A self-supporting porous carbon current collector, a preparation method thereof and application thereof in lithium-sulfur batteries

Abstract

The present application relates to the technical field of lithium-sulfur batteries, and particularly relates to a self-supporting porous carbon current collector, a preparation method thereof and application thereof in lithium-sulfur batteries. A non-woven fabric or melamine sponge is used as a macroporous matrix framework, a precursor solution containing PAN and PVP is filled into the matrix pores, non-solvent induced phase separation is performed, a pore-forming agent is removed by water washing, cobalt salt is impregnated, and high-temperature carbonization treatment is performed in an inert atmosphere to obtain the self-supporting porous carbon current collector. The self-supporting porous carbon current collector has good electrical conductivity and mechanical stability, can maintain structural integrity, has a high effective deposition area and porosity, is used in a lithium-sulfur battery positive electrode, can reduce the amount of electrolyte while achieving high sulfur loading, and can improve electrode structural stability and electrochemical reaction kinetics, thereby improving the cycle stability and rate performance of the lithium-sulfur battery.

Description

Technical Field

[0001] This invention relates to the field of lithium-sulfur battery technology, and more specifically, to a self-supporting porous carbon current collector, its preparation method, and its application in lithium-sulfur batteries. Background Technology

[0002] Lithium-sulfur batteries are considered an important direction for the development of next-generation rechargeable batteries due to their advantages such as high theoretical specific capacity (1675 mAh / g) and high theoretical specific energy density (2600 Wh / kg). However, lithium-sulfur batteries still face many key technical challenges in practical applications, which seriously restricts their commercialization process.

[0003] First, sulfur and its discharge product, lithium sulfide (Li₂S / Li₂S₂), have low conductivity, leading to slow electrode reaction kinetics and limited utilization of active materials. Second, the polysulfide intermediates formed during charge and discharge are easily soluble in the electrolyte and exhibit a "shuttle effect," causing capacity decay and reduced coulombic efficiency. Furthermore, under high sulfur loading conditions, lithium sulfide deposition typically occurs in limited conductive surface areas, easily forming localized accumulation and passivation layers, further limiting electrode reactivity. Simultaneously, traditional coated cathode structures usually use metal foils such as aluminum foil as current collectors, with the electrode active material coated on their surface. This structure has a limited deposition interface, making it difficult to provide sufficient space for lithium sulfide deposition, which is detrimental to achieving high areal capacity and high sulfur loading. To ensure ion transport and electrode wetting, a high electrolyte volume is often required, thus reducing the actual energy density of the battery.

[0004] In recent years, researchers have attempted to use materials such as metal foam, carbon cloth, and porous carbon as current collectors to increase the loading of active materials and the deposition interface. However, the improvement in electrochemical performance has been unsatisfactory, and stable cycling is difficult to achieve under conditions of high sulfur loading and low electrolyte usage.

[0005] In view of this, the present invention is hereby proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a self-supporting porous carbon current collector, its preparation method, and its application in lithium-sulfur batteries. The self-supporting porous carbon current collector has good mechanical stability, can maintain structural integrity, and has sufficient deposition area and conductivity. It can effectively improve the sulfur loading capacity, promote uniform deposition of lithium sulfide, reduce electrolyte consumption, and thus improve the overall electrochemical performance and actual energy density of lithium-sulfur batteries.

[0007] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: A method for preparing a self-supporting porous carbon current collector includes the following steps: S1. Polyacrylonitrile and polyvinylpyrrolidone are dissolved in N,N-dimethylformamide to prepare a precursor solution; the precursor solution is loaded onto a sheet-like porous matrix material. S2. The porous matrix material loaded with the precursor solution is immersed in deionized water for phase separation, and then dried to obtain composite sheet material A; S3. The composite sheet material A is washed to remove the polyvinylpyrrolidone, and then dried to obtain the composite sheet material B; S4. The composite sheet material B is impregnated in a cobalt salt solution and then dried to obtain the composite sheet material C; S5. The composite sheet material C is carbonized under an inert atmosphere to obtain the self-supporting porous carbon current collector.

[0008] Preferably, in the precursor solution, the mass ratio of the polyacrylonitrile to the polyvinylpyrrolidone is 1:1 to 2.5:1.

[0009] Preferably, the total concentration of the polyacrylonitrile and the polyvinylpyrrolidone in the precursor solution is 100~200 mg / mL.

[0010] Preferably, the porous matrix material includes nonwoven fabric or melamine sponge.

[0011] Preferably, in step S1, the loading amount of the precursor solution in the porous matrix material is 6~10 mL / 100 cm³. 2 .

[0012] Preferably, in step S2, the time for immersion in deionized water for phase separation is 2-4 hours.

[0013] Preferably, in step S3, deionized water is used for washing.

[0014] Preferably, in step S4, the concentration of the cobalt salt solution is 10~40 mg / mL.

[0015] Preferably, in step S5, the carbonization temperature is 700~900℃, the heating rate is 2~8℃ / min, and the carbonization time is 1~3h.

[0016] A self-supporting porous carbon current collector is prepared using the method described in any of the preceding embodiments, wherein the cumulative pore volume of the self-supporting porous carbon current collector is 0.18~0.60 cm³. 3 g -1 Furthermore, the pore volume of macropores accounts for 20% to 78%, of which the pore volume of pores with a diameter of 280 to 1000 nm accounts for 10% to 70%.

[0017] A lithium-sulfur battery cathode includes the self-supporting porous carbon current collector described in the foregoing embodiments.

[0018] A lithium-sulfur battery, comprising the lithium-sulfur battery positive electrode described in the foregoing embodiments.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: The self-supporting porous carbon current collector provided by this invention possesses a rich pore structure, high cumulative pore volume, and a pore volume ratio of macropores (>50 nm) of 20%-78%. Specifically, the pore volume ratio of macropores (280-1000 nm) in its pore structure is 10%-70%, providing abundant ion / electron channels and an effective deposition surface. This significantly accelerates the conversion of liquid polysulfides to solid lithium sulfide, improving electrochemical performance. Furthermore, the preparation process is simple; the pore structure of the porous current collector can be controlled by adjusting the concentration of the precursor solution and the mass ratio of polyacrylonitrile and polyvinylpyrrolidone. This ensures good electrochemical performance, increases sulfur loading, and reduces electrolyte usage, thereby achieving a high energy density. Attached Figure Description

[0020] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0021] Figure 1 Optical images of the self-supporting porous carbon current collector (DPP-HPC-3) prepared in Example 3 of the present invention and the porous carbon (HPC) prepared in Comparative Example 2; Figure 2 SEM images of the self-supporting porous carbon current collector (DPP-HPC-3) prepared in Example 3, the self-supporting porous carbon current collector (MS-HPC) prepared in Example 5, and the self-supporting carbon fiber current collector (DPP) prepared in Comparative Example 1. Figure 3 TEM image of the DPP-HPC-3 current collector prepared in Example 3 of this invention; Figure 4 The XRD patterns of the DPP-HPC-3 current collector prepared in Example 3 of the present invention and the DPP current collector prepared in Comparative Example 1 are shown below. Figure 5 The bar chart shows the cumulative pore volume and pore volume ratio of different pore sizes of the current collectors prepared in Examples 1-4 and Comparative Example 1 of this invention. Figure 6The rate performance of lithium-sulfur batteries assembled with current collectors prepared in Examples 1-4 and Comparative Examples 1-2 of this invention at different current densities; Figure 7 The cycling performance of lithium-sulfur batteries assembled with current collectors prepared in Examples 1-4 and Comparative Examples 1-2 of this invention at a current density of 0.5 C is shown. Figure 8 This is a cycle performance diagram of the DPP-HPC-3 current collector used in a high-load lithium-sulfur battery in Embodiment 3 of the present invention; Figure 9 This is a cycle performance diagram of the MS-HPC current collector used in a high-load lithium-sulfur battery in Embodiment 5 of the present invention. Detailed Implementation

[0022] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0023] The first aspect of the present invention provides a method for preparing a self-supporting porous carbon current collector, comprising the following steps: S1. Polyacrylonitrile (PAN) and polyvinylpyrrolidone (PVP) are dissolved in N,N-dimethylformamide (DMF) to prepare a precursor solution; the precursor solution is loaded onto a sheet-like porous matrix material so that the precursor solution fills the pores of the porous matrix material. S2. The porous matrix material loaded with the precursor solution is immersed in deionized water for phase separation, and then dried to obtain composite sheet material A. The purpose of this step is to use the exchange between the solvent and the non-solvent to cause phase separation in the system. The PAN-enriched phase solidifies to form a continuous skeleton, while the PAN-depleted phase forms a porous structure in the subsequent washing and drying. S3. Wash the composite sheet material A to remove polyvinylpyrrolidone, and dry it to obtain the composite sheet material B; the purpose of this step is to wash away the pore-forming agent PVP and form a more abundant pore structure. S4. After impregnating the composite sheet material B in a cobalt salt solution, remove and dry it to obtain the composite sheet material C; introduce metallic cobalt into the porous carbon framework by the impregnation method; S5. The composite sheet material C is carbonized under an inert atmosphere to obtain a self-supporting porous carbon current collector.

[0024] This invention provides a method for preparing a self-supporting porous carbon current collector based on a pore-filling strategy. Using a porous substrate as a macroporous matrix framework, a precursor solution containing PAN and PVP is filled into the pores of the matrix. Following solvent-induced phase separation, water washing to remove the pore-forming agent, cobalt salt impregnation, and high-temperature carbonization under an inert atmosphere, a self-supporting porous carbon current collector with a continuous conductive network and a hierarchical pore structure is constructed. The porous matrix material acts as a carrier for the porous carbon phase, providing support for the overall structure and ensuring the material remains intact after carbonization. The porous carbon phase has a high effective deposition area and porosity, enabling high sulfur loading while reducing electrolyte consumption and improving electrode structural stability and electrochemical reaction kinetics, thereby improving the cycle stability and rate performance of lithium-sulfur batteries. The combined effect of the two components provides a volume buffer space and sufficient lithium sulfide deposition surface, while the porous matrix network shortens the electron transport path and accelerates charge transfer. This synergistic effect contributes to achieving high discharge capacity and excellent rate performance.

[0025] The method of this invention is simple, with adjustable porosity. The resulting current collector has a rich pore structure, high cumulative pore volume, and a pore volume ratio of macropores (>50nm) of 20%-78%, of which the pore volume ratio of macropores (280~1000nm) is 10%~70%. It can provide abundant ion / electron channels and an effective deposition surface, and provide sufficient buffer space for volume expansion, significantly accelerating the conversion of liquid polysulfides to solid lithium sulfide. While ensuring good electrochemical performance and increasing sulfur loading, it can also reduce the amount of electrolyte used and achieve high energy density. It can be used as a positive electrode current collector in lithium-sulfur batteries with poor electrolyte. By loading sulfur-containing slurry inside it to construct a positive electrode structure, the stability of the electrode structure and electrochemical performance can be improved.

[0026] In some specific embodiments of the present invention, the mass ratio of polyacrylonitrile and polyvinylpyrrolidone in the precursor solution is 1:1 to 2.5:1. For example, it can be any one value or a range of any two values ​​from 1:1, 1.5:1, 2:1, 2.5:1.

[0027] In some specific embodiments of the present invention, the total concentration of polyacrylonitrile and polyvinylpyrrolidone in the precursor solution is 100~200 mg / mL. For example, it can be any one value or a range of any two values ​​among 100 mg / mL, 125 mg / mL, 150 mg / mL, 175 mg / mL, and 200 mg / mL.

[0028] In some specific embodiments of the present invention, the porous matrix material includes nonwoven fabric or melamine sponge.

[0029] In some specific embodiments of the present invention, the loading amount of the precursor solution in the porous matrix material in step S1 is 6~10 mL / 100 cm³. 2 For example, it can be 6mL / 100cm 2 7mL / 100cm 2 8mL / 100cm 2 9mL / 100cm 2 10mL / 100cm 2 The range of values ​​consisting of any one point value or any two point values.

[0030] In some specific embodiments of the present invention, the method of loading the precursor solution onto the porous material matrix in step S1 includes: laying the porous matrix material flat on a glass plate and fixing it, pouring the precursor solution onto the porous matrix material, and uniformly coating it onto the surface of the matrix material using a coating machine.

[0031] In some specific embodiments of the present invention, in step S2, the time for immersion in deionized water for phase separation is 2 to 4 hours. For example, it can be any one value or a range of any two values ​​among 2 hours, 2.5 hours, 3 hours, 3.5 hours, and 4 hours.

[0032] In some specific embodiments of the present invention, in step S3, deionized water is used for washing to remove the pore-forming agent PVP.

[0033] In some specific embodiments of the present invention, in step S4, the concentration of the cobalt salt solution is 10~40 mg / mL. For example, it can be any one value or a range of any two values ​​among 10 mg / mL, 20 mg / mL, 30 mg / mL, and 40 mg / mL.

[0034] In some specific embodiments of the present invention, the purpose of drying in steps S2-S4 is to remove the solvent. The specific drying conditions are not limited, as long as the solvent can be removed.

[0035] In some specific embodiments of the present invention, the carbonization temperature in step S5 is 700~900℃, for example, it can be any one value or a range of any two values ​​among 700℃, 750℃, 800℃, 850℃, and 900℃; the heating rate is 2~8℃ / min, for example, it can be any one value or a range of any two values ​​among 2℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, and 8℃ / min; the carbonization time is 1~3h, for example, it can be any one value or a range of any two values ​​among 1h, 1.5h, 2h, 2.5h, and 3h.

[0036] A second aspect of the present invention provides a self-supporting porous carbon current collector, prepared by the method described in any of the foregoing embodiments, wherein the cumulative pore volume of the obtained self-supporting porous carbon current collector is 0.18~0.60 cm³. 3 g -1 For example, it can be 0.18cm 3 g -1 0.3cm 3 g -1 0.43cm 3 g -1 0.56cm 3 g -1 0.60cm 3 g -1 The value is any one point value or a range of any two point values; preferably 0.43~0.60cm. 3 g -1 Furthermore, a selection of 0.56~0.60cm is preferred. 3 g -1 Furthermore, the pore volume ratio of macropores (>50 nm) is 20%~78%, for example, it can be any single value or a range of any two values ​​from 20%, 34%, 50%, 60%, 70%, 78%; preferably 70%~78%. The pore volume ratio of pores from 280~1000 nm is 10%~70%, for example, it can be any single value or a range of any two values ​​from 10%, 16%, 33%, 50%, 60%, 68%, 70%, preferably 60%-68%. According to porous electrode theory, pore structure has a significant impact on lithium sulfide deposition. During discharge, solid products tend to deposit at the openings of micropores, clogging them and causing severe polarization. Macropores can provide an effective deposition surface for Li₂S deposition, helping to reduce the thickness of deposited Li₂S, which is of great significance for mass transfer. The cumulative pore volume is controlled at 0.56~0.60 cm⁻¹. 3 g -1The proportion of macropores is controlled at 70%~80%, and the proportion of 280~1000nm macropores is controlled at 60%~68%. This can effectively alleviate volume expansion during charging and discharging, while providing sufficient specific surface area to achieve high capacity. If the proportion of macropores is too low, it cannot effectively alleviate volume expansion; if the proportion of macropores is too high, the specific surface area will decrease, failing to provide sufficient effective deposition surface, and intermediate polysulfides will more easily migrate to the negative electrode, causing loss of active material.

[0037] A third aspect of the present invention provides a lithium-sulfur battery cathode comprising the self-supporting porous carbon current collector described in the foregoing embodiments. As an example, the lithium-sulfur battery cathode is prepared by dropping a sulfur-containing slurry onto the self-supporting porous carbon current collector.

[0038] A fourth aspect of the present invention provides a lithium-sulfur battery, including the lithium-sulfur battery positive electrode described in the foregoing embodiments. As an example, the lithium-sulfur battery is a lean-electrolyte lithium-sulfur battery.

[0039] The following detailed description of some embodiments of the present invention is provided in conjunction with specific examples. Unless otherwise specified, all raw materials used in the embodiments can be purchased commercially. In the embodiments and comparative examples, the nonwoven fabric used was manufactured by Zhejiang Yuhong Daily Necessities Co., Ltd., with a specification of 20cm × 20cm; the melamine sponge was manufactured by Henan Langcui Technology Co., Ltd., with a density of 9.5 kg / m³. 3 .

[0040] Example 1 This embodiment provides a method for preparing a self-supporting porous carbon current collector, including the following steps: S1. Dissolve PAN and PVP in DMF at a mass ratio of 1:1 to obtain a homogeneous precursor solution with a total concentration of PAN and PVP of 100 mg / mL. Dry the nonwoven fabric and lay it flat on a glass plate, fixing it with tape. Apply 8 mL / 100 cm³ of the solution. 2 The loading amount of the precursor solution was poured onto the nonwoven fabric and coated evenly on the surface of the nonwoven fabric using a coating machine. The total thickness after coating was approximately 1000 μm. S2. Immerse the nonwoven fabric coated with the precursor solution in deionized water for 3 hours, then remove it and dry it in an oven to obtain composite sheet material A. S3. Use deionized water to wash composite sheet material A to remove PVP, and then put it in an oven to dry to obtain composite sheet material B; S4. Dissolve cobalt acetate in deionized water to form a cobalt salt solution with a concentration of 10 mg / mL. Immerse composite sheet material B in the cobalt salt solution for 10 min, remove it and dry it in an oven to obtain composite sheet material C. S5. The composite sheet material C is placed in a tube furnace for heat treatment (carbonization). The heat treatment temperature is 800℃, the heating rate is 5℃ / min, the heat treatment time is 2 h, the heat treatment atmosphere is argon, and after natural cooling, a self-supporting porous carbon current collector is obtained, denoted as DPP-HPC-1.

[0041] Example 2 Example 2 is similar to Example 1, except that the total concentration of PAN and PVP in the precursor solution is 200 mg / mL; all other conditions are the same as in Example 1, and the resulting product is designated as DPP-HPC-2.

[0042] Example 3 Example 3 is similar to Example 1, except that the total concentration of PAN and PVP in the precursor solution is 125 mg / mL and the mass ratio of PAN to PVP is 3:2; all other conditions are the same as in Example 1, and the resulting product is denoted as DPP-HPC-3.

[0043] Example 4 Example 4 is similar to Example 1, except that the total concentration of PAN and PVP in the precursor solution is 105 mg / mL and the mass ratio of PAN to PVP is 5:2; all other conditions are the same as in Example 1, and the resulting product is designated as DPP-HPC-4.

[0044] Example 5 Example 5 is similar to Example 1, except that the macroporous matrix is ​​replaced with melamine sponge instead of nonwoven fabric, the total concentration of PAN and PVP in the precursor solution is 125 mg / mL, and the mass ratio of PAN to PVP is 3:2; all other conditions are the same as in Example 1, and the resulting product is denoted as MS-HPC.

[0045] Comparative Example 1 Comparative Example 1 is similar to Example 1, except that: no precursor solution is used to fill the nonwoven fabric; all other conditions are the same as in Example 1, and the resulting product is denoted as DPP.

[0046] Comparative Example 2 Comparative Example 2 is similar to Example 3, except that: no nonwoven fabric matrix is ​​used, and the precursor solution is coated on a glass plate to prepare a sheet material; all other conditions are the same as in Example 3, and the resulting product is denoted as HPC.

[0047] Test case 1. Product Structure Characterization The current collector products prepared in the examples and comparative examples were tested by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD).

[0048] Figure 1 Images a and b are optical images of HPC in Comparative Example 2 and DPP-HPC-3 in Example 3, respectively. It can be seen that Example 3 can be cut into 12 mm diameter discs without breaking, exhibiting good mechanical stability and integrity. In contrast, Comparative Example 2, lacking the support of nonwoven fibers, is extremely prone to breakage during carbonization and cutting, making it unsuitable as a positive electrode current collector for battery assembly.

[0049] like Figure 2 As shown in Figures a and b, the DPP current collector in Comparative Example 1 exhibits a distinct three-dimensional interwoven fiber network structure. The fibers are intertwined to form a continuous skeleton, resulting in a loose overall structure with large pore spaces. The fiber diameter is approximately 7–8 μm, and the rough, porous surface is beneficial for increasing the specific surface area and exposing active sites. Figure 2 Figures c and d show the DPP-HPC-3 current collector prepared in Example 3. It can be observed that the fiber network is filled with a continuous porous carbon phase, exhibiting a composite structure of a three-dimensional interwoven network and a sponge-like porous structure. The fiber network originates from the carbonized nonwoven fabric, while the continuous porous carbon phase originates from the non-solvent-induced phase separation of the filled precursor solution and the skeleton formed after carbonization. The continuous porous carbon phase exhibits a typical sponge-like porous structure with smooth pore walls and interconnected channels. The pore size is mainly in the submicron to micron scale, belonging to an open-pore structure, indicating that the material has high porosity and good electrolyte wetting and ion transport channels. Figure 2 Figures e and f show the MS-HPC current collector prepared in Example 5. The melamine sponge skeleton has a relatively fine mesh structure, and the porous carbon phase is attached to and connected to its surface, forming a continuous composite porous network structure. After the introduction of the porous carbon phase, its pore structure changes significantly, the pore structure becomes more abundant, and the specific surface area is significantly increased.

[0050] Figure 3 The image shows a TEM image of the DPP-HPC-3 current collector in Example 3. The results show that cobalt metal particles are uniformly distributed in the porous carbon current collector, and the metal particles are tightly bonded to the carbon matrix. The cobalt metal particles have clear lattice fringes with a crystal plane spacing of approximately 0.204 nm, corresponding to the Co(111) crystal plane of Co, proving that the particles have a good crystal structure.

[0051] Depend on Figure 4 The XRD patterns show that the current collector samples in Example 3 and Comparative Example 1 both exhibit broad diffuse peaks, corresponding to the (002) plane of the carbon material, indicating that the material is mainly amorphous or weakly graphitized. Obvious diffraction peaks can be observed near 44° and 51°, corresponding to the (111) and (200) crystal planes of metallic Co, indicating that there is a crystalline metallic Co phase in the sample.

[0052] 2. Characterization of pore structure The pore structure of the current collectors in Examples 1-4 and Comparative Example 1 was characterized by nitrogen adsorption-desorption combined with mercury intrusion porosimetry. In Comparative Example 1, the pore structure of the DPP current collector was tested, which was the pore structure of the fiber itself, rather than the pores formed by the interweaving of fibers. from Figure 5 It can be observed that the pore structure can be controlled by adjusting the concentration of the precursor solution and the ratio of PAN to PVP. The DPP-HPC-3 sample showed a significantly higher proportion of macropores (78%) and macropores in the 280-1000 nm range (68%) compared to the other samples, followed by the DPP-HPC-4 sample; both also exhibited high cumulative pore volumes. In the other samples, micropores (0-2 nm) and mesopores (2-50 nm) contributed more to the pore volume, while the pore volume decreased.

[0053] 3. Electrochemical performance testing Battery assembly: 1) The self-supporting porous carbon current collectors prepared in each embodiment and comparative example were cut to a size of 1.13 cm. 2 ; 2) Mix sulfur powder and conductive carbon black evenly at a mass ratio of 8:1 and place them in a hydrothermal reactor filled with argon. Heat to 155℃ and keep warm for 12 hours to obtain mixture I; mix mixture I and polyvinylidene fluoride evenly at a mass ratio of 9:1 to obtain mixture II. 3) Add mixture II to N-methylpyrrolidone and stir for 12 h to obtain solution I; place the cut current collector on a wire mesh, add solution I dropwise on the surface of the current collector, and transfer it to an oven at 50°C to dry for 24 h to obtain the positive electrode of the lithium-sulfur battery; For low-load lithium-sulfur batteries: the concentration of solution I is 50 mg / mL, the amount of solution I added to the current collector surface is 30 μL, and the surface loading of sulfur in each positive electrode is approximately 1.1 mg / cm². 2 ; For high-load lithium-sulfur batteries: when the concentration of solution I is 113 mg / mL and the amount of solution I added to the surface of the current collector is 60 μL, the sulfur surface loading in each positive electrode is approximately 6 mg / cm². 2 When the addition volume is 80 μL, the sulfur surface loading in each positive electrode is approximately 8 mg / cm³. 2 ; 4) Assemble lithium-sulfur batteries using the above-described positive electrode. Assemble CR 2025 button batteries in an argon-filled glove box, following the order of assembly: positive electrode shell, positive electrode sheet, electrolyte, separator, negative electrode sheet, gasket, spring sheet, and negative electrode shell. The electrolyte is a 1:1 solution of 1,3-dioxolane (DOL) and dimethyl ethylene glycol (DME) containing 1 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and 2 wt.% lithium nitrate (LiNO3), with a volume ratio of 45 μL. The positive electrode sheet is obtained by drop-feeding a sulfur-containing suspension onto a carbon-based current collector. The separator is a 19 mm thick polypropylene separator (PP, Celgard 2500). The negative electrode sheet is a 15.6 mm diameter battery-grade lithium metal sheet.

[0054] Figure 6 The rate performance of low-load lithium-sulfur batteries assembled with current collectors in different embodiments and comparative examples is shown. In Example 3, the battery assembled with DPP-HPC-3 current collector has a discharge specific capacity of 1411.9 mAh / g, 1285.3 mAh / g, 1177.2 mAh / g, 1112.5 mAh / g, and 1031.2 mAh / g at current rates of 0.1, 0.2, 0.5, 1C, and 2C, respectively, and recovers to 1171.1 mAh / g when returning to 0.5C. It maintains a high capacity level at different rates and exhibits superior rate performance, especially at 2C, where the capacity is much higher than the other samples, indicating that it has superior electron transport and lithium-ion transport capabilities.

[0055] Figure 7 The surface loading of the current collector assembly in different embodiments and comparative examples is 1.1 mg / cm². 2 The cycling performance of lithium-sulfur batteries at a current density of 0.5 C was compared. In Example 3, the battery assembled with DPP-HPC-3 current collector had an initial discharge capacity of 1135 mAh / g, which remained at 1004 mAh / g after 100 cycles. In contrast, the battery assembled with DPP current collector in Comparative Example 1 had an initial discharge capacity of only 608 mAh / g, which remained at 497 mAh / g after 100 cycles. This indicates that porous carbon current collectors with high cumulative pore volume and a high proportion of macropores in the 280-1000 nm range have a significant effect on improving electrochemical performance.

[0056] Figure 8 The areal loading of the DPP-HPC-3 current collector assembly in Example 3 is 8 mg / cm². 2The cycling performance of the lithium-sulfur battery at a current density of 0.05C was analyzed. It can be seen that even under high sulfur load, by reducing the electrolyte dosage to 5 μL / mg sulfur, the DPP-HPC-3 battery still achieves a high specific capacity of 1067.2 mAh / g and maintains stable cycling for 80 cycles. This indicates that pore size adjustment can effectively reduce the electrolyte dosage, thereby improving the energy density of the lithium-sulfur battery.

[0057] Figure 9 The areal loading of the MS-HPC current collector assembly in Example 5 was 6 mg / cm². 2 The cycling performance of the lithium-sulfur battery at a current density of 0.1 C was observed. It can be seen that the battery exhibits a high initial discharge capacity (1393.1 mAh / g) and a coulombic efficiency close to 100%, indicating good reaction reversibility. The excellent electrochemical performance of the melamine sponge composite current collector battery under high load conditions demonstrates that the three-dimensional conductive framework and porous carbon composite structure can effectively promote electron / ion transport and provide sufficient reaction interfaces for polysulfide conversion, confirming the universality of the pore-filling strategy.

[0058] In summary, the self-supporting porous carbon current collector prepared by the pore-filling strategy of this invention can have its pore size distribution controlled by adjusting the solution concentration and the ratio of PAN to PVP, and the cumulative pore volume is 0.56~0.60 cm³. 3 g -1 Samples with a pore volume ratio of 70%~80% for macropores (>50nm) and 60%-68% for macropores of 280-1000nm exhibit superior electron transport and lithium-ion transport capabilities, and have higher specific capacity under high sulfur loading and low electrolyte usage conditions.

[0059] Although the present invention has been illustrated and described with specific embodiments, it should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and scope of the present invention; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention; therefore, this means that all such substitutions and modifications that fall within the scope of the present invention are included in the appended claims.

Claims

1. A method for preparing a self-supporting porous carbon current collector, characterized in that, Includes the following steps: S1. Polyacrylonitrile and polyvinylpyrrolidone are dissolved in N,N-dimethylformamide to prepare a precursor solution; the precursor solution is loaded onto a sheet-like porous matrix material. S2. The porous matrix material loaded with the precursor solution is immersed in deionized water for phase separation, and then dried to obtain composite sheet material A; S3. The composite sheet material A is washed to remove the polyvinylpyrrolidone, and then dried to obtain the composite sheet material B; S4. The composite sheet material B is impregnated in a cobalt salt solution and then dried to obtain the composite sheet material C; S5. The composite sheet material C is carbonized under an inert atmosphere to obtain the self-supporting porous carbon current collector.

2. The method for preparing a self-supporting porous carbon current collector according to claim 1, characterized in that, In the precursor solution, the mass ratio of the polyacrylonitrile to the polyvinylpyrrolidone is 1:1 to 2.5:

1.

3. The method for preparing a self-supporting porous carbon current collector according to claim 1 or 2, characterized in that, In the precursor solution, the total concentration of the polyacrylonitrile and the polyvinylpyrrolidone is 100~200 mg / mL.

4. The method for preparing a self-supporting porous carbon current collector according to claim 1, characterized in that, The porous matrix material includes nonwoven fabric or melamine sponge.

5. The method for preparing a self-supporting porous carbon current collector according to claim 1, characterized in that, In step S1, the loading amount of the precursor solution in the porous matrix material is 6~10 mL / 100 cm³. 2 .

6. The method for preparing a self-supporting porous carbon current collector according to claim 1, characterized in that, It meets at least one of the following characteristics: (1) In step S2, the time for immersion in deionized water to carry out the phase separation is 2-4 hours; (2) In step S3, deionized water is used for washing; (3) In step S4, the concentration of the cobalt salt solution is 10~40 mg / mL.

7. The method for preparing a self-supporting porous carbon current collector according to claim 1, characterized in that, In step S5, the carbonization temperature is 700~900℃, the heating rate is 2~8℃ / min, and the carbonization time is 1~3h.

8. A self-supporting porous carbon current collector, characterized in that, The self-supporting porous carbon current collector is prepared by the method described in any one of claims 1 to 7, wherein the cumulative pore volume of the self-supporting porous carbon current collector is 0.18 to 0.60 cm³. 3 g -1 Furthermore, the pore volume of macropores accounts for 20% to 78%, of which the pore volume of pores with a diameter of 280 to 1000 nm accounts for 10% to 70%.

9. A lithium-sulfur battery cathode, characterized in that, Includes the self-supporting porous carbon current collector as described in claim 8.

10. A lithium-sulfur battery, characterized in that, Includes the lithium-sulfur battery cathode as described in claim 9.

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