A flexible carbon paper-based lithium ion battery negative electrode material and a preparation method and application thereof

Abstract

This invention discloses a method for preparing a flexible carbon paper-based lithium-ion battery anode material, belonging to the technical field of self-supporting electrode preparation and energy storage devices. Polyacrylonitrile fibers (PAN) are fibrillated using a PFI pulping and papermaking equipment. The fibrillated fibers are then sieved using a Pall sieve. The sieved nanofibers are then mixed with carbon fibers (CFs) to form paper. After pre-oxidation and carbonization, a flexible carbon paper electrode (FCP) is obtained. This material exhibits good flexibility, mechanical strength, and electrochemical performance when used as a flexible lithium-ion battery anode, making it suitable for flexible electronic devices. Furthermore, the material preparation is simple, green, efficient, and low-consumption, providing guidance for the production of flexible electrodes and improving the feasibility of carbon paper-based materials in the industrial application of flexible batteries.

Description

Technical Field

[0001] This invention relates to the fields of special paper-based materials and new energy technology, specifically to a flexible carbon paper-based lithium-ion battery anode material, its preparation method, and its application. Background Technology

[0002] With the rapid development of wearable electronic devices, foldable screens, and implantable medical devices, the demand for flexible energy storage devices is becoming increasingly strong. Lithium-ion batteries have been widely used due to their advantages such as long service life and high energy density. Meanwhile, to meet the development needs of flexible devices, the application of flexible lithium-ion batteries has received widespread attention. Research on materials such as carbon cloth, carbon paper, carbon nanotubes, graphene, and conductive polymers as flexible electrode or substrate materials has emerged in large numbers, providing a reference for the rapid development of flexible batteries.

[0003] The preparation of flexible carbon nanofiber anode materials reported so far mainly involves spinning in different ways, which requires high-end equipment, is complex, expensive, and difficult to scale up. The strength of the prepared electrode materials is also difficult to meet the requirements of high capacity and good physical properties at the same time.

[0004] Therefore, exploring flexible anode materials with high capacity without compromising mechanical properties has become a major challenge for the industrialization of flexible lithium-ion batteries. Summary of the Invention

[0005] This invention provides a method for preparing a flexible carbon paper-based lithium-ion battery anode material. Utilizing the fibrillability of PAN (polyacrylonitrile) fibers, the fiber is fibrillated using pulping and papermaking machinery, and then combined with highly conductive and high-strength CFs (carbon fiber) materials to prepare a highly flexible and highly conductive flexible anode material using a wet forming process, which is then used in flexible lithium-ion batteries.

[0006] This invention is achieved through the following technical solution:

[0007] A method for preparing a flexible carbon paper-based lithium-ion battery anode material, characterized by comprising the following steps:

[0008] (1) After fibrillation treatment of PAN fiber aqueous solution, PAN fibers of 30 mesh or larger are screened out;

[0009] (2) After mixing the PAN fibers obtained in step (1) with CFs, the paper is formed, dried, pre-oxidized, and carbonized at 600-800°C to obtain a flexible carbon paper-based lithium-ion battery anode material; the amount of CFs added is 10-30 wt% of the PAN fibers.

[0010] Preferably, PAN fibers with a mesh size of 100 or larger are screened out in step (1).

[0011] Preferably, PAN fibers with a mesh size of 200 or larger are screened out in step (1).

[0012] Preferably, the amount of CFs added in step (2) is (20±5)wt% of the PAN fiber.

[0013] Preferably, the carbonization temperature in step (2) is 700℃, the heating rate is 1~10℃ / min, and the holding time is 0.5~4h.

[0014] Preferably, the concentration of the PAN fiber aqueous solution in step (1) is 10-30 wt%; the fibrillation treatment in step (1) refers to refining using a PFI refiner under a linear pressure of 0.5-3 N / m; and the fiber obtained after the fibrillation treatment has a freeness of 60-80°SR.

[0015] Preferably, the basis weight of the paper used in step (2) is 20–100 g / m³. 2 .

[0016] Preferably, the pre-oxidation in step (2) refers to heating to 100-300°C at a heating rate of 1-5°C / min and then holding at that temperature for 1-3 hours.

[0017] The flexible carbon paper-based lithium-ion battery anode material prepared by the method described in this invention.

[0018] Application of the flexible carbon paper-based lithium-ion battery anode material described in this invention.

[0019] Compared with the prior art, the present invention has the following advantages and effects:

[0020] (1) Excellent mechanical and electrochemical properties: The fibrillated PAN fibers of this invention are sieved through a Pall sieve to obtain nanofibers, which can increase the specific surface area of ​​the negative electrode material while shortening the diffusion path of lithium ions in the material, and also enhance the bonding force between fibers, thus significantly improving the mechanical properties of the negative electrode material. At the same time, the addition of CFs further enhances the conductivity of the electrode material, thereby ensuring the excellent electrochemical performance of the flexible negative electrode. The flexible electrode material for lithium-ion batteries prepared by this invention has a maximum tensile strength of 1.12 MPa and a conductivity of 1253 S / m, exhibiting good cycle performance and capacity stability at high rates.

[0021] (2) This invention uses inexpensive PAN fiber as raw material. After fibrillation, it is combined with CFs and then subjected to low-temperature annealing to prepare a highly flexible flexible anode material. It is low in cost, simple in process and excellent in performance. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the PAN fiber fibrillation and sieving process of the present invention.

[0023] Figure 2 The images show scanning electron microscope (SEM) images and fiber width distributions of fibers with different mesh counts in Example 1; where (a), (b), (c), (d), and (e) represent SEM images of fibers with mesh counts of <30 mesh, 30–50 mesh, 50–100 mesh, 100–200 mesh, and >200 mesh, respectively.

[0024] Figure 3(a) shows the conductivity and thickness test results of flexible electrodes prepared with different CFs mass ratios; Figure 3(b) shows the tensile strength test results of flexible electrodes prepared with different CFs mass ratios.

[0025] Figure 4(a) shows the conductivity and thickness test results of flexible electrodes prepared with PAN fibers of different mesh sizes in Example 1; Figure 4(b) shows the tensile strength test curves of flexible electrodes prepared with PAN fibers of different mesh sizes in Example 1.

[0026] Figure 5 Flexibility testing of the negative electrode material prepared in this invention.

[0027] Figure 6(a) shows the cyclic voltammetry curve of the flexible anode prepared in Example 1; Figure 6(b) shows the cyclic capacity retention curves at different carbonization temperatures; Figure 6(c) shows the cyclic capacity retention curve of the flexible anode prepared in Example 1 at a high rate of 1C; Figure 6(d) shows the cyclic capacity retention curves of the flexible anode prepared in Example 1 under different rate conditions. Detailed Implementation

[0028] The present invention will be further described below with reference to specific embodiments.

[0029] Example 1

[0030] A method for preparing a flexible carbon paper-based lithium-ion battery anode material includes the following steps: First, PAN fibers with a concentration of 30% are soaked in pure water overnight. After thorough immersion, the PAN fibers, along with the water, are transferred to a PFI refiner. The linear pressure is adjusted to 1 N / m to fibrillate the PAN. The pulp is removed and stored in a sealed bag for later use when the fiber freeness reaches 60°SR. Each time, 10g (octane dry weight) of fibrillated PAN fibers is placed in a Pall sieve for sieving. The sieved fibers are divided into five mesh sizes. PAN fibers with a mesh size <30 are referred to as PAN-1, PAN fibers with a mesh size of 30–50 are referred to as PAN-2, PAN fibers with a mesh size of 50–100 are referred to as PAN-3, PAN fibers with a mesh size of 100–200 are referred to as PAN-4, and PAN fibers with a mesh size >200 are referred to as PAN-5.

[0031] Weigh out PAN-5 fibers and mix them with CFs according to the ratio of PAN fiber to CFs = 8:2, then form a paper machine with a yield of 80g / m³. 2 The paper sheets were dried and then transferred to an oven to be pre-oxidized at a heating rate of 1℃ / min to 250℃ and held for 1 hour. The pre-oxidized paper sheets were then carbonized in a tube furnace at a carbonization temperature of 700℃, a heating rate of 5℃ / min, and a holding time of 1 hour.

[0032] Example 2

[0033] A method for preparing a flexible carbon paper-based lithium-ion battery anode material includes the following steps: First, PAN fibers with a concentration of 10% are soaked in pure water overnight. After thorough immersion, the PAN and water are transferred to a PFI refiner, and the linear pressure is adjusted to 3 N / m to fibrillate the PAN. The pulp is removed and stored in a sealed bag when the fiber freeness reaches 80°SR. Each time, 10g (octane dry weight) of fibrillated PAN fibers is taken and sieved through a Pall sieve to obtain 100-200 mesh fibers for later use. PAN-4 fibers are weighed and mixed with CFs at a ratio of PAN fiber:CFs = 7:3, and then formed into 20g / m³ paper. 2 The paper sheets were dried and then transferred to an oven to be pre-oxidized at a heating rate of 5℃ / min to 100℃ and held for 2 hours. The pre-oxidized paper sheets were then carbonized in a tube furnace at a carbonization temperature of 800℃, a heating rate of 10℃ / min, and a holding time of 0.5 hours.

[0034] Example 3

[0035] A method for preparing a flexible carbon paper-based lithium-ion battery anode material includes the following steps: First, PAN fibers with a concentration of 20% are soaked in pure water overnight. After thorough immersion, the PAN and water are transferred to a PFI refiner, and the linear pressure is adjusted to 2 N / m to fibrillate the PAN. The pulp is removed and stored in a sealed bag when the fiber freeness reaches 70°SR. Each time, 10g (octane dry weight) of fibrillated PAN fibers is taken and sieved through a Pall sieve to obtain 30-50 mesh fibers for later use. PAN-2 fibers are weighed and mixed with CFs at a ratio of PAN fiber:CFs = 7.2:2.5, and then formed into a 20g / m³ sheet. 2 The paper sheets were dried and then transferred to an oven to be pre-oxidized at a heating rate of 2℃ / min to 300℃ and held for 3 hours. The pre-oxidized paper sheets were then carbonized in a tube furnace at a temperature of 900℃, a heating rate of 10℃ / min, and a holding time of 4 hours.

[0036] Example 4

[0037] A method for preparing a flexible carbon paper-based lithium-ion battery anode material includes the following steps: First, PAN fibers with a concentration of 20% are soaked in pure water overnight. After thorough immersion, the PAN and water are transferred to a PFI refiner, and the linear pressure is adjusted to 3 N / m to fibrillate the PAN. The pulp is removed and stored in a sealed bag when the fiber freeness reaches 75°SR. Each time, 10g (octane dry weight) of fibrillated PAN fibers is taken and sieved through a Pall sieve to obtain 50-100 mesh fibers for later use. PAN-1 fibers are weighed and mixed with CFs at a ratio of PAN fiber:CFs = 10:0, and then formed into 50g / m³ paper. 2 The paper sheets were dried and then transferred to an oven to be pre-oxidized at a heating rate of 5℃ / min to 200℃ and held for 1.5h. The pre-oxidized paper sheets were then carbonized in a tube furnace at a carbonization temperature of 1000℃, a heating rate of 1℃ / min, and a holding time of 2h.

[0038] Example 5

[0039] A method for preparing a flexible carbon paper-based lithium-ion battery anode material includes the following steps: First, PAN fibers with a concentration of 15% are soaked in pure water overnight. After thorough immersion, the PAN and water are transferred to a PFI refiner, and the linear pressure is adjusted to 1.5 N / m to fibrillate the PAN. The pulp is removed and stored in a sealed bag when the fiber freeness reaches 80°SR. Each time, 10g (octane dry weight) of fibrillated PAN fibers is taken and sieved through a Pall sieve to obtain 100-200 mesh fibers for later use. PAN-4 fibers are weighed and mixed with CFs at a ratio of PAN fiber:CFs = 9:1, and then formed into 80g / m³ paper. 2 The paper sheets were dried and then transferred to an oven to be pre-oxidized at a heating rate of 5℃ / min to 100℃ and held for 0.5h. The pre-oxidized paper sheets were then carbonized in a tube furnace at a carbonization temperature of 750℃, a heating rate of 5℃ / min, and a holding time of 1.5h.

[0040] The preparation process and material characterization of the flexible anode material of the present invention are analyzed:

[0041] Figure 1 This diagram illustrates the process of PAN fibers undergoing PFI refining and Pall grading. After refining, the fibers become fibrillated, resulting in smaller fiber sizes. Furthermore, after grading, fibers of different mesh sizes can be obtained, leading to a more concentrated aspect ratio.

[0042] Figure 2These are SEM images and size distributions of fibers with different mesh sizes after sieving using a grading sieve in Example 1. PAN-1 to PAN-5 represent fibers with mesh sizes <30, 30-50, 50-100, 100-200, and >200, respectively. It can be seen that the fiber size decreases as the mesh size increases. Statistical analysis of the width of 100 fibers shows that fibers obtained by sieving through a larger mesh size can reach the nanometer scale.

[0043] Figure 3 shows the FCP prepared according to the preparation method of Example 1 after fibrillation and mixing of unscreened PAN fibers with different amounts of CFs. The conductivity and thickness increase with increasing CFs content. When the CF ratio is 20 wt%, the conductivity increases from 476 S / m to a maximum of 763 S / m. The addition of CFs helps improve the conductivity of FCP, but when the CFs ratio exceeds 20 wt%, the conductivity decreases, and the continuous increase in thickness is unaffected. This indicates that within a certain thickness range, adding CFs can enhance the conductivity of the electrode.

[0044] Figure 4 shows the conductivity and tensile strength performance curves of FCP prepared according to the preparation method of Example 1 after mixing PAN fibers of different mesh sizes with 20 wt% CFs through a grading sieve. As can be seen from Figure 4(a), with the CFs addition ratio remaining constant, the thickness of the flexible electrode decreases and the conductivity increases rapidly with the increase of PAN fiber mesh size. The conductivity of the electrode prepared with PAN-5 is 1253 S / m, and the tensile strength also reaches a maximum of 1.12 MPa.

[0045] Figure 5 The flexibility of the FCP electrode was tested. After bending, folding and winding the electrode back and forth, the electrode was not damaged. This indicates that the electrode material prepared by this method has good flexibility and can be used as a candidate material for flexible lithium-ion batteries.

[0046] Figure 6 shows the electrochemical performance of the electrode material prepared in Example 1 assembled into a coin-type lithium-ion battery. Figure 6(a) shows the cyclic voltammetry curves of the Li / / FCP half-cell at voltages of 0.01–3 V and scan rates of 0.1 mV / s. After the first cycle, a significant reduction peak appears at 0.35 V, due to the irreversible reaction between the negative electrode and the electrolyte, resulting in the formation of an SEI film. After the first cycle, the CV curves almost completely overlap, indicating the formation of a stable SEI film protecting the electrode surface. Figure 6(b) compares the capacity retention of the electrode at different carbonization temperatures. It can be seen that the flexible electrode prepared by carbonization at 700 °C exhibits better capacity retention, maintaining a specific capacity of 307.97 mAh / g after 100 cycles at a 0.1 C rate. Furthermore, as shown in Figure 6(c), at a high 1 C rate, the capacity retention is 100% after 100 cycles, showing an increase rather than a decrease. Figure 6(d) shows the tests of FCP under different rate conditions, starting with 10 cycles at 0.05C, followed by 0.1C, 0.2C, 0.5C, 1C, 2C, 5C, and 10C, and finally returning to 0.1C. It can be seen that even under these different test conditions, the specific capacity of the electrode material remains constant at 413.26 mAh / g. This observation demonstrates that the electrode exhibits excellent durability and capacity retention even under harsh cycling conditions, indicating its strong and long-lasting performance potential in practical applications.

[0047] The above description is a preferred embodiment of the present invention, but the present invention should not be limited to the content disclosed in the embodiments and drawings. Therefore, any equivalent or modified embodiments made without departing from the spirit of the present invention fall within the protection scope of the present invention.

Claims

1. A method for preparing a flexible carbon paper-based anode material for lithium ion batteries, characterized in that, Includes the following steps: (1) After fibrillation treatment of the PAN fiber aqueous solution, PAN fibers of 30 mesh or larger are sieved out; the fibrillation treatment refers to refining using a PFI refiner at a linear pressure of 0.5~3 N / m; the freeness obtained after the fibrillation treatment is 60~80. o SR fibers; (2) The PAN fibers obtained in step (1) are mixed with CFs, formed into paper, dried, pre-oxidized, and carbonized at 600~800 °C to obtain a flexible carbon paper-based lithium-ion battery anode material; the amount of CFs added is 10~30% of the PAN fibers. wt %.

2. The method of claim 1, wherein, In step (1), PAN fibers with a mesh size of 100 or higher are screened out.

3. The method according to claim 2, characterized in that, In step (1), PAN fibers with a mesh size of 200 or higher are screened out.

4. The method according to claim 1, 2, or 3, characterized in that, The CFs addition amount in step (2) is (20±5) wt% of the PAN fiber wt .

5. The method of claim 4, wherein, The carbonization temperature in step (2) is 700℃, and the heating rate is 1~10. o C / min, keep warm for 0.5~4h.

6. The method according to claim 5, characterized in that, The concentration of the PAN fiber aqueous solution in step (1) is 10-30 wt % 7. The method of claim 6, wherein, The basis weight of the paper used in step (2) is 20~100 g / m³. 2 .

8. The method according to claim 7, characterized in that, The pre-oxidation mentioned in step (2) refers to 1~5 o Heating rate increased to 100~300 °C / min o After temperature C, keep warm for 1-3 hours.

9. The flexible carbon paper-based lithium-ion battery anode material prepared by the method according to any one of claims 1-8.

10. The application of the flexible carbon paper-based lithium-ion battery anode material according to claim 9.

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