Method, material and application of piezoelectric-semiconductor heterojunction for strengthening performance of lithium-sulfur battery

Abstract

This invention discloses a method, materials, and applications for enhancing the performance of lithium-sulfur batteries using a piezoelectric-semiconductor heterojunction. The method employs an in-situ sulfidation strategy to partially sulfide Bi₄Ti₃O₂. 12 The precursor is converted into Bi2S3 to construct Bi4Ti3O with an atomically tightly coupled interface. 12 A Bi₂S₃ ferroelectric-semiconductor heterojunction was constructed and coated onto the surface of a lithium-sulfur battery separator as a multifunctional catalytic coating. This heterojunction utilizes the built-in electric field at the interface and Bi₄Ti₃O₂... 12 The synergistic effect of spontaneous ferropolar polarization structurally enhances the chemisorption of lithium polysulfides to suppress the shuttle effect, significantly reduces the activation energy of bidirectional Li2S precipitation / decomposition to accelerate liquid-solid conversion kinetics, and simultaneously homogenizes lithium-ion flux through a localized polarization field to stabilize the lithium metal anode. The lithium-sulfur battery using the modified separator of this invention achieves an initial discharge capacity of 1172 mAh g⁻¹ at 0.5 C rate. ‑1 After 500 cycles, the capacity decay rate per cycle is only 0.096%, and it can still provide 854mAh g at a high rate of 2C. ‑1 Its discharge specific capacity demonstrates excellent cycle stability and rate performance.

Description

Technical Field

[0001] This invention belongs to the field of lithium-sulfur battery technology, specifically relating to a method, materials, and applications for enhancing the performance of lithium-sulfur batteries using a piezoelectric-semiconductor heterojunction. Background Technology

[0002] Lithium-sulfur batteries are known for their high theoretical energy density (2600 Wh kg). -1 With its advantages of low cost and environmental friendliness, lithium-sulfur batteries are considered one of the most promising next-generation energy storage systems. However, the practical application of lithium-sulfur batteries still faces many challenges, mainly including: the "shuttle effect" caused by soluble lithium polysulfide intermediates (LiPSs), leading to irreversible loss of active material and rapid capacity decay; the electronic insulation of sulfur and its discharge product lithium sulfide (Li2S) resulting in slow electrochemical reaction kinetics; and the huge volume change of the sulfur cathode during charging and discharging, leading to electrode structural instability. These problems severely limit the cycle life and rate performance of lithium-sulfur batteries.

[0003] To address the aforementioned issues, introducing electrocatalysts into the cathode or separator of lithium-sulfur batteries has become a recognized effective strategy. An ideal catalyst needs to possess two functions simultaneously: strong anchoring ability for soluble lithium polysulfides to suppress the shuttle effect, and high electrocatalytic activity to accelerate their redox conversion. However, these two functions are often mutually exclusive in single-component materials, making it difficult to achieve both simultaneously.

[0004] Ferroelectric materials, due to their spontaneous polarization properties, possess polar surfaces that can serve as strong electrostatic anchors for polar lithium polysulfides. Furthermore, their long-range, directionally tunable polarization fields can profoundly influence ion transport and interfacial charge transfer kinetics. However, most ferroelectric oxides, such as barium titanate (BaTiO3), have inherently low electronic conductivity, limiting electron supply and slowing conversion kinetics. Integrating the ferroelectric phase into a heterojunction structure can overcome this limitation. Through the synergistic coupling of the ferroelectric polarization field and the built-in electric field at the heterojunction interface, more efficient polysulfide capture and catalytic conversion can be achieved than single-phase ferroelectrics or traditional heterojunction catalysts. However, existing ferroelectric heterojunctions are mostly synthesized through non-in-situ physical mixing, resulting in porous interfaces and high contact resistance, making it difficult to fully utilize the synergistic advantages of the built-in electric field and ferroelectric effect.

[0005] Therefore, how to construct ferroelectric heterojunctions with tight coupling and seamless interfaces to achieve optimal synergy between polarization and catalysis is a key technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing technologies by providing a method, materials, and applications for enhancing the performance of lithium-sulfur batteries using piezoelectric-semiconductor heterojunctions. This method involves constructing bismuth titanate-bismuth sulfide (Bi4Ti3O) through an in-situ sulfidation strategy. 12-Bi2S3) ferroelectric-semiconductor heterojunction, utilizing the strong atomic-level coupling at the heterojunction interface to establish a stable built-in electric field, with Bi4Ti3O 12 The spontaneous ferropolarization synergistic effect structurally enhances the chemisorption of polysulfides, significantly reduces the activation energy of bidirectional Li2S precipitation / decomposition, and homogenizes the lithium-ion flux to stabilize the lithium anode, thereby comprehensively improving the cycle stability, rate performance and coulombic efficiency of lithium-sulfur batteries.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for enhancing the performance of lithium-sulfur batteries using a piezoelectric-semiconductor heterojunction includes the following steps:

[0009] S1: Preparation of Bi4Ti3O 12 Precursor;

[0010] S2: Bi4Ti3O 12 The precursor and sulfur source are placed in a reaction medium, and Bi4Ti3O is sulfided in situ. 12 Partially converted to Bi2S3, yielding Bi4Ti3O 12 -Bi2S3 ferroelectric-semiconductor heterojunction material;

[0011] S3: Bi4Ti3O 12 Bi2S3 heterojunction material, conductive agent and binder are mixed in proportion to form a slurry, which is then coated on the surface of a lithium-sulfur battery separator and dried to obtain a modified separator.

[0012] S4: Assemble the modified separator in a lithium-sulfur battery.

[0013] Furthermore, the Bi4Ti3O mentioned in step S1 12 The precursor was prepared by a hydrothermal method, specifically: bismuth and titanium sources were dissolved in an alkaline aqueous solution at a Bi:Ti molar ratio of 4:3, and the mixture was hydrothermally reacted at 160-200℃ for 6-18 hours to obtain Bi4Ti3O. 12 Precursor.

[0014] Furthermore, the bismuth source in step S1 includes at least one of bismuth pentahydrate, bismuth nitrate, bismuth chloride, and bismuth acetate; the titanium source includes at least one of tetrabutyl titanate, titanium tetrachloride, and titanium oxysulfate; and the alkaline aqueous solution is an aqueous solution of sodium hydroxide or potassium hydroxide with a concentration of 2-8M.

[0015] Furthermore, the sulfur source mentioned in step S2 includes at least one of sodium hydrosulfide, sodium sulfide, thioacetamide, and thiourea.

[0016] Furthermore, the Bi4Ti3O mentioned in step S2 12The molar ratio of precursor to sulfur source is 1:1 to 1:5.

[0017] Furthermore, the in-situ sulfidation reaction in step S2 is carried out at a temperature of 140-200℃ for 6-18 hours.

[0018] Furthermore, the Bi4Ti3O mentioned in step S3 12 The mass ratio of the Bi2S3 heterojunction material, conductive agent, and binder is 7:2:1.

[0019] Furthermore, the conductive agent in step S3 includes at least one of Ketjen Black, acetylene black, Super P, carbon nanotubes, and graphene; the binder includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, sodium alginate, and sodium carboxymethyl cellulose.

[0020] Furthermore, the diaphragm mentioned in step S3 includes one of a polypropylene diaphragm, a polyethylene diaphragm, or a polypropylene / polyethylene / polypropylene three-layer composite diaphragm.

[0021] Furthermore, the coating thickness described in step S3 is 1-10 micrometers.

[0022] This invention also provides Bi4Ti3O prepared by the above method. 12 -Bi2S3 ferroelectric-semiconductor heterojunction material.

[0023] The present invention also provides a lithium-sulfur battery assembled from the above-described modified separator.

[0024] The present invention also provides the above-mentioned Bi4Ti3O 12 Applications of Bi2S3 ferroelectric-semiconductor heterojunction materials in lithium-sulfur battery cathode materials, separator coatings, intermediate layers, or polysulfide adsorbents.

[0025] The beneficial effects of this invention are as follows:

[0026] 1. This invention constructs Bi4Ti3O through an in-situ sulfidation strategy. 12 The -Bi2S3 ferroelectric-semiconductor heterojunction forms an atomically tightly coupled chemical bonding interface between the two materials, overcoming the defects of loose interface and high contact resistance in traditional non-in-situ physical mixing methods, and establishing a strong built-in electric field.

[0027] 2. Built-in electric field at the heterogeneous interface and Bi4Ti3O 12 The spontaneous ferropolarization synergistic effect structurally enhances the chemisorption of polysulfides and effectively suppresses the shuttle effect.

[0028] 3. This heterojunction significantly reduces the activation energy of Li2S precipitation / decomposition, achieving bidirectional catalytic acceleration of key liquid-solid conversion steps and greatly improving sulfur oxidation-reduction kinetics.

[0029] 4.Bi4Ti3O 12 The ferroelectric polarization generates a localized uniform polarization field, which can homogenize the lithium-ion flux, suppress lithium dendrite growth, and stabilize the lithium metal anode.

[0030] 5. Lithium-sulfur batteries using the modified separator of this invention exhibit excellent cycle stability and rate performance, with an initial discharge capacity of 1000-1200 mAh g at 0.5C. -1 It has a high capacity retention rate after 500 cycles, with a capacity decay rate of less than 0.1% per cycle. Attached Figure Description

[0031] Figure 1 Bi4Ti3O prepared for this invention 12 - Schematic diagram of the process of Bi2S3 heterojunction and modified diaphragm.

[0032] Figure 2 Bi4Ti3O prepared in Example 1 of this invention 12 -X-ray diffraction (XRD) pattern of Bi2S3 heterojunction.

[0033] Figure 3 Bi4Ti3O prepared in Example 1 of this invention 12 -Scanning electron microscope (SEM) image of a Bi2S3 heterojunction.

[0034] Figure 4 Bi4Ti3O prepared in Example 1 of this invention 12 Transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) images of the Bi2S3 heterojunction.

[0035] Figure 5 Bi4Ti3O prepared in Example 1 of this invention 12 - EDS Mapping diagram of Bi2S3 heterojunction.

[0036] Figure 6 The images show SEM and EDS mappings of the lithium-sulfur battery separator prepared in Example 1 of this invention.

[0037] Figure 7 The graph shows a comparison of the cycle performance of lithium-sulfur batteries assembled with separators in Examples 1, 2, and 3.

[0038] Figure 8 The chart shows a comparison of the rate performance of lithium-sulfur batteries obtained by assembling the separators in Examples 1, 2, and 3.

[0039] Figure 9The chart shows comparative data on the cycle performance of lithium-sulfur batteries assembled with separators from Examples 1, 1, 2, and 3.

[0040] Figure 10 The data chart shows the rate performance comparison of lithium-sulfur batteries assembled with separators in Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3. Detailed Implementation

[0041] To make the technical solutions and advantages of the present invention clearer, the present invention and its beneficial effects will be described in further detail below with reference to specific embodiments and accompanying drawings. However, the embodiments of the present invention are not limited thereto.

[0042] Example 1

[0043] A method for enhancing the performance of lithium-sulfur batteries using a piezoelectric-semiconductor heterojunction includes the following steps:

[0044] S1, Bi4Ti3O 12 Preparation of the precursor: 3.23 g of bismuth nitrate pentahydrate and 1.70 g of tetrabutyl titanate (Bi:Ti molar ratio approximately 4:3) were weighed and dissolved in 60 mL of 5 M NaOH aqueous solution. After magnetic stirring for 30 minutes, the mixture was ultrasonically dispersed for 20 minutes. The resulting suspension was transferred to a 100 mL high-pressure reactor lined with polytetrafluoroethylene, sealed, and placed in an oven at 180 °C for 12 hours. After the reaction was complete, the mixture was allowed to cool naturally to room temperature. The solid product was collected by centrifugation, washed three times alternately with deionized water and anhydrous ethanol, and dried overnight at 70 °C to obtain Bi₄Ti₃O₃. 12 Precursor powder.

[0045] S2, Bi4Ti3O 12 Preparation of Bi2S3 heterojunction: Weigh 0.2343g of the above Bi4Ti3O 12 The precursor powder (approximately 0.2 mmol) was dispersed in 30 mL of deionized water. (Prepared according to Bi₄Ti₃O₄) 12 A 1:3 molar ratio of sodium hydrosulfide (NaHS) was used. 0.0336 g of NaHS was dissolved in an appropriate amount of deionized water and added dropwise to the above suspension. Deionized water was then added to bring the total volume to 60 mL. The mixture was transferred to a 100 mL autoclave, sealed, and placed in an oven at 180 °C for 12 hours. After the reaction was complete, the mixture was allowed to cool naturally to room temperature. The black product was collected by centrifugation, washed three times alternately with deionized water and anhydrous ethanol, and dried overnight at 70 °C to obtain Bi₄Ti₃O₃. 12 -Bi2S3 heterojunction material, denoted as BTO-BS-1:3.

[0046] S3. Preparation of the modified separator: The above-mentioned BTO-BS-1:3 heterojunction material, Ketjen Black (KB), and polyvinylidene fluoride (PVDF) were thoroughly ground and mixed in an agate mortar at a mass ratio of 7:2:1. An appropriate amount of N-methylpyrrolidone (NMP) was added, and the mixture was magnetically stirred until a uniform slurry was formed. The slurry was uniformly coated onto the surface of a commercial polypropylene (Celgard 2325) separator using a scraper, controlling the coating thickness to approximately 3 micrometers. The coated separator was placed in a vacuum drying oven at 60°C and dried overnight. The dried modified separator was punched into round pieces with a diameter of 19 mm and labeled as BTO-BS separators.

[0047] S4. Lithium-sulfur battery assembly and testing: Sublimed sulfur and Ketjen black were mixed at a mass ratio of 75:25 and heat-treated at 155℃ for 12 hours to obtain the S / KB composite cathode material. The S / KB composite material, Ketjen black, and PVDF were mixed in NMP at a mass ratio of 80:10:10 to form a slurry, which was then coated onto carbon-coated aluminum foil, vacuum dried at 60℃, and punched into 12mm diameter discs as the cathode material, with a sulfur loading of 0.8~1.1 mg / cm³. -2 CR2032 coin cells were assembled in an argon glove box using lithium foil as the negative electrode and 1.0 M LiTFSI / (DOL+DME, volume ratio 1:1, containing 2 wt% LiNO3) as the electrolyte, along with the above-mentioned BTO-BS modified separator.

[0048] Testing showed that the lithium-sulfur battery assembled in this embodiment had an initial discharge capacity of 1172 mAh g at a 0.5C rate. -1 After 500 cycles, the reversible capacity is 609 mAh g. -1 The capacity decay rate per cycle is 0.096%. It still provides 854mAh g at 2C rate. -1 The specific discharge capacity.

[0049] Figure 2 The Bi4Ti3O prepared in Example 1 is shown. 12 -X-ray diffraction (XRD) pattern of Bi2S3 heterojunction.

[0050] Figure 3 The Bi4Ti3O prepared in Example 1 is shown. 12 -Scanning electron microscope (SEM) image of a Bi2S3 heterojunction.

[0051] Figure 4 The Bi4Ti3O prepared in Example 1 is shown. 12 Transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) images of the Bi2S3 heterojunction.

[0052] Example 2

[0053] A method for enhancing the performance of lithium-sulfur batteries using a piezoelectric-semiconductor heterojunction includes the following steps:

[0054] S1, Bi4Ti3O 12 Preparation of precursor: Same as in Example 1.

[0055] S2, Bi4Ti3O 12 Preparation of Bi2S3 heterojunction: Weigh 0.2343g of the above Bi4Ti3O 12 Precursor powder, according to Bi4Ti3O 12 Weigh 0.056 g of NaHS with sodium hydrosulfide (NaHS) in a molar ratio of 1:5, and perform the remaining operations as in Example 1. The resulting product is denoted as BTO-BS-1:5.

[0056] S3. Preparation of modified membrane: Same as in Example 1, using BTO-BS-1:5 as the active material.

[0057] S4. Lithium-sulfur battery assembly and testing: Same as Example 1.

[0058] Testing showed that the lithium-sulfur battery assembled in this embodiment has an initial discharge capacity of 1055 mAh g at a 0.5C rate. -1 After 500 cycles, the reversible capacity is 611 mAh g. -1 .

[0059] Example 3

[0060] A method for enhancing the performance of lithium-sulfur batteries using a piezoelectric-semiconductor heterojunction includes the following steps:

[0061] S1, Bi4Ti3O 12 Preparation of precursor: Same as in Example 1.

[0062] S2, Bi4Ti3O 12 Preparation of Bi2S3 heterojunction: Weigh 0.2343g of the above Bi4Ti3O 12 Precursor powder, according to Bi4Ti3O 12 Weigh 0.0112 g of NaHS with a molar ratio of 1:1, and perform the remaining operations as in Example 1. The resulting product is denoted as BTO-BS-1:1.

[0063] S3. Preparation of modified membrane: Same as in Example 1, using BTO-BS-1:1 as the active material.

[0064] S4. Lithium-sulfur battery assembly and testing: Same as Example 1.

[0065] Testing showed that the lithium-sulfur battery assembled in this embodiment had an initial discharge capacity of 1071 mAh g at a 0.5C rate. -1 After 500 cycles, the reversible capacity is 601 mAh g. -1 .

[0066] Comparative Example 1

[0067] With pure Bi4Ti3O 12 Replacement of Bi4Ti3O 12 -Bi2S3 heterojunction, prepare modified separator according to step S3 of Example 1 and assemble battery.

[0068] Tests showed that the lithium-sulfur battery assembled in this comparative example had an initial discharge capacity of 1127 mAh g at a 0.5C rate. -1 After 500 cycles, the reversible capacity is 568 mAh g. -1 Its performance is better than that of the unmodified diaphragm, but not as good as that of Example 1.

[0069] Comparative Example 2

[0070] Replacing Bi4Ti3O with pure Bi2S3 12 -Bi2S3 heterojunction, prepare modified separator according to step S3 of Example 1 and assemble battery.

[0071] Tests showed that the lithium-sulfur battery assembled in this comparative example had an initial discharge capacity of 1083 mAh g at a 0.5C rate. -1 After 500 cycles, the reversible capacity is 533 mAh g. -1 Its performance is better than that of the unmodified diaphragm, but not as good as that of Example 1.

[0072] Comparative Example 3

[0073] Lithium-sulfur batteries were directly assembled using commercially available unmodified polypropylene (Celgard 2325) separator PP. The cathode preparation and battery assembly steps were the same as in Example 1, S4.

[0074] Testing showed that the lithium-sulfur battery assembled in this comparative example had an initial discharge capacity of 829 mAh g at a 0.5C rate. -1 After 500 cycles, the reversible capacity is 443 mAh g. -1 The capacity decay is significant.

[0075] Results Analysis

[0076] The electrochemical performance comparison of Examples 1 to 3 and Comparative Examples 1 to 3 is shown in the table below:

[0077]

[0078] As can be seen from the table above, the Bi4Ti3O prepared in the embodiments of the present invention...12 Bi2S3 heterojunction modified separator significantly improves the initial discharge capacity and cycle stability of lithium-sulfur batteries, with effects that are significantly better than unmodified separators and single-component Bi4Ti3O. 12 Or a Bi2S3 modified membrane. Among them, Bi4Ti3O 12 The best overall performance was achieved when the molar ratio with NaHS was 1:3 (Example 1), indicating that a moderate degree of sulfidation can form the optimal heterogeneous interface density and synergistic catalytic effect.

[0079] Based on the disclosure and guidance of the foregoing specification, those skilled in the art can make changes and modifications to the above embodiments. Therefore, the present invention is not limited to the specific embodiments described above, and any obvious improvements, substitutions, or modifications made by those skilled in the art based on the present invention are within the scope of protection of the present invention. Furthermore, although some specific terms are used in this specification, these terms are only for convenience of explanation and do not constitute any limitation on the present invention.

Claims

1. A method for enhancing the performance of lithium-sulfur batteries using a piezoelectric-semiconductor heterojunction, characterized in that, Includes the following steps: S1: Bi₄Ti₃O₃ is prepared by dissolving bismuth and titanium sources in an alkaline aqueous solution at a Bi:Ti molar ratio of 4:3 and reacting the solutions hydrothermally at 160-200℃ for 6-18 hours. 12 Precursor; S2: Bi4Ti3O 12 The precursor and sulfur source are placed in a reaction medium at a molar ratio of 1:1 to 1:5, and an in-situ sulfidation reaction is carried out at 140-200℃ for 6-18 hours, thereby partially removing Bi4Ti3O. 12 It is converted to Bi2S3 to obtain Bi4Ti3O 12 -Bi2S3 ferroelectric-semiconductor heterojunction material; S3: Bi4Ti3O 12 Bi2S3 heterojunction material, conductive agent and binder are mixed in a mass ratio of 7:2:1 to form a slurry, which is then coated on the surface of a lithium-sulfur battery separator with a coating thickness of 1-10 micrometers. After drying, a modified separator is obtained. S4: Assemble the modified separator in a lithium-sulfur battery.

2. The method according to claim 1, characterized in that, The bismuth source in step S1 includes at least one of bismuth pentahydrate, bismuth nitrate, bismuth chloride, and bismuth acetate; the titanium source includes at least one of tetrabutyl titanate, titanium tetrachloride, and titanium oxysulfate; and the alkaline aqueous solution is an aqueous solution of sodium hydroxide or potassium hydroxide with a concentration of 2-8M.

3. The method according to claim 1, characterized in that, The sulfur source mentioned in step S2 includes at least one of sodium hydrosulfide, sodium sulfide, thioacetamide, and thiourea.

4. The method according to claim 1, characterized in that, The conductive agent in step S3 includes at least one of Ketjen Black, acetylene black, Super P, carbon nanotubes, and graphene; the binder includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, sodium alginate, and sodium carboxymethyl cellulose; and the membrane includes one of polypropylene membrane, polyethylene membrane, and polypropylene / polyethylene / polypropylene three-layer composite membrane.

5. A Bi4Ti3O 12 -Bi2S3 ferroelectric-semiconductor heterojunction material, characterized in that... Prepared by the method described in any one of claims 1-4.

6. A modified separator for lithium-sulfur batteries, characterized in that, Contains the Bi4Ti3O as described in claim 5 12 -Bi2S3 ferroelectric-semiconductor heterojunction material.

7. A lithium-sulfur battery, characterized in that, It includes the modified diaphragm as described in claim 6.

8. The Bi4Ti3O as described in claim 5 12 Applications of Bi2S3 ferroelectric-semiconductor heterojunction materials in lithium-sulfur battery cathode materials, separator coatings, intermediate layers, or polysulfide adsorbents.

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