Lithium-sulfur composite positive electrode, preparation method thereof and all-solid-state lithium-sulfur battery

Abstract

The invention provides a lithium-sulfur composite positive electrode, a preparation method thereof and an all-solid-state lithium-sulfur battery, and particularly relates to the technical field of lithium batteries. The lithium-sulfur composite positive electrode mainly comprises sulfur, conductive carbon and sulfide electrolyte in a mass ratio of (2-5): 1: (2-5); wherein the chemical formula of the sulfide electrolyte is Li6PS5X, and X is Cl, Br, I or F. According to the lithium-sulfur composite positive electrode provided by the invention, the sulfur, the conductive carbon and the sulfide electrolyte jointly form the positive electrode material, so that the specific capacity and the utilization rate of the sulfur are improved. In a first-circle charge-discharge test, the specific capacity of the composite positive electrode is as high as 1468mAh / g, and the utilization rate of sulfur reaches 87.6%, which shows that the shuttle effect of polysulfide is effectively inhibited, and the irreversible loss of active substances is reduced. Therefore, the first discharge capacity of the battery can be improved, and a good foundation is laid for capacity maintenance and cycling stability in the subsequent cycling process.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium batteries, in particular to a lithium-sulfur composite positive electrode, a preparation method thereof and an all-solid-state lithium-sulfur battery. BACKGROUND

[0002] With the rapid development of the electric vehicle industry, there is an increasing demand for high-energy density, high safety, and low-cost energy storage systems. The energy density of traditional lithium-ion batteries is close to the bottleneck due to the limitation of the theoretical specific capacity of the positive electrode material. Under this background, all-solid-state lithium-sulfur batteries (ASSLSBs) have become an important candidate for the next generation of high-specific-energy energy storage technology because of their high theoretical energy density of 2600 Wh / kg (based on the mass of sulfur), and the fact that sulfur is abundant, low in cost, and environmentally friendly.

[0003] However, the sulfur positive electrode still faces many key challenges in practical applications, which seriously restricts the commercialization process of all-solid-state lithium-sulfur batteries: 1. Poor conductivity of sulfur: Sulfur itself is an electronic insulator, and its electronic and ionic conduction ability is extremely weak, resulting in low active material utilization and limited battery rate performance.

[0004] 2. "Shuttle effect" of lithium polysulfides: During charging and discharging, sulfur will undergo a series of intermediate product-lithium polysulfide generation and conversion. These polysulfides are easily dissolved and migrated in the electrolyte to the negative electrode, causing side reactions with metallic lithium, resulting in irreversible loss of active material and consumption of negative electrode lithium, and thus leading to rapid capacity decay of the battery.

[0005] 3. Poor interface stability: The shuttle of polysulfides not only consumes active lithium, but also forms an unstable interface layer at the electrode / electrolyte interface, resulting in continuous increase of interface impedance, affecting the cycle stability and power output capability of the battery.

[0006] 4. Volume expansion problem of sulfur: When sulfur is completely lithiated to form Li2S, the volume expansion can reach about 80%. This severe volume change easily causes electrode structure damage, electrolyte cracking, and even interface contact failure, seriously affecting the mechanical stability and cycle life of the battery.

[0007] Although all-solid-state lithium-sulfur batteries have significant advantages in theory, the poor conductivity of sulfur positive electrode, the serious shuttle effect, the unstable interface, and the volume expansion problem are still the key technical bottlenecks that restrict the performance improvement and practical application of the battery.

[0008] In view of the above, the present application is proposed. SUMMARY

[0009] The present application aims to provide a lithium-sulfur composite cathode, a preparation method thereof and a full solid-state lithium-sulfur battery, and aims to solve at least one of the above technical problems in the prior art.

[0010] In order to achieve the above-mentioned purpose of the present application, the following technical solutions are adopted: The first aspect of the present application provides a lithium-sulfur composite cathode, mainly composed of sulfur, conductive carbon and sulfide electrolyte in a mass ratio of (2-5):1:(2-5); wherein the chemical formula of the sulfide electrolyte is Li6PS5X, X is Cl, Br, I or F.

[0011] Further, the conductive carbon includes at least one of Ketjen black, VGCF and carbon nanofiber.

[0012] Further, the particle size of the sulfur is 30-90 nm.

[0013] The second aspect of the present application provides a preparation method of the lithium-sulfur composite cathode, under the protection of inert gas, the sulfur, conductive carbon and sulfide electrolyte are mixed and then first ground to obtain a premix; then grinding beads are added to the premix for high-speed ball milling to obtain the lithium-sulfur composite cathode.

[0014] Further, in the inert gas environment, the water content is <1 ppm and the oxygen content is <1 ppm.

[0015] And / or, the rotation speed of the high-speed ball milling is 1000-2500 rpm.

[0016] And / or, the time of the high-speed ball milling is 4-8 h.

[0017] Further, the high-speed ball milling is carried out in a cycle of forward rotation, intermittent, reverse rotation and intermittent.

[0018] And / or, the time of the forward rotation is 20-40 min.

[0019] And / or, the time of the intermittent is 3-8 min.

[0020] And / or, the time of the reverse rotation is 20-40 min.

[0021] Further, the sulfur is subjected to second grinding and ball milling in the order before use to obtain sulfur with a particle size of 30-90 nm.

[0022] Further, the rotation speed of the second grinding is 300-800 rpm.

[0023] Further, the rotation speed of the ball milling is 300-800 rpm and the time is 2-6 h.

[0024] And / or, the ball mill bead material ratio is (20~40):1.

[0025] The third aspect of the present application provides a full solid-state lithium-sulfur battery, comprising a negative electrode, a solid-state electrolyte and the lithium-sulfur composite positive electrode.

[0026] Compared with the prior art, the present application has at least the following beneficial effects: The lithium-sulfur composite positive electrode provided by the present application uses sulfur, conductive carbon and sulfide electrolyte to jointly constitute the positive electrode material composition, thereby improving the specific capacity and the utilization rate of sulfur. In the first cycle charge-discharge test, the specific capacity of the composite positive electrode is as high as 1468 mAh / g, and the utilization rate of sulfur reaches 87.6%, which indicates that the shuttle effect of polysulfide is effectively inhibited, and the irreversible loss of active material is reduced. This not only helps to improve the initial discharge capacity of the battery, but also lays a good foundation for the capacity retention and cycle stability in the subsequent cycle process.

[0027] The preparation method provided by the present application releases lithium halide on the surface of the composite positive electrode in situ to form an interface layer with a nanoscale thickness during the high-speed ball milling of the premix, thereby giving the composite positive electrode good chemical stability and mechanical flexibility, effectively inhibiting the shuttle effect of polysulfide, reducing the loss of active material, improving the utilization rate of sulfur, and further improving the initial discharge specific capacity and cycle life of the battery.

[0028] The full solid-state lithium-sulfur battery provided by the present application has higher capacity, better cycle stability and safety due to the advantages of the above-mentioned lithium-sulfur composite positive electrode, and can better meet the demand for high-energy-density energy storage devices in the fields of electric vehicles, portable electronic devices and the like. BRIEF DESCRIPTION OF DRAWINGS

[0029] In order to more clearly illustrate the specific embodiments of the present application or the technical solutions in the prior art, the following will briefly introduce the drawings needed to be used in the specific embodiments or prior art description. Obviously, the drawings in the following description are some embodiments of the present application, and those skilled in the art can also obtain other drawings according to these drawings without creative labor.

[0030] Figure 1 The first cycle charge-discharge performance comparison chart of the batteries prepared for example 1, example 10 and example 11 at 0.1C rate; Figure 2 The first cycle charge-discharge performance comparison chart of the batteries prepared for example 1, example 12 and example 13 at 0.1C rate; Figure 3is a long cycle performance comparison chart of batteries prepared in Example 1, Example 10, and Example 11 at a 0.5C rate; Figure 4 is a long cycle performance comparison chart of batteries prepared in Example 1, Example 12, and Example 13 at a 0.5C rate; Figure 5 is a comparison chart of pressure changes in the charging and discharging process of batteries prepared in Example 1, Example 10, and Example 12 when the charging and discharging cycle is 50 times. DETAILED DESCRIPTION

[0031] To make the objectives, technical solutions, and advantages of the present application clearer, the following will combine embodiments of the present application to clearly and completely describe technical solutions in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments.

[0032] Hereinafter, the terms "include", "have", and their synonymous words used in various embodiments of the present application are only intended to indicate that specific features, numbers, steps, operations, elements, components, or combinations of the foregoing are present, and should not be understood as excluding the presence or possibility of adding one or more features, numbers, steps, operations, elements, components, or combinations of the foregoing.

[0033] The first aspect of the present application provides a lithium-sulfur composite cathode mainly composed of sulfur, conductive carbon, and sulfide electrolyte in a mass ratio of (2-5):1:(2-5); wherein the chemical formula of the sulfide electrolyte is Li6PS5X, and X is Cl, Br, I, or F.

[0034] The lithium-sulfur composite cathode provided by the present application uses sulfur, conductive carbon, and sulfide electrolyte to jointly constitute the cathode material composition, thereby improving the specific capacity and the utilization rate of sulfur. In the first cycle charging and discharging test, the specific capacity of the composite cathode is as high as 1468 mAh / g, and the utilization rate of sulfur reaches 87.6%, indicating that the shuttle effect of polysulfide is effectively inhibited, and the irreversible loss of active material is reduced. This not only helps to improve the initial discharge capacity of the battery, but also lays a good foundation for the capacity retention and cycle stability in the subsequent cycle process.

[0035] Typically but not limitedly, the mass ratio of the sulfur, conductive carbon, and sulfide electrolyte may be, for example, 2:1:2, 3:1:3, 4:1:4, 5:1:5, or any ratio combination within the range of (2-5):1:(2-5).

[0036] Further, the conductive carbon includes at least one of Ketjen black, VGCF, and carbon nanofiber.

[0037] Further, the particle size of the sulfur is 30-90 nm.

[0038] Typically but not exclusively, the particle size of the sulfur may be, for example, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm or 90 nm, or any particle size value within the range of 30-90 nm.

[0039] The second aspect of the present application provides a preparation method of the lithium-sulfur composite cathode. The sulfur, conductive carbon and sulfide electrolyte are mixed and then subjected to first grinding under inert gas protection to obtain a premix; then grinding beads are added to the premix for high-speed ball milling to obtain the lithium-sulfur composite cathode.

[0040] The preparation method provided by the present application decomposes the sulfide electrolyte during the high-speed ball milling of the premix, releases lithium halide in situ on the surface of the composite cathode, forms an interface layer with a nanoscale thickness, and thus endows the composite cathode with good chemical stability and mechanical flexibility, can effectively inhibit the shuttle effect of polysulfides, reduce the loss of active materials, improve the utilization rate of sulfur, and thus improve the initial discharge specific capacity and cycle life of the battery.

[0041] Further, the water content is <1 ppm and the oxygen content is <1 ppm in the inert gas environment.

[0042] And / or, the rotation speed of the high-speed ball milling is 1000-2500 rpm. During the high-speed ball milling, the friction heat and shear force synergistically induce a mechanochemical reaction. Specifically, the friction heat promotes the decomposition of the halogen-containing solid-state electrolyte to release halide anions; at the same time, the shear force causes the particles to break and uniformly mix to form lithium halide, which is deposited in situ on the surface of the material to form an interface layer with a nanoscale thickness.

[0043] The lithium halide interface layer plays a dual role in improving the performance of the battery: on the one hand, its nanostructure provides a fast transmission channel for Li⁺, significantly improves the ionic conductivity, and thus improves the cycle stability of the battery; on the other hand, the interface layer effectively inhibits the volume expansion of sulfur during charging and discharging, maintains the integrity of the electrode structure, and further enhances the cycle life and safety of the battery.

[0044] And / or, the time of the high-speed ball milling is 4-8 h.

[0045] Typically but not exclusively, the rotation speed of the high-speed ball mill can be, for example, 1000 rpm, 1200 rpm, 1500 rpm, 1800 rpm, 2000 rpm, 2200 rpm or 2500 rpm, or any rotation speed value within the range of 1000-2500 rpm; the time of the high-speed ball mill can be, for example, 4 h, 5 h, 6 h, 7 h or 8 h, or any time value within the range of 4-8 h.

[0046] Further, the high-speed ball mill is performed in a cycle of forward rotation, intermittence, reverse rotation and intermittence, which ensures uniform mixing of the material.

[0047] And / or, the time of the forward rotation is 20-40 min. Typically but not exclusively, the time of the forward rotation can be, for example, 20 min, 25 min, 30 min, 35 min or 40 min, or any time value within the range of 20-40 min.

[0048] And / or, the time of the intermittence is 3-8 min. Typically but not exclusively, the time of the intermittence can be, for example, 3 min, 4 min, 5 min, 6 min, 7 min or 8 min, or any time value within the range of 3-8 min.

[0049] And / or, the time of the reverse rotation is 20-40 min. Typically but not exclusively, the time of the reverse rotation can be, for example, 20 min, 25 min, 30 min, 35 min or 40 min, or any time value within the range of 20-40 min.

[0050] Further, the sulfur is subjected to second grinding and ball milling in sequence before use, to obtain sulfur with a particle size of 30-90 nm.

[0051] Further, the rotation speed of the second grinding is 300-800 rpm. Typically but not exclusively, the rotation speed of the second grinding can be, for example, 300 rpm, 400 rpm, 500 rpm, 600 rpm, 700 rpm or 800 rpm, or any rotation speed value within the range of 300-800 rpm.

[0052] Further, the rotation speed of the ball milling is 300-800 rpm and the time is 2-6 h. Typically but not exclusively, the rotation speed of the ball milling can be, for example, 300 rpm, 400 rpm, 500 rpm, 600 rpm, 700 rpm or 800 rpm, or any rotation speed value within the range of 300-800 rpm; the time of the ball milling can be, for example, 2 h, 3 h, 4 h, 5 h or 6 h, or any time value within the range of 2-6 h.

[0053] And / or, the ball mill has a bead-to-material ratio of (20-40):1. Typically but not limitedly, the bead-to-material ratio of the ball mill may be, for example, 20:1, 25:1, 30:1, 35:1 or 40:1, or any ratio within the range of (20-40):1.

[0054] The third aspect of the present application provides a full solid-state lithium-sulfur battery, comprising a negative electrode, a solid-state electrolyte and the lithium-sulfur composite positive electrode.

[0055] The full solid-state lithium-sulfur battery provided by the present application has higher capacity, better cycle stability and safety due to the advantages of the lithium-sulfur composite positive electrode, and can better meet the demand for high-energy-density energy storage devices in the fields of electric vehicles, portable electronic devices and the like.

[0056] The present application will be further described below through specific examples and comparative examples, but it should be understood that these examples are only for more detailed description and should not be understood as limiting the present application in any form. In the examples and comparative examples of the present application, the raw materials used are not specified under specific conditions, and are carried out under conventional conditions or manufacturer's recommended conditions. The reagents or instruments used are not specified by the manufacturer, and are all conventional products that can be purchased on the market.

[0057] Example 1 This example provides a lithium-sulfur composite positive electrode, and the specific preparation process is as follows: (1) In an argon-filled glove box (the water content of argon in the glove box is less than 1 ppm, and the oxygen content is less than 1 ppm), 500 mg of sulfur particles were weighed and manually ground in a mortar for 30 min to obtain S powder. Zirconia beads with a diameter of 5 mm and S powder in the mortar were added to a 100 mL zirconia ball mill tank at a ball-to-material ratio of 30:1, and the tank was sealed with tape and transferred out of the glove box. The ball mill tank containing the S powder was placed on the ball mill, and the ball milling was carried out at a rotation speed of 500 rpm for 4 hours, with a forward rotation of 30 min, an intermittent rotation of 5 min, a reverse rotation of 30 min, and an intermittent rotation of 5 min. The refined S powder was obtained (the particle size was 40-80 nm).

[0058] (2) In the glove box filled with argon, 400 mg of Li6PS5Cl and 100 mg of Ketjenblack were weighed, and 500 mg of the S powder ball-milled in (1) were put into a mortar and hand ground for 20 min to obtain a premix. The premix was put into a 100 mL zirconium oxide ball mill jar, and 5 mm diameter zirconium oxide beads with a mass ratio of ball to material of 30:1 were added. The jar was sealed with tape and put into a high-energy ball mill, and high-speed ball milling was performed at a rotation speed of 2000 rpm for 30 min, with an interval of 5 min, and then reverse rotation for 30 min, with an interval of 5 min, and the cycle was repeated for 6 hours. After the mixing was completed, the mixture was taken out to obtain a lithium-sulfur composite positive electrode.

[0059] Example 2 This example provides a lithium-sulfur composite positive electrode, and the specific preparation process is as follows: (1) The same as the step in Example 1.

[0060] (2) In the glove box filled with argon, 300 mg of Li6PS5Cl and 100 mg of Ketjenblack were weighed, and 300 mg of the S powder ball-milled in (1) were put into a mortar and hand ground for 30 min to obtain a premix. The premix was put into a 100 mL zirconium oxide ball mill jar, and 5 mm diameter zirconium oxide beads with a mass ratio of ball to material of 30:1 were added. The jar was sealed with tape and put into a high-energy ball mill, and high-speed ball milling was performed at a rotation speed of 1000 rpm for 20 min, with an interval of 6 min, and then reverse rotation for 20 min, with an interval of 6 min, and the cycle was repeated for 8 hours. After the mixing was completed, the mixture was taken out to obtain a lithium-sulfur composite positive electrode.

[0061] Example 3 This example provides a lithium-sulfur composite positive electrode, and the specific preparation process is as follows: (1) The same as the step in Example 1.

[0062] (2) In the glove box filled with argon, 200 mg of Li6PS5Cl and 100 mg of Ketjenblack were weighed, and 500 mg of the S powder ball-milled in (1) were put into a mortar and hand ground for 40 min to obtain a premix. The premix was put into a 100 mL zirconium oxide ball mill jar, and 5 mm diameter zirconium oxide beads with a mass ratio of ball to material of 30:1 were added. The jar was sealed with tape and put into a high-energy ball mill, and high-speed ball milling was performed at a rotation speed of 2500 rpm for 30 min, with an interval of 5 min, and then reverse rotation for 30 min, with an interval of 5 min, and the cycle was repeated for 6 hours. After the mixing was completed, the mixture was taken out to obtain a lithium-sulfur composite positive electrode.

[0063] Example 4 The embodiment provides a lithium-sulfur composite positive electrode, which is different from the lithium-sulfur composite positive electrode in Embodiment 1 in that VGCF is used to replace the Ketjen black, and the rest of the raw materials and the preparation method are the same as those in Embodiment 1, which will not be repeated here.

[0064] Embodiment 5 The embodiment provides a lithium-sulfur composite positive electrode, which is different from the lithium-sulfur composite positive electrode in Embodiment 1 in that Li6PS5F is used to replace Li6PS5Cl, and the rest of the raw materials and the preparation method are the same as those in Embodiment 1, which will not be repeated here.

[0065] Embodiment 6 The embodiment provides a lithium-sulfur composite positive electrode, which is different from the lithium-sulfur composite positive electrode in Embodiment 1 in that Li6PS5Br is used to replace Li6PS5Cl, and the rest of the raw materials and the preparation method are the same as those in Embodiment 1, which will not be repeated here.

[0066] Embodiment 7 The embodiment provides a lithium-sulfur composite positive electrode, which is different from the lithium-sulfur composite positive electrode in Embodiment 1 in that the amount of Li6PS5Cl is 200 mg, the amount of Ketjen black is 100 mg, and the amount of S powder is 200 mg, and the rest of the raw materials and the preparation method are the same as those in Embodiment 1, which will not be repeated here.

[0067] Embodiment 8 The embodiment provides a lithium-sulfur composite positive electrode, which is different from the lithium-sulfur composite positive electrode in Embodiment 1 in that the amount of Li6PS5Cl is 500 mg, the amount of Ketjen black is 100 mg, and the amount of S powder is 500 mg, and the rest of the raw materials and the preparation method are the same as those in Embodiment 1, which will not be repeated here.

[0068] Embodiment 9 The embodiment provides a lithium-sulfur composite positive electrode, which is different from the lithium-sulfur composite positive electrode in Embodiment 1 in that the amount of Li6PS5Cl is 200 mg, the amount of Ketjen black is 100 mg, and the amount of S powder is 500 mg, and the rest of the raw materials and the preparation method are the same as those in Embodiment 1, which will not be repeated here.

[0069] Embodiment 10 The embodiment provides a lithium-sulfur composite positive electrode, which is different from the lithium-sulfur composite positive electrode in Embodiment 1 in that the rotating speed of the high-energy ball mill is controlled to be 500 rpm, and the rest of the raw materials and the preparation method are the same as those in Embodiment 1, which will not be repeated here.

[0070] Embodiment 11 The embodiment provides a lithium-sulfur composite positive electrode, which is different from the lithium-sulfur composite positive electrode in Embodiment 1 in that the rotating speed of the high-energy ball mill is controlled to be 1000 rpm, and the rest of the raw materials and the preparation method are the same as those in Embodiment 1, which will not be repeated here.

[0071] Embodiment 12 The embodiment provides a lithium-sulfur composite positive electrode, different from the embodiment 1, the ball milling time of the high-energy ball mill is 2 hours, the rest of the raw materials and the preparation method are the same as those of the embodiment 1, and details are not repeated here.

[0072] Example 13 The embodiment provides a lithium-sulfur composite positive electrode, different from the embodiment 1, the ball milling time of the high-energy ball mill is 10 hours, the rest of the raw materials and the preparation method are the same as those of the embodiment 1, and details are not repeated here.

[0073] Example 14 The embodiment provides a lithium-sulfur composite positive electrode, different from the embodiment 1, the high-energy ball mill is rotated at 2000 rpm for 6 hours, the rest of the raw materials and the preparation method are the same as those of the embodiment 1, and details are not repeated here.

[0074] Comparative Example 1 The comparative example provides a lithium-sulfur composite positive electrode, different from the embodiment 1, the amount of Li6PS5Cl is 100 mg, the amount of Ketjen black is 100 mg, the amount of S powder is 100 mg, the rest of the raw materials and the preparation method are the same as those of the embodiment 1, and details are not repeated here.

[0075] Test Example 1 The lithium-sulfur composite positive electrode obtained in the embodiment and the comparative example is used to prepare a full-solid-state lithium-sulfur battery according to the following preparation method: (1) Electrolyte: 80 mg of solid-state electrolyte Li6PS5Cl powder (D50=5 μm, ion conductivity is 10.32 mS / cm) is placed in a pressure cell mold with an inner diameter of 10 mm, and the solid electrolyte powder is pressed on a tablet press at 100 MPa for 2 min to form a tablet.

[0076] (2) Positive electrode: 8 mg of lithium-sulfur composite positive electrode powder provided in the embodiment and the comparative example is placed on one side of the electrolyte tablet, and the pressure is kept at 500 MPa for 6 min.

[0077] (3) Negative electrode: an indium sheet with a diameter of 10 mm and a thickness of 100 mm is placed on one side of the electrolyte tablet, and a lithium sheet with a diameter of 10 mm and a thickness of 60 mm is placed on the indium sheet.

[0078] (4) Current collector: an aluminum foil with a diameter of 10 mm and a thickness of 80 um is used as a positive electrode current collector, and the side in contact with the positive electrode has a carbon coating; a copper foil with a diameter of 10 mm and a thickness of 40 μm is used as a negative electrode current collector, and the full-solid-state lithium-sulfur battery is assembled.

[0079] The prepared all-solid-state lithium-sulfur battery was placed in a pressure mold, a pressure sensor was placed on one layer of the battery to record the pressure change of the battery during charging and discharging, a constant external force of 60 MPa was applied, and the battery was placed in a constant temperature box at 50° and connected to a charge-discharge tester for charging and discharging test at a rate of 0.1-0.5C, with upper and lower cut-off voltage of 0.4-3.2V. The measured pressure change data during the electrochemical test was collected, and the pressure change rate was obtained according to the ratio of the pressure change amount to the initial constant pressure 60 MPa.

[0080] The obtained data is shown in Table 1.

[0081] Table 1

[0082] As can be seen from Table 1, the all-solid-state battery prepared by the sulfur composite positive electrode of Example 1 has a high specific capacity at a rate of 0.1C, and can fully utilize sulfur while maintaining a high capacity retention rate of 90.2% during 200 cycles of long cycle. Example 4 uses different conductive carbon KB to achieve excellent conductivity. Examples 5 and 6 use different electrolytes, and the electrochemical performance is good under the same process parameters, but the effect is not as good as Example 1. Examples 7-9 and Comparative Example 1 use different proportions of conductive carbon, electrolyte and active material for compounding, and the results show that when the material ratio is 1:4:5, better electrochemical performance can be achieved. Examples 10-11 and Examples 12-13 are sulfur composite positive electrodes prepared by different ball milling process parameters, which cannot achieve the effect of the process parameters of the composite positive electrode of Example 1. Example 14 uses a positive transmission method for ball milling, and through comparison, it is found that the intermittent ball milling method of Example 1 can achieve the effect of the sulfur composite positive electrode and improve the utilization rate of S.

[0083] The data during the process is plotted into a curve, Figure 1 is a comparison chart of the first cycle charging and discharging performance of the batteries prepared in Examples 1, 10 and 11 at a rate of 0.1C; Figure 2 is a comparison chart of the first cycle charging and discharging performance of the batteries prepared in Examples 1, 12 and 13 at a rate of 0.1C; Figure 3 is a comparison chart of the long cycle performance of the batteries prepared in Examples 1, 10 and 11 at a rate of 0.5C; Figure 4 is a comparison chart of the long cycle performance of the batteries prepared in Examples 1, 12 and 13 at a rate of 0.5C; Figure 5 is a comparison chart of the pressure change during the charging and discharging process of the batteries prepared in Examples 1, 10 and 12 when the charging and discharging cycle is 50 times.

[0084] From Figure 1It can be seen that the figure shows that as the ball milling speed increases, the first circle discharge specific capacity also increases (Example 1 is 1468 mAh / g), and the higher the speed, the higher the utilization rate of sulfur (87.6%). Examples 10 and 11 do not reach the electrochemical capacity of the composite positive electrode of Example 1.

[0085] From Figure 2 It can be seen that the ball milling time is best at about 6h, which can achieve higher specific capacity, and shorter or longer ball milling time cannot achieve the composite effect of Example 1.

[0086] From Figure 3 It can be seen that the higher the ball milling speed, the better the capacity retention rate of the prepared sulfur composite positive electrode in the full battery long cycle test, mainly because the higher the ball milling speed, the more Cl - can be decomposed from the electrolyte in the ball milling process, and then coated on the surface of the S particles, thereby improving the cycle performance.

[0087] From Figure 4 It can be seen that the shorter ball milling time cannot achieve uniform particle dispersion and Cl - decomposition, and at the same time, the ball milling time is too long, which will cause the material to stick to the wall, and the battery capacity retention rate prepared is low.

[0088] From Figure 5 It can be seen that the internal pressure of the battery changes during the 50th cycle of charge and discharge of the full solid-state lithium-sulfur battery. Compared with the low ball milling speed and the low ball milling time, the internal pressure of the battery prepared using the ball milling parameters in Example 1 does not change significantly, effectively inhibiting the volume expansion of sulfur, and further verifying the excellent performance in the long cycle process.

[0089] Finally, it should be noted that the above-described examples are only specific embodiments of the present application, which are used to illustrate the technical solutions of the present application, but not to limit it. The protection scope of the present application is not limited to this. Although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that any person skilled in the art within the technical scope disclosed by the present application can modify or easily think of changes to the technical solutions recorded in the foregoing examples, or make equivalent replacements to some technical features. These modifications, changes or replacements do not make the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application, and should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A lithium-sulfur composite positive electrode, characterized in that It is mainly composed of sulfur, conductive carbon and sulfide electrolyte in a mass ratio of (2~5):1:(2~5); The chemical formula of the sulfide electrolyte is Li6PS5X, where X is Cl, Br, I or F.

2. The lithium-sulfur composite positive electrode according to claim 1, characterized in that The conductive carbon includes at least one of Ketjen black, VGCF and carbon nanofiber.

3. The lithium-sulfur composite positive electrode according to claim 1, characterized in that The particle size of the sulfur is 30-90 nm.

4. A method for preparing a lithium-sulfur composite positive electrode according to any one of claims 1 to 3, characterized in that: Under the protection of inert gas, sulfur, conductive carbon and sulfide electrolyte are mixed and then subjected to a first grinding to obtain a premix; then grinding beads are added to the premix and high-speed ball milling is performed to obtain the lithium-sulfur composite positive electrode.

5. The preparation method according to claim 4, characterized in that In an inert gas environment, the water content is less than 1ppm and the oxygen content is less than 1ppm; And / or, the rotation speed of the high-speed ball mill is 1000-2500 rpm; And / or, the high-speed ball milling time is 4 to 8 hours.

6. The preparation method according to claim 4, characterized in that The high-speed ball milling is carried out by adopting a cycle of forward rotation, intermittent rotation, reverse rotation, and intermittent rotation; And / or, the forward rotation time is 20 to 40 minutes; And / or, the intermittent time is 3 to 8 minutes; And / or, the reversal time is 20 to 40 minutes.

7. The preparation method according to any one of claims 4 to 6, characterized in that The sulfur is subjected to a second grinding and a ball milling in that order before use to obtain sulfur with a particle size of 30 to 90 nm.

8. The preparation method according to claim 7, characterized in that The second grinding speed is 300-800 rpm.

9. The preparation method according to claim 7, characterized in that The ball milling speed is 300-800 rpm, and the time is 2-6 hours; And / or, the bead-to-material ratio of the ball mill is (20-40):

1.

10. An all-solid-state lithium-sulfur battery, characterized in that: The invention comprises a negative electrode, a solid electrolyte and the lithium-sulfur composite positive electrode according to any one of claims 1 to 3.

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