Carbon-coated nanosulfide lithium composite material, preparation and application thereof

Abstract

The present application relates to the field of electrode materials, in particular to a preparation method of carbon-coated nano lithium sulfide composite material, which comprises sulfuration roasting of a composite of organic lithium containing structure (R-O-Li) of formula 1 and organic carbon source in a hydrogen sulfide-containing atmosphere to obtain the carbon-coated nano lithium sulfide composite material; R is C1-C 10 alkyl or C2-C 10 acyl; in the sulfuration roasting stage, the volume content of H2S in the hydrogen sulfide-containing atmosphere is not less than 1%, the flow is not less than 90 sccm; and the temperature is 500-750 DEG C. The present application also includes the material prepared by the method and its application in batteries. The material prepared by the method has excellent electrochemical performance.

Description

Technical Field

[0001] This invention belongs to the field of lithium secondary battery material technology, specifically relating to the field of positive electrode materials for lithium secondary batteries. Background Technology

[0002] Rapid economic development demands next-generation rechargeable batteries that are lower in cost, lighter in weight and volume, and more portable. Due to maximum (loadable) weight limitations, lightweight batteries are indispensable in the field of large-scale power batteries, particularly important for applications such as electric trucks and trains, underwater vehicles, and high-efficiency aerial equipment (unmanned aerial vehicles and spacecraft). Lithium sulfide cathode materials offer advantages such as high capacity and safe performance in storage batteries. Furthermore, elemental sulfur (S) is gaining increasing attention in the field of storage battery materials due to its high natural abundance, low cost, and environmental friendliness. S-based cathodes operate through a conversion reaction, with each redox center (S atom) providing two electron transfers. Conversion-type sulfur-based cathodes are mainly subdivided into elemental sulfur (S) and lithium sulfide (Li2S), providing 1675 and 1166 mAh g⁻¹, respectively. -1 Given its theoretical gravimetric capacity, lithium sulfide (S)-based cathodes are considered one of the most promising candidates for next-generation ultralight lithium and lithium-ion battery cathodes. Lithium sulfide can replace sulfur cathode materials to use lithium-free anodes (such as graphite), avoiding the direct use of Li metal anodes. However, the widespread application of lithium sulfide cathode materials faces several challenges: poor electronic and Li-ion conductivity, slow conversion reaction kinetics, cathode dissolution and the shuttle effect of related polysulfides, and high price all hinder the commercial application of lithium sulfide cathodes.

[0003] To address this challenge, lithium sulfide composite materials can be effectively used. Preparation methods primarily involve embedding nano- or micron-sized lithium sulfide particles into composite materials of various morphologies. Currently, the main preparation methods for lithium sulfide composite materials include ball milling of commercial Li₂S or LiH with elemental S, thermal carbon reduction, and hydrogen sulfide sulfidation, as detailed below.

[0004] Ball milling of commercial Li₂S or LiH with elemental sulfur: Lithium sulfide is hard and has insulating properties. Ball milling is generally used to reduce the size of lithium sulfide and combine it with carbon materials to increase conductivity. The ball milling method typically uses commercial-grade lithium sulfide (Li₂S) or elemental sulfur (S) and LiH as precursors, mechanically mixing them with carbon materials (2LiH + S → Li₂S + H₂↑) to form nano / micron Li₂S / C composites. The lithium sulfide composites prepared by this method have inhomogeneous morphology, large particle size, and the precursors Li₂S or LiH are both expensive.

[0005] Thermal carbon reduction method: The thermal carbon reduction method is considered a very economical approach. Generally, lithium sulfate is reduced to lithium sulfide by carbon at approximately 800°C (Li₂SO₄ + 2C → Li₂S + 2CO₂↑). For example, it has been reported that a spray drying process converts a lithium sulfate solution and a carbon-containing mixture into droplets or aerosols, followed by a heating process to obtain a carbon-coated lithium sulfide composite. This method is low-cost and can produce Li₂S / C composites on a large scale. However, the resulting Li₂S particles are relatively large and prone to aggregation. This is because the reduction reaction consumes the carbon material surrounding the Li₂SO₄, affecting the coating effect and the contact between the lithium sulfide and the conductive carbon material. Furthermore, the required reduction temperature is too high (which can lead to the aggregation of the formed Li₂S particles).

[0006] Hydrogen sulfide sulfidation is a common method for preparing metal sulfides. Hydrogen sulfide is an industrial waste gas and is highly toxic, therefore it must be handled with caution. Hydrogen sulfide has strong reducing properties and can reduce most lithium-containing compounds. For example, lithium sulfide can be prepared at room temperature by passing hydrogen sulfide gas into a solution of inexpensive lithium ethoxide; however, the resulting lithium sulfide exhibits severe agglomeration and large particle size. Summary of the Invention

[0007] In order to overcome the shortcomings and deficiencies of the prior art, the purpose of this invention is to provide a method for preparing carbon-coated nano-lithium sulfide composite materials, which aims to form in-situ carbon-coated lithium sulfide composite materials by further sulfidation of organic lithium in a carbon confinement, and to improve the electrochemical performance of the prepared materials.

[0008] The second objective of this invention is to provide a carbon-coated nano-lithium sulfide composite material prepared by the aforementioned method and its application as a positive electrode active material for lithium secondary batteries.

[0009] A third objective of this invention is to provide a lithium secondary battery comprising the aforementioned carbon-coated nano-lithium sulfide composite material and its positive electrode and other components.

[0010] Existing carbon-coated lithium sulfide preparation methods require high temperatures and are prone to agglomeration, hindering the effective utilization of material performance. Furthermore, the sulfide exhibits a significant expansion effect, leading to more pronounced electrochemical degradation at high loading levels. To address these issues, this invention provides the following improvements:

[0011] A method for preparing carbon-coated nano-lithium sulfide composite material involves calcining an organic lithium and an organic carbon source containing a structure of formula 1 under a hydrogen sulfide atmosphere to obtain the carbon-coated nano-lithium sulfide composite material.

[0012] RO-Li

[0013] Formula 1

[0014] The R mentioned is C1 to C10 Alkyl or C2-C 10 Acyl group;

[0015] During the sulfurization roasting stage, the volume content of H2S in the atmosphere containing hydrogen sulfide is not less than 1 vol.%, the flow rate is not less than 90 sccm, and the temperature is between 500 and 750℃.

[0016] This invention proposes a method for preparing carbon-coated Li₂S based on a one-step sulfidation calcination of organic lithium within a carbon confinement environment. It innovatively combines the joint control of the organic lithium composition, hydrogen sulfide atmosphere content and flow rate, and sulfidation calcination temperature to achieve synergistic effects and solve the problem of insufficient sulfidation faced by traditional one-step sulfidation methods. This enables in-situ carbon-confined sulfidation of lithium sulfide, improving phase composition and grain size. Furthermore, it achieves in-situ carbon coating, reducing particle agglomeration and improving the conductive network between particles. The method described in this invention effectively improves the electronic and ionic conductivity of the prepared material, enhances structural stability, and improves rate capability and cycling stability, particularly contributing to improved cycling stability under low-temperature conditions.

[0017] In this invention, the composite simultaneous sulfurization and calcination of Formula 1 and the organic carbon source, as well as the joint control of the components, atmosphere flow rate, and temperature of Formula 1, are key to synergistically achieving carbon-confined sulfurization, reducing agglomeration, improving structural stability, and enhancing the electrochemical performance of the material.

[0018] In this invention, the organic lithium and the carbon source described in Formula 1 are combined to improve their distribution state based on the chemical interaction between the organic lithium structure and the organic carbon source groups. This facilitates the subsequent in-situ carbon confined sulfidation and improves the material's performance.

[0019] In this invention, the alkyl group is a straight-chain or branched alkyl group. The acyl group is, for example, R1CO-, and R1 can be a C1 to C9 alkyl group.

[0020] Preferably, R is a C1-C3 alkyl group or a C2-C4 alkyl acyl group, more preferably methyl, ethyl, or isopropyl. Studies have shown that when R is an alkyl group, it can further synergize with the carbon-confined one-step sulfidation process and parameters, helping to further improve the electrochemical performance of the prepared material, especially its low-temperature stability.

[0021] In this invention, the organic carbon source is at least one of starch, glucose, PVP, alginate, chitosan, and cellulose.

[0022] This invention has found that joint control of the structure of Formula 1 and the composition of organic carbon helps to further improve the chemical composite characteristics of the two, helps to further synergistically improve the grain size and structural stability of the prepared material, and helps to further improve the electrochemical performance of the prepared material.

[0023] In this invention, when R in Formula 1 is a C2-C4 alkyl group, the organic carbon source is at least one of starch and glucose; or, when R is a C1-C3 alkyl group, the organic carbon source is PVP.

[0024] Preferably, the organic lithium and organic carbon source are mixed with a solvent in the liquid phase, and then the solvent is evaporated to obtain the composite.

[0025] In this invention, the mixing based on the liquid phase facilitates the chemical assembly, fusion, and distribution of Formula 1 and the organic carbon source, which helps to further improve the grain size and structural stability of the prepared material, and further improves the electrochemical performance of the prepared material, especially its rate capability and low-temperature cycling stability.

[0026] In this invention, the weight ratio of lithium element to organic carbon source in organic lithium is 1:1 to 15, and considering cost, it can be further 1:3 to 10.

[0027] In this invention, the composite also contains an additive, which is at least one of carbon black, TiO2, and SiO2, and more preferably TiO2 and / or SiO2.

[0028] The present invention also found that further addition of additives to the system containing Formula 1 and an organic carbon source, and further addition of a subsequent one-step sulfidation and calcination process, can further synergistically improve the stability of the structure and help to further improve the rate capability and cycle stability of the prepared material, especially the cycle stability under low temperature conditions.

[0029] Preferably, the molar ratio between the additive and the lithium element in the organolithium is (0.01-0.2):1, more preferably 0.04-0.1:1.

[0030] In this invention, when adding an auxiliary agent, the organic lithium, organic carbon source and auxiliary agent can be mixed in the liquid phase, and then the solvent can be removed by evaporation to obtain the composite.

[0031] In this invention, the organic lithium and organic carbon source complex is innovatively subjected to a one-step sulfidation process. By combining the gas flow rate and temperature control during the process, the process not only ensures a good one-step sulfidation effect, but also helps to control the grain size and transport network, thereby improving the electrochemical performance of the prepared material.

[0032] In this invention, the solvent used in the liquid-phase mixing process is a solvent capable of dissolving organolithium and organic carbon sources, such as water, alcohol, acetone, etc. There are no particular requirements for the amount of solvent used; considering processing efficiency and cost, the liquid-to-solid ratio can be 1–20 ml / g.

[0033] The temperature of the evaporation and solvent removal stage can be below 110℃. To improve efficiency, the evaporation and solvent removal process can be carried out under vacuum.

[0034] The hydrogen sulfide-containing atmosphere can be a mixture of H2S and a diluent gas, such as at least one of helium or argon.

[0035] In this invention, the volume content of H2S in the hydrogen sulfide-containing atmosphere is 2-15 vol.%, more preferably 5-10 vol.%.

[0036] During the sintering process, the flow rate of the hydrogen sulfide atmosphere is 100–300 sccm.

[0037] In this invention, the preferred temperature for the roasting process is 550℃~720℃.

[0038] In this invention, the roasting stage may include two heat preservation platforms, wherein the temperature of the first heat preservation platform is 550-650°C and the temperature of the second heat preservation platform can be 680-720°C.

[0039] Preferably, the sulfidation roasting time is 1–6 hours, more preferably 2–3 hours. When a two-stage roasting mechanism is used, the temperature of each stage can be 1–2 hours.

[0040] The present invention also provides a carbon-coated nano-lithium sulfide composite material prepared by the preparation method described above.

[0041] In this invention, based on the combination of the preparation methods, the prepared materials can be endowed with special physicochemical characteristics, and the materials prepared by the methods can exhibit excellent electrochemical performance.

[0042] The present invention also provides an application of the carbon-coated lithium sulfide nanocomposite material prepared by the above preparation method, which is used as a positive electrode active material for the preparation of lithium secondary batteries.

[0043] In this invention, the desired lithium secondary battery can be prepared by using the carbon-coated nano-lithium sulfide composite material described in this invention based on known methods.

[0044] The present invention also provides a lithium secondary battery cathode, comprising a current collector and a cathode material composite thereon, wherein the cathode active material in the cathode material comprises the carbon-coated nano-lithium sulfide composite material obtained by the preparation method.

[0045] In the aforementioned cathode material, the weight content of the cathode active material can be adjusted as needed, for example, it can be 50-90 wt.%, further can be 60-85 wt.%, and even further can be 75-80 wt.%. Thanks to the aforementioned preparation process, the present invention can still exhibit excellent performance under high loading.

[0046] Preferably, the positive electrode material further comprises a binder, which can be a conventional component in the industry, such as CMC, PVDF, etc. The content of the binder can be adjusted as needed; for example, the content of the binder is not higher than 15 wt.%, for example, it can be 5-10 wt.%.

[0047] Preferably, the positive electrode material further comprises a conductive agent, which can be a conventional component in the industry, such as acetylene black or carbon black. In this invention, the content of the conductive agent can be adjusted as needed; for example, its content is not higher than 15 wt.%, and can be 5–10 wt.%.

[0048] The present invention also provides a lithium secondary battery, comprising a positive electrode, a separator and a negative electrode cell sequentially composited, wherein the positive electrode is the positive electrode comprising the carbon-coated nano-lithium sulfide composite material of the present invention.

[0049] In this invention, the lithium secondary battery and its positive electrode, apart from containing the carbon-coated nano-lithium sulfide composite material described in this invention, can have other components and structures that are conventional in the industry.

[0050] Beneficial effects

[0051] This invention proposes a method for preparing carbon-coated Li₂S based on a one-step sulfidation calcination of organic lithium within a carbon confinement environment. It innovatively combines the joint control of organic lithium composition, hydrogen sulfide atmosphere content and flow rate, and sulfidation calcination temperature to achieve synergistic effects. This addresses the difficulty of achieving complete sulfidation in traditional one-step sulfidation methods, enabling in-situ carbon-confined sulfidation of lithium sulfide, improving phase composition and grain size. Furthermore, it achieves in-situ carbon coating, reducing particle agglomeration and improving the conductive network between particles. The method described in this invention effectively improves the electronic and ionic conductivity of the prepared material, enhances structural stability, and improves rate capability and cycling stability, particularly contributing to improved cycling stability under low-temperature conditions.

[0052] The present invention also shows that the use of organolithium compounds with R as alkyl, and / or the use of the aforementioned additives, especially TiO2 and SiO2, can further improve the synergy of the process and further improve the performance of the prepared materials, particularly contributing to the low-temperature stability of the materials.

[0053] In this invention, the innovative one-step carbon-confined sulfidation process, combined with the use of the aforementioned additives, helps to further improve the electrochemical performance of the prepared materials. Attached Figure Description

[0054] Figure 1 Here is a scanning electron microscope image of the Li2S@C material prepared in Example 1;

[0055] Figure 2 XRD patterns of the materials prepared in Examples 1 and 4;

[0056] Figure 3 Here is a scanning electron microscope image of the Li2S@C material prepared in Example 2;

[0057] Figure 4 Scanning electron microscope image of CB-Li2S@C prepared in Example 4A;

[0058] Figure 5 Scanning electron microscope image of TiO2-Li2S@C prepared in Example 4B;

[0059] Figure 6 XRD patterns of the materials prepared in Examples 5A and 5B; Detailed Implementation

[0060] The present invention will be further described in detail below with reference to specific embodiments, but the implementation of the present invention is not limited thereto.

[0061] I. Supplementary Suggestions for Implementation Examples

[0062] To address the key innovations of the preparation process in this application, typical cases are presented to demonstrate that successful preparation can be achieved under all critical conditions, and that these cases consistently deliver superior results compared to the comparative examples:

[0063] The setup method is as follows:

[0064] Example 1: Preparation of Li2S@C.

[0065] 1.02 g of organolithium (in this case, formula 1-A(CH3COOLi), with 0.1 g of Li and a molar mass of 0.0155 mol) and 0.9 g of glucose were dissolved in 3 ml of water. 0.1 mL of acetic acid was added, and the mixture was stirred and dissolved on a hot plate at 80°C. The solution was then evaporated to dryness to obtain a solid. The solid was transferred to a calcining boat and placed in a tube furnace under a 5 vol.% H2S / Ar atmosphere (flow rate 200 sccm). The furnace was heated to 600°C at a rate of 3°C / min and held for 3 hours. This invention relates to carbon-coated lithium sulfide Li2S@C. SEM images are available. Figure 1 XRD (see) Figure 2 .

[0066] Example 2

[0067] 0.069 g of lithium sheet was placed in 5 ml of methanol solution to obtain an organolithium solution containing MeOLi. Then, 0.23 g of PVP was added and stirred to obtain a mixed solution. The solution was then placed on a hot plate at 80-110 °C and stirred until the solvent evaporated to dryness, yielding a white, fluffy solid. The solid was transferred to a calcining boat and placed in a tube furnace under a 5 vol.% H2S / Ar atmosphere (flow rate 200 sccm). It was heated to 600 °C at a rate of 3 °C / min and held for 2 hours, then heated to 700 °C at a rate of 3 °C / min and held for 1 hour to obtain Li2S@C (also known as Li2S@C-PVP). Figure 3 The scanning electron microscope (SEM) morphology details of Li2S@C are shown.

[0068] Example 3

[0069] Compared to Example 2, the only difference is the change in the organic lithium; the experimental groups are as follows:

[0070] Group A: The organic lithium is EtOLi, that is, the methanol in Example 2 is replaced by an equal volume of ethanol, and other operations and parameters are the same as in Example 2;

[0071] Group B: The only difference from Group A is that the organic lithium is Formula 1-A. That is, Formula 1-A with the same molar amount of lithium as in Example 2 is dispersed in ethanol to obtain an organic lithium dispersion, and then the experiment is carried out according to the operation of Group A.

[0072] Example 4

[0073] Compared to Example 2, the only difference is that an auxiliary agent was added to the mixed solution. The experimental groups were as follows:

[0074] Group 4A: Contains 0.006g of CB additive (Li / CB molar ratio of 20:1);

[0075] 0.069 g of lithium sheet was placed in 5 ml of methanol solution. After the reaction was complete, 0.23 g of PVP was added and stirred to obtain a mixed solution. 0.006 g of CB additive was added, and the solution was then stirred on a hot plate at 80-110 °C until the solvent evaporated to obtain a white, fluffy solid. The solid was transferred to a flaking boat and placed in a tube furnace under a 5 vol.% H2S / Ar atmosphere (flow rate 200 sccm). It was heated to 600 °C (labeled T1) at a rate of 3 °C / min and held for 2 hours. Then, it was heated to 700 °C (labeled T2) at a rate of 3 °C / min and held for 1 hour. XRD is shown in [reference needed]. Figure 2 . Figure 4 The scanning electron microscope (SEM) morphology details of CB-Li2S@C are shown.

[0076] Group 4B: Contains 0.04g of TiO2 additive (Li / TiO2 molar ratio of 20:1);

[0077] 0.069 g of lithium sheet was placed in 5 ml of methanol solution. After the reaction was complete, 0.23 g of PVP was added and stirred to obtain a mixed solution. 0.04 g of TiO2 was added as an auxiliary agent. The solution was then stirred on a hot plate at 80-110 °C until the solvent evaporated to obtain a white, fluffy solid. The solid was transferred to a sintering boat and placed in a tube furnace under a 5 vol.% H2S / Ar atmosphere (flow rate 200 sccm). The furnace was heated to 600 °C at a rate of 3 °C / min and held for 2 hours. Then, it was heated to 700 °C at a rate of 3 °C / min and held for 1 hour. XRD is shown in [reference needed]. Figure 2 . Figure 5 The scanning electron microscope (SEM) morphology details of TiO2-Li2S@C are shown.

[0078] Group 4C: Contains 0.03g of SiO2 as an additive (Li / SiO2 molar ratio of 20:1);

[0079] 0.069g of lithium sheet was placed in 5ml of methanol solution. After the reaction was complete, 0.23g of PVP was added and stirred to obtain a mixed solution. 0.03g of SiO2 additive was added, and the solution was then stirred on a hot plate at 80-110℃ until the solvent evaporated to obtain a white, fluffy solid. The solid was transferred to a sintering boat and placed in a tube furnace under a 5 vol.% H2S / Ar atmosphere (flow rate 200 sccm). The furnace was heated to 600℃ at a rate of 3℃ / min and held for 2 hours, then heated to 700℃ at a rate of 3℃ / min and held for 1 hour. XRD is shown in [reference needed]. Figure 2 .

[0080] 4D Group

[0081] Compared with Example 2, the only difference is that the positive electrode active material is a physical mixture of Li2S@C and TiO2 prepared in Example 2, wherein the molar ratio of Li to TiO2 in Li2S@C is the same as 4B.

[0082] Example 5:

[0083] Compared to Example 4A, the only difference is that the flow rate and temperature during the calcination stage were changed. The experimental groups were as follows:

[0084] 5A: In an H2S / Ar atmosphere, H2S is 8 vol%, the flow rate is 100 sccm, and other operations and parameters are the same as in Example 4A;

[0085] 5B: Change the temperature of T1 to 500℃, and other operations and parameters are the same as in Example 1.

[0086] Both 5A and 5B yielded materials similar to 4A, as shown in the XRD diagram. Figure 6 .

[0087] Comparative Example 1

[0088] Compared with Example 1, the only difference is that lithium carbonate with an equal molar amount of Li is used to replace the organic lithium, while other operations and parameters are the same as in Example 1.

[0089] The preparation method of the carbon-coated lithium sulfide composite cathode includes the following steps:

[0090] Battery assembly: The carbon-coated lithium sulfide composites obtained from each case were mixed and ground with the conductive agent Super P and the binder polyvinylpyrrolidone (PVP) in a ratio of 8:1:1. N-methylpyrrolidone (NMP) was added to prepare the positive electrode slurry. After drying, the slurry was coated and die-cut. A positive electrode was obtained. Using lithium foil as the negative electrode and a Celgard 2500 separator, a CR2025 coin cell was assembled. It was activated by three cycles at 0.01C, and then the charge-discharge performance was tested at room temperature (25°C) and a 0.2C rate. Furthermore, the low-temperature performance of the battery was further tested at 0°C and a 0.2C rate.

[0091] The test results for each case are shown in Table 1:

[0092]

[0093] In summary, the research of this invention shows that when using organic lithium, especially organic lithium in Formula 1 where R is an alkyl group, better results can be obtained. Moreover, further addition of TiO2 / SiO2 as an auxiliary agent can further improve the performance. For example, it can achieve good performance under high loading and high current, especially with excellent low-temperature performance.

Claims

1. A method for preparing a carbon-coated nano-lithium sulfide composite material, characterized in that, A carbon-coated nano-lithium sulfide composite material was prepared by sulfidation and calcination of a composite material containing an organic lithium and an organic carbon source with a structure of formula 1 under a hydrogen sulfide atmosphere. RO-Li Formula 1 During the sulfurization roasting stage, the volume content of H2S in the atmosphere containing hydrogen sulfide is not less than 1%, the flow rate is not less than 90 sccm, and the temperature is 500~750℃. In Formula 1, when R is a C2-C4 alkyl acyl group, the organic carbon source is at least one of starch and glucose. Alternatively, when R is a C1~C3 alkyl group, the organic carbon source is PVP; The weight ratio of lithium to organic carbon source in organolithium is 1:1 to 15.

2. The preparation method of the carbon-coated nano-lithium sulfide composite material as described in claim 1, characterized in that, Organic lithium and organic carbon sources are mixed with a solvent in the liquid phase, and then the solvent is evaporated to obtain the composite.

3. The method for preparing carbon-coated nano-lithium sulfide composite material as described in claim 1, characterized in that, The weight ratio of lithium to organic carbon source in organolithium is 1:3~10.

4. The method for preparing carbon-coated nano-lithium sulfide composite material according to any one of claims 1 to 3, characterized in that, The composite also contains an auxiliary agent, which is at least one of TiO2 and SiO2. The molar ratio between the additive and the lithium element in the organolithium is (0.01~0.2):

1.

5. The method for preparing carbon-coated nano-lithium sulfide composite material as described in claim 4, characterized in that, The molar ratio between the additive and the lithium element in the organolithium is 0.04~0.1:

1.

6. The method for preparing carbon-coated nano-lithium sulfide composite material as described in claim 1, characterized in that, The volume content of H2S in the hydrogen sulfide-containing atmosphere is 2~10v.

7. The method for preparing carbon-coated nano-lithium sulfide composite material as described in claim 1, characterized in that, The sulfidation roasting time is 1~6 hours.

8. The method for preparing carbon-coated nano-lithium sulfide composite material as described in claim 7, characterized in that, The sulfurization roasting time is 2-3 hours.

9. A carbon-coated nano-lithium sulfide composite material prepared by the preparation method according to any one of claims 1 to 8.

10. The application of a carbon-coated nano-lithium sulfide composite material prepared by the preparation method according to any one of claims 1 to 8, characterized in that, It is used as a positive electrode active material in the preparation of lithium secondary batteries.

11. A lithium secondary battery positive electrode, comprising a current collector and a positive electrode material composited thereon, characterized in that, The positive electrode active material in the positive electrode material includes the carbon-coated nano-lithium sulfide composite material prepared by the preparation method according to any one of claims 1 to 8.

12. The lithium secondary battery positive electrode as described in claim 11, characterized in that, In the aforementioned cathode material, the weight content of the cathode active material is 50~90 wt.%.

13. The lithium secondary battery positive electrode as described in claim 11, characterized in that, The cathode material also contains a binder, the content of which is not higher than 15 wt.%. The positive electrode material also contains a conductive agent, the content of which is not higher than 15 wt.%.

14. A lithium secondary battery, comprising a positive electrode, a separator, and a negative electrode cell sequentially laminated together, characterized in that, The positive electrode described herein is the positive electrode according to any one of claims 11 to 13.

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