] Table 1. Performance comparison results of examples and comparative examples

[0135]

[0136] From the comparison results of Examples 1-3 and Comparative Examples 1-2 in Table 1 above, it can be seen that the present invention mixes nickel-cobalt-manganese oxide solid particles, nickel-cobalt-manganese composite basic carbonate ternary precursor solid particles and lithium salts and additives, and sintering and crushing the obtained mixture. The obtained single-crystal ternary positive electrode material has a lower hardness than that of Comparative Example 1, does not need to be separated by a stronger crushing method, and has a higher capacity. Although Comparative Example 2 is provided with a single crystal layer and a polycrystalline layer, no gas-producing layer is added. Compared with Comparative Example 1, although the hardness is reduced, the effect is not obvious. In addition, it can be clearly seen that if the gas-producing layer is directly in contact with the single crystal layer, foreign matter may be introduced, which will lead to the inability of the method and material to be industrially produced on a large scale. At the same time, the comparison of the electrical properties of Example 1 with Comparative Examples 1 and Comparative Examples 2 shows that the low-hardness material has less crushing due to the strong external force on the particles, and the relatively complete particles improve the electrical properties of the material in terms of charging capacity and first efficiency. However, although the charging and first efficiency of Comparative Example 2 are improved compared with Comparative Example 1, they are not obvious enough. In addition, Figure 7 Comparison of the cycling performance of the materials shows that the material prepared in Example 1 is superior. Therefore, the present invention improves the strong agglomeration between particles during the sintering process, reduces the strong external forces used in the crushing process, protects the mechanical strength of individual single-crystal ternary cathode material particles, and improves the service life and cycling performance of the single-crystal ternary cathode material.

[0137] The present invention has been described in detail above. For those skilled in the art, without departing from the purpose and scope of the present invention, can implement the present invention in a wider range under equivalent parameters, concentration and conditions. Although the present invention provides specific embodiments, it should be understood that the present invention can be further improved. In a word, according to the principle of the present invention, the application is intended to include any variation, purposes or improvements of the present invention, including departing from the disclosed scope in the application and the changes made with conventional techniques known in the art.

Claims

1. A method for preparing a single crystal ternary cathode material, characterized in that: The following steps are involved: 1) subjecting an aqueous solution of a first metal salt containing nickel, cobalt, and manganese, a first precipitant, and a first complexing agent to a first coprecipitation reaction to obtain single-crystalline nickel-cobalt-manganese hydroxide ternary precursor solid particles; 2) subjecting an aqueous solution of a second metal salt comprising nickel, cobalt, and manganese, a second precipitant, and a second complexing agent to a second coprecipitation reaction to obtain polycrystalline nickel-cobalt-manganese basic composite carbonate ternary precursor solid particles; 3) mixing the single crystal nickel-cobalt-manganese hydroxide ternary precursor solid particles, lithium salt and additives to obtain a first mixture; The additive is one or a mixture of strontium carbonate, zirconium oxide, aluminum oxide, niobium oxide, and tungsten oxide; 4) mixing the polycrystalline nickel-cobalt-manganese basic composite carbonate ternary precursor solid particles and a lithium salt to obtain a second mixture; 5) filling the container with the sealed gas-generating material, the second mixture, and the first mixture in order from bottom to top to form a gas-generating layer, a polycrystalline layer, and a single crystal layer from bottom to top; The gas-generating substance is one or a mixture of calcium carbonate, magnesium carbonate, strontium carbonate, and coking pitch; 6) cutting the single crystal layer into blocks from top to bottom, and then sintering the container in an oxygen-containing atmosphere to obtain solid particle agglomerates with upper, middle, and lower layers; 7) Collecting the solid particle agglomerates in the upper layer and crushing them to obtain the single crystal ternary cathode material.

2. The method for preparing a single crystal ternary cathode material according to claim 1, wherein: The specific surface area of ​​the nickel-cobalt-manganese hydroxide ternary precursor solid particles is 6-18 m2 / g; the tap density is 1.6-2.2 g / cm 3 , the average particle size D50 is 2.5 to 6.0 μm; The first coprecipitation reaction comprises the following steps: under the protection of an inert atmosphere, continuously adding the aqueous solution of the first metal salt, the first precipitant and the first complexing agent to a reaction kettle containing a first base liquid to react; The first base liquid is an aqueous solution of sodium hydroxide and ammonia, with a pH value of 12.0 to 13.0 and an ammonia concentration of 0.3 to 1.5 g / L; The total molar concentration of the metal salt in the first metal salt solution is 1.0 to 3.0 mol / L; The first precipitant is a metal hydroxide; The amount of the first precipitant added is controlled so that the pH value of the reaction solution is 11.50 to 12.50; The first precipitant is added in the form of an aqueous solution with a mass concentration of 20 to 50%; The first complexing agent is ammonia water; The first complexing agent is added in the form of an aqueous solution with a concentration of 8 to 20 mol / L; The amount of the first complexing agent added is controlled so that the concentration of ammonia in the reaction solution is 0.6 to 2.5 g / L; The temperature of the first coprecipitation reaction is 40-80°C.

3. The method for preparing a single crystal ternary cathode material according to claim 2, wherein: The first precipitant is one or a mixture of sodium hydroxide, potassium hydroxide and lithium hydroxide.

4. The method for preparing a single crystal ternary cathode material according to claim 1, wherein: The nickel-cobalt-manganese basic composite carbonate ternary precursor solid particles have a specific surface area of ​​20 to 80 m2 / g and a tap density of 0.9 to 1.8 g / cm 3 , the average particle size D50 is 8.0~17.0μm; The second coprecipitation reaction comprises the following steps: under the protection of an inert atmosphere, continuously adding the aqueous solution of the second metal salt, the second precipitant and the second complexing agent to a reaction kettle containing a second base liquid to react; The second base liquid is composed of sodium carbonate, ammonia water and water, with a pH of 7.5 to 8.5 and an ammonia concentration of 1 to 5 g / L; The aqueous solution of the second metal salt is the same as the aqueous solution of the first metal salt; The second precipitant is a metal carbonate; The second precipitant is added in the form of an aqueous solution with a concentration of 3 to 6 g / L; The amount of the second precipitant added is controlled so that the pH value of the reaction solution is 6.5 to 7.5; The second complexing agent is ammonia water; The second complexing agent is added in the form of an aqueous solution with a concentration of 8 to 20 mol / L; The amount of the second complexing agent added is controlled so that the concentration of aqueous ammonia in the reaction solution is 2 to 10 g / L; The temperature of the second coprecipitation reaction is 40-80°C.

5. The method for preparing a single crystal ternary cathode material according to claim 4, characterized in that: The second precipitant is one of sodium carbonate and potassium carbonate or a mixture of several of them.

6. The method for preparing a single crystal ternary cathode material according to claim 1, wherein: In the first mixture, the molar ratio of lithium: (nickel + cobalt + manganese) is (1.0-1.20):1; The lithium salt in the first mixture is one or a mixture of lithium hydroxide and lithium carbonate; The mass of the additive is 0.05% to 0.8% of the nickel-cobalt-manganese hydroxide ternary precursor solid particles.

7. The method for preparing a single crystal ternary cathode material according to claim 1, wherein: In the second mixture, the molar ratio of lithium: (nickel + cobalt + manganese) is (1.0-1.20):1; The lithium salt in the second mixture is the same as the lithium salt in the first mixture.

8. The method for preparing a single crystal ternary cathode material according to claim 1, wherein: The sealing is made of aluminum foil; The thickness of the gas production layer is 1 to 2 cm; When forming the polycrystalline layer, spraying a solution on the surface of the second mixture to solidify the surface; The thickness of the polycrystalline layer is 0.7 to 2.5 cm; The thickness of the single crystal layer is 3 to 6 cm; The container is a sagger made of alumina.

9. The method for preparing a single crystal ternary cathode material according to claim 8, characterized in that: The thickness of the aluminum foil is 8 to 30 μm.

10. The method for preparing a single crystal ternary cathode material according to claim 8, characterized in that: The solution is a mixture of ethanol and starch, the mass ratio of ethanol to starch is 1:(5-10), and the mass of the solution is 20-50% of the mass of the second mixture.

11. The method for preparing a single crystal ternary cathode material according to claim 1, wherein: In the step of cutting into blocks, the upper surface of each block after cutting is a square with a length × width of (0.5 to 8) cm * (0.5 to 8) cm, and the distance between two adjacent blocks is 0.2 to 0.5 cm; The oxygen-containing atmosphere is air, oxygen or a mixture thereof; The sintering temperature is 800-1000° C., and the heat preservation time is 8-17 hours.

12. The method for preparing a single crystal ternary cathode material according to claim 11, characterized in that: The size of the square is (2-4) cm*(2-4) cm.

13. The method for preparing a single crystal ternary cathode material according to claim 1, wherein: The Rockwell hardness of the single crystal layer solid particle agglomerates obtained after the sintering step is 10 to 40 HRC; The crushing is first coarse crushing and then mechanical grinding, and the coarse crushing is roller crushing, crocodile crushing or rotary grinding; The average particle size of the single crystal ternary positive electrode material is 1.0 to 3.0 μm, and the particle size distribution (D90-D10) / D50 value is 0.7 to 1.

5.

14. The single crystal ternary cathode material obtained by the preparation method according to any one of claims 1 to 13.

15. A lithium-ion battery comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, characterized in that: The positive electrode plate includes the single crystal ternary positive electrode material according to claim 14.

Images