Co-doped ternary hydrotalcite and method for preparing the same

Abstract

The application provides a Co-doped ternary hydrotalcite and a preparation method thereof. The Co-doped NiCoMo ternary hydrotalcite material is synthesized by a simple water bath heating method in one step, has a nanoflower surface morphology, increases the specific surface area of the material, and the incorporation of Co elements improves the electrochemical performance and storage performance of the positive electrode material. The preparation method comprises the following steps: dissolving nickel salt, cobalt salt and molybdenum salt in deionized water, adding an intercalation agent and a pH regulator, washing and drying the obtained precipitate after the reaction is completed, and the Co-doped ternary hydrotalcite is obtained.

Description

Technical Field

[0001] This invention belongs to the field of energy technology, specifically to the field of electrode material technology, and in particular to a Co-doped ternary hydrotalcite material and its preparation method. Background Technology

[0002] Hydrotalcite (LDH) is an anionic layered compound with anions distributed between its layers to balance the charge on the layers. Based on the anionic and cationic groups between the layers, LDH materials can adsorb large amounts of anions and cations. Hydrotalcite is a typical two-dimensional layered material, and its general formula is generally represented as [M]. 2+ 1-x M' 3+ x (OH)2] z+ A n- z / n ·mH₂O, where M and M' are metal ions, A n- As an exchangeable anion in the interlayer region, it shows great potential in the field of electrochemical energy storage due to its broad selectivity for divalent and trivalent main metal ions and the diversity of interlayer anions.

[0003] Currently, most hydrotalcite materials are synthesized using the coprecipitation method, which is widely used in practice due to the low cost of raw materials and stable product performance. However, adding a strong alkaline solution during the preparation process may lead to excessively high local concentrations, resulting in rapid precipitation of metal ions. This makes it difficult to regulate and control the reaction, causing product agglomeration, and resulting in a uniform morphology and general specific surface area of ​​the synthesized material. The structure of hydrotalcite mainly exhibits a bulk shape composed of stacked hexagonal nanosheets. As charging and discharging proceed, anions are continuously released from the lattice, and the stacked bulk structure hinders the entry of ions from the electrolyte, leading to localized acidity within the lattice, dissolving the crystal structure, and reducing the material's cycling performance. Furthermore, as charging and discharging continue, divalent metal ions irreversibly form a layer of metal hydroxyl oxides on the material surface, reducing the material's conductivity and cycling stability.

[0004] Due to the characteristics of hydrotalcite materials, the interior of the sheet-like hydrotalcite cannot fully contact the electrolyte, and carrier transport can only be carried out through surface channels. Therefore, at high current densities, the internal crystals cannot respond to carrier transport and cannot participate in the electrochemical reaction, thus reducing the material's rate performance. Hydrotalcite materials synthesized by conventional co-precipitation methods often have most of the metal ions deeply embedded within the particles, making it difficult to expose active sites and hindering the full progress of the electrochemical reaction, resulting in insufficient energy storage capacity. Summary of the Invention

[0005] To address the problems in existing hydrotalcite material preparation processes, such as difficulty in adjusting and controlling the reaction, resulting in materials with small specific surface area, poor conductivity and cycle stability, and low rate performance and energy storage capacity, this invention aims to at least partially solve one of the technical problems in related technologies. Therefore, this application proposes a method for preparing Co-doped ternary hydrotalcite, which synthesizes Co-doped NiCoMo ternary hydrotalcite material in one step using a simple water bath heating method. This material exhibits a nanoflower-like surface morphology, increasing its specific surface area, and the incorporation of Co element enhances the electrochemical and storage performance of the cathode material.

[0006] In a first aspect, the present invention provides a method for preparing Co-doped ternary hydrotalcite, comprising: dissolving nickel salt, cobalt salt, and molybdenum salt in deionized water, adding an intercalating agent and a pH adjuster, and washing and drying the precipitate after the reaction is completed to obtain the Co-doped ternary hydrotalcite.

[0007] According to embodiments of the present invention, the above method may further include at least one of the following additional technical features:

[0008] According to a specific embodiment of the present invention, the intercalating agent is at least one selected from carbonate, bicarbonate, nitrate, and hydrochloride.

[0009] Preferably, the carbonate is at least one selected from sodium carbonate, potassium carbonate, and ammonium carbonate.

[0010] Preferably, the bicarbonate is at least one of sodium bicarbonate, ammonium bicarbonate, and potassium bicarbonate.

[0011] Preferably, the nitrate is at least one of sodium nitrate, potassium nitrate, and ammonium nitrate.

[0012] Preferably, the hydrochloride is at least one of sodium chloride, potassium chloride, ammonium chloride, and lithium chloride.

[0013] According to a specific embodiment of the present invention, the intercalating agent is a 1-2 mol / L solution of carbonate, bicarbonate, nitrate or hydrochloride.

[0014] According to a specific embodiment of the present invention, the pH adjuster is at least one selected from ammonia, NaOH, KOH, and LiOH.

[0015] Preferably, the pH adjuster is at least one of 25-28 wt% ammonia water, or 0.1-0.2 mol / L NaOH, KOH, or LiOH solution.

[0016] According to a specific embodiment of the present invention, the nickel salt is at least one selected from nickel sulfate, nickel nitrate, nickel acetate, nickel chloride, and nickel bromide.

[0017] According to a specific embodiment of the present invention, the cobalt salt is at least one selected from cobalt sulfate, cobalt nitrate, cobalt acetate, cobalt chloride, and cobalt bromide.

[0018] According to a specific embodiment of the present invention, the molybdenum salt is at least one selected from molybdenum sulfate, molybdenum nitrate, molybdenum acetylacetonate, ammonium molybdate, and sodium molybdate.

[0019] According to a specific embodiment of the present invention, the amounts of nickel salt, cobalt salt, and molybdenum salt are such that the molar ratio of Ni:Co:Mo is (1-2):1:(1-2).

[0020] According to a specific embodiment of the present invention, the reaction conditions are as follows: the pH value of the reaction is adjusted to 7-8.5, and the reaction is heated in a water bath at 60-90°C for 12-24 hours under normal pressure.

[0021] According to a specific embodiment of the present invention, the amount of intercalating agent and pH adjuster added is as follows: the intercalating agent is added in a ratio of the total molar amount of nickel salt, cobalt salt and molybdenum salt to the molar amount of intercalating agent of 1:1 to 1:2, and then the pH adjuster is added to adjust the pH value of the solution to 7-8.5.

[0022] Existing technologies for synthesizing ternary layered double hydroxides (TLHs) mostly involve hydrothermal conditions and high pressure (or in a reactor). These harsh conditions result in rapid precipitation reactions that are difficult to regulate and control, leading to poor product morphology and impacting final performance. This application addresses this by adjusting the reaction raw materials and conditions. Firstly, specific types and amounts of intercalating agents and pH adjusters are selected. The intercalating agent is added to the reaction system initially, preventing the reaction from initiating. Then, the pH adjuster is added to adjust the pH to a suitable range, initiating the reaction. Secondly, by controlling the reaction temperature and time, the pH adjuster both regulates the pH and controls the reaction rate, preventing excessively rapid reaction and avoiding product agglomeration. This allows for the direct synthesis of ternary TLDs under normal pressure and water bath heating conditions. Compared to existing technologies, this method offers milder and more controllable reaction conditions, and the resulting product exhibits a nanoflower morphology with a large specific surface area and excellent electrical properties.

[0023] In a second aspect, the present invention provides a Co-doped ternary hydrotalcite, wherein the Co-doped ternary hydrotalcite is prepared by the preparation method of the first aspect.

[0024] According to a specific embodiment of the present invention, the molecular formula of the Co-doped ternary hydrotalcite is [NiCoMo(OH)2]. x+ ·(A n- ) x / n ·mH2O, where A n- CO3 2- NO3 -Or Cl-, where m is an integer between 2 and 8.

[0025] In the above molecular formula, x refers to the charge carried by the ternary hydrotalcite layer, n refers to the charge number of interlayer anions, and A refers to the interlayer anions.

[0026] Those skilled in the art should know that when the intercalating agent is a carbonate, the molecular formula of the resulting ternary hydrotalcite will have A n- CO3 2- When the intercalating agent is a nitrate, the molecular formula of the resulting ternary hydrotalcite contains A. n- NO3 - When the intercalating agent is hydrochloride, the molecular formula of the resulting ternary hydrotalcite contains A. n- For Cl - .

[0027] According to a specific embodiment of the present invention, the Co-doped ternary hydrotalcite has a particle size of 5-6 μm.

[0028] According to a specific embodiment of the present invention, the specific surface area of ​​the Co-doped ternary hydrotalcite is 200-250 m². 2 / g, preferably 220-240m 2 / g.

[0029] In a third aspect, the present invention provides the application of the above-mentioned Co-doped ternary hydrotalcite in lithium-ion batteries or supercapacitors.

[0030] Preferably, the Co-doped ternary hydrotalcite can be used as a precursor for lithium-ion battery cathode materials.

[0031] Preferably, the Co-doped ternary hydrotalcite described above can be used as an anode material for supercapacitors.

[0032] The beneficial effects of this invention are as follows:

[0033] (1) This application synthesizes NiCoMo ternary layered double hydroxides with high specific surface area by a simple water bath heating method. The high specific surface area allows for more complete contact between the material and the electrolyte, thereby increasing the double layer capacitance of the material; at the same time, more active sites are exposed, improving the energy storage activity of the material.

[0034] (2) During the charging and discharging process, conventional ternary layered hydroxides can easily cause the crystal skeleton to dissolve and lose performance due to the release of hydroxide ions from the interlayer. In contrast, ternary hydrotalcite nanoflowers are composed of thinner nanosheets, which are more conducive to the electrolyte penetrating into the crystal and maintaining the stability of the crystal structure.

[0035] (3) The ternary hydrotalcite of this application introduces high-valence Mo element. The addition of high-valence Mo element adjusts the valence distribution of Ni and Co elements, optimizes the adsorption of charge carriers during the electrochemical reaction, and reduces the interfacial transfer resistance.

[0036] Terminology Definition

[0037] Unless explicitly stated otherwise, all scopes referenced in this invention include end values.

[0038] The term "at least one" is used in this invention to describe the elements and components described herein. This is done merely for convenience and to provide a general meaning regarding the scope of the invention. This description should be understood to include one or at least one, and the singular includes the plural, unless clearly otherwise indicated.

[0039] All figures in this invention are approximate values, regardless of whether words such as "approximately" or "about" are used. The numerical values ​​may vary by 1%, 2%, 5%, 7%, 8%, 10%, etc. Whenever a number with a value of N is disclosed, any number having a value of N+ / -1%, N+ / -2%, N+ / -3%, N+ / -5%, N+ / -7%, N+ / -8%, or N+ / -10% will be explicitly disclosed, where "+ / -" indicates addition or subtraction, and the range between N-10% and N+10% is also disclosed.

[0040] Unless otherwise stated, the following definitions as used in this invention shall apply. For the purposes of this invention, chemical elements are consistent with the CAS version of the periodic table and the 75th edition of the *Handbook of Chemistry and Physics*, 1994. Furthermore, general principles of organic chemistry can be found in *Organic Chemistry*, Thomas Sorrell, University Science Books, Sausalito: 1999, and *March's Advanced Organic Chemistry* by Michael B. Smith and Jerry March, John Wiley & Sons, New York: 2007, the entire contents of which are incorporated herein by reference.

[0041] Unless otherwise defined, all technical terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Although similar or equivalent methods and materials may be used in the implementation or testing of embodiments of this invention, suitable methods and materials are described below. All publications, patent applications, patents, and other references mentioned in this invention are incorporated herein by reference in their entirety, except where specific paragraphs are cited. In case of any conflict, this specification and its included definitions shall prevail. Furthermore, materials, methods, and examples are illustrative only and are not intended to be limiting. Attached Figure Description

[0042] Figure 1 The XRD patterns are of the hydrotalcite prepared in Example 1 and Comparative Example 1 of this invention.

[0043] Figure 2 This is a 10,000x magnified SEM image of the hydrotalcite prepared in Example 1 of the present invention.

[0044] Figure 3 This is a 3500x magnified SEM image of the hydrotalcite prepared in Example 1 of this invention. Detailed Implementation

[0045] The preparation method of Co-doped ternary hydrotalcite proposed in this invention will be described in detail below:

[0046] S1: Dissolve nickel salt, cobalt salt, and molybdenum salt in deionized water at a molar ratio of Ni:Co:Mo of (1-2):1:(1-2).

[0047] Wherein, the nickel salt is at least one of nickel sulfate, nickel nitrate, nickel acetate, nickel chloride, and nickel bromide; the cobalt salt is at least one of cobalt sulfate, cobalt nitrate, cobalt acetate, cobalt chloride, and cobalt bromide; and the molybdenum salt is at least one of molybdenum sulfate, molybdenum nitrate, molybdenum acetylacetonate, ammonium molybdate, and sodium molybdate.

[0048] S2: Weigh the intercalating agent according to the ratio of the total molar amount of nickel salt, cobalt salt, and molybdenum salt to the molar amount of intercalating agent of 1:1 to 1:2, and prepare a pH adjusting agent solution.

[0049] The intercalating agent is at least one of carbonate, nitrate, and hydrochloride, and the pH adjuster is at least one of 25-28 wt% ammonia water or 0.1-0.2 mol / L NaOH, KOH, and LiOH solution.

[0050] S3: Add the intercalating agent from S2 to the solution of S1, stir and mix evenly, then slowly add the pH adjuster until the pH value of the solution is 7-8.5, and obtain a clear and homogeneous solution.

[0051] S4: The solution obtained in S3 is heated in a water bath at 60-90℃ for 12-24h. After the reaction is complete, it is cooled to room temperature and filtered to obtain crude NiCoMo-LDH precipitate.

[0052] S5: Wash the crude precipitate obtained in S4 with deionized water and ethanol, and dry it at 70-90℃ to obtain the Co-doped ternary hydrotalcite.

[0053] The following description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

[0054] Example 1

[0055] Dissolve 20 mmol NiSO4, 10 mmol CoSO4, and 20 mmol Na2MoO4·2H2O in 300 mL of deionized water. While stirring continuously, add 50 mL of 1 mol / L sodium carbonate solution (the total molar ratio of nickel, cobalt, and molybdenum salts to the molar ratio of intercalating agent is 1:1). Then, slowly add ammonia to adjust the pH to 7 to obtain a clear, homogeneous solution. Transfer the solution to a three-necked flask and heat in a water bath at 90 °C for 24 hours. After cooling to room temperature, wash the formed crude NiCoMo-LDH precipitate with deionized water and ethanol, and dry at 80 °C to obtain the final product.

[0056] Example 2

[0057] Compared with Example 1, the difference is that the pH of the solution was adjusted to 8.5, while the rest of the operation was the same.

[0058] Example 3

[0059] Compared with Example 1, the difference is that the solution was heated in a water bath at 60°C for 18 hours, while the rest of the operation was the same.

[0060] Example 4

[0061] Compared with Example 1, the difference is that the intercalating agent is sodium nitrate, while the rest of the operation is the same.

[0062] Example 5

[0063] Compared with Example 1, the difference is that the intercalating agent is sodium chloride, while the rest of the operation is the same.

[0064] Example 6

[0065] Compared with Example 1, the difference is that the amount of 1 mol / L sodium carbonate used is 100 mL (the ratio of the total molar amount of nickel salt, cobalt salt, and molybdenum salt to the molar amount of intercalating agent is 1:2), and the rest of the operation is the same.

[0066] Comparative Example 1

[0067] 20 mmol NiSO4 and 20 mmol Na2MoO4·2H2O were dissolved in 300 mL of deionized water. While stirring continuously, 40 mL of 1 mol / L sodium carbonate solution was added (the total molar ratio of nickel salt and molybdenum salt to intercalating agent was 1:1). Ammonia was then slowly added dropwise to adjust the pH to 7 to obtain a clear, homogeneous solution. This solution was then transferred to a three-necked flask and heated in a water bath at 90 °C for 24 hours. After cooling to room temperature, the resulting crude NiMo-LDH precipitate was washed with deionized water and ethanol, and dried at 80 °C to obtain undoped binary hydrotalcite NiMo-LDH.

[0068] Comparative Example 2

[0069] Dissolve 20 mmol NiSO4, 10 mmol CoSO4, and 20 mmol Na2MoO4·2H2O in 75 mL of deionized water, add 50 mmol urea, stir well, and pour into a 100 mL Teflon reactor. Heat to 180 °C in a forced-air drying oven and maintain for 24 h. After cooling to room temperature, wash the obtained material with deionized water and ethanol, and dry at 80 °C overnight to obtain the final product.

[0070] Comparative Example 3

[0071] The difference from Example 1 is that the pH value of the reaction was adjusted to 6, while the rest of the operation was the same, and NiCoMo-LDH could not be obtained.

[0072] Comparative Example 4

[0073] The difference from Example 1 is that the pH value of the reaction is adjusted to 9.5, while the rest of the operation is the same.

[0074] Performance Evaluation

[0075] The specific surface area, electrical conductivity and electrical properties of the hydrotalcite materials obtained in Examples 1-6 and Comparative Examples 1, 2 and 4 were tested respectively. The test results are shown in Table 1.

[0076] The specific surface area was obtained using the BET method.

[0077] The conductivity was obtained using the four-probe method.

[0078] The electrical properties were tested using a three-electrode system (Ag / AgCl electrode as reference electrode, Pt electrode as counter electrode, working electrode made of synthetic material, and 1M KOH solution as electrolyte solution).

[0079] Table 1

[0080]

[0081]

[0082] As can be seen from the table, the Co-doped ternary hydrotalcite obtained by the preparation method provided in this application has a large specific surface area and good electrical conductivity and cycling stability.

[0083] The hydrotalcites obtained in Example 1 and Comparative Example 1 were subjected to XRD tests, and the test results are shown in the appendix. Figure 1 .from Figure 1 It can be seen that the two materials have obvious characteristic peaks at 2θ of 11.5°, 23.8°, 34.9°, 39.4°, 60.8° and 62.4°. Among them, the diffraction peak at 11.5° is the strongest. The diffraction peaks at 11.5°, 23.8° and 34.9° correspond to the (003), (006) and (012) crystal planes of hydrotalcite NiMo-LDH, respectively.

[0084] Comparing the XRD patterns of the two materials revealed no significant changes, indicating that Co ions were successfully incorporated into the hydrotalcite crystal without altering its crystal structure, resulting in pure-phase hydrotalcite. Comparing the asterisked areas in the figures, it can be seen that these two characteristic peaks become significantly sharper with the incorporation of Co ions, indicating an increase in the material's crystallinity. The sharp and symmetrical diffraction peaks in the figures further demonstrate the good crystallinity of the prepared sample. Therefore, it can be concluded that the crystal structure of NiCoMo-LDH did not change due to the incorporation of Co ions.

[0085] Appendix Figure 2 and 3 The image shows the SEM image of the Co-doped ternary hydrotalcite obtained in Example 1. It can be seen that the NiCoMo-LDH material obtained in this application is a uniform nanoflower sphere with a diameter of about 5-6 μm. The material has a distinct three-dimensional porous flower-like structure. The entire nanoflower is composed of multiple uniform nanosheets. Therefore, the specific surface area of ​​the material is increased, the migration channel of the electrolyte is shortened, and the interaction between the electrode and the electrolyte occurs. This allows the Faraday redox reaction to proceed rapidly and reversibly, thereby improving the electrochemical performance.

[0086] In Comparative Example 1, because there was no cobalt doping, there was no synergistic effect between nickel and cobalt, resulting in no improvement in the material's electrical conductivity and electrochemical activity.

[0087] Comparative Example 2 uses a conventional hydrothermal method, which requires high temperature and high pressure conditions. The preparation method of this application is simpler.

[0088] In Comparative Example 3, the experiment failed because no precipitate could be obtained under acidic conditions.

[0089] In Comparative Example 4, the high pH value of the reaction caused the formation of hydroxyl oxides on the surface of the material, which reduced the conductivity of the material.

[0090] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing Co-doped ternary hydrotalcite, characterized in that, The preparation method includes: dissolving nickel salt, cobalt salt, and molybdenum salt in deionized water, adding intercalating agent and pH adjuster, and washing and drying the precipitate after the reaction is completed to obtain the Co-doped ternary hydrotalcite. The intercalating agent is one of carbonate, bicarbonate, nitrate, and hydrochloride; the pH adjuster is at least one of ammonia, NaOH, KOH, and LiOH. The carbonate is at least one of sodium carbonate, potassium carbonate, and ammonium carbonate; The bicarbonate is at least one of sodium bicarbonate, ammonium bicarbonate, and potassium bicarbonate. The nitrate is at least one of sodium nitrate, potassium nitrate, and ammonium nitrate; The hydrochloride is at least one of sodium chloride, potassium chloride, ammonium chloride, and lithium chloride; Under normal pressure, heat in a water bath at 60-90℃ for 12-24 hours; Add the intercalating agent according to the ratio of the total molar amount of nickel salt, cobalt salt, and molybdenum salt to the molar amount of intercalating agent of 1:1 to 1:2, and then add a pH adjuster to adjust the pH of the solution to 7-8.

5. The molecular formula of the ternary hydrotalcite is [NiCoMo(OH)2]. x+ •(A n ) x / n •mH2O, wherein the ternary hydrotalcite has a particle size of 5-6 μm; wherein, A n CO3 2 NO3 or Cl m is an integer between 2 and 8; the amount of nickel salt, cobalt salt and molybdenum salt used is: the molar ratio of Ni:Co:Mo elements is (1~2):1:(1~2).

2. The preparation method according to claim 1, characterized in that, The nickel salt is at least one of nickel sulfate, nickel nitrate, nickel acetate, nickel chloride, and nickel bromide; The cobalt salt is at least one of cobalt sulfate, cobalt nitrate, cobalt acetate, cobalt chloride, and cobalt bromide; The molybdenum salt is at least one of molybdenum sulfate, molybdenum nitrate, molybdenum acetylacetonate, ammonium molybdate, and sodium molybdate.

3. Co-doped ternary hydrotalcite obtained by the preparation method according to any one of claims 1 to 2.

4. The application of the Co-doped ternary hydrotalcite as described in claim 3 in lithium-ion batteries or supercapacitors.

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