Composite materials and their preparation methods and applications, positive electrode sheets, sodium-ion batteries

Abstract

This invention provides a composite material, its preparation method and application, a positive electrode sheet, and a sodium-ion battery, relating to the field of battery technology. The composite material provided by this invention includes a positive electrode material and Na+ coated on the surface of the positive electrode material. 0.44 MnO2; where Na in the composite material 0.44 The mass percentage of MnO2 is 5%-20%, and the cathode material includes sodium iron pyrophosphate and / or sodium ferrous sulfate. This composite material, through coating with Na... 0.44 MnO2 adjusts the pH value of the acidic cathode material to reduce the formation of aqueous acid in the material, thus alleviating the Fe content of the sodium iron pyrophosphate / sodium iron sulfate material. 3+ The dissolution phenomenon broadens the voltage window of sodium iron pyrophosphate / sodium iron sulfate, improves the stability against metal ions and acid-base conditions, and enhances specific capacity. This composite material can be used in the fabrication of sodium-ion batteries, improving their safety and cycle life.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a composite material, its preparation method and application, a positive electrode, and a sodium-ion battery. Background Technology

[0002] Sodium-ion batteries are batteries that use layered oxides (mainly nickel-iron-manganese oxides and copper-iron-manganese oxides), Prussian blue analogues (such as iron-based Prussian white), and polyanionic materials (such as sodium iron sulfate and sodium iron phosphate) as the positive electrode, and carbon materials (such as hard carbon and soft carbon) as the negative electrode. They primarily use esters and ethers as solvents, with sodium added as the negative electrode. + A metal salt (such as sodium fluoride, sodium boron, and perchlorate), an electrolyte, and various additives (such as film-forming agents, flame retardants, and overcharge protection agents) form an electrolyte. Although polyanionic materials (sodium ferric sulfate) have advantages such as low cost, high safety, and long cycle life, their synthesis is often carried out under acidic conditions, resulting in sodium ferric sulfate itself being highly acidic, which interacts with the Fe during its own charging process. 3+ The dissolution of sodium dendrites has become one of the two unavoidable problems, and the uneven deposition of sodium dendrites further accelerates the capacity decay and short circuit of the battery.

[0003] In view of this, the present invention is hereby proposed. Summary of the Invention

[0004] The primary objective of this invention is to provide a composite material to solve the aforementioned technical problems.

[0005] A second objective of this invention is to provide a method for preparing the aforementioned composite material.

[0006] A third objective of this invention is to provide the application of the above-mentioned composite material in the preparation of sodium-ion batteries.

[0007] The fourth objective of this invention is to provide a positive electrode.

[0008] The fifth objective of this invention is to provide a sodium-ion battery.

[0009] To achieve the above objectives, the following technical solution is adopted:

[0010] In a first aspect, the present invention provides a composite material comprising a cathode material and Na. 0.44 MnO2, the Na 0.44 MnO2 is coated on the surface of the cathode material;

[0011] Na in the composite material 0.44 The mass percentage of MnO2 is 5%-20%;

[0012] The positive electrode material includes sodium iron pyrophosphate and / or sodium ferrous sulfate.

[0013] Secondly, the present invention provides a method for preparing the above-mentioned composite material, comprising the following steps:

[0014] a. Sodium source, manganese source and chelating agent are mixed in water to form a chelate, and then the positive electrode material is added. The mixture is then mixed at pH 7-8 and temperature 60-90℃ to form a hydrosol.

[0015] b. The hydrosol obtained in step a is dispersed in an organic solvent, and then the composite material is prepared by heating and calcining in sequence;

[0016] The temperature of the heating reaction is 190-210℃;

[0017] The calcination temperature is 250-350℃.

[0018] As a further technical solution, the sodium source includes at least one of sodium acetate, sodium sulfate, and sodium nitrate;

[0019] The manganese source includes at least one of manganese acetate, manganese sulfate, and manganese nitrate.

[0020] The chelating agent includes at least one of citric acid, sodium citrate, ethylenediaminetetraacetic acid, and ethylenediaminepentaacetic acid.

[0021] As a further technical solution, in step a, the pH of the solution is adjusted to 7-8 using ammonia.

[0022] As a further technical solution, the organic solvent includes at least one of cyclohexane, cyclobutane, n-pentanol, or isopropanol.

[0023] As a further technical solution, the organic solvent contains a surfactant;

[0024] The surfactant includes at least one of dodecyltrimethylammonium chloride, octadecyltrimethylammonium chloride, or benzalkonium chloride.

[0025] As a further technical solution, the heating reaction time is 10-20 hours;

[0026] The calcination time is 2-5 hours.

[0027] Thirdly, the present invention provides the application of the above-mentioned composite material in the preparation of sodium-ion batteries.

[0028] Fourthly, the present invention provides a positive electrode sheet, comprising a current collector and a positive electrode slurry coated on the current collector;

[0029] The positive electrode slurry includes the aforementioned composite material.

[0030] Fifthly, the present invention provides a sodium-ion battery, wherein the positive electrode of the sodium-ion battery is the aforementioned positive electrode.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] The composite material provided by this invention, through coating Na 0.44 MnO2 adjusts the pH value of the acidic cathode material to reduce the formation of aqueous acid in the material, thus alleviating the Fe content of the sodium iron pyrophosphate / sodium iron sulfate material. 3+ Dissolution phenomenon; Na 0.44 MnO2 has a wide voltage range and coats Na 0.44 MnO2 can broaden the voltage window of sodium iron pyrophosphate / sodium iron sulfate, improve the stability of metal ions and acid-base properties, and enhance specific capacity. This composite material can be used in the fabrication of sodium-ion batteries, improving their safety and cycle life.

[0033] Because ferric pyrophosphate / sodium ferric sulfate has a heat resistance of no more than 400℃, it is difficult to coat it with other materials that are active for sodium ions. However, the composite material preparation method provided by this invention combines the sol-gel method and the solvothermal method, which greatly reduces the sodium content. 0.44 The synthesis temperature of MnO2. Detailed Implementation

[0034] The embodiments and examples of the present invention will be described in detail below. However, those skilled in the art will understand that the following embodiments and examples are for illustrative purposes only and should not be considered as limiting the scope of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention. Unless otherwise specified, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0035] In a first aspect, the present invention provides a composite material comprising a cathode material and Na. 0.44 MnO2, the Na 0.44 MnO2 is coated on the surface of the cathode material;

[0036] Na in the composite material 0.44 The mass percentage of MnO2 can be, for example, but not limited to, 5%, 10%, 15% or 20%;

[0037] The positive electrode material includes sodium iron pyrophosphate and / or sodium ferrous sulfate.

[0038] The composite material provided by this invention, through coating Na 0.44MnO2 adjusts the pH value of the acidic cathode material to reduce the formation of aqueous acid in the material, thus alleviating the Fe content of the sodium iron pyrophosphate / sodium iron sulfate material. 3+ Dissolution phenomenon; Na 0.44 MnO2 has a wide voltage range and coats Na 0.44 MnO2 can broaden the voltage window of sodium iron pyrophosphate / sodium iron sulfate, improve the stability of metal ions and acid-base properties, and enhance specific capacity. This composite material can be used in the fabrication of sodium-ion batteries, improving their safety and cycle life.

[0039] Secondly, the present invention provides a method for preparing the above-mentioned composite material, comprising the following steps:

[0040] a. Sodium source, manganese source and chelating agent are mixed in water to form a chelate, and then the positive electrode material is added. The mixture is then mixed at pH 7-8 and temperature 60-90℃ to form a hydrosol.

[0041] b. The hydrosol obtained in step a is dispersed in an organic solvent, and then the composite material is prepared by heating and calcining in sequence;

[0042] The temperature of the heating reaction can be, for example, but not limited to, 190°C, 200°C or 210°C;

[0043] The calcination temperature can be, for example, but not limited to, 250°C, 300°C, or 350°C.

[0044] Because ferric pyrophosphate / sodium ferric sulfate has a heat resistance of no more than 400℃, it is difficult to coat it with other materials that are active for sodium ions. However, the composite material preparation method provided by this invention combines the sol-gel method and the solvothermal method, which greatly reduces the sodium content. 0.44 The synthesis temperature of MnO2.

[0045] In some alternative embodiments, the sodium source includes, but is not limited to, sodium acetate, sodium sulfate, and sodium nitrate, or other sodium sources well known to those skilled in the art;

[0046] The manganese source includes, but is not limited to, manganese acetate, manganese sulfate and manganese nitrate, or other manganese sources well known to those skilled in the art;

[0047] The chelating agent includes, but is not limited to, citric acid, sodium citrate, ethylenediaminetetraacetic acid and ethylenediaminepentaacetic acid, or other chelating agents well known to those skilled in the art.

[0048] In some alternative implementations, step a involves adjusting the solution to a pH of 7-8 using ammonia.

[0049] Adjusting the pH with ammonia can prevent the introduction of impurities during the preparation process.

[0050] In some alternative embodiments, the organic solvent includes, but is not limited to, cyclohexane, cyclobutane, n-pentanol or isopropanol, or other organic solvents well known to those skilled in the art.

[0051] In some alternative embodiments, the organic solvent contains a surfactant; the surfactant is indicated to promote the dispersion of the hydrosol.

[0052] The surfactants include, but are not limited to, dodecyltrimethylammonium chloride, octadecyltrimethylammonium chloride or benzalkonium chloride, or other surfactants known to those skilled in the art.

[0053] In some alternative embodiments, the heating reaction time may be, for example, but not limited to, 10h, 15h or 20h;

[0054] The calcination time can be, but is not limited to, 2h, 3h, 4h or 5h.

[0055] In this invention, Na is prepared by heating reaction. 0.44 MnO2-coated ferric pyrophosphate / sodium ferric sulfate; calcination removes excess moisture from the material and improves its toughness.

[0056] Thirdly, the present invention provides the application of the above-mentioned composite material in the preparation of sodium-ion batteries.

[0057] The composite material provided by this invention is used to prepare sodium-ion batteries, which can improve the safety and cycle life of sodium-ion batteries.

[0058] Fourthly, the present invention provides a positive electrode sheet, comprising a current collector and a positive electrode slurry coated on the current collector;

[0059] The positive electrode slurry includes the aforementioned composite material.

[0060] The battery made with this positive electrode has good safety and long cycle life.

[0061] Fifthly, the present invention provides a sodium-ion battery, wherein the positive electrode of the sodium-ion battery is the aforementioned positive electrode.

[0062] This battery has good safety and a long cycle life.

[0063] The present invention will be further illustrated below with specific embodiments. However, it should be understood that these embodiments are merely for the purpose of more detailed illustration and should not be construed as limiting the present invention in any way.

[0064] Example 1

[0065] A composite material comprising a positive electrode material (sodium iron pyrophosphate) and Na coated on the surface of the positive electrode material. 0.44 MnO2, where Na 0.44 The mass percentage of MnO2 is 5%.

[0066] The preparation method of this composite material is as follows:

[0067] 1. Dissolve sodium acetate and manganese acetate (Na:Mn molar ratio of 0.5:1) in 100 ml of deionized water. Add 2 mL of 2 mol / L citric acid solution to form a chelate. Add 5 g of commercially available sodium ferric pyrophosphate and adjust the pH to 7.5 with ammonia. Heat and stir at 80 °C for 2 hours. The remaining 50 ml of the mixed hydrosol contains a uniformly dispersed sodium ferric pyrophosphate, yielding hydrosol A.

[0068] 2. Prepare 100 mL of an organic solvent (cyclohexane) containing 1 mol / L cationic surfactant (dodecyltrimethylammonium chloride), and label it as solution B.

[0069] 3. Pour hydrosol A into a 50ml syringe and use a laboratory automated syringe pump to drop hydrosol A into solution B at a uniform rate of 1mm / min. While adding the hydrosol, stir at high speed to disperse hydrosol A into smaller water units. Continue stirring for 1 hour after the addition is complete.

[0070] 4. After completely dispersing A evenly in B, place it in a hydrothermal reactor and react in a 200℃ oven for 15 hours to obtain Na. 0.44 The MnO2@sodium iron pyrophosphate composite material was washed three times with pure water.

[0071] 5. Put Na 0.44 The MnO2@sodium iron pyrophosphate composite material was calcined in a muffle furnace at 300℃ for 3 hours, followed by annealing for 1-2 hours. This process removed excess moisture and improved the material's toughness.

[0072] It should be noted that sodium ions appear in MnO2 in an intercalated form. Since there will be some free sodium ions in the solution, a slight excess is needed.

[0073] Example 2

[0074] A composite material comprising a positive electrode material (sodium ferrous sulfate) and Na+ coated on the surface of the positive electrode material. 0.44 MnO2, where Na 0.44 The mass percentage of MnO2 is 20%.

[0075] The preparation method of this composite material is as follows:

[0076] 1. Dissolve sodium nitrate and manganese nitrate (Na:Mn molar ratio of 0.5:1) in 100 ml of deionized water. Add 2 mL of 2 mol / L citric acid solution to form a chelate. Add 5 g of commercially available sodium ferrous sulfate and adjust the pH to 7 with ammonia. Heat and stir at 60 °C for 3 hours. The remaining 50 ml of the mixed hydrosol contains a uniformly dispersed sodium ferrous sulfate, yielding hydrosol A.

[0077] 2. Prepare 100 mL of an organic solvent (cyclobutane) containing 1 mol / L cationic surfactant (octadecyltrimethylammonium chloride), and denote it as solution B.

[0078] 3. Pour hydrosol A into a 50ml syringe and use a laboratory automated syringe pump to drop hydrosol A into solution B at a uniform rate of 1mm / min. While adding the hydrosol, stir at high speed to disperse hydrosol A into smaller water units. Continue stirring for 1 hour after the addition is complete.

[0079] 4. After completely dispersing A evenly in B, place it in a hydrothermal reactor and react in an oven at 190℃ for 20 hours to obtain Na. 0.44 The MnO2@sodium ferrous sulfate composite material was washed three times with pure water.

[0080] 5. Put Na 0.44 The MnO2@sodium ferrous sulfate composite material was calcined in a muffle furnace at 250°C for 5 hours, followed by annealing for 1–2 hours. This process removed excess moisture and improved the material's toughness.

[0081] Example 3

[0082] A composite material comprising a positive electrode material (sodium iron pyrophosphate) and Na coated on the surface of the positive electrode material. 0.44 MnO2, where Na 0.44 The mass percentage of MnO2 is 10%.

[0083] The preparation method of this composite material is as follows:

[0084] 1. Dissolve sodium sulfate and manganese sulfate (Na:Mn molar ratio of 0.5:1) in 100 ml of deionized water. Add 2 mL of 2 mol / L ethylenediaminetetraacetic acid solution to form a chelate. Add 5 g of commercially available sodium ferric pyrophosphate and adjust the pH to 8 by adding ammonia. Heat and stir at 90 °C for 1.5 h. The remaining 50 ml of the mixed hydrosol contains a uniformly dispersed sodium ferric pyrophosphate, yielding hydrosol A.

[0085] 2. Prepare 100 mL of an organic solvent (n-pentanol) containing 1 mol / L cationic surfactant (such as dodecyltrimethylammonium chloride / octadecyltrimethylammonium chloride / benzalkonium chloride, etc.), and denote it as solution B.

[0086] 3. Pour hydrosol A into a 50ml syringe and use a laboratory automated syringe pump to drop hydrosol A into solution B at a uniform rate of 1mm / min. While adding the hydrosol, stir at high speed to disperse hydrosol A into smaller water units. Continue stirring for 1 hour after the addition is complete.

[0087] 4. After completely dispersing A evenly in B, place it in a hydrothermal reactor and react in an oven at 210℃ for 10 hours to obtain Na. 0.44 The MnO2@sodium iron pyrophosphate composite material was washed three times with pure water.

[0088] 5. Put Na 0.44 The MnO2@sodium iron pyrophosphate composite material was calcined in a muffle furnace at 350℃ for 2 hours, followed by annealing for 1-2 hours. This process removed excess moisture and improved the material's toughness.

[0089] Comparative Example 1

[0090] A positive electrode material is sodium iron pyrophosphate.

[0091] Comparative Example 2

[0092] A composite material, which differs from Example 1 in that pH adjustment was not performed in step 1.

[0093] Comparative Example 3

[0094] A positive electrode material, comprising a positive electrode material (sodium iron pyrophosphate) and Na. 0.44 The difference between MnO2 and Example 1 is that the cathode material and Na... 0.44 MnO2 is directly mixed, rather than Na. 0.44 MnO2 is coated on the surface of the cathode material.

[0095] Comparative Example 3

[0096] A composite material, differing from Example 1 in that Na 0.44 The mass percentage of MnO2 is 50%.

[0097] Experimental Example 1

[0098] The materials of the above embodiments and comparative examples were used as positive electrode materials to prepare positive electrode sheets. The current collector of the positive electrode sheet was aluminum foil. An oil-based coating formula (using N-methylpyrrolidone as solvent, the solid composition of which is positive electrode material, PVDF (polyvinylidene chloride), SP (carbon black) and PVP (polyvinylpyrrolidone), with a mass ratio of positive electrode material, PVDF, SP and PVP of 100:7:10:3) was used to coat the positive electrode.

[0099] Then, a sodium-ion battery was prepared using the obtained positive and negative electrode sheets, separator, and electrolyte. The current collector of the negative electrode sheet was aluminum foil, and a hard carbon aqueous formulation (using water as solvent, the solid composition of which was hard carbon, SP, SBR (styrene-butadiene rubber), and CMC (sodium carboxymethyl cellulose, with a mass ratio of hard carbon, SP, SBR, and CMC of 90:3:5:2) was used to coat the negative electrode. The electrolyte consisted of 1M sodium salt + 1% by mass of vinylene carbonate + solvent (40% by volume of EC (ethylene carbonate) and 60% by volume of DMC (diethyl carbonate)).

[0100] The performance of the prepared battery was tested, and the results are as follows:

[0101] Example 1: 0.1C / 0.1C charge / discharge capacity (93.5mAh / g), initial coulombic efficiency (92.8%), capacity retention at 5C rate (91.9%), capacity retention after 100 cycles of 0.1C / 0.1C charge / discharge (99.79%), output after 100 cycles of 0.1C / 0.1C charge / discharge (3mL), capacity retention after 300 cycles at 0.5C / 1C high temperature (45°C) is 93.1%.

[0102] Example 2: 0.1C / 0.1C charge / discharge capacity (96.7mAh / g), initial coulombic efficiency (95.3%), capacity retention at 5C rate (93.3%), capacity retention after 100 cycles of 0.1C / 0.1C charge / discharge (99.12%), gas production after 100 cycles of 0.1C / 0.1C charge / discharge (5mL), and capacity retention of 89.1% after 300 cycles at 0.5C / 1C high temperature (45°C).

[0103] Example 3: 0.1C / 0.1C charge / discharge capacity (95.3mAh / g), initial coulombic efficiency (93.1%), capacity retention at 5C rate (92.4%), capacity retention after 100 cycles of 0.1C / 0.1C charge / discharge (99.52%), gas production after 100 cycles of 0.1C / 0.1C charge / discharge (4mL), and capacity retention of 91.7% after 300 cycles at 0.5C / 1C high temperature (45°C).

[0104] Comparative Example 1: 0.1C / 0.1C charge / discharge capacity (89.2 mAh / g), initial coulombic efficiency (88.2%), capacity retention at 5C rate (84.1%), capacity retention after 100 cycles of 0.1C / 0.1C charge / discharge (92.7%), gas production after 100 cycles of 0.1C / 0.1C charge / discharge (15 mL), and capacity retention after 300 cycles at 0.5C / 1C high temperature (45℃) for 75.9%.

[0105] Comparative Example 2: 0.1C / 0.1C charge / discharge capacity (78.7 mAh / g), initial coulombic efficiency (79.2%), capacity retention at 5C rate (77.8%), capacity retention after 100 cycles of 0.1C / 0.1C charge / discharge (82.4%), and gas production after 100 cycles of 0.1C / 0.1C charge / discharge (20 mL). After 300 cycles at 0.5C / 1C high temperature (45℃), the capacity retention was 70.7%.

[0106] Comparative Example 3: 0.1C / 0.1C charge / discharge capacity (105.5mAh / g), initial coulombic efficiency (95.8%), capacity retention at 5C rate (86.2%), capacity retention after 100 cycles of 0.1C / 0.1C charge / discharge (96.58%), output after 100 cycles of 0.1C / 0.1C charge / discharge (8mL), and capacity retention after 300 cycles at 0.5C / 1C high temperature (45℃) for 84.9%.

[0107] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A composite material, characterized in that, Including cathode materials and Na 0.44 MnO2, the Na 0.44 MnO2 is coated on the surface of the cathode material; Na in the composite material 0.44 The mass percentage of MnO2 is 5%-20%; The positive electrode material is sodium iron pyrophosphate and / or sodium ferrous sulfate. The method for preparing the composite material includes the following steps: a. Sodium source, manganese source and chelating agent are mixed in water to form a chelate, and then the positive electrode material is added. The mixture is then mixed at pH 7-8 and temperature 60-90℃ to form a hydrosol. b. The hydrosol obtained in step a is dispersed in an organic solvent, and then the composite material is prepared by heating and calcining in sequence; The temperature of the heating reaction is 190-210℃; The calcination temperature is 250-350℃.

2. The composite material according to claim 1, characterized in that, The sodium source includes at least one of sodium acetate, sodium sulfate, and sodium nitrate; The manganese source includes at least one of manganese acetate, manganese sulfate, and manganese nitrate. The chelating agent includes at least one of citric acid, sodium citrate, ethylenediaminetetraacetic acid, and ethylenediaminepentaacetic acid.

3. The composite material according to claim 1, characterized in that, In step a, the solution is adjusted to pH 7-8 using ammonia.

4. The composite material according to claim 1, characterized in that, The organic solvent includes at least one of cyclohexane, cyclobutane, n-pentanol, or isopropanol.

5. The composite material according to claim 1, characterized in that, The organic solvent contains a surfactant; The surfactant includes at least one of dodecyltrimethylammonium chloride, octadecyltrimethylammonium chloride, or benzalkonium chloride.

6. The composite material according to claim 1, characterized in that, The heating reaction time is 10-20 hours; The calcination time is 2-5 hours.

7. The application of the composite material according to claim 1 in the preparation of sodium-ion batteries.

8. A positive electrode plate, characterized in that, Includes a current collector and a positive electrode slurry coated on the current collector; The positive electrode slurry includes the composite material described in claim 1.

9. A sodium-ion battery, characterized in that, The positive electrode of the sodium-ion battery is the positive electrode as described in claim 8.