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

Abstract

The application discloses a preparation method and application of a composite sulfur positive electrode packaged by a sulfide-halide composite electrolyte shell. The composite sulfur positive electrode packaged by the sulfide-halide composite electrolyte shell 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. Based on the unique heterostructure of the sulfide-halide composite electrolyte shell, the volume change effect of sulfur in the charging and discharging process can be effectively relieved, the uniform stress distribution and effective contact in the composite positive electrode are ensured, and the utilization rate of the positive active material and the energy density of the whole battery are improved. At the same time, the composite sulfur positive electrode provided by the application has high ionic conductivity at room temperature, can significantly improve the positive electrode reaction kinetics, improve the capacity and rate performance of the battery, can be used for assembling and preparing solid-state lithium-sulfur batteries, has good safety performance and high energy density, and has a wide application prospect.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium-sulfur battery cathode materials, and particularly relates to a preparation method of a sulfur cathode based on a sulfide-halide composite electrolyte filler and application thereof in a solid-state lithium-sulfur battery. BACKGROUND

[0002] With the popularity 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. The traditional liquid lithium ion battery is difficult to meet the requirements of the new generation of electronic devices for high-energy-density energy storage systems due to the low theoretical capacity of the electrode material. In addition, with the gradual expansion of the battery energy storage scale, the safety of the battery becomes increasingly important. The liquid electrolyte applied in the traditional battery system has the risk of electrolyte leakage, combustion and explosion. Therefore, it is particularly important to develop a new generation of energy storage system with high energy density and high safety, among which the solid-state lithium-sulfur battery has attracted widespread attention.

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

[0004] Although the solid-state lithium-sulfur battery has great development potential, it still faces many challenges. The low actual energy density and poor cycle stability of the positive electrode are the biggest obstacles to the commercial application of the solid-state lithium-sulfur battery, and the reasons include: (1) low active material loading. Due to the low ion / electron conductivity of the positive active material such as sulfur / lithium sulfide (<10 -9 Scm -1), a large amount of electronic conductors (conductive agents) and ionic conductors (solid-state electrolytes) are usually needed to build an efficient electron / ion conduction network, which limits the proportion of sulfur in the composite cathode and the improvement of the energy density of solid-state lithium-sulfur batteries.(2) There is a chemical-mechanical failure phenomenon in the composite sulfur cathode. In the charging and discharging process, the large volume expansion and contraction effect of the sulfur / lithium sulfide active material will cause the contact failure of the components in the cathode. This chemical-mechanical failure phenomenon makes the transport path of the current carriers in the cathode more tortuous, resulting in poor cycle stability and rate performance of the battery.(3) Electrolyte degradation. The high interface contact area between the components is essential for fully utilizing the sulfur cathode active material, but the large interface area between the solid electrolyte and the conductive additive may cause non-negligible electrolyte degradation. For example, sulfide solid electrolytes can be degraded at the composite interface, and these degradation products always adhere to the vicinity of the active material and solid electrolyte phase, eventually affecting the charging and discharging performance of the composite material itself. SUMMARY

[0005] Therefore, the purpose of the present application is to provide a preparation method of a composite sulfur cathode packaged by a sulfide-halide composite electrolyte shell and its application in a solid-state lithium-sulfur battery. The preparation method can be used to scale up the preparation of a composite sulfur cathode with high discharge specific capacity and high cycle stability. The solid-state lithium-sulfur battery assembled by the scale-prepared composite sulfur cathode has excellent cycle performance and high energy density.

[0006] In the present application, the composite sulfur cathode provided by the present application has a core-shell structure, the inner core is a sulfur-carbon active material, and 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 an LYB type halide fast ion conductor, and the sulfur-carbon material is an S / CNT composite material. The preparation method comprises the following steps:

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

[0008] Step (2): Sulfide electrolyte preparation process, lithium sulfide, phosphorus pentasulfide and lithium chloride are placed in a ball mill jar and ball milled to obtain a sulfide electrolyte LPSC precursor. The obtained sulfide electrolyte LPSC precursor is subjected to a heating sintering treatment to obtain a sulfide electrolyte LPSC;

[0009] Step (3): Halide electrolyte preparation process, lithium bromide and yttrium bromide are placed in a ball mill jar and ball milled to obtain a halide electrolyte precursor LYB. The obtained halide electrolyte LYB precursor is subjected to a heating sintering treatment to obtain a halide electrolyte LYB;

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

[0011] Step (5): Composite positive electrode sheet preparation process, grinding and mixing the composite sulfur positive electrode powder obtained in step 4 with PTFE binder and rolling multiple times to obtain a composite sulfur positive electrode powder encapsulated by a sulfide-halide composite electrolyte shell.

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

[0013] In step (1), the mass ratio of the elemental sulfur and conductive carbon is 7:2-4, and the most preferred is 7:3, the temperature of the molten sulfur infiltration treatment is preferably 150-160℃, and the holding time is preferably 8-10h.

[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 5-20h, and the rotation speed is preferably 200-800r / min.

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

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

[0018] The preparation method of the composite sulfur positive electrode encapsulated by a sulfide-halide composite electrolyte shell and its application in solid-state lithium-sulfur batteries according to the present application uses metal lithium or lithium alloy as the negative electrode material, stacks with a solid-state electrolyte film and a composite positive electrode sheet to assemble and prepare a solid-state lithium-sulfur battery. Specifically includes:

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

[0020] A solid-state lithium-sulfur battery is prepared by stacking the electrolyte thin film and the composite positive electrode with the metal lithium or the Li-In alloy with a mass fraction of 0-3wt% as the negative electrode material.

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

[0022] I. The core-shell structure of the LPSC / LYB composite electrolyte spherical shell encapsulating sulfur has good confinement effect on the sulfur active material, compared with the traditional sulfur positive electrode component and process, the core-shell structure inhibits the volume change of the sulfur active material during charging and discharging, ensures stable contact of each phase, and improves the cycle stability and capacity retention rate of the sulfur positive electrode.

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

[0024] III. The LPSC / LYB composite electrolyte spherical shell introduced in the composite sulfur positive electrode combines the advantages of halide electrolyte used as a filler for the sulfur positive electrode, has excellent ion conductivity and electrochemical stability, ensures that the composite sulfur positive electrode has stable ion conductivity, and overcomes the problem of poor chemical compatibility of halide electrolyte with sulfur active material, ensuring the structural stability of the composite sulfur positive electrode.

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

[0026] Five, the composite sulfur positive electrode packaged by the sulfide-halide composite electrolyte shell 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. Based on the unique heterogeneous structure of the sulfide-halide composite electrolyte shell, the volume change effect of sulfur in the charging and discharging process can be effectively relieved, the uniform stress distribution and effective contact in the composite positive electrode are ensured, and the utilization rate of the positive active material and the energy density of the battery as a whole are improved. At the same time, the composite sulfur positive electrode provided by the application has high ionic conductivity at room temperature, 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 packaged by the sulfide-halide composite electrolyte shell has good safety performance and high energy density, can replace the traditional lithium ion battery, is suitable for electric vehicles, power storage and other purposes, and has a wide application prospect. BRIEF DESCRIPTION OF DRAWINGS

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

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

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

[0030] The application provides a preparation method of a high-performance composite sulfur positive electrode, comprising the following steps:

[0031] Step 1: a sulfur-carbon composite material preparation process, sulfur and carbon nanotubes are fully ground and mixed according to a mass ratio of 7:3, sealed in a vacuum tube, subjected to a molten sulfur infiltration treatment at 150-170 DEG C, and kept warm for 4-24 h to obtain a sulfur-carbon composite material S / CNT.

[0032] Step 2: a sulfide electrolyte preparation process, lithium sulfide, phosphorus pentasulfide and lithium chloride are placed in a ball mill pot according to a certain stoichiometric ratio, and are subjected to ball milling mixing at a speed of 200-800 rpm, the reaction time is 5-20 h, a sulfide electrolyte LPSC precursor is obtained, the obtained sulfide electrolyte LPSC precursor is placed in a sintering furnace, and is subjected to heating and sintering treatment in an inert atmosphere, the temperature rising program is 1-20 DEG C / min, the temperature is raised to 400-600 DEG C, and the temperature is kept warm for 2-10 h, and then the temperature is naturally cooled to room temperature, to obtain a sulfide electrolyte LPSC.

[0033] Step 3: halide electrolyte preparation process, lithium bromide and yttrium bromide are placed in a ball mill tank according to a certain stoichiometric ratio, and ball milling is carried out at a speed of 200-800 rpm, and the reaction time is 5-20 h, to obtain halide electrolyte LYB precursor, and the halide electrolyte LYB precursor is placed in a sintering furnace for heating and sintering treatment in an inert atmosphere, the temperature increasing procedure is 1-20 ℃ / min, the temperature is increased to 400-700 ℃, and the temperature is kept for 2-10 h, and then the temperature is naturally cooled to room temperature, to obtain halide electrolyte LYB.

[0034] Step 4: composite positive electrode powder preparation process, the S / CNT, LPSC, LYB and conductive carbon are placed in a ball mill tank according to a certain stoichiometric ratio, and ball milling is carried out at a speed of 200-800 rpm, and the reaction time is 5-20 h, to obtain a composite sulfur positive electrode powder packaged by a sulfide-halide composite electrolyte spherical shell.

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

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

[0037] In step 1 of the present application, the grinding process is not specially limited, and a grinding method well known to those skilled in the art can be used, the grinding time is preferably 0.2-3 h, and more preferably 0.5-1 h; the temperature of the molten sulfur infiltration treatment is preferably 150-160 ℃, and more preferably 152-158 ℃; and the holding time is preferably 6-20 h, and more preferably 8-15 h.

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

[0039] In step 3 of the present application, the rotation speed of the ball milling 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 temperature rising speed is preferably 5-20 ℃ / min, more preferably 5-10 ℃ / min; the holding temperature is preferably 450-650 ℃, more preferably 500-600 ℃; and the holding time is preferably 4-6 h, more preferably 4.5-5.5 h.

[0040] In step 4 of the present application, the stoichiometry of 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 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; and the conductive carbon is preferably Super P, carbon nanotube or carbon nanofiber, more preferably carbon nanofiber.

[0041] In step 5 of the present application, the mass ratio of the sulfide electrolyte and PTFE is preferably 100:(0.5-2), more preferably 100:(0.5-1); the rolling process is not particularly limited in the present application, and any rolling method known to those skilled in the art can be used; and the rolling time is preferably 0.2-3 h, more preferably 0.5-2 h.

[0042] In the present application, the LPSC-LYB composite solid-state electrolyte is used as the lithium ion conductor in the composite sulfur cathode, instead of directly using the sulfide electrolyte LPSC or the halide electrolyte LYB. The technical concept is that, on the one hand, compared with the sulfide electrolyte LPSC, the LPSC-LYB has higher electrochemical stability and a wider stable voltage range, and better meets the need for fast ion conduction in the cathode under long cycle conditions; on the other hand, compared with the halide electrolyte LYB, the LPSC-LYB has higher ionic conductivity and better interface compatibility with sulfur, which improves the reaction kinetics in the cathode and reduces the electrochemical polarization.

[0043] In order to further illustrate the present application, the high-performance composite sulfur cathode material provided by the present application, the preparation method and application thereof are described in detail below in conjunction with examples, but they should not be understood as limiting the protection scope of the present application. Obviously, the described examples are only some of the examples of the present application, but not all. Based on the examples in the present application, all other examples obtained by those skilled in the art without creative labor fall within the protection scope of the present application.

[0044] Example 1

[0045] After 0.7 g of sulfur and 0.3 g of carbon nanotubes were ground thoroughly for 0.5 h, they were sealed in a vacuum tube, heated to 155°C for molten sulfur treatment, and kept for 12 h to obtain 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 jar and ball-milled at a speed of 550 rpm for 10 h to obtain a precursor of sulfide electrolyte Li6PS5Cl (LPSC), the LPSC precursor was placed in a quartz boat, which was placed in a tube furnace, and sintered by heating under argon, with a temperature rising program of 5°C / min, the temperature was raised to 550°C and kept for 6 h, and then naturally cooled to room temperature to obtain the sulfide electrolyte LPSC; 0.88 g of lithium bromide and 1.12 g of yttrium bromide were placed in a ball mill jar and ball-milled at a speed of 550 rpm for 10 h to obtain halide electrolyte Li3YBr6 (LYB), the LYB precursor was placed in a quartz boat, which was placed in a tube furnace, and sintered by heating under argon, with a temperature rising program of 5°C / min, the temperature was raised to 550°C and kept for 6 h, and then naturally cooled to room temperature to obtain the halide electrolyte LYB. The above obtained 0.23 g of S / CNT, 0.23 g of LPSC, 0.079 g of LYB, and 0.079 g of carbon nanofiber were placed in a ball mill jar and mixed by ball-milling at a speed of 500 rpm to obtain S / LPSC-LYB powder with a core-shell structure; 0.1 g of the above obtained S / LPSC-LYB powder was mixed with 0.001 g of PTFE by grinding and rolling multiple times to obtain a S / LPSC-LYB composite positive electrode film with a thickness of about 40 microns.

[0046] Example 2

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

[0048] Example 3

[0049] Sulfur and carbon nanotubes were ground for 0.5 h and then sealed in a vacuum tube, heated to 155°C for sulfur infiltration treatment, and kept for 12 h to obtain sulfur-carbon composite material S / CNT; lithium sulfide 0.86 g, phosphorus pentasulfide 0.83 g, and lithium chloride 0.32 g were placed in a ball mill jar and ball-milled at a speed of 550 rpm for 10 h to obtain a precursor of sulfide electrolyte Li6PS5Cl (LPSC), which was placed in a quartz boat and then placed in a tube furnace for sintering treatment under argon, with a temperature rising program of 5°C / min, heating to 550°C, keeping for 6 h, and naturally cooling to room temperature to obtain sulfide electrolyte LPSC; lithium bromide 0.88 g and yttrium bromide 1.12 g were placed in a ball mill jar and ball-milled at a speed of 550 rpm for 10 h to obtain halide electrolyte Li3YBr6 (LYB), which was placed in a quartz boat and then placed in a tube furnace for sintering treatment under argon, with a temperature rising program of 5°C / min, heating to 550°C, keeping for 6 h, and naturally cooling to room temperature to obtain halide electrolyte LYB. The above obtained 0.23 g S / CNT, 0.079 g LPSC, 0.23 g LYB, and 0.079 g carbon nanofiber were placed in a ball mill jar and ball-mixed at a speed of 500 rpm to obtain S / LPSC-LYB powder with a core-shell structure; 0.1 g of the above obtained S / LPSC-LYB powder was mixed with 0.001 g PTFE by grinding and rolling multiple times to obtain S / LPSC-LYB composite positive electrode film with a thickness of about 40 microns.

[0050] Comparative Example 1

[0051] Sulfur and carbon nanotubes were ground for 0.5 h and then sealed in a vacuum tube, heated to 155°C for sulfur infiltration treatment, and kept for 12 h to obtain sulfur-carbon composite material S / CNT; lithium sulfide 0.86 g, phosphorus pentasulfide 0.83 g, and lithium chloride 0.32 g were placed in a ball mill jar and ball-milled at a speed of 550 rpm for 10 h to obtain a precursor of sulfide electrolyte Li6PS5Cl (LPSC), which was placed in a quartz boat and then placed in a tube furnace for sintering treatment under argon, with a temperature rising program of 5°C / min, heating to 550°C, keeping for 6 h, and naturally cooling to room temperature to obtain sulfide electrolyte LPSC; lithium bromide 0.88 g and yttrium bromide 1.12 g were placed in a ball mill jar and ball-milled at a speed of 550 rpm for 10 h to obtain halide electrolyte Li3YBr6 (LYB), which was placed in a quartz boat and then placed in a tube furnace for sintering treatment under argon, with a temperature rising program of 5°C / min, heating to 550°C, keeping for 6 h, and naturally cooling to room temperature to obtain halide electrolyte LYB. The above obtained 0.23 g S / CNT, 0.079 g LPSC, 0.23 g LYB, and 0.079 g carbon nanofiber were placed in a ball mill jar and ball-mixed at a speed of 500 rpm to obtain S / LPSC-LYB powder with a core-shell structure; 0.1 g of the above obtained S / LPSC-LYB powder was mixed with 0.001 g PTFE by grinding and rolling multiple times to obtain S / LPSC-LYB composite positive electrode film with a thickness of about 40 microns. 11A precursor of the sulfide electrolyte LPS is prepared by placing 0.86 g of lithium sulfide, 0.83 g of phosphorus pentasulfide and 0.32 g of lithium chloride in a ball mill jar and ball milling at a speed of 550 rpm for 10 h. The precursor of the LPS is placed in a quartz boat, which is placed in a tube furnace for sintering under argon. The temperature is raised to 550 °C at a rate of 5 °C / min and held for 6 h. The temperature is then allowed to cool to room temperature to obtain the sulfide electrolyte LPS. A precursor of the halide electrolyte Li3YBr6 (LYB) is prepared by placing 0.88 g of lithium bromide and 1.12 g of yttrium bromide in a ball mill jar and ball milling at a speed of 550 rpm for 10 h. The precursor of the LYB is placed in a quartz boat, which is placed in a tube furnace for sintering under argon. The temperature is raised to 550 °C at a rate of 5 °C / min and held for 6 h. The temperature is then allowed to cool to room temperature to obtain the halide electrolyte LYB. The S / CNT, LPS and LYB obtained above are placed in a ball mill jar and ball mixed at a speed of 500 rpm to obtain a S / LPS-LYB powder having a core-shell structure. The S / LPS-LYB powder obtained above is mixed with PTFE and roll-pressed to obtain a S / LPS-LYB composite cathode film having a thickness of about 40 microns.

[0052] Comparative Example 2

[0053] A sulfur-carbon composite material S / CNT is prepared by placing 0.7 g of elemental sulfur and 0.3 g of carbon nanotubes in a vacuum tube and heating to 155 °C for 12 h. A precursor of the sulfide electrolyte Li6PS5Cl (LPSC) is prepared by placing 0.86 g of lithium sulfide, 0.83 g of phosphorus pentasulfide and 0.32 g of lithium chloride in a ball mill jar and ball milling at a speed of 550 rpm for 10 h. The precursor of the LPSC is placed in a quartz boat, which is placed in a tube furnace for sintering under argon. The temperature is raised to 550 °C at a rate of 5 °C / min and held for 6 h. The temperature is then allowed to cool to room temperature to obtain the sulfide electrolyte LPSC. The S / CNT, LPSC and carbon nanofiber obtained above are placed in a ball mill jar and ball mixed at a speed of 500 rpm to obtain a S / LPSC powder. The S / LPSC powder obtained above is mixed with PTFE and roll-pressed to obtain a S / LPSC composite cathode film having a thickness of about 40 microns.

[0054] Comparative Example 3

[0055] Sulfur and carbon nanotubes were ground for 0.5 h and then sealed in a vacuum tube, heated to 155°C for sulfur melting and infiltration, and kept for 12 h to obtain sulfur-carbon composite S / CNT; lithium bromide and yttrium bromide were placed in a ball mill jar and ball-milled at 550 rpm for 10 h to obtain halide electrolyte Li3YBr6(LYB), which was placed in a quartz boat and then placed in a tube furnace for sintering under argon, with a heating rate of 5°C / min, a temperature of 550°C, and a holding time of 6 h, to obtain halide electrolyte LYB. The obtained 0.23 g S / CNT, 0.31 g LYB, and 0.079 g carbon nanofiber were placed in a ball mill jar and ball-milled at 500 rpm to obtain S / LYB powder; 0.1 g of the obtained S / LYB powder and 0.001 g PTFE were ground and rolled multiple 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 The SEM image of the LPSC electrolyte obtained in Example 1 is shown in FIG. 1. Figure 1 It can be seen that the particle size of the LPSC is in the range of 2-5 microns.

[0058] 2. The LYB electrolyte obtained in Example 1 was subjected to scanning electron microscopy test, Figure 2 The SEM image of the LYB electrolyte obtained in Example 1 is shown in FIG. 2. Figure 2 It can be seen that the particle size of the LYB is in the range of 2-5 microns.

[0059] 3. The S / LPSC-LYB obtained in Example 1 was subjected to scanning electron microscopy test, Figure 3 The SEM image of the S / LPSC-LYB obtained in Example 1 is shown in FIG. 3.

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

[0061] 5. In an argon glove box with a water and oxygen concentration of less than 0.1 ppm, a full-solid-state lithium-sulfur battery was assembled in the order of positive electrode shell, positive electrode sheet, electrolyte film, lithium sheet, gasket, spring, and negative electrode shell, and then tightly sealed using a full-automatic sealing machine.

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

[0063] Table 1. Performance comparison table of the assembled solid-state battery of each example and comparative example

[0064]

[0065] Test results: (1) The interface impedance 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 respectively before cycling was 25, 33, 40, 30, 28 and 108 Ω. It shows that the high-performance composite sulfur positive electrode provided by the application 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 and electrolyte interface to some extent. The smaller the interface impedance, the better the kinetics of lithium ions at the electrode interface, which is conducive to the electrochemical reaction and further improves the electrochemical performance of the battery.

[0066] (2) Under the conditions of a voltage range of 1.5-3.0 V and a current density of 0.1 C, the assembled battery was subjected to constant current charge-discharge test. The initial discharge capacity 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 was 1450, 1318, 1198, 1380, 1420 and 584 mAh g -1 , respectively. The discharge capacity of Example 1 was 1190 mAh g -1 after stable cycling for 200 cycles, and there was no dramatic increase in polarization and short circuit; the discharge capacity of Example 2 was 948 mA h g -1 after stable cycling for 200 cycles, and there was no dramatic increase in polarization and short circuit; the discharge capacity of Example 3 was 767 mAh g -1 after stable cycling for 200 cycles; the discharge capacity of Comparative Example 2 was only 20 mA h g -1 after cycling for 200 cycles. It shows that the high-performance composite sulfur positive electrode provided by the application has excellent long cycle stability.

[0067] (3) The solid-state lithium-sulfur battery assembled in Example 1 was tested. Under the conditions of a voltage range of 1.5-3.0 V and a current density of 0.5 C, and a high active material loading of 4 mg cm -2 , the discharge capacity of the battery was 534 mAh g -1 after cycling for 500 cycles. It shows that the high-performance composite sulfur positive electrode provided by the application has excellent long cycle stability under the conditions of high active material loading and high current density.

[0068] The above merely describes the preferred embodiments of the present application, and it should be pointed out that, for those skilled in the art, several improvements and refinements can be made without departing from the principles of the present application, and these improvements and refinements should also be considered as falling within the protection scope of the present application.

Claims

1. A method for preparing a composite sulfur positive electrode encapsulated by a sulfide-halide composite electrolyte shell, comprising the following steps: Step (1) : Sulfur and carbon nanotubes are ground and sealed in a vacuum tube, and subjected to a molten sulfur infiltration treatment to obtain a sulfur-carbon composite material S / CNT; Step (2) : Lithium sulfide, phosphorus pentasulfide and lithium chloride are ball-mixed to obtain a sulfide electrolyte LPSC precursor, and the sulfide electrolyte LPSC precursor is subjected to a heating sintering treatment to obtain a sulfide electrolyte LPSC; Step (3) : Lithium bromide and yttrium bromide are ball-mixed to obtain a halide electrolyte LYB precursor, and the halide electrolyte LYB precursor is subjected to a heating sintering treatment to obtain a halide electrolyte LYB; Step (4) : The sulfur-carbon composite material S / CNT, the sulfide electrolyte LPSC, the halide electrolyte LYB and conductive carbon are ball-mixed to obtain a composite sulfur positive electrode powder encapsulated by a sulfide-halide composite electrolyte shell; Step (5) : The composite sulfur positive electrode powder obtained in step 4 is ground and mixed with a binder and subjected to multiple rollings to obtain a composite sulfur positive electrode encapsulated by a sulfide-halide composite electrolyte shell.

2. The production method according to claim 1, characterized by, The grinding, molten sulfur infiltration, ball-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 and the conductive carbon is 7:2-4, and the molten sulfur infiltration treatment is carried out at a temperature of 150-160℃ for 8-10h.

4. The method of claim 1, wherein, In step 2, the stoichiometric ratio of the lithium sulfide, the phosphorus pentasulfide and the lithium chloride is (2-2.5) : 0.5 : (1-1.5), the ball-mixing time is 5-20h, the rotation speed is 200-800r / min, the heating sintering treatment temperature is 400-600℃, and the holding time is 2-10h.

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

6. The method of claim 1, wherein, 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, and the ball-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 method of claim 1, wherein, In step 5, the mass ratio of the composite sulfur positive electrode powder and the binder is 100: (0.5-2).

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

10. Use according to claim 9, characterized in that, comprising: stacking a metal lithium or lithium alloy as a negative electrode material, a solid-state electrolyte thin film and a composite sulfur positive electrode encapsulated by a sulfide-halide composite electrolyte shell to prepare a solid-state lithium-sulfur battery.

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