Method for preparing positive electrode sheet, positive electrode sheet, and lithium ion battery

Abstract

This application provides a method for preparing a positive electrode sheet, a positive electrode sheet, and a lithium-ion battery. The method for preparing the positive electrode sheet includes lithium intercalation treatment of a niobium-based material to obtain a lithium-containing niobium-based composite. The lithium-containing niobium-based composite, a positive electrode active material, a conductive agent, and a binder are mixed to obtain a slurry. The slurry is then formed on the surface of a current collector to prepare the positive electrode sheet. This application first performs lithium intercalation treatment on the niobium-based material. When lithium ions are intercalated into the crystal lattice of the niobium-based material, not only is electron transfer involved, causing a change in the valence state of the niobium ions in the niobium-based material, but the crystal structure of the niobium-based material is also altered, creating effective electron transport paths between crystals and enhancing electron migration capabilities. By mixing the lithium-containing niobium-based composite obtained after lithium intercalation with the positive electrode active material, conductive agent, and binder, the excellent ionic and electronic conductivity of the lithium-containing niobium-based composite can improve fast charging efficiency.

Description

Technical Field

[0001] This application relates to the field of lithium-ion battery technology, and more specifically, to a method for preparing a positive electrode, the positive electrode, and a lithium-ion battery. Background Technology

[0002] With the rapid development of smart electronic devices, higher demands are being placed on the fast-charging performance of lithium-ion batteries. Existing lithium-ion batteries typically have an ion-conducting coating layer, such as a solid electrolyte membrane, coated on the surface of the electrode active material to improve the battery's ionic conductivity. They also improve the battery's electronic conductivity by adding conductive agents, such as conductive carbon black, to the electrode active material, or by coating the electrode active material with an electronically conductive coating layer, such as an amorphous carbon layer.

[0003] When the surface of the electrode active material is coated with an ion conductor coating layer and an electronic conductor coating layer, the process of ions or electrons transporting from the active material to the outside is easily hindered by the coating layer. This hinders the migration of ions or electrons inside the coating layer, causing ions or electrons to accumulate on the surface of the electrode active material. This exacerbates the battery's side reactions, leading not only to a decrease in the battery's specific capacity and cycle life, but also affecting the battery's fast charging performance. Summary of the Invention

[0004] This application provides a method for preparing a positive electrode sheet, a positive electrode sheet, and a lithium-ion battery, which can improve fast charging efficiency.

[0005] Specifically, this application is implemented through the following technical solution:

[0006] This application provides a method for preparing a positive electrode sheet, comprising:

[0007] Lithium-based materials are subjected to lithium intercalation treatment to obtain lithium-containing niobium-based composites;

[0008] The lithium-niobium-based composite, positive electrode active material, conductive agent and binder are mixed to obtain a mixed slurry, and the mixed slurry is formed on the surface of the current collector to prepare a positive electrode sheet.

[0009] Optionally, in the mixed slurry, the content of the conductive agent and the content of the binder are both less than the content of the lithium-niobium-based composite, and the content of the lithium-niobium-based composite is less than the content of the positive electrode active material.

[0010] Optionally, the mass ratio of the positive electrode active material, the lithium-niobium-based composite, the conductive agent, and the binder is (90-92):(1-3):(0.5-2.5):(0.5-2.5).

[0011] Optionally, lithium intercalation treatment of niobium-based materials includes:

[0012] A niobium-based positive electrode is made from niobium-based material and combined with a lithium metal negative electrode to form an electrochemical device.

[0013] The electrochemical device is controlled to perform at least one discharge process, causing lithium ions to be inserted into the niobium-based material.

[0014] Optionally, the discharge process includes:

[0015] A constant current discharge is performed using a preset current density until the niobium-based material reaches a preset specific capacity, at which point the discharge ends.

[0016] Optionally, the preset current density is 20-30 mA / g;

[0017] And / or, the preset specific capacity is 40-50 mAh / g.

[0018] Optionally, after controlling the electrochemical device to perform at least one discharge process, the method further includes:

[0019] Disassemble the electrochemical device and collect the niobium-based material that has embedded lithium ions;

[0020] The niobium-based material with embedded lithium ions is washed with an ester cleaning agent and then dried, and / or the niobium-based material with embedded lithium ions is ground.

[0021] Optionally, fabricating a niobium-based positive electrode from a niobium-based material includes:

[0022] First, the niobium-based material and the binder are mixed and then coated onto the surface of the electrode substrate, and then pressed into a sheet to form a niobium-based positive electrode.

[0023] Optionally, the niobium-based material includes niobium oxide and / or niobium-based metal composite oxides.

[0024] Optionally, the lithium-niobium-based composite has a particle size of 2–5 μm, the positive electrode active material has a particle size of 5–17 μm, and the conductive agent has a particle size of 50–200 nm.

[0025] This application also provides a positive electrode sheet, which is prepared using any of the positive electrode sheet preparation methods described above.

[0026] This application also provides a lithium-ion battery, including the positive electrode as described above.

[0027] The technical solution provided in this application can achieve the following beneficial effects:

[0028] This application provides a method for preparing a positive electrode sheet, the positive electrode sheet itself, and a lithium-ion battery. By first subjecting a niobium-based material to lithium intercalation, when lithium ions are inserted into the crystal lattice of the niobium-based material, not only is electron transfer observed, causing a change in the valence state of the niobium ions, but the crystal structure of the niobium-based material is also altered, creating effective electron transport paths between crystals and enhancing electron mobility. By mixing the lithium-containing niobium-based composite obtained after lithium intercalation with a positive electrode active material, a conductive agent, and a binder, the excellent ionic and electronic conductivity of the lithium-containing niobium-based composite can improve fast charging efficiency. Attached Figure Description

[0029] Figure 1 This is a schematic flowchart illustrating a method for preparing a positive electrode sheet according to an exemplary embodiment of this application. Detailed Implementation

[0030] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings.

[0031] Please see Figure 1 This application provides a method for preparing a positive electrode sheet, comprising:

[0032] S1: Lithium-based materials are subjected to lithium intercalation treatment to obtain lithium-containing niobium-based composites.

[0033] Niobium-based materials possess an inherent ion diffusion network, providing numerous transport paths for lithium ions and exhibiting excellent ionic conductivity. Furthermore, niobium-based materials are structurally stable and do not readily undergo volume expansion during reactions. However, the electronic structure of niobium (Nb) in niobium-based materials results in relatively low electronic conductivity. Therefore, by subjecting niobium-based materials to lithium intercalation, the insertion of lithium ions into the crystal lattice not only involves electron transfer, changing the valence state of niobium ions, but also alters the crystal structure. This creates effective electron transport paths between crystals, enhancing electron migration and improving the electronic conductivity of the niobium-based material.

[0034] S2: The lithium-niobium-based composite, positive electrode active material, conductive agent and binder are mixed to obtain a mixed slurry, and the mixed slurry is formed on the surface of the current collector to prepare a positive electrode sheet.

[0035] Existing positive electrode sheets of a certain thickness exhibit lower porosity and poorer electrolyte wettability on the side near the current collector, resulting in slower ion transport efficiency. On the side further from the current collector, closer to the electrolyte, the electrode's electronic conductivity becomes more crucial. Therefore, during fast charging, to increase both ion and electron transport efficiency, ion-conducting and electron-conducting coatings are typically applied to the surface of the electrode active material, allowing ions and electrons to transport rapidly within their respective independent channels. However, the presence of these coatings not only hinders the migration of ions or electrons within the coating layer, resulting in slower ion or electron transport rates, but also leads to ion or electron accumulation on the surface of the electrode active material. This exacerbates battery side reactions, affecting charge transfer at the electrode active material surface and causing asynchronous charge transport. Consequently, the migration of ions or electrons from the electrode active material to the electrolyte and from the electrode active material to the conductive agent is impeded.

[0036] This application mixes a lithium-niobium-based composite obtained after lithium intercalation with a positive electrode active material, a conductive agent, and a binder. During the mixing process, the lithium-niobium-based composite adheres to the surface of the positive electrode active material. Due to the excellent ionic conductivity of the lithium-niobium-based composite itself and the excellent electronic conductivity formed after lithium intercalation, the positive electrode can maintain high ion transport efficiency both near the current collector and near the electrolyte. Simultaneously, it allows all regions within the electrode to maintain high ionic and electronic conductivity, improving the fast-charging performance and cycle stability of the positive electrode. This application eliminates the hindering effect of traditional coating layers on ion and electron transport. Since no new blocking layer is generated to impede ion or electron transport, it effectively solves the problem of low charging efficiency caused by coating layers in existing electrodes. It also reduces side reactions on the surface of the electrode active material, enabling simultaneous rapid diffusion of ions and electrons at the surface of the electrode active material.

[0037] It should be noted that the positive electrode active material can be selected from different lithium-containing materials according to the different performance requirements of lithium-ion batteries, such as including but not limited to at least one of lithium cobalt oxide, lithium iron phosphate, or lithium nickel cobalt manganese oxide.

[0038] The conductive agent can be a common conductive agent used in existing lithium-ion batteries, such as, but not limited to, conductive carbon black or conductive graphene. The binder can also be a common binder used in existing lithium-ion batteries, such as, but not limited to, polyvinylidene fluoride or sodium carboxymethyl cellulose. Furthermore, the mixing process of the above substances can be any existing method, such as, but not limited to, ultrasonic stirring. The method of forming the mixed slurry onto the current collector can also be any existing method, including but not limited to coating or deposition, which are known existing techniques and will not be elaborated upon here.

[0039] In one embodiment, the content of the conductive agent and the content of the binder in the mixed slurry are both less than the content of the lithium-niobium-based composite, and the content of the lithium-niobium-based composite is less than the content of the positive electrode active material. Therefore, without significantly affecting the performance of the battery, each region within the electrode can maintain as high an ionic and electronic conductivity as possible. In one embodiment, the mass ratio of the positive electrode active material, the lithium-niobium-based composite, the conductive agent, and the binder is (90–92):(1–3):(0.5–2.5):(0.5–2.5). This allows each region within the electrode to maintain as high an ionic and electronic conductivity as possible.

[0040] In one embodiment, the lithium intercalation treatment of the niobium-based material in step S1 includes: fabricating a niobium-based positive electrode from the niobium-based material and forming an electrochemical device with a lithium metal negative electrode; controlling the electrochemical device to perform at least one discharge process to intercalate lithium ions into the niobium-based material. Thus, by assembling an electrochemical device for electrochemical lithium intercalation, the amount of lithium ions intercalated can be precisely adjusted. The electrochemical device can be a battery device, but is not limited to it. Furthermore, during the lithium intercalation process, the electrochemical device can be controlled to charge first and then discharge, or the electrochemical device can be controlled to discharge directly. The number of discharges is not specifically limited; it can be one or two times, but is not limited to these.

[0041] In one embodiment, the discharge process includes constant current discharge using a preset current density, ending the discharge once the niobium-based material reaches a preset specific capacity. This allows for precise adjustment of the lithium-ion intercalation amount by controlling the current, preventing over-discharge after reaching the preset specific capacity. Of course, in other embodiments, constant voltage discharge can also be used. In one embodiment, the preset current density is 20–30 mA / g, for example, 20 mA / g, 22 mA / g, 25 mA / g, 28 mA / g, or 30 mA / g, but not limited thereto. In one embodiment, the preset specific capacity is 40–50 mAh / g, for example, 40 mAh / g, 42 mAh / g, 45 mAh / g, 48 mAh / g, or 50 mAh / g, but not limited thereto. This prevents the niobium-based material from affecting battery performance due to excessive lithium-ion intercalation.

[0042] It should be noted that, in addition to the electrochemical lithium intercalation process described above, conventional chemical lithium intercalation can also be used. For example, niobium-based materials and metallic lithium can be reacted in an organic solvent, including but not limited to tetrahydrofuran, to allow lithium ions to migrate from metallic lithium to the niobium-based material. However, since the reaction process of conventional chemical lithium intercalation is more difficult to control and may introduce more impurities, the specific choice should be made based on the different needs of actual production.

[0043] In one embodiment, fabricating a niobium-based positive electrode from a niobium-based material includes: first mixing the niobium-based material and an adhesive, then coating the mixture onto the surface of an electrode substrate, followed by pressing to form a niobium-based positive electrode. This allows the adhesive to firmly bond the niobium-based material together and tightly press it onto the electrode substrate, thus creating a simple niobium-based positive electrode that facilitates subsequent lithium intercalation. The electrode substrate can be aluminum foil, but is not limited to this.

[0044] In one embodiment, after controlling the electrochemical device to perform at least one discharge process, the method further includes:

[0045] The electrochemical device was disassembled to collect the niobium-based material that had been embedded with lithium ions.

[0046] The niobium-based material with embedded lithium ions is washed with an ester cleaning agent and then dried, and / or the niobium-based material with embedded lithium ions is ground.

[0047] For example, after collecting the niobium-based material with lithium-ion intercalation, it can be washed with ester-based cleaning agents, including but not limited to dimethyl carbonate, to remove electrolyte or other impurities. Alternatively, the niobium-based material with lithium-ion intercalation can be ground using a grinding device to achieve a more uniform particle size distribution. Of course, in other examples, the niobium-based material with lithium-ion intercalation can be both washed with ester-based cleaning agents and ground. The order of washing and grinding is not specifically limited here; for example, it can be washed first and then ground, or ground first and then washed.

[0048] The collection of the aforementioned niobium-based material with embedded lithium ions can be achieved through mechanical stripping, for example, by using stripping tools, including but not limited to blades, to scrape off the material coated on the electrode substrate. Of course, the collection methods are not limited to this.

[0049] In one embodiment, the niobium-based material includes niobium oxide and / or niobium-based metal composite oxides (M-Nb-O). Niobium oxide includes, but is not limited to, niobium pentoxide (Nb₂O₅), and the niobium-based metal composite oxide includes, but is not limited to, titanium niobium oxide, niobium phosphorus oxide, or niobium tungsten oxide.

[0050] In one embodiment, the particle size of the lithium-niobium-based composite is 2–5 μm, for example, 2 μm, 3 μm, 4 μm, or 5 μm, but not limited thereto; the particle size of the positive electrode active material is 5–17 μm, for example, 5 μm, 10 μm, 13 μm, 15 μm, or 17 μm, but not limited thereto; the particle size of the conductive agent is 50–200 nm, for example, 50 μm, 100 μm, 150 μm, or 200 μm, but not limited thereto.

[0051] In one embodiment, this application also provides a positive electrode sheet, prepared using any of the positive electrode sheet preparation methods described above. In another embodiment, this application also provides a lithium-ion battery, including the positive electrode sheet described above.

[0052] The positive electrode prepared using the method provided in this application, after being assembled into a lithium-ion battery, exhibits high specific capacity and specific capacity retention during charge-discharge performance testing. See the following specific embodiments for details:

[0053] Example 1

[0054] I. Preparation of the positive electrode sheet

[0055] (1) Titanium niobium oxide (TiNb2O7) and binder polyvinylidene fluoride (PVDF) were dry-mixed at a mass ratio of 95:5 for 10 min, coated onto aluminum foil, and then cold-pressed at 20 MPa for 10 min using a tablet press to obtain a dense niobium-based positive electrode.

[0056] (2) A battery device is made up of a niobium-based positive electrode, a glass fiber diaphragm (with a small amount of electrolyte added to both sides of the diaphragm) and a lithium metal negative electrode. The device is then discharged at a constant current density of 20 mA / g (g is the total mass of the niobium-based positive electrode) to 1.7V. The discharge is stopped after the specific capacity of the niobium-based positive electrode reaches 50 mAh / g.

[0057] (3) Disassemble the battery device, collect and grind the titanium niobium oxide that has embedded lithium ions, wash it with dimethyl carbonate, and dry it naturally in a glove box to obtain a lithium niobium-based composite.

[0058] (4) The positive electrode active material lithium cobalt oxide (LiCoO2), lithium-niobium-based composite, conductive agent conductive carbon black and binder polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 92:3:2.5:2.5 to prepare a mixed slurry, which is then coated on the surface of copper foil, dried with a blower, and then cold-pressed and slit to obtain the positive electrode sheet.

[0059] Example 2

[0060] (1) Niobium pentoxide (Nb2O5) and binder polyvinylidene fluoride (PVDF) were dry-mixed at a mass ratio of 95:5 for 10 min. The mixture was then coated onto aluminum foil and cold-pressed at 20 MPa for 10 min using a tablet press to obtain a dense niobium-based positive electrode.

[0061] (2) A battery device is made up of a niobium-based positive electrode, a glass fiber diaphragm (with a small amount of electrolyte added to both sides of the diaphragm) and a lithium metal negative electrode. The device is then discharged at a constant current density of 20 mA / g (g is the total mass of the niobium-based positive electrode) to 1.7V. The discharge is stopped after the specific capacity of the niobium-based positive electrode reaches 50 mAh / g.

[0062] (3) Disassemble the battery device, collect and grind the niobium pentoxide that has been embedded with lithium ions, wash it with dimethyl carbonate, and dry it naturally in a glove box to obtain a lithium-niobium-based composite.

[0063] (4) The positive electrode active material NCM811, lithium-niobium based composite, conductive agent conductive carbon black and binder polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 90:9:0.5:0.5 to prepare a mixed slurry, which is then coated on the surface of copper foil, dried with a blower, and then cold-pressed and slit to obtain the positive electrode sheet.

[0064] Comparative Example 1

[0065] A mixed slurry was prepared by mixing lithium cobalt oxide (LiCoO2), non-lithium-intercalated titanium niobium oxide (TiNb2O7), conductive carbon black, and polyvinylidene fluoride (PVDF) in a mass ratio of 92:3:2.5:2.5. This slurry was then coated onto the surface of copper foil, dried with a blower, and subsequently cold-pressed and slit to obtain the positive electrode sheet.

[0066] Test example:

[0067] The positive electrode sheet, separator (polyethylene film), and graphite negative electrode sheet prepared in Examples 1-2 and Comparative Example 1 were sequentially stacked, with the separator acting as a separator between the positive and negative electrode sheets. The resulting cells were then wound to obtain a bare battery cell. The bare battery cell was placed in an outer packaging shell, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping processes, a lithium-ion battery was obtained. At 25°C, the lithium-ion battery was charged to 4.55V at a 0.5C rate, allowed to stand for 5 minutes, and then discharged at a 0.5C rate to 2.5V. Specific test results are shown in Table 1 (specific capacity is calculated based on the content of the positive electrode active material).

[0068] Table 1

[0069]

[0070]

[0071] As shown in Table 1, both Examples 1 and 2 of this application first subjected the niobium-based material to lithium intercalation treatment. The resulting lithium-containing niobium-based composite was then mixed with the positive electrode active material, conductive agent, and binder. Due to the excellent ionic and electronic conductivity of the lithium-containing niobium-based composite, the specific capacity and specific capacity retention of the lithium-ion battery can be improved. In contrast, Comparative Example 1, which mixed unintercalated niobium-based material with the positive electrode active material, conductive agent, and binder, showed poorer specific capacity and specific capacity retention.

[0072] It should be noted that the technical solutions or features described in the above embodiments can be combined or supplemented with each other without conflict. The scope of protection of this application is not limited to the precise structures described in the above embodiments and shown in the accompanying drawings; all modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A method for preparing a positive electrode sheet, characterized in that, include: Lithium-based materials are subjected to lithium intercalation treatment to obtain lithium-containing niobium-based composites; The lithium-niobium-based composite, positive electrode active material, conductive agent and binder are mixed to obtain a mixed slurry, and the mixed slurry is formed on the surface of the current collector to prepare a positive electrode sheet.

2. The method for preparing the positive electrode sheet according to claim 1, characterized in that, In the mixed slurry, the content of the conductive agent and the content of the binder are both less than the content of the lithium-niobium-based composite, and the content of the lithium-niobium-based composite is less than the content of the positive electrode active material.

3. The method for preparing the positive electrode sheet according to claim 2, characterized in that, The mass ratio of the positive electrode active material, the lithium-niobium-based composite, the conductive agent, and the binder is (90-92):(1-3):(0.5-2.5):(0.5-2.5).

4. The method for preparing the positive electrode sheet according to claim 1, characterized in that, Lithium intercalation treatment of niobium-based materials includes: A niobium-based positive electrode is made from niobium-based material and combined with a lithium metal negative electrode to form an electrochemical device. The electrochemical device is controlled to perform at least one discharge process, causing lithium ions to be inserted into the niobium-based material.

5. The method for preparing the positive electrode sheet according to claim 4, characterized in that, The discharge process includes: A constant current discharge is performed using a preset current density until the niobium-based material reaches a preset specific capacity, at which point the discharge ends.

6. The method for preparing the positive electrode sheet according to claim 5, characterized in that, The preset current density is 20-30 mA / g; And / or, the preset specific capacity is 40-50 mAh / g.

7. The method for preparing the positive electrode sheet according to claim 4, characterized in that, After controlling the electrochemical device to perform at least one discharge process, the method further includes: Disassemble the electrochemical device and collect the niobium-based material that has embedded lithium ions; The niobium-based material with embedded lithium ions is washed with an ester cleaning agent and then dried, and / or the niobium-based material with embedded lithium ions is ground.

8. The method for preparing the positive electrode sheet according to claim 4, characterized in that, Fabricating niobium-based positive electrodes from niobium-based materials includes: First, the niobium-based material and the binder are mixed and then coated onto the surface of the electrode substrate, and then pressed into a sheet to form a niobium-based positive electrode.

9. The method for preparing the positive electrode sheet according to any one of claims 1 to 8, characterized in that, The niobium-based material includes niobium oxide and / or niobium-based metal composite oxides; And / or, the particle size of the lithium-niobium-based composite is 2-5 μm, the particle size of the positive electrode active material is 5-17 μm, and the particle size of the conductive agent is 50-200 nm.

10. A positive electrode plate, characterized in that, It is prepared by the method for preparing the positive electrode sheet as described in any one of claims 1 to 9.

11. A lithium-ion battery, characterized in that, Includes the positive electrode sheet as described in claim 10.

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