High-load sulfur positive electrode for high-performance lithium-sulfur battery and preparation method of high-load sulfur positive electrode

Abstract

The invention discloses a high-load sulfur positive plate for a high-performance lithium-sulfur battery and a preparation and modification method of the high-load sulfur positive plate. The active material of the positive plate is sulfurized polyacrylonitrile (SPAN), and the surface of the positive plate is subjected to laser etching treatment with specific power to form a porous structure. The preparation method comprises the following steps: preparing SPAN, a binder and a conductive agent into a slurry according to a specific ratio, and after coating and drying, etching the surface of the electrode by using 1.5-6W laser. According to the invention, the regular micron-sized grooves are created in the surface of the positive plate through laser etching, and the patterned structure effectively enhances electrolyte infiltration, improves charge transfer dynamics and relieves stress accumulation in the charge-discharge process, so that the structural stability and cycle performance of the electrode under high sulfur loading capacity are remarkably improved. The method is simple in process and low in cost, and an effective scheme is provided for preparing the high-performance and high-load lithium-sulfur battery.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical technology, specifically relating to a high-capacity lithium-sulfur battery cathode and its preparation method. Background Technology

[0002] Energy is a crucial foundation for the survival and development of human society. With the increase in global population and the continuous development of various countries, the consumption of non-renewable energy is increasing, and the demand for energy storage systems from the emerging consumer electronics industry is also growing. Using sulfur as the cathode material, its theoretical specific capacity reaches 1675 mAh g-1, far exceeding that of traditional lithium-ion batteries. (Yan J, Li W, Wang R, et al. An in Situ Prepared Covalent Sulfur–Carbon Composite Electrode for High-Performance Room-Temperature Sodium–Sulfur Batteries [J].ACS Energy Letters, 2020, 5(4): 1307~1315). Furthermore, sulfur used in sulfur cathodes is abundant in the Earth's crust and inexpensive, which can greatly reduce costs. Considering the influence of other inactive components such as current collectors, electrolytes, and conductive agents, the actual energy density of lithium-sulfur batteries can also reach 600 Wh kg-1, which is far higher than that of existing lithium-ion batteries on the market.

[0003] Currently, lithium-sulfur batteries still face several limitations in their practical application: 1) Shuttle effect: During battery discharge, elemental sulfur on the positive electrode carbon material is reduced and combines with lithium ions in the electrolyte, transforming into lithium polysulfides (LiPS). Some LiPS detach from the positive electrode material and dissolve in the electrolyte, then migrate through the separator to the negative electrode and react with lithium, resulting in the loss of active material; 2) Poor conductivity of sulfur, Li2S2, and Li2S. The conductivity of elemental sulfur and Li2S at room temperature is 5 × 10⁻³⁰ S cm⁻¹ and 3.6 × 10⁻⁷ S cm⁻¹, respectively; 3) Volume effect. The densities of elemental sulfur and its discharge end product Li2S are 2.03 g cm⁻³ and 1.66 g cm⁻³, respectively. As the battery charges and discharges, the volume of the electrode system changes continuously with the reaction, leading to reduced contact between the active and conductive materials, and even peeling off of the active material, thus damaging the electrode structure.

[0004] While existing cathodes have shown some effectiveness through modifications to carbon materials (such as porous carbon) or the introduction of catalysts, they suffer from drawbacks such as complex processes, high costs, and poor compatibility. Therefore, a simple and efficient method is urgently needed to achieve stable cycling in batteries (especially under high load conditions) without posing safety hazards. Summary of the Invention

[0005] The purpose of this invention is to overcome the technical problems of unstable electrode structure and slow charge transport dynamics in high-capacity lithium-sulfur battery cathodes during cycling, and to provide a high-capacity lithium-sulfur battery with excellent cycle stability. The key is to provide a cathode sheet that has undergone laser surface modification.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A high-capacity lithium-sulfur battery includes a positive electrode, a lithium negative electrode, a separator, and an electrolyte. The active material of the positive electrode is sulfurized polyacrylonitrile (SPAN), and the surface of the active material layer of the positive electrode is laser-etched to form a patterned microstructure.

[0008] Furthermore, the positive electrode is prepared by the following method: vulcanized polyacrylonitrile active material, binder and conductive agent are mixed in a preset ratio and dispersed in an organic solvent to form a uniform slurry; then the slurry is coated on a current collector and dried to form a positive electrode substrate; finally, the surface of the positive electrode substrate is etched by laser.

[0009] Preferably, the power of the laser etching can be selected and optimized within a certain range.

[0010] Preferably, the electrolyte comprises a lithium salt and an organic solvent, wherein the organic solvent may be selected from ester or ether solvents.

[0011] Preferably, the lithium anode sheet is a lithium metal foil.

[0012] The present invention also provides a method for preparing the above-mentioned high-capacity lithium-sulfur battery, which mainly includes laser etching of the positive electrode, stacking of battery elements, and liquid injection and encapsulation steps under an inert atmosphere.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0014] This invention utilizes laser etching to create regular micron-scale groove structures on the surface of a sulfurized polyacrylonitrile cathode. This patterned structure effectively promotes electrolyte wetting and ion transport, improves charge transport dynamics of the electrode, and alleviates stress changes in the active material during charging and discharging, thereby significantly enhancing the structural stability of the electrode. High-capacity lithium-sulfur batteries assembled based on this cathode exhibit higher reversible specific capacity, superior rate performance, and a more stable long cycle life. This method is simple and allows for precise control, providing an effective strategy for fabricating high-performance, high-capacity electrodes.

[0015] Instruction manual with accompanying drawings

[0016] Figure 1 This is a SEM image of the vulcanized polypropylene powder synthesized in Example 1 of the present invention;

[0017] Figure 2 The image shows the XRD pattern of the vulcanized polypropylene powder synthesized in Example 1 of this invention.

[0018] Figure 3 Raman blotting of the vulcanized polypropylene powder synthesized in Example 1 of this invention.

[0019] Figure 4 The images shown are SEM images of the electrode surfaces in Embodiments 1, 2, and 3 of the present invention and the comparative example, wherein (a) is an SEM image of the original electrode surface A0, (b) is an SEM image of electrode sheet A1, (c) is an SEM image of electrode sheet A2, and (d) is an SEM image of electrode sheet A3.

[0020] Figure 5 This is a side SEM image of electrode sheet A2 in Embodiment 2 of the present invention;

[0021] Figure 6 The above are charge-discharge curves of the first and second cycles during the cycling process of the Li||SPAN full cell assembled from electrode sheets A0, A1 and A2 obtained in Embodiments 1, 2 and the comparative example of the present invention.

[0022] Figure 7 The diagram shows the cycle-specific capacity during the cycling process of Li||SPAN full cells assembled from electrode sheets A0, A1, and A2 obtained in Embodiments 1, 2, and the comparative example of the present invention.

[0023] Figure 8 The graph shows the rate performance of the Li||SPAN full cell assembled from electrode sheets A0, A1 and A2 obtained in Embodiments 1, 2 and the comparative example of the present invention during cycling.

[0024] Figure 9The graphs show the charge-discharge curves at different rates during the cycling process of the Li||SPAN full cell assembled from electrode sheets A0, A1, and A2 obtained in Embodiments 1, 2, and the comparative example of this invention.

[0025] Figure 10 Impedance diagrams of Li||SPAN full cells assembled from electrode sheets A0, A1, and A2 obtained in Embodiments 1, 2, and the comparative example of the present invention. Detailed Implementation

[0026] The present invention will be further described in detail below through specific implementation examples. These implementation examples are based on the technology of the present invention, and detailed implementation methods and specific operating procedures are given. However, the scope of protection of the present invention is not limited to the implementation examples given below.

[0027] In the following embodiments, the basic electrolyte contains LiPF6 and a solvent, wherein the concentration of LiPF6 is 1 M, and the solvent is a mixture of diethyl carbonate (DEC), methyl ethyl carbonate (EMC), and ethylene carbonate (EC) in a volume ratio of 1:1:1, with 10% FEC added.

[0028] In the following embodiments, the Li||SPAN full cell includes a modified positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode is synthesized by the company itself, with SPAN composite material as the main raw material. The negative electrode is lithium metal foil. The separator is Celgard2325.

[0029] The preparation method of the positive electrode includes: mixing SPAN, polyvinylidene fluoride (molecular weight of 500,000), and Ketjen black in a mass ratio of 8:1:1, grinding, and dispersing in N-methylpyrrolidone to form a slurry; coating the slurry onto aluminum foil, vacuum drying at 60°C for 12 hours, and stamping it into a disc with a diameter of 10 mm. Then, etching the surface of the electrode disc using a pulsed laser of a certain power under a protective atmosphere.

[0030] The preparation steps of the high-capacity lithium-sulfur battery include: injecting electrolyte into the battery casing in an argon glove box, wherein 40 μL of electrolyte is added to both the positive and negative electrode sides; and then stacking and encapsulating the modified positive electrode, separator, and negative electrode in sequence.

[0031] Example 1

[0032] A high-capacity lithium-sulfur battery system is prepared by the following steps:

[0033] (1) At room temperature, in a glove box filled with Ar gas, take the prepared untreated electrode sheet (SPAN) and denot it as A0. Use a 3W laser to etch the surface of the electrode sheet to obtain the modified electrode sheet denoted as A1.

[0034] (2) Battery assembly;

[0035] A Li||SPAN full cell was assembled by using a prepared SPAN-modified positive electrode sheet on the positive electrode side of the separator and an untreated lithium foil on the negative electrode side, and adding 40 µL of electrolyte to each side.

[0036] The electron microscope image of the SPAN composite material obtained in this embodiment is as follows: Figure 1 As shown, the vulcanized polyacrylonitrile is composed of nanoscale particles. The particle surfaces are rough and lack obvious crystalline features, indicating that the material has a highly disordered amorphous morphology. This hierarchical structure is beneficial for improving the dispersibility of sulfur and mitigating volume changes during charge and discharge.

[0037] The SPAN composite material obtained in this embodiment was characterized by XRD, and the results are as follows: Figure 2 As shown, SPAN exhibits only a broad, diffuse peak in the range of 2θ = 20–30°, with no sharp diffraction peaks observed, indicating that the material has a typical amorphous structure. Furthermore, no characteristic diffraction peaks of elemental sulfur (S8) were detected, suggesting that sulfur has been successfully fixed in the PAN framework via covalent bonds, rather than existing as crystalline sulfur.

[0038] The SPAN composite material obtained in this embodiment was characterized using Raman spectroscopy, and the results are as follows: Figure 3 As shown, the Raman spectrum exhibits D and G bands at approximately 1350 and 1580 cm⁻¹, respectively, indicating that PAN formed a disordered conjugated carbon framework structure after sulfurization. Simultaneously, characteristic peaks related to C–S and short-chain S–S vibrations were observed in the low wavenumber region, and no characteristic peaks of crystalline sulfur were detected, further proving that sulfur is covalently fixed in the PAN framework.

[0039] SEM characterization was performed on the electrode surfaces treated with different laser powers in Example 1, and the results are as follows: Figure 4 As shown in the figure, the surface morphology of the electrodes after treatment with different laser powers is as follows. The surface of electrode A0 is dense, with only randomly distributed dry cracks. As the laser power increases, a groove structure gradually forms on the electrode surface along the scanning direction. Uniform and continuous parallel grooves can be observed on electrode A1, which effectively constructs ion transport channels and significantly increases the electrode / electrolyte contact area. However, further increasing the power (A3) leads to excessive ablation and structural damage, which is detrimental to the stability of the electrode structure.

[0040] Regarding electrode A1 obtained in this embodiment, its side view was observed under an electron microscope, and the results are as follows: Figure 5As shown in the SEM image of the side of electrode A1, the laser-induced trench structure extends inward along the electrode thickness direction, forming a continuous longitudinal channel with a depth of approximately 17 μm without compromising the integrity of the current collector. This three-dimensional through-structure facilitates electrolyte penetration and ion transport, thereby reducing electrode polarization.

[0041] The Li||SPAN full cell obtained in this embodiment was subjected to charge-discharge tests under the condition of 0.2C.

[0042] The full-cell constant current charge-discharge curves of the Li||SPAN obtained in this embodiment for the first and second cycles are shown in the figure below. Figure 6 As shown, laser etching effectively improves the charge and discharge capacity of the full battery.

[0043] The constant current charge-discharge cycle test of the Li||SPAN full battery obtained in this embodiment is as follows: Figure 7 As shown, laser etching effectively improves the charge-discharge performance of the full cell. The untreated electrode A0 exhibits rapid capacity decay during cycling, while the cycle stability of the laser-treated electrode is significantly improved. Electrode A1 demonstrates the lowest capacity decay rate and the highest capacity retention rate during long-term cycling, exhibiting excellent structural stability and reversible reaction.

[0044] The Li||SPAN full cell obtained in this embodiment was subjected to rate charge-discharge tests under the conditions of 0.1C-0.5C.

[0045] The comparison chart of the Li||SPAN full cell rate test obtained in this embodiment is shown below. Figure 8 As shown, the rate performance of electrodes treated with different laser powers varies significantly under different current densities. Compared to the untreated electrode A0, the laser-treated electrode exhibits significantly higher specific capacity and better capacity retention under high rate conditions. Electrode A1 demonstrates the best rate response capability across the entire rate range, especially maintaining a high reversible capacity even at high current densities. This result indicates that the ordered channel structure constructed by appropriate laser etching effectively alleviates mass transfer limitations under high rate conditions and significantly improves reaction kinetics.

[0046] The charge-discharge curves obtained from the different rate charge-discharge tests of the Li||SPAN full cell obtained in this embodiment are as follows: Figure 9 As shown, compared to the untreated electrode A0, the laser-treated electrode exhibits a more stable charge-discharge voltage plateau and a significantly reduced voltage hysteresis, indicating a substantial decrease in polarization. Electrode A1 demonstrates the smallest voltage difference during charge-discharge, indicating that its interfacial charge transfer impedance and ion diffusion resistance are effectively reduced.

[0047] For the Li||SPAN full cells obtained using different electrode sheets in this embodiment, EIS impedance analysis was performed, and the results are as follows: Figure 10 Electrochemical impedance spectroscopy further revealed the impact of laser treatment on electrode kinetics. Electrode A1 exhibited a smaller charge transfer resistance and a steeper low-frequency slope, indicating faster interfacial reaction kinetics and superior ion transport capabilities. This is highly consistent with the through-channel structure formed by laser etching;

[0048] Example 2

[0049] A high-capacity lithium-sulfur battery system is prepared in a manner similar to that of Example 1, except that the surface of the electrode sheet is etched using a 1.5W laser to obtain the modified electrode sheet, denoted as A2.

[0050] Example 3

[0051] A high-capacity lithium-sulfur battery system is prepared in a manner similar to that of Example 1, except that the surface of the electrode sheet is etched using a 6W laser to obtain the modified electrode sheet, denoted as A3.

[0052] Following the method described above, three full cells were assembled using electrode sheets A1, A2, and A3, respectively. The resulting full cells were then subjected to constant current charge-discharge tests using the Blue Electricity testing system.

[0053] Comparative Example 1

[0054] A high-capacity lithium-sulfur battery system is prepared in a manner similar to that of Example 1, except that laser etching is not used on the surface of the electrode sheet to obtain the modified electrode sheet, denoted as A0.

[0055] This invention is not limited to the embodiments described above. Those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications are also considered within the scope of protection of this invention. Contents not described in detail in this specification are prior art known to those skilled in the art.

Claims

1. A positive electrode sheet for high-capacity lithium-sulfur batteries, characterized in that, The device includes a current collector and a positive electrode material layer coated thereon, the positive electrode material layer comprising an active material, a binder, and a conductive agent; wherein the active material is a sulfurized polyacrylonitrile, and the surface of the positive electrode material layer is laser-etched to form a porous structure.

2. The positive electrode sheet according to claim 1, characterized in that, In the positive electrode material layer, the mass ratio of the active material, binder and conductive agent is (7~9):(1.8~2.2):2, wherein the binder is polyvinylidene fluoride and the conductive agent is Ketjen Black.

3. The positive electrode sheet according to claim 2, characterized in that, The bulk density of the Ketjen black is 17.0~50.0 g / L, and the DBP oil absorption value is 440~510 mL / 100g.

4. The positive electrode sheet according to claim 1, characterized in that, The laser power for the laser etching process is 1.5 W to 6 W.

5. A high-capacity lithium-sulfur battery, characterized in that, It includes the positive electrode, lithium negative electrode, separator, and electrolyte as described in any one of claims 1-4.

6. The high-capacity lithium-sulfur battery according to claim 5, characterized in that, The electrolyte contains a lithium salt and an organic solvent, wherein the lithium salt is at least one of LiPF6, LiTFSI, and LiFSI, and the organic solvent is an ether solvent or an ester solvent.

7. The high-capacity lithium-sulfur battery according to claim 5, characterized in that, The lithium anode sheet is a metallic lithium foil.

8. A method for preparing a positive electrode sheet as described in any one of claims 1 to 4, characterized in that, Includes the following steps: (1) Slurry preparation: Vulcanized polyacrylonitrile active material, polyvinylidene fluoride binder and Ketjen Black conductive agent are mixed in proportion, ground and dispersed in organic solvent to form a uniform slurry; (2) Coating and drying: The slurry is coated onto the current collector and dried to obtain the positive electrode substrate; (3) Laser etching: The surface of the positive electrode substrate is etched using a laser with a power of 1.5 W to 6 W to obtain a positive electrode with a porous structure on the surface.

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