A carbon-nitrogen compound-coated ternary cathode material and its preparation method

Abstract

The present invention discloses a carbon-nitrogen compound-coated ternary cathode material and a preparation method thereof. The preparation method of the material is as follows: First, melamine and phthalaldehyde are subjected to a condensation reaction to obtain an organic framework material (COF). The COF material is ultrasonically exfoliated to obtain sheet-like COF nanomaterials; after mixing the sheet-like COF nanomaterials with the ternary cathode material, high-temperature annealing treatment is carried out in a protective gas environment, and the COF material is carbonized to derive sheet-like porous carbon-nitrogen compounds (C-N x )), which are successfully coated on the surface of the ternary cathode material to obtain a carbon-nitrogen compound-coated ternary cathode material. The present invention utilizes the excellent conductivity of the carbon-nitrogen compound to accelerate the migration of electrons and lithium ions during charge and discharge, and significantly improves the rate performance of the ternary cathode material. At the same time, the carbon-nitrogen material is coated on the surface of the ternary cathode, effectively reducing the erosion of side reactions and improving the cycle stability of the ternary cathode material.

Description

Technical Field

[0001] The present invention belongs to the field of preparation of lithium-ion battery materials, and particularly relates to a carbon-nitrogen compound-coated ternary cathode material and a preparation method thereof. Background Art

[0002] With the development of new energy, lithium-ion batteries have developed rapidly. Among lithium-ion battery materials, cathode materials have been widely used in fields such as digital cameras, laptop computers, and electric vehicles due to their advantages of high energy density, long cycle life, and low environmental pollution. The cathode material is one of the key materials determining the performance of lithium-ion batteries and occupies a very important position in lithium-ion batteries.

[0003] Currently, commercial cathode materials include lithium cobalt oxide (LiCoO2), lithium iron phosphate (LiFePO4), lithium nickel cobalt manganese oxide (NCM111, NCM523), etc., but they all have the defect of low energy density, which limits their further commercial application. Among them, the high-nickel ternary cathode material LiNi x Co y Mn 1-x-y O2 (0.6 ≤ x ≤ 0.9, y < 0.4, 1 - x - y < 0.4), due to its high nickel content, can provide a relatively high energy density and is the main development direction of future lithium-ion battery cathode materials. The high-nickel cathode material can solve the defect of low energy density of lithium-ion batteries, but there are also some deficiencies: poor cycling and thermal stability, and poor rate performance.

[0004] In order to improve the safety and stability performance of the nickel cobalt manganese ternary cathode material NCM, doping modification and surface coating are two main means. The authorized patent CN109888273B discloses a preparation method of a K, Ti element co-doped high-nickel-based ternary cathode material. By co-doping K and Ti elements, the cycling performance and rate performance of the high-nickel ternary cathode material are improved. However, it is difficult to avoid the erosion of the cathode material by HF generated during the side reaction process due to element doping. The authorized patent CN111785973B discloses a ternary cathode material with an organic double-layer coating and its preparation and application. By coating the ternary cathode material with an organic double-layer, the corrosion of the cathode material by the electrolyte is effectively reduced, and the cycling performance and rate performance of the ternary cathode material are improved. However, the conductivity of its coating layer is poor, and the synthesis process is relatively complex. How to prepare a coating layer with high conductivity, which can effectively inhibit harmful side reactions and improve the rate performance and cycling stability of the ternary cathode material is the technical problem to be solved by the present invention. Summary of the Invention

[0005] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a carbon-nitrogen compound-coated ternary cathode material and a preparation method thereof.

[0006] To achieve the above object, the technical solution adopted by the present invention is:

[0007] A new COF derivative nitrogen-carbon compound (CN x ) A method for preparing a coated ternary positive electrode material, comprising the following steps:

[0008] (1) The ternary precursor material and the lithium source are fully mixed in a certain proportion, and sintered at a high temperature in an oxygen-containing atmosphere to prepare a ternary positive electrode matrix material; the general structural formula of the ternary precursor is Ni x Co y Mn 1-x-y (OH)2, wherein 0.5≤x≤0.85, 0<y≤0.2; preferably, the lithium source is selected from at least one of lithium hydroxide and lithium carbonate; the ternary precursor and the lithium source are fully mixed and ground according to the molar ratio of Li:(Ni+Co+Mn)=(1.04-1.06):1. The oxygen-containing atmosphere is at least one of oxygen and air; the gas intake is 20-40L / min; at the same time, the temperature of the first stage of high-temperature sintering is 450-500°C, and the insulation time is 4-6h; the temperature of the second stage is 850-920°C, and the insulation time is 12-16h.

[0009] (2) Weigh a certain amount of melamine, disperse it in a dimethyl sulfoxide solution (DMSO), and completely dissolve it at a certain temperature; then add o-phthalaldehyde (OPA) and an ethanol solution in sequence, stir and mix to obtain a mixed solution; preferably, the molar ratio of melamine to o-phthalaldehyde is (8-12): (12-15), the temperature for dissolving melamine is 80-100°C; the volume ratio of DMSO to ethanol is (50-70): (10-15).

[0010] (3) The mixed solution is transferred to a Teflon-lined reactor, and the heating temperature and insulation time are set to carry out a solvent thermal reaction; the off-white product after the solvent thermal reaction is washed and purified with tetrahydrofuran, acetone, and methanol in turn, and dried to obtain a COF material; preferably, the temperature of the solvent thermal reaction is 120-140° C., and the insulation time is 48-72 h.

[0011] (4) Wet-mixing the dried COF material with N,N-dimethylformamide (DMF) solution in a certain proportion, ultrasonically exfoliating the nanosheets, centrifuging, and vacuum drying to obtain flaky COF nanomaterials; preferably, the ratio of COF material to DMF is (2-4 g): (80-120 mL); the ultrasonic intensity is 100 W, and the ultrasonic time is 16-24 h; the centrifugal speed is 3000-5000 rpm, and the vacuum drying temperature is 40-50 ° C.

[0012] (5) Weigh the flaky COF nanomaterial and the ternary cathode matrix material in a certain proportion, and perform dry coating through mechanical mixing; preferably, the mass of the flaky COF nanomaterial is 0.2-0.4% of the mass of the ternary cathode matrix material.

[0013] (6) Place the coated material in a protective gas environment and obtain the carbon-nitrogen compound-coated ternary cathode material through high-temperature annealing treatment. Preferably, the protective gas is at least one of nitrogen and argon; the high-temperature annealing temperature is 450-550 °C, and the heat preservation duration is 5-10 h.

[0014] The present invention has the following beneficial effects compared with the prior art:

[0015] The present invention makes melamine and phthalaldehyde undergo a condensation reaction to synthesize a covalent organic framework material (COF) rich in C, N, and H elements. The COF material is a micron-scale polymer, which is beneficial for subsequent ultrasonic exfoliation. The synthesized COF material is further exfoliated into nanosheets by ultrasound, and then the COF nanosheet material and the ternary cathode matrix material are uniformly mixed by mechanical mixing, and then through high-temperature annealing treatment, the COF material is carbonized and derived into flaky porous carbon-nitrogen compounds (C-N x ), and it is successfully and uniformly coated on the surface of the ternary cathode material. The nano-scale carbon-nitrogen compounds synthesized by the method of the present invention are more likely to be coated on the surface of the ternary material and are not easily shed. This method improves the disadvantage of poor conductivity of the traditional coating layer. Utilizing the excellent conductivity of the carbon-nitrogen compound material, it accelerates the migration of electrons and lithium ions during the charge and discharge process, and significantly improves the rate performance of the ternary cathode material. At the same time, the carbon-nitrogen material is coated on the surface of the ternary cathode, effectively reducing the erosion of side reactions and improving the cycle stability of the ternary cathode material. Through the method in the present invention, a ternary cathode material with excellent performance is prepared. Description of the Drawings

[0016] Figure 1 SEM image of the carbon-nitrogen compound-coated ternary cathode material prepared in Example 1;

[0017] Figure 2 Rate performance graph of the coin cells made of the ternary cathode materials prepared in Examples 1 to 3 and the comparative example. Detailed Embodiments

[0018] The technical solutions of the present invention will be described in detail through specific embodiments below. The specific embodiments described are only to help better understand the present invention. At the same time, the present invention can be implemented in more different forms and is not limited to the embodiments described herein. The methods mentioned in the following embodiments are considered common methods in the art unless otherwise specified.

[0019] Example 1

[0020] (1) Weigh lithium hydroxide and the ternary precursor Ni 0.8 Co 0.1 Mn 0.1 (OH)₂ according to the molar ratio Li:(Ni + Co + Mn)=1.04:1, and fully mix the precursor with lithium hydroxide; then place it in an oxygen atmosphere furnace, control the air intake of the gas flow to be 20 L / min; heat it to 450 °C in the first stage and keep it warm for 4 h, heat it to 850 °C in the second stage and keep it warm for 12 h; after cooling, grinding, and sieving, obtain the ternary cathode matrix material Li(Ni 0.8 Co 0.1 Mn 0.1 )O₂;

[0021] (2) Weigh 8 mmol of melamine and disperse it in 50 mL of DMSO; heat it to 80 °C to completely dissolve it; then sequentially add 12 mmol of OPA and 10 mL of an ethanol solution with a concentration of 5 mol / L, and mix evenly;

[0022] (3) Transfer the mixed solution into a hydrothermal reactor and react at 120 °C for 48 h; wash, purify, and dry the grayish-white product after the reaction with tetrahydrofuran, acetone, and methanol to finally obtain the COF material;

[0023] (4) Weigh 2 g of the COF material prepared in step (3) and disperse it in 80 mL of DMF solution. When the ultrasonic intensity is 100 W, ultrasonically exfoliate it for 16 h; centrifuge and filter the exfoliated product at a rotation speed of 3000 rpm, and vacuum dry it at 40 °C overnight to finally obtain COF nanosheets;

[0024] (5) Weigh the COF nanosheets prepared in step (4) according to 0.2% of the mass of the ternary cathode matrix material, and mix and coat it with the ternary cathode matrix material Li(Ni 0.8 Co 0.1 Mn 0.1 )O₂; then sinter and react in a nitrogen atmosphere at 450 °C for 5 h to finally obtain a ternary cathode material with carbon-nitrogen compound-coated Li(Ni 0.8 Co 0.1 Mn 0.1 )O₂.

[0025] Figure 1 SEM image of the ternary cathode material coated with carbon-nitrogen compound prepared in Example 1. From Figure 1It can be seen that the surface of the ternary cathode material is rough and uneven, with particulate matter accumulation. These particulate matters are carbon-nitrogen compounds. This further demonstrates that a carbon-nitrogen compound coating layer has been successfully introduced onto the surface of the ternary material through the methods of thermal polycondensation, ultrasonic exfoliation, and mixed sintering.

[0026] Example 2

[0027] (1) Lithium hydroxide and the ternary precursor Ni 0.8 Co 0.1 Mn 0.1 (OH)2 were weighed according to the molar ratio Li:(Ni + Co + Mn) = 1.05:1, and the precursor and lithium hydroxide were fully mixed; and placed in an oxygen atmosphere furnace, controlling the air intake volume of the gas flow to 30 L / min; heated to 450 °C in the first stage and held for 5 h, and then heated to 850 °C in the second stage and held for 14 h; after cooling, grinding, and sieving, the ternary cathode matrix material Li(Ni 0.8 Co 0.1 Mn 0.1 )O2 was obtained;

[0028] (2) 10 mmol of melamine was weighed and dispersed in 60 mL of DMSO; and heated to 90 °C to completely dissolve it; then 14 mmol of OPA and 12 mL of an ethanol solution with a concentration of 5 mol / L were added in sequence and mixed evenly;

[0029] (3) The mixed solution was transferred to a hydrothermal autoclave and reacted at 130 °C for 60 h; the grayish-white product after the reaction was washed, purified, and dried with tetrahydrofuran, acetone, and methanol, and finally the COF material was obtained;

[0030] (4) 3 g of the COF material prepared in step (3) was weighed and dispersed in 100 mL of DMF solution, and ultrasonically exfoliated for 20 h at an ultrasonic intensity of 100 W; the exfoliated product was centrifuged and filtered at a rotation speed of 4000 rpm and vacuum dried overnight at 45 °C, and finally the COF nanosheets were obtained;

[0031] (5) According to 0.3% of the mass of the ternary cathode matrix material, the COF nanosheets prepared in step (4) were weighed and mixed and coated with the ternary cathode matrix material Li(Ni 0.8 Co 0.1 Mn 0.1 )O2; then sintered and reacted in an argon atmosphere at 500 °C for 8 h, and finally the COF-derived material, the ternary cathode material with carbon-nitrogen compound coating on Li(Ni 0.8 Co 0.1 Mn 0.1 )O2, was obtained.

[0032] Example 3

[0033] (1) Weigh lithium hydroxide and the ternary precursor Ni 0.8 Co 0.1 Mn 0.1 (OH)2 according to the molar ratio Li:(Ni + Co + Mn)=1.06:1, and fully mix the precursor with lithium carbonate; and place it in an air atmosphere furnace, controlling the air intake volume of the gas flow to be 40 L / min; heat it to 450 °C in the first stage and keep it warm for 6 h, and heat it to 850 °C in the second stage and keep it warm for 16 h; obtain the ternary cathode matrix material Li(Ni 0.8 Co 0.1 Mn 0.1 )O2 through cooling, grinding, and sieving;

[0034] (2) Weigh 12 mmol of melamine and disperse it in 70 mL of DMSO; and heat it to 100 °C to completely dissolve it; then sequentially add 15 mmol of OPA and 15 mL of an ethanol solution with a concentration of 5 mol / L, and mix evenly;

[0035] (3) Transfer the mixed solution into a hydrothermal autoclave and react at 140 °C for 72 h; wash and purify the grayish-white product after the reaction with tetrahydrofuran, acetone, and methanol, and dry it to finally obtain the COF material;

[0036] (4) Weigh 4 g of the COF material prepared in step (3) and disperse it in 120 mL of DMF solution, and ultrasonically exfoliate it for 24 h at an ultrasonic intensity of 100 W; centrifuge and filter the exfoliated product at a rotation speed of 5000 rpm, and vacuum dry it overnight at 50 °C to finally obtain COF nanosheets;

[0037] (5) Weigh the COF nanosheets prepared in step (4) according to 0.4% of the mass of the ternary cathode matrix material, and mix and coat it with the ternary cathode matrix material Li(Ni 0.8 Co 0.1 Mn 0.1 )O2; then sinter and react it at 550 °C for 10 h in an argon atmosphere to finally obtain a ternary cathode material with a carbon-nitrogen compound coating Li(Ni 0.8 Co 0.1 Mn 0.1 )O2.

[0038] Example 4

[0039] (1) Weigh lithium hydroxide and the ternary precursor Ni 0.75 Co 0.1 Mn 0.15(OH)2, and fully mix the precursor with lithium hydroxide; place it in an oxygen atmosphere furnace, and control the air intake volume of the gas flow to 30 L / min; heat it to 480 °C in the first stage, keep it warm for 5 h, heat it to 870 °C in the second stage, and keep it warm for 14 h; obtain the ternary cathode matrix material Li(Ni 0.75 Co 0.1 Mn 0.15 )O2 through cooling, grinding, and sieving;

[0040] (2) Weigh 10 mmol of melamine and disperse it in 60 mL of DMSO; heat it to 90 °C to completely dissolve it; then successively add 14 mmol of OPA and 12 mL of an ethanol solution with a concentration of 5 mol / L, and mix evenly;

[0041] (3) Transfer the mixed solution into a hydrothermal reactor and react at 130 °C for 60 h; wash and purify the grayish-white product after the reaction with tetrahydrofuran, acetone, and methanol, and dry it to finally obtain the COF material;

[0042] (4) Weigh 3 g of the COF material prepared in step (3) and disperse it in 100 mL of DMF solution. When the ultrasonic intensity is 100 W, ultrasonically exfoliate it for 20 h; centrifuge and filter the exfoliated product at a rotation speed of 4000 rpm, and vacuum dry it at 45 °C overnight to finally obtain COF nanosheets;

[0043] (5) Weigh the COF nanosheets prepared in step (4) according to 0.3% of the mass of the ternary cathode matrix material, and mix and coat it with the ternary cathode matrix material Li(Ni 0.75 Co 0.1 Mn 0.15 )O2; then sinter and react in an argon atmosphere at 500 °C for 8 h to finally obtain a ternary cathode material of carbon-nitrogen compound-coated Li(Ni 0.75 Co 0.1 Mn 0.15 )O2.

[0044] Example 5

[0045] (1) Weigh lithium hydroxide and the ternary precursor Ni 0.65 Co 0.1 Mn 0.25 (OH)2 according to the molar ratio Li:(Ni + Co + Mn)=1.06:1, and fully mix the precursor with lithium carbonate; place it in an air atmosphere furnace, and control the air intake volume of the gas flow to 40 L / min; heat it to 500 °C in the first stage, keep it warm for 6 h, heat it to 920 °C in the second stage, and keep it warm for 16 h; obtain the ternary cathode matrix material Li(Ni 0.65Co 0.1 Mn 0.25 )O2;

[0046] (2) Weigh 12 mmol of melamine, disperse it in 70 mL of DMSO; heat it to 100 °C until it completely dissolves; then successively add 15 mmol of OPA and 15 mL of ethanol solution with a concentration of 5 mol / L, and mix evenly;

[0047] (3) Transfer the mixed solution into a hydrothermal reactor and react at 140 °C for 72 h; wash, purify and dry the grayish-white product after the reaction with tetrahydrofuran, acetone and methanol to finally obtain the COF material;

[0048] (4) Weigh 4 g of the COF material prepared in step (3), disperse it in 120 mL of DMF solution, and ultrasonically exfoliate it for 24 h at an ultrasonic intensity of 100 W; centrifuge and filter the exfoliated product at a rotation speed of 5000 rpm, and vacuum dry it overnight at 50 °C to finally obtain COF nanosheets;

[0049] (5) According to 0.4% of the mass of the ternary cathode matrix material, weigh the COF nanosheets prepared in step (4), and mix and coat them with the ternary cathode matrix material Li(Ni 0.65 Co 0.1 Mn 0.25 )O2; then sinter and react in an argon atmosphere at 550 °C for 10 h to finally obtain a ternary cathode material with a carbon-nitrogen compound coated Li(Ni 0.65 Co 0.1 Mn 0.25 )O2.

[0050] Comparative Example

[0051] (1) Weigh lithium hydroxide and the ternary precursor Ni 0.8 Co 0.1 Mn 0.1 (OH)2 according to the molar ratio Li:(Ni + Co + Mn)=1.04:1, and fully mix the precursor and lithium hydroxide; place it in an oxygen atmosphere furnace, control the air flow inlet volume to be 20 L / min; heat it to 450 °C in the first stage and keep it warm for 4 h, heat it to 850 °C in the second stage and keep it warm for 12 h; obtain the ternary cathode matrix material Li(Ni 0.8 Co 0.1 Mn 0.1 )O2 after cooling, grinding and sieving;

[0052] (2) Weigh the ternary cathode matrix material Li(Ni 0.8 Co 0.1 Mn0.1 ) O2 was placed in a reaction furnace; then, it was sintered and reacted at 450 °C for 5 h in a nitrogen atmosphere, and finally, the uncoated Li(Ni 0.8 Co 0.1 Mn 0.1 )O2 ternary cathode material was obtained.

[0053] Performance Test

[0054] The ternary cathode materials prepared in Examples 1-3 and the comparative example were respectively assembled into coin cells, and their charge-discharge specific capacities were measured.

[0055] (1) Preparation of the positive electrode sheet

[0056] The positive electrode material, conductive agent (acetylene black), and binder (PVDF) were weighed according to a mass ratio of 80:10:10. The weighed positive electrode material and acetylene black were mixed and ground in an agate mortar. After grinding evenly, they were added to N-methylpyrrolidone (NMP) that had fully reacted with PVDF and continuously ground until the slurry became a viscous liquid with a certain fluidity. The ground slurry was evenly transferred onto an aluminum foil, and the sample was evenly coated with a coater with a thickness of 300 μm. Subsequently, it was pre-burned in air at 60 °C for 5 hours, then evacuated, and dried at 90 °C for 12 hours to remove water and organic substances in the coated sample. The electrode sheet was cut to size for standby.

[0057] (2) Coin cell assembly and testing

[0058] Using graphite as the negative electrode and the prepared electrode sheet as the positive electrode, with an electrolyte ratio of EC:DMC = 1:1, a coin cell was assembled and subjected to charge-discharge testing with a BTV charge-discharge tester. After testing, at 25 °C, the first discharge capacity and capacity retention rate of the lithium-ion battery assembled with this electrode sheet at a working voltage of 2.8-4.3 V under 0.2C / 1C are shown in Table 1, and the rate performance is as Figure 1 shown.

[0059] Table 1 Specific capacity and capacity retention rate of the positive electrode materials prepared in Examples 1-3 and the comparative example during the first discharge at a 0.2C / 1C rate

[0060]

[0061] From the above test results, it can be seen that the rate performance and cycle stability of the coin cells made of the positive electrode materials prepared in Examples 1 to 3 are significantly higher than those of the comparative example, indicating that the performance of the materials prepared by the method in the present invention has been significantly improved.

[0062] The above-described embodiments are preferred embodiments of the present invention. However, the embodiments of the present invention are not limited by the above embodiments. The technical features of the embodiments can be combined arbitrarily. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A preparation method of a carbon-nitrogen compound-coated ternary cathode material, characterized in that: It includes the following steps: Melamine and phthalaldehyde are subjected to a condensation reaction to obtain a COF material, and the COF material is ultrasonically exfoliated to obtain flaky COF nanomaterials; After the flaky COF nanomaterials are mixed with the ternary cathode matrix material, they are placed in a protective gas environment for high-temperature annealing treatment to obtain a ternary cathode material coated with a carbon-nitrogen compound.

2. The preparation method of the carbon-nitrogen compound-coated ternary cathode material according to claim 1, wherein: The method for the condensation reaction of melamine and phthalaldehyde is as follows: Melamine and phthalaldehyde are dissolved in a solvent to obtain a mixed solution, and the mixed solution is transferred to a reaction kettle and reacted at a temperature of 120-140 °C for 48-72 h to obtain the COF material.

3. The preparation method of the carbon-nitrogen compound-coated ternary cathode material according to claim 2, characterized in that: The molar ratio of the melamine to the phthalaldehyde is (8-12):(12-15).

4. The preparation method of the carbon-nitrogen compound-coated ternary cathode material according to claim 1, characterized in that: The method for ultrasonically exfoliating the COF material to obtain flaky COF nanomaterials is as follows: The COF material is dispersed in N,N-dimethylformamide to obtain a dispersion; the dispersion is ultrasonically treated, and then centrifuged and vacuum dried to obtain flaky COF nanomaterials.

5. The preparation method of the carbon-nitrogen compound-coated ternary cathode material according to claim 1, characterized in that: The mass of the flaky COF nanomaterials is 0.2-0.4% of the mass of the ternary cathode matrix material.

6. The preparation method of the ternary cathode material coated with carbon-nitrogen compound according to claim 1 or 5, characterized in that: The preparation method of the ternary cathode matrix material is as follows: mix the ternary precursor with a lithium source and then place it in an oxygen-containing atmosphere for high-temperature sintering to obtain the ternary cathode matrix material; the structural general formula of the ternary precursor is Ni x Co y Mn 1-x-y (OH)2, where 0.5 ≤ x ≤ 0.85 and 0 < y ≤ 0.

2.

7. The preparation method of the ternary cathode material coated with carbon-nitrogen compound according to claim 6, characterized in that: The lithium source is at least one of lithium hydroxide and lithium carbonate; the Ni x Co y Mn 1-x-y (OH)2 and the lithium source are mixed in a molar ratio of Li:(Ni + Co + Mn)=(1.04 to 1.06):

1.

8. The preparation method of the ternary cathode material coated with carbon-nitrogen compound according to claim 6, characterized in that: The oxygen-containing atmosphere is oxygen or air, and the intake air volume is 20-40 L / min; the temperature in the first stage of the high-temperature sintering is 450-500 °C, and the heat preservation duration is 4-6 h; the temperature in the second stage is 850-920 °C, and the heat preservation duration is 12-16 h.

9. The preparation method of the carbon-nitrogen compound-coated ternary cathode material according to claim 1, wherein: The protective gas is nitrogen or argon; the temperature of the high-temperature annealing treatment is 450-550 °C, and the heat preservation duration is 5-10 h.

10. A carbon-nitrogen compound-coated ternary cathode material, characterized in that: It is prepared by using the preparation method described in any one of claims 1 to 9.

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