Composite-coated sodium-ion battery cathode material and preparation method thereof

Abstract

This invention provides a composite-coated sodium-ion battery cathode material and its preparation method. The preparation method involves using a metal hydroxide (Ni) x Mn y M 1‑x‑y Sodium-ion battery cathode material is prepared by uniformly mixing (OH)₂ and sodium salt at a total metal to sodium molar ratio of (0.6~1.1):1 and sintering. Tellurium source solution is prepared by mixing TeO₂, ethylene glycol, and a strong alkali and heating. A reducing agent is then added to the tellurium source solution and kept at a constant temperature before adding AgNO₃, a surfactant, and a carbon source. After the reaction is complete, the mixture is centrifuged, washed, and dried to obtain a mixture of Ag₂Te nanotubes and hollow carbon microspheres. The sodium-ion battery cathode material is then mechanically mixed uniformly with the Ag₂Te nanotube and hollow carbon microsphere mixture and sintered to obtain a composite-coated sodium-ion battery cathode material. This preparation method can form a uniform nano-coating layer on the surface of the sodium-ion battery cathode material, effectively blocking interfacial side reactions between the electrolyte and the cathode material, thus making the cathode material structure more stable.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of sodium ion battery positive electrode materials, in particular to a composite-coated sodium ion battery positive electrode material and a preparation method thereof. BACKGROUND

[0002] Environmental and energy problems are the topics of concern in today's society. The reserves of non-renewable energy are limited, and the environmental problems caused by the use of non-renewable energy are becoming increasingly serious, which makes electrochemical energy storage the most popular green energy today. Among them, lithium ion batteries have been widely used in mobile phones, notebook computers, digital cameras, electric tools, new energy vehicles and other fields due to their high energy density, high working voltage, long cycle life, small self-discharge rate and green environmental protection. The continuous expansion of the market demand for lithium ion batteries will also face the problem of raw material shortage, so the metal sodium with abundant reserves and similar performance to lithium has broad prospects in the field of energy storage.

[0003] The existing oxide-type sodium ion battery positive electrode material has the advantages of high capacity and good cycle performance; however, the residual sodium on the surface of the positive electrode material is easy to react with water and carbon dioxide in the environment to generate sodium carbonate and sodium hydroxide, and the sodium carbonate and sodium hydroxide are enriched on the surface of the positive electrode material, resulting in poor stability of the oxide-type sodium ion battery positive electrode material.

[0004] Therefore, it is necessary to provide a composite-coated sodium ion battery positive electrode material and a preparation method thereof to solve the problems existing in the prior art. SUMMARY

[0005] Therefore, the application provides a composite-coated sodium ion battery positive electrode material and a preparation method thereof, which coats a nanomaterial on the surface of the sodium ion battery positive electrode material to improve the structural stability.

[0006] To achieve the above-mentioned purpose, the application provides a composite-coated sodium ion battery positive electrode material and a preparation method thereof, which adopts the following technical scheme:

[0007] A preparation method of a composite-coated sodium ion battery positive electrode material, comprising the following steps:

[0008] a. mixing, heating and stirring TeO2, ethylene glycol and a strong base uniformly to prepare a tellurite source solution with a tellurite concentration of 40 mmol / L;

[0009] b. adding a reducing agent to the tellurite source solution prepared in step a, once heating, keeping constant temperature, then adding AgNO3, a surfactant and a carbon source, twice heating, keeping constant temperature until the reaction is completed, centrifuging, washing and drying to prepare a mixture of Ag2Te nanotubes and hollow carbon microspheres;

[0010] c、mixing the metal hydroxide (Ni x Mn y M 1-x-y ) (OH)2 with sodium salt in a ratio of (0.6~1.1):1 of the total metal to sodium, and sintering to obtain a sodium ion battery cathode material;

[0011] d、mixing the sodium ion battery cathode material obtained in step c with the mixture of Ag2Te nanotubes and hollow carbon microspheres obtained in step b, and sintering to obtain a composite coated sodium ion battery cathode material;

[0012] The molecular formula of the sodium ion battery cathode material obtained in step c is Na m (Ni x Mn y M 1-x-y )O2, wherein M is a metal element with an ionic radius of 0.05~0.08 nm, 0.60≤m≤1.10, 0.20≤x≤0.50, and 0.20≤y≤0.80.

[0013] Further, in step a, the strong base is one or a mixture of at least two of sodium hydroxide, lithium hydroxide, and potassium hydroxide.

[0014] Further, in step a, the heating temperature is 100-150℃.

[0015] Further, in step b, the reducing agent is one or a mixture of at least two of ethylene glycol, hydrazine, sodium borohydride, and ascorbic acid; the surfactant is one or a mixture of at least two of polyvinylpyrrolidone and sodium dodecyl sulfate; and the carbon source is one or a mixture of at least two of glucose, sucrose, and starch.

[0016] Further, in step b, the molar ratio of the reducing agent to the tellurite in the tellurium source solution is (1.0~1.2):1.

[0017] Further, in step b, the molar ratio of AgNO3 to the tellurite in the tellurium source solution is 2:1.

[0018] Further, in step b, the reaction temperature is 100~180℃, the reaction time is 1~15h, and the drying temperature is 50~80℃.

[0019] Further, in step c, the sintering temperature is 750~950℃, and the sintering time is 7~13h.

[0020] Further, in step d, the mass ratio of the sodium ion battery cathode material to the mixture of Ag2Te nanotubes and hollow carbon microspheres is 1:(0.02~0.05).

[0021] Further, in step d, the sintering temperature is 200-600 DEG C, and the sintering time is 5-8h.

[0022] The composite-coated sodium ion battery positive electrode material is prepared by the preparation method, and is a sodium ion battery positive electrode material with a mixed nanocoating layer of Ag2Te nanotubes and hollow carbon microspheres on the surface.

[0023] The above technical solutions of the present application at least have the following beneficial effects:

[0024] 1. The preparation method can form a uniform nanocoating layer on the surface of the sodium ion battery positive electrode material, effectively blocks the interface side reaction between the electrolyte and the positive electrode material, and makes the structure of the positive electrode material more stable.

[0025] 2. The Ag2Te nanotubes have excellent thermoelectric properties and high conductivity, which can play a certain conductive role in the positive electrode material and improve the rate and cycle performance of the positive electrode material.

[0026] 3. The hollow structure of the Ag2Te nanotubes and the hollow carbon microspheres does not hinder the embedding and extraction of sodium ions, is more conducive to the rapid embedding and extraction of sodium ions in the charging and discharging process, and further improves the electrochemical performance of the positive electrode material. BRIEF DESCRIPTION OF DRAWINGS

[0027] Fig. 1 Charge-discharge curves of Examples 1-3 and Comparative Examples 1-2;

[0028] Fig. 2 The graph is a comparison of the room temperature 25 DEG C cycles of Examples 1-3 and Comparative Examples 1-2. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solutions and advantages of the embodiments of the present application more clear, the following will combine the drawings of the embodiments of the present application to make a better description. Figs. 1-2 The technical solutions of the embodiments of the present application are clearly and completely described. Obviously, the described embodiments are part of the embodiments of the present application, not all the embodiments. Based on the described embodiments of the present application, all other embodiments obtained by those skilled in the art belong to the scope of protection of the present application.

[0030] Example 1

[0031] Take the positive electrode material Na 1.00 (Ni 1 / 3 Mn 1 / 3 Fe 1 / 3 )O2 as an example, in Na 1.00 (Ni 1 / 3 Mn 1 / 3 Fe 1 / 3The preparation method of the Ag2Te nanotube and hollow carbon microsphere nanolayer coated on the surface of the O2 cathode material has the following specific steps:

[0032] (1) uniformly mixing the precursor (Ni 1 / 3 Mn 1 / 3 Fe 1 / 3 )(OH)2 and sodium carbonate according to a molar ratio of sodium to total metal of 1:1, heating at 900 DEG C for 10 h to obtain a primary synthesis product, and crushing the primary synthesis product by using an airflow mill to obtain a sodium ion battery cathode material Na 1.00 (Ni 1 / 3 Mn 1 / 3 Fe 1 / 3 )O2;

[0033] (2) mixing TeO2, ethylene glycol and NaOH according to a ratio, uniformly stirring and heating at 150 DEG C to prepare a tellurite source solution with a concentration of 40 mmol / L;

[0034] Experiments prove that the structure and morphology of the Ag2Te nanotube and hollow carbon microsphere prepared by different concentrations of the tellurite source solution are different, and the structure and morphology of the Ag2Te nanotube and hollow carbon microsphere prepared by the tellurite source solution with a concentration of 40 mmol / L are the best. In the experiment process of the present application, the inventors prepared the composite coated sodium ion battery cathode material by using the tellurite source solutions with concentrations of 35 mmol / L, 38 mmol / L, 42 mmol / L and 45 mmol / L, respectively, and the results show that the electrochemical performance of the prepared composite coated sodium ion battery cathode material is poor, which also proves that the structure and morphology of the Ag2Te nanotube and hollow carbon microsphere prepared by the tellurite source solution with a concentration of 40 mmol / L are the best, which is most beneficial to the rapid embedding and extraction of sodium ions in the charging and discharging process, thereby better improving the electrochemical performance of the cathode material;

[0035] (3) mixing the prepared tellurite source solution and ascorbic acid (tellurite in the tellurite source solution and ascorbic acid) according to a molar ratio of 1:1, heating to 120 DEG C, keeping the temperature for 110 min, then adding AgNO3 (tellurite in the tellurite source solution and AgNO3) into the mixed solution according to a molar ratio of 1:2, keeping the temperature for 10 min, finally adding SDS and glucose, heating to 150 DEG C, keeping the temperature for 12 h, after the reaction, centrifuging, washing with anhydrous ethanol for 3 times, and drying at 60 DEG C to prepare the Ag2Te nanotube and hollow carbon microsphere mixture;

[0036] (4) mixing the above sodium ion battery cathode material Na 1.00 (Ni 1 / 3 Mn 1 / 3 M 1 / 3O2 was mechanically mixed with Ag2Te nanotubes and hollow carbon microspheres at a mass ratio of 1.00:0.03 until homogeneous, and then kept at 300℃ for 6 hours to obtain a composite-coated sodium-ion battery cathode material.

[0037] The execution order of steps (1) and (2) and (3) in the above preparation method is not important. In other embodiments, the specific steps are: first execute steps (2) and (3), then execute step (1), and finally execute step (4).

[0038] The sodium-ion battery cathode material Na with Ag2Te nanotubes and hollow carbon microspheres composite coating prepared in the above embodiments 1.00 (Ni 1 / 3 Mn 1 / 3 Fe 1 / 3 O2 was used as the positive electrode material for sodium-ion batteries. When assembled into a coin cell, its electrochemical performance was tested. The test voltage was 2.0~4.0V. The initial discharge capacity at 0.1C was 136.0 mAh / g, the initial discharge efficiency was 93.7%, and the capacity retention rate was 93.9% after 50 cycles at room temperature (25℃).

[0039] Example 2

[0040] With Na as the positive electrode material 0.95 (Ni 0.30 Mn 0.35 Fe 0.30 Cu 0.05 Taking O2 as an example, in Na 0.95 (Ni 0.30 Mn 0.35 Fe 0.30 Cu 0.05 The preparation method of coating the surface of O2 cathode material with Ag2Te nanotubes and hollow carbon microspheres involves the following specific steps:

[0041] (1) The precursor (Ni 0.30 Mn 0.35 Fe 0.30 Cu 0.05 (OH)₂ and sodium carbonate were mixed uniformly at a sodium to total metal molar ratio of 0.95:1.00, and heated to 880℃ and held at that temperature for 10 hours to obtain a primary synthesis product. This product was then pulverized using an air jet mill to obtain sodium-ion battery cathode material Na. 0.95 (Ni 0.30 Mn 0.35 Fe 0.30 Cu 0.05 O2;

[0042] (2) TeO2, ethylene glycol and NaOH were mixed in proportion, heated to 150°C and stirred evenly to prepare a 40 mmol / L tellurium source solution;

[0043] The experiment proves that the structure and morphology of the Ag2Te nanotubes and hollow carbon microspheres prepared by different concentrations of tellurium source solution are different, and the structure and morphology of the Ag2Te nanotubes and hollow carbon microspheres prepared by the tellurium source solution with a concentration of 40 mmol / L of tellurite are the best. In the experiment of the present application, the inventors prepared the composite-coated sodium ion battery cathode material using the tellurium source solution with a concentration of 35 mmol / L, 38 mmol / L, 42 mmol / L and 45 mmol / L of tellurite, respectively, and the result is that the electrochemical performance of the composite-coated sodium ion battery cathode material prepared is not good, which also proves that the structure and morphology of the Ag2Te nanotubes and hollow carbon microspheres prepared by the tellurium source solution with a concentration of 40 mmol / L of tellurite are the best, which is most beneficial to the rapid embedding and extraction of sodium ions in the charging and discharging process, thereby better improving the electrochemical performance of the cathode material.

[0044] (3) The above-prepared tellurium source solution is mixed with ascorbic acid (tellurite in the tellurium source solution and ascorbic acid) at a molar ratio of 1:1, heated to 120℃, and kept at 110℃ for 110 minutes. Then, AgNO3 is added to the mixed solution at a molar ratio of 1:2 of the tellurium source solution and AgNO3 (tellurite in the tellurium source solution and AgNO3), and kept at 110℃ for 10 minutes. Finally, SDS and glucose are added, heated to 150℃, and kept at 150℃ for 12 hours. After the reaction, centrifugation, washing with anhydrous ethanol for 3 times, and drying at 60℃, the Ag2Te nanotubes and hollow carbon microspheres mixture is prepared.

[0045] (4) The above-prepared sodium ion battery cathode material Na 0.95 (Ni 0.30 Mn 0.35 Fe 0.30 Cu 0.05 )O2 is mechanically mixed with the Ag2Te nanotubes and hollow carbon microspheres mixture at a mass ratio of 1.00:0.03, and kept at 300℃ for 6 hours to obtain the composite-coated sodium ion battery cathode material.

[0046] The above-prepared sodium ion battery cathode material Na 0.95 (Ni 0.30 Mn 0.35 Fe 0.30 Cu 0.05 )O2 with Ag2Te nanotubes and hollow carbon microspheres composite coating is used as a sodium ion battery cathode material, and a button cell is assembled to test its electrochemical performance. The test voltage is 2.0-4.0V, the initial discharge capacity at 0.1C is 134.4 mAh / g, the initial discharge efficiency is 92.3%, and the capacity retention rate after 50 cycles at room temperature of 25℃ is 90.5%.

[0047] Example 3

[0048] Na 0.95 (Ni 0.33 Mn 0.35 Zr 0.32 )O2 as an example, the preparation method of the Ag2Te nanotube and hollow carbon microsphere nanolayer coated on the surface of the Na 0.95 (Ni 0.33 Mn 0.35 Zr 0.32 )O2 cathode material has the following specific steps:

[0049] (1) the precursor (Ni 0.33 Mn 0.35 Zr 0.32 ) (OH)2 is uniformly mixed with sodium carbonate according to the molar ratio of sodium to total metal of 0.95:1.00, heated to 950℃, and kept for 10h to obtain a primary synthesis product, which is crushed by a gas flow mill to obtain a sodium ion battery cathode material Na 0.95 (Ni 0.33 Mn 0.35 Zr 0.32 )O2;

[0050] (2) TeO2, ethylene glycol and NaOH are mixed and heated at 150℃ and stirred uniformly to prepare a 40mmol / L tellurium source solution;

[0051] Experiments prove that the structure and morphology of Ag2Te nanotubes and hollow carbon microspheres prepared by different concentrations of tellurium source solution are different, and the structure and morphology of Ag2Te nanotubes and hollow carbon microspheres prepared by a tellurium source solution with a concentration of 40mmol / L of tellurite are the best. In the test process of the present application, the inventors prepared a composite coated sodium ion battery cathode material using a tellurium source solution with a concentration of 35mmol / L, 38mmol / L, 42mmol / L and 45mmol / L of tellurite, respectively. The results show that the electrochemical performance of the composite coated sodium ion battery cathode material is not good, which also proves that the structure and morphology of Ag2Te nanotubes and hollow carbon microspheres prepared by a tellurium source solution with a concentration of 40mmol / L of tellurite are the best, which is most beneficial to the rapid embedding and extraction of sodium ions during charging and discharging, thereby better improving the electrochemical performance of the cathode material.

[0052] (3) The prepared tellurium source solution is mixed with ascorbic acid (molar ratio of tellurite in the tellurium source solution to ascorbic acid is 1:1.1) and heated to 120°C, and kept at 110°C for 110 minutes. Then, AgNO3 is added to the mixture (molar ratio of tellurite in the tellurium source solution to AgNO3 is 1:2) and kept at 110°C for 10 minutes. Finally, SDS and glucose are added, and the mixture is heated to 150°C and kept at 150°C for 12 hours. After the reaction, centrifugation, washing with anhydrous ethanol for 3 times, and drying at 60°C, a mixture of Ag2Te nanotubes and hollow carbon microspheres is prepared.

[0053] (4) The above sodium ion battery positive electrode material Na 0.95 (Ni 0.33 Mn 0.35 Zr 0.32 )O2 is mechanically mixed with the mixture of Ag2Te nanotubes and hollow carbon microspheres at a mass ratio of 1.00:0.02, and kept at 250°C for 6 hours to obtain a sodium ion battery positive electrode material with composite coating.

[0054] The above sodium ion battery positive electrode material Na 0.95 (Ni 0.33 Mn 0.35 Zr 0.32 )O2 with Ag2Te nanotubes and hollow carbon microspheres composite coating prepared in the above example is used as a sodium ion battery positive electrode material, and a button cell is assembled. The electrochemical performance is tested at a test voltage of 2.0~4.0V, and the initial discharge capacity at 0.1C is 137.3 mAh / g, the initial discharge efficiency is 94.6%, and the capacity retention rate after 50 cycles at room temperature 25°C is 91.8%.

[0055] Comparative Example 1

[0056] Comparative Example 1 uses the method described in Example 1 to prepare a sodium ion battery positive electrode material Na 1.00 (Ni 1 / 3 Mn 1 / 3 Fe 1 / 3 )O2 without Ag2Te nanotubes and hollow carbon microspheres composite coating. The sodium ion battery positive electrode material Na 1.00 (Ni 1 / 3 Mn 1 / 3 Fe 1 / 3 )O2 without Ag2Te nanotubes and hollow carbon microspheres composite coating is used as a sodium ion battery positive electrode material, and a button cell is assembled. The electrochemical performance is tested at a test voltage of 2.0~4.0V, and the initial discharge capacity at 0.1C is 134.3 mAh / g, the initial discharge efficiency is 91.7%, and the capacity retention rate after 50 cycles at room temperature 25°C is 91.8%.

[0057] Comparative Example 2

[0058] Comparative Example 2 Na 0.95 (Ni 0.33 Mn 0.35 Zr 0.32 )O2 was prepared by the method described in Example 3. The reducing agent was replaced by hydrazine instead of ascorbic acid to obtain Na 0.95 (Ni 0.33 Mn 0.35 Zr 0.32 )O2 coated with Ag2Te nanotubes and hollow carbon microspheres as the positive electrode material of sodium ion battery. The button cell was assembled and the electrochemical performance was tested. The test voltage was 2.0-4.0 V, the initial discharge capacity at 0.1 C was 135.1 mAh / g, the initial discharge efficiency was 93.3%, and the capacity retention rate after 50 cycles at room temperature 25°C was 90.1%.

[0059]

[0060] Table 1

[0061] Table 1 is the button cell test results of Examples 1-3 and Comparative Examples 1-2. The button cell capacities of Example 1, Example 2, and Example 3 are 136.0 mAh / g, 134.4 mAh / g, and 137.3 mAh / g, respectively. Example 1 is a type 111 Ni, Fe, and Mn sodium ion battery positive electrode material. Example 2 increases the Cu content by 5% based on Example 1. Although the addition of Cu can improve the air stability of the sodium ion battery positive electrode material, the capacity is slightly reduced. The button cell capacities and capacity retention rates after 50 cycles at room temperature 25°C of Example 1 and Comparative Example 1 are 136.0 mAh / g and 93.9%, and 134.3 mAh / g and 91.8%, respectively. Therefore, the button cell performance of Na 1.00 (Ni 1 / 3 Mn 1 / 3 Fe 1 / 3 )O2 coated with Ag2Te nanotubes and hollow carbon microspheres is better than that of Na 1.00 (Ni 1 / 3 Mn 1 / 3 Fe 1 / 3 )O2 without Ag2Te nanotubes and hollow carbon microspheres. The Ag2Te nanotubes and hollow carbon microspheres composite coating effectively improves the electrochemical performance of the positive electrode material by blocking the side reaction between the electrolyte and the positive electrode material. The button cell performance of the positive electrode material prepared in Example 3 and Comparative Example 2 is slightly different due to the use of different types of reducing agents. After comparison, ascorbic acid, which is environmentally friendly and non-polluting, is preferred as the reducing agent.

[0062] The above are preferred embodiments of the present application. It should be pointed out that, for those skilled in the art, several improvements and refinements can be made without departing from the principles of the present application, and these improvements and refinements should also be considered as falling within the scope of protection of the present application.

Claims

1. A method for preparing a composite-coated sodium-ion battery cathode material, characterized in that, It comprises the following steps: a. mixing, heating and stirring TeO2, ethylene glycol and strong base to prepare a tellurium source solution, wherein the concentration of tellurite in the tellurium source solution is 40 mmol / L; b. adding a reducing agent to the tellurium source solution prepared in step a, heating once, keeping constant temperature, then adding AgNO3, a surfactant and a carbon source, heating twice, keeping constant temperature until the reaction is completed, centrifuging, washing and drying to prepare a mixture of Ag2Te nanotubes and hollow carbon microspheres; the molar ratio of the reducing agent to the tellurite in the tellurium source solution is (1.0-1.2):1, and the molar ratio of AgNO3 to the tellurite in the tellurium source solution is 2:1; c. mixing the metal hydroxide (Ni x Mn y M 1-x-y ) (OH)2 with the sodium salt in a molar ratio of total metal to sodium of (0.6-1.1):1, mixing uniformly, sintering, and obtaining a sodium-ion battery positive electrode material; d. mixing the sodium-ion battery cathode material prepared in step c with the mixture of Ag2Te nanotubes and hollow carbon microspheres prepared in step b mechanically and uniformly, sintering, to obtain a composite coated sodium-ion battery cathode material; the molecular formula of the sodium-ion battery cathode material prepared in step c is Na m (Ni x Mn y M 1-x-y )O2, wherein M is a metal element with an ionic radius of 0.05-0.08 nm, 0.60≤m≤1.10, 0.20≤x≤0.50, and 0.20≤y≤0.

80.

2. The method for preparing the composite-coated sodium-ion battery cathode material according to claim 1, characterized in that, In step a, the heating temperature is 100-150℃.

3. The method of claim 1, wherein the composite-coated sodium-ion battery cathode material is prepared by a process comprising: In step b, the reducing agent is one or a mixture of at least two of ethylene glycol, hydrazine, sodium borohydride and ascorbic acid; the surfactant is one or a mixture of at least two of polyvinylpyrrolidone and sodium dodecyl sulfate; and the carbon source is one or a mixture of at least two of glucose, sucrose and starch.

4. The method of claim 1, wherein the composite-coated sodium-ion battery cathode material is prepared by a process comprising: In step b, the reaction temperature is 100-180℃, the reaction time is 1-15h, and the drying temperature is 50-80℃.

5. The method of claim 1, wherein the composite-coated sodium-ion battery cathode material is prepared by a process comprising: In step c, the sintering temperature is 750-950℃, and the sintering time is 7-13h.

6. The method of claim 1, wherein the composite-coated sodium-ion battery cathode material is prepared by a process comprising: In step d, the mass ratio of the sodium ion battery positive electrode material to the mixture of Ag2Te nanotubes and hollow carbon microspheres is 1:(0.02-0.05).

7. The method for preparing the composite-coated sodium-ion battery cathode material according to claim 1, characterized in that, In step d, the sintering temperature is 200-600℃, and the sintering time is 5-8h.

8. A composite-coated sodium-ion battery cathode material prepared by the method of any one of claims 1 to 7, characterized in that, The sodium ion battery positive electrode material has a mixed nanometer coating layer of Ag2Te nanotubes and hollow carbon microspheres on the surface.

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