Preparation method and application of composite sulfur positive electrode packaged by sulfide-halide composite electrolyte spherical shell

Abstract

The invention discloses a preparation method and application of a composite sulfur positive electrode packaged by a sulfide-halide composite electrolyte spherical shell. The composite sulfur positive electrode packaged by the sulfide-halide composite electrolyte spherical shell provided by the invention has a core-shell structure, the inner core is a sulfur-carbon composite material, and the outer layer is a sulfide-halide composite electrolyte shell; the sulfur volume change effect in the charging and discharging process can be effectively relieved, uniform stress distribution and effective contact in the composite positive electrode are ensured, and the utilization rate of positive electrode active substances and the overall energy density of the battery are improved. Meanwhile, the composite sulfur positive electrode provided by the invention has high ionic conductivity at room temperature, can significantly improve the reaction kinetics of the positive electrode and improve the capacity and rate capability of the battery, can be used for assembling and preparing a solid-state lithium-sulfur battery, has good safety performance and high energy density, and has a wide application prospect.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium-sulfur battery positive electrode materials, and particularly relates to a preparation method of a sulfur positive electrode based on a sulfide-halide composite electrolyte filler and an application of the same in a solid-state lithium-sulfur battery. Background Art

[0002] With the popularization of portable electronic devices, the application and promotion of electric vehicles, the demand for energy storage devices in today's society is increasing day by day. Traditional liquid lithium-ion batteries are limited by the low theoretical capacity of electrode materials and are difficult to meet the requirements of new generation electronic devices for high energy density energy storage systems. In addition, as the scale of battery energy storage gradually expands, battery safety has become increasingly important. The liquid electrolytes used in traditional battery systems are subject to the dangers of electrolyte leakage, combustion, and explosion. Therefore, it is particularly important to develop a new generation of energy storage systems with high energy density and high safety, among which solid-state lithium-sulfur batteries have attracted widespread attention.

[0003] The sulfur in the positive electrode of solid-state lithium-sulfur batteries has a high theoretical specific capacity (1672 mAh g -1 ), sulfur also has the advantages of abundant mineral resources and low cost, and the metal lithium anode has a very low standard electrode potential (-3.04V vs.SHE) and a very high theoretical capacity density (3860mAh g -1 ), in addition, the non-flammable solid electrolyte used in solid-state lithium-sulfur batteries replaces the traditional organic electrolyte and diaphragm, fundamentally avoiding the safety risks of liquid batteries. At the same time, the solid electrolyte inhibits the dissolution and shuttle effect of polysulfide, the intermediate product of positive electrode charge and discharge, and theoretically has better cycle stability. Therefore, solid-state lithium-sulfur batteries are expected to be widely used as a new generation of battery systems with both high energy density and high safety performance.

[0004] Although solid-state lithium-sulfur batteries have great development potential, they still face many challenges. Among them, the low actual energy density and poor cycle stability of the positive electrode are the biggest obstacles to the commercial application of solid-state lithium-sulfur batteries. The reasons include: (1) Low active material loading. Due to the low ion / electronic conductivity (<10 -9 Scm -1), a large amount of electronic conductors (conductive agents) and ion conductors (solid electrolytes) are usually required to build an efficient electronic / ion conduction network inside the positive electrode, which limits the proportion of sulfur in the composite positive electrode and the improvement of the energy density of solid-state lithium-sulfur batteries. (2) There is a chemical-mechanical failure phenomenon inside the composite sulfur positive electrode. During the charge and discharge process, the large volume expansion and contraction effect of the positive electrode active materials such as sulfur / lithium sulfide will cause poor contact between the components inside the positive electrode. This chemical-mechanical failure phenomenon makes the carrier transmission path inside the positive electrode more tortuous, resulting in poor battery cycle stability and rate performance. (3) Electrolyte degradation. A high interface contact area between components is crucial for fully utilizing the sulfur positive electrode active material. However, the huge interface area between the solid electrolyte and the conductive additive may lead to electrolyte degradation that cannot be ignored. For example, sulfide solid electrolytes can degrade at the composite interface. These degradation products always adhere to the active material and the solid electrolyte phase, which ultimately affects the charge and discharge performance of the composite material itself. Summary of the invention

[0005] In view of this, the purpose of the present invention is to provide a preparation method of a composite sulfur positive electrode encapsulated by a sulfide-halide composite electrolyte spherical shell and its application in a solid-state lithium-sulfur battery. The preparation method can be used to prepare a composite sulfur positive electrode with high discharge specific capacity and high cycle stability on a large scale, and a solid-state lithium-sulfur battery assembled with the composite sulfur positive electrode prepared on a large scale has the characteristics of excellent cycle performance and high energy density.

[0006] In the present invention, the composite sulfur positive electrode provided by the present invention is a core-shell structure, the core is a sulfur-carbon active material, the outer layer is a sulfide-halide composite electrolyte shell, the sulfide electrolyte is an LPSC type sulfide fast ion conductor, the halide electrolyte is a LYB type halide fast ion conductor, and the sulfur-carbon material is a S / CNT composite material. The preparation method comprises the following steps:

[0007] Step (1): a sulfur-carbon composite material preparation process, wherein sulfur and carbon nanotubes are fully ground and sealed in a vacuum tube, and subjected to melt sulfurization treatment to obtain a sulfur-carbon composite material S / CNT;

[0008] Step (2): a sulfide electrolyte preparation process, wherein lithium sulfide, phosphorus pentasulfide and lithium chloride are placed in a ball mill for ball milling and mixing to obtain a sulfide electrolyte LPSC precursor, and the obtained sulfide electrolyte LPSC precursor is subjected to heating and sintering treatment to obtain a sulfide electrolyte LPSC;

[0009] Step (3): a halide electrolyte preparation process, placing lithium bromide and yttrium bromide in a ball mill for ball milling and mixing to obtain a halide electrolyte precursor LYB, and heating and sintering the obtained halide electrolyte LYB precursor to obtain a halide electrolyte LYB;

[0010] Step (4): a composite positive electrode powder preparation process, wherein the S / CNT, LPSC, LYB and conductive carbon are ball-milled to obtain a composite sulfur positive electrode powder encapsulated in a sulfide-halide composite electrolyte spherical shell.

[0011] Step (5): a composite positive electrode sheet preparation process, wherein the composite sulfur positive electrode powder obtained in step 4 is ground and mixed with a PTFE binder and rolled multiple times to obtain a composite sulfur positive electrode powder encapsulated in a sulfide-halide composite electrolyte spherical shell.

[0012] The following is a preferred technical solution of the present invention:

[0013] In step (1), the mass ratio of the sulfur element to the conductive carbon is 7:2-4, and most preferably 7:3. The temperature of the melt sulfurization treatment is preferably 150-160° C., and the holding time is preferably 8-10 h.

[0014] In step (2), the stoichiometric ratio of lithium sulfide, phosphorus pentasulfide and lithium chloride is preferably (2-2.5):0.5:(1-1.5), the ball milling mixing time is preferably 5-20 hours, and the rotation speed is preferably 200-800 r / min.

[0015] In step (3), the stoichiometric ratio of lithium bromide to yttrium bromide is preferably 3:0.8-1.2, most preferably 3:1, the ball milling mixing time is preferably 5-20 hours, and the rotation speed is preferably 200-800 r / min.

[0016] In step (4), the mass ratio of S / CNT, LPSC, LYB and conductive agent is preferably 3:(1-3):(1-3):1, the ball milling mixing time is preferably 5-20 h, and the rotation speed is preferably 200-800 r / min.

[0017] In step (5), the mass ratio of the composite sulfur positive electrode powder to PTFE is preferably 100:(0.5-2).

[0018] The present invention discloses a method for preparing a composite sulfur positive electrode encapsulated by a sulfide-halide composite electrolyte spherical shell and its application in a solid-state lithium-sulfur battery, wherein metallic lithium or lithium alloy is used as a negative electrode material, and is stacked with a solid-state electrolyte film and a composite positive electrode plate to assemble and prepare a solid-state lithium-sulfur battery. Specifically, the method includes:

[0019] Prepare a solid electrolyte film, the solid electrolyte film includes a sulfide electrolyte film and a polymer electrolyte film. The preparation method of the sulfide electrolyte film is as follows: a sulfide solid electrolyte (including but not limited to Li6PS5Cl, Li 10 GeP2S 12 and Li7P3S 11) and polytetrafluoroethylene binder are mixed and ground in a ratio of 100:0.5-2 and shear force is applied to prepare an electrolyte film with a thickness of about 0.05-0.3 mm; the polymer electrolyte film preparation method is as follows: PEO and 20wt% LLZTO electrolyte are dispersed in acetonitrile solvent, coated on a polytetrafluoroethylene template material, and prepared into an electrolyte film with a thickness of about 0.05-0.3 mm.

[0020] Metallic lithium or a Li-In alloy with a metal lithium mass fraction of 0 to 3 wt% is used as the negative electrode material, which is stacked with an electrolyte film and a composite positive electrode to assemble and prepare a solid-state lithium-sulfur battery.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] 1. The core-shell structure of spherical shell encapsulated sulfur in LPSC / LYB composite electrolyte has a good confinement effect on sulfur active substances. Compared with traditional sulfur positive electrode components and processes, the core-shell structure inhibits the volume change of sulfur active substances during charging and discharging, ensures stable contact of each phase, and improves the cycling stability and capacity retention rate of the sulfur positive electrode.

[0023] 2. The LPSC / LYB composite electrolyte shell introduced inside the composite sulfur positive electrode combines the advantages of sulfide electrolyte used as sulfur positive electrode filler. It has excellent lithium ion conductivity and good chemical and mechanical compatibility with active substances. It can ensure that the composite sulfur positive electrode has an efficient ion conduction network, overcome the problem of poor electrochemical stability of sulfide electrolyte, and ensure the cycle stability of the composite sulfur positive electrode.

[0024] 3. The LPSC / LYB composite electrolyte spherical shell introduced inside the composite sulfur positive electrode combines the advantages of halide electrolyte as sulfur positive electrode filler, and has excellent ionic conductivity and electrochemical stability, ensuring that the composite sulfur positive electrode has stable ionic conductivity. At the same time, it overcomes the problem of poor chemical compatibility of halide electrolyte with sulfur active substances, ensuring the structural stability inside the composite sulfur positive electrode.

[0025] 4. The solid-state lithium-sulfur battery using the composite sulfur positive electrode developed by the present invention has the characteristics of excellent cycle performance, high charge and discharge specific capacity, and good safety.

[0026] 5. The composite sulfur positive electrode encapsulated by the sulfide-halide composite electrolyte spherical shell provided by the present invention has a core-shell structure, the core is a sulfur-carbon composite material, and the outer layer is a sulfide-halide composite electrolyte shell. Based on the unique heterogeneous structure of the sulfide-halide composite electrolyte shell, the sulfur volume change effect during charging and discharging can be effectively alleviated, and the uniform stress distribution and effective contact inside the composite positive electrode can be ensured, which is conducive to improving the utilization rate of the positive electrode active material and the overall energy density of the battery. At the same time, the composite sulfur positive electrode provided by the present invention has high ionic conductivity at room temperature, which can significantly improve the positive electrode reaction kinetics, improve the capacity and rate performance of the battery; the test results of the embodiment show that the solid-state lithium-sulfur battery based on the composite sulfur positive electrode encapsulated by the sulfide-halide composite electrolyte spherical shell provided by the present invention has good safety performance and high energy density, can replace traditional lithium-ion batteries, is suitable for electric vehicles, power storage and other uses, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is the SEM image of the LPSC electrolyte obtained in Example 1.

[0028] Figure 2 This is the SEM image of the LYB electrolyte obtained in Example 1.

[0029] Figure 3 This is the SEM image of the S / LPSC-LYB composite sulfur positive electrode obtained in Example 1. DETAILED DESCRIPTION

[0030] The present invention provides a method for preparing a high-performance composite sulfur positive electrode, comprising the following steps:

[0031] Step 1: Preparation process of sulfur-carbon composite material, sulfur element and carbon nanotubes are fully ground and mixed in a mass ratio of 7:3, sealed in a vacuum tube, and melt-sulfurized at 150-170° C. for 4-24 hours to obtain sulfur-carbon composite material S / CNT;

[0032] Step 2: Sulfide electrolyte preparation process, lithium sulfide, phosphorus pentasulfide and lithium chloride are placed in a ball mill according to a certain stoichiometric ratio, and ball-milled at a rotation speed of 200-800 rpm. The reaction time is 5-20 hours to obtain a sulfide electrolyte LPSC precursor. The obtained sulfide electrolyte LPSC precursor is placed in a sintering furnace and heated and sintered in an inert atmosphere. The temperature rise program is adjusted to 1-20°C / min, and the temperature is raised to 400-600°C. Keep warm for 2-10 hours and naturally cool to room temperature to obtain a sulfide electrolyte LPSC.

[0033] Step 3: Preparation process of halide electrolyte, lithium bromide and yttrium bromide are placed in a ball mill according to a certain stoichiometric ratio, and ball milled at a speed of 200-800 rpm for 5-20 hours to obtain a halide electrolyte LYB precursor, and the obtained halide electrolyte LYB precursor is placed in a sintering furnace, and heated and sintered in an inert atmosphere. The temperature is adjusted to 1-20°C / min, and the temperature is raised to 400-700°C, kept warm for 2-10 hours, and naturally cooled to room temperature to obtain a halide electrolyte LYB. ;

[0034] Step 4: Composite cathode powder preparation process, the S / CNT, LPSC, LYB and conductive carbon are placed in a ball mill according to a certain stoichiometric ratio, and ball milled at a speed of 200 to 800 rpm for 5 to 20 hours to obtain a composite sulfur cathode powder encapsulated in a sulfide-halide composite electrolyte shell.

[0035] Step 5: a composite positive electrode preparation process, wherein the composite sulfur positive electrode powder obtained in step 4 is ground and mixed with a PTFE binder in a certain mass ratio and rolled multiple times to obtain a composite sulfur positive electrode encapsulated in a sulfide-halide composite electrolyte spherical shell.

[0036] In the present invention, unless otherwise specified, the components are commercially available products well known to those skilled in the art.

[0037] In step 1 of the present invention, the present invention has no special limitation on the grinding process, and a grinding method well known to those skilled in the art can be used. The grinding time is preferably 0.2 to 3 hours, more preferably 0.5 to 1 hour; the temperature of the melt sulfurization treatment is preferably 150 to 160° C., more preferably 152 to 158° C.; the holding time is preferably 6 to 20 hours, more preferably 8 to 15 hours.

[0038] In step 2 of the present invention, the stoichiometric ratio of lithium sulfide, phosphorus pentasulfide and lithium chloride is preferably (1.5-3):0.5:(0.5-2), more preferably (2-2.5):0.5:(1-1.5); the rotation speed of the ball milling mixing is preferably 300-700 rpm, more preferably 400-600 rpm; the ball milling reaction time is preferably 5-15 h, more preferably 10-15 h; the heating rate is preferably 5-20 ° C / min, more preferably 5-10 ° C / min; the insulation temperature is preferably 450-650 ° C, more preferably 500-600 ° C; the insulation time is preferably 4-6 h, more preferably 4.5-5.5 h.

[0039] In step 3 of the present invention, the rotation speed of the ball milling mixing is preferably 300-700 rpm, more preferably 400-600 rpm; the ball milling reaction time is preferably 5-15 h, more preferably 10-15 h; the heating rate is preferably 5-20 ° C / min, more preferably 5-10 ° C / min; the insulation temperature is preferably 450-650 ° C, more preferably 500-600 ° C; the insulation time is preferably 4-6 h, more preferably 4.5-5.5 h.

[0040] In step 4 of the present invention, the stoichiometry of the S / CNT, LPSC, LYB and conductive carbon is preferably 3:(1-3):(1-3):1, more preferably 3:(2-3):(1-2):1; the rotation speed of the ball milling mixing is preferably 300-700 rpm, more preferably 400-600 rpm; the ball milling reaction time is preferably 5-15 h, more preferably 10-15 h; the conductive carbon is preferably Super P, carbon nanotubes, carbon nanofibers, more preferably carbon nanofibers.

[0041] In step 5 of the present invention, the mass ratio of the sulfide electrolyte to the PTFE is preferably 100:(0.5-2), more preferably 100:(0.5-1); the present invention has no special limitation on the rolling process, and a rolling method well known to those skilled in the art can be used, and the rolling time is preferably 0.2-3h, more preferably 0.5-2h;

[0042] The present invention adopts LPSC-LYB composite solid electrolyte as the lithium ion conductor in the composite sulfur positive electrode, rather than directly using sulfide electrolyte LPSC or halide electrolyte LYB. The technical concept is that, on the one hand, compared with sulfide electrolyte LPSC, LPSC-LYB has higher electrochemical stability and a wider stable voltage range, which can better meet the needs of rapid ion conduction inside the positive electrode under long cycle conditions; on the other hand, compared with halide electrolyte LYB, LPSC-LYB has higher ionic conductivity and interfacial compatibility with sulfur, which improves the reaction kinetics inside the positive electrode and reduces electrochemical polarization.

[0043] In order to further illustrate the present invention, a high-performance composite sulfur positive electrode material provided by the present invention and its preparation method and application are described in detail below in combination with the embodiments, but they should not be understood as limiting the scope of protection of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0044] Example 1

[0045] 0.7 g of sulfur and 0.3 g of carbon nanotubes were fully ground for 0.5 h and then sealed in a vacuum tube. The temperature was raised to 155 ° C for melt sulfurization treatment and kept warm for 12 h to obtain a sulfur-carbon composite material S / CNT. 0.86 g of lithium sulfide, 0.83 g of phosphorus pentasulfide and 0.32 g of lithium chloride were placed in a ball mill and subjected to ball milling reaction at a speed of 550 rpm for 10 h to obtain a precursor of the sulfide electrolyte Li6PS5Cl (LPSC). The LPSC precursor was placed in a quartz boat, and the quartz boat was placed in a tube furnace for heating and sintering under argon conditions. The reaction temperature was adjusted. The temperature was raised to 550°C at 5°C / min, kept at this temperature for 6 hours, and naturally cooled to room temperature to obtain the sulfide electrolyte LPSC. 0.88g lithium bromide and 1.12g yttrium bromide were placed in a ball mill and subjected to ball milling reaction at a speed of 550rpm for 10 hours to obtain the halide electrolyte Li3YBr6 (LYB). The LYB precursor was placed in a quartz boat, and the quartz boat was placed in a tube furnace for heating and sintering treatment under argon conditions. The temperature was adjusted to 5°C / min, raised to 550°C, kept at this temperature for 6 hours, and naturally cooled to room temperature to obtain the halide electrolyte LYB. The above-obtained 0.23g S / CNT, 0.23g LPSC, 0.079g LYB and 0.079g carbon nanofiber were placed in a ball mill and mixed by ball milling at a rotation speed of 500rpm to obtain S / LPSC-LYB powder with a core-shell structure; 0.1g of the above-obtained S / LPSC-LYB powder was ground and mixed with 0.001g PTFE and rolled several times to obtain a S / LPSC-LYB composite positive electrode film with a thickness of about 40 microns.

[0046] Example 2

[0047] 0.7 g of sulfur and 0.3 g of carbon nanotubes were fully ground for 0.5 h and then sealed in a vacuum tube. The temperature was raised to 155 ° C for melt sulfurization treatment and kept warm for 12 h to obtain a sulfur-carbon composite material S / CNT. 0.86 g of lithium sulfide, 0.83 g of phosphorus pentasulfide and 0.32 g of lithium chloride were placed in a ball mill and subjected to ball milling reaction at a speed of 550 rpm for 10 h to obtain a precursor of the sulfide electrolyte Li6PS5Cl (LPSC). The LPSC precursor was placed in a quartz boat, and the quartz boat was placed in a tube furnace for heating and sintering under argon conditions. The reaction temperature was adjusted. The temperature was raised to 550°C at 5°C / min, kept at this temperature for 6 hours, and naturally cooled to room temperature to obtain the sulfide electrolyte LPSC. 0.88g lithium bromide and 1.12g yttrium bromide were placed in a ball mill and subjected to ball milling reaction at a speed of 550rpm for 10 hours to obtain the halide electrolyte Li3YBr6 (LYB). The LYB precursor was placed in a quartz boat, and the quartz boat was placed in a tube furnace for heating and sintering treatment under argon conditions. The temperature was adjusted to 5°C / min, raised to 550°C, kept at this temperature for 6 hours, and naturally cooled to room temperature to obtain the halide electrolyte LYB. The above-obtained 0.23g S / CNT, 0.158g LPSC, 0.158g LYB and 0.079g carbon nanofiber were placed in a ball mill and mixed by ball milling at a rotation speed of 500rpm to obtain S / LPSC-LYB powder with a core-shell structure; 0.1g of the above-obtained S / LPSC-LYB powder was ground and mixed with 0.001g PTFE and rolled several times to obtain a S / LPSC-LYB composite positive electrode film with a thickness of about 40 microns.

[0048] Example 3

[0049] 0.7 g of sulfur and 0.3 g of carbon nanotubes were fully ground for 0.5 h and then sealed in a vacuum tube. The temperature was raised to 155 ° C for melt sulfurization treatment and kept warm for 12 h to obtain a sulfur-carbon composite material S / CNT. 0.86 g of lithium sulfide, 0.83 g of phosphorus pentasulfide and 0.32 g of lithium chloride were placed in a ball mill and subjected to ball milling reaction at a speed of 550 rpm for 10 h to obtain a precursor of the sulfide electrolyte Li6PS5Cl (LPSC). The LPSC precursor was placed in a quartz boat, and the quartz boat was placed in a tube furnace for heating and sintering under argon conditions. The reaction temperature was adjusted. The temperature was raised to 550°C at 5°C / min, kept at this temperature for 6 hours, and naturally cooled to room temperature to obtain the sulfide electrolyte LPSC. 0.88g lithium bromide and 1.12g yttrium bromide were placed in a ball mill and subjected to ball milling reaction at a speed of 550rpm for 10 hours to obtain the halide electrolyte Li3YBr6 (LYB). The LYB precursor was placed in a quartz boat, and the quartz boat was placed in a tube furnace for heating and sintering treatment under argon conditions. The temperature was adjusted to 5°C / min, raised to 550°C, kept at this temperature for 6 hours, and naturally cooled to room temperature to obtain the halide electrolyte LYB. The above-obtained 0.23g S / CNT, 0.079g LPSC, 0.23g LYB and 0.079g carbon nanofiber were placed in a ball mill and mixed by ball milling at a rotation speed of 500rpm to obtain S / LPSC-LYB powder with a core-shell structure; 0.1g of the above-obtained S / LPSC-LYB powder was ground and mixed with 0.001g PTFE and rolled several times to obtain a S / LPSC-LYB composite positive electrode film with a thickness of about 40 microns.

[0050] Comparative Example 1

[0051] 0.7g of sulfur and 0.3g of carbon nanotubes were fully ground for 0.5h and then sealed in a vacuum tube. The temperature was raised to 155℃ for melt sulfurization treatment and kept warm for 12h to obtain a sulfur-carbon composite material S / CNT. 0.65g of lithium sulfide and 1.35g of phosphorus pentasulfide were placed in a ball mill and ball milled at a speed of 550rpm for 10h to obtain a sulfide electrolyte Li7P3S 11The precursor of (LPS) was prepared, and the LPS precursor was placed in a quartz boat, which was placed in a tube furnace, and heated and sintered under argon conditions. The heating program was adjusted to 5°C / min, and the temperature was raised to 550°C, kept warm for 6 hours, and naturally cooled to room temperature to obtain the sulfide electrolyte LPS; 0.88g of lithium bromide and 1.12g of yttrium bromide were placed in a ball mill, and ball milled at a speed of 550rpm for 10 hours to obtain the halide electrolyte Li3YBr6(LYB), and the LYB precursor was placed in a quartz boat, which was placed in a tube furnace, and heated and sintered under argon conditions. The heating program was adjusted to 5°C / min, and the temperature was raised to 550°C, kept warm for 6 hours, and naturally cooled to room temperature to obtain the halide electrolyte LYB. The above-obtained 0.23g S / CNT, 0.23g LPS, 0.079g LYB and 0.079g carbon nanofiber were placed in a ball mill and mixed by ball milling at a rotation speed of 500rpm to obtain S / LPSC-LYB powder with a core-shell structure; 0.1g of the above-obtained S / LPS-LYB powder was ground and mixed with 0.001g PTFE and rolled several times to obtain a S / LPS-LYB composite positive electrode film with a thickness of about 40 microns.

[0052] Comparative Example 2

[0053] 0.7g of sulfur and 0.3g of carbon nanotubes were fully ground for 0.5h and then sealed in a vacuum tube, heated to 155℃ for melt sulfurization treatment, and kept warm for 12h to obtain a sulfur-carbon composite material S / CNT; 0.86g of lithium sulfide, 0.83g of phosphorus pentasulfide and 0.32g of lithium chloride were placed in a ball mill and ball milled at a speed of 550rpm for 10h to obtain a precursor of a sulfide electrolyte Li6PS5Cl (LPSC), the LPSC precursor was placed in a quartz boat, the quartz boat was placed in a tube furnace, and heated and sintered under argon conditions, the heating program was adjusted to 5℃ / min, the temperature was raised to 550℃, kept warm for 6h, and naturally cooled to room temperature to obtain a sulfide electrolyte LPSC; the above-obtained 0.23g S / CNT, 0.31g LPSC and 0.079 g of carbon nanofibers were placed in a ball mill and mixed by ball milling at a speed of 500 rpm to obtain S / LPSC powder; 0.1 g of the S / LPSC powder obtained above was ground and mixed with 0.001 g of PTFE and rolled several times to obtain a S / LPSC composite cathode film with a thickness of about 40 μm.

[0054] Comparative Example 3

[0055] 0.7g of sulfur and 0.3g of carbon nanotubes were fully ground for 0.5h and then sealed in a vacuum tube. The temperature was raised to 155°C for melt sulfurization treatment and kept warm for 12h to obtain a sulfur-carbon composite material S / CNT. 0.88g of lithium bromide and 1.12g of yttrium bromide were placed in a ball mill and ball milled at 550rpm for 10h to obtain a halide electrolyte Li3YBr6 (LYB). The LYB precursor was placed in a quartz boat, and the quartz boat was placed in a tubular furnace. Heating and sintering treatment was performed under argon conditions. The heating program was adjusted to 5°C / min, the temperature was raised to 550°C, the temperature was kept warm for 6h, and the halide electrolyte LYB was obtained naturally. The above-obtained 0.23g S / CNT, 0.31g LYB and 0.079g carbon nanofibers were placed in a ball mill and mixed by ball milling at a rotation speed of 500rpm to obtain S / LYB powder; 0.1g of the above-obtained S / LYB powder was ground and mixed with 0.001g PTFE and rolled several times to obtain a S / LYB composite positive electrode film with a thickness of about 40 microns.

[0056] test:

[0057] 1. The LPSC electrolyte obtained in Example 1 was subjected to scanning electron microscopy test. Figure 1 is the SEM image of the LPSC electrolyte obtained in Example 1. Figure 1 It can be seen that the particle size range of LPSC is 2 to 5 μm.

[0058] 2. Scanning electron microscopy test was performed on the LYB electrolyte obtained in Example 1. Figure 2 is the SEM image of the LYB electrolyte obtained in Example 1. Figure 2 It can be seen that the particle size range of LYB is 2 to 5 μm.

[0059] 3. Scanning electron microscopy test was performed on the S / LPSC-LYB obtained in Example 1. Figure 3 This is the SEM image of S / LPSC-LYB obtained in Example 1.

[0060] 4. Sulfide solid electrolyte (including but not limited to Li6PS5Cl, Li 10 GeP2S 12 and Li7P3S 11 ) and polytetrafluoroethylene binder in a ratio of 100:0.5-2, and then ground and sheared to prepare an electrolyte film with a thickness of about 0.05 mm.

[0061] 5. In an argon glove box where the concentrations of water and oxygen are both less than 0.1 ppm, assemble the positive electrode shell, positive electrode sheet, electrolyte film, lithium sheet, gasket, spring sheet, and negative electrode shell in this order, and use a fully automatic sealing machine to compress and seal to obtain an all-solid-state lithium-sulfur battery;

[0062] The obtained all-solid-state lithium-sulfur battery was subjected to constant current charge and discharge and electrochemical impedance tests using a blue battery test system and an electrochemical workstation. The electrochemical tests were all carried out at 25°C. The test data are listed in Table 1.

[0063] Table 1. Comparison of solid-state battery performances assembled in various embodiments and comparative examples

[0064]

[0065] After testing: (1) The interface impedances of the solid-state lithium-sulfur batteries assembled in Example 1, Example 2, Example 3, Comparative Example 1, Comparative Example 2 and Comparative Example 3 before cycling were 25, 33, 40, 30, 28 and 108 Ω, respectively. This indicates that the high-performance composite sulfur positive electrode provided by the present invention can improve the mass transfer kinetics of lithium ions and electrons at the electrode interface. The interface impedance can reflect the ion mass transfer kinetics at the electrode-electrolyte interface to a certain extent. The smaller the interface impedance, the better the kinetics of lithium ions at the electrode interface, which is more conducive to the electrochemical reaction and further improves the electrochemical performance of the battery.

[0066] (2) The assembled batteries were subjected to constant current charge and discharge tests at a voltage range of 1.5-3.0 V and a current density of 0.1 C. The initial discharge capacities of the solid-state lithium-sulfur batteries assembled in Example 1, Example 2, Example 3, Comparative Example 1, Comparative Example 2, and Comparative Example 3 were 1450, 1318, 1198, 1380, 1420, and 584 mAh g, respectively. -1 The discharge capacity of Example 1 after 200 stable cycles is 1190 mAh g -1 , and there is no sharp increase in polarization and short circuit; the discharge capacity of Example 2 after 200 stable cycles is 948mA hg -1 , and there is no sharp increase in polarization and short circuit; the discharge capacity of Example 3 after 200 stable cycles is 767mAh g -1 ; Comparative Example 2 has a discharge capacity of only 20 mA hg after 200 cycles -1 This indicates that the high-performance composite sulfur cathode provided by the present invention has excellent long-cycle stability.

[0067] (3) The solid-state lithium-sulfur battery of Example 1 was assembled and tested in the voltage range of 1.5-3.0 V, the current density of 0.5 C, and the -2 Under high active material loading conditions, the discharge capacity after 500 cycles is 534 mAh g -1 This indicates that the high-performance composite sulfur cathode provided by the present invention has excellent long-cycle stability under the conditions of high active material loading and high current density.

[0068] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a composite sulfur positive electrode encapsulated by a sulfide-halide composite electrolyte spherical shell, comprising the following steps: Step (1): fully grinding sulfur and carbon nanotubes and sealing them in a vacuum tube, and performing melt sulfurization treatment to obtain a sulfur-carbon composite material S / CNT; Step (2): ball-milling lithium sulfide, phosphorus pentasulfide and lithium chloride to obtain a sulfide electrolyte LPSC precursor, and heating and sintering the obtained sulfide electrolyte LPSC precursor to obtain a sulfide electrolyte LPSC; Step (3): ball-milling lithium bromide and yttrium bromide to obtain a halide electrolyte LYB precursor, and heating and sintering the obtained halide electrolyte LYB precursor to obtain a halide electrolyte LYB; Step (4): ball-milling the sulfur-carbon composite material S / CNT, the sulfide electrolyte LPSC, the halide electrolyte LYB and the conductive carbon to obtain a composite sulfur positive electrode powder encapsulated in a sulfide-halide composite electrolyte spherical shell; Step (5): Grind and mix the composite sulfur positive electrode powder obtained in step 4 with a binder and perform rolling pressing for multiple times to obtain a composite sulfur positive electrode encapsulated in a sulfide-halide composite electrolyte spherical shell.

2. The preparation method according to claim 1, characterized in that: The grinding, melt sulfurization, ball milling mixing and heating sintering are all carried out in an inert gas atmosphere.

3. The preparation method according to claim 1, characterized in that: In step 1, the mass ratio of the sulfur element to the conductive carbon is 7:2-4, and the conditions for the melt sulfurization treatment are: temperature of 150-160° C. and holding time of 8-10 hours.

4. The preparation method according to claim 1, characterized in that: In step 2, the stoichiometric ratio of lithium sulfide, phosphorus pentasulfide and lithium chloride is (2-2.5):0.5:(1-1.5), the ball milling mixing time is 5-20 hours, the rotation speed is 200-800 r / min, the heating sintering treatment temperature is 400-600° C., and the insulation time is 2-10 hours.

5. The preparation method according to claim 1, characterized in that: In step 3, the stoichiometric ratio of lithium bromide to yttrium bromide is 3:0.8-1.2, the ball milling mixing time is 5-20 hours, the rotation speed is 200-800 r / min, the heating sintering treatment temperature is 400-600° C., and the insulation time is 2-10 hours.

6. The preparation method according to claim 1, characterized in that: In step 4, the mass ratio of the sulfur-carbon composite material S / CNT, the sulfide electrolyte LPSC, the halide electrolyte LYB and the conductive carbon is 3:(1-3):(1-3):1, the ball milling mixing time is 5-20h, and the rotation speed is 200-800r / min.

7. The preparation method according to claim 1, characterized in that: In step 4, the conductive carbon is one or more of acetylene black, Ketjen black, carbon nanofiber, carbon nanotube, graphene, and graphene oxide.

8. The preparation method according to claim 1, characterized in that: In step 5, the mass ratio of the composite sulfur positive electrode powder to the binder is 100:(0.5-2).

9. Use of a composite sulfur positive electrode encapsulated in a spherical shell of a sulfide-halide composite electrolyte prepared by the preparation method according to any one of claims 1 to 8 in a solid-state lithium-sulfur battery.

10. The use according to claim 9, characterized in that: include: Solid-state lithium-sulfur batteries are prepared by using metallic lithium or lithium alloy as the negative electrode material, stacking it with a composite sulfur positive electrode encapsulated by a solid electrolyte film and a sulfide-halide composite electrolyte spherical shell.

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