Novel lithium sulfide composite material and preparation method and application thereof

Abstract

The embodiment of the invention relates to a novel lithium sulfide composite material as well as a preparation method and application thereof. The preparation method comprises the following steps: adding a lithium source, sublimed sulfur, asphalt and a conductive agent into a rotary furnace, adding zirconium balls in a protective gas atmosphere, and uniformly mixing and granulating to form powder; heating the rotary furnace in a protective gas atmosphere, and sintering the powder at a first set temperature to obtain a lithium sulfide powder material; and adjusting the temperature of the rotary furnace in a protective gas atmosphere, introducing a gas containing a carbon source at a second set temperature, and coating the lithium sulfide powder material through chemical vapor deposition to obtain the novel lithium sulfide composite material with the core-shell structure.

Description

Technical Field

[0001] The present invention relates to the technical field of new energy materials, and in particular to a novel lithium sulfide composite material and a preparation method and application thereof. Background Art

[0002] With continuous development, energy storage as an indispensable part of smart grid has brought huge market demand. Lithium-ion battery is the most mature and largest-scale battery in the current battery industry. As an important energy storage device, it is widely used in electric vehicles, mobile electronic devices and other fields. Among them, the performance of the positive electrode material directly affects the performance indicators of the battery, such as cycle performance, first coulomb efficiency and rate performance. As the current mainstream lithium-ion positive electrode material, ternary lithium has a maximum specific capacity of only 210mAh / g.

[0003] Lithium sulfide is a potential excellent cathode material with high specific capacity and relatively low battery voltage platform, but its application in lithium-ion batteries is restricted by a series of problems.

[0004] Pure lithium sulfide materials are difficult to synthesize stably on a large scale. Pure lithium sulfide easily reacts with water to generate toxic hydrogen sulfide gas. At the same time, as a positive electrode material for lithium-ion batteries, pure lithium sulfide also has disadvantages such as low first coulomb efficiency, poor cycle performance, and poor conductivity. In addition, lithium sulfide will expand and shrink in volume during the charging and discharging process, resulting in structural rupture of the battery positive electrode material, thereby reducing the cycle life and safety performance of the battery. Therefore, how to improve the cycle performance, first coulomb efficiency and safety performance of lithium sulfide materials has become a research hotspot. It is necessary to seek a new method for preparing lithium sulfide composite materials to improve the performance of lithium sulfide materials and solve many problems in their battery applications. Summary of the invention

[0005] The purpose of the present invention is to provide a novel lithium sulfide composite material and its preparation method and application. The process is simple and suitable for large-scale synthesis, and the material can be modified during the synthesis process, so that the synthesized finished material has good first coulomb efficiency, cycle performance, and conductivity as a positive electrode material for lithium ion batteries.

[0006] To this end, in a first aspect, an embodiment of the present invention provides a method for preparing a novel lithium sulfide composite material, comprising:

[0007] Add lithium source, sublimated sulfur, asphalt and conductive agent into a rotary kiln, add zirconium balls under a protective gas atmosphere, mix and granulate evenly to form powder;

[0008] heating the rotary kiln under a protective gas atmosphere, and sintering the powder at a first set temperature to obtain a lithium sulfide powder material;

[0009] The temperature of the rotary kiln is adjusted under a protective gas atmosphere, a gas containing a carbon source is introduced at a second set temperature, and the lithium sulfide powder material is coated by chemical vapor deposition to obtain a new lithium sulfide composite material with a core-shell structure.

[0010] Preferably, the protective gas includes: one or more of nitrogen, argon, and helium;

[0011] The lithium source includes: any one or more of lithium hydride, lithium nitride, and metallic lithium;

[0012] The conductive agent includes: any one or more of multi-walled carbon nanotube powder, single-walled carbon nanotube powder, graphene powder, and superconductive carbon black;

[0013] The mass ratio of the lithium source, sublimated sulfur, asphalt and conductive agent is 1:1-10:0.01-0.5:0.01-0.5;

[0014] In the mixing and granulating process, the rotation speed of the rotary kiln is 0.3 to 10 rpm, and the mixing time is 20 to 300 minutes.

[0015] Further preferably, the mass ratio of the lithium source, sublimated sulfur, asphalt and conductive agent is 1:2-5:0.05-0.2:0.01-0.2.

[0016] Further preferably, during the mixing and granulation process, the rotation speed of the rotary kiln is 3 to 8 rpm, and the mixing time is 60 to 180 minutes.

[0017] Preferably, heating the rotary kiln under a protective gas atmosphere and sintering the powder at a first set temperature specifically includes:

[0018] Under a protective gas atmosphere, the temperature is raised at a rate of 1°C / min to 5°C / min, the first set temperature is 350°C to 800°C, and the sintering time is 1 to 20 hours; during the sintering process, the lithium source reacts with the sublimated sulfur to generate lithium sulfide.

[0019] Preferably, the first set temperature is 400°C to 650°C.

[0020] Preferably, the step of adjusting the temperature of the rotary kiln under a protective gas atmosphere, introducing a gas containing a carbon source at a second set temperature, and coating the lithium sulfide powder material by chemical vapor deposition specifically comprises:

[0021] Adjusting the temperature from a first set temperature to a second set temperature under a protective gas atmosphere, wherein the second set temperature is 500° C. to 800° C., and the chemical vapor deposition time is 1 to 12 hours;

[0022] The carbon source-containing gas is specifically a mixed gas of a carbon source gas and a protective gas; the carbon source gas includes: one or more of methane, acetylene, ethylene, propylene, benzene, and carbon monoxide; the mixed volume ratio of the protective gas to the carbon source gas is 5:1 to 1:5.

[0023] Preferably, the mixed volume ratio of the protective gas and the carbon source gas is 1:4 to 2:1; and the chemical vapor deposition time is 3 to 9 hours.

[0024] In a second aspect, an embodiment of the present invention provides a positive electrode material, including a novel lithium sulfide composite material prepared by the preparation method described in the first aspect above.

[0025] In a third aspect, an embodiment of the present invention provides a lithium-ion battery, comprising the positive electrode material described in the second aspect.

[0026] The preparation method of the novel lithium sulfide composite material provided by the embodiment of the present invention adopts a rotary kiln to prepare a lithium sulfide composite material with a core-shell structure, and the preparation process and equipment are relatively simple and suitable for large-scale production. Granulation is carried out by asphalt during the reaction preparation process, and a conductive agent is added in the granulation process to obtain a lithium sulfide composite carbon core, and a carbon-coated shell is formed by chemical vapor deposition coating, so that the prepared finished composite material has good first coulomb efficiency, cycle performance, and conductive performance of a lithium sulfide composite material with a core-shell structure when used as a positive electrode material for a lithium ion battery. The conductive agent and the lithium sulfide particles generated by the reaction are constructed into a core under the action of asphalt through the granulation process, which can provide a certain buffer space for the expansion of lithium sulfide during the charge and discharge cycle, and the conductive agent can increase the conductivity of the material, further optimize the material rate new energy, and finally the carbon coating layer can solve the problem that the lithium sulfide material is easy to react with moisture in the air to generate hydrogen sulfide toxic gas, so that it can be safely used in the battery preparation process. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 A flow chart of a method for preparing a novel lithium sulfide composite material provided by an embodiment of the present invention;

[0028] Figure 2 A schematic structural diagram of a novel lithium sulfide composite material provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0029] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments.

[0030] The present invention provides a novel method for preparing a lithium sulfide composite material. The main steps are as follows: Figure 1 As shown, including:

[0031] Step 110, adding lithium source, sublimated sulfur, asphalt, and conductive agent into a rotary kiln, adding zirconium balls under a protective gas atmosphere, uniformly mixing and granulating to form a powder.

[0032] In this step and the following steps, the protective gas includes one or more of nitrogen, argon and helium.

[0033] The lithium source includes: any one or more of lithium hydride, lithium nitride, and metallic lithium; the conductive agent includes: any one or more of multi-walled carbon nanotube powder, single-walled carbon nanotube powder, graphene powder, and superconductive carbon black; the mass ratio of the lithium source, sublimated sulfur, asphalt, and the conductive agent is 1:1-10:0.01-0.5:0.01-0.5. More preferably, the mass ratio of the lithium source, sublimated sulfur, asphalt, and the conductive agent is 1:2-5:0.05-0.2:0.01-0.2.

[0034] During the mixing and granulation process, the rotation speed of the rotary kiln is 0.3 to 10 rpm, and the mixing time is 20 to 300 minutes. Preferably, the rotation speed of the rotary kiln is 3 to 8 rpm, and the mixing time is 60 to 180 minutes.

[0035] Step 120, heating the rotary kiln under a protective gas atmosphere, sintering the powder at a first set temperature to obtain a lithium sulfide powder material.

[0036] Specifically, under a protective gas atmosphere, the temperature is increased at a rate of 1°C / min to 5°C / min, the first set temperature is 350°C to 800°C, and the sintering time is 1 to 20 hours; during the sintering process, the lithium source reacts with the sublimated sulfur to generate lithium sulfide. The first set temperature is more preferably 400°C to 650°C.

[0037] The lithium source is lithium hydride: 2LiH+2S→Li 2 S+H 2 S↑;

[0038] Lithium source is lithium nitride: 2Li 3 N+3S→3Li 2 S+3N 2 ↑;

[0039] The lithium source is metallic lithium: 2Li+S→Li 2 S.

[0040] Step 130, adjusting the temperature of the rotary kiln under a protective gas atmosphere, introducing a gas containing a carbon source at a second set temperature, and coating the lithium sulfide powder material by chemical vapor deposition to obtain a new lithium sulfide composite material with a core-shell structure.

[0041] Specifically, the temperature is adjusted from the first set temperature to the second set temperature under the protective gas atmosphere, the second set temperature is 500° C. to 800° C., and the chemical vapor deposition time is 1 to 12 hours, more preferably 3 to 9 hours;

[0042] The gas containing the carbon source is specifically a mixed gas of a carbon source gas and a protective gas; the carbon source gas includes: one or more of methane, acetylene, ethylene, propylene, benzene, and carbon monoxide; the mixed volume ratio of the protective gas and the carbon source gas is 5:1 to 1:5, and more preferably 1:4 to 2:1.

[0043] The novel lithium sulfide composite material prepared by the above preparation method of the present invention has a structure as follows Figure 2 As shown, the inner core includes an asphalt matrix and a conductive agent and lithium sulfide particles dispersed in the asphalt matrix, and the outer layer is a carbon coating layer. The invention adopts a rotary kiln to prepare a lithium sulfide composite material with a core-shell structure. The preparation process and equipment are relatively simple and suitable for large-scale production. In the reaction preparation process, asphalt is used for granulation, and a conductive agent is added in the granulation process to obtain a lithium sulfide composite carbon inner core, and a carbon-coated outer shell is formed by chemical vapor deposition coating, so that the prepared finished composite material has good first coulomb efficiency, cycle performance, and conductive performance of a lithium sulfide composite material with a core-shell structure when used as a positive electrode material for a lithium ion battery. Through the granulation process, the conductive agent and the lithium sulfide particles generated by the reaction are constructed into an inner core under the action of asphalt, which can provide a certain buffer space for the expansion of lithium sulfide during the charge and discharge cycle. At the same time, the conductive agent can increase the conductivity of the material, further optimize the material rate new energy, and finally the carbon coating layer can solve the problem that the lithium sulfide material is easy to react with moisture in the air to generate hydrogen sulfide toxic gas, so that it can be used safely in the battery preparation process.

[0044] The process of the present invention can be completed in a rotary kiln, which reduces process material loss and equipment loss, and also has a high energy-saving and cost-reducing effect.

[0045] The novel lithium sulfide composite material prepared by the present invention can be used as a positive electrode material in lithium ion batteries.

[0046] In order to more clearly illustrate the purpose and advantages of the present invention, the present invention is further described below in conjunction with the embodiments. In addition, the embodiments described in the present invention are only partial embodiments. Based on the embodiments described in the present invention, all other embodiments obtained by those skilled in the art without creative work are within the protection scope of the present invention. In addition, it should be understood that these embodiments are only used for more detailed description and should not be understood as limiting the present invention in any form, that is, they are not intended to limit the protection scope of the present invention.

[0047] Example 1

[0048] This embodiment provides a process for preparing a novel lithium sulfide composite material with a core-shell structure, and the specific steps are as follows.

[0049] Step 1, adding lithium hydride, sublimed sulfur, asphalt and multi-walled carbon nanotube powder in a mass ratio of 1:5:0.05:0.05 into a nitrogen-protected rotary kiln for mixing for 2 hours, with the rotary kiln rotating at 3 rpm.

[0050] Step 2: In a nitrogen protective gas atmosphere, the rotary kiln is heated at a rate of 3°C / min to 550°C and kept at this temperature for 5 hours.

[0051] Step 3: In a nitrogen protective gas atmosphere, the rotary kiln is heated at 3°C / min to 700°C, and then a mixed gas of acetylene and nitrogen is introduced for carbon coating, wherein the volume ratio of nitrogen to acetylene gas is 2:1. The carbon coating time is 4 hours, and a lithium sulfide composite material with a core-shell structure is obtained.

[0052] Example 2

[0053] This embodiment provides a process for preparing a lithium sulfide composite material with a core-shell structure, and the specific steps are as follows.

[0054] Step 1, adding lithium hydride, sublimed sulfur, asphalt and multi-walled carbon nanotube powder in a mass ratio of 1:2:0.05:0.05 into a nitrogen-protected rotary kiln for mixing for 2 hours, and the rotating speed of the rotary kiln is 3 revolutions per minute.

[0055] Step 2: In a nitrogen protective gas atmosphere, the rotary kiln is heated at a rate of 3°C / min to 550°C and kept at this temperature for 5 hours.

[0056] Step 3: In a nitrogen protective gas atmosphere, the rotary kiln is heated at 3°C / min to 700°C, and then a mixed gas of acetylene and nitrogen is introduced for carbon coating, wherein the volume ratio of nitrogen to acetylene gas is 2:1. The carbon coating time is 4 hours, and a lithium sulfide composite material with a core-shell structure is obtained.

[0057] Example 3

[0058] This embodiment provides a process for preparing a lithium sulfide composite material with a core-shell structure, and the specific steps are as follows.

[0059] Step 1, adding lithium hydride, sublimed sulfur, asphalt and multi-walled carbon nanotube powder in a mass ratio of 1:5:0.05:0.05 into a nitrogen-protected rotary kiln for mixing for 2 hours, with the rotary kiln rotating at 3 rpm.

[0060] Step 2: In a nitrogen protective gas atmosphere, the rotary kiln is heated at a rate of 3°C / min to 350°C and kept at this temperature for 5 hours.

[0061] Step 3: In a nitrogen protective gas atmosphere, the rotary kiln is heated at 3°C / min to 700°C, and then a mixed gas of acetylene and nitrogen is introduced for carbon coating, wherein the volume ratio of nitrogen to acetylene gas is 2:1. The carbon coating time is 4 hours, and a lithium sulfide composite material with a core-shell structure is obtained.

[0062] Example 4

[0063] This embodiment provides a process for preparing a lithium sulfide composite material with a core-shell structure, and the specific steps are as follows.

[0064] Step 1, adding lithium hydride, sublimed sulfur, asphalt and multi-walled carbon nanotube powder in a mass ratio of 1:5:0.05:0.05 into a nitrogen-protected rotary kiln for mixing for 2 hours, with the rotary kiln rotating at 3 rpm.

[0065] Step 2: In a nitrogen protective gas atmosphere, the rotary kiln is heated at a rate of 3°C / min to 650°C and kept at this temperature for 5 hours.

[0066] Step 3: In a nitrogen protective gas atmosphere, the rotary kiln is heated at 3°C / min to 700°C, and then a mixed gas of acetylene and nitrogen is introduced for carbon coating, wherein the volume ratio of nitrogen to acetylene gas is 2:1. The carbon coating time is 4 hours, and a lithium sulfide composite material with a core-shell structure is obtained.

[0067] Example 5

[0068] This embodiment provides a process for preparing a lithium sulfide composite material with a core-shell structure, and the specific steps are as follows.

[0069] Step 1, adding lithium hydride, sublimed sulfur, asphalt and multi-walled carbon nanotube powder in a mass ratio of 1:5:0.05:0.05 into a nitrogen-protected rotary kiln for mixing for 2 hours, with the rotary kiln rotating at 3 rpm.

[0070] Step 2: In a nitrogen protective gas atmosphere, the rotary kiln is heated at a rate of 3°C / min to 550°C and kept at this temperature for 5 hours.

[0071] Step 3: In a nitrogen protective gas atmosphere, the rotary kiln is heated at 3°C / min, the temperature is adjusted to 500°C, and then a mixed gas of acetylene and nitrogen is introduced for carbon coating, wherein the volume ratio of nitrogen to acetylene gas is 2:1. The carbon coating time is 4 hours, and a lithium sulfide composite material with a core-shell structure is obtained.

[0072] Example 6

[0073] This embodiment provides a process for preparing a lithium sulfide composite material with a core-shell structure, and the specific steps are as follows.

[0074] Step 1, adding lithium hydride, sublimed sulfur, asphalt and multi-walled carbon nanotube powder in a mass ratio of 1:5:0.05:0.05 into a nitrogen-protected rotary kiln for mixing for 2 hours, with the rotary kiln rotating at 3 rpm.

[0075] Step 2: In a nitrogen protective gas atmosphere, the rotary kiln is heated at a rate of 3°C / min to 550°C and kept at this temperature for 5 hours.

[0076] Step 3: In a nitrogen protective gas atmosphere, the rotary kiln is heated at 3°C / min to 700°C, and then a mixed gas of methane and nitrogen is introduced for carbon coating, wherein the volume ratio of nitrogen to methane is 2:1. The carbon coating time is 4 hours, and a lithium sulfide composite material with a core-shell structure is obtained.

[0077] Example 7

[0078] This embodiment provides a process for preparing a lithium sulfide composite material with a core-shell structure, and the specific steps are as follows.

[0079] Step 1, adding lithium hydride, sublimed sulfur, asphalt and multi-walled carbon nanotube powder in a mass ratio of 1:5:0.05:0.05 into a nitrogen-protected rotary kiln for mixing for 2 hours, with the rotary kiln rotating at 3 rpm.

[0080] Step 2: In a nitrogen protective gas atmosphere, the rotary kiln is heated at a rate of 3°C / min to 550°C and kept at this temperature for 5 hours.

[0081] Step 3: In a nitrogen protective gas atmosphere, the rotary kiln is heated at 3°C / min to 700°C, and then a mixed gas of acetylene and nitrogen is introduced for carbon coating, wherein the volume ratio of nitrogen to acetylene gas is 1:3. The carbon coating time is 4 hours, and a lithium sulfide composite material with a core-shell structure is obtained.

[0082] Example 8

[0083] This embodiment provides a process for preparing a lithium sulfide composite material with a core-shell structure, and the specific steps are as follows.

[0084] Step 1, adding lithium hydride, sublimed sulfur, asphalt and multi-walled carbon nanotube powder in a mass ratio of 1:5:0.05:0.05 into a nitrogen-protected rotary kiln for mixing for 2 hours, with the rotary kiln rotating at 3 rpm.

[0085] Step 2: In a nitrogen protective gas atmosphere, the rotary kiln is heated at a rate of 3°C / min to 550°C and kept at this temperature for 5 hours.

[0086] Step 3: In a nitrogen protective gas atmosphere, the rotary kiln is heated at 3°C / min to 700°C, and then a mixed gas of acetylene and nitrogen is introduced for carbon coating, wherein the volume ratio of nitrogen to acetylene gas is 2:1. The carbon coating time is 6 hours, and a lithium sulfide composite material with a core-shell structure is obtained.

[0087] Comparative Example 1

[0088] This comparative example provides a process for preparing a lithium sulfide material, and the specific steps are as follows.

[0089] Step 1: adding lithium hydride and sublimed sulfur in a mass ratio of 1:5 into a nitrogen-protected rotary kiln for mixing for 2 hours at a rotary kiln speed of 3 revolutions per minute.

[0090] Step 2: In a nitrogen protective gas atmosphere, the rotary kiln is heated at 3°C / min to 550°C and kept at this temperature for 5 hours to obtain a lithium sulfide material.

[0091] Comparative Example 2

[0092] This comparative example provides a process for preparing a lithium sulfide composite material with a core-shell structure, and the specific steps are as follows.

[0093] Step 1, adding lithium hydride, sublimed sulfur and asphalt in a mass ratio of 1:5:0.05 into a nitrogen-protected rotary kiln for mixing for 2 hours, with the rotary kiln rotating at 3 rpm.

[0094] Step 2: In a nitrogen protective gas atmosphere, the rotary kiln is heated at a rate of 3°C / min to 550°C and kept at this temperature for 5 hours.

[0095] Step 3: The rotary kiln was heated at 3°C / min to 700°C under a nitrogen protective gas atmosphere, and then a mixed gas of acetylene and nitrogen was introduced for carbon coating, wherein the volume ratio of nitrogen to acetylene gas was 2:1. The carbon coating time was 4 hours, and a lithium sulfide composite material with a core-shell structure for comparison was obtained.

[0096] In order to test the electrochemical performance of the lithium sulfide composite material with a core-shell structure prepared by the present invention when applied to a positive electrode material of a lithium ion battery, the composite material is used as an active material and then subjected to slurry preparation, pole piece preparation and battery assembly to conduct relevant electrical performance tests.

[0097] The preparation of the slurry specifically includes the following steps:

[0098] (1) Add 0.15 g of polyvinylidene fluoride (PVDF) to 15 g of N-methylpyrrolidone (NMP) at a dispersion plate speed of 2000 r / min for 30 min until the gel solution becomes clear;

[0099] (2) adding 3.75 g of single-walled carbon nanotube slurry (solid content 0.4%) to the glue solution, with the dispersion disk rotating at 2000 r / min for 40 min to form a slurry;

[0100] (3) 12 g of the lithium sulfide composite material or lithium sulfide material prepared in the above embodiment or comparative example is added to the slurry, the dispersion disk speed is 2000 r / min, the dispersion is carried out for 40 min, an appropriate amount of water is added to adjust the viscosity to 1000-3000 mPa.s, and then the material is discharged to form a positive electrode slurry.

[0101] The preparation and assembly method of the half-cell can be carried out according to the existing known method, and a specific process may include the following steps.

[0102] Preparation of positive electrode sheet: The above slurry is used through coating, drying, cutting and other steps to obtain the positive electrode sheet.

[0103] Assemble the full battery: The prepared positive electrode sheet, commercial separator (polyethylene (PE) separator in this example), and commercial lithium sheet as the positive electrode are assembled in an alternating manner, and injected with commercial electrolyte (1 mol / L LiPF in this example). 6 @ethylene carbonate (EC) + diethyl carbonate (DEC) volume ratio 1:1), and after sealing, a button battery for testing was obtained.

[0104] Test method: The charge cut-off voltage is 3V, the discharge cut-off voltage is 1V, and the charge and discharge performance of the half-battery is tested at a current rate of 0.1C. The cycle is repeated for 300 cycles. The cycle capacity retention rates of 10, 50, 100, 200, and 300 cycles, as well as the cycle capacity retention rates of 5 weeks at rates of 0.5C, 1C, and 3C are tested.

[0105] The data are shown in Table 1.

[0106]

[0107] Table 1

[0108] By comparison, it can be seen that compared with the hydrogen sulfide material in comparative example 1 which is not coated, does not add a conductive agent, and does not use an asphalt base, the embodiment of the present invention has significant improvements in the first-week charge-discharge specific capacity, cycle capacity retention performance, and high-rate performance, indicating that the core-shell structure can greatly improve the first-week efficiency and cycle capacity retention performance of the material. Compared with the material in comparative example 2 which does not add a conductive agent, the addition of a conductive agent can effectively improve the rate performance, especially at a high rate.

[0109] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a novel lithium sulfide composite material, It is characterized in that The preparation method comprises: Add lithium source, sublimated sulfur, asphalt and conductive agent into a rotary kiln, add zirconium balls under a protective gas atmosphere, mix and granulate evenly to form powder; heating the rotary kiln under a protective gas atmosphere, and sintering the powder at a first set temperature to obtain a lithium sulfide powder material; The temperature of the rotary kiln is adjusted under a protective gas atmosphere, a gas containing a carbon source is introduced at a second set temperature, and the lithium sulfide powder material is coated by chemical vapor deposition to obtain a new lithium sulfide composite material with a core-shell structure.

2. The preparation method according to claim 1, It is characterized in that The protective gas includes: one or more of nitrogen, argon and helium; The lithium source includes: any one or more of lithium hydride, lithium nitride, and metallic lithium; The conductive agent includes: any one or more of multi-walled carbon nanotube powder, single-walled carbon nanotube powder, graphene powder, and superconductive carbon black; The mass ratio of the lithium source, sublimated sulfur, asphalt and conductive agent is 1:1-10:0.01-0.5:0.01-0.5; In the mixing and granulating process, the rotation speed of the rotary kiln is 0.3 to 10 rpm, and the mixing time is 20 to 300 minutes.

3. The preparation method according to claim 2, It is characterized in that The mass ratio of the lithium source, sublimated sulfur, asphalt and conductive agent is 1:2-5:0.05-0.2:0.01-0.

2.

4. The preparation method according to claim 2, It is characterized in that In the mixing and granulating process, the rotating speed of the rotary kiln is 3 to 8 revolutions per minute, and the mixing time is 60 to 180 minutes.

5. The preparation method according to claim 1, It is characterized in that The step of heating the rotary kiln under a protective gas atmosphere and sintering the powder at a first set temperature specifically includes: Under a protective gas atmosphere, the temperature is raised at a rate of 1°C / min to 5°C / min, the first set temperature is 350°C to 800°C, and the sintering time is 1 to 20 hours; during the sintering process, the lithium source reacts with the sublimated sulfur to generate lithium sulfide.

6. The preparation method according to claim 5, It is characterized in that The first set temperature is 400°C to 650°C.

7. The preparation method according to claim 1, It is characterized in that The step of adjusting the temperature of the rotary kiln under a protective gas atmosphere, introducing a gas containing a carbon source at a second set temperature, and coating the lithium sulfide powder material by chemical vapor deposition specifically includes: Adjusting the temperature from a first set temperature to a second set temperature under a protective gas atmosphere, wherein the second set temperature is 500° C. to 800° C., and the chemical vapor deposition time is 1 to 12 hours; The carbon source-containing gas is specifically a mixed gas of a carbon source gas and a protective gas; the carbon source gas includes: one or more of methane, acetylene, ethylene, propylene, benzene, and carbon monoxide; the mixed volume ratio of the protective gas to the carbon source gas is 5:1 to 1:

5.

8. The preparation method according to claim 7, It is characterized in that The mixed volume ratio of the protective gas and the carbon source gas is 1:4 to 2:1; and the chemical vapor deposition time is 3 to 9 hours.

9. A positive electrode material, It is characterized in that The positive electrode material comprises a novel lithium sulfide composite material prepared by any preparation method described in claims 1-8.

10. A lithium ion battery, It is characterized in that The lithium-ion battery comprises the positive electrode material according to claim 9 above.

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