A lithium-sulfur battery with high discharge specific capacity and good cycle stability, and a preparation method and application thereof

Abstract

The application discloses a lithium-sulfur battery with high discharge specific capacity and good cycle stability, and a preparation method and application thereof, and belongs to the technical field of lithium-sulfur batteries. The lithium-sulfur battery comprises a composite positive electrode, a negative electrode, a diaphragm and an electrolyte. The composite positive electrode comprises an aluminum foil, an In2O3 modification layer on the aluminum foil and a sulfur-containing active material layer on the In2O3 modification layer. The In2O3 modification layer is prepared on the surface of the aluminum foil by a magnetron sputtering technology. The In2O3 modification layer provides adsorption sites and reaction sites for lithium polysulfide, reduces the diffusion and accumulation of soluble lithium polysulfide in the electrolyte, and promotes the conversion of lithium polysulfide into low-order products, so that the loss of active sulfur is reduced, and the utilization rate of active substances is improved. Meanwhile, the In2O3 modification layer can improve the interface charge transmission between the aluminum foil current collector and the sulfur-containing active material layer, reduce the interface film impedance and charge transfer impedance.

Description

Technical Field

[0001] This invention belongs to the technical field of lithium-sulfur batteries, specifically relating to a lithium-sulfur battery with high discharge specific capacity and good cycle stability, as well as its preparation method and application. Background Technology

[0002] With the rapid development of portable electronic devices, electric vehicles, and large-scale energy storage systems, the market demand for high-energy-density energy storage devices is becoming increasingly urgent. Lithium-sulfur batteries, with a theoretical energy density of 2600Wh / kg, far exceeding that of traditional lithium-ion batteries, are considered one of the most promising next-generation high-energy-density energy storage systems.

[0003] However, the commercialization of lithium-sulfur batteries is constrained by several key issues. First, during charge and discharge, the sulfur cathode undergoes a multi-step redox reaction from S8 to Li2S, generating soluble lithium polysulfides (LiPSs) as intermediates. Due to the large concentration gradient between the cathode and the electrolyte, lithium polysulfides readily diffuse from the cathode region into the electrolyte, leading to a severe "shuttle effect." This not only causes irreversible loss of active sulfur but also corrodes and passivates the anode surface, reducing coulombic efficiency and ultimately severely inhibiting the long-term cycle stability of the battery. Second, sulfur and its discharge end products (Li2S2 / Li2S) are both electronic insulators. The electrochemical reaction kinetics within the sulfur cathode are sluggish, resulting in severe electrode polarization, which limits the utilization rate of active materials and the improvement of rate performance.

[0004] To address the aforementioned issues, researchers have proposed various improvement strategies, such as introducing porous carbon host materials into the sulfur cathode to physically confine sulfur species, adding polar metal oxides or sulfides as functional additives to chemically adsorb lithium polysulfides, and optimizing electrolyte formulations to reduce the solubility of lithium polysulfides. These methods have alleviated the shuttle effect to some extent, but none have effectively solved the problems of electron conduction and reaction kinetics at the interface between the current collector and the sulfur-containing active material layer.

[0005] Commercial lithium-sulfur batteries typically use aluminum foil as the positive electrode current collector, whose surface readily oxidizes in air to form a thin Al2O3 film. This oxide layer exhibits poor conductivity and insufficient affinity for polar lithium polysulfides, hindering both rapid interfacial charge transport and the diffusion and migration of lithium polysulfides from the active layer towards the current collector. While some studies have attempted to improve interfacial performance by modifying the aluminum foil surface with graphene, carbon nanotubes, or conductive polymers, these methods generally suffer from drawbacks such as complex processes, demanding equipment, high costs, and difficulty in large-scale production, hindering practical application.

[0006] Therefore, there is an urgent need to develop a current collector modification technology that is simple to process, cost-controllable, and easy to scale up, in order to effectively improve the current collector / active layer interface performance and simultaneously enhance the rate performance and long-term cycle stability of lithium-sulfur batteries without changing the existing positive electrode active material system. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a lithium-sulfur battery with high discharge specific capacity and good cycle stability, as well as its preparation method and application, so as to solve the problems mentioned in the background art or achieve better technical effects.

[0008] In order to solve the above-mentioned technical problems, the inventors derived the technical solution of the present invention through practice and summary. The present invention discloses a composite positive electrode for lithium-sulfur batteries, including an aluminum foil, an In2O3 modified layer on the aluminum foil, and a sulfur-containing active material layer on the In2O3 modified layer.

[0009] The In2O3 modified layer has a thickness of nanometers, and In2O3 nano-sized particles are distributed on the surface of the In2O3 modified layer, with a particle size of 10~40nm.

[0010] The sulfur-containing active material layer is composed of a sulfur-carbon composite material, conductive carbon black, and a binder; the sulfur-carbon composite material is a porous carbon / sulfur composite material, and the sulfur content of the sulfur-carbon composite material is 70 wt%.

[0011] Furthermore, the In2O3 modified layer is prepared on the surface of the aluminum foil by physical vapor deposition; the sulfur-containing active material layer is formed on the surface of the In2O3 modified layer by coating.

[0012] Furthermore, the method for preparing the composite cathode of the lithium-sulfur battery includes the following steps:

[0013] S1: Cleaning and pretreatment of the aluminum foil surface;

[0014] S2: An In2O3 modified layer is deposited on the surface of aluminum foil that has been cleaned and pretreated by S1 using physical vapor deposition technology;

[0015] S3: A sulfur-containing active material layer is formed on the surface of the In2O3 modified layer described in S2.

[0016] Furthermore, in S1, the cleaning pretreatment is argon glow discharge cleaning, with the following process conditions: bias voltage -800V, gas pressure 0.8Pa, and time 5min.

[0017] Furthermore, in S2, the physical vapor deposition technology is DC pulsed magnetron sputtering technology, and the process conditions include: working gas pressure of 0.55~0.65Pa, argon flow rate of 70~90sccm, aluminum foil substrate bias voltage of -80~-120V, and deposition time of 5~15min.

[0018] Furthermore, the aluminum foil substrate is biased at -100V and the deposition time is 5 minutes.

[0019] Furthermore, in S3, the method for forming the sulfur-containing active material layer is as follows: a slurry is prepared by mixing sulfur-carbon composite material, conductive carbon black and binder in a mass ratio of 8:1:1, which is then coated onto the surface of the In2O3 modified layer and dried to obtain the final product.

[0020] Furthermore, a lithium-sulfur battery with high discharge specific capacity and good cycle stability includes a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode is any of the composite positive electrodes described above; the negative electrode is a lithium sheet; the separator is a polypropylene microporous separator; and the electrolyte is a mixed solution of organic solvents containing lithium bis(trifluoromethanesulfonyl)imide and lithium nitrate.

[0021] Furthermore, the lithium-sulfur battery has a discharge specific capacity of 826.9 mAh / g at a 0.2C rate. sulfur The discharge specific capacity at 0.5C rate is 664.7 mAh / g. sulfur The discharge specific capacity at a 1.0C rate is 492.7 mAh / g. sulfur The discharge specific capacity at a 2.0C rate is 336.2 mAh / g. sulfur The lithium-sulfur battery retains 70.2% of its capacity after 400 cycles at 0.5C.

[0022] Furthermore, the lithium-sulfur battery with high discharge specific capacity and good cycle stability is applied in the field of energy storage devices.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] (1) In this invention, an In2O3 modified layer is introduced between the aluminum foil current collector and the sulfur-containing active material layer. In2O3 is a polar metal oxide, and its surface In and O sites can generate strong interfacial interactions with S and Li in lithium polysulfides, providing abundant adsorption and reaction sites for lithium polysulfides. On the one hand, this is beneficial for confining soluble lithium polysulfides in the positive electrode region, reducing their diffusion and accumulation in the electrolyte, and effectively suppressing the shuttle effect; on the other hand, it can catalyze and promote the rapid conversion of lithium polysulfides to low-order discharge products such as Li2S2 and Li2S, shortening the existence time of lithium polysulfides in the electrolyte, thereby significantly reducing the irreversible loss of active sulfur and improving the utilization rate of active materials.

[0025] (2) The In2O3 modified layer of the present invention can act as a functional interface layer between the aluminum foil current collector and the sulfur-containing active material layer, effectively reducing the interfacial film impedance and charge transfer impedance between the two. The improved interfacial charge transport efficiency improves the electrochemical reaction kinetics, promoting the rapid redox conversion of lithium polysulfides under various charge and discharge rates. Experimental data show that, compared with lithium-sulfur batteries using conventional unmodified aluminum foil current collectors, the lithium-sulfur batteries prepared in this invention have a discharge specific capacity increased by approximately 160~220 mAh / g at 0.2C, 0.5C, 1.0C, and 2.0C rates, respectively, exhibiting excellent rate performance.

[0026] (3) The In2O3 modified layer prepared by this invention has both "adsorption-catalysis" dual functions and good interfacial charge transport characteristics. During repeated charge and discharge processes, the shuttle loss of lithium polysulfides is continuously suppressed, the utilization rate of active sulfur remains stable, and the interfacial impedance does not show a significant increase. Experimental results show that after 400 cycles at 0.5C rate, the capacity retention rate of the preferred embodiment of this invention can reach 70.2%.

[0027] (4) This invention uses physical vapor deposition (magnetron sputtering) technology to prepare an In2O3 modified layer on the surface of aluminum foil. The deposition time is only 5-15 minutes, the process parameters are easy to control, and there is no need for complex wet chemical reactions, high-temperature sintering or post-treatment processes, which has good process compatibility. This invention only performs functional modification on the surface of the aluminum foil current collector, without changing the mature formula and coating process of existing sulfur cathode active materials (sulfur-carbon composite materials, conductive agents, binders), which facilitates rapid promotion and application on existing lithium-sulfur battery production lines.

[0028] (5) By adjusting key parameters such as deposition time and substrate bias during the magnetron sputtering process, this invention can effectively control the thickness, particle size, density, and interfacial bonding state of the In2O3 modified layer, thereby obtaining the optimal comprehensive electrochemical performance for different application scenarios. The preferred process conditions of this invention (deposition time 5 min, bias voltage -100V) can achieve the best balance between fully realizing the function of the modified layer and the interfacial transport efficiency, demonstrating good process window and controllability. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the composite cathode structure of the lithium-sulfur battery of the present invention (aluminum foil substrate, In2O3 layer, active material layer).

[0030] Figure 2 SEM images of the In2O3 modified aluminum foil current collector prepared in Example 1 and the pure aluminum foil current collector in Comparative Example 1; where (a) is Example 1; (b) is Comparative Example 1;

[0031] Figure 3 This is a comparison chart of the EIS of lithium-sulfur batteries prepared in Example 1 and Comparative Example 1.

[0032] Figure 4 This is a comparison chart of the rate performance of lithium-sulfur batteries prepared in Example 1 and Comparative Example 1;

[0033] Figure 5 This is a comparison chart showing the performance results of the lithium-sulfur batteries prepared in Example 1 and Comparative Example 1 after 400 cycles at a 0.5C rate. Detailed Implementation

[0034] To make the above-mentioned objectives, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to specific examples.

[0035] Unless otherwise specified, all raw materials or reagents used in the following examples are commercially available products.

[0036] Among them, the pure aluminum foil comes from single-sided aluminum foil from KELUDE Company;

[0037] The sulfur-carbon composite material (YP80 / S) has a sulfur content of 70 wt% and is prepared by a melt method using sulfur powder S and carbon powder YP80 (the sulfur powder and carbon powder are mixed evenly in a 7:3 ratio and then heated to 158℃ and held for 12 hours).

[0038] The conductive carbon black (SuperP) is from Kuraray, Japan;

[0039] The adhesive is model LA133 and is sourced from Duoduo Reagents.

[0040] The purity of In2O3 is 99.9%;

[0041] The lithium sheets were sourced from KELU.

[0042] The detection method for the lithium-sulfur battery prepared by this invention is as follows:

[0043] EIS was performed using a Chenhua 760e electrochemical workstation, with a frequency range of 10 at open circuit potential. -2 ~10 6 Hz. Rate capability and long-cycle performance were tested using the CT2001ALand battery testing system at a voltage range of 1.7~2.8V. All test parameters are measured in universal physical units.

[0044] A composite cathode for lithium-sulfur batteries, such as Figure 1 As shown, it includes pure aluminum foil, an In2O3 modified layer on the aluminum foil, and a sulfur-containing active material layer on the In2O3 modified layer;

[0045] The thickness of the In2O3 modified layer is in the nanometer range, and its surface is distributed with In2O3 nano-sized particles with a particle size of 10~40nm.

[0046] The In2O3 modified layer was prepared by magnetron sputtering, and the steps are as follows:

[0047] S1: Before deposition, the aluminum foil surface is cleaned by argon glow discharge (bias voltage -800V, 0.8Pa, 5min) to enhance adhesion;

[0048] S2: An In2O3 modified layer is deposited on the surface of aluminum foil using a DC pulse magnetron sputtering device;

[0049] The specific operation process is as follows:

[0050] a) Install an In2O3 target with a purity of 99.9% and a size of 97mm×4mm on the magnetron sputtering target position, and fix the aluminum foil on the rotatable substrate holder so that the surface of the aluminum foil to be deposited faces the In2O3 target.

[0051] b) Close the vacuum chamber and start the vacuum system to evacuate the vacuum, while simultaneously starting heating at a set temperature of 120°C;

[0052] c) After the chamber reaches the base vacuum set by the equipment, argon gas is introduced, and the argon gas flow rate is adjusted to maintain the working gas pressure in the chamber at 0.8pa. A bias voltage of -800V is applied to perform glow discharge cleaning on the aluminum foil for 5 minutes.

[0053] d) After glow discharge cleaning, turn off the bias voltage, adjust the argon flow rate to 70~90 sccm, and adjust the working pressure in the chamber to 0.55~0.65 Pa; turn on the DC pulse power supply connected to the In2O3 target and apply a bias voltage of -80~-120V to the aluminum foil substrate. After the argon plasma discharge stabilizes, open the target baffle and start timing; under the bombardment of argon ions, the particles on the surface of the In2O3 target are sputtered out and deposited on the rotating aluminum foil surface, thereby forming an In2O3 modified layer. The deposition time is 5~15 min; during glow discharge cleaning and deposition, the substrate holder is kept rotating at a constant speed of 3 r / min to ensure the uniformity of the film;

[0054] e) After deposition, turn off the target power supply, substrate bias voltage, gas input and heating device. After the sample cools down, restore the vacuum chamber to normal pressure, take out the sample and obtain the In2O3 modified aluminum foil current collector.

[0055] The sulfur-containing active material layer is composed of a sulfur-carbon composite material (YP80 / S), conductive carbon black (SuperP), and binder LA133; the preparation method is as follows:

[0056] Porous carbon YP80 / S composite material (sulfur content 70wt%), conductive carbon black (SuperP) and LA133 are mixed and ground at a mass ratio of 8:1:1 to form a suspension. The suspension is coated on the surface of In2O3-Al current collector or pure aluminum current collector and dried in an oven at 50℃ for 12h to obtain a sulfur-containing active material layer.

[0057] The present invention discloses a lithium-sulfur battery with high discharge specific capacity and good cycle stability, comprising a lithium sheet as a negative electrode, a composite positive electrode, a separator and an electrolyte;

[0058] The method for preparing the lithium-sulfur battery is as follows:

[0059] A lithium-sulfur battery was assembled with the composite positive electrode prepared above, using lithium sheet as the negative electrode, Celgard 2400 polypropylene membrane as the separator, and a mixed solution of 1,3-dioxolane / 1,2-dimethoxyethane (DOL / DME) containing 1.0M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and 2wt% lithium nitrate (LiNO3) as the electrolyte.

[0060] Example 1

[0061] A composite cathode for a lithium-sulfur battery includes a pure aluminum foil, an In2O3 modified layer on the aluminum foil, and a sulfur-containing active material layer on the In2O3 modified layer.

[0062] The In2O3 modified layer was prepared by magnetron sputtering, and the steps are as follows:

[0063] S1: Before deposition, the aluminum foil surface is cleaned by argon glow discharge (bias voltage -800V, 0.8Pa, 5min) to enhance adhesion;

[0064] S2: An In2O3 modified layer is deposited on the surface of aluminum foil using a DC pulse magnetron sputtering device;

[0065] The specific operation process is as follows:

[0066] a) Install an In2O3 target with a purity of 99.9% and a size of 97mm×4mm on the magnetron sputtering target position, and fix the aluminum foil on the rotatable substrate holder so that the surface of the aluminum foil to be deposited faces the In2O3 target.

[0067] b) Close the vacuum chamber and start the vacuum system to evacuate the vacuum, while simultaneously starting heating at a set temperature of 120°C;

[0068] c) After the chamber reaches the base vacuum set by the equipment, argon gas is introduced, and the argon gas flow rate is adjusted to maintain the working gas pressure in the chamber at 0.8pa. A bias voltage of -800V is applied to perform glow discharge cleaning on the aluminum foil for 5 minutes.

[0069] d) After glow discharge cleaning, turn off the bias voltage, adjust the argon flow rate to 75 sccm, and adjust the working pressure in the chamber to 0.55~0.65 Pa; turn on the DC pulse power supply connected to the In2O3 target and apply a -100V bias voltage to the aluminum foil substrate. After the argon plasma discharge stabilizes, open the target baffle and start timing; under the bombardment of argon ions, the particles on the surface of the In2O3 target are sputtered out and deposited on the rotating aluminum foil surface, thereby forming an In2O3 modified layer. The deposition time is 5 min; during glow discharge cleaning and deposition, the substrate holder is kept rotating at a constant speed of 3 r / min to ensure the uniformity of the film;

[0070] e) After deposition, turn off the target power supply, substrate bias voltage, gas input and heating device. After the sample cools down, restore the vacuum chamber to normal pressure, take out the sample and obtain the In2O3 modified aluminum foil current collector.

[0071] The sulfur-containing active material layer is composed of a sulfur-carbon composite material (YP80 / S), conductive carbon black (SuperP), and binder LA133; the preparation method is as follows:

[0072] Porous carbon YP80 / S composite material (sulfur content 70wt%), conductive carbon black (SuperP) and LA133 are mixed and ground at a mass ratio of 8:1:1 to form a suspension. The suspension is coated on the surface of In2O3-Al current collector or pure aluminum current collector and dried in an oven at 50℃ for 12h to obtain a sulfur-containing active material layer.

[0073] A lithium-sulfur battery includes a lithium sheet as the negative electrode, a composite positive electrode, a separator, and an electrolyte; the preparation method is as follows:

[0074] A lithium-sulfur battery was assembled with a lithium sheet as the negative electrode, a Celgard 2400 polypropylene membrane as the separator, and a mixed solution of 1,3-dioxolane / 1,2-dimethoxyethane (DOL / DME) containing 1.0M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and 2wt% lithium nitrate (LiNO3) as the electrolyte and a composite positive electrode.

[0075] Example 2

[0076] The difference from Example 1 is that the deposition time of the In2O3 modified layer in the preparation step of the composite cathode is adjusted from 5 min to 15 min, while the other preparation steps and process conditions are the same as in Example 1.

[0077] Example 3

[0078] The only difference from Example 1 is that the bias voltage of the aluminum foil substrate is adjusted from -100V to -80V in the In2O3 modified layer preparation step of the composite cathode. All other preparation steps and process conditions are the same as in Example 1.

[0079] Example 4

[0080] Unlike Example 1, the only difference is that in the preparation step of the In2O3 modified layer of the composite cathode, the bias voltage of the aluminum foil substrate is adjusted from -100V to -120V, and the deposition time of the In2O3 modified layer is still 5min. All other preparation steps and process conditions are the same as in Example 1.

[0081] Comparative Example 1

[0082] A lithium-sulfur battery, unlike Example 1, does not use a composite cathode, but directly uses untreated commercial pure aluminum foil as the cathode to assemble the battery.

[0083] Comparative Example 2

[0084] Unlike Example 1, the only difference is that in the preparation step of the In2O3 modified layer of the composite cathode, the deposition time of the In2O3 modified layer is extended from 5 min to 45 min, the bias voltage of the aluminum foil substrate remains at -100V, and the other preparation steps and process conditions are the same as in Example 1.

[0085] Comparative Example 3

[0086] Unlike Example 1, only in the preparation step of the In2O3 modified layer of the composite cathode, no bias voltage is applied to the aluminum foil substrate, that is, the bias voltage of the aluminum foil substrate is 0V, the deposition time of the In2O3 modified layer is still 5min, and the other preparation steps and process conditions are the same as in Example 1.

[0087] Depend on Figure 2 (a) It can be seen that a large number of nanoscale bright contrast particles are distributed on the surface of the indium oxide modified current collector. The particles are generally nearly spherical or irregular polyhedral in shape, with relatively clear boundaries. The particles are widely distributed in the observation area, but certain gaps are still maintained between the particles, indicating that indium oxide has formed a relatively uniform coating layer on the aluminum foil surface. At the same time, no obvious cracks or large-area peeling were observed in the figure, indicating that the modified layer has good surface integrity. In contrast, Figure 2 (b) shows a relatively smooth surface with no obvious granular deposits. The comparison indicates that indium oxide modification transforms the aluminum foil surface from a relatively smooth morphology to a rough surface with a rich granular structure. This granular structure helps increase the effective specific surface area of ​​the current collector and provides more interfacial contact sites, thus facilitating the adhesion of the positive electrode active material and the wetting of the electrolyte. Combined with the polar characteristics of indium oxide, this surface structure may also provide more active sites for the adsorption and conversion of lithium polysulfides, thereby improving the interfacial reaction kinetics of lithium-sulfur batteries.

[0088] Depend on Figure 3 It can be seen that the semicircle diameters of the curves corresponding to Example 1 in the high-frequency and mid-frequency regions are significantly smaller than those of Comparative Example 1. Through equivalent circuit fitting, the interfacial film impedance Rsf and charge transfer impedance Rct of Example 1 are approximately 4.777Ω and 3.391Ω, respectively, both significantly lower than the 10.17Ω and 8.964Ω of Comparative Example 1. These results indicate that the In2O3 modified layer can reduce the electron transport resistance at the interface between the current collector and the active material layer, promote charge transfer and the redox conversion of lithium polysulfides, thereby improving the reaction kinetics of the sulfur cathode.

[0089] The lithium-sulfur batteries prepared in Examples 1-4 and Comparative Examples 1-3 were subjected to rate performance tests (at rates of 0.2C, 0.5C, 1.0C, and 2.0C), and the test results are shown in Table 1 below.

[0090] Table 1. Lithium-sulfur batteries prepared in Examples 1-4 and Comparative Examples 1-3

[0091] Comparison of discharge specific capacity and cycle stability indicators

[0092]

[0093] Based on Table 1 Figure 4 and Figure 5 It can be seen that among the seven groups of samples in Examples 1-4 and Comparative Examples 1-3, Example 1 had the highest discharge specific capacity at 0.2C, 0.5C, 1.0C, and 2.0C rates, reaching 826.9 mAh / g. sulfur 664.7mAh / g sulfur 492.7mAh / g sulfur and 336.2mAh / g sulfur After 400 cycles at a 0.5C rate, its capacity retention was 70.2%, which was also higher than that of the other groups. These results indicate that under the process conditions tested in this application, when the deposition time of the In2O3 modified layer is 5 min and the aluminum foil substrate bias voltage is -100V, the obtained In2O3 modified aluminum foil current collector exhibits good overall rate performance and cycle stability.

[0094] Compared to Comparative Example 1, which used untreated aluminum foil, Example 1 showed an increase of 163.7 mAh / g in discharge specific capacity at rates of 0.2C, 0.5C, 1.0C, and 2.0C. sulfur 220.1mAh / g sulfur 197.6mAh / g sulfur and 138.9mAh / g sulfurAfter 400 cycles, the capacity retention rate increased from 31.6% to 70.2%. This indicates that setting an In2O3 modified layer between the aluminum foil and the sulfur-containing active material layer can significantly improve the rate performance and long-term cycle stability of lithium-sulfur batteries.

[0095] Depend on Figure 4 It can be seen that the discharge specific capacity of Example 1 at 0.2C, 0.5C, 1.0C, and 2.0C rates is higher than that of Comparative Example 1 at the corresponding rates. When the rate is reduced, the discharge specific capacity of Example 1 can be recovered well, indicating that it has good electrochemical reversibility. This is because the In2O3 modified layer reduces the interfacial charge transfer resistance and is conducive to the adsorption and rapid conversion of lithium polysulfides, enabling the battery to maintain a high active sulfur utilization rate even at large charge and discharge currents.

[0096] Depend on Figure 5 It can be seen that during 400 charge-discharge cycles, the discharge specific capacity of Example 1 was consistently higher than that of Comparative Example 1, and the capacity retention rate after 400 cycles was significantly higher than that of Comparative Example 1. Furthermore, the coulombic efficiency remained generally stable during the cycling process. These results indicate that the In2O3 modified layer can improve the long-term cycling stability of lithium-sulfur batteries. This is because the adsorption and conversion of lithium polysulfides by In2O3 reduces the diffusion of soluble lithium polysulfides and the loss of active sulfur, while the lower interfacial impedance helps maintain the reversibility of the reaction during charge and discharge.

[0097] In Example 2, the deposition time of the In2O3 modified layer was extended to 15 min, and its discharge specific capacity at 0.2C, 0.5C, 1.0C, and 2.0C rates was 792.4 mAh / g. sulfur 627.8mAh / g sulfur 454.2mAh / g sulfur and 305.6mAh / g sulfur The capacity retention rate after 400 cycles was 65.8%. Although the performance of Example 2 was slightly lower than that of Example 1, it was still significantly higher than that of the comparative examples, indicating that by appropriately extending the deposition time to 15 min, the resulting composite cathode could still maintain good rate performance and cycle stability. However, as the deposition time is extended, the In2O3 modified layer may gradually thicken, the electron and lithium ion transport distance will increase accordingly, and the utilization efficiency of some reaction sites may decrease. Therefore, its performance is slightly lower than that of Example 1 with a deposition time of 5 min.

[0098] In Examples 3 and 4, the deposition time was 5 minutes, and the aluminum foil substrate bias voltages were -80V and -120V, respectively. The discharge specific capacity at each rate and the capacity retention after 400 cycles were higher in both groups than in the comparative examples, but lower than in Example 1 with a bias voltage of -100V. This indicates that the aluminum foil substrate bias voltage affects the energy of the deposited particles, surface migration, and the nucleation and growth state of the In2O3 modified layer. When the bias voltage is -80V, the energy obtained by the deposited particles is relatively low, which may be unfavorable for forming a modified layer with a more suitable density and interfacial bonding state. When the bias voltage increases to -120V, excessive ion bombardment may cause re-sputtering, increased internal stress, or an increase in local defects, thereby weakening the promoting effect of the In2O3 modified layer on interfacial charge transport and polysulfide conversion. Therefore, in the bias voltage conditions tested in this invention, -100V can better balance the deposition quality, interfacial bonding state, and electrochemical performance of the modified layer.

[0099] Comparative Example 2, with its deposition time extended to 45 minutes, showed significantly lower discharge specific capacities at all rates compared to Examples 1-4, and a capacity retention rate of only 40.8% after 400 cycles. This may be because the excessively long deposition time resulted in an overly thick In2O3 modified layer, increasing the resistance to electron and lithium-ion transport. Furthermore, the thicker modified layer may generate greater internal stress during repeated charge-discharge cycles, which is detrimental to maintaining the interfacial stability between the modified layer and the aluminum foil. Therefore, excessively extending the deposition time cannot further improve battery performance.

[0100] Comparative Example 3, in which no bias voltage was applied to the aluminum foil substrate during deposition, exhibited lower discharge specific capacity at various rates and lower capacity retention after 400 cycles compared to Examples 1-4. Without substrate bias, the surface migration ability of deposited particles and the ion-assisted bombardment effect are relatively weak. The resulting In2O3 modified layer's density, uniformity, and bonding with the aluminum foil may be inferior to the modified layer with a suitable negative bias, thus limiting its promoting effect on interfacial charge transport and polysulfide conversion. However, Comparative Example 3's performance is still slightly higher than Comparative Example 1, which uses untreated aluminum foil, indicating that even without substrate bias, the In2O3 modified layer deposited on the aluminum foil surface can still improve the electrochemical performance of lithium-sulfur batteries to some extent.

[0101] The aforementioned performance differences are mainly related to the adsorption, conversion, and interfacial charge transport effects of the In₂O₃ modified layer on lithium polysulfides. In₂O₃ is a polar metal oxide, and its surface In and O sites can generate strong interfacial interactions with S and Li in lithium polysulfides. This helps limit the diffusion of soluble lithium polysulfides into the electrolyte, mitigating the shuttle effect and loss of active sulfur. Simultaneously, the In₂O₃ modified layer provides reaction sites between the aluminum foil and the sulfur-containing active material layer, promoting the conversion of lithium polysulfides to lower-order products such as Li₂S₂ and Li₂S, thereby improving the utilization rate of active materials and the reversibility of redox reactions.

[0102] The above mechanism is consistent with the electrochemical impedance spectroscopy results. The interfacial film impedance Rsf and charge transfer impedance Rct of Example 1 were 4.777 Ω and 3.391 Ω, respectively, significantly lower than the 10.17 Ω and 8.964 Ω of Comparative Example 1. This indicates that the In2O3 modified layer prepared using a suitable process can reduce interfacial reaction resistance and promote electron transport and the redox conversion of lithium polysulfides. Therefore, appropriate deposition time and substrate bias voltage are important conditions for the In2O3 modified layer to exert its effect. Among the process conditions tested in this invention, the best overall performance was obtained when the deposition time was 5 min and the aluminum foil substrate bias voltage was -100 V.

Claims

1. A composite cathode for a lithium-sulfur battery, characterized in that, It includes an aluminum foil, an In2O3 modified layer on the aluminum foil, and a sulfur-containing active material layer on the In2O3 modified layer; The In2O3 modified layer has a thickness of nanometers, and In2O3 nano-sized particles are distributed on the surface of the In2O3 modified layer, with a particle size of 10~40nm. The sulfur-containing active material layer is composed of a sulfur-carbon composite material, conductive carbon black, and a binder; the sulfur-carbon composite material is a porous carbon / sulfur composite material, and the sulfur content of the sulfur-carbon composite material is 70 wt%.

2. The composite cathode of the lithium-sulfur battery according to claim 1, characterized in that, The In2O3 modified layer is prepared on the surface of the aluminum foil by physical vapor deposition; the sulfur-containing active material layer is formed on the surface of the In2O3 modified layer by coating.

3. A method for preparing a composite cathode for a lithium-sulfur battery as described in claim 1 or 2, characterized in that, Includes the following steps: S1: Cleaning and pretreatment of the aluminum foil surface; S2: An In2O3 modified layer is deposited on the surface of aluminum foil that has been cleaned and pretreated by S1 using physical vapor deposition technology; S3: A sulfur-containing active material layer is formed on the surface of the In2O3 modified layer described in S2.

4. The method for preparing the composite cathode of the lithium-sulfur battery according to claim 3, characterized in that, In S1, the cleaning pretreatment is argon glow discharge cleaning, and the process conditions are: bias voltage -800V, gas pressure 0.8Pa, and time 5min.

5. The method for preparing the composite cathode of the lithium-sulfur battery according to claim 3, characterized in that, In S2, the physical vapor deposition technology is DC pulsed magnetron sputtering technology, and the process conditions include: working gas pressure of 0.55~0.65Pa, argon flow rate of 70~90sccm, aluminum foil substrate bias voltage of -80~-120V, and deposition time of 5~15min.

6. The method for preparing the composite cathode of the lithium-sulfur battery according to claim 5, characterized in that, The aluminum foil substrate is biased at -100V and the deposition time is 5 minutes.

7. The method for preparing the composite cathode of the lithium-sulfur battery according to claim 3, characterized in that, In S3, the sulfur-containing active material layer is formed by mixing sulfur-carbon composite material, conductive carbon black and binder in a mass ratio of 8:1:1 to prepare a slurry, coating it on the surface of the In2O3 modified layer, and drying it to obtain the final product.

8. A lithium-sulfur battery with high discharge specific capacity and good cycle stability, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, characterized in that, The positive electrode is the composite positive electrode according to any one of claims 1 to 2; the negative electrode is a lithium sheet; the separator is a polypropylene microporous separator; and the electrolyte is a mixed solution of organic solvents containing lithium bis(trifluoromethanesulfonyl)imide and lithium nitrate.

9. The lithium-sulfur battery with high discharge specific capacity and good cycle stability according to claim 8, characterized in that, The lithium-sulfur battery has a discharge specific capacity of 826.9 mAh / g at a 0.2C rate. sulfur The discharge specific capacity at 0.5C rate is 664.7 mAh / g. sulfur The discharge specific capacity at a 1.0C rate is 492.7 mAh / g. sulfur The discharge specific capacity at a 2.0C rate is 336.2 mAh / g. sulfur The lithium-sulfur battery retains 70.2% of its capacity after 400 cycles at 0.5C.

10. The application of the lithium-sulfur battery with high discharge specific capacity and good cycle stability as described in claim 8 in the field of energy storage devices.

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