Preparation method of nickel-cobalt-lithium aluminate positive electrode material

Abstract

The application discloses a preparation method of a nickel-cobalt-lithium aluminate positive electrode material. In the application, aluminum elements are enriched on the surface layer of the material through a non-uniform structure design, so that a loose porous structure surface layer is formed. That is, the application can effectively increase the contact area of the material and electrolyte by constructing a loose porous material surface, so as to increase the transmission path (site) of lithium ions, and then the positive electrode material has good rate performance. Meanwhile, the method can reduce the content of Ni on the surface layer of the nickel-cobalt-lithium aluminate positive electrode material, so as to improve the interface stability of the positive electrode material, and the additional coating process is avoided.

Description

Technical Field

[0001] This invention relates to a method for preparing lithium nickel cobalt aluminum oxide cathode material. Background Technology

[0002] The rapid development of electric vehicles has spurred extensive research into power lithium-ion batteries. However, the high price and limited capacity of lithium cobalt oxide cathodes, commonly used in 3C consumer electronics, restrict their application in power batteries. Lithium nickel cobalt aluminum oxide (NiCOA) cathode materials, with their high discharge capacity, high tap density, and lower production cost, have become strong competitors in the field of power lithium-ion battery cathode materials. However, due to the high reactivity of nickel, the surface reactions between NiCOA and the electrolyte are severe, leading to irreversible phase transitions and capacity loss. Furthermore, the operating environment of power batteries requires cathode materials with good rate performance. Therefore, improving the specific surface area of ​​NiCOA materials while simultaneously enhancing the stability of the electrode-electrolyte interface is crucial for improving the performance of NiCOA materials.

[0003] To improve the interfacial stability and ion transport capacity of lithium nickel cobalt manganese oxide materials, researchers have conducted extensive modification studies, commonly employing methods such as doping, coating, and nanostructuring. Chinese patent (CN110444762B) discloses a lithium nickel cobalt manganese oxide material with activated carbon and boron co-coated on an organic binder film and its preparation method. By coating lithium borate onto the material surface to form a fast ion conductor, the dissolution of transition metal ions by the electrolyte is reduced, enhancing the interfacial stability of the material and improving cycle life. Chinese patent (CN111009646B) discloses a high-rate near-single-crystal lithium nickel cobalt aluminum oxide cathode material with a coating layer and its preparation method. This involves mixing a precursor and a lithium salt in an oxygen-rich environment... The process involves sintering in an environmentally friendly environment, washing with water, mixing with a coating agent, and then sintering at high temperature to obtain a coated, near-single-crystal lithium nickel cobalt aluminum oxide material. The near-single-crystal morphology of the coating improves the cycle performance and rate performance of lithium nickel cobalt aluminum oxide. Chinese patent (CN115632115A) discloses a lanthanum aluminate-coated ternary cathode material for lithium nickel cobalt manganese oxide and its preparation method. By forming a coating layer of lanthanum aluminate on the surface of the lithium nickel cobalt manganese oxide material, the dissolution of transition metal ions is reduced, side reactions between the material and the electrolyte and corrosion by HF acid are suppressed, and the interfacial stability of the material is improved. Although the above modification methods can improve the interfacial stability of the material, the coating method is detrimental to lithium-ion transport, leading to a decrease in the capacity of the electrode material. Summary of the Invention

[0004] Purpose of the invention: The purpose of this invention is to provide a method for preparing lithium nickel cobalt aluminum oxide cathode material. The lithium nickel cobalt aluminum oxide cathode material prepared by this method has a loose and porous surface structure, which can improve rate performance and maintain good interfacial stability.

[0005] Technical solution: The preparation method of lithium nickel cobalt aluminum oxide cathode material of the present invention includes the following steps:

[0006] (1) Add 20% (volume fraction) of ammonia water with a concentration of 0.1-0.5 mol / L to the reactor as a base solution; the base solution is used to provide the initial reaction environment;

[0007] (2) A portion of the nickel-cobalt solution and an equal volume of ammonia solution with a concentration of 0.5 mol / L were pumped into the reactor to obtain a mixture. The pH of the mixture was adjusted to 10-11.5 using sodium hydroxide solution.

[0008] (3) After the mixture reacts at high temperature for 30-80 hours, aluminum solution, the remaining nickel-cobalt solution, and ammonia water of the same volume as the nickel-cobalt solution are continuously pumped into the reactor. The pumping flow rate of aluminum solution and nickel-cobalt solution is adjusted so that the nickel-cobalt solution and aluminum solution are added at the same time. When aluminum solution is added, 80-90% (volume percentage) of nickel-cobalt solution has already been added to the reactor. That is, aluminum solution is added to the reactor only after 80-90% of nickel-cobalt solution has been added to the reactor. By feeding in stages, aluminum solution is added in the later stage of the synthesis reaction. During the precipitation and growth of the precursor, it is naturally enriched on the surface of the material particles, realizing the non-uniform distribution of aluminum element inside the material particles.

[0009] (4) After aging for 10 to 60 hours, the precipitate obtained is filtered and separated. After separation, the precipitate is washed and dried to obtain the precursor. The precursor is a spherical powder with a diameter of about 10 micrometers. The interior of a single particle is nickel and cobalt, and aluminum is distributed on the surface of the particle, showing an uneven distribution in the particle.

[0010] (5) The precursor is mixed with lithium salt and placed in a tube furnace for high-temperature calcination in an oxygen-filled atmosphere. After calcination, it is naturally cooled to room temperature, ground and pulverized, and sieved to obtain lithium nickel cobalt aluminum oxide cathode material.

[0011] In step (2), Ni in the nickel-cobalt solution 2+ and Co 2+ The concentration of total metal ions is 1–2 mol / L; the concentration of ammonia is 0.5–2 mol / L.

[0012] Among them, Ni 2+ and Co 2+ The molar ratio is 1-xy:x; x takes values ​​of 0.03 to 0.1, and y takes values ​​of 0.02 to 0.1.

[0013] In step (2), sodium hydroxide solution is used to adjust the pH of the mixture, and the concentration of sodium hydroxide solution is 1 to 5 mol / L.

[0014] In step (2), the pumping flow rates of the nickel-cobalt solution and ammonia are both 1 to 5 mL / min.

[0015] In step (3), the temperature inside the reactor is maintained at 50-70°C and the stirring speed is 400-800 rpm / min, and the mixture reacts.

[0016] In step (3), in the aluminum solution, Al 3+ The concentration is 0.2–0.8 mol / L.

[0017] In step (4), the precipitate is washed with deionized water until the pH of the filtrate is neutral, and then dried in a forced-air drying oven at 110°C for 10–48 h.

[0018] In step (4), the molecular formula of the precursor is Ni. (1-x-y) Co x Al y (OH)2, x takes values ​​of 0.03 to 0.1, and y takes values ​​of 0.02 to 0.1.

[0019] In step (5), the lithium salt is LiOH·H2O, and the molar ratio of lithium salt to precursor is Li + :(Ni 2+ +Co 2+ +Al 3 + = 1.0~1.2:1.

[0020] In step (5), the calcination process is divided into two stages: the first stage is to raise the temperature to 300-500℃ and hold it for 6-10 hours; the second stage is to continue to raise the temperature to 650-850℃ and hold it for 8-18 hours.

[0021] This invention utilizes the uneven distribution of aluminum within the material particles to enrich aluminum on the material's surface, resulting in a loose and porous surface structure. This is because the high aluminum content during deposition leads to poor adsorption between the deposited particles, causing loose particle packing on the surface and altering the core-gathering behavior, thus creating a loose and porous surface structure. Furthermore, the enriched aluminum effectively improves the stability of the surface structure (reducing the nickel content), thereby improving interfacial stability and preventing significant capacity loss due to the introduction of new coatings. This invention employs a co-precipitation method to prepare the precursor material. By controlling the timing of aluminum solution addition, aluminum is primarily distributed in the outer layer of the precursor material, resulting in a loose and porous surface morphology after calcination. This invention, through the enrichment of aluminum on the material's surface, constructs a loose surface structure, increasing the contact area between the cathode material and the electrolyte, and expanding lithium-ion transport sites, thus giving the material excellent rate performance.

[0022] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: The method of the present invention enriches aluminum elements on the surface of the material through non-uniform structural design, thereby forming a loose and porous surface morphology. By constructing a loose and porous material surface, the contact area between the material and the electrolyte can be effectively increased, thereby increasing the transport path (sites) of lithium ions, and thus enabling the cathode material to have good rate performance. At the same time, the method of the present invention can reduce the Ni content on the surface of the lithium nickel cobalt aluminum oxide cathode material, thereby improving the interfacial stability of the cathode material and avoiding additional coating processes. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the co-precipitation process for preparing lithium nickel cobalt aluminum oxide cathode material precursors according to the present invention;

[0024] Figure 2 This is a SEM image of the cross-section of the cathode material particles obtained after calcination in Example 2.

[0025] Figure 3 for Figure 2 EDS line scan at the arrow in the cross-section of medium-sized particles;

[0026] Figure 4 The image shows a SEM image of the cross-section of the cathode material particles in Comparative Example 1.

[0027] Figure 5 Rate performance diagrams of coin cells made from the cathode materials in Example 2 and Comparative Example 1;

[0028] Figure 6 The graph shows the cycle performance of the coin cells made from the cathode materials in Example 2 and Comparative Example 1. Detailed Implementation

[0029] Example 1

[0030] The method for preparing lithium nickel cobalt aluminum oxide cathode material of the present invention includes the following steps:

[0031] (1) Weigh out NiSO4, CoSO4, and Al2(SO4)3 according to the molar ratio Ni:Co:Al = 0.8:0.1:0.1; dissolve NiSO4 and CoSO4 in deionized water to prepare 10L of nickel-cobalt solution. In the nickel-cobalt solution, Ni 2+ and Co 2+ The total concentration is 2 mol / L. Al₂(SO₄)₃ is dissolved in deionized water to prepare 2.22 L of aluminum solution. In the aluminum solution, Al… 3+ The concentration of ammonia is 0.5 mol / L; prepare ammonia solution with a concentration of 0.5 mol / L and sodium hydroxide solution with a concentration of 1 mol / L;

[0032] (2) Adopting such Figure 1 The reaction apparatus shown has a base solution of 20% of the reactor volume of ammonia water with a concentration of 0.1 mol / L added to the reactor.

[0033] (3) 8L of nickel-cobalt solution and an equal volume of ammonia solution with a concentration of 0.5-2mol / L were pumped into the reactor using a peristaltic pump. The pumping flow rate of both the nickel-cobalt solution and the ammonia solution was 1mL / min. The mixture was obtained. The temperature inside the reactor was kept at 50℃ and the stirring speed was 400rpm / min. The pH of the mixture was adjusted to 10.0 by adding a 1mol / L sodium hydroxide solution.

[0034] (4) After reacting for 80 hours, the aluminum solution, the remaining 2L of nickel-cobalt solution and ammonia water of the same volume as the nickel-cobalt solution are pumped into the reactor by a peristaltic pump. The pumping flow rate of the aluminum solution and the nickel-cobalt solution is adjusted so that the nickel-cobalt solution and the aluminum solution are added at the same time.

[0035] (5) After aging for 60 hours, the resulting precipitate was filtered and separated. The precipitate was washed with deionized water until the pH of the filtrate was about 7. Then, it was dried in a forced-air drying oven at 110°C for 10 hours to obtain precursor particles. The average composition of the obtained precursor can be expressed as Ni 0.8 Co 0.1 Al 0.1 (OH)2, the distribution of each element in the precursor is as follows: nickel and cobalt are mainly located inside the particles, while aluminum is mainly enriched on the surface of the particles; that is, the interior of a single particle is nickel and cobalt, while aluminum is mainly enriched on the surface of the particles, and aluminum exhibits a non-uniform distribution in the particles.

[0036] (6) Take 1g of the dried precursor powder and mix it with LiOH·H2O according to the Li + :(Ni 2+ +Co 2+ +Al 3+ The materials were thoroughly mixed and ground in a mortar with a molar ratio of 1.02:1, then placed in a tube furnace, O2 was introduced, the temperature was raised to 300℃ and held for 6 hours, then the temperature was raised to 650℃ in a second stage and held for 8 hours. After calcination, the materials were naturally cooled to room temperature, and the sintered materials were ground into powder and sieved to obtain lithium nickel cobalt aluminum oxide cathode material with a loose surface structure.

[0037] Example 2

[0038] The method for preparing lithium nickel cobalt aluminum oxide cathode material of the present invention includes the following steps:

[0039] (1) Weigh out NiSO4, CoSO4, and Al2(SO4)3 according to the molar ratio Ni:Co:Al = 0.95:0.03:0.02; dissolve NiSO4 and CoSO4 in deionized water to prepare 5L of nickel-cobalt solution. In the nickel-cobalt solution, Ni 2+ and Co 2+ The total concentration is 2 mol / L. Al₂(SO₄)₃ is dissolved in deionized water to prepare a 0.2 L aluminum solution. In the aluminum solution, Al… 3+ The concentration of ammonia is 0.5 mol / L; prepare ammonia solution with a concentration of 0.5 mol / L and sodium hydroxide solution with a concentration of 2 mol / L;

[0040] (2) Adopting such Figure 1 The reaction apparatus shown has a base solution of 20% of the reactor volume of ammonia water with a concentration of 0.1 mol / L added to the reactor.

[0041] (3) 4.5L of nickel-cobalt solution and an equal volume of ammonia solution with a concentration of 0.5mol / L were pumped into the reactor using a peristaltic pump. The pumping flow rate of both the nickel-cobalt solution and the ammonia solution was 2mL / min. The mixture was obtained. The temperature inside the reactor was kept at 55℃ and the stirring speed was 800rpm / min. The pH of the mixture was adjusted to 10.7 by adding a sodium hydroxide solution with a concentration of 2mol / L.

[0042] (4) After the reaction has been going on for 30 hours, the aluminum solution, the remaining 0.5L nickel-cobalt solution and ammonia water of the same volume as the nickel-cobalt solution are pumped into the reactor by a peristaltic pump. The pumping flow rate of the aluminum solution and the nickel-cobalt solution is adjusted so that the nickel-cobalt solution and the aluminum solution are added at the same time.

[0043] (5) After aging for 10 hours, the resulting precipitate was filtered and separated. The precipitate was washed with deionized water until the pH of the filtrate was about 7. Then, it was dried in a forced-air drying oven at 110°C for 10 hours to obtain precursor particles. The average composition of the obtained precursor can be expressed as Ni 0.95 Co 0.03 Al 0.02 (OH)2, the distribution of each element in the precursor body is as follows: nickel and cobalt are mainly located inside the particles, while aluminum is mainly enriched on the surface of the particles.

[0044] (6) Take 1g of the dried precursor powder and mix it with LiOH·H2O according to the Li + :(Ni 2+ +Co 2+ +Al 3+ The materials were thoroughly mixed and ground in a mortar with a molar ratio of 1.05:1, then placed in a tube furnace, O2 was introduced, and the temperature was raised to 500℃ and held for 6 hours. The temperature was then raised to 700℃ in a second stage and held for 14 hours. After calcination, the materials were naturally cooled to room temperature. The sintered material was then ground into powder and sieved to obtain a lithium nickel cobalt aluminum oxide cathode material with a porous surface structure, morphological as shown in the figure. Figure 2 As shown. Its cross-section is as follows. Figure 3 As shown, the elemental variation is that nickel and cobalt are mainly distributed in the core, while aluminum is mainly distributed in the outer shell.

[0045] Example 3

[0046] The method for preparing lithium nickel cobalt aluminum oxide cathode material of the present invention includes the following steps:

[0047] (1) Weigh out NiSO4, CoSO4, and Al2(SO4)3 according to the molar ratio Ni:Co:Al = 0.85:0.08:0.07; dissolve NiSO4 and CoSO4 in deionized water to prepare 10L of nickel-cobalt solution. In the nickel-cobalt solution, Ni 2+ and Co 2+ The total concentration is 1 mol / L. Al₂(SO₄)₃ is dissolved in deionized water to prepare a 0.75 L aluminum solution. In the aluminum solution, Al… 3+ The concentration of ammonia is 0.3 mol / L; prepare ammonia solution with a concentration of 0.5 mol / L and sodium hydroxide solution with a concentration of 2 mol / L;

[0048] (2) Adopting such Figure 1 The reaction apparatus shown has a base solution of 20% of the reactor volume of ammonia water with a concentration of 0.1 mol / L added to the reactor.

[0049] (3) 9L of nickel-cobalt solution and an equal volume of ammonia solution with a concentration of 0.5mol / L were pumped into the reactor using a peristaltic pump. The pumping flow rate of both the nickel-cobalt solution and the ammonia solution was 5mL / min. The mixture was obtained. The temperature inside the reactor was kept at 60℃ and the stirring speed was 600rpm / min. The pH of the mixture was adjusted to 10.7 by adding a sodium hydroxide solution with a concentration of 2mol / L.

[0050] (4) After reacting for 60 hours, the aluminum solution, the remaining 1L of nickel-cobalt solution and ammonia water of the same volume as the nickel-cobalt solution are pumped into the reactor by a peristaltic pump. The pumping flow rate of the aluminum solution and the nickel-cobalt solution is adjusted so that the nickel-cobalt solution and the aluminum solution are added at the same time.

[0051] (5) After aging for 20 hours, the resulting precipitate was filtered and separated. The precipitate was washed with deionized water until the pH of the filtrate was about 7. Then, it was dried in a forced-air drying oven at 110°C for 10 hours to obtain precursor particles. The average composition of the obtained precursor can be expressed as Ni 0.85 Co 0.08 Al 0.07 (OH)2, the distribution of each element in the precursor body is as follows: nickel and cobalt are mainly located inside the particles, while aluminum is mainly enriched on the surface of the particles.

[0052] (6) Take 1g of the dried precursor powder and mix it with LiOH·H2O according to the Li + :(Ni 2+ +Co 2+ +Al 3+ The materials were thoroughly mixed and ground in a mortar with a molar ratio of 1.1:1, then placed in a tube furnace, O2 was introduced, the temperature was raised to 500℃ and held for 8 hours, then the temperature was raised to 750℃ in a second stage and held for 16 hours. After calcination, the materials were naturally cooled to room temperature, and the sintered materials were ground into powder and sieved to obtain lithium nickel cobalt aluminum oxide cathode material with a loose surface structure.

[0053] Example 4

[0054] The method for preparing lithium nickel cobalt aluminum oxide cathode material of the present invention includes the following steps:

[0055] (1) Weigh out NiSO4, CoSO4, and Al2(SO4)3 according to the molar ratio Ni:Co:Al = 0.90:0.05:0.05; dissolve NiSO4 and CoSO4 in deionized water to prepare 10L of nickel-cobalt solution. In the nickel-cobalt solution, Ni 2+ and Co 2+ The total concentration is 2 mol / L. Al₂(SO₄)₃ is dissolved in deionized water to prepare 1.05 L of aluminum solution. In the aluminum solution, Al… 3+The concentration of ammonia is 0.2 mol / L; prepare ammonia solution with a concentration of 2 mol / L and sodium hydroxide solution with a concentration of 5 mol / L;

[0056] (2) Adopting such Figure 1 The reaction apparatus shown has a base solution of 20% of the reactor volume of ammonia water with a concentration of 0.1 mol / L added to the reactor.

[0057] (3) 8.5L of nickel-cobalt solution and an equal volume of ammonia solution with a concentration of 2mol / L were pumped into the reactor using a peristaltic pump. The pumping flow rate of both the nickel-cobalt solution and the ammonia solution was 5mL / min. The mixture was obtained. The temperature inside the reactor was kept at 55℃ and the stirring speed was 600rpm / min. The pH of the mixture was adjusted to 11 by adding a 5mol / L sodium hydroxide solution.

[0058] (4) After the reaction has been going on for 25 hours, the aluminum solution, the remaining 1.5L nickel-cobalt solution and ammonia water of the same volume as the nickel-cobalt solution are pumped into the reactor by a peristaltic pump. The pumping flow rate of the aluminum solution and the nickel-cobalt solution is adjusted so that the nickel-cobalt solution and the aluminum solution are added at the same time.

[0059] (5) After aging for 10 hours, the resulting precipitate was filtered and separated. The precipitate was washed with deionized water until the pH of the filtrate was about 7. Then, it was dried in a forced-air drying oven at 110°C for 10 hours to obtain precursor particles. The average composition of the obtained precursor can be expressed as Ni 0.90 Co 0.05 Al 0.05 (OH)2, the distribution of each element in the precursor body is as follows: nickel and cobalt are mainly located inside the particles, while aluminum is mainly enriched on the surface of the particles.

[0060] (6) Take 1g of the dried precursor powder and mix it with LiOH·H2O according to the Li + :(Ni 2+ +Co 2+ +Al 3+ The materials were thoroughly mixed and ground in a mortar with a molar ratio of 1.05:1, then placed in a tube furnace, O2 was introduced, the temperature was raised to 500℃ and held for 6 hours, then the temperature was raised to 700℃ in a second stage and held for 14 hours. After calcination, the materials were naturally cooled to room temperature, and the sintered materials were ground into powder and sieved to obtain lithium nickel cobalt aluminum oxide cathode material with a loose surface structure.

[0061] Example 5

[0062] The method for preparing lithium nickel cobalt aluminum oxide cathode material of the present invention includes the following steps:

[0063] (1) Weigh out NiSO4, CoSO4, and Al2(SO4)3 according to the molar ratio Ni:Co:Al = 0.92:0.06:0.02; dissolve NiSO4 and CoSO4 in deionized water to prepare 10L of nickel-cobalt solution. In the nickel-cobalt solution, Ni 2+ and Co 2+ The total concentration is 2 mol / L. Al₂(SO₄)₃ is dissolved in deionized water to prepare a 0.41 L aluminum solution. In the aluminum solution, Al… 3+ The concentration of ammonia is 0.8 mol / L; prepare ammonia solution with a concentration of 1 mol / L and sodium hydroxide solution with a concentration of 4 mol / L;

[0064] (2) Adopting such Figure 1 The reaction apparatus shown has a base solution of 20% of the reactor volume of ammonia water with a concentration of 0.5 mol / L added to the reactor.

[0065] (3) 8.5L of nickel-cobalt solution and an equal volume of ammonia solution with a concentration of 1mol / L were pumped into the reactor using a peristaltic pump. The pumping flow rate of both the nickel-cobalt solution and the ammonia solution was 2mL / min. The mixture was obtained. The temperature inside the reactor was kept at 70℃ and the stirring speed was 600rpm / min. The pH of the mixture was adjusted to 11.5 by adding a sodium hydroxide solution with a concentration of 4mol / L.

[0066] (4) After reacting for 60 hours, the aluminum solution, the remaining 1.5L nickel-cobalt solution, and ammonia water of the same volume as the nickel-cobalt solution are pumped into the reactor by a peristaltic pump. The pumping flow rate of the aluminum solution and the nickel-cobalt solution is adjusted so that the nickel-cobalt solution and the aluminum solution are added at the same time.

[0067] (5) After aging for 60 hours, the resulting precipitate was filtered and separated. The precipitate was washed with deionized water until the pH of the filtrate was about 7. Then, it was dried in a forced-air drying oven at 110°C for 48 hours to obtain precursor particles. The average composition of the obtained precursor can be expressed as Ni 0.92 Co 0.06 Al 0.02 (OH)2, the distribution of each element in the precursor body is as follows: nickel and cobalt are mainly located inside the particles, while aluminum is mainly enriched on the surface of the particles.

[0068] (6) Take 1g of the dried precursor powder and mix it with LiOH·H2O according to the Li + :(Ni 2+ +Co 2+ +Al 3+The materials were thoroughly mixed and ground in a mortar with a molar ratio of 1.2:1, then placed in a tube furnace, O2 was introduced, the temperature was raised to 500℃ and held for 10 hours, then the temperature was raised to 850℃ in a second stage and held for 18 hours. After calcination, the materials were naturally cooled to room temperature, and the sintered materials were ground into powder and sieved to obtain lithium nickel cobalt aluminum oxide cathode material with a loose surface structure.

[0069] Example 6

[0070] The method for preparing lithium nickel cobalt aluminum oxide cathode material of the present invention includes the following steps:

[0071] (1) Weigh out NiSO4, CoSO4, and Al2(SO4)3 according to the molar ratio Ni:Co:Al = 0.88:0.06:0.06; dissolve NiSO4 and CoSO4 in deionized water to prepare 10L of nickel-cobalt solution. In the nickel-cobalt solution, Ni 2+ and Co 2+ The total concentration is 2 mol / L. Al₂(SO₄)₃ is dissolved in deionized water to prepare 1.27 L of aluminum solution. In the aluminum solution, Al… 3+ The concentration of ammonia is 0.5 mol / L; prepare ammonia solution with a concentration of 2 mol / L and sodium hydroxide solution with a concentration of 4 mol / L;

[0072] (2) Adopting such Figure 1 The reaction apparatus shown has a base solution of 20% of the reactor volume of ammonia water with a concentration of 0.5 mol / L added to the reactor.

[0073] (3) 8.5L of nickel-cobalt solution and ammonia water with an equal volume and a concentration of 2mol / L were pumped into the reactor using a peristaltic pump. The pumping flow rate of both the nickel-cobalt solution and ammonia water was 5mL / min. The mixture was obtained. The temperature inside the reactor was kept at 60℃ and the stirring speed was 700rpm / min. The pH of the mixture was adjusted to 11.0 by adding sodium hydroxide solution with a concentration of 4mol / L.

[0074] (4) After the reaction has been going on for 25 hours, the aluminum solution, the remaining 1.5L nickel-cobalt solution and ammonia water of the same volume as the nickel-cobalt solution are pumped into the reactor by a peristaltic pump. The pumping flow rate of the aluminum solution and the nickel-cobalt solution is adjusted so that the nickel-cobalt solution and the aluminum solution are added at the same time.

[0075] (5) After aging for 30 hours, the resulting precipitate was filtered and separated. The precipitate was washed with deionized water until the pH of the filtrate was about 7. Then, it was dried in a forced-air drying oven at 110°C for 24 hours to obtain precursor particles. The average composition of the obtained precursor can be expressed as Ni 0.88 Co 0.06 Al 0.06(OH)2, the distribution of each element in the precursor body is as follows: nickel and cobalt are mainly located inside the particles, while aluminum is mainly enriched on the surface of the particles.

[0076] (6) Take 1g of the dried precursor powder and mix it with LiOH·H2O according to the Li + :(Ni 2+ +Co 2+ +Al 3+ The materials were thoroughly mixed and ground in a mortar with a molar ratio of 1.1:1, then placed in a tube furnace, O2 was introduced, the temperature was raised to 500℃ and held for 8 hours, then the temperature was raised to 750℃ in a second stage and held for 14 hours. After calcination, the materials were naturally cooled to room temperature, and the sintered materials were ground into powder and sieved to obtain lithium nickel cobalt aluminum oxide cathode material with a loose surface structure.

[0077] Comparative Example 1

[0078] A method for preparing lithium nickel cobalt aluminum oxide cathode material, specifically:

[0079] (1) Weigh out NiSO4, CoSO4, and Al2(SO4)3 according to the molar ratio Ni:Co:Al = 0.95:0.03:0.02; dissolve NiSO4 and CoSO4 in deionized water to prepare 5L of nickel-cobalt solution. In the nickel-cobalt solution, Ni 2+ and Co 2+ The total concentration is 2 mol / L. Al₂(SO₄)₃ is dissolved in deionized water to prepare a 0.2 L aluminum solution. In the aluminum solution, Al… 3+ The concentration of ammonia is 0.5 mol / L; prepare ammonia solution with a concentration of 2 mol / L and sodium hydroxide solution with a concentration of 2 mol / L.

[0080] (2) Add 20% of the volume of the reaction vessel and a concentration of 0.1 mol / L of ammonia water to the reaction vessel as the base liquid;

[0081] (3) The nickel-cobalt solution prepared in step (1), ammonia water of the same volume as the nickel-cobalt solution, and aluminum solution are added to the reaction vessel using a peristaltic pump. The pumping flow rate of the nickel-cobalt solution and ammonia water is 2 mL / min. The flow rate of the aluminum solution and nickel-cobalt solution is adjusted so that the aluminum solution and nickel-cobalt solution are added at the same time to obtain a mixture. The temperature inside the reaction vessel is kept at 55℃ and the stirring speed is 800 rpm / min. The pH of the mixture is adjusted to 10.7 by adding sodium hydroxide solution with a concentration of 2 mol / L.

[0082] (3) After feeding is complete, age for 10 hours, filter and separate the resulting precipitate, wash the precipitate with deionized water until the pH of the filtrate is about 7, and dry it in a forced-air drying oven at 110℃ for 10 hours to obtain precursor particles. The average composition of the precursor particles can be expressed as Ni 0.95 Co0.03 Al 0.02 (OH)2.

[0083] (4) Take 1g of the dried precursor powder and mix it with LiOH·H2O according to the Li + :(Ni 2+ +Co 2+ +Al 3+ The materials were thoroughly mixed and ground in a mortar with a molar ratio of 1.05:1, then placed in a tube furnace, O2 was introduced, and the temperature was raised to 500℃ and held for 6 hours. The temperature was then raised to 700℃ in a second stage and held for 14 hours. After calcination, the material was naturally cooled to room temperature. The sintered material was then ground into powder and sieved to obtain a lithium nickel cobalt aluminum oxide cathode material without a porous surface, with the chemical formula LiNi. 0.95 Co 0.03 Al 0.02 O2.

[0084] Comparative Example 1 is a lithium nickel cobalt aluminum oxide cathode material that does not form a loose and porous surface layer, and its microstructure is as follows: Figure 4 As shown, the material surface does not have a loose, porous structure, and the core and surface morphology of the cathode material are consistent.

[0085] The cathode materials obtained in Example 2 and Comparative Example 1 were assembled into coin half-cells, and their electrochemical performance was tested. Their rate performance is as follows: Figure 5 As shown, the cycle performance is as follows Figure 6 As shown. (Through) Figures 5-6 It is known that lithium nickel cobalt aluminum oxide cathode materials with a loose and porous surface structure have higher capacity at high current rates and better cycle stability.

Claims

1. A method for preparing a lithium nickel cobalt aluminum oxide cathode material, characterized in that, Includes the following steps: (1) Add 20-25% of the volume of ammonia water with a concentration of 0.1-0.5 mol / L to the reactor as the base solution; (2) Pump a portion of the nickel-cobalt solution and an equal volume of ammonia into the reactor to obtain a mixture. Adjust the pH of the mixture to 10-11.5 using sodium hydroxide solution. (3) After the mixture reacts at high temperature for 30-120 hours, the aluminum solution, the remaining nickel-cobalt solution, and an equal volume of ammonia water are pumped into the reactor. The pumping flow rates of the aluminum solution and the nickel-cobalt solution are adjusted so that the nickel-cobalt solution and the aluminum solution are added simultaneously. The amount of nickel-cobalt solution added in step (3) is 10-20% of the total volume of the nickel-cobalt solution. In the nickel-cobalt solution, Ni 2+ and Co 2+ The total concentration is 1~2 mol / L; in aluminum solution, Al 3+ The concentration is 0.2~0.8 mol / L; (4) After aging for 10-60 hours, the precipitate is filtered and separated. After separation, the precipitate is washed and dried to obtain the precursor. The distribution of each element in the precursor is as follows: nickel and cobalt are mainly located inside the particles, and aluminum is mainly enriched on the surface of the particles. The molecular formula of the precursor is Ni (1-x-y) Co x Al y (OH)2, x takes values ​​of 0.03~0.1, y takes values ​​of 0.02~0.1; (5) The precursor is mixed with lithium salt and placed in a tube furnace for high-temperature calcination in an oxygen-filled atmosphere. After calcination, it is naturally cooled to room temperature, ground and pulverized, and sieved to obtain lithium nickel cobalt aluminum oxide cathode material with a loose surface structure.

2. The method for preparing lithium nickel cobalt aluminum oxide cathode material according to claim 1, characterized in that: In steps (2) to (3), the concentration of ammonia water is 0.5 to 2 mol / L.

3. The method for preparing lithium nickel cobalt aluminum oxide cathode material according to claim 1, characterized in that: In step (2), the pumping flow rate of both the nickel-cobalt solution and ammonia is 1~5 mL / min.

4. The method for preparing lithium nickel cobalt aluminum oxide cathode material according to claim 1, characterized in that: In step (3), the temperature inside the reactor is maintained at 50~70℃ and the stirring speed is 400~800 rpm / min, and the mixture reacts.

5. The method of claim 1, wherein the lithium nickel cobalt aluminate cathode material is prepared by the steps of: In step (4), the precipitate is washed with deionized water until the pH of the filtrate is neutral, and then dried in a forced-air drying oven at 110°C for 10-48 hours. ​ 6. The method of claim 1, wherein the lithium nickel cobalt aluminate cathode material is prepared by the steps of: In step (5), the lithium salt is LiOH×H2O, and the molar ratio of lithium salt to precursor is Li + :(Ni 2+ +Co 2+ +Al 3+ =1.0~1.2:

1. ​ 7. The method of claim 1, wherein the lithium nickel cobalt aluminate cathode material is prepared by the steps of: In step (5), the calcination process is divided into two stages. In the first stage, the temperature is raised to 300~500℃ and held for 6~10 hours. In the second stage, the temperature is raised to 650~850℃ and held for 8~18 hours. ​

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