CN107946579B - A kind of lithium manganate coated nickel cobalt lithium aluminate cathode material and preparation method thereof - Google Patents

Abstract

The lithium manganate coated lithium nickel cobalt aluminate cathode material and the preparation method thereof are disclosed, wherein the mass percentage of lithium manganate in the material is 1-10 wt%, and lithium manganate forms a coating layer with the thickness of 2-20 nm and is coated on the lithium nickel cobalt aluminate; the positive electrode material is spherical particles with the particle size of 5-15 mu m. The method comprises the following steps: (1) dissolving a surfactant in water, heating and stirring; (2) adding a manganese source, stirring for dissolving, then adding nickel, cobalt and aluminum hydroxide, heating, stirring and evaporating to dryness; (3) calcining in air atmosphere, and cooling; (4) adding lithium salt, and sintering in flowing oxidizing atmosphere for two stages. The anode material has better cycle stability and high-rate discharge performance, the coating layer can stabilize the material structure, and the side reaction between the electrolyte and the active substance is effectively inhibited; the method has low cost and simple process, and is suitable for large-scale industrial production.

Description

A kind of lithium manganate coated nickel cobalt lithium aluminate cathode material and preparation method thereof

technical field

The invention relates to a positive electrode material and a preparation method thereof, in particular to a nickel cobalt lithium aluminate positive electrode material coated with lithium manganate and a preparation method thereof.

Background technique

Lithium-ion batteries have the advantages of stable voltage, high capacity, high energy density, less self-discharge, long cycle life, and environmental friendliness, and are widely used in electric vehicles, power tools, mobile phones, notebook computers and other fields. From mobile devices to electric vehicles, with the continuous expansion of the application of energy storage systems, the demand for high-energy density lithium-ion batteries is also increasing, and the cathode material in lithium-ion batteries is the key material that determines the performance of lithium-ion batteries. Cathode materials with long cycle life and high safety have become a hot spot of research and development and attention in countries around the world.

Nickel-rich high-capacity cathode materials, such as LiNi _0.8 Co _0.15 Al _0.05 O ₂ , have attracted extensive attention for their applications in lithium-ion batteries due to their high capacity and low price. Although higher Ni content in the structure of the material can achieve higher specific capacity, however, with the increase of Ni content, the material exhibits accelerated decay and thermal instability due to cation mixing and surface reactions. This adverse effect is more pronounced especially at elevated temperatures. In view of the above shortcomings, many researchers have improved their cycling stability by using surface coatings (metal oxides, metal phosphates, etc.).

For example, CN106711444A discloses a preparation method of an in-situ coating modified nickel-cobalt aluminate cathode material, and CN106910881A discloses a preparation method of a lithium metatitanate-coated nickel-cobalt aluminate cathode material, both of which use In-situ coating of nickel cobalt lithium aluminate is to mix the coating material and the lithium source with the precursor at the same time, and directly calcine after drying. However, doing so may make the coating non-uniform and affect the electrochemical performance.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to overcome the above-mentioned defects in the prior art, and to provide a lithium manganate-coated nickel with excellent specific capacity and cycle performance by utilizing the surface cation mixing to form a stable pillar layer to suppress the surface reaction. Lithium cobalt aluminate cathode material.

The further technical problem to be solved by the present invention is to overcome the above-mentioned defects in the prior art, and to provide a method for preparing a lithium manganate-coated lithium manganate lithium aluminate cathode material with low cost and simple process, which is suitable for large-scale industrial production. .

The technical solution adopted by the present invention to solve the technical problem is as follows: a lithium manganate-coated nickel-cobalt-aluminate cathode material, the mass percentage of the lithium manganate is 1-10 wt%, and the lithium manganate forms a thickness of The coating layer of 2-20 nm is coated on the nickel-cobalt lithium aluminate; the positive electrode material is spherical particles with a particle size of 5-15 μm.

Preferably, the lithium manganate is one or more of LiMn ₂ O ₄ , LiMnO ₂ , Li ₂ MnO ₃ or LiMn ₃ O ₄ .

The technical solution adopted by the present invention to further solve the technical problem is: a preparation method of a lithium manganate-coated nickel cobalt lithium aluminate positive electrode material, comprising the following steps:

(1) Dissolve the surfactant in water, heat and stir to obtain a surfactant solution;

(2) adding manganese source to the surfactant solution obtained in step (1), stirring and dissolving, then adding nickel cobalt aluminum hydroxide, heating and stirring, stirring and evaporating to dryness under oil bath conditions to obtain manganese source-coated hydroxide Ni-Co-Al precursor;

(3) calcining the manganese source-coated nickel-cobalt-aluminum precursor obtained in step (2) in an air atmosphere, and naturally cooling to room temperature to obtain a manganese oxide-coated nickel-cobalt-aluminum precursor;

(4) Lithium salt is added to the manganese oxide-coated nickel-cobalt-aluminum precursor obtained in step (3), and two-stage sintering is performed in a flowing oxidizing atmosphere to obtain lithium manganate-coated nickel-cobalt aluminate lithium positive electrode material.

Preferably, in step (1), the mass-volume ratio (g/mL) of the surfactant to water is 2-10:100 (more preferably 4-6:100).

Preferably, in step (1), the temperature of the heating and stirring is 30-60° C., and the time is 12-20 h.

Preferably, in step (1), the surfactant is one or more of polyvinylpyrrolidone, polyethylene glycol, polyvinyl alcohol or polyacrylamide. The addition of the water-soluble surfactant to disperse agglomerated manganese sources or nickel-cobalt-aluminum hydroxide solid particles is more conducive to the subsequent uniform coating of nickel-cobalt-aluminum hydroxide by manganese salts in a liquid phase environment.

Preferably, in step (2), the mass-volume ratio (g/mL) of the nickel-cobalt-aluminum hydroxide to the surfactant solution is 2-10:100. If the ratio is too large, it will be unfavorable for the dispersion of nickel-cobalt-aluminum hydroxide.

Preferably, in step (2), the molar ratio of manganese atoms to nickel-cobalt-aluminum hydroxide in the manganese source is 2-30:100 (more preferably 2.2-12.0:100).

Preferably, in step (2), the manganese source is one or more of manganese acetate, manganese chloride, manganese nitrate or manganese sulfate, and hydrates thereof.

Preferably, in step (2), the particle size of the nickel-cobalt-aluminum hydroxide is 5-15 μm.

Preferably, in step (2), the temperature of the heating and stirring reaction is 30-60° C., and the time is 12-20 h. Heating and stirring the reaction can promote the dissolution of manganese salts.

Preferably, in step (2), the temperature of the stirring to dryness is 100-150°C (more preferably 120-140°C). Compared with other drying methods, stirring and evaporation to dryness can effectively prevent agglomeration.

Preferably, in step (3), the calcination refers to: raising the temperature to 450-500° C. at a rate of 3-5° C./min, and calcining for 4-6 hours. The function of calcination is to oxidize the manganese salt into manganese oxide, which is more conducive to uniformly coating the surface of the nickel-cobalt-aluminum precursor, and the temperature is more conducive to the oxidation of the manganese salt.

Preferably, in step (4), the amount of lithium salt added is such that the number of moles of lithium in the lithium salt=(0.2～2.0)*the number of moles of manganese in the manganese source+(1.01～1.10)*nickel cobalt aluminum hydroxide of moles.

Preferably, in step (4), the lithium salt is one or more of lithium carbonate, lithium hydroxide, lithium nitrate or lithium acetate, and hydrates thereof. The lithium salt should not only react with nickel-cobalt-aluminum oxide to form lithium nickel-cobalt aluminate as a nucleation matrix of the positive electrode material, but also react with the manganese source to form lithium manganate. The first calcination is mainly to form manganese oxide and coat it on nickel cobalt aluminum oxide, and then add lithium salt for sintering reaction to obtain positive electrode material. Therefore, lithium salt is added after the first calcination.

Preferably, in step (4), the oxidizing atmosphere refers to an ozone atmosphere, an air atmosphere or an oxygen atmosphere with a purity of ≥99.9%.

Preferably, in step (4), the flow rate is 0.05-0.10 m ³ /h.

Preferably, in step (4), the two-stage sintering refers to: first heating to 400-550°C at a rate of 3-5°C/min, sintering for 3-8h (more preferably 4-6h), and then sintering at a rate of 3-5°C/min The temperature is raised to 700-850°C at a rate of 5°C/min, and sintered for 10-20h (more preferably 15-18h). The method of the invention utilizes the difference in the diffusion rates of manganese and lithium at high temperature to form a shell structure through sintering, that is, during the first stage of sintering, the lithium salt is melted and diffused into the nickel-cobalt-aluminum matrix, and during the second stage of sintering, Lithium salt reacts with nickel cobalt aluminum oxide to form lithium nickel cobalt aluminate, and lithium salt reacts with manganese oxide to form lithium manganate wrapped on the surface of lithium nickel cobalt aluminate. The main purpose of controlling the heating rate is to control the gap between the primary particles in the secondary particles, and to avoid the reduction of physical properties due to the excessive gap.

The molecular formula of the sodium nickel cobalt aluminum hydroxide of the present invention is Ni _0.8 Co _0.15 Al _0.05 (OH) ₂ , and the molecular formula of the lithium nickel cobalt aluminate is LiNi _0.8 Co _0.15 Al _0.05 O ₂ .

The principle of the present invention is as follows: the present invention uses nickel cobalt aluminum hydroxide as a matrix, first disperses the manganese source with a surfactant, and in a liquid phase environment, coats the nickel cobalt aluminum hydroxide particles by stirring and evaporating to dryness, and then passes It is oxidized into manganese oxide by calcination, which is closely deposited on its surface, and finally the obtained powder material is sintered in two stages. The cathode material of nickel-cobalt-aluminate lithium battery. After lithium manganate is coated with nickel cobalt aluminate, Mn ⁴⁺ will be formed on the surface during the charge-discharge cycle. In order to maintain the valence balance, nickel will be changed to Ni ²⁺ , so that the surface will be formed due to the mixed arrangement of nickel and lithium. The nano-pillar layer can stabilize the structure. In addition, it can effectively suppress the side reaction between the electrolyte and the active material, and improve its cycle stability.

The beneficial effects of the present invention are as follows:

(1) In the lithium manganate-coated nickel-cobalt lithium aluminate cathode material of the present invention, the lithium manganate forms a coating layer with a thickness of 2-20 nm, and the cathode material is spherical particles with a particle size of 5-15 μm;

(2) The lithium manganate-coated nickel-cobalt lithium aluminate cathode material of the present invention is assembled into a battery. At 2.7-4.3V and 0.1C, the gram capacity of the first discharge can be as high as 209.7mAh/g; The capacity can be as high as 184.4mAh/g, and after 100 cycles, the capacity retention rate can be as high as 84.1%; at the rate of 0.5C, 1C, 2C, and 5C, the first discharge capacity can be as high as 196.3mAh/g and 184.4mAh/g, respectively. , 167.8mAh/g, 139.7mAh/g, indicating that the lithium manganate-coated nickel cobalt lithium aluminate cathode material of the present invention has better cycle stability and high rate discharge performance;

(3) After the method of the present invention coats manganese oxide on the lithium nickel cobalt aluminate, during the electrochemical cycle process, a nano-pillar layer formed by the mixed arrangement of nickel and lithium is formed on the surface of the nickel cobalt lithium aluminate to stabilize the structure, and also Effectively inhibit the side reaction between the electrolyte and the active material, and improve its cycle stability;

(4) The method of the present invention has low cost and simple process, and is suitable for large-scale industrial production.

Description of drawings

1 is a SEM image of the Li ₂ MnO ₃ /LiNi _0.8 Co _0.15 Al _0.05 O ₂ positive electrode material obtained in Example 1 of the present invention;

2 is a TEM image of the Li ₂ MnO ₃ /LiNi _0.8 Co _0.15 Al _0.05 O ₂ positive electrode material obtained in Example 1 of the present invention;

3 is an XRD pattern of the Li ₂ MnO ₃ /LiNi _0.8 Co _0.15 Al _0.05 O ₂ positive electrode material obtained in Example 1 of the present invention;

4 is a SEM image of the LiNi _0.8 Co _0.15 Al _0.05 O ₂ positive electrode material obtained in Comparative Example 1 of the present invention;

5 is a comparison diagram of the capacity cycle of the battery assembled with the positive electrode materials obtained in Example 1 and Comparative Example 1 of the present invention at a rate of 1C.

Detailed ways

The present invention will be further described below with reference to the embodiments and accompanying drawings.

The nickel-cobalt-aluminum hydroxide used in the embodiment of the present invention was purchased from Ningbo Jinhe New Materials Co., Ltd., and the particle size was 5-15 μm; the chemical reagents used in the embodiment of the present invention, unless otherwise specified, were all obtained through conventional commercial channels. get.

Example 1

A lithium manganate-coated nickel cobalt lithium aluminate cathode material:

The mass percentage content of Li ₂ MnO ₃ is 3 wt %, and Li ₂ MnO ₃ forms a coating layer with a thickness of 3 nm and coats the nickel cobalt lithium aluminate; the positive electrode material is spherical particles with a particle size of 5-15 μm, and the molecular formula is Li ₂ MnO ₃ /LiNi _0.8 Co _0.15 Al _0.05 O ₂ .

As shown in FIG. 1 , the lithium manganate-coated nickel-cobalt lithium aluminate cathode material obtained in the embodiment of the present invention is spherical particles with a particle size of 5-15 μm, and the surface has a lithium manganate coating layer.

As shown in FIG. 2 , the base part of the lithium manganate-coated nickel-cobalt aluminate cathode material obtained in the embodiment of the present invention is lithium nickel-cobalt aluminate, and a lithium manganate coating layer with a thickness of 3 nm is formed on its surface.

As shown in Figure 3, the 006 and 102, 108 and 110 faces are clearly separated in the XRD data, indicating that the layered structure of the nickel-cobalt lithium aluminate cathode material coated with lithium manganate obtained in the embodiment of the present invention is obvious, and the surface is coated with lithium manganate. The layered structure of nickel cobalt aluminate was not destroyed.

A preparation method of a lithium manganate-coated nickel cobalt lithium aluminate cathode material:

(1) Dissolve 2g of polyvinylpyrrolidone in 50mL of deionized water, and stir at 50°C for 12h to obtain a surfactant solution;

(2) Add 0.3024g (1.234mmol) manganese acetate tetrahydrate to the surfactant solution obtained in step (1), stir to dissolve, then add 4.589g (50mmol) nickel cobalt aluminum hydroxide, and stir at 50°C for 12h , stirred and evaporated to dryness in an oil bath at 120 °C to obtain a nickel cobalt aluminum hydroxide precursor coated with a manganese source;

(3) The nickel-cobalt-aluminum hydroxide precursor coated with the manganese source obtained in step (2) is heated to 450 °C at a rate of 5 °C/min in an air atmosphere, calcined for 6 h, and cooled to room temperature naturally to obtain manganese oxide coated Coated nickel oxide cobalt aluminum precursor;

(4) 2.313 g (31.3 mmol) Li ₂ CO ₃ was added to the manganese oxide-coated nickel-cobalt-aluminum precursor obtained in step (3), and placed in a tube furnace, at a purity of 0.05 m ³ /h flowing In an oxygen atmosphere of ≥99.9%, the temperature was first heated to 480 °C at a rate of 5 °C/min, sintered for 5 h, then heated to 780 °C at a rate of 5 °C/min, and sintered for 15 h to obtain Li ₂ MnO ₃ /LiNi _0.8 Co _0.15 Al _0.05 O ₂ cathode material.

Assembly of the battery: Weigh 0.4 g of the Li ₂ MnO ₃ /LiNi _0.8 Co _0.15 Al _0.05 O ₂ positive electrode material obtained in the embodiment of the present invention, add 0.05 g of acetylene black as a conductive agent and 0.05 g of PVDF (polyvinylidene fluoride) as a bonding agent After mixing evenly, coat it on aluminum foil to make a positive electrode sheet. In a vacuum glove box, use a metal lithium sheet as the negative electrode, use Celgard 2300 as the separator, and 1mol/L LiPF ₆ /EC:DMC (volume ratio 1:1) as the electrolyte. liquid, and assembled into a CR2025 button battery.

After testing, the assembled battery has a specific capacity of 209.7mAh/g for the first discharge at a voltage range of 2.7-4.3V and a rate of 0.1C.

As shown in Fig. 5, the assembled battery has a specific capacity of 184.4 mAh/g for the first discharge in the voltage range of 2.7-4.3 V and a rate of 1 C, and the capacity retention rate is 83.2% after 100 cycles.

After testing, the assembled battery has a first discharge capacity of 193.2mAh/g, 184.4mAh/g, 163.1mAh/g and 139.2mAh/g.

Example 2

A lithium manganate-coated nickel cobalt lithium aluminate cathode material:

The mass percentage content of LiMnO ₂ is 8wt%, and LiMnO ₂ forms a coating layer with a thickness of 6 nm and coats the nickel cobalt aluminate lithium; the positive electrode material is spherical particles with a particle size of 5-15 μm, and the molecular formula is LiMnO ₂ /LiNi _0.8 Co _0.15 Al _0.05 O ₂ .

After testing, the lithium manganate-coated nickel-cobalt lithium aluminate cathode material obtained in the embodiment of the present invention is spherical particles with a particle size of 5-15 μm, and the surface has a lithium manganate coating layer.

After testing, the matrix portion of the lithium manganate-coated lithium manganate lithium aluminate positive electrode material obtained in the embodiment of the present invention is lithium nickel cobalt aluminate, and a lithium manganate coating layer with a thickness of 6 nm is formed on the surface thereof.

After testing, 006 and 102, 108 and 110 faces are clearly separated in the XRD data, indicating that the layered structure of the nickel-cobalt lithium aluminate cathode material coated with lithium manganate obtained in the embodiment of the present invention is obvious, and the surface is not damaged after coating with lithium manganate. Layered structure of nickel cobalt lithium aluminate.

A preparation method of a lithium manganate-coated nickel cobalt lithium aluminate cathode material:

(1) Dissolve 3g of polyvinyl alcohol in 60mL of deionized water, and stir at 50°C for 15h to obtain a surfactant solution;

(2) Add 0.728g (4.5mmol) manganese chloride dihydrate to the surfactant solution obtained in step (1), stir to dissolve, then add 5.048g (55mmol) nickel cobalt aluminum hydroxide, stir at 50°C 13h, stirring and evaporating to dryness in an oil bath at 120 °C to obtain a nickel-cobalt-aluminum hydroxide precursor coated with a manganese source;

(3) The nickel-cobalt-aluminum hydroxide precursor coated with the manganese source obtained in step (2) is heated to 480 °C at a rate of 5 °C/min in an air atmosphere, calcined for 5 h, and cooled to room temperature naturally to obtain manganese oxide coated Coated nickel-cobalt-aluminum precursor;

(4) Add 2.631 g (62.7 mmol) LiOH·H ₂ O to the manganese oxide-coated nickel-cobalt-aluminum precursor obtained in step (3), place it in a tube furnace, and place it in a tube furnace with a flow rate of 0.08 m ³ /h. In an oxygen atmosphere with a purity of ≥99.9%, the temperature was first heated to 500°C at a rate of 5°C/min, sintered for 5h, then heated to 800°C at a rate of 5°C/min, and sintered for 18h to obtain LiMnO ₂ /LiNi _0.8 Co _0.15 Al _0.05 O _cathode material.

Assembly of the battery: Weigh 0.4 g of the LiMnO ₂ /LiNi _0.8 Co _0.15 Al _0.05 O ₂ positive electrode material obtained in the embodiment of the present invention, add 0.05 g of acetylene black as a conductive agent and 0.05 g of PVDF (polyvinylidene fluoride) as a binder, After mixing evenly, coat it on aluminum foil to make a positive electrode sheet. In a vacuum glove box, use a metal lithium sheet as a negative electrode, use Celgard 2300 as a separator, and 1mol/L LiPF ₆ /EC:DMC (volume ratio 1:1) as an electrolyte. Assembled into a CR2025 button battery.

After testing, the assembled battery has a specific capacity of 200.8mAh/g for the first discharge at a voltage range of 2.7-4.3V and a rate of 0.1C.

After testing, the assembled battery has a specific capacity of 179.8mAh/g for the first discharge in the voltage range of 2.7-4.3V and a rate of 1C, and the capacity retention rate is 84.1% after 100 cycles.

After testing, the assembled battery has a first discharge capacity of 191.4mAh/g, 179.8mAh/g, 167.8mAh/g, 0.5C, 1C, 2C, and 5C in the voltage range of 2.7~4.3V, respectively. 139.7mAh/g.

Example 3

A lithium manganate-coated nickel cobalt lithium aluminate cathode material:

The mass percentage of LiMn ₂ O ₄ is 10 wt %, and LiMn ₂ O ₄ forms a coating layer with a thickness of 15 nm and coats the nickel cobalt lithium aluminate; the positive electrode material is spherical particles with a particle size of 5-15 μm, and the molecular formula is LiMn ₂ O ₄ /LiNi _0.8 Co _0.15 Al _0.05 O ₂ .

After testing, the lithium manganate-coated nickel-cobalt lithium aluminate cathode material obtained in the embodiment of the present invention is spherical particles with a particle size of 5-15 μm, and the surface has a lithium manganate coating layer.

After testing, the matrix portion of the lithium manganate-coated lithium manganate lithium aluminate cathode material obtained in the embodiment of the present invention is lithium nickel cobalt aluminate, and a lithium manganate coating layer with a thickness of 15 nm is formed on its surface.

After testing, 006 and 102, 108 and 110 faces are clearly separated in the XRD data, indicating that the layered structure of the nickel-cobalt lithium aluminate cathode material coated with lithium manganate obtained in the embodiment of the present invention is obvious, and the surface is not damaged after coating with lithium manganate. Layered structure of nickel cobalt lithium aluminate.

A preparation method of a lithium manganate-coated nickel cobalt lithium aluminate cathode material:

(1) Dissolve 5g polyethylene glycol in 100mL deionized water, and stir at 40°C for 20h to obtain a surfactant solution;

(2) Add 1.302 g (5.314 mmol) of manganese acetate tetrahydrate to the surfactant solution obtained in step (1), stir to dissolve, then add 4.589 g (50 mmol) of nickel cobalt aluminum hydroxide, and stir at 40 ° C for 15 h , stirred and evaporated to dryness in an oil bath at 130 °C to obtain a nickel cobalt aluminum hydroxide precursor coated with a manganese source;

(3) The manganese source-coated nickel-cobalt-aluminum hydroxide precursor obtained in step (2) is heated to 500 °C at a rate of 4 °C/min in an air atmosphere, calcined for 4 h, and naturally cooled to room temperature to obtain manganese oxide coated Coated nickel-cobalt-aluminum precursor;

(4) Add 2.039 g (27.6 mmol) Li ₂ CO ₃ to the manganese oxide-coated nickel-cobalt-aluminum precursor obtained in step (3), place it in a tube furnace, and place it in a tube furnace with 0.1 m ³ /h of air flowing Under the atmosphere, the temperature was first heated to 550°C at a rate of 4°C/min, sintered for 4h, then heated to 820°C at a rate of 4°C/min, and sintered for 18h to obtain LiMn ₂ O ₄ /LiNi _0.8 Co _0.15 Al _0.05 O ₂ positive electrode Material.

Assembly of the battery: Weigh 0.4 g of the LiMn ₂ O ₄ /LiNi _0.8 Co _0.15 Al _0.05 O ₂ positive electrode material obtained in the embodiment of the present invention, add 0.05 g of acetylene black as a conductive agent and 0.05 g of PVDF (polyvinylidene fluoride) as a bonding agent After mixing evenly, coat it on aluminum foil to make a positive electrode sheet. In a vacuum glove box, use a metal lithium sheet as the negative electrode, use Celgard 2300 as the separator, and 1mol/L LiPF ₆ /EC:DMC (volume ratio 1:1) as the electrolyte. liquid, and assembled into a CR2025 button battery.

After testing, the assembled battery has a specific capacity of 204.2mAh/g for the first discharge at a voltage range of 2.7-4.3 V and a rate of 0.1C.

After testing, the assembled battery has a specific capacity of 180.7mAh/g for the first discharge in the voltage range of 2.7-4.3 V and a rate of 1C, and the capacity retention rate is 82.9% after 100 cycles.

After testing, the assembled battery has a first discharge capacity of 196.3mAh/g, 180.7mAh/g, 163.9mAh/g and 134.2mAh/g.

Comparative Example 1

Add 2.313g (31.3mmol) of Li ₂ CO ₃ to 4.589g (50 mmol) of nickel-cobalt-aluminum hydroxide, put it in a tube furnace, in an oxygen atmosphere with a purity of ≥99.9% flowing at 0.05m ³ /h, first The temperature was raised to 480°C at a rate of 5°C/min, sintered for 5 hours, then heated to 780°C at a rate of 5°C/min, and sintered for 15 hours to obtain LiNi _0.8 Co _0.15 Al _0.05 O ₂ positive electrode material.

Assembly of the battery: Weigh 0.4 g of the obtained nickel-cobalt lithium aluminate positive electrode material, add 0.05 g of acetylene black as a conductive agent and 0.05 g of PVDF (polyvinylidene fluoride) as a binder, mix evenly and coat it on aluminum foil to make a positive electrode A CR2025 button cell was assembled in a vacuum glove box with a lithium metal sheet as the negative electrode, Celgard 2300 as the separator, and 1 mol/L LiPF ₆ /EC:DMC (volume ratio 1:1) as the electrolyte.

As shown in FIG. 4 , the nickel-cobalt lithium aluminate cathode material obtained in the comparative example of the present invention is spherical particles with a particle size of 5-15 μm.

After testing, the assembled battery has a specific capacity of 201.4mAh/g for the first discharge at a voltage range of 2.7-4.3V and a rate of 0.1C.

As shown in Figure 5, the assembled battery has a specific capacity of 180.4 mAh/g for the first discharge in the voltage range of 2.7-4.3 V and a rate of 1 C, and the capacity retention rate is 64.4% after 100 cycles.

After testing, the assembled battery has a first discharge capacity of 194.3mAh/g, 180.4mAh/g, 158.9mAh/g, 0.5C, 1C, 2C, and 5C in the voltage range of 2.7~4.3V, respectively. 128.4mAh/g.

To sum up, the method of the present invention can uniformly coat the lithium manganate on the lithium nickel cobalt aluminate, which effectively improves the cycle retention rate and the high rate of the material compared with the lithium nickel cobalt aluminate without coating the lithium manganate. Discharge performance, and simple process, suitable for large-scale industrial production.

Claims (23)

1. a lithium manganate-coated nickel-cobalt lithium aluminate positive electrode material is characterized in that: the mass percentage of the lithium manganate is 1～10wt%, and the lithium manganate forms a coating layer with a thickness of 2～20nm It is coated on lithium nickel cobalt aluminate; the positive electrode material is spherical particles with a particle size of 5-15 μm; the preparation method of the lithium manganate coated lithium nickel cobalt aluminate positive electrode material includes the following steps: (1) Dissolve the surfactant in water, heat and stir to obtain a surfactant solution; (2) adding manganese source to the surfactant solution obtained in step (1), stirring and dissolving, then adding nickel cobalt aluminum hydroxide, heating and stirring, stirring and evaporating to dryness under oil bath conditions to obtain manganese source-coated hydroxide Ni-Co-Al precursor; (3) calcining the manganese source-coated nickel-cobalt-aluminum precursor obtained in step (2) in an air atmosphere, and naturally cooling to room temperature to obtain a manganese oxide-coated nickel-cobalt-aluminum precursor; (4) Lithium salt is added to the manganese oxide-coated nickel-cobalt-aluminum precursor obtained in step (3), and two-stage sintering is performed in a flowing oxidizing atmosphere to obtain lithium manganate-coated nickel-cobalt aluminate lithium positive electrode material; In step (3), the calcination refers to: heating to 450-500°C at a rate of 3-5°C/min, and calcining for 4-6 hours. 2. The lithium manganate-coated nickel-cobalt lithium aluminate cathode material according to claim 1, wherein the lithium manganate is in LiMn ₂ O ₄ , LiMnO ₂ , Li ₂ MnO ₃ or LiMn ₃ O ₄ one or more of them. 3. according to the lithium manganate-coated lithium nickel-cobalt aluminate positive electrode material of claim 1 or 2, it is characterized in that: in step (1), the mass volume ratio of described surfactant and water is 2～10: 100; the temperature of the heating and stirring is 30-60° C. and the time is 12-20 h; the surfactant is one or more of polyvinylpyrrolidone, polyethylene glycol, polyvinyl alcohol or polyacrylamide. 4. The lithium manganate-coated lithium nickel cobalt aluminate cathode material according to claim 1 or 2, characterized in that: in step (2), the mass volume ratio of the nickel cobalt aluminum hydroxide to the surfactant solution is 2-10:100; the molar ratio of manganese atoms to nickel-cobalt-aluminum hydroxide in the manganese source is 2-30:100; the manganese source is manganese acetate, manganese chloride, manganese nitrate or manganese sulfate, and One or more of hydrates; the particle size of the nickel-cobalt-aluminum hydroxide is 5-15 μm. 5. The lithium manganate-coated lithium nickel cobalt aluminate cathode material according to claim 3, wherein in step (2), the mass volume ratio of the nickel cobalt aluminum hydroxide to the surfactant solution is 2 ~10:100; the molar ratio of manganese atoms to nickel, cobalt, and aluminum hydroxide in the manganese source is 2 to 30:100; the manganese source is manganese acetate, manganese chloride, manganese nitrate or manganese sulfate, and hydrates thereof One or more of the above; the particle size of the nickel-cobalt-aluminum hydroxide is 5-15 μm. 6 . The lithium manganate-coated lithium nickel cobalt aluminate cathode material according to claim 1 or 2, wherein in step (2), the temperature of the heating and stirring reaction is 30 to 60° C., and the time is 12 ~20h; the temperature of the stirring and evaporation to dryness is 100-150°C. 7 . The lithium manganate-coated lithium nickel cobalt aluminate cathode material according to claim 3 , wherein in step (2), the temperature of the heating and stirring reaction is 30-60° C., and the time is 12-20 h. 8 . ; The temperature of the stirring and evaporation to dryness is 100 to 150 °C. 8 . The lithium manganate-coated lithium nickel cobalt alumina cathode material according to claim 4 , wherein in step (2), the temperature of the heating and stirring reaction is 30-60° C., and the time is 12-20 h. 9 . ; The temperature of the stirring and evaporation to dryness is 100 to 150 °C. 9. The lithium manganate-coated lithium nickel-cobalt aluminate cathode material according to claim 1 or 2, wherein in step (4), the amount of lithium salt added is such that the number of moles of lithium in the lithium salt= (0.2～2.0)*moles of manganese in manganese source+(1.01～1.10)*moles of nickel, cobalt, and aluminum hydroxide; the lithium salt is lithium carbonate, lithium hydroxide, lithium nitrate or lithium acetate, and its hydration one or more of these. 10. The lithium manganate-coated lithium nickel cobalt aluminate cathode material according to claim 3, wherein in step (4), the lithium salt is added in such an amount that the number of moles of lithium in the lithium salt=(0.2 ~2.0) * moles of manganese in the manganese source + (1.01 ~ 1.10) * moles of nickel, cobalt and aluminum hydroxide; the lithium salt is lithium carbonate, lithium hydroxide, lithium nitrate or lithium acetate, and the one or more of them. 11. The lithium manganate-coated lithium nickel cobalt aluminate cathode material according to claim 4, characterized in that: in step (4), the lithium salt is added in such an amount that the number of moles of lithium in the lithium salt=(0.2 ~2.0) * moles of manganese in the manganese source + (1.01 ~ 1.10) * moles of nickel, cobalt and aluminum hydroxide; the lithium salt is lithium carbonate, lithium hydroxide, lithium nitrate or lithium acetate, and the one or more of them. 12 . The lithium manganate-coated lithium nickel cobalt aluminate cathode material according to claim 6 , wherein in step (4), the lithium salt is added in such an amount that the number of moles of lithium in the lithium salt=(0.2 ~2.0) * moles of manganese in the manganese source + (1.01 ~ 1.10) * moles of nickel, cobalt and aluminum hydroxide; the lithium salt is lithium carbonate, lithium hydroxide, lithium nitrate or lithium acetate, and the one or more of them. 13. The lithium manganate-coated lithium nickel cobalt aluminate cathode material according to claim 1 or 2, characterized in that: in step (4), the oxidizing atmosphere refers to an ozone atmosphere, an air atmosphere or a purity of ≥99.9 % oxygen atmosphere; the flow rate is 0.05-0.10 m ³ /h. 14. The lithium manganate-coated lithium nickel cobalt aluminate cathode material according to claim 3, wherein in step (4), the oxidizing atmosphere refers to an ozone atmosphere, an air atmosphere or a material with a purity of ≥99.9% Oxygen atmosphere; the flow rate is 0.05 to 0.10 m ³ /h. 15. The lithium manganate-coated lithium nickel cobalt aluminate cathode material according to claim 4, characterized in that: in step (4), the oxidizing atmosphere refers to an ozone atmosphere, an air atmosphere or a material with a purity of ≥99.9% Oxygen atmosphere; the flow rate is 0.05 to 0.10 m ³ /h. 16 . The lithium manganate-coated nickel-cobalt-aluminate cathode material according to claim 6 , wherein in step (4), the oxidizing atmosphere refers to an ozone atmosphere, an air atmosphere or a material with a purity of ≥99.9%. 17 . Oxygen atmosphere; the flow rate is 0.05 to 0.10 m ³ /h. 17. The lithium manganate-coated lithium nickel cobalt aluminate cathode material according to claim 9, characterized in that: in step (4), the oxidizing atmosphere refers to an ozone atmosphere, an air atmosphere or a material with a purity of ≥99.9% Oxygen atmosphere; the flow rate is 0.05 to 0.10 m ³ /h. 18. The lithium manganate-coated lithium nickel cobalt aluminate cathode material according to claim 1 or 2, characterized in that: in step (4), the two-stage sintering refers to: first sintering at 3-5°C/min The temperature is raised to 400-550°C at a rate of 3-5°C, sintered for 3-8 hours, and then heated to 700-850°C at a rate of 3-5°C/min, and sintered for 10-20 hours. 19. The lithium manganate-coated lithium nickel-cobalt-aluminate cathode material according to claim 3, wherein in step (4), the two-stage sintering means: firstly at a rate of 3-5°C/min The temperature is raised to 400-550°C, sintered for 3-8 hours, and then heated to 700-850°C at a rate of 3-5°C/min, and sintered for 10-20 hours. 20. The lithium manganate-coated lithium nickel cobalt aluminate cathode material according to claim 4, characterized in that: in step (4), the two-stage sintering means: firstly at a rate of 3 to 5°C/min The temperature is raised to 400-550°C, sintered for 3-8 hours, and then heated to 700-850°C at a rate of 3-5°C/min, and sintered for 10-20 hours. 21. The lithium manganate-coated lithium nickel cobalt aluminate cathode material according to claim 6, wherein in step (4), the two-stage sintering means: firstly at a rate of 3 to 5°C/min The temperature is raised to 400-550°C, sintered for 3-8 hours, and then heated to 700-850°C at a rate of 3-5°C/min, and sintered for 10-20 hours. 22 . The lithium manganate-coated lithium nickel cobalt alumina cathode material according to claim 9 , wherein in step (4), the two-stage sintering means: firstly at a rate of 3 to 5° C./min. 23 . The temperature is raised to 400-550°C, sintered for 3-8 hours, and then heated to 700-850°C at a rate of 3-5°C/min, and sintered for 10-20 hours. 23 . The lithium manganate-coated lithium nickel cobalt alumina cathode material according to claim 13 , wherein in step (4), the two-stage sintering means: firstly at a rate of 3 to 5° C./min. 24 . The temperature is raised to 400-550°C, sintered for 3-8 hours, and then heated to 700-850°C at a rate of 3-5°C/min, and sintered for 10-20 hours.

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