Hard carbon paper negative electrode material based on papermaking process regulation and preparation method and application thereof

Abstract

The application discloses a kind of hard carbon paper negative materials based on papermaking process regulation and preparation method and application thereof.The preparation method comprises: after paper pulp fiber is defibrated, it is treated by beating with PFI beater, and the beating degree of the pulp is controlled to be 5°SR to 92°SR by controlling beating line pressure and beating revolution number;The obtained pulp is mixed and defibrated again, and the original paper with basis weight of 30 to 130 g / m² is prepared by wet papermaking process;The original paper is treated by high-temperature carbonization under protective atmosphere, and the hard carbon paper negative material is obtained.The preparation method is simple, green and efficient, the obtained hard carbon paper negative electrode does not need to be coated on the current collector, and does not need to add any binder and conductive agent, and the integrated structure greatly reduces the production cost;At the same time, the material effectively overcomes the problem of low reversible capacity and low initial efficiency of traditional self-supporting negative electrode, and shows excellent sodium storage performance.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery technology, specifically relating to a hard carbon paper anode material based on papermaking process control, its preparation method, and its application. Background Technology

[0002] Sodium-ion batteries, due to their abundant raw materials, low cost, and high safety, show great promise for large-scale energy storage. The key to their commercial application lies in developing high-performance, low-cost anode materials. Hard carbon materials, with their large interlayer spacing suitable for sodium-ion storage and abundant defect sites, are considered one of the most promising anode materials for sodium-ion batteries.

[0003] However, the preparation of traditional powdered hard carbon anodes typically requires mixing hard carbon powder with binders and conductive agents before coating it onto a metal current collector. This process is complex, and the introduction of inactive materials (binder, conductive agent, and current collector) not only increases cost and weight but also hinders ion / electron transport, leading to a decrease in battery volumetric energy density and rate performance. Although some studies have attempted to prepare self-supporting hard carbon electrodes to eliminate inactive materials, such electrodes often suffer from low reversible capacity and poor first-cycle coulombic efficiency due to insufficient control over microstructure (such as porosity and pore size distribution), severely limiting their electrochemical performance. Therefore, it is crucial to develop a simple, low-cost method for preparing high-performance self-supporting hard carbon anodes that allows for precise control over electrode microstructure. Summary of the Invention

[0004] To address the issues of low reversible capacity and low initial efficiency in existing self-supporting hard carbon anode materials, the primary objective of this invention is to provide a method for preparing hard carbon paper anode materials based on papermaking process control. This method is simple, green, and efficient, and allows for effective control of the electrode microstructure.

[0005] Another object of the present invention is to provide a hard carbon paper anode material obtained by the above preparation method.

[0006] Another object of the present invention is to provide the application of the above-mentioned hard carbon paper anode material.

[0007] The objective of this invention is achieved through the following technical solution: A method for preparing a hard carbon paper anode material based on papermaking process control includes the following steps: (I) After the pulp fibers are loosened, they are beating with a PFI refiner and the refining line pressure is controlled at 3.33 N / m to obtain pulp with the target freeness. The obtained pulp is then mixed and loosened again, and then prepared into base paper with a basis weight of 30 to 130 g / m² by wet papermaking process. (II) The base paper is subjected to high-temperature carbonization treatment under a protective atmosphere. The carbonization temperature is 1000 to 1500 °C and the holding time is 1 to 5 h to obtain the hard carbon paper negative electrode material.

[0008] Further, in step I, the pulp is one or more of the following papermaking pulps: pine pulp, eucalyptus pulp, cotton pulp, bamboo pulp, viscose fiber pulp, straw pulp, etc., with pine pulp being the most preferred.

[0009] Further, in step I, the PFI refiner has a refining speed of 0 to 30,000 revolutions and a beating degree of 5 °SR to 92 °SR, preferably 5 °SR to 60 °SR, and most preferably 5 °SR beating degree.

[0010] Furthermore, in step I, the basis weight of the base paper is preferably 80 g / m².

[0011] Furthermore, in step II, the protective atmosphere is one or a mixture of nitrogen and argon.

[0012] Furthermore, in step II, the heating rate of the carbonization treatment is 2 °C / min.

[0013] Furthermore, in step II, the carbonization temperature is 1300 ℃ and the holding time is 3 h.

[0014] Furthermore, in step II, the carbonization process employs a two-stage heating procedure: first, the temperature is raised to 300°C at a rate of 2°C / min and held for 2 hours, then the temperature is raised to 1300°C at a rate of 2°C / min and held for 3 hours.

[0015] The present invention also discloses a hard carbon paper anode material for sodium-ion batteries, which is prepared by the preparation method described above.

[0016] The present invention also discloses a sodium-ion battery, wherein the negative electrode is the hard carbon paper negative electrode material described above.

[0017] Compared with the prior art, the present invention has the following advantages and beneficial effects: This invention innovatively uses a mature papermaking process to prepare a self-supporting electrode precursor. By precisely controlling the two core papermaking parameters of beating degree and paper basis weight, the pore structure and densification degree of the carbonized hard carbon paper are effectively controlled, and an integrated negative electrode with high reversible capacity and high first-efficiency is successfully prepared, solving the problem of poor performance of traditional self-supporting electrodes.

[0018] The hard carbon paper anode prepared by the method described in this invention does not require the use of inactive binders, conductive agents, and additional metal current collectors, which simplifies the electrode preparation process, significantly reduces production costs, and improves the overall energy density of the battery.

[0019] This invention uses widely available, renewable, and low-cost natural wood fiber as raw material, and the process is green and environmentally friendly, providing a new and feasible technical path for the large-scale production of high-performance, low-cost sodium-ion battery anode materials.

[0020] In the preparation method described in this invention, as the basis weight of the paper increases, the dense porous structure induces the formation of a uniform and thin SEI film on the surface of the hard carbon paper anode, which reduces the energy barrier for electrolyte desolvation, thereby improving the reversible capacity and first-cycle coulombic efficiency of the hard carbon paper anode. Attached Figure Description

[0021] Figure 1 The first charge-discharge curves of sodium-ion batteries are obtained by grinding the hard carbon paper anode materials prepared by Comparative Examples 9, 10 and 11 of this invention into powder anode materials. The experimental results are all stable data repeated three times. Figure 2 The first charge-discharge curves of sodium-ion batteries for the hard carbon paper anode materials prepared in Comparative Examples 1, 1, and 2 of this invention and the powder anode material prepared in Comparative Example 9 are shown. The experimental results are all stable data repeated three times. Figure 3 The figures show the rate cycling curves of sodium-ion batteries for the hard carbon paper anode materials prepared in Comparative Examples 1, 1, and 2 of this invention, and the powder anode material prepared in Comparative Example 9. The experimental results are all stable data obtained by repeating the experiment three times. Figure 4 The diagram shows the cycle stability of sodium-ion batteries prepared with hard carbon paper anode materials in Comparative Examples 1, 1, and 2 and with powder anode materials prepared in Comparative Example 9 at a current density of 1 A / g. The experimental results are all stable data repeated three times. Figure 5 These are CT three-dimensional scan images of Comparative Example 1 and Example 1 of the present invention; Figure 6 The first charge-discharge curves of sodium-ion batteries for the hard carbon paper anode materials prepared in Comparative Examples 1, 2, 3 and 4 of this invention are shown. The experimental results are all stable data obtained by repeating the experiment three times. Figure 7 This is a schematic diagram of the hard carbon paper anode material prepared in Examples 1 and 5 of the present invention; Figure 8 The BET specific surface area data of the hard carbon paper anode material prepared in Comparative Example 1, Example 1, and Example 2 of this invention and the powder anode material prepared in Comparative Example 9 are shown in the figure. The experimental results are all stable data repeated three times. Figure 9The figures show the true density and closed-cell volume data of the hard carbon paper anode materials prepared in Comparative Examples 1, 1, and 2 of this invention, and the powder anode material prepared in Comparative Example 9. The experimental results are all stable data obtained by repeating the experiment three times. Detailed Implementation

[0022] The present invention will be further described in detail below with reference to embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto. All raw materials involved in the present invention can be purchased directly from the market. For process parameters not specifically specified, conventional techniques can be referred to.

[0023] Regarding the "range" mentioned in this application, it is defined by setting a lower limit and an upper limit, which define the boundaries of a specific range. Such a range may or may not include its endpoints, and can be freely combined; that is, any lower limit can be combined with any upper limit to form a new range.

[0024] Unless otherwise specified, all embodiments and their optional solutions in this application can be combined with each other to create new technical solutions. Similarly, unless otherwise specified, all technical features and their optional features in this application can also be combined with each other to form new technical solutions.

[0025] The present invention will now be described in detail, and includes the following specific steps: (I) After the pulp fibers are loosened, they are beating with a PFI refiner, with the refining line pressure controlled at 3.33 N / m and the rotation speed from 0 to 30,000 revolutions, to obtain pulp with the target freeness; the obtained pulp is then mixed and loosened again, and then prepared into base paper with a basis weight of 30 to 130 g / m² by wet papermaking process; (II) The base paper is subjected to high-temperature carbonization treatment under a protective atmosphere. First, the temperature is increased to 300℃ at 2℃ / min and kept at 2h, then increased to 1000-1500℃ at 2℃ / min and kept at 1-5h to obtain the hard carbon paper negative electrode material.

[0026] Example 1 (I) After the pine pulp fibers are loosened, they are pulped using a PFI refiner to obtain a pulp with a target freeness of 5°SR; the obtained pulp is then mixed and loosened again, and a base paper with a basis weight of 80 g / m² is prepared by wet papermaking process. (II) The base paper was subjected to high-temperature carbonization under argon atmosphere. First, the temperature was increased to 300 °C at a rate of 2 °C / min and held for 2 h, then increased to 1300 °C at a rate of 2 °C / min and held for 3 h to obtain a sodium-ion battery hard carbon paper anode material. As shown in Table 1, the anode material prepared in this embodiment has a reversible charging capacity of 330.4 mAh / g and a first-cycle coulombic efficiency of 93.17%.

[0027] Example 2 Example 2 follows the same preparation process as Example 1, except that in step I of preparing the sodium-ion battery hard carbon paper anode material, a base paper with a basis weight of 130 g / m² is prepared by a wet papermaking process. As shown in Table 1, the anode material prepared in this example has a reversible charging capacity of 313.2 mAh / g and a first-cycle coulombic efficiency of 94.97%.

[0028] Example 3 Example 3 follows the same preparation process as Example 1, except that in step I of preparing the sodium-ion battery hard carbon paper anode material, a PFI refiner was used for pulping to obtain a pulp with a target freeness of 28 °SR. This pulp was then processed using a wet papermaking process to obtain a base paper with a basis weight of 80 g / m². As shown in Table 1, the anode material prepared in this example has a reversible charging capacity of 327.4 mAh / g and a first-cycle coulombic efficiency of 93.68%.

[0029] Example 4 Example 4 follows the same preparation process as Example 1, except that in step I of preparing the sodium-ion battery hard carbon paper anode material, a PFI refiner was used for pulping to obtain a pulp with a target freeness of 60 °SR. This pulp was then processed using a wet papermaking process to obtain a base paper with a basis weight of 80 g / m². As shown in Table 1, the anode material prepared in this example has a reversible charging capacity of 328.8 mAh / g and a first-cycle coulombic efficiency of 94.32%.

[0030] Example 5 Example 5 follows the same preparation process as Example 1, except that in step I of preparing the sodium-ion battery hard carbon paper anode material, a PFI refiner was used for pulping to obtain a pulp with a target freeness of 92 °SR. This pulp was then processed using a wet papermaking process to obtain a base paper with a basis weight of 80 g / m². As shown in Table 1, the anode material prepared in this example has a reversible charging capacity of 320.1 mAh / g and a first-cycle coulombic efficiency of 93.02%.

[0031] Example 6 Example 6 follows the same preparation process as Example 1, except that in step I of preparing the sodium-ion battery hard carbon paper anode material, a PFI refiner was used for pulping to obtain a pulp with a target freeness of 28 °SR. This pulp was then processed using a wet papermaking process to obtain a base paper with a basis weight of 130 g / m². As shown in Table 1, the anode material prepared in this example has a reversible charging capacity of 313.4 mAh / g and a first-cycle coulombic efficiency of 94.57%.

[0032] Example 7 Example 7 follows the same preparation process as Example 1, except that in step I of preparing the sodium-ion battery hard carbon paper anode material, a PFI refiner was used for pulping to obtain a pulp with a target freeness of 60 °SR. This pulp was then processed using a wet papermaking process to obtain a base paper with a basis weight of 130 g / m². As shown in Table 1, the anode material prepared in this example has a reversible charging capacity of 307.1 mAh / g and a first-cycle coulombic efficiency of 93.9%.

[0033] Example 8 Example 8 follows the same preparation process as Example 1, except that in step I of preparing the sodium-ion battery hard carbon paper anode material, a PFI refiner was used for pulping to obtain a pulp with a target freeness of 92 °SR. This pulp was then processed using a wet papermaking process to obtain a base paper with a basis weight of 130 g / m². As shown in Table 1, the anode material prepared in this example has a reversible charging capacity of 306.7 mAh / g and a first-cycle coulombic efficiency of 93.71%.

[0034] Example 9 Example 9 follows the same preparation process as Example 1, except that in step I of preparing the sodium-ion battery hard carbon paper anode material, eucalyptus pulp is used, and the paper basis weight is 80 g / m². As shown in Table 1, the anode material prepared in this example has a reversible charging capacity of 319.3 mAh / g and a first-cycle coulombic efficiency of 93.5%.

[0035] Example 10 Example 10 follows the same preparation process as Example 1, except that in step I of preparing the sodium-ion battery hard carbon paper anode material, cotton pulp was used, and the paper basis weight was 80 g / m². As shown in Table 1, the anode material prepared in this example has a reversible charging capacity of 320.7 mAh / g and a first-cycle coulombic efficiency of 93.2%.

[0036] Example 11 Example 11 follows the same preparation process as Example 1, except that in step I of preparing the sodium-ion battery hard carbon paper anode material, bamboo pulp is used and the paper basis weight is 80 g / m². As shown in Table 1, the anode material prepared in this example has a reversible charging capacity of 306.6 mAh / g and a first-cycle coulombic efficiency of 92.5%.

[0037] Example 12 Example 12 follows the same preparation process as Example 1, except that in step I of preparing the sodium-ion battery hard carbon paper anode material, the pulp used is viscose fiber pulp, and the paper basis weight is 80 g / m². As shown in Table 1, the anode material prepared in this example has a reversible charging capacity of 299.0 mAh / g and a first-cycle coulombic efficiency of 88.9%.

[0038] Comparative Example 1 Comparative Example 1 follows the same preparation process as Example 1, except that in step I of preparing the sodium-ion battery hard carbon paper anode material, a base paper with a basis weight of 30 g / m² was prepared using a wet papermaking process. As shown in Table 1, the anode material prepared in this comparative example has a reversible charging capacity of 305.8 mAh / g and a first-cycle coulombic efficiency of 88.97%.

[0039] Comparative Example 2 Comparative Example 2 follows the same preparation process as Example 1, except that in step I of preparing the sodium-ion battery hard carbon paper anode material, a PFI refiner was used for pulping to obtain a pulp with a target freeness of 28 °SR. This pulp was then processed using a wet papermaking process to obtain a base paper with a basis weight of 30 g / m². As shown in Table 1, the anode material prepared in this comparative example has a reversible charging capacity of 305.4 mAh / g and a first-cycle coulombic efficiency of 88.99%.

[0040] Comparative Example 3 Comparative Example 3 follows the same preparation process as Example 1, except that in step I of preparing the sodium-ion battery hard carbon paper anode material, a PFI refiner was used for pulping to obtain a pulp with a target freeness of 60 °SR. This pulp was then processed using a wet papermaking process to obtain a base paper with a basis weight of 30 g / m². As shown in Table 1, the anode material prepared in this comparative example has a reversible charging capacity of 310.3 mAh / g and a first-cycle coulombic efficiency of 85.84%.

[0041] Comparative Example 4 Comparative Example 4 follows the same preparation process as Example 1, except that in step I of preparing the sodium-ion battery hard carbon paper anode material, a PFI refiner was used for pulping to obtain a pulp with a target freeness of 92 °SR. This pulp was then processed using a wet papermaking process to obtain a base paper with a basis weight of 30 g / m². As shown in Table 1, the anode material prepared in this comparative example has a reversible charging capacity of 309.2 mAh / g and a first-cycle coulombic efficiency of 89.20%.

[0042] Comparative Example 5 Comparative Example 5 follows the same preparation process as Example 1, except that in step I of preparing the sodium-ion battery hard carbon paper anode material, eucalyptus pulp was used, and the base paper with a basis weight of 30 g / m² was prepared by a wet papermaking process. As shown in Table 1, the anode material prepared in this comparative example has a reversible charging capacity of 306.6 mAh / g and a first-cycle coulombic efficiency of 83.6%.

[0043] Comparative Example 6 Comparative Example 6 follows the same preparation process as Example 1, except that in step I of preparing the sodium-ion battery hard carbon paper anode material, cotton pulp was used, and the paper was prepared with a basis weight of 30 g / m² through a wet papermaking process. As shown in Table 1, the anode material prepared in this comparative example has a reversible charging capacity of 315.2 mAh / g and a first-cycle coulombic efficiency of 86.7%.

[0044] Comparative Example 7 Comparative Example 7 follows the same preparation process as Example 1, except that in step I of preparing the sodium-ion battery hard carbon paper anode material, bamboo pulp was used, and the paper was prepared using a wet papermaking process to obtain a base paper with a basis weight of 30 g / m². As shown in Table 1, the anode material prepared in this comparative example has a reversible charging capacity of 301.4 mAh / g and a first-cycle coulombic efficiency of 88.3%.

[0045] Comparative Example 8 Comparative Example 8 follows the same preparation process as Example 1, except that in step I of preparing the sodium-ion battery hard carbon paper anode material, the pulp used is viscose fiber pulp, which is prepared by a wet papermaking process to obtain a base paper with a basis weight of 30 g / m². As shown in Table 1, the anode material prepared in this comparative example has a reversible charging capacity of 288.6 mAh / g and a first-cycle coulombic efficiency of 79.4%.

[0046] Comparative Example 9 Comparative Example 9 follows the same preparation process as Comparative Example 1, except that the hard carbon paper anode in Comparative Example 1 is ground into powder and then coated onto copper foil to obtain the anode material. As shown in Table 1, the anode material prepared in this comparative example has a reversible charging capacity of 280.2 mAh / g and a first-cycle coulombic efficiency of 86.2%.

[0047] Comparative Example 10 Comparative Example 10 follows the same preparation process as Example 1, except that the hard carbon paper anode from Example 1 is ground into powder and prepared into a conductive paste, which is then coated onto copper foil to obtain the anode material. As shown in Table 1, the anode material prepared in this comparative example has a reversible charging capacity of 277.6 mAh / g and a first-cycle coulombic efficiency of 87.4%.

[0048] Comparative Example 11 Comparative Example 11 follows the same preparation process as Example 2, except that the hard carbon paper anode from Example 2 is ground into powder and prepared into a conductive paste, which is then coated onto copper foil to obtain the anode material. As shown in Table 1, the anode material prepared in this comparative example has a reversible charging capacity of 279.6 mAh / g and a first-cycle coulombic efficiency of 88.0%.

[0049] Comparative Example 12 Comparative Example 12 follows the same preparation process as Example 1, except that in step I of preparing the sodium-ion battery hard carbon paper anode material, the pulp used is straw pulp, which is prepared by a wet papermaking process to obtain a base paper with a basis weight of 30 g / m². As shown in Table 1, the anode material prepared in this comparative example has a reversible charging capacity of 270.1 mAh / g and a first-cycle coulombic efficiency of 75.6%.

[0050] Comparative Example 13 Comparative Example 13 follows the same preparation process as Example 1, except that in step I of preparing the sodium-ion battery hard carbon paper anode material, the pulp used is straw pulp, which is prepared by a wet papermaking process to obtain a base paper with a basis weight of 80 g / m². As shown in Table 1, the anode material prepared in this comparative example has a reversible charging capacity of 286.6 mAh / g and a first-cycle coulombic efficiency of 85.2%.

[0051] Comparative Example 14 Comparative Example 14 follows the same preparation process as Comparative Example 1, except that in step II of preparing the sodium-ion battery hard carbon paper anode material, the temperature was first increased to 300 °C at 2 °C / min and held for 2 h, then increased to 1100 °C at 2 °C / min and held for 3 h, resulting in a sodium-ion battery hard carbon paper anode material. As shown in Table 1, the anode material prepared in this comparative example has a reversible charging capacity of 240.5 mAh / g and a first-cycle coulombic efficiency of 79.2%.

[0052] Comparative Example 15 Comparative Example 15 follows the same preparation process as Comparative Example 1, except that in step II of preparing the sodium-ion battery hard carbon paper anode material, the temperature was first increased to 300 °C at 2 °C / min and held for 2 h, then increased to 1500 °C at 2 °C / min and held for 3 h, resulting in a sodium-ion battery hard carbon paper anode material. As shown in Table 1, the anode material prepared in this comparative example has a reversible charging capacity of 297.2 mAh / g and a first-cycle coulombic efficiency of 86.5%.

[0053] Comparative Example 16 Comparative Example 16 follows the same preparation process as Comparative Example 1, except that in step II of preparing the sodium-ion battery hard carbon paper anode material, the temperature was first increased to 300 °C at 2 °C / min and held for 2 h, then increased to 1300 °C at 2 °C / min and held for 1 h, resulting in a sodium-ion battery hard carbon paper anode material. As shown in Table 1, the anode material prepared in this comparative example has a reversible charging capacity of 279.5 mAh / g and a first-cycle coulombic efficiency of 82.9%.

[0054] Comparative Example 17 Comparative Example 17 follows the same preparation process as Comparative Example 1, except that in step II of preparing the sodium-ion battery hard carbon paper anode material, the temperature was first increased to 300 °C at 2 °C / min and held for 2 h, then increased to 1300 °C at 2 °C / min and held for 5 h, resulting in a sodium-ion battery hard carbon paper anode material. As shown in Table 1, the anode material prepared in this comparative example has a reversible charging capacity of 302.1 mAh / g and a first-cycle coulombic efficiency of 86.7%.

[0055] The negative electrode materials prepared according to the various embodiments and comparative examples of this invention are assembled into sodium-ion batteries. The specific assembly components include the following: a negative electrode shell, negative electrode material, glass fiber separator, sodium sheet, gasket, spring sheet, and positive electrode shell. A 1 mol / L NaPF6 electrolyte is used. The electrochemical performance of the hard carbon paper negative electrode material for sodium-ion batteries is typically tested using a half-cell system with a Newway button cell system.

[0056] Galvanostatic charge-discharge (GCD) testing was conducted on the Xinwei button battery testing system. The test procedure involved discharging followed by charging, with the charge and discharge test currents sequentially set to 0.02 A / g, 0.05 A / g, 0.1 A / g, 0.2 A / g, 0.5 A / g, 1 A / g, 3 A / g, and 0.02 A / g. Five cycles were performed at each current density to obtain the first-cycle charge-discharge curve and rate performance curve of the prepared material. The corresponding cycle stability test was conducted by setting the current density to 1 A / g and performing 2000 cycles.

[0057] X-ray computed tomography (CT) analysis was performed using X-ray computed tomography (CT) technology for three-dimensional imaging analysis. The reconstructed three-dimensional model clearly revealed the complex three-dimensional pore network structure inside the sample.

[0058] Figure 1 The first charge-discharge curves of sodium-ion batteries prepared from hard carbon paper materials with different pore structures after being ground into powder are shown. It can be seen that the reversible capacity (280 mAh / g) and initial efficiency (87%) of the powder electrode are similar, indicating that the properties of the carbon material have not changed, and the performance difference of the hard carbon paper comes from the difference in its pore structure.

[0059] Figure 2The initial charge-discharge curves of sodium-ion batteries prepared with the hard carbon paper anode materials of Comparative Examples 1, 1, and 2 of this invention and the powder anode material prepared in Comparative Example 9 were compared. The figures show that the battery performance of the hard carbon paper anode is superior to that of the powder electrode made of the same material. Furthermore, with the increase of paper basis weight, the reversible capacity increased to 330.4 mAh / g, and the initial efficiency increased to 93.2%. This is because the denser pore structure induces the formation of a uniform and thin SEI film on the surface of the hard carbon paper anode, reducing the energy barrier for electrolyte desolvation and thus improving battery performance. However, the excessively dense pore structure hinders electrolyte wetting, resulting in a decrease in reversible capacity.

[0060] Figure 3 The rate cycle performance of sodium-ion batteries was compared between the hard carbon paper anode materials prepared in Comparative Examples 1, 1, and 2 of this invention and the powder anode material prepared in Comparative Example 9. The figures show that the rate performance of the hard carbon paper anode is superior to that of the powder electrode made of the same material. Furthermore, the rate performance decreases with increasing active mass of the hard carbon paper, especially under high current. The hard carbon paper anode can achieve a balance between reversible capacity and rate performance through structural control.

[0061] Depend on Figure 4 As can be seen from the cycle stability curves, the hard carbon paper anode sodium-ion batteries of Comparative Example 1 and Example 1 still exhibit excellent stability after 2000 cycles at a high current of 1 A / g, with a capacity retention of approximately 97%. Therefore, adjusting the paper basis weight can not only improve the reversible capacity and first-cycle coulombic efficiency of the hard carbon paper anode, but also enable it to maintain excellent capacity retention under high current.

[0062] Depend on Figure 5 As can be seen from the CT three-dimensional network structure, the pores of Example 1 are relatively loose. After adjusting the paper weight, the pore structure of the hard carbon paper becomes more compact.

[0063] Figure 6 The initial charge-discharge curves of sodium-ion batteries using hard carbon paper anode materials prepared in Comparative Examples 1, 2, 3, and 4 of this invention were compared. It can be seen that, under the same paper basis weight, changing the beating degree has a relatively small impact on battery performance. With increasing beating degree, the entanglement of fine fibers increases, resulting in a slight improvement in plateau capacity.

[0064] Figure 7 The diagram shows the hard carbon paper negative electrode of Examples 1 and 5. It can be seen that as the beating degree increases, the hard carbon paper becomes more brittle, while Example 1 with a low beating degree has flexibility and easy processing.

[0065] Figure 8By comparing the specific surface areas of the hard carbon paper anode materials prepared in Comparative Examples 1, 1, and 2 of this invention with the powder anode material prepared in Comparative Example 9, it can be seen that under nitrogen adsorption-desorption, as the paper weight increases, the specific surface area of ​​the hard carbon paper first increases and then decreases, and the pore structure becomes denser. However, excessive density will affect the wettability of the electrolyte and thus affect the battery performance.

[0066] Figure 9 By comparing the true density and closed-cell volume of the hard carbon paper anode material prepared in Comparative Example 1, Example 1, and Example 2 of this invention with the powder anode material prepared in Comparative Example 9, it can be seen that as the paper weight increases, the closed-cell volume of the hard carbon paper first increases and then decreases.

[0067] To better illustrate the differences between the various embodiments and comparative examples, the test results of the embodiments and comparative examples are summarized in Table 1.

[0068] Table 1 Test results of Examples 1-12 and Comparative Examples 1-17

[0069] Analysis of the table shows that: Comparative Examples 5 and 9 show the reversible capacity and first-efficiency of sodium-ion batteries with eucalyptus pulp hard carbon paper anodes at 5 °SR, with capacities of 30 g / m² and 80 g / m². It can be seen that the dense porous structure increases the first-efficiency from 83.6% to 93.5%, while the reversible capacity is slightly improved.

[0070] As can be seen from Comparative Example 6 and Example 10, the initial efficiency of the cotton pulp hard carbon paper negative electrode sodium-ion battery is significantly improved as the pore structure becomes denser. In addition, Comparative Example 7 and Example 11 (bamboo pulp), Comparative Example 8 and Example 12 (viscose fiber pulp), and Comparative Example 12 and Comparative Example 13 (straw pulp) also show the same trend: as the pore structure of the hard carbon paper becomes denser, the first-cycle coulombic efficiency is significantly improved.

[0071] Comparative Examples 14, 1, and 15 show that the reversible capacity and first-cycle coulombic efficiency initially increase and then decrease with increasing carbonization temperature. Comparative Examples 16, 1, and 17 also show that the reversible capacity and first-cycle coulombic efficiency initially increase and then decrease with increasing holding time. The carbonization temperature and holding time affect the degree of carbon graphitization. A low degree of graphitization increases defects and provides more sodium adsorption sites, leading to lower coulombic efficiency. A high degree of graphitization results in denser carbon interlayer spacing, hindering interlayer insertion of sodium ions and reducing adsorption sites. Therefore, the optimal carbonization temperature is 1300 ℃, and the holding time is 3 h.

[0072] This invention covers wood, bamboo, and straw pulps; classified by forest tree properties, it covers coniferous wood pulp (pine pulp) and hardwood pulp (eucalyptus pulp); classified by fiber length, it covers long fibers (cotton pulp) and short fibers; classified by fiber properties, it covers regenerated cellulose (viscose fiber) and natural cellulose. Therefore, this invention relates to a wide range of papermaking fibers, and through the same pore structure control, the first-cycle coulombic efficiency and reversible capacity of the hard carbon paper anode sodium-ion battery are significantly improved, highlighting the universality of this invention. The large-scale production process of pulp papermaking is simple, green, and efficient. The resulting hard carbon paper anode has stable and controllable pores. The obtained hard carbon paper anode does not need to be coated on the current collector, nor does it require the addition of any binders or conductive agents. The integrated structure significantly reduces production costs.

[0073] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing sodium-ion battery hard carbon paper anode material based on papermaking process control, characterized in that, Includes the following steps: (I) After the pine pulp fibers are loosened, they are pulped using a PFI refiner, with the refining linear pressure controlled at 3.33 N / m and the refining speed of the PFI refiner ranging from 0 to 30,000 rpm, to obtain a pulp with a freeness of 5 °SR. The obtained pulp is then mixed and loosened again, and prepared using a wet papermaking process to obtain a basis weight of 80 g / m³. 2 The base paper; (II) The base paper is subjected to high-temperature carbonization under a protective atmosphere. The carbonization process adopts a two-stage heating program: first, the temperature is raised to 300℃ at 2℃ / min and held for 2 hours, and then the temperature is raised to 1300℃ at 2℃ / min and held for 3 hours to obtain a self-supporting hard carbon paper anode material.

2. The preparation method according to claim 1, characterized in that, In step (II), the protective atmosphere is one or a mixture of nitrogen and argon.

3. A hard carbon paper anode material for sodium-ion batteries, characterized in that, It is prepared by the preparation method described in claim 1 or 2.

4. A sodium-ion battery, characterized in that, Its negative electrode is the sodium-ion battery hard carbon paper negative electrode material as described in claim 3.

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