A composite cathode material, its preparation method and application

Abstract

The present invention discloses a composite positive electrode material, a preparation method and an application thereof, which relate to the field of electrochemical energy storage technology. First, S9I and conductive carbon are intermittently ball-milled under a protective atmosphere, and then a solid sulfide electrolyte is added, and intermittent ball-milling is performed again in a protective atmosphere to obtain a composite positive electrode material. This preparation method cleverly combines step-by-step ball milling with intermittent ball milling to ensure uniform dispersion of each component, efficiently construct an ion and electron transport network, and stabilize material performance. The all-solid-state lithium-sulfur battery based on the composite positive electrode material is matched with a lithium-silicon alloy negative electrode, and with the help of the volume expansion compensation mechanism of the positive and negative electrodes, the close contact of the electrode / electrolyte interface is firmly maintained. The composite positive electrode has a first discharge specific capacity of up to 1064 mAh g at 60°C. ‑1 By utilizing the low melting point of S9I and periodically remelting to repair damaged interfaces, the battery retains 96% of its capacity after 200 cycles, significantly improving its cycle stability and service life.

Description

Technical Field

[0001] The present invention relates to the technical field of electrochemical energy storage, and in particular to a composite positive electrode material and a preparation method and application thereof. Background Art

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

[0003] However, all-solid-state lithium-sulfur batteries have encountered many difficult challenges in their development. The first and foremost challenge is the intrinsic insulation of the sulfur cathode, which has an extremely low electronic conductivity of only about 5×10 -18 S cm -1 This directly leads to the long-term difficulty of breaking through the bottleneck of 70% in the utilization rate of active materials. At the same time, during the battery charge and discharge cycle, the sulfide positive electrode will experience a volume change of up to 80%, which will cause serious interface contact problems, causing the interface impedance to soar to more than 3000Ω·cm², which has a fatal impact on battery performance and long-term cycle stability. In addition, polysulfide (Li2S x , 4 ≤x≤ 8) Chemical permeation in the solid electrolyte triggers a shuttle effect, resulting in irreversible capacity decay. For example, after 100 cycles, the capacity retention is less than 60%. The development of all-solid-state lithium-sulfur batteries has historically been hampered by sulfur's insulating properties and its large volume changes during cycling, leading to poor interfacial contact and hindering charge transfer between the different solid components. Therefore, improving the insulation and volume expansion of the sulfur cathode and the interfacial contact issues are of great significance.

[0004] To address these challenges, researchers are actively exploring solutions. In terms of positive electrode materials, the sulfide positive electrode materials of all-solid-state lithium-sulfur batteries come in various forms. In addition to the commonly used elemental sulfur positive electrode, there are also lithium sulfide (Li2S) positive electrodes, iron disulfide (FeS2) positive electrodes, etc. By combining sulfur with different metal oxides, the conductivity of sulfur can be significantly improved, and the electrochemical reaction kinetics can be improved.

[0005] The composite cathode of an all-solid-state lithium-sulfur battery consists primarily of three components: an active material, a conductive agent, and a solid electrolyte. Conventional composite cathodes are mixed with conductive carbon and PVDF, then applied to the electrode in the form of a slurry. However, in all-solid-state batteries, dry-processing is required. Ensuring efficient electron and ion transport across the solid particles, despite the unstable interface caused by volume changes and insulating products, remains a crucial challenge.

[0006] All-solid-state lithium-sulfur batteries usually use metallic lithium as the negative electrode material, but the lithium metal negative electrode will produce dendrite problems during the deposition and dissolution process. Common methods to improve the negative electrode interface stability include: optimizing the sulfide solid electrolyte components, forming an artificial electrolyte membrane at the interface, controlling interface defects to reduce lithium dendrite nucleation sites, and using lithium alloys to directly replace the lithium metal negative electrode. Summary of the Invention

[0007] In view of this, the object of the present invention is to provide a composite positive electrode material and a preparation method and application thereof.

[0008] The object of the present invention is achieved through the following technical solutions:

[0009] <First Aspect>

[0010] The present invention provides a method for preparing a composite positive electrode material, comprising the following steps:

[0011] S1, intermittently ball-milling S9I and conductive carbon under a protective atmosphere to obtain a premix;

[0012] S2. intermittently ball-milling the premix and the solid sulfide electrolyte under a protective atmosphere to obtain the composite positive electrode material;

[0013] The intermittent ball milling comprises ball milling for 20 to 30 minutes, pausing for 5 to 10 minutes, and then ball milling for 6 to 7 hours.

[0014] As an embodiment, the conductive carbon includes one or more of nano-carbon fiber, Ketjen black, and super-P.

[0015] In some embodiments, the conductive carbon is nano-carbon fiber.

[0016] As an embodiment, 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.

[0017] In some embodiments, the sulfide electrolyte is selected from Li 5.5 PS4.5 Cl 1 .5 .

[0018] As an embodiment, the mass ratio of the S9I, conductive carbon and sulfide electrolyte is (3.5~4.5):(3.5~4.5):2.

[0019] In some embodiments, the mass ratio of the S9I, conductive carbon, and sulfide electrolyte is 4:4:2.

[0020] As an embodiment, the ball milling parameters are: the ball milling medium is zirconia grinding balls with a diameter of 4 to 6 mm, the ball-to-material ratio is 35 to 40:1, and the rotation speed is 350 to 450 rpm / min.

[0021] As an embodiment, the preparation method of the S9I is: uniformly mix elemental S and elemental I2 according to the atomic ratio, then place it in a sealed container for heat treatment at 80-100°C for 2-4 hours, and naturally cool to room temperature to obtain the S9I material.

[0022] As an embodiment, the heating rate of the heat treatment is 1°C / min.

[0023] <Second Aspect>

[0024] The present invention provides a composite positive electrode material prepared by the above method.

[0025] <Third Aspect>

[0026] The present invention provides an all-solid-state lithium-sulfur battery prepared by using the composite positive electrode material.

[0027] As an embodiment, the all-solid-state lithium-sulfur battery includes an electrolyte, a positive electrode and a negative electrode, wherein:

[0028] 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.

[0029] 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 positive electrode material on one side of the electrolyte sheet and pressing it to obtain a positive electrode sheet-electrolyte sheet double-layer material, and then placing the lithium silicon alloy on the other side of the electrolyte sheet and pressing it to obtain a positive electrode sheet-electrolyte sheet-negative electrode sheet three-layer material; finally, placing the positive electrode current collector on the surface of the positive electrode sheet and the negative electrode current collector on the surface of the negative electrode sheet, and after the assembly is completed, pressing is performed to obtain the all-solid-state lithium-sulfur battery.

[0030] In some embodiments, the sulfide electrolyte is selected from Li 5.5 PS 4.5Cl 1.5 pink.

[0031] In some embodiments, the positive electrode current collector is aluminum foil; and the negative electrode current collector is copper foil.

[0032] In some embodiments, the mass ratio of the composite cathode material to the sulfide electrolyte is 8:100.

[0033] <Fourth Aspect>

[0034] The present invention provides an application of the above-mentioned all-solid-state lithium-sulfur battery, which repairs the interface damaged by cycling through periodic remelting.

[0035] In some embodiments, the periodic remelting is performed by keeping the temperature at 100° C. for 3 hours after every 50 cycles.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] 1) This invention provides an S9I composite cathode, which is made from S9I, a sulfide electrolyte, and conductive carbon through mechanical ball milling. The conductive carbon improves the composite's electronic conductivity, while the sulfide electrolyte provides interparticle contact, optimizing ion transport from the composite cathode to the cathode / electrolyte interface. S9I exhibits semiconductor-level electrical conductivity, 11 orders of magnitude higher than sulfur itself.

[0038] 2) The present invention utilizes a combination of step-by-step ball milling and intermittent ball milling to prepare the S9I composite cathode. Step-by-step ball milling ensures thorough premixing of the S9I and conductive carbon prior to mixing with the sulfide electrolyte. This facilitates uniform distribution of the conductive carbon and electrolyte, allowing direct contact between the conductive carbon and the active material, enhancing the conductivity of the sulfide cathode. The indirect contact of the sulfide electrolyte further ensures ion transfer from the composite cathode to the electrolyte surface. Intermittent ball milling releases energy generated during the milling process, preventing S9I melting and decomposition due to energy accumulation. It also prevents excessive energy from causing localized lattice distortion in the sulfide electrolyte crystals. This combined milling method offers two major advantages: first, it ensures a homogeneous distribution of the S9I, electrolyte, and conductive carbon, creating conditions for sufficient interparticle contact and establishing an efficient ion-electron transport network; second, it controls the heat energy generated by particle friction above the phase transition threshold, thereby maintaining the stable physical and chemical properties of each component. Furthermore, ball-milling the sulfide cathode material and conductive carbon before adding electrolyte powder for further compounding ensures full contact between the sulfide cathode material and the conductive carbon, ensuring high electronic conductivity. This also allows the electrolyte powder to be evenly distributed between the cathode material and the conductive carbon, creating a more optimal ion transport channel. Intermittent ball milling also alleviates material agglomeration caused by excess heat during the milling process, ensuring a more uniform mixing of the components within the composite cathode.

[0039] 3) The composite cathode of the present invention exhibits a capacity of 1064 mAh g at 60 °C. -1 The first discharge specific capacity and rate performance are also significantly improved.

[0040] 4) This invention also provides a negative electrode that is more compatible with the S9I composite positive electrode. A lithium-silicon alloy is used as the negative electrode material. During the lithiation / delithiation process, the volume expansion of silicon in the S9I molecular crystal is approximately 300%. During the charge and discharge process, the phase transition from S to Li2S is accompanied by an 80% volume expansion. By controlling the ratio of the positive and negative electrode materials, the expansion directions of the two can be made complementary to the volume change of the positive electrode. During charging, the positive electrode (S9I) contracts upon delithiation, while the negative electrode (Li-Si) expands upon insertion. These expansions occur in opposite directions, offsetting mechanical stress and suppressing electrode / electrolyte interface separation. During discharge, the positive electrode expands upon insertion, while the negative electrode contracts upon delithiation. These expansions complement each other, maintaining overall battery structural stability. The Li-Si alloy negative electrode can effectively alleviate the strain caused by the large volume expansion of the sulfide positive electrode during the charging and discharging process. Through the synergistic volume expansion compensation mechanism of the lithium silicon alloy (Li-Si) negative electrode and the sulfur iodine molecular crystal (S9I) positive electrode, it can dynamically maintain close contact between the electrode / electrolyte interface in the all-solid-state battery, significantly improving the battery cycle stability and energy density.

[0041] 5) The present invention utilizes the low melting point of the S9I material and repairs the cycle-damaged interface through periodic remelting of the composite positive electrode material, restoring the impedance to a level close to the initial level. The all-solid-state battery using this composite positive electrode material and periodic remelting method still has a capacity retention rate of 96% after 200 cycles, greatly extending the cycle life. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Other features, objects and advantages of the present invention will become more apparent upon reading the detailed description of non-limiting embodiments with reference to the following drawings:

[0043] Figure 1 A comparison of the first cycle charge and discharge performance of full batteries assembled with S and I composite positive electrodes of different ratios prepared in Example 2 and Comparative Examples 4 to 7;

[0044] Figure 2 The first cycle charge-discharge curves of the S9I composite positive electrode prepared in different mixing orders in Example 2 and Comparative Examples 8 and 9;

[0045] Figure 3 The first cycle charge-discharge curves of the S9I composite positive electrode prepared using different ball milling parameters in Examples 2 to 4 and Comparative Example 10;

[0046] Figure 4 A comparison chart of the cycle performance of all-solid-state lithium-sulfur batteries assembled using different negative electrodes in Test Examples 1 to 3;

[0047] Figure 5 The full battery cycle performance comparison chart of test example 1 (continuous test) and test example 4 (remelting cycle test);

[0048] Figure 6 EIS spectra of the full batteries of Test Example 1 and Test Example 4 at different cycle numbers. DETAILED DESCRIPTION

[0049] The present invention will be described in detail below with reference to the examples. The following examples will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that those skilled in the art may make several adjustments and improvements without departing from the scope of the present invention. These all fall within the scope of protection of the present invention.

[0050] For ease of understanding, the abbreviations or nouns mentioned below are first explained:

[0051] Sulfur: CAS7704-34-9, purity 99.98%, brand SIGALD;

[0052] Iodine: CAS7553-56-2, purity 99.5%, brand SIGALD;

[0053] Sulfur powder and iodine powder are both sulfur and iodine elements ground into powder in a mortar;

[0054] Sample bottle: 20ml transparent sample bottle, 27.5×57mm, borosilicate glass;

[0055] VGCF: nanocarbon fiber, purchased from Guangdong Candlelight New Energy Co., Ltd., model VGCF-H, fiber diameter 15 nm, fiber length 6 μm, aspect ratio 40, conductivity 1.0E-04 Ω·cm.

[0056] First, this specific embodiment provides S x I. Preparation method of positive electrode material.

[0057] Example 1

[0058] A method for preparing an S9I positive electrode material comprises the following steps:

[0059] S11. Grind sulfur powder and iodine powder according to the atomic ratio in a mortar for 10 min to prepare 1 g of S / I mixture, which is placed in a 20 mL sealed sample bottle;

[0060] S12. Place the sample bottle in a muffle furnace, heat to 80°C at a rate of 1°C / min, keep warm for 3 hours, and then cool naturally to obtain the S9I positive electrode material.

[0061] Comparative Example 1

[0062] A method for preparing an S6I positive electrode material, the steps are basically the same as those in Example 1, except that:

[0063] In step S11, sulfur powder and iodine powder are prepared according to an atomic ratio of 6:1.

[0064] Comparative Example 2

[0065] A S 16 The steps for preparing the positive electrode material I are basically the same as those in Example 1, except that:

[0066] In step S11 , sulfur powder and iodine powder are prepared according to an atomic ratio of 16:1.

[0067] Comparative Example 3

[0068] A S 36 The steps for preparing the positive electrode material I are basically the same as those in Example 1, except that:

[0069] In step S11, sulfur powder and iodine powder are prepared according to an atomic ratio of 36:1.

[0070] Next, this specific embodiment provides S xI positive electrode material is used for the preparation method of the composite positive electrode of sulfide-based all-solid-state lithium battery.

[0071] Example 2

[0072] A method for preparing a composite positive electrode using an S9I positive electrode material comprises the following steps:

[0073] S21. After drying the zirconia beads in an oven at 60°C for 4 hours, 600 mg of S9I and 300 mg of VGCF were ground in an argon glove box (the water content and oxygen content of the argon in the glove box were less than 1 ppm and less than 1 ppm) for 10 minutes to pre-mix them. The mixture was then added to a zirconia ball mill jar with dried zirconia beads of 5 mm in diameter at a ball-to-material ratio of 40:1. The jar was sealed with insulating tape in the glove box and then transferred out of the glove box for ball milling. The mixture was intermittently ball milled at a speed of 400 rpm for 6 hours, i.e., after ball milling for 25 minutes, it was stopped for 5 minutes. This cycle was repeated 12 times. After the ball milling was completed, the mixture was transferred to the glove box for ball-to-material separation to obtain the first ball milling mixture.

[0074] S23. In the glove box, the first ball milled mixture and 600 mg of solid electrolyte Li 5.5 PS 4.5 Cl 1.5 The premix was ground in a mortar and then transferred to a ball mill jar. After sealing with insulating tape, it was transferred out of the glove box for ball milling. The ball milling was performed intermittently at a speed of 400 rpm for 6 hours, that is, after ball milling for 25 minutes, it was stopped for 5 minutes. This cycle was repeated 12 times. After the ball milling was completed, it was transferred to the glove box for ball-material separation to obtain the second ball milling mixture, that is, the S9I composite positive electrode.

[0075] Example 3

[0076] A method for preparing a composite positive electrode using S9I positive electrode material differs from Example 2 in that:

[0077] The parameters of each intermittent ball milling were as follows: milling for 20 min, stopping for 10 min, and repeating 12 times.

[0078] Example 4

[0079] A method for preparing a composite positive electrode using S9I positive electrode material differs from Example 2 in that:

[0080] The parameters of each intermittent ball milling were as follows: ball milling for 30 min, rest for 5 min, and repeated 12 times.

[0081] Comparative Example 4

[0082] A method for preparing a composite positive electrode using S6I positive electrode material, the steps are basically the same as those in Example 2, except that:

[0083] The positive electrode material S9I was replaced with S6I prepared in Comparative Example 1.

[0084] Comparative Example 5

[0085] A method using S 16 The steps of the method for preparing a composite positive electrode from a positive electrode material are basically the same as those in Example 2, except that:

[0086] The positive electrode material S9I was replaced by S prepared in Comparative Example 2. 16 I.

[0087] Comparative Example 6

[0088] A method using S 36 I. Method for preparing composite positive electrode from positive electrode material. The steps are basically the same as those in Example 2, except that:

[0089] The positive electrode material S9I was replaced by S prepared in Comparative Example 3. 36 I.

[0090] Comparative Example 7

[0091] A method for preparing a composite positive electrode using S positive electrode material, the steps are basically the same as those in Example 2, except that:

[0092] The positive electrode material S9I was replaced with raw material S.

[0093] Comparative Example 8

[0094] A method for preparing a composite positive electrode using S9I positive electrode material differs from Example 2 in that the sulfide positive electrode material and the solid electrolyte are first composited, and then VGCF is added to prepare the composite positive electrode, specifically:

[0095] S81, referring to Example 2, first dry the zirconium oxide beads, then place the zirconium oxide beads in a zirconium oxide ball mill at a ball-to-material ratio of 40:1 under an argon atmosphere, and mix 600 mg of S9I and 600 mg of solid electrolyte Li 5.5 PS 4.5 Cl 1.5 After premixing in a mortar, add it to the ball mill jar, seal it with insulating tape, and intermittently ball mill at a speed of 400 rpm for 6 hours. After the ball milling is completed, transfer it to a glove box and separate the ball and material;

[0096] S82. Premix 300 mg of VGCF with the material separated in step S81, transfer the mixture to a ball mill, seal it with insulating tape, and intermittently ball mill it at a speed of 400 rpm for 6 h. After the ball milling is completed, transfer it to a glove box for ball-material separation to obtain the S9I composite positive electrode.

[0097] In this embodiment, the parameters of ball milling are referred to Example 2.

[0098] Comparative Example 9

[0099] A method for preparing a composite positive electrode using an S9I positive electrode material differs from Example 2 in that a sulfide positive electrode material, a solid electrolyte, and VGCF are simultaneously added and ball milled to prepare the composite positive electrode, specifically:

[0100] In an argon glove box, the dried zirconia grinding balls were added to the ball mill according to the ball-to-material ratio of 40:1, and 600 mg of S9I, 300 mg of VGCF, 600 mg of solid electrolyte Li 5.5 PS 4.5 Cl 1.5 Add to the ball mill jar, seal with insulating tape, and intermittently ball mill for 12 hours at a speed of 400 rpm (intermittent mode: ball milling for 25 minutes, stop for 5 minutes). After the ball milling is completed, transfer to the glove box for ball-material separation to obtain the S9I composite positive electrode.

[0101] Comparative Example 10

[0102] A method for preparing a composite positive electrode using S9I positive electrode material differs from Example 2 in that:

[0103] Intermittent ball milling was replaced with non-intermittent ball milling, and the ball milling time for both times was 5 h.

[0104] Detection and Analysis

[0105] The method for preparing an all-solid-state lithium-sulfur battery under an argon environment using the composite positive electrodes prepared in Examples 2 to 4 and Comparative Examples 4 to 10 respectively comprises the following steps:

[0106] Electrolyte: 100 mg of solid electrolyte Li 5.5 PS 4.5 Cl 1.5 Pink (D 50 =5μm, ionic conductivity 10.32 mS / cm) was placed in a φ10mm pressure battery mold, and the electrolyte powder was rotated and flattened by a rotating stainless steel column. The tablet was pressed into tablets on a tablet press at a pressure of 120MPa and maintained for 2min.

[0107] Positive electrode: Place 8 mg of composite positive electrode powder on one side of the electrolyte sheet and maintain the pressure at 360 MPa for 10 minutes;

[0108] Negative electrode: 12 mg of Li-Si alloy (Li 22 Si5) negative electrode powder is placed on the other side of the electrolyte sheet, flattened, and maintained at 360 MPa for 2 minutes;

[0109] The thickness of φ10mm is 85 The Al foil is placed on the surface of the positive electrode as the positive electrode current collector; the negative electrode current collector is 45 After the stacking assembly is completed, a pressure of 30 MPa is applied and the pressure is maintained for 2 minutes to obtain an all-solid-state lithium-sulfur battery.

[0110] The assembled battery was placed in a press mold, subjected to a constant pressure of 30 MPa, and placed in a 60°C constant temperature and humidity incubator. Connected to a cell tester, the battery was tested at a charge and discharge rate of 0.1C to 0.5C, with a charge and discharge cutoff voltage of 1.2V to 2.8V. The charge and discharge capacities described herein are the specific capacities calculated based on the corresponding active materials.

[0111] Charge / discharge specific capacity (mAh g -1 ) =

[0112] Figure 1 This is a comparison of the first cycle charge and discharge performance of full batteries assembled from composite cathodes with different ratios of S to I prepared in Comparative Examples 4 to 7 and Example 2. It can be seen that S9I has the best S / I ratio, which is the element ratio with better performance. Compared with composite cathode materials prepared with other element ratios, it has higher conductivity, ensuring efficient ion and electron transport channels, allowing it to fully utilize its higher specific capacity (1064 mAh·g in Example 2). -1 ), while Comparative Examples 4 to 7 cannot reach the electrochemical capacity of the composite positive electrode of Example 2.

[0113] Figure 2 These are the first cycle charge and discharge curves of the S9I composite positive electrodes prepared in different mixing orders in Comparative Examples 8 and 9, and Example 2. The different mixing orders in Comparative Examples 8 and 9 cannot achieve the effect of the composite positive electrode prepared in Example 2.

[0114] Figure 3 The first cycle charge-discharge curves of the S9I composite cathode prepared using different ball milling parameters in Examples 2 to 4 and Comparative Example 10 are shown. The graph shows that the composite cathode prepared using intermittent ball milling has better performance, especially Example 2.

[0115] Test Example 1

[0116] An all-solid-state lithium-sulfur battery was prepared using the S9I composite positive electrode prepared in Example 2 according to the above method.

[0117] Test Example 2

[0118] The all-solid-state lithium-sulfur battery was assembled according to the steps of Test Example 1, with the following differences:

[0119] The negative electrode is selected with a diameter of 10mm and a thickness of 50 The metallic lithium sheet is used as the negative electrode.

[0120] Test Example 3

[0121] The all-solid-state lithium-sulfur battery was assembled according to the steps of Test Example 1, with the following differences:

[0122] The negative electrode is selected with a diameter of 10mm and a thickness of 100 Indium sheet and thickness 50 The lithium sheets are stacked as the negative electrode, and the indium sheet is next to the electrolyte layer.

[0123] In a 60°C constant temperature and humidity incubator, the tested charge and discharge rates were 0.1C to 0.5C, and the charge and discharge cut-off voltages were 1.2V to 2.8V. The charge and discharge capacities described in the present invention are the specific capacities calculated based on the corresponding active materials.

[0124] Figure 4 This is a comparison chart of the cycle performance of all-solid-state lithium-sulfur batteries assembled with different negative electrodes in test examples 1 to 3. Relatively speaking, the use of lithium-silicon alloy negative electrode and S9I composite positive electrode has a better matching mechanism, which makes the strain effect caused by smaller volume expansion inside the battery smaller, which ensures that the crystal offsets the influence of the internal conductive network collapse and interface cracking of the positive electrode caused by the intense volume expansion under long cycles. As can be seen from test examples 2 and 3, during the cycle process, the metallic lithium negative electrode causes its active material to undergo relatively serious phase fission and interface side reactions, resulting in poor cycle performance; the lithium-indium alloy negative electrode can alleviate the occurrence of negative electrode interface side reactions to a certain extent, but the effect is not as good as that of lithium-silicon alloy.

[0125] Test Example 4

[0126] After 50 cycles, the full battery and pressure mold prepared in Test Example 1 were removed from the test equipment and transferred to an oven for heating. They were heated to 100°C at a heating rate of 1°C / min and kept warm for 3 hours. At 100°C, the active material in the composite positive electrode was converted into liquid and refilled the composite positive electrode interface damaged by the cycle, ensuring that the positive electrode material active material S9I, VGCF and the solid electrolyte were fully contacted again. After the insulation was completed, they were naturally cooled to room temperature, and the battery and pressure mold were assembled back into the test equipment to continue the performance test.

[0127] Test Example 5

[0128] After 200 cycles, the full battery and pressure mold prepared in Test Example 1 were removed from the test equipment and transferred to an oven for heating. They were heated to 100°C at a heating rate of 1°C / min and kept warm for 3 hours. At 100°C, the active material in the composite positive electrode was converted into liquid and refilled the composite positive electrode interface damaged by the cycle, ensuring that the positive electrode material active material S9I, VGCF and the solid electrolyte were fully contacted again. After the insulation was completed, they were naturally cooled to room temperature, and the battery and pressure mold were assembled back into the test equipment to continue the performance test.

[0129] Figure 5 This is a comparison of the full battery cycling performance of Test Example 1 (continuous test) and Test Example 4 (remelting cycle test). Clearly, the battery capacity increases significantly after each remelting cycle. In Test Example 3, the capacity retention rate decreases to 87% after 200 cycles, while the periodically remelted battery in Test Example 4 maintains a 96% capacity retention rate after 200 stable cycles.

[0130] Figure 6 Figure 1 is the EIS spectrum of the full battery of Test Example 1 and Test Examples 4 and 5 at different cycle times. It can be seen that the interface impedance of the full battery increases significantly after 50 and 200 cycles, and after heating and repair, the interface impedance returns to a level close to 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 continuous cycles of Test Example 1, Test Example 4-1st represents the data after 1 cycle of Test Example 4 (i.e., the first cycle after remelting after 50 cycles of Test Example 1), Test Example 1-200th represents the data after 200 continuous cycles of Test Example 1, and Test Example 5-1st represents the data after 1 cycle of Test Example 5 (i.e., the first cycle after remelting after 200 cycles of Test Example 1).

[0131] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art may make various variations or modifications within the scope of the claims, which do 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 the SiI, conductive carbon, and sulfide electrolyte is (3.5-4.5): (3.5-4.5): 2, and the intermittent ball milling is performed for 20-30 min, followed by a pause of 5-10 min and a final milling of 6-7 h. The S9I material is obtained by uniformly mixing elemental S and elemental I2 according to an atomic ratio, then placing the mixture in a sealed container for heat treatment at 80-100° C. for 2-4 hours, and then naturally cooling the mixture to room temperature.

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 as follows: uniformly mix elemental S and elemental I2 according to an atomic ratio, then place the mixture in a sealed container for heat treatment at 80-100°C for 2-4 hours, and naturally cool 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: The all-solid-state lithium-sulfur battery includes an electrolyte, a positive electrode and a negative electrode, wherein the positive electrode is prepared from the composite positive electrode material according to claim 5, the electrolyte is a sulfide electrolyte, and the negative electrode is a lithium-silicon alloy.

7. The all-solid-state lithium-sulfur battery according to claim 6, 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 and pressed to obtain a positive electrode sheet-electrolyte sheet double-layer material; then the lithium silicon alloy is placed on the other side of the electrolyte sheet and pressed to obtain a positive electrode sheet-electrolyte sheet-negative electrode sheet three-layer material; 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.

8. 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.

9. The use of the all-solid-state lithium-sulfur battery according to claim 8, characterized in that: The periodic remelting is performed by keeping the temperature at 100° C. for 3 hours after every 50 cycles.

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