A preparation method and application of a ternary precursor with structural density difference, nickel-tungsten concentration gradient and in-situ cobalt coating

Abstract

The present invention discloses a preparation method and application of a quaternary precursor with differences in structural compactness, nickel-tungsten concentration gradient, and in-situ cobalt coating. Among them, the contents of nickel and tungsten gradually increase from the inside to the outside. Cobalt is coated on the surface of the material by a coprecipitation process. The material has a structure of "inner layer with low nickel and tungsten and low compactness - outer layer with high nickel and tungsten and high compactness - cobalt-coated surface" from the inside to the outside. By controlling the concentration and flow rate, a certain difference in structural compactness is generated. The outer layer structure is relatively compact and nickel is enriched in the outer layer, making it easier to participate in the reaction, release capacity, and the structural stability is enhanced by means of wet doping with tungsten; at the same time, the compactness of the inner layer structure is relatively lower than that of the outer layer. The stable structure of low nickel in the inner layer and cobalt coating on the surface tightly protects the high nickel outer layer. After synthesizing the cathode material, it provides a buffer space for the large volume change during the charge and discharge process, effectively reducing the generation of microcracks and harmful side reactions. The present invention provides a preparation scheme for a precursor with low cost, short process, and high performance, which is suitable for industrial production.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion battery materials, and particularly relates to a method for preparing a ternary precursor with nickel and tungsten concentration gradients and in-situ cobalt coating and its application. Background Art

[0002] Lithium-ion batteries are widely used in portable electronic devices, electric vehicles, aerospace and other fields due to their high energy density and long cycle life. Among them, high-nickel ternary cathode materials (LiNi x Co y Mn z O2, NCM, Ni≥0.7) have attracted much attention due to their high energy density and low cost. However, their inherent defects, such as poor structural stability and intense surface side reactions, seriously hinder their further development and application.

[0003] Existing modification methods mainly act on the cathode material, which not only increases energy consumption but also has unsatisfactory modification effects. It is worth noting that the precursor, as the front-end product of the cathode material, has a crucial impact on the performance of the cathode material. Therefore, in order to obtain a ternary cathode material with excellent electrochemical performance, it is necessary to design and regulate the structure of its precursor. Summary of the Invention

[0004] Aiming at the problems existing in the prior art, the purpose of the present invention is to provide a precursor and its cathode material with both high energy density and high stability.

[0005] Another object of the present invention is to provide a method for preparing the above precursor and cathode material.

[0006] The present invention creatively discovers that the structural design of nickel and tungsten surface enrichment and coprecipitation cobalt coating can make the material have higher activity, release more capacity, and can alleviate the volume and stress changes during the cycle to maintain long cycle stability.

[0007] The present invention provides the following technical solutions.

[0008] A ternary precursor with nickel and tungsten concentration gradients and in-situ cobalt coating, with the chemical formula Ni x Co y Mn z W p (OH)2@Co(OH)2, where 0.7≤x<1, 0≤y≤0.2, 0<z≤0.3, 0≤p≤0.1, and x + y + z + p = 1; characterized in that the nickel and tungsten contents show a gradually decreasing trend from the inside to the outside, cobalt is coated on the surface of the material by a coprecipitation process, and the material has a structure of "low nickel and tungsten, low density inner layer - high nickel and tungsten, high density outer layer - cobalt-coated surface" from the inside to the outside.

[0009] Furthermore, in the ternary precursor with nickel, tungsten concentration gradient and cobalt in-situ coating, in the inner layer with low nickel, low tungsten and low compactness, the molar ratio of nickel ions to total metal cations is 0.3 - 0.85:1, the proportion of tungsten ions is 0 - 0.003:1, and the layer thickness is 1 - 9 μm; in the outer layer with high nickel, high tungsten and high compactness, the molar ratio of nickel ions to total metal cations is 0.6 - 0.95:1, the layer thickness is 1 - 6 μm, and the proportion of tungsten ions is 0 - 0.04:1; the thickness of the cobalt-coated surface is 0 - 2 μm.

[0010] Based on the same inventive concept, the present invention provides a method for preparing the above ternary precursor, comprising the following steps:

[0011] (1) Prepare high-concentration nickel salt solution, cobalt salt solution, manganese salt solution, tungsten salt solution and low-concentration nickel salt solution, cobalt salt solution, manganese salt solution, tungsten salt solution, precipitant solution and complexing agent solution;

[0012] (2) Controlled by a peristaltic pump, introduce the high-concentration nickel, cobalt, manganese, tungsten metal salt solutions, precipitant solution and complexing agent solution into the reaction kettle. First, control the lower flow rates of the nickel and tungsten metal salts. After the particles grow to 1 - 9 μm, replace the high-concentration metal salts with low-concentration metal salt solutions and increase the flow rates of the nickel and tungsten metal salts. After the particles grow to 2 - 12 μm, only carry out the precipitation reaction of the cobalt metal salt. Finally, after washing, filtering, drying, sieving, and demagnetization, obtain Ni x CoyMn z W p (OH)2@Co(OH)2;

[0013] Furthermore, in the above preparation method, the molar ratio of nickel and tungsten in the inner high-concentration solution is low, and the molar ratio of nickel and tungsten in the outer low-concentration solution increases.

[0014] Furthermore, in the above preparation method, the nickel salt, cobalt salt, and manganese salt are one or more of sulfates, nitrates, and chlorides; the precipitant is sodium hydroxide; the complexing agent is ammonia water.

[0015] Furthermore, in the above preparation method, the concentration of the tungsten salt solution is one or more of ammonium metatungstate, ammonium paratungstate, tungsten trichloride, tungsten hexachloride, tungsten pentachloride, tungsten sulfide, ammonium tetrathiotungstate, and tungsten acetate.

[0016] Based on the same inventive concept, the present invention further provides a cathode material, which is obtained by mixing and sintering the above ternary precursor with lithium.

[0017] The sintering process is divided into two stages. The sintering temperature in the first stage is 400 - 500 °C, and the heat preservation time is 3 - 5 h; the sintering temperature in the second stage is 700 - 1000 °C, and the heat preservation time is 9 - 60 h.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] (1) Different from the traditional gradient design of nickel gradually decreasing from the inside out, the structure of "low-nickel, low-tungsten low-density inner layer - high-nickel, high-tungsten high-density outer layer - cobalt-coated surface" designed by the present invention innovatively enriches nickel in the outer layer of the material. In this way, the defect of incomplete reaction of nickel in the inner layer can be avoided, and the capacity can be released better. Again, the wet doping modification of tungsten ions can greatly improve the stability of the structure. In addition, the low-nickel, low-tungsten low-density inner layer and the cobalt-coated surface enclose the high-nickel, high-tungsten region, which can relieve the volume and stress changes caused by phase transformation and inhibit the generation and expansion of microcracks.

[0020] (2) The co-precipitation coating process designed by the present invention is different from the traditional coating process. The precipitation of the coating layer during the preparation of the precursor helps the connection between the two, and at the same time the coating is more complete, which is beneficial to improving the interface stability.

[0021] (3) Gradient doping, structure regulation and in-situ coating are achieved in one step during the preparation stage of the precursor. Without additional experimental processes, precursor materials with excellent quality can be obtained, greatly improving economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is the SEM image of the precursor obtained in Example 1 of the present invention

[0023] Figure 2 is the electrochemical performance cycle of the cathode materials obtained in Example 1, Comparative Example 1 and Comparative Example 2 of the present invention

[0024] Figure 3 is the electrochemical performance cycle diagram of the cathode material obtained in Example 2 of the present invention DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] The present invention will be described in detail below. The description of this part is only exemplary and explanatory, and should not have any restrictive effect on the protection scope of the present invention.

[0026] It should be noted that unless otherwise specified, the technical terms or scientific terms used in this application should have the ordinary meaning understood by those skilled in the art to which the present invention belongs.

[0027] Example 1

[0028] A ternary precursor with a nickel and tungsten concentration gradient and cobalt in-situ coating. The chemical formula of the low-nickel, low-tungsten low-density inner layer is Ni 0.499 Co 0.2 Mn 0.3 W 0.001 (OH)2, with a thickness of 4 μm; the chemical formula of the high-nickel, high-tungsten high-density outer layer is Ni 0.78Co 0.2 Mn 0.3 W 0.02 (OH)2, thickness is 6μm; the coating layer chemical formula is Co(OH)2, thickness is 0.1μm.

[0029] The overall chemical formula of the material is Ni 0.715 Co 0.1 Mn 0.17 W 0.015 (OH)2@Co(OH)2.

[0030] The preparation of the ternary precursor in this embodiment includes the following steps:

[0031] (1) Prepare high concentration nickel salt solution, cobalt salt solution, manganese salt solution, tungsten salt solution and low concentration nickel salt solution, cobalt salt solution, manganese salt solution, tungsten salt solution, sodium hydroxide solution and ammonia complexing agent solution respectively.

[0032] (2) Using a peristaltic pump to control the flow of high-concentration nickel, cobalt, manganese, and tungsten metal salt solutions, a precipitant solution, and a complexing agent solution into the reactor, first control the flow rate of the nickel and tungsten metal salts to a low level. After the particles grow to 4 μm, the high-concentration metal salts are replaced with low-concentration metal salt solutions, and the flow rates of the nickel and tungsten metal salts are accelerated. After the particles grow to 10 μm, the addition of the nickel, manganese, and tungsten metal salt solutions is stopped, and only the cobalt salt solution is pumped in. After the particles continue to grow to 10.1 μm, the feed is stopped to obtain a precursor slurry.

[0033] (3) The precursor slurry obtained in step (2) is subjected to solid-liquid separation, the solid is collected, and the solid is washed, dried, sieved, and demagnetized to obtain a ternary precursor - Ni-T with a nickel and tungsten concentration gradient and cobalt in situ coating. 0.715 Co 0.1 Mn 0.17 W 0.015 (OH)2@Co(OH)2.

[0034] (4) The ternary precursor lithium hydroxide monohydrate obtained in step (3) was ball-milled and mixed at a molar ratio of 1:1.06, and then calcined at 450°C for 3.5h in an oxygen atmosphere, and then raised to 890°C for 20h to obtain the positive electrode material - LiNi 0.715 Co 0.1 Mn 0.17 W 0.015 O2@LiCoO2.

[0035] Comparative Example 1

[0036] The only difference between Comparative Example 1 and Example 1 is that the concentration of the metal salt injected into the reactor is always the same, with no difference in high or low, and no significant concentration gradient.

[0037] The specific steps are as follows:

[0038] (1) Prepare nickel salt solution, cobalt salt solution, manganese salt solution, tungsten salt solution, sodium hydroxide solution, and ammonia complexing agent solution with certain concentrations respectively.

[0039] (2) Controlled by a peristaltic pump, feed the nickel, cobalt, manganese, and tungsten metal salt solutions, precipitant solution, and complexing agent solution into the reaction kettle. First, control the lower flow rates of the nickel and tungsten metal salts. After the particles grow to 4 μm, increase the flow rates of the nickel and tungsten metal salts. After the particles grow to 10 μm, stop adding the nickel, manganese, and tungsten metal salt solutions and only pump in the cobalt salt solution. After the particles continue to grow to 10.1 μm, stop feeding to obtain the precursor slurry.

[0040] (3) Perform solid-liquid separation on the precursor slurry obtained in step (2), collect the solid, and wash, dry, sieve, and demagnetize the solid to obtain the ternary precursor with nickel and tungsten concentration gradients and cobalt in-situ coating - Ni 0.715 Co 0.1 Mn 0.17 W 0.015 (OH)2@Co(OH)2.

[0041] (4) Ball-mill and mix the ternary precursor obtained in step (3) with lithium hydroxide monohydrate at a molar ratio of 1:1.06, then calcine it at 450 °C for 3.5 h in an oxygen atmosphere, and then raise the temperature to 890 °C and calcine it for 20 h to obtain the cathode material ---- LiNi 0.715 Co 0.1 Mn 0.17 W 0.015 O2@LiCoO2.

[0042] Comparative Example 2

[0043] The difference between Comparative Example 2 and Example 1 is only that: the injection rate is not adjusted, the injection is carried out at a uniform speed, and there is no difference in compactness.

[0044] Example 2

[0045] A ternary precursor with nickel and tungsten concentration gradients and cobalt in-situ coating. The inner layer with low nickel and tungsten and low compactness has the chemical formula Ni 0.499 Co 0.2 Mn 0.3 W 0.001 (OH)2, with a thickness of 3 μm; the outer layer with high nickel and tungsten and high compactness has the chemical formula Ni 0.78 Co 0.2 Mn 0.3 W 0.02 (OH)2, with a thickness of 7 μm; the coating layer has the chemical formula Co(OH)2, with a thickness of 0.1 μm.

[0046] The overall chemical formula of the material is Ni0.705 Co 0.1 Mn 0.17 W 0.025 (OH)2@Co(OH)2。

[0047] The ternary precursor in this embodiment is prepared through the following steps:

[0048] (1) Prepare high-concentration nickel salt solution, cobalt salt solution, manganese salt solution, tungsten salt solution, low-concentration nickel salt solution, cobalt salt solution, manganese salt solution, tungsten salt solution, sodium hydroxide solution, and ammonia complexing agent solution respectively.

[0049] (2) Controlled by a peristaltic pump, the high-concentration nickel, cobalt, manganese, and tungsten metal salt solutions, precipitant solution, and complexing agent solution are introduced into the reaction kettle. First, control the lower flow rates of the nickel and tungsten metal salts. After the particles grow to 3 μm, replace the high-concentration metal salts with low-concentration metal salt solutions and increase the flow rates of the nickel and tungsten metal salts. After the particles grow to 10 μm, stop adding the nickel, manganese, and tungsten metal salt solutions and only pump in the cobalt salt solution. After the particles continue to grow to 10.1 μm, stop feeding to obtain the precursor slurry.

[0050] (3) Perform solid-liquid separation on the precursor slurry obtained in step (2), collect the solid, and wash, dry, screen, and demagnetize the solid to obtain the ternary precursor with nickel and tungsten concentration gradients and cobalt in-situ coating - Ni 0.705 Co 0.1 Mn 0.17 W 0.025 (OH)2@Co(OH)2。

[0051] (4) Ball-mill and mix the ternary precursor obtained in step (3) with lithium hydroxide monohydrate at a molar ratio of 1:1.06, then calcine it in an oxygen atmosphere at 450 °C for 3.5 h, and then raise the temperature to 895 °C and calcine for 20 h to obtain the positive electrode material ---- LiNi 0.705 Co 0.1 Mn 0.17 W 0.025 O2@LiCoO2。

[0052] Coat the positive electrode material, conductive agent, and binder in a ratio of 8:1:1 into a pole piece. After assembling it into a lithium-ion button battery, conduct electrochemical performance tests. In the voltage range of 2.7 - 4.3 V at room temperature, the first cycle at 1 C has a specific capacity of 183.2 mAh g -1 and after 200 cycles, it has a specific capacity of 171.7 mAh g -1 and the capacity retention rate is 93%.

[0053] The positive electrode materials obtained in Examples 1-2 and Comparative Examples 1-2 were assembled into batteries. The specific assembly process was as follows: The positive electrode material was mixed with PVDF and acetylene black in a mass ratio of 8:1:1, dissolved in an appropriate amount of N-methylpyrrolidone, coated on the surface of aluminum foil, baked at 110 °C for 12 h, the positive electrode sheet was cut out on a cutting machine, and then assembled in a glove box filled with argon, and sealed in the order of positive electrode shell - positive electrode sheet - separator - electrolyte - negative electrode sheet - gasket - spring piece - negative electrode shell.

[0054] The assembled batteries were tested on a Blue Power test system. The test voltage was 2.7 - 4.3 V, the temperature was 25 °C, the activation rate condition was 0.1 C, and the cycling rate condition was 1 C for cycling tests.

[0055] Figure 2 The following is a comparison of the high-voltage cycling performance of the batteries assembled with the positive electrode materials prepared in Example 1 and Comparative Examples 1-2 respectively:

[0056] For the battery assembled with the positive electrode material prepared in Example 1, in the voltage range of 2.7 - 4.3 V and under the rate condition of 1 C, the initial discharge capacity reached 181.5 mAh / g, and the capacity retention rate after 100 cycles was 92.6%.

[0057] For the battery assembled with the positive electrode material prepared in Comparative Example 1, in the voltage range of 2.7 - 4.3 V and under the rate condition of 1 C, the initial discharge capacity reached 172.2 mAh / g, and the capacity retention rate after 100 cycles was 90%.

[0058] For the battery assembled with the positive electrode material prepared in Comparative Example 2, in the voltage range of 2.7 - 4.3 V and under the rate condition of 1 C, the initial discharge capacity reached 177.6 mAh / g, and the capacity retention rate after 100 cycles was 94.7%.

[0059] Figure 3 The following is the high-voltage cycling curve of the battery assembled with the positive electrode material prepared in Example 2. In the high-voltage range of 2.7 - 4.3 V and under the rate condition of 1 C, the initial discharge capacity reached 180.6 mAh / g, and the capacity retention rate after 100 cycles was 93.7%.

[0060] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A ternary precursor with structural compactness difference, nickel and tungsten concentration gradient and cobalt in situ coating, the chemical formula is Ni x Co y Mn z W p (OH)2@Co(OH)2, wherein 0.7≤x<1, 0≤y≤0.2, 0<z≤0.3, 0≤p≤0.1, x+y+z+p=1; characterized in that, The nickel and tungsten content tends to gradually increase from the inside to the outside, and cobalt is coated on the surface of the material using a co-precipitation process. The difference in density between the inside and the outside is achieved by adjusting the concentration flow rate. The material presents a structure from the inside to the outside of "low nickel, low tungsten density inner layer - high nickel, high tungsten density outer layer - cobalt-covered surface".

2. The ternary precursor according to claim 1, characterized in that In the low-nickel, tungsten, low-density inner layer, the molar ratio of nickel ions to total metal cations is 0.3-0.85:1, the proportion of tungsten ions is 0-0.003:1, and the layer thickness is 1-9 μm; in the high-nickel, tungsten, high-density outer layer, the molar ratio of nickel ions to total metal cations is 0.6-0.95:1, the layer thickness is 1-6 μm, and the proportion of tungsten ions is 0-0.04:1; the thickness of the cobalt-coated surface is 0-2 μm.

3. The method for preparing a ternary precursor with nickel and tungsten concentration gradients and cobalt in-situ coating according to claim 1, characterized in that: The following steps are involved: (1) preparing a high-concentration inner layer nickel salt solution, cobalt salt solution, manganese salt solution, and tungsten salt solution and a low-concentration outer layer nickel salt solution, cobalt salt solution, manganese salt solution, tungsten salt solution, precipitant solution, and complexing agent solution, wherein the molar ratio of nickel to tungsten in the inner layer solution is low and the molar ratio of nickel to tungsten in the outer layer solution is increased; (2) Using a peristaltic pump to control, nickel, cobalt, manganese, tungsten metal salt solutions, precipitant solution and complexing agent solution are introduced into the reactor, and gradient doping is achieved by controlling the flow rate of nickel and tungsten metal salts. First, a high concentration metal salt solution is added, and the flow rate is adjusted to make the precipitation rate faster and the structure relatively loose. Then, a low concentration metal salt solution is added, and the flow rate is adjusted to make the precipitation rate slower and the structure relatively compact. When the particles grow to 3-14 μm, the addition of nickel, manganese and tungsten metal salt solutions is stopped, and only the precipitation reaction of cobalt metal salt is carried out. Finally, Ni is obtained after washing, filtering, drying, screening and demagnetization. x Co y Mn z W p (OH)2@Co(OH)2.

4. The preparation method according to claim 3, wherein The nickel salt, cobalt salt and manganese salt are one or more of sulfate, nitrate and chloride; the precipitant is sodium hydroxide; and the complexing agent is ammonia water.

5. The preparation method according to claim 3, wherein The concentration of the tungsten salt solution is one or more of ammonium metatungstate, ammonium paratungstate, tungsten trichloride, tungsten hexachloride, tungsten pentachloride, tungsten sulfide, ammonium tetrathiotungstate and tungsten acetate.

6. A positive electrode material, characterized in that It is obtained by sintering the ternary precursor mixed with lithium as claimed in claim 1 or 2.

7. The positive electrode material according to claim 6, wherein The sintering process is divided into two stages. The sintering temperature of the first stage is 400-500° C. and the holding time is 3-5 hours. The sintering temperature of the second stage is 700-1000° C. and the holding time is 9-60 hours.

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