Composite sodium iron sulfate positive electrode material and preparation method therefor, positive electrode sheet of sodium-ion battery, and sodium-ion battery

Abstract

The present disclosure relates to the technical field of batteries, and provides a composite sodium iron sulfate positive electrode material and a preparation method therefor, a positive electrode sheet of a sodium-ion battery, and a sodium-ion battery. In the preparation method for the composite sodium iron sulfate positive electrode material provided by the present disclosure, boron is doped during the preparation of a conductive agent, which can improve the conductivity of the conductive agent and reduce the amount of the conductive agent; the conductive agent is added during the preparation of the positive electrode material, which can improve the dispersion uniformity of the conductive agent; and high-temperature sintering is performed, which can make the contact between the conductive agent and an active material more reliable. A dry electrode sheet prepared by using the material has a lower electrode sheet resistance value.

Description

Composite sodium ferric sulfate cathode material and its preparation method, sodium-ion battery cathode sheet and sodium-ion battery

[0001] Cross-references to related applications

[0002] This application claims priority to Chinese Patent Application No. 202410959831.5, filed on July 17, 2024, entitled "Composite Sodium Ferric Sulfate Cathode Material and Preparation Method Thereof, Sodium-ion Battery Cathode Sheet and Sodium-ion Battery", the entire contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure relates to the field of battery technology, and in particular to a composite sodium iron sulfate cathode material and its preparation method, a sodium-ion battery cathode sheet, and a sodium-ion battery. Background Technology

[0004] Due to the scarcity of lithium resources and fluctuations in raw material prices, the development of lithium-ion batteries has been significantly affected, negatively impacting the entire industry. As an effective supplement to lithium-ion batteries, sodium-ion batteries have experienced rapid development in recent years.

[0005] Similar to lithium-ion batteries, sodium-ion battery technology can be mainly divided into three types based on the cathode material system: layered oxide system, Prussian blue / white system, and polyanion system. Among them, the layered oxide system has the highest energy density but relatively poor safety performance, and its cost is relatively high due to the presence of nickel in the material; Prussian blue / white system suffers from the problem of difficult removal of water of crystallization, which is difficult to solve in the short term; polyanion system, mainly composed of sodium iron pyrophosphate and sodium iron sulfate, has very high safety and cycle performance, but its bulk conductivity and specific capacity are relatively low.

[0006] Currently, the preparation method for the positive and negative electrodes of sodium-ion batteries still follows the same process as lithium-ion batteries, namely the wet slurry process. While the wet process ensures good material uniformity, it inevitably leads to the problem of binders and conductive agents floating to the surface during coating. Furthermore, the material preparation and coating processes are energy-intensive, require large initial equipment investments, and occupy a large area. Therefore, sodium batteries using this process struggle to gain a cost advantage. Some patents, however, are exploring dry processes to address the problems associated with the wet process.

[0007] Patent CN202310607206.X uses a metal mesh as a current collector, which can improve the contact between the active material and the substrate, but it cannot solve the problem of poor contact between the conductive networks of the active particles.

[0008] Patent CN115332486A adds a polymer adhesive emulsion to the active material and conductive agent, but there are still liquid components present, so it does not belong to a true dry process.

[0009] Patent CN116565123A uses positive electrode active material, carboxyl-modified conductive agent and conductive binder to prepare dry electrode sheets, which improves the electrolyte wetting performance of the electrode sheets. However, the method still involves mixing and adding the three powders at the same time, which has the problem of dispersion uniformity.

[0010] Currently, all dry electrode patents involve adding conductive agents and binders during the electrode mixing stage. The conductive agents used, such as conductive carbon black and CNT, are materials with large specific surface areas and are prone to agglomeration. Direct dry mixing makes it difficult to achieve uniform dispersion of the conductive agents, resulting in high impedance, poor uniformity, and unsatisfactory performance of the prepared electrodes. Moreover, current dry processes cannot introduce ceramic edges in subsequent processes, posing certain safety risks to the battery cells.

[0011] In view of this, this disclosure is hereby made.

[0012] Summary of the Invention

[0013] The primary objective of this disclosure is to provide a method for preparing a composite sodium ferric sulfate cathode material. This method is simple and convenient, and the prepared composite sodium ferric sulfate cathode material has good conductivity. The electrode sheet prepared using this material has a lower resistance.

[0014] The second objective of this disclosure is to provide a composite sodium ferric sulfate cathode material.

[0015] A third objective of this disclosure is to provide a positive electrode for a sodium-ion battery.

[0016] The fourth objective of this disclosure is to provide a sodium-ion battery.

[0017] To achieve the above objectives, the following technical solution is adopted:

[0018] In a first aspect, this disclosure provides a method for preparing a composite sodium ferric sulfate cathode material, comprising the following steps:

[0019] a. A boron-doped conductive agent is prepared by dispersing a conductive agent and boric acid in an aqueous solution, followed by drying and calcination under a protective atmosphere.

[0020] b. Weigh out ferrous sulfate and sodium salt according to the molar ratio of iron and sodium in sodium ferrous sulfate Na6Fe4(SO4)7, then mix them with the boron-doped conductive agent prepared in step a by ball milling, and then sinter the ball-milled mixture under a protective atmosphere to prepare a composite sodium ferrous sulfate cathode material.

[0021] In the boron-doped conductive agent, the mass percentage of the conductive agent is 97%-99.5%;

[0022] In the composite sodium ferric sulfate cathode material, the mass percentage of boron-doped conductive agent is 1% to 4%.

[0023] The sintering temperature is 300–400°C.

[0024] As a further technical solution, the conductive agent includes point-type conductive agents, linear conductive agents, and area-type conductive agents;

[0025] The dot-type conductive agent includes conductive carbon black;

[0026] The linear conductive agent includes carbon nanotubes;

[0027] The planar conductive agent includes graphene;

[0028] The mass ratio of the point-type conductive agent, the linear conductive agent, and the area-type conductive agent is (0.5-0.7):(0.1-0.25):(0.05-0.2).

[0029] As a further technical solution, the calcination temperature is 900–1200°C.

[0030] As a further technical solution, the sodium salt includes sodium carbonate or sodium bicarbonate.

[0031] As a further technical solution, the particle size of the composite sodium ferric sulfate cathode material is 1μm to 5μm.

[0032] Secondly, this disclosure provides a composite sodium ferric sulfate cathode material, which is prepared using the above-described preparation method.

[0033] Thirdly, this disclosure provides a sodium-ion battery positive electrode sheet, including a current collector and a membrane bonded to the surface of the current collector;

[0034] The membrane is mainly obtained by hot pressing a mixture of the composite sodium ferric sulfate cathode material and a binder.

[0035] As a further technical solution, the adhesive includes polytetrafluoroethylene (PTFE);

[0036] In the diaphragm, the adhesive accounts for 0.5% to 2% of the mass.

[0037] As a further technical solution, the current collector includes an aluminum foil with a conductive coating on its surface and ceramic edges.

[0038] Fourthly, this disclosure provides a sodium-ion battery, wherein the positive electrode of the sodium-ion battery includes the above-mentioned sodium-ion battery positive electrode.

[0039] Compared with the prior art, this disclosure has the following beneficial effects:

[0040] The method for preparing composite sodium ferric sulfate cathode material disclosed herein improves the conductivity of the conductive agent and reduces its dosage by doping boron during the preparation of the conductive agent; the addition of the conductive agent during the preparation of the cathode material improves the dispersion uniformity of the conductive agent; and high-temperature sintering makes the contact between the conductive agent and the active material more reliable. The dry electrode sheet prepared with this material has a lower electrode resistance. Attached Figure Description

[0041] To more clearly illustrate the technical solutions in the specific embodiments of this disclosure or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this disclosure. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0042] Figure 1 is an electron microscope image of the fibrous powder material provided in Embodiment 4 of this disclosure;

[0043] Figure 2 is an electron microscope image of the electrode surface provided in Embodiment 4 of this disclosure. Detailed Implementation

[0044] The embodiments and examples of this disclosure 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 this disclosure. All other embodiments obtained by those skilled in the art based on the embodiments of this disclosure without inventive effort are within the scope of protection of this disclosure. 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.

[0045] In a first aspect, this disclosure provides a method for preparing a composite sodium ferric sulfate cathode material, comprising the following steps:

[0046] a. A boron-doped conductive agent is prepared by dispersing a conductive agent and boric acid in an aqueous solution, followed by drying and calcination under a protective atmosphere.

[0047] b. Weigh out ferrous sulfate and sodium salt according to the molar ratio of iron and sodium in sodium ferrous sulfate Na6Fe4(SO4)7, then mix them with the boron-doped conductive agent prepared in step a by ball milling, and then sinter the ball-milled mixture under a protective atmosphere to prepare a composite sodium ferrous sulfate cathode material.

[0048] In the boron-doped conductive agent, the mass percentage of the conductive agent can be, for example, but not limited to, 97%, 98%, or 99.5%.

[0049] In the composite sodium ferric sulfate cathode material, the mass percentage of boron-doped conductive agent can be, for example, but not limited to, 1%, 2%, 3%, or 4%.

[0050] The sintering temperature can be, for example, but not limited to, 300°C, 320°C, 340°C, 360°C, 380°C, or 400°C.

[0051] The method for preparing composite sodium ferric sulfate cathode material disclosed herein improves the conductivity of the conductive agent and reduces its dosage by doping boron during the preparation of the conductive agent; the addition of the conductive agent during the preparation of the cathode material improves the dispersion uniformity of the conductive agent; and high-temperature sintering makes the contact between the conductive agent and the active material more reliable. The dry electrode sheet prepared with this material has a lower electrode resistance.

[0052] In some optional embodiments, the conductive agent includes a point-type conductive agent, a linear conductive agent, and a surface-type conductive agent;

[0053] The dot-type conductive agent includes, but is not limited to, conductive carbon black;

[0054] The linear conductive agent includes, but is not limited to, carbon nanotubes;

[0055] The surface-type conductive agent includes, but is not limited to, graphene;

[0056] The mass ratio of the point-type conductive agent, the linear conductive agent, and the area-type conductive agent can be, for example, but not limited to, 0.5:0.25:0.25, 0.8:0.1:0.1, or 0.6:0.2:0.2.

[0057] The inventors discovered that by constructing a composite conductive agent system to form a point-line-surface conductive pattern, the conductivity of the conductive agent can be further improved.

[0058] In some alternative embodiments, the calcination temperature may be, for example, but not limited to, 900°C, 1000°C, 1100°C, or 1200°C.

[0059] Lower temperatures are insufficient to achieve the desired doping effect, while the aforementioned calcination temperatures ensure the reliability of boron doping.

[0060] In some alternative embodiments, the sodium salt includes sodium carbonate or sodium bicarbonate.

[0061] In some optional embodiments, the composite sodium ferric sulfate cathode material is a solid particle with a particle size of 1 μm to 5 μm.

[0062] Secondly, this disclosure provides a composite sodium ferric sulfate cathode material, which is prepared using the above-described preparation method.

[0063] In this composite sodium ferric sulfate cathode material, the conductive agent is uniformly dispersed, and the electrode sheet prepared using it as a raw material has a lower resistance.

[0064] Thirdly, this disclosure provides a sodium-ion battery positive electrode sheet, including a current collector and a membrane bonded to the surface of the current collector;

[0065] The membrane is mainly obtained by hot pressing the composite sodium ferric sulfate cathode material and binder.

[0066] The low resistance of this electrode helps improve the electrochemical performance of the battery.

[0067] In some alternative embodiments, the adhesive comprises polytetrafluoroethylene;

[0068] In the diaphragm, the mass percentage of the binder can be, for example, but not limited to, 0.5%, 1%, 1.5%, or 2%. Too much binder will result in high electrode resistance, while too little binder will result in low electrode peel strength, both of which will lead to poor performance.

[0069] In some alternative embodiments, the current collector comprises an aluminum foil with a conductive coating (e.g., a carbon coating) on ​​its surface and ceramic edges (alumina or boehmite).

[0070] The primer can enhance the adhesion strength between the film and the foil, reduce the use of adhesives, improve the interface bonding, and the ceramic edge can improve the safety of the battery cell.

[0071] Fourthly, this disclosure provides a sodium-ion battery, wherein the positive electrode of the sodium-ion battery includes the above-mentioned sodium-ion battery positive electrode.

[0072] This battery has better electrochemical performance.

[0073] The present disclosure is further illustrated below with specific embodiments and comparative examples. 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 disclosure in any way.

[0074] It should be noted that, unless otherwise specified, in the following examples or comparative examples, the chemical formula of sodium ferrous sulfate is Na6Fe4(SO4)7; the carbon nanotube model is Xianfeng XFM38; the graphene model is Xianfeng XF001H; the ceramic edge is an alumina ceramic edge; and the positive electrode size is 134mm×214mm.

[0075] Example 1

[0076] A method for preparing a composite sodium ferric sulfate cathode material includes the following steps:

[0077] 1. Commercially available conductive carbon black (specific surface area of ​​50-80 m²) 2A mixture of conductive carbon black (carbon black): carbon nanotubes (CNTs): graphene in a ratio of 0.6:0.2:0.2 was prepared, then mixed uniformly with boric acid in an aqueous solution, dried, and calcined in a hydrogen-nitrogen-argon atmosphere (calcination temperature 1000℃) to obtain a boron-doped composite modified conductive agent powder. The conductive agent constituted 99.5% of the total mass of this boron-doped conductive agent.

[0078] 2. Ferrous sulfate and sodium salt (sodium carbonate) were weighed according to the molar ratio of iron to sodium in sodium ferrous sulfate. They were then ball-milled and mixed with the prepared boron-doped conductive agent. The ball-milled mixture was then sintered under a protective atmosphere (sintering temperature 350℃) to prepare a composite sodium ferrous sulfate cathode material. In this composite sodium ferrous sulfate cathode material, the mass percentage of the boron-doped conductive agent was 4%, and the particle size D of the cathode material was... 50 It is 2μm.

[0079] Example 2

[0080] A method for preparing a composite sodium ferric sulfate cathode material includes the following steps:

[0081] 1. Commercially available conductive carbon black (specific surface area of ​​50-80 m²) 2 A mixture of conductive carbon black (carbon black): carbon nanotubes (CNTs): graphene in a ratio of 0.5:0.25:0.25 was prepared, then mixed uniformly with boric acid in an aqueous solution, dried, and calcined in a hydrogen-nitrogen-argon atmosphere (calcination temperature 900℃) to obtain a boron-doped composite modified conductive agent powder. In this boron-doped conductive agent, the conductive agent accounts for 97% of the total mass.

[0082] 2. Ferrous sulfate and sodium salt (sodium carbonate) were weighed according to the molar ratio of iron to sodium in sodium ferrous sulfate. These were then ball-milled and mixed with the prepared boron-doped conductive agent. The ball-milled mixture was then sintered under a protective atmosphere (sintering temperature 300℃) to prepare a composite sodium ferrous sulfate cathode material. In this composite sodium ferrous sulfate cathode material, the mass percentage of the boron-doped conductive agent was 3%, and the particle size D of the cathode material was... 50 It is 5μm.

[0083] Example 3

[0084] A method for preparing a composite sodium ferric sulfate cathode material includes the following steps:

[0085] 1. Commercially available conductive carbon black (specific surface area of ​​50-80 m²) 2A mixture of conductive carbon black (carbon black): carbon nanotubes (CNTs): graphene in a ratio of 0.7:0.1:0.2 was prepared, then mixed uniformly with boric acid in an aqueous solution, dried, and calcined in a hydrogen-nitrogen-argon atmosphere (calcination temperature 1200℃) to obtain a boron-doped composite modified conductive agent powder. In this boron-doped conductive agent, the conductive agent accounts for 98% of the total mass.

[0086] 2. Ferrous sulfate and sodium salt (sodium carbonate) were weighed according to the molar ratio of iron to sodium in sodium ferrous sulfate. These were then ball-milled and mixed with the prepared boron-doped conductive agent. The ball-milled mixture was then sintered under a protective atmosphere (sintering temperature 400℃) to prepare a composite sodium ferrous sulfate cathode material. In this composite sodium ferrous sulfate cathode material, the mass percentage of the boron-doped conductive agent was 1%, and the particle size D of the cathode material was... 50 It is 1μm.

[0087] Comparative Example 1

[0088] A method for preparing a composite sodium ferric sulfate cathode material differs from Example 1 in that the calcination temperature is set to 400℃.

[0089] Comparative Example 2

[0090] A method for preparing a composite sodium ferric sulfate cathode material differs from Example 1 in that the conductive agent is entirely conductive carbon black.

[0091] Comparative Example 3

[0092] A method for preparing a composite sodium ferric sulfate cathode material differs from Example 1 in that the conductive agent is entirely composed of carbon nanotubes.

[0093] Comparative Example 4

[0094] A method for preparing a composite sodium ferric sulfate cathode material differs from Example 1 in that the conductive agent is entirely graphene.

[0095] Example 4

[0096] A positive electrode includes a current collector and a membrane bonded to the current collector, which are composited by hot pressing.

[0097] Preparation of the membrane: The composite sodium ferric sulfate cathode material provided in Example 1 was mixed and sheared with PTFE to form a fibrous powder material (as shown in Figure 1), and then a membrane was obtained by hot pressing (as shown in Figure 2), wherein the mass percentage of PTFE was 1%.

[0098] The current collector is an aluminum foil with a conductive coating on its surface and ceramic edges (3mm wide).

[0099] Example 5

[0100] A positive electrode includes a current collector and a membrane bonded to the current collector, which are composited by hot pressing.

[0101] Preparation of the membrane: The composite sodium ferric sulfate cathode material provided in Example 2 was mixed and sheared with PTFE to form a fibrous powder material, and then a membrane was obtained by hot pressing, wherein the mass ratio of PTFE was 0.5%;

[0102] The current collector is an aluminum foil with a conductive coating on its surface and ceramic edges (3mm wide).

[0103] Example 6

[0104] A positive electrode includes a current collector and a membrane bonded to the current collector, which are composited by hot pressing.

[0105] Preparation of the membrane: The composite sodium ferric sulfate cathode material provided in Example 3 was mixed and sheared with PTFE to form a fibrous powder material, and then a membrane was obtained by hot pressing, wherein the mass ratio of PTFE was 2%.

[0106] The current collector is an aluminum foil with a conductive coating on its surface and ceramic edges (3mm wide).

[0107] Comparative Example 5

[0108] A positive electrode sheet, which differs from Example 4 in that it is prepared using the positive electrode material provided in Comparative Example 1.

[0109] Comparative Example 6

[0110] A positive electrode sheet, which differs from Example 4 in that it is prepared using the positive electrode material provided in Comparative Example 2.

[0111] Comparative Example 7

[0112] A positive electrode sheet, which differs from Example 4 in that it is prepared using the positive electrode material provided in Comparative Example 3.

[0113] Comparative Example 8

[0114] A positive electrode sheet, which differs from Example 4 in that it is prepared using the positive electrode material provided in Comparative Example 4.

[0115] Comparative Example 9

[0116] A positive electrode sheet is prepared as follows:

[0117] Conductive agent powder, sodium ferric sulfate and PTFE are simultaneously added to an inclined mixer and sheared at high speed to obtain fibrous material, which is then composited with aluminum foil by hot pressing to obtain an electrode sheet;

[0118] The conductive agent powder is the boron-doped composite modified conductive agent powder from Example 1; the amount and ratio of the conductive agent powder, sodium ferric sulfate, and PTFE are the same as in Example 4.

[0119] Experimental Example 1

[0120] Sodium-ion batteries were prepared using the positive electrode sheets provided in the examples and comparative examples, wherein the negative electrode sheet of the sodium-ion battery was an electrode sheet prepared using hard carbon as the active material.

[0121] The diaphragm is a commercially available 20μm PP diaphragm.

[0122] The mass ratio of each component in the electrolyte is: EC (ethylene carbonate): PC (propylene carbonate): EMC (ethyl methyl carbonate): NaPF6: FEC (fluoroethylene carbonate): PS (propylene sulfite) = 10:15:60:11:3:1.

[0123] The performance of the prepared sodium-ion battery was tested, and the results are as follows:

[0124] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this disclosure, and are not intended to limit them. Although this disclosure 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 therein. Such 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 this disclosure. Industrial applicability

[0125] This disclosure provides a composite sodium ferric sulfate cathode material, its preparation method, a sodium-ion battery cathode sheet, and a sodium-ion battery. The preparation method is simple and convenient, and the resulting composite sodium ferric sulfate cathode material exhibits good conductivity. Electrodes prepared using this material have lower resistance, and the resulting sodium-ion batteries demonstrate better electrochemical performance. Specifically, doping with boron during the conductive agent preparation process improves the conductivity of the conductive agent and reduces its dosage. Adding a conductive agent during the cathode material preparation process improves the uniformity of its dispersion. High-temperature sintering ensures a stronger contact between the conductive agent and the active material. Dry-process electrodes prepared using this material have lower electrode resistance.

Claims

1. A method for preparing a composite sodium ferric sulfate cathode material, characterized in that, The method comprises the following steps: a. dispersing the conductive agent and boric acid in an aqueous solution, then preparing a boron-doped conductive agent after drying treatment and calcination treatment under a protective atmosphere; b. according to the molar ratio of iron and sodium in sodium ferrous sulfate Na6Fe4(SO4)7, weighing ferrous sulfate and sodium salt, then ball-milling the mixture with the boron-doped conductive agent prepared in step a, and then sintering the ball-milled mixture under a protective atmosphere to prepare a composite sodium ferric sulfate positive electrode material; The mass percentage of the conductive agent in the boron-doped conductive agent is 97%-99.5%; The mass percentage of the boron-doped conductive agent in the composite sodium ferric sulfate positive electrode material is 1%-4%; The sintering temperature is 300-400℃.

2. The production method according to claim 1, characterized by, The conductive agent includes point-type conductive agent, line-type conductive agent and surface-type conductive agent; The point-type conductive agent includes conductive carbon black; The line-type conductive agent includes carbon nanotubes; The surface-type conductive agent includes graphene; The mass ratio of the point-type conductive agent, line-type conductive agent and surface-type conductive agent is (0.5-0.8):(0.1-0.25):(0.1-0.25).

3. The preparation method according to claim 1, characterized in that, The calcination temperature is 900-1200℃.

4. The method of claim 1, wherein, The sodium salt includes sodium carbonate or sodium bicarbonate.

5. The preparation method according to claim 1, characterized in that, The particle size of the composite sodium ferric sulfate positive electrode material is 1-5μm.

6. A composite sodium iron sulfate positive electrode material, characterized in that, The method is prepared by any one of claims 1-5.

7. A sodium-ion battery cathode sheet, characterized by, The positive electrode sheet of the sodium ion battery comprises the positive electrode sheet of the sodium ion battery according to any one of claims 7-9. The positive electrode sheet of the sodium ion battery comprises the positive electrode sheet of the sodium ion battery according to any one of claims 7-9.

8. The sodium-ion battery cathode sheet according to claim 7, characterized in that, ​ ​ 9.The sodium-ion battery cathode sheet of claim 7, wherein, ​ 10. A sodium-ion battery, characterized in that, ​

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