Composite positive electrode material and preparation method and application thereof

Abstract

The invention discloses a composite positive electrode material and a preparation method and application thereof, and relates to the technical field of electrochemical energy storage, S9I and conductive carbon are subjected to intermittent ball milling in a protective atmosphere, then a solid sulfide electrolyte is added, intermittent ball milling is performed in the protective atmosphere again, and thus the composite positive electrode material is prepared. According to the preparation method, step-by-step ball milling and intermittent ball milling are ingeniously combined, uniform dispersion of all components is ensured, an ion and electron transport network is efficiently constructed, and the performance of the material is stabilized. The all-solid-state lithium-sulfur battery based on the composite positive electrode material is matched with a lithium-silicon alloy negative electrode, and tight contact of an electrode / electrolyte interface is stably maintained by virtue of a positive and negative electrode synergistic volume expansion compensation mechanism. The first specific discharge capacity of the composite positive electrode is up to 1064 mAh g <-1 > in an environment of 60 DEG C. By utilizing the low melting point characteristic of S9I, a damaged interface is repaired through periodic remelting, so that the capacity retention rate still reaches 96% after the battery is circulated for 200 times, and the cycling stability and the service life of the battery are remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of electrochemical energy storage, and particularly relates to a composite cathode material, a preparation method thereof, and an application thereof. Background Art

[0002] As a new generation of energy storage devices, all-solid-state lithium batteries replace traditional organic electrolytes with non-flammable solid electrolytes, achieving a breakthrough improvement in both intrinsic safety and energy density at the theoretical level. The energy density of all-solid-state lithium batteries depends on the capacity of the electrode materials. Due to multi-electron conversion reactions, sulfide cathode materials have higher specific capacities than layered oxide cathode materials. Therefore, all-solid-state lithium-sulfur batteries equipped with sulfide cathodes and having ultra-high theoretical energy densities have become a research hotspot in high-energy energy storage systems.

[0003] However, all-solid-state lithium-sulfur batteries encounter many difficult challenges during the development process. The most prominent one is the intrinsic insulation of the sulfur cathode, whose electronic conductivity is extremely low, only about 5×10 -18 S·cm -1 , which directly leads to the long-term difficulty in breaking through the bottleneck of the utilization rate of active substances being less than 70%. At the same time, during the charge and discharge cycles of the battery, the sulfide cathode will have a volume change of up to 80%, resulting in serious interfacial contact problems, causing the interfacial impedance to soar above 3000Ω·cm², which has a fatal impact on the battery performance and long-cycle stability. In addition, the chemical penetration of polysulfides (Li 2 S x , 4 ≤x≤ 8) in the solid electrolyte triggers a shuttle effect, resulting in irreversible capacity decay. For example, the capacity retention rate is <60% after 100 cycles. The development of all-solid-state lithium-sulfur batteries has been historically troubled by the insulation of sulfur and the poor interfacial contact caused by its large volume change during cycling, which hinders the charge transfer between different solid components. Therefore, how to improve the insulation of the sulfur cathode and the interfacial contact problems caused by volume expansion is a very meaningful research direction.

[0004] To address these problems, researchers actively explore solutions. In terms of cathode materials, the sulfide cathode materials of all-solid-state lithium-sulfur batteries present various forms. In addition to the commonly used elemental sulfur cathode, there are also lithium sulfide (Li 2 S) cathodes, iron disulfide (FeS 2 ) cathodes, etc. By compounding sulfur with different metal oxides, the conductivity of sulfur is significantly improved, and the electrochemistry reaction kinetics is improved.

[0005] The composite cathode of the all-solid-state lithium-sulfur battery mainly consists of three parts, namely active materials, conductive agents, and solid electrolytes. General composite cathodes are mixed with conductive carbon and PVDF, and then coated on the electrode sheet in the form of slurry. However, in all-solid-state batteries, dry process standards need to be met. How to ensure the effective transmission of electrons and ions while maintaining the unstable interfacial contact caused by volume changes and insulating products between solid particles is an important problem to be solved urgently.

[0006] The all-solid-state lithium-sulfur battery usually uses metallic lithium as the anode material. However, dendritic problems will occur during the deposition and dissolution of the lithium metal anode. Common methods to improve the anode interface stability include: optimizing the composition of sulfide solid electrolytes, forming artificial electrolyte membranes at the interface, controlling interface defects to reduce the nucleation sites of lithium dendrites, and directly replacing the lithium metal anode with lithium alloys. Summary of the Invention

[0007] In view of this, the purpose of the present invention is to provide a composite cathode material, its preparation method, and application.

[0008] The purpose of the present invention is achieved through the following technical solutions: <First aspect> The present invention provides a preparation method of a composite cathode material, including the following steps: S1. S 9 I and conductive carbon are subjected to intermittent ball milling under a protective atmosphere to obtain a premix; S2. The premix and solid sulfide electrolyte are subjected to intermittent ball milling under a protective atmosphere to obtain the composite cathode material; Among them, the intermittent ball milling is ball milling for 20 - 30 min, pausing for 5 - 10 min, and ball milling for 6 - 7 h.

[0009] As an embodiment, the conductive carbon includes one or more of carbon nanofibers, Ketjen black, and super-P.

[0010] In some embodiments, the conductive carbon is selected as carbon nanofibers.

[0011] As an embodiment, the sulfide electrolyte includes Li 3 PS 4 , Li 5.5 PS 4.5 X 1.5 or more, where X is selected from at least one of F, Cl, Br, and I.

[0012] In some embodiments, the sulfide electrolyte is selected as Li 5.5 PS 4.5 Cl 1 .5 .

[0013] As an embodiment, the S 9 I, the mass ratio of conductive carbon to sulfide electrolyte is (3.5~4.5) : (3.5~4.5) : 2.

[0014] In some embodiments, the S 9 I, the mass ratio of conductive carbon to sulfide electrolyte is 4:4:2.

[0015] As an embodiment, the ball milling parameters are as follows: the ball milling medium is zirconia grinding balls with a diameter of 4~6 mm, the ball-to-material ratio is 35~40 : 1, and the rotation speed is 350~450 rpm / min.

[0016] As an embodiment, the preparation method of the S 9 I is as follows: elemental S and elemental I are mixed evenly according to the atomic ratio, 2 then placed in a sealed container for heat treatment at 80~100 °C for 2~4 h, and naturally cooled to room temperature to obtain the S 9 I material.

[0017] As an embodiment, the heating rate of the heat treatment is 1 °C / min.

[0018] <Second aspect> The present invention provides a composite cathode material prepared by the above method.

[0019] <Third aspect> The present invention provides an all-solid-state lithium-sulfur battery prepared by using the above composite cathode material.

[0020] As an embodiment, the all-solid-state lithium-sulfur battery includes an electrolyte, a cathode, and an anode, wherein, the cathode is prepared from the composite cathode material, the electrolyte is a sulfide electrolyte, and the anode is a lithium-silicon alloy.

[0021] As an embodiment, the preparation method of the all-solid-state lithium-sulfur battery includes: first pressing the sulfide electrolyte into an electrolyte sheet; then placing the composite cathode material on one side of the electrolyte sheet for pressing to obtain a bilayer material of a cathode electrode sheet - electrolyte sheet, and then placing the lithium-silicon alloy on the other side of the electrolyte sheet for pressing to obtain a trilayer material of a cathode electrode sheet - electrolyte sheet - anode electrode sheet; finally, placing a positive current collector on the surface of the cathode electrode sheet and placing a negative current collector on the surface of the anode electrode sheet, and performing pressing after assembly to obtain the all-solid-state lithium-sulfur battery.

[0022] In some embodiments, the sulfide electrolyte is selected as Li 5.5 PS 4.5 Cl1.5 powder

[0023] In some embodiments, the positive current collector is aluminum foil; the negative current collector is copper foil.

[0024] In some embodiments, the mass ratio of the composite cathode material to the sulfide electrolyte is 8:100.

[0025] <Fourth aspect> The present invention provides an application of the above all-solid-state lithium-sulfur battery, and repairs the damaged interface due to cycling through periodic remelting.

[0026] In some embodiments, the periodic remelting is to keep the temperature at 100 °C for 3 h after every 50 cycles.

[0027] Compared with the prior art, the present invention has the following beneficial effects: 1) The present invention provides an S 9 I composite cathode, and the composite material thereof is made of S 9 I, a sulfide electrolyte, and conductive carbon by mechanical ball milling. Among them, the addition of conductive carbon can improve the electronic conductivity of the composite material; the sulfide electrolyte can provide particle-to-particle contact and optimize the ion transport from the inside of the composite cathode to the cathode / electrolyte interface; S 9 I is a material with semiconductor-level conductivity, and its conductivity is increased by 11 orders of magnitude compared with sulfur itself. 2) When preparing the S 9 I composite cathode, the present invention adopts a combination of step-by-step ball milling and intermittent ball milling. Step-by-step ball milling can ensure that S 9 I and conductive carbon are pre-mixed sufficiently, and then mixed with the sulfide electrolyte, which is beneficial to the uniform distribution of conductive carbon and electrolyte, enables the conductive carbon to be in direct contact with the active substance, improves the conductivity of the sulfide cathode, and the indirectly contacted sulfide electrolyte further ensures the ion transport from the inside of the composite cathode to the electrolyte surface. Intermittent ball milling can release the generated energy during the ball milling process, avoid the melting and decomposition of S 9 I caused by energy accumulation, and at the same time prevent the local crystal lattice distortion of the sulfide electrolyte crystal due to excessive energy. The combination of this ball milling method has two major advantages: one is to ensure S 9I. The homogeneous distribution of the electrolyte and conductive carbon creates conditions for sufficient contact between particles and constructs an efficient ion-electron transport network. Second, from the energy perspective, the thermal energy generated by particle friction above the phase change threshold is controlled to protect the physical and chemical properties of each component to be stable. In addition, by first ball-milling and compounding the sulfide cathode material with conductive carbon spheres and then adding electrolyte powder for further compounding, the sulfide cathode material can be in full contact with the conductive carbon, ensuring a high electronic conductivity. At the same time, the electrolyte powder is evenly distributed between the cathode materials wrapped with conductive carbon, forming a better ion transport channel. The intermittent ball-milling can also alleviate the problem of material caking caused by excess heat during the ball-milling process, making the mixing of each component in the composite cathode more uniform. 3) The composite cathode of the present invention exhibits an initial discharge specific capacity of 1064 mAh g -1 at a temperature of 60 °C, and the rate performance is also significantly improved. 4) The present invention also provides a negative electrode that is more compatible with the S 9 I composite cathode. Lithium-silicon alloy is selected as the negative electrode material, and its volume expansion rate of silicon during lithiation / delithiation is about 300%. During the charge and discharge process of the S 9 I molecular crystal, S is converted into Li 2 2S, and the phase change of S is accompanied by an 80% volume expansion. By controlling the content ratio of the cathode and negative electrode materials, the expansion directions of the two can be complementary to the volume change of the cathode. During charging, the cathode (S 9 I) de-lithiates and shrinks, and the negative electrode (Li - Si) intercalates lithium and expands. The expansion directions of the two are opposite, and the mechanical stress is offset to inhibit the separation of the electrode / electrolyte interface. During discharging, the cathode intercalates lithium and expands, and the negative electrode de-lithiates and shrinks. The expansion directions are complementary, maintaining the stability of the overall battery structure. The Li - Si alloy negative electrode can effectively alleviate the strain effect caused by the large volume expansion of the sulfide cathode during the charge and discharge process. Through the cooperative volume expansion compensation mechanism of the lithium-silicon alloy (Li - Si) negative electrode and the sulfur-iodine molecular crystal (S 9 I) cathode, the close contact of the electrode / electrolyte interface in the all-solid-state battery can be dynamically maintained, significantly improving the cycle stability and energy density of the battery.

[0028] 5) The present invention utilizes the low melting point characteristic of the S 9 I material to repair the damaged interface periodically by remelting the composite cathode material, so that the impedance is restored to near the initial level. The all-solid-state battery using this composite cathode material and the periodic remelting method still has a capacity retention rate of 96% after 200 cycles, greatly extending the cycle life. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] By reading the detailed description of the non-limiting embodiments with reference to the following drawings, other features, objects, and advantages of the present invention will become more apparent: Figure 1 The first charge-discharge performance comparison diagram of all-solid-state batteries assembled with different ratios of S and I composite cathodes prepared in Example 2 and Comparative Examples 4 to 7; Figure 2 For the S prepared in Example 2 and Comparative Examples 8 and 9 with different mixing orders 9 The first charge-discharge curves of the I composite cathode; Figure 3 For the S prepared in Examples 2 to 4 and Comparative Example 10 with different ball-milling parameters 9 The first charge-discharge curves of the I composite cathode; Figure 4 The cycle performance comparison diagram of all-solid-state lithium-sulfur batteries assembled with different anodes in Test Examples 1 to 3; Figure 5 The cycle performance comparison diagram of all-solid-state batteries in Test Example 1 (continuous test) and Test Example 4 (re-melting cycle test); Figure 6 The EIS spectra of all-solid-state batteries in Test Example 1 and Test Example 4 at different cycle numbers. Detailed implementation manners

[0030] The present invention will be described in detail below with reference to the embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that for those of ordinary skill in the art, several adjustments and improvements can be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0031] For easy understanding, the abbreviations or nouns mentioned in the following text will be explained first: Sulfur: CAS 7704-34-9, purity 99.98%, brand SIGALD; Iodine: CAS 7553-56-2, purity 99.5%, brand SIGALD; Both sulfur powder and iodine powder are ground into powder by a mortar for sulfur and iodine in their elemental forms; Sample bottle: 20 ml transparent sample bottle, 27.5×57 mm, borosilicate glass; VGCF: Carbon nanofiber, purchased from Guangdong Zhuguang New Energy Co., Ltd., model VGCF-H, fiber diameter 15 nm, fiber length 6 μm, aspect ratio 40, conductivity 1.0E-04 Ω·cm.

[0032] First, the present detailed implementation manner provides a method for preparing the S x I cathode material.

[0033] Example 1 A kind of S 9Preparation method of I cathode material, comprising the steps of: S11. Grind sulfur powder and iodine powder configured according to the atomic ratio in a mortar for 10 min to prepare 1 g of S / I mixture, and place it in a 20 mL sealed sample bottle; S12. Place the sample bottle in a muffle furnace, heat it to 80 °C at a rate of 1 °C / min, keep it warm for 3 h, and then cool it naturally to obtain S 9 I cathode material.

[0034] Comparative Example 1 A preparation method of S 6 I cathode material, the steps are basically the same as those in Example 1, the difference is that: In step S11, sulfur powder and iodine powder are configured according to the atomic ratio of 6:1.

[0035] Comparative Example 2 A preparation method of S 16 I cathode material, the steps are basically the same as those in Example 1, the difference is that: In step S11, sulfur powder and iodine powder are configured according to the atomic ratio of 16:1.

[0036] Comparative Example 3 A preparation method of S 36 I cathode material, the steps are basically the same as those in Example 1, the difference is that: In step S11, sulfur powder and iodine powder are configured according to the atomic ratio of 36:1.

[0037] Next, this specific embodiment provides a method for preparing a composite cathode of S x I cathode material for a sulfide-based all-solid-state lithium battery.

[0038] Example 2 A method for preparing a composite cathode using S 9 I cathode material, comprising the steps of: S21. Place the zirconia beads in an oven at 60 °C for drying for 4 h, and then in an argon 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), mix 600 mg of S 9 I and 300 mg of VGCF are premixed by grinding in the glove box for 10 min, and added to a zirconia ball mill tank with the zirconia beads with a diameter of 5 mm at a ball-to-material ratio of 40:1. After sealing with insulating tape in the glove box, transfer it out of the glove box and carry out ball milling treatment. Intermittently ball mill at a speed of 400 rpm for 6 h, that is, after ball milling for 25 min, stop for 5 min, and repeat this cycle 12 times. After the ball milling is completed, transfer it into the glove box and carry out ball-material separation to obtain the first ball-milled mixture; S23. Inside the glove box, mix the first ball-milled mixture with 600 mg of solid electrolyte Li 5.5 PS 4.5 Cl 1.5 and grind and premix them in a mortar. Then transfer them to a ball mill jar, seal it with insulating tape, transfer it out of the glove box, and perform ball milling. Ball mill intermittently at a speed of 400 rpm for 6 h. That is, after ball milling for 25 min, stop for 5 min, and repeat this cycle 12 times. After the ball milling is completed, transfer it into the glove box, separate the balls from the materials, and obtain the second ball-milled mixture, that is, obtain the S 9 I composite cathode.

[0039] Example 3 A method for preparing a composite cathode using S 9 I cathode material is different from Example 2 in that: The parameters of each intermittent ball milling are: ball milling for 20 min, stopping for 10 min, and repeating 12 times.

[0040] Example 4 A method for preparing a composite cathode using S 9 I cathode material is different from Example 2 in that: The parameters of each intermittent ball milling are: ball milling for 30 min, stopping for 5 min, and repeating 12 times.

[0041] Comparative Example 4 A method for preparing a composite cathode using S 6 I cathode material is basically the same as that in Example 2, and the difference is that: Replace the cathode material S 9 I with the S 6 I prepared in Comparative Example 1.

[0042] Comparative Example 5 A method for preparing a composite cathode using S 16 cathode material is basically the same as that in Example 2, and the difference is that: Replace the cathode material S 9 I with the S 16 I prepared in Comparative Example 2.

[0043] Comparative Example 6 A method for preparing a composite cathode using S 36 I cathode material is basically the same as that in Example 2, and the difference is that: Replace the cathode material S 9 I with the S 36 I prepared in Comparative Example 3.

[0044] Comparative Example 7 A method for preparing a composite cathode using a cathode material S, the steps are basically the same as those in Example 2, the difference is that: Replace the cathode material S 9 I with raw material S.

[0045] Comparative Example 8 A method for preparing a composite cathode using a cathode material S 9 I, the difference from Example 2 is that: the sulfide cathode material and the solid electrolyte are first compounded, and then VGCF is added to prepare the composite cathode. Specifically: S81. Refer to Example 2 to dry the zirconia beads first, and then in an argon atmosphere, according to a ball-to-material ratio of 40:1, place the zirconia beads in a zirconia ball mill jar, and place 600 mg of S 9 I and 600 mg of the solid electrolyte Li 5.5 PS 4.5 Cl 1.5 Premix in a mortar and then add it to the ball mill jar, seal it with insulating tape, and perform intermittent ball milling at 400 rpm for 6 h. After the ball milling is completed, transfer it to a glove box and separate the ball from the material; S82. Premix 300 mg of VGCF with the material separated in step S81, then transfer it to the ball mill jar, seal it with insulating tape, and perform intermittent ball milling at 400 rpm for 6 h. After the ball milling is completed, transfer it to a glove box for ball-material separation to obtain S 9 I composite cathode.

[0046] In this example, the parameters for ball milling refer to Example 2.

[0047] Comparative Example 9 A method for preparing a composite cathode using a cathode material S 9 I, the difference from Example 2 is that: the sulfide cathode material, the solid electrolyte, and VGCF are simultaneously fed for ball milling to prepare the composite cathode. Specifically: In an argon glove box, according to a ball-to-material ratio of 40:1, add the dried zirconia grinding balls to the ball mill jar, and place 600 mg of S 9 I, 300 mg of VGCF, 600 mg of the solid electrolyte Li 5.5 PS 4.5 Cl 1.5 Add to the ball mill jar, seal it with insulating tape, and perform intermittent ball milling at 400 rpm for 12 h (intermittent mode: ball milling for 25 min, stopping for 5 min). After the ball milling is completed, transfer it to a glove box for ball-material separation to obtain S 9 I composite cathode.

[0048] Comparative Example 10 A method for using S9 The method for preparing a composite cathode using a positive electrode material is different from that of Example 2 in that: The batch ball milling is replaced by non-batch ball milling, and the time for both ball millings is 5 h.

[0049] Detection and analysis The methods for preparing all-solid-state lithium-sulfur batteries using the composite cathodes prepared in Examples 2 to 4 and Comparative Examples 4 to 10 respectively in an argon environment include the steps: Electrolyte: 100 mg of solid electrolyte Li 5.5 PS 4.5 Cl 1.5 powder (D 50 = 5 μm, ionic conductivity is 10.32 mS / cm) is placed in a pressure cell mold with a diameter of φ10 mm, and the electrolyte powder is flattened by rotating a stainless steel column, and then pressed into a sheet on a tablet press, with a pressure of 120 MPa and a pressure holding time of 2 min; Cathode: 8 mg of the composite cathode powder is placed on one side of the electrolyte sheet, and the pressure is held for 10 min at a pressure of 360 MPa; Anode: 12 mg of Li-Si alloy (Li 22 Si 5 ) anode powder is placed on the other side of the electrolyte sheet. After being flattened, the pressure is held for 2 min at 360 MPa; An Al foil with a thickness of 85 and a diameter of φ10 mm is placed on the surface of the positive electrode sheet as the positive electrode current collector; the negative electrode current collector is a Cu foil with a thickness of 45 . After the laminated assembly is completed, a pressure of 30 MPa is applied and the pressure is held for 2 min to obtain an all-solid-state lithium-sulfur battery.

[0050] The assembled battery is applied with a constant pressure of 30 MPa through a pressure mold, placed in a constant temperature and humidity incubator at 60 °C, connected to a battery tester, and the charge and discharge rate is 0.1 C to 0.5 C, and the charge and discharge cut-off voltage is 1.2 V to 2.8 V. The charge and discharge capacities described in the present invention are specific capacities calculated based on the corresponding active materials.

[0051] Charge / discharge specific capacity (mAh·g -1 ) =

[0052] Figure 1 It is a comparison chart of the first-cycle charge and discharge performance of all-solid-state batteries assembled with composite cathodes with different S and I ratios prepared in Comparative Examples 4 to 7 and Example 2. It can be seen that S 9I having the best S / I is the elemental ratio with better performance, which has higher conductivity compared to the composite cathode materials prepared with other elemental ratios, ensuring efficient ion and electron transport channels and enabling it to fully exhibit a higher specific capacity (1064 mAh·g in Example 2 -1 ), while Comparative Examples 4 to 7 cannot reach the electrochemical capacity of the composite cathode in Example 2.

[0053] Figure 2 are the first charge-discharge curves of the S 9 I composite cathodes prepared by Example 2 and Comparative Examples 8 and 9 with different mixing orders. Different mixing orders in Comparative Examples 8 and 9 cannot achieve the effect of the composite cathode prepared in Example 2.

[0054] Figure 3 are the first charge-discharge curves of the S 9 I composite cathodes prepared by Examples 2 to 4 and Comparative Example 10 with different ball-milling parameters. As shown in the figure, the composite cathodes prepared by the intermittent ball-milling method have better effects, especially in Example 2.

[0055] Test Example 1 Using the S 9 I composite cathode prepared in Example 2 to prepare an all-solid-state lithium-sulfur battery according to the above method.

[0056] Test Example 2 Assemble an all-solid-state lithium-sulfur battery with reference to the steps in Test Example 1, with the difference being that: The negative electrode selects a metallic lithium sheet with a diameter of 10 mm and a thickness of 50 as the negative electrode.

[0057] Test Example 3 Assemble an all-solid-state lithium-sulfur battery with reference to the steps in Test Example 1, with the difference being that: The negative electrode selects an indium sheet with a diameter of 10 mm and a thickness of 100 and a lithium sheet with a thickness of 50 stacked as the negative electrode, and the indium sheet is adjacent to the electrolyte layer.

[0058] In a constant temperature and humidity incubator at 60 °C, the charge-discharge rate tested is 0.1C to 0.5 C, and the charge-discharge cut-off voltage is 1.2 V to 2.8 V. The charge and discharge capacities described in the present invention are the specific capacities calculated for the corresponding active materials.

[0059] Figure 4 is a comparison chart of the cycle performance of the all-solid-state lithium-sulfur batteries assembled with different negative electrodes in Test Examples 1 to 3. Relatively speaking, using a lithium-silicon alloy negative electrode and S 9The composite cathode has a better matching mechanism, enabling the battery to have a smaller strain effect caused by volume expansion inside, which ensures that the crystal can offset the effects of severe volume expansion on the collapse of the internal conductive network and interface cracking of the cathode during long cycles. From Test Example 2 and Test Example 3, it can be seen that during the cycling process, the metallic lithium anode causes its active material to undergo relatively severe phase fission and interfacial side reactions, resulting in poor cycling performance; the lithium-indium alloy anode can alleviate the occurrence of interfacial side reactions to a certain extent, but the effect is not as good as that of the lithium-silicon alloy.

[0060] Test Example 4 After cycling 50 times, the full battery and the pressure mold prepared in Test Example 1 were removed from the test equipment and transferred to an oven for heating. The temperature was raised at a rate of 1 °C / min to 100 °C and held for 3 h. At 100 °C, the active material in the composite cathode turned into a liquid state and refilled the damaged composite cathode interface due to cycling, ensuring that the active material S of the cathode material 9 I, VGCF, and the solid electrolyte were in full contact again. After the heat preservation ended, it was naturally cooled to room temperature, and the battery and the pressure mold were reassembled into the test equipment again to continue the performance test.

[0061] Test Example 5 After cycling 200 times, the full battery and the pressure mold prepared in Test Example 1 were removed from the test equipment and transferred to an oven for heating. The temperature was raised at a rate of 1 °C / min to 100 °C and held for 3 h. At 100 °C, the active material in the composite cathode turned into a liquid state and refilled the damaged composite cathode interface due to cycling, ensuring that the active material S of the cathode material 9 I, VGCF, and the solid electrolyte were in full contact again. After the heat preservation ended, it was naturally cooled to room temperature, and the battery and the pressure mold were reassembled into the test equipment again to continue the performance test.

[0062] Figure 5 It is a comparison chart of the full battery cycling performance of Test Example 1 (continuous test) and Test Example 4 (remelting cycle test). It can be clearly seen that the battery capacity has a relatively obvious increase after each remelting. The capacity retention rate of Test Example 3 decayed to 87% after 200 cycles, while the battery with periodic remelting in Test Example 4 still had a capacity retention rate of 96% after 200 stable cycles.

[0063] Figure 6It is the EIS spectra of the full cells of Test Example 1, Test Example 4 and 5 at different cycle numbers. It can be seen that after 50 cycles and 200 cycles of the full cells, the interfacial impedance increases significantly. After heating and repair, the interfacial impedance recovers to near the initial level. In the figure, Test Example 1-1st represents the data after 1 cycle of Test Example 1, Test Example 1-50th represents the data after 50 consecutive cycles of Test Example 1, Test Example 4-1st represents the data after 1 cycle of Test Example 4 (i.e., the 1st cycle after remelting after 50 cycles of Test Example 1), Test Example 1-200th represents the data after 200 consecutive cycles of Test Example 1, and Test Example 5-1st represents the data after 1 cycle of Test Example 5 (i.e., the 1st cycle after remelting after 200 cycles of Test Example 1).

[0064] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various deformations or modifications within the scope of the claims, which does not affect the essence of the present invention.

Claims

1. A method for preparing a composite positive electrode material, characterized in that: The following steps are involved: S1, intermittently ball-milling S9I and conductive carbon under a protective atmosphere to obtain a premix; S2, intermittently ball-milling the premix and the solid sulfide electrolyte under a protective atmosphere to obtain the composite positive electrode material; The mass ratio of S9I, conductive carbon and sulfide electrolyte is (3.5-4.5): (3.5-4.5): 2, and the intermittent ball milling is 20-30 min, pausing for 5-10 min, and then ball milling for 6-7 h.

2. The preparation method according to claim 1, characterized in that: The conductive carbon includes one or more of nano carbon fiber, Ketjen black, and super-P.

3. The preparation method according to claim 1, characterized in that: The sulfide electrolyte includes Li3PS4, Li 5.5 PS 4.5 X 1.5 One or more of, wherein X is selected from at least one of F, Cl, Br, and I.

4. The preparation method according to claim 1, characterized in that: The preparation method of the S9I is: uniformly mix the elemental S and the elemental I2 according to the atomic ratio, then place them in a sealed container for heat treatment at 80-100° C. for 2-4 hours, and naturally cool them to room temperature to obtain the S9I material.

5. A composite positive electrode material, characterized in that: The composite positive electrode material is prepared according to the method according to any one of claims 1 to 3.

6. An all-solid-state lithium-sulfur battery, characterized in that: Including the composite positive electrode material as described in claim 5.

7. The all-solid-state lithium-sulfur battery according to claim 6, characterized in that: The all-solid-state lithium-sulfur battery comprises an electrolyte, a positive electrode and a negative electrode, wherein the positive electrode is made of a composite positive electrode material, the electrolyte is a sulfide electrolyte, and the negative electrode is a lithium-silicon alloy.

8. The all-solid-state lithium-sulfur battery according to claim 7, characterized in that: First, the sulfide electrolyte is pressed into an electrolyte sheet; then the composite positive electrode material is placed on one side of the electrolyte sheet for pressing to obtain a double-layer material of a positive electrode sheet-electrolyte sheet, and then the lithium silicon alloy is placed on the other side of the electrolyte sheet for pressing to obtain a three-layer material of a positive electrode sheet-electrolyte sheet-negative electrode sheet; finally, the positive electrode current collector is placed on the surface of the positive electrode sheet, and the negative electrode current collector is placed on the surface of the negative electrode sheet. After the assembly is completed, the battery is pressed to obtain the all-solid-state lithium-sulfur battery.

9. The use of the all-solid-state lithium-sulfur battery according to any one of claims 6 to 7, characterized in that: The interface damaged by cycling is repaired by periodic remelting.

10. The use of the all-solid-state lithium-sulfur battery according to claim 9, characterized in that: The periodic remelting is performed by keeping the temperature at 100° C. for 3 hours after each 50 cycles.

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