Sulfur-based battery pole piece and preparation method thereof

Abstract

The invention relates to a sulfur-based battery pole piece and a preparation method thereof, and is characterized in that an electrolyte is used as a mixed medium, vulcanized polyacrylonitrile (SPAN) active particles (particle size of 0.2-20 microns) and a conductive agent are mixed to prepare slurry with certain viscosity, the slurry is subjected to 3D printing or directly coated on the surface of a current collector to form a slurry-state battery pole piece, and the slurry-state battery pole piece is directly used for battery assembly without drying. Wherein the conductive agent is a mixture of more than two of conductive graphite (KS), Supper P (SP), acetylene black (AB), Ketjen black (KB), carbon nanotubes (CNT) and vapor deposition carbon fibers (VGCF), the mass percent of the conductive agent is 2-10%, one part of the conductive agent coats the surfaces of the active particles, and the other part of the conductive agent forms a three-dimensional conductive agent network which is mutually communicated. The active particles in the slurry electrode are dynamically connected with the conductive agent network, so that the lithiation expansion volume and stress of the active particles can be effectively buffered. Meanwhile, the method avoids high energy consumption and electrode thickness limitation of a traditional drying process, and electrode-electrolyte interface impedance is reduced through sufficient pre-infiltration of electrolyte.

Description

Technical Field

[0001] This invention belongs to the field of lithium batteries, specifically relating to a sulfur-based battery electrode and its preparation method. Background Technology

[0002] In lithium-sulfur (Li-S) batteries, solid sulfur (S8) dissolves and undergoes a continuous reduction reaction during discharge, eventually being stored as lithium sulfide (Li2S) in a porous conductive carbon substrate. The sulfur shuttle phenomenon is a key factor limiting battery performance. By heat-treating a mixture of sulfur (S) and polyacrylonitrile (PAN), PAN undergoes dehydrogenation at high temperatures to generate a conductive framework, fixing atomic or molecular-level S within the framework to obtain a stable sulfur-based composite cathode material, polyacrylonitrile sulfide (SPAN). The energy storage process of SPAN is a solid-solid conversion process, thus largely solving the problems of polysulfide intermediate generation and dissolution. However, SPAN still exhibits significant volume changes during charge-discharge cycles, generating substantial mechanical stress in localized electrode regions, leading to coating delamination, SEI interface film breakage and regrowth, and electrolyte loss.

[0003] Traditional lithium-sulfur battery cathodes are prepared by coating a mixture into a slurry, then drying it to remove the solvent. This traditional process suffers from high energy consumption during coating, drying, and solvent recovery; environmental pollution caused by the solvent; uneven composition due to binder floating during drying; and drying cracking limiting electrode thickness.

[0004] To mitigate the issue of volume expansion, patent 202311647154.5 discloses a hollow carbon nanotube containing sulfur. By adjusting the helicity of the carbon nanotubes, different active sites and specific surface areas are achieved. Utilizing the hollow structure of the carbon nanotubes and the van der Waals forces between the tubes, the conductivity of the material can be improved while alleviating sulfur expansion. Meanwhile, patent 202311326774.9 provides a method for preparing a lithium-sulfur electrode based on nanoscale rod-shaped conductive polymers. Sulfur is synthesized in situ in an aqueous solution containing dispersed rod-shaped conductive polymers, and then filtered to form a film, resulting in a self-supporting lithium-sulfur battery positive electrode film with high sulfur loading and uniform dispersion. This electrode has a porous structure that can accommodate sulfur expansion during charge and discharge, thereby improving cycle performance. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a slurry-based sulfur-based battery electrode and its preparation technology, solving the problems of high energy consumption during drying, limited thickness, and stress concentration and electrode cracking caused by large volume changes due to electrode particle expansion in traditional sulfur electrodes. To achieve this objective, the present invention adopts the following technical solution:

[0006] The sulfur-based electrode comprises a current collector and a slurry coating thereon. The current collector is selected from aluminum foil, carbon-coated aluminum foil, aluminum foam, or nickel foam; the slurry layer is composed of the following components (the sum of the mass percentages of each component is 100%):

[0007] (1) Sulphurized polyacrylonitrile (SPAN) active particles with a particle size of 0.2 to 20 μm, accounting for 40% to 70% of the total mass of the slurry;

[0008] (2) Conductive agent, accounting for 2% to 10% of the total mass of the slurry, is a mixture of at least two types selected from conductive graphite (KS), Super P (SP), acetylene black (AB), Ketjen black (KB), carbon nanotubes (CNT) and vapor-deposited carbon fibers (VGCF).

[0009] (3) Battery electrolyte, accounting for 25% to 60% of the total mass of slurry, includes at least one solvent among ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC), and at least one lithium salt among lithium hexafluorophosphate (LiPF6), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and lithium bis(fluorosulfonyl)imide (LiFSI).

[0010] The conductive agent in the slurry layer works synergistically in two parts: the first part coats the surface of the SPAN particles to reduce interfacial contact resistance, and the second part constructs an interconnected three-dimensional conductive network in the suspension slurry. Simultaneously, the slurry layer is not dried, and the electrolyte is used directly as a solvent to maintain liquid ion channels. This slurry has a viscosity of 5000–20000 mPa·s and a conductivity of 5–100 mS / cm at 25°C, ensuring coating uniformity and ion / electron synergistic transport capability.

[0011] The method for preparing the slurry-state sulfur-based electrode is characterized by using a battery electrolyte as a solvent to prepare the slurry-state sulfur-based battery electrode, specifically including the following steps:

[0012] (1) Dry powder premixing and coating: Vulcanized polyacrylonitrile (SPAN) active particles with a particle size of 0.2-20 μm are mixed with a conductive agent at a mass ratio of 87-97:3-13. The conductive agent is added in two parts in stages. The first part is 30%-70% of the total conductive agent mass, which is mixed with the SPAN particles to form a surface coating layer. The first part of the conductive agent is selected from one or more of conductive graphite (KS), Super P (SP), acetylene black (AB), and Ketjen black (KB), accounting for 70%-100% of the total mass of the first added conductive agent. The dry powder is mixed using a high-speed disperser so that the surface of the active particles is coated with a layer of conductive agent particles. The other part of the conductive agent is selected from one or more of Ketjen black (KB), carbon nanotubes (CNT), and vapor-deposited carbon fiber (VGCF), accounting for 0%-30% of the total mass of the first added conductive agent. The remaining conductive agent is added simultaneously with the electrolyte to construct a three-dimensional conductive network.

[0013] (2) Add the mixture formed in step (1) with battery electrolyte as solvent, control the solid content of slurry to 40-75 wt%, and use one of the following equipment: double centrifugal degasser, ball mill, air jet mill, sand mill, to form a homogeneous slurry by high-speed shear dispersion;

[0014] (3) Use one of the following coating equipment: 3D printer, comma blade transfer coating machine, or slot extrusion coating machine to coat the slurry onto the surface of the current collector, and control the thickness of the electrode slurry layer to be 100-500 μm.

[0015] (4) The drying process is omitted, and the slurry-state electrode sheets are directly used for battery assembly. The specific assembly process is as follows:

[0016] (a) According to the size specifications of the electrode, a square frame mold for plastic sealing film is made. The thickness of the mold determines the thickness of the electrode paste. The square frame mold is attached to the surface of the carbon-coated current collector, and paste is added to one side of the mold. The paste is evenly distributed in the square frame by a scraping process, and the excess paste exceeding the thickness of the mold is scraped off. Positive and negative electrode pastes with specified thickness are prepared by this method.

[0017] Alternatively, the shape, length, width, and thickness of the electrodes can be input into the 3D printing control system. Then, the syringe containing the positive and negative electrode slurry is fixed in the designated position on the 3D printer. After ensuring a good seal at the syringe's propulsion end, the nozzle cap is opened. During printing, the nozzle specifications are adjusted according to the required battery thickness, and the height between the nozzle and the printing substrate, printing speed, and output per unit time are calibrated to ensure consistent and accurate print quality. The positive electrode current collector is then placed before proceeding with the 3D printing of the slurry electrodes.

[0018] (b) A separator is then applied, and a negative electrode slurry is 3D printed onto it, or lithium metal is placed on it to achieve an alternating arrangement of positive and negative electrode slurries. Finally, a negative electrode current collector is attached to the negative electrode slurry layer or lithium metal to form a complete battery cell.

[0019] (c) The battery cells described above are then thermoplastic film encapsulated. Using a vacuum sealing machine, the positive and negative electrode tabs of the current collector are first top-sealed, and then the remaining bottom edge and one side edge are heat-sealed at a temperature of 95°C. Finally, the remaining edges are vacuum-sealed at a vacuum level of -95 kPa, with a pre-sealing time of 3 seconds and a pressure holding time of 8 seconds. The battery is then wrapped in aluminum-plastic film and sealed using a vacuum sealing machine, ultimately producing a slurry-based single-layer battery.

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] On the one hand, this invention directly uses battery electrolyte to prepare a slurry of SPAN active particles and conductive agents, which can be used directly for battery assembly without drying. The active particles and conductive agent network in the slurry electrode are dynamically connected, which can effectively buffer the expansion volume and stress of the active particles during lithiation. At the same time, this method avoids the high energy consumption and electrode thickness limitations of traditional drying processes, and reduces the electrode-electrolyte interface impedance through sufficient pre-wetting with electrolyte. On the other hand, the conductive agent is a compound of zero-dimensional conductive agent and linear one-dimensional conductive agent. In the preparation process, the zero-dimensional conductive agent and SPAN dry powder are first mixed to form a conductive agent-coated SPAN particle microstructure, which increases short-range electronic conductivity and reduces particle interface contact resistance. Then, a one-dimensional conductive agent is selected in a high-speed dispersion process to prepare a uniform slurry. The linear conductive agent can not only play a steric hindrance role to maintain the stability of the slurry, but also form an interconnected three-dimensional conductive agent network to form a long-range electronic conduction path. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the electrode fabrication process of the present invention. Detailed Implementation

[0023] The examples listed below are further explanations of the contents of the instruction manual and should not be regarded as limitations thereof.

[0024] This invention uses battery electrolyte as a dispersion solvent to prepare SPAN active particles and conductive agents into a slurry, which is then coated onto a current collector to prepare a slurry-state sulfur-based battery electrode sheet that can be directly used for battery assembly without drying.

[0025] Example 1

[0026] This embodiment details the preparation method of slurry-state sulfur-based battery electrodes, including the following steps:

[0027] (1) Dry powder mixing: Select thiopolyacrylonitrile (SPAN) active material with a specific capacity of 600 mAh / g and an average particle size of 10 μm and SP conductive agent. The mass ratio of SPAN to SP is 50:3. Mix them evenly for 60 min using a double centrifugal vacuum degassing machine.

[0028] (2) Homogenization of slurry: Add 2% Ketjen Black (KB) conductive agent and 45% 0.5M LiTFSI PC electrolyte by mass ratio, and use a double centrifugal vacuum degassing machine to shear and mix at high speed for 60 minutes to homogenize the slurry. The viscosity of the slurry at 25℃ is 5000~8000mPa·s and the conductivity is 40~60mS / cm.

[0029] (3) Slurry 3D Printing: The prepared positive or negative electrode slurry is evenly loaded into the printer syringe. The shape, length, width, and thickness of the electrode are input into the 3D printing control system. The syringe containing the positive and negative electrode slurries is then fixed in the designated position on the 3D printer. After ensuring a good seal at the syringe's propulsion end, the nozzle cap is opened. During printing, the nozzle specifications are adjusted, and the height between the nozzle and the printing substrate, the printing speed, and the output per unit time are calibrated to control the slurry layer thickness to 150 μm. A carbon-coated aluminum foil positive electrode current collector is then placed before proceeding with the 3D printing of the slurry electrode.

[0030] (4) Assemble the negative electrode: Cover with a membrane and place a lithium metal negative electrode on it. Attach a negative electrode current collector to the negative electrode to form a complete battery cell.

[0031] (5) Battery Packaging: The battery cells described above are thermoplastic film packaged. Using a vacuum sealing machine, the positive and negative electrode tabs of the current collector are first top-sealed, and then the remaining bottom edge and one side edge are heat-sealed, with the heat-sealing temperature set at 95℃. Finally, the remaining edges are vacuum-sealed, with the vacuum degree set at -95kPa, the pre-sealing time at 3s, and the pressure holding time at 8s. The battery is wrapped with aluminum-plastic film and sealed using a vacuum sealing machine, ultimately producing a slurry-state electrode monolayer battery.

[0032] Example 2

[0033] The difference from Example 1 is that in step (1), the average particle size of SPAN is 0.2 μm and the mass ratio of SPAN to SP is 40:3.

[0034] In step (2), the mass ratio of electrolyte is 55%, the viscosity of slurry at 25℃ is 4000~7000mPa·s, and the conductivity is 30~50mS / cm.

[0035] Example 3

[0036] The difference from Example 1 is that step (3) controls the slurry layer thickness to be 500 μm.

[0037] Example 4

[0038] The difference from Example 1 is that the mass ratio of SPAN to SP in step (1) is 50:5.

[0039] In step (2), the mass ratio of Ketjen Black (KB) conductive agent is 2%, the mass ratio of electrolyte is 40%, the viscosity of slurry at 25℃ is 14000~16000mPa·s, and the conductivity is 80~100mS / cm.

[0040] Example 5

[0041] The difference from Example 1 is that in step (1), SP and KB conductive agents are added at the same time, and the mass ratio of SPAN, SP and KB is 50:3:2.

[0042] In step (2), Ketjenblack (KB) conductive agent is no longer added.

[0043] Comparative Example 1

[0044] The difference from Example 1 is that in step (1), the mass ratio of SPAN to SP is 50:5.

[0045] In step (2), Ketjenblack (KB) conductive agent is no longer added.

[0046] Comparative Example 2

[0047] The difference from Example 1 is that in step (1), no SP conductive agent is added, and the mass ratio of SPAN to SP is 50:0.

[0048] In step (2), 5% by mass of Ketjen Black (KB) conductive agent is added.

[0049] Comparative Example 3

[0050] The difference from Example 1 is that the mass ratio of SPAN to SP in step (1) is 75:3.

[0051] In step (2), the mass ratio of electrolyte is 20%, the viscosity of slurry at 25℃ is 20000~22000mPa·s, and the conductivity is 50~80mS / cm.

[0052] The above electrodes were subjected to charge-discharge performance tests. After standing at 25°C for 24 hours, the battery was clamped with a plastic clamp and subjected to a 0.1C constant current charge-discharge test at room temperature. The cutoff voltage was 1.0 to 3.0V. The specific capacity of the material is the discharge capacity after activation. The specific values ​​of the results are listed in Table 1.

[0053] Implementation effect

[0054] The specific capacity and first-efficiency of the electrodes corresponding to the embodiments and comparative examples of this invention are listed in Table 1. As can be seen from the table, the slurry electrode coating process requires a suitable viscosity range. When the content of active particles or conductive agents is too high, especially when the content of cross-linked conductive agents such as KB and CNT is high, the slurry viscosity increases significantly, making electrode coating difficult. The prepared slurry electrodes are uneven and have poor uniformity, resulting in poor electrode performance (Examples 1, 2, 5 vs. Example 4 and Comparative Example 1). The slurry electrode uses a mixture of zero-dimensional and one-dimensional conductive agents as the conductive agent. Part of the conductive agent coats the surface of the active particles, while the other part forms an interconnected three-dimensional conductive agent network. This coating structure is mainly formed by dry mixing zero-dimensional conductive agents and SPAN. The one-dimensional conductive agent forms a three-dimensional network structure during the high-speed dispersion process. Without a phased addition process, the most effective conductive agent network structure cannot be formed, resulting in even worse electrode performance (Examples 1, 2 vs. Example 5 and Comparative Examples 1, 2). When the slurry electrode thickness is too thick, the electrode performance is poor due to the restriction of ion and electron transport (Example 3). The optimal performance of the slurry state electrode (Example 1) is achieved by selecting the appropriate slurry content, adding the conductive agent in stages, and using an optimized process with suitable electrode thickness.

[0055] Table 1. Electrochemical performance of each battery electrode in the examples and comparative examples.

[0056]

Claims

1. A sulfur-based battery electrode and its preparation method, characterized in that... include: (1) Current collector; (2) A slurry layer coated on the surface of the current collector, the slurry layer being composed of the following components: (a) Sulphurized polyacrylonitrile (SPAN) active particles with a particle size of 0.2–20 μm, accounting for 40%–70% of the total mass of the slurry; (b) A conductive agent, comprising 2% to 10% of the total mass of the slurry, is a mixture of at least two of conductive graphite (KS), Super P (SP), acetylene black (AB), Ketjen black (KB), carbon nanotubes (CNT), and vapor-deposited carbon fibers (VGCF). (c) The battery electrolyte is used as a solvent for the slurry, accounting for 25% to 60% of the total mass of the slurry; (d) The sum of the mass percentages of the above-mentioned active particulate material, conductive agent and electrolyte is 100%; The conductive agent is partially coated on the surface of the SPAN active particles, and the other part forms an interconnected three-dimensional conductive network; the slurry layer does not require drying treatment and can be directly coated or 3D printed on the surface of the current collector.

2. The sulfur-based battery electrode according to claim 1, characterized in that: The current collector is one of aluminum foil, carbon-coated aluminum foil, aluminum foam, and nickel foam.

3. The slurry-state sulfur-based battery electrode according to claim 1, characterized in that: The battery electrolyte comprises a solvent and a lithium salt. The solvent is at least one of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). The lithium salt is at least one of lithium hexafluorophosphate (LiPF6), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and lithium bis(fluorosulfonyl)imide (LiFSI).

4. The slurry-state sulfur-based battery electrode according to claim 1, characterized in that: The slurry has a viscosity of 5000–20000 mPa·s at 25°C and an electrical conductivity of 5–100 mS / cm.

5. A method for preparing a slurry-based sulfur-based battery electrode, characterized in that, Includes the following steps: (1) Mix the active particles of vulcanized polyacrylonitrile (SPAN) and the conductive agent at a mass ratio of 87-97:3-13. The particle size of SPAN is 2-20μm. The conductive agent is added in two parts in batches. The dry powder is mixed using a high-speed disperser so that the surface of the active particles is coated with a layer of conductive agent particles. (2) Add the battery electrolyte as a solvent to the mixture formed in step (1), control the solid content of the slurry to be 40-75 wt%, and disperse it by high-speed shearing to form a homogeneous slurry; (3) The slurry is 3D printed or coated onto the surface of the current collector using a coating equipment, and the electrode slurry layer thickness is 100-500μm; (4) The drying process is omitted, and the slurry-state electrode sheet is directly used for battery assembly.

6. The method for preparing slurry-based sulfur-based battery electrodes according to claim 5, characterized in that: The high-speed dispersion equipment is one of the following: a dual centrifugal degassing machine, a ball mill, an air jet mill, or a sand mill.

7. The preparation method according to claim 5, characterized in that: The conductive agent in step (1) is added in two parts: First, 30% to 70% of the total conductive agent mass is added and mixed with SPAN particles to form a surface coating layer. The first part of the conductive agent is selected from one or more of conductive graphite (KS), Super P (SP), acetylene black (AB), and Ketjen black (KB), accounting for 70% to 100% of the total mass of the first added conductive agent. The other part is selected from one or more of Ketjen black (KB), carbon nanotubes (CNT), and vapor-deposited carbon fiber (VGCF), accounting for 0% to 30% of the total mass of the first added conductive agent. The remaining conductive agent is added simultaneously with the electrolyte in step (2) to construct a three-dimensional conductive network.

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