CQDs-coated Al-doped high-nickel ternary material as well as preparation method and application thereof

Abstract

The invention discloses a CQDs-coated Al-doped high-nickel ternary material as well as a preparation method and application of the CQDs-coated Al-doped high-nickel ternary material. According to the invention, the Al element is doped in the high-nickel ternary material, so that the effects of reducing lithium-nickel mixed arrangement and improving the structural stability of the material are achieved, the collapse of the crystal structure of the material in the lithium ion deintercalation process is slowed down, the stability of the battery material is improved, and the cycle performance of a battery cell is improved. The carbon quantum dot coated Al / NCM is prepared by adopting an electrostatic self-assembly mode, extra energy does not need to be provided, the operation is simple, and no other impurity element participates in the coating process; according to the CQDs / CQDs composite material and the preparation method thereof, the defects of small particle size, high specific surface energy and easiness in agglomeration of the CQDs are overcome by utilizing the principle that positive and negative charges attract each other, and a stable and uniform thin-layer CQDs coating layer is prepared, so that the CQDs coating layer has good electronic conductivity while forming a protective layer on a solid-liquid interface, and the cycle performance and the rate capability of the material are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of battery material preparation, and in particular to a CQDs-coated Al-doped high-nickel ternary material and a preparation method and application thereof. Background Art

[0002] The ternary material system NCM has the advantages of high capacity, high voltage, and low cost, and is one of the most widely used lithium-ion battery materials. In the ternary material system NCM, Ni is the main active substance. During the charge and discharge process, Ni 2+ / Ni 3+ and Ni 3 + / Ni 4+ The higher the content of the electrode pair, the higher the reversible lithium insertion capacity provided. Therefore, high-nickel ternary materials have become the direction of high energy density development. However, the low content of Co and Mn in high-nickel ternary materials leads to poor material cycle and rate performance; the Ni content in the material is 2+ With Li + The radius is relatively close, so the material is prone to Ni / Li mixing during the lithium insertion and extraction process, affecting the structural stability of the material; in addition, in the preparation process of high-nickel ternary materials, due to the low sintering temperature, the amount of residual lithium on the surface of the material is high, and it is easy to react with CO2 and H2O in the air to generate Li2CO3 and LiOH, causing flatulence and generating HF during the battery cycle, affecting the cycle performance. Summary of the invention

[0003] The present invention aims to solve one of the technical problems in the related art at least to a certain extent.

[0004] To this end, an embodiment of the present invention proposes a CQDs-coated Al-doped high-nickel ternary material and a preparation method and application thereof.

[0005] In the first aspect, the present invention proposes a CQDs-coated Al-doped high-nickel ternary material, comprising:

[0006] A negatively charged Al-doped high-nickel ternary material is obtained by modifying the Al-doped high-nickel ternary material with a surface modifier;

[0007] A coating layer with positive charge is coated on the surface of the Al-doped high-nickel ternary material, and the coating layer includes carbon quantum dots containing amino groups.

[0008] The CQDs (carbon quantum dots) coated Al-doped high-nickel ternary material in the first aspect of the present invention utilizes the mutual attraction between the negatively charged Al-doped high-nickel ternary material and the positively charged coating layer, and coats the coating layer on the surface of the Al-doped high-nickel ternary material through electrostatic self-assembly. No additional energy is required, and no other impurity elements are involved in the coating process, and the operation is simple.

[0009] Furthermore, the surface modifier includes at least one of polydiallyldimethylammonium chloride and γ-aminopropyltriethoxysilane. The surface of the Al-doped high-nickel ternary material is modified by the surface modifier to make it negatively charged.

[0010] In a second aspect, the present invention proposes a method for preparing the CQDs-coated Al-doped high-nickel ternary material proposed in the first aspect of the present invention, comprising the following steps:

[0011] (a) preparing an Al-doped high-nickel ternary material, and modifying the material using a surface modifier to obtain a modified Al-doped high-nickel ternary material having a negative charge;

[0012] (b) preparing carbon quantum dots containing amino groups;

[0013] (c) electrostatically self-assembling the carbon quantum dots containing amino groups and the modified Al-doped high-nickel ternary material to obtain CQDs-coated Al-doped high-nickel ternary material, wherein the coating amount of the carbon quantum dots containing amino groups is within 5%.

[0014] The high-nickel ternary material is NCM622 or NCM811. The modified Al-doped high-nickel ternary material has a negative charge, and the carbon quantum dots containing amino groups have a positive charge. The two are self-assembled through the electrostatic attraction of positive and negative charges to obtain Al-doped high-nickel ternary materials uniformly coated with CQDs, which overcomes the disadvantage of uneven coating caused by high specific surface energy and easy agglomeration of CQDs. The uniform CQDs coating layer can better isolate the electrolyte, reduce the side reaction between the positive electrode and the electrolyte, and effectively inhibit the degradation of the material structure.

[0015] The coating amount of the carbon quantum dots containing amino groups is within 5%, so that the coating layer is thinner. The thinner nanoscale CQDs coating layer has good conductivity, which is beneficial to the dynamic properties of the material. When the coating amount is too large, the coating layer is thicker and the conductivity of the material is reduced.

[0016] Furthermore, the step (a) comprises:

[0017] The Al source and the nickel-cobalt-manganese precursor are mixed evenly, and then the Li source is added and mixed evenly, and sintered in oxygen to obtain the Al-doped high-nickel ternary material;

[0018] Under alkaline conditions, the solvent in which the Al-doped high-nickel ternary material is dispersed is stirred and mixed with the surface modifier, and the modified Al-doped high-nickel ternary material is obtained by suction filtration and washing.

[0019] The pH value of the solvent in which the Al-doped high-nickel ternary material is dispersed is adjusted to alkaline by adding ammonia water, and then the surface modifier is added and stirred and mixed, wherein the solvent is an ethanol solution. The excess modifier and solvent are washed away by ethanol in the filtration and washing process.

[0020] Furthermore, the mass ratio of Al element in the Al source to the nickel-cobalt-manganese precursor is 0.01 to 0.05. That is, the doping ratio of Al is 0.01 to 0.05. In some embodiments, the doping ratio of Al is 0.01, 0.02, 0.03, 0.04, 0.05 or a value within the range of any two numerical values. A small amount of doping with Al element can stabilize the crystal structure of the ternary material, improve the stability and safety of the crystal structure, and significantly improve the cycle performance and safety performance of the battery. Excessive Al doping will cause the material's gram capacity to decrease, and the energy density of the final finished battery cell will decrease; too little Al doping will not significantly improve the stability of the material, and will not improve the cycle performance and safety performance of the battery.

[0021] Furthermore, the Al source includes at least one of aluminum oxide, aluminum chloride, aluminum nitrate and aluminum sulfate.

[0022] Furthermore, the molar ratio of the Li element in the Li source to the Ni element in the nickel-cobalt-manganese precursor is 1.01 to 1.1. Adding too much Li source causes material waste and increases costs, while adding too little Li source reduces the conversion rate of the nickel-cobalt-manganese precursor.

[0023] Furthermore, the lithium source includes at least one of lithium hydroxide and lithium carbonate.

[0024] Further, the step (b) comprises:

[0025] Mixing an organic substance containing an amino group and a carbon source in a molar ratio of 0.5:1 to 1:0.5 to perform a hydrothermal reaction to obtain a suspension;

[0026] The suspension is freeze-dried to obtain the carbon quantum dots containing amino groups.

[0027] Adding too much organic matter containing amino groups will lead to impurities in the prepared carbon quantum dots, requiring multiple washing and filtering, increasing the synthesis steps and wasting resources; adding too little will result in a small number of surface functional groups in the prepared carbon quantum dots, and the electrostatic attraction in the subsequent synthesis is insufficient, resulting in agglomeration of carbon quantum dots on the surface of the material, too thick and uneven surface coating, poor physical isolation effect, and electrolyte erosion of the exposed ternary material surface. The prepared carbon quantum dots containing amino groups are nano-sized, and the freeze-drying method avoids the influence of temperature on the structure of carbon quantum dots during oven drying.

[0028] Furthermore, the organic matter containing an amino group includes at least one of formamide, ethanolamine, ethylenediamine and polyethylenediamine.

[0029] Furthermore, the carbon source includes at least one of citric acid, glucose, vitamins, lactic acid, and fructose.

[0030] Further, the step (c) comprises:

[0031] Adding dropwise a solution containing the modified Al-doped high-nickel ternary material to a solution containing the carbon quantum dots containing amino groups;

[0032] After stirring, the mixture is filtered, washed, and freeze-dried to obtain the CQDs-coated Al-doped high-nickel ternary material.

[0033] Ultrasonic dispersion is used in the dispersion process to improve the dispersion rate and uniformity, and the freeze-drying method avoids the influence of high temperature on the structure of CQDs-coated Al-doped high-nickel ternary material during oven drying.

[0034] In a third aspect, the present invention provides the use of the CQDs-coated Al-doped high-nickel ternary material prepared by the method provided in the second aspect or the CQDs-coated Al-doped high-nickel ternary material provided in the first aspect in lithium-ion batteries.

[0035] Compared with the prior art, the beneficial effects of the present invention are:

[0036] In the present invention, doping Al element into the high-nickel ternary material plays a role in reducing lithium-nickel mixing and improving the stability of the material structure, slowing down the collapse of the material crystal structure during the lithium ion insertion and extraction process, improving the stability of the battery material, and improving the cycle performance of the battery cell.

[0037] In the present invention, an electrostatic self-assembly method is adopted to prepare carbon quantum dots coated with Al / NCM, which does not require the provision of additional energy, is simple to operate, and no other impurity elements are involved in the coating process; the principle of mutual attraction between positive and negative charges is utilized to overcome the shortcomings of small particle size, high specific surface energy, and easy agglomeration of CQDs, and a stable and uniform thin layer of CQDs coating layer is prepared, so that the CQDs coating layer forms a protective layer at the solid-liquid interface and has good electronic conductivity, thereby improving the cycle performance and rate performance of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the following description of the embodiments in conjunction with the accompanying drawings, in which:

[0039] Figure 1 This is a flow chart of the preparation method of the CQDs coated Al-doped high-nickel ternary material of the present invention;

[0040] Figure 2 This is a flow chart of the process of preparing CQDs coated with Al-doped high-nickel ternary materials in Example 1 of the present invention. DETAILED DESCRIPTION

[0041] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0042] The preparation method of the CQDs coated Al-doped high nickel ternary material of the present invention is as follows: Figure 1 As shown, the following is a detailed description in conjunction with embodiments and comparative examples.

[0043] Unless otherwise specified, the test materials and reagents used in the following examples can be obtained from commercial sources.

[0044] If no specific techniques or conditions are specified in the examples, they can be carried out according to the techniques or conditions described in the literature in the art or according to the product instructions.

[0045] Example 1

[0046] The preparation process flow chart of CQDs coated with Al-doped high-nickel ternary materials, such as Figure 2 As shown, the specific steps include:

[0047] (1) Al2O3 and nickel-cobalt-manganese precursor (Ni 0.8 Co 0.1 Mn 0.1(OH)2) was ball-milled at 500r / min for 6h to mix evenly, wherein the Al doping ratio was 0.03; lithium hydroxide was ball-milled and mixed with the precursor for 6h to obtain a mixture, wherein the lithium-nickel ratio was 1.06. The obtained mixture was sintered in oxygen to obtain an Al-doped high-nickel ternary material (Al / NCM), wherein the sintering process was first heated to 450°C at a heating rate of 5°C / min, kept warm for 4h, and then heated to 750°C at a heating rate of 2°C / min and kept warm for 18h.

[0048] (2) The Al-doped high-nickel ternary material is added to an ethanol solution to obtain a suspension, and an ammonia solution is added to adjust the pH to 9, and immediately a surface modifier γ-aminopropyltriethoxysilane is added at a mass ratio of 2% to the Al-doped high-nickel ternary material. The suspension is stirred magnetically at room temperature for half an hour, and then filtered, and the excess modifier and solvent are washed away with ethanol.

[0049] (3) Formamide and citric acid were mixed in a molar ratio of 1:1, and hydrothermally reacted at 150° C. for 15 h. The resulting suspension was freeze-dried for 24 h to obtain carbon quantum dots containing amino groups.

[0050] (4) The carbon quantum dots containing amino groups and the modified ternary material are ultrasonically dispersed in an ethanol solution to obtain a ternary material solution and a carbon quantum dot solution, wherein the coating amount of the carbon quantum dots is 2 wt%. The ternary material solution is then added dropwise to the carbon quantum dot solution placed on a magnetic stirring table, stirred for half an hour, filtered, washed three times, and freeze-dried for 24 hours to obtain a CQDs-coated Al-doped high-nickel ternary material (CQDs@NCM).

[0051] Example 2

[0052] The difference from Example 1 is that the hydrothermal reaction is carried out at 180° C. for 20 h when preparing carbon quantum dots, and the other processes are the same as Example 1.

[0053] Example 3

[0054] The difference from Example 1 is that the surface modifier is replaced by polydiallyldimethylammonium chloride, and the other processes are the same as Example 1.

[0055] Example 4

[0056] The difference from Example 1 is that the coating amount of carbon quantum dots is 1 wt %, and the other processes are the same as Example 1.

[0057] Example 5

[0058] The difference from Example 1 is that the coating amount of carbon quantum dots is 4 wt % and the other processes are the same as Example 1.

[0059] Comparative Example 1

[0060] Al2O3 and nickel-cobalt-manganese precursor (Ni 0.8 Co 0.1 Mn 0.1 (OH)2) was ball-milled at 500r / min for 6h to mix evenly, wherein the Al doping ratio was 0.03; lithium hydroxide was ball-milled and mixed with the precursor for 6h to obtain a mixture, wherein the lithium-nickel ratio was 1.06. The obtained mixture was sintered in oxygen to obtain an Al-doped high-nickel ternary material (Al / NCM), wherein the sintering process was first heated to 450°C at a heating rate of 5°C / min, kept warm for 4h, and then heated to 750°C at a heating rate of 2°C / min and kept warm for 18h.

[0061] Test Example 1

[0062] The specific surface area, conductivity and direct current resistance (DCR) of the products obtained in Examples 1 to 5 and Comparative Example 1 were tested respectively. The test results are shown in Table 1.

[0063] Table 1:

[0064] serial number <![CDATA[Specific surface area (m 2 / g)]]> <![CDATA[Conductivity (×10 -4 S*cm -1 )]]> DCR(Ω) Example 1 0.31 6.9 24.9 Example 2 0.28 6.6 31.8 Example 3 0.31 6.8 25.1 Example 4 0.29 5.4 27.6 Example 5 0.33 7.2 30.5 Comparative Example 1 0.26 4.2 33.7

[0065] By comparing Comparative Example 1, Example 1, Example 4 and Example 5, it can be seen that the specific surface area of ​​the material after coating with carbon quantum dots is significantly increased, and as the coating amount increases, the specific surface area increases and the conductivity increases. By comparing Example 1, Example 4 and Example 5, it can be seen that within a certain range, as the coating amount increases, the DCR decreases, and when the coating amount is large, the DCR increases.

[0066] It can be seen from Comparative Examples 1 and 2 that when the hydrothermal reaction time and temperature for preparing carbon quantum dots are increased, the size of the carbon quantum dots is too large, and the electrical conductivity and specific surface area of ​​the material are reduced.

[0067] Test Example 2

[0068] Using NMP as solvent, the products obtained in Examples 1 to 5 and Comparative Example 1 were mixed with acetylene black conductive agent and PVDF binder in a mass ratio of 8:1:1 to prepare a uniform slurry. The slurry was evenly coated on a copper foil with a coating surface density of 5 mg / cm. The copper foil was then placed in a vacuum drying oven and dried at 80°C for 12 h. The dried copper foil was cut into 2 cm 2 The discs are made into working electrodes and assembled into button batteries.

[0069] Electrochemical test: Under normal temperature conditions, the charge and discharge voltage range is 3.0-4.3V, and the capacity retention rate is tested for 200 cycles at a current density of 1C. The 200-week capacity retention rate is the ratio of the 200th cycle discharge capacity to the first discharge capacity; rate performance test: the battery is charged to the charge cut-off voltage at a current density of 0.33C, and then the constant voltage charge is cut off at 0.05C. The discharge capacity of the battery is tested at current densities of 0.2C, 0.5C, 1C, 2C, and 5C respectively. The test results are shown in Table 2. Three samples are tested in parallel for each group of batteries.

[0070] Table 2:

[0071]

[0072] By comparing Comparative Example 1 with Examples 1, 4, and 5, it can be seen that after coating with carbon quantum dots, the rate performance and cycle performance of the material are significantly improved, wherein the best effect is achieved when the coating amount is 2wt%, and the cycle retention rate is increased from 87.9% to 95.2%. The reason is that after coating with carbon quantum dots, a uniform and extremely thin coating layer is formed on the surface of the material, which can isolate the electrolyte from corrosion while having good conductivity, thereby improving the rate performance and cycle performance of the material.

[0073] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms may be for different embodiments or examples. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, unless they are contradictory.

[0074] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0075] Although the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the claims and their equivalents.

Claims

1. A CQDs coated Al-doped high-nickel ternary material, characterized in that: include: A negatively charged Al-doped high-nickel ternary material is obtained by modifying the Al-doped high-nickel ternary material with a surface modifier; A coating layer with positive charge is coated on the surface of the Al-doped high-nickel ternary material, and the coating layer includes carbon quantum dots containing amino groups.

2. The CQDs coated Al-doped high-nickel ternary material according to claim 1, characterized in that: The surface modifier includes at least one of polydiallyldimethylammonium chloride and γ-aminopropyltriethoxysilane.

3. A method for preparing CQDs coated with Al-doped high-nickel ternary material, characterized in that: The method for preparing the CQDs-coated Al-doped high-nickel ternary material according to claim 1 comprises the following steps: (a) preparing an Al-doped high-nickel ternary material, and modifying the material using a surface modifier to obtain a modified Al-doped high-nickel ternary material having a negative charge; (b) preparing carbon quantum dots containing amino groups; (c) electrostatically self-assembling the carbon quantum dots containing amino groups and the modified Al-doped high-nickel ternary material to obtain CQDs-coated Al-doped high-nickel ternary material, wherein the coating amount of the carbon quantum dots containing amino groups is within 5%.

4. The method according to claim 3, characterized in that The step (a) comprises: The Al source and the nickel-cobalt-manganese precursor are mixed evenly, and then the Li source is added and mixed evenly, and sintered in oxygen to obtain the Al-doped high-nickel ternary material; Under alkaline conditions, the solvent in which the Al-doped high-nickel ternary material is dispersed is stirred and mixed with the surface modifier, and the modified Al-doped high-nickel ternary material is obtained by suction filtration and washing.

5. The method according to claim 4, characterized in that The mass ratio of Al element in the Al source to the nickel-cobalt-manganese precursor is 0.01-0.05, and the Al source includes at least one of aluminum oxide, aluminum chloride, aluminum nitrate, and aluminum sulfate.

6. The method according to claim 3, characterized in that The step (b) comprises: Mixing an organic substance containing an amino group and a carbon source at a molar ratio of 0.5:1 to 1:0.5 to perform a hydrothermal reaction to obtain a suspension; The suspension is freeze-dried to obtain the carbon quantum dots containing amino groups.

7. The method according to claim 6, characterized in that The organic matter containing an amino group includes at least one of formamide, ethanolamine, ethylenediamine and polyethylenediamine.

8. The method according to claim 6, characterized in that The carbon source includes at least one of citric acid, glucose, vitamins, lactic acid and fructose.

9. The method according to claim 3, characterized in that The step (c) comprises: Adding dropwise a solution containing the modified Al-doped high-nickel ternary material to a solution containing the carbon quantum dots containing amino groups; After stirring, the mixture is filtered, washed, and freeze-dried to obtain the CQDs-coated Al-doped high-nickel ternary material.

10. Use of the CQDs-coated Al-doped high-nickel ternary material prepared by the method described in any one of claims 3 to 9 or the CQDs-coated Al-doped high-nickel ternary material described in claim 1 or 2 in lithium-ion batteries.

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