Lithium sulfide nano-composite positive electrode material with high reaction kinetics and preparation method and application of lithium sulfide nano-composite positive electrode material

Abstract

The invention belongs to the technical field of all-solid-state lithium-sulfur battery materials, and relates to a lithium sulfide nano-composite positive electrode material with high reaction kinetics as well as a preparation method and application of the lithium sulfide nano-composite positive electrode material. The invention aims to overcome the defects of the lithium sulfide positive electrode material in the aspects of ion and electron conductivity, reduce the activation potential barrier of the lithium sulfide positive electrode material, improve the redox kinetics of the battery and further improve the rate capability and the cycle capacity of the battery. The lithium sulfide nano-composite positive electrode material is prepared by adopting an in-situ synthesis method, the obtained composite material has abundant metal atomic crystals embedded in a lithium sulfide matrix, and the surface of the composite material is uniformly coated with a layer of amorphous carbon. And the finally obtained lithium sulfide nano composite positive electrode material shows relatively high reversible capacity and excellent rate capability. The method has the characteristics of uniform coating, simple process and the like, is suitable for large-scale production, and has a wide application prospect in the field of all-solid-state lithium-sulfur batteries.

Description

Technical Field

[0001] The present invention relates to the technical field of all-solid-state lithium-sulfur battery materials, and particularly relates to a preparation method and application of a lithium sulfide nano-composite cathode material with high reaction kinetics. Background Art

[0002] In recent years, with continuous development, lithium-ion batteries have become very mature. However, to meet the increasing demands of the electric vehicle industry in terms of energy density and safety, it is of great significance to develop secondary batteries with higher specific energy.

[0003] All-solid-state lithium-sulfur batteries are regarded as one of the most promising directions for the next-generation energy storage system due to their theoretical energy density of up to 2600 Wh / kg -1 and intrinsic safety advantages. Compared with traditional liquid lithium-sulfur batteries, the all-solid-state system can fundamentally solve two core problems through the application of solid electrolytes: First, the dissolution of polysulfides during discharge leads to the "shuttle effect", which significantly reduces the Coulomb efficiency and causes rapid capacity decay; Second, the replacement of flammable organic electrolytes with solid electrolytes also effectively improves the thermal stability of the battery system, completely eliminating the safety hazards of the liquid system. However, the use of sulfur cathode materials in all-solid-state lithium-sulfur batteries still causes structural collapse problems due to volume expansion of up to 80% during charge and discharge, and elemental sulfur materials also have problems such as low electrical conductivity, seriously affecting the rate performance of the battery.

[0004] Using lithium sulfide (Li2S) as the cathode material provides a new idea for the development of all-solid-state lithium-sulfur batteries. Compared with elemental sulfur, Li2S has a high theoretical specific capacity of 1166 mAh / g -1 and a melting point of 938 °C, which is more conducive to the diversity of chemical modification means at high temperatures. Lithium sulfide as the cathode material can also reduce the problem of volume expansion of the cathode during charge and discharge, thereby improving mechanical stability. And lithium sulfide itself as the cathode material can provide lithium ions, which enables it to be compatible with lithium-free anodes such as graphite and silicon-carbon, fundamentally avoiding the risk of dendrite growth of metal lithium anodes. However, lithium sulfide materials still have many problems. For example, lithium sulfide has low electronic conductivity, and its conductivity at room temperature is only 10 -13 S cm -1 , which hinders the electron conduction between lithium sulfide and the current collector, thus reducing the rate of electrochemical reactions. Secondly, the lithium ion conductivity of lithium sulfide is also very poor and it is difficult to be activated during the first charge, requiring overcoming a very high activation barrier.

[0005] In order to solve the above-mentioned problems of lithium sulfide positive electrodes, researchers have proposed a variety of strategies, including nanostructure design, core-shell encapsulation and redox medium catalysis, and have made certain progress in these directions. Patent CN118359172A obtains high-purity nanoscale lithium sulfide materials by sequentially performing material purification, nanoscale wet grinding, homogeneous reaction, and ball milling processes. Patent CN115714169A prepares lithium sulfate spheres by spray drying, and then fully mixes them with a carbon source precursor and obtains carbon-coated lithium sulfide hollow sphere materials by in-situ oxidation and reduction. However, a single modification cannot completely solve the problems of lithium sulfide positive electrodes. To this end, the present invention proposes an in-situ synthesized high reaction kinetics lithium sulfide nanocomposite positive electrode material and a preparation method thereof. Summary of the invention

[0006] In order to solve the problems existing in the prior art of insufficient ion and electron conductivity of lithium sulfide positive electrode materials and high activation energy barrier, the present invention provides a lithium sulfide nanocomposite positive electrode material with high reaction kinetics, a preparation method and application thereof in an all-solid-state lithium-sulfur battery.

[0007] The present invention firstly reacts a lithium source, a metal sulfide and carbon disulfide in situ, and then performs an in-situ electrochemical reduction reaction, thereby obtaining a lithium sulfide nanocomposite positive electrode material having a shell structure and containing a metal atom catalyst.

[0008] In order to achieve the above technical objectives, the present invention provides the following specific technical solutions:

[0009] The present invention relates to a method for preparing a lithium sulfide nanocomposite positive electrode material with high reaction kinetics, comprising the following steps:

[0010] (1) Mixing: fully mixing the lithium source and the metal sulfide to obtain a mixed material;

[0011] (2) heating treatment: the mixed material obtained in step (1) is mixed with carbon disulfide (CS2) and then heated, and after the reaction is completed, a drying treatment is performed to obtain a carbon-coated lithium sulfide nanocomposite positive electrode material doped with metal sulfide;

[0012] (3) In-situ electrochemical reduction reaction: using the composite positive electrode material obtained in step (2) as an active material to prepare an electrode composite material, assembling an all-solid-state lithium-sulfur battery, and performing electrochemical discharge to obtain a lithium sulfide nanocomposite positive electrode material doped with elemental metal atoms through an in-situ electrochemical reduction reaction.

[0013] By adopting the above technical solution, the present invention can in-situ generate metal doping during the reaction by mixing a lithium source with a metal sulfide, achieving a uniform doping effect, which is more uniform and efficient compared to direct metal mixed doping, and further improving the material performance; meanwhile, lithium sulfide can be generated to further increase the content of the active material; subsequently, by mixing and reacting with carbon disulfide, uniform carbon coating can be achieved in-situ while generating lithium sulfide, further improving the conductivity of the material, and being able to alleviate the volume change problem and maintain the structural stability of the cathode material, further enhancing the battery performance.

[0014] The following are further preferred technical solutions of the present invention:

[0015] Preferably, in step (1), the lithium source is at least one of lithium powder (Li), lithium sheet (Li), and lithium hydride (LiH);

[0016] And / or, the metal sulfide is at least one of manganese disulfide (MnS2), iron disulfide (FeS2), cobalt disulfide (CoS2), nickel disulfide (NiS2), molybdenum disulfide (MoS2), titanium disulfide (TiS2), vanadium disulfide (VS2), zinc disulfide (ZnS2), chromium disulfide (CrS2), copper sulfide (CuS), manganese sulfide (MnS), iron sulfide (FeS), cobalt sulfide (CoS), nickel sulfide (NiS), molybdenum sulfide (MoS), titanium sulfide (TiS), vanadium sulfide (VS), zinc sulfide (ZnS), chromium sulfide (CrS);

[0017] And / or, the molar ratio of the lithium source to the metal sulfide is 2 - 8:1.

[0018] Preferably, in step (1), sufficient mixing is carried out by ball milling, and the ball milling mixing conditions are: the ball milling rotation speed is 100 - 700 rpm, and the ball milling time is 4 - 20 h; more preferably, the ball milling rotation speed is 300 - 600 rpm, and the ball milling time is 8 - 16 h. By adopting ball milling for mixing, the metal sulfide and the lithium source can be effectively and uniformly mixed. If the metal sulfide and the lithium source are not evenly mixed, it will lead to insufficient reaction or almost no reaction, and then the lithium source will directly react with carbon disulfide instead of reacting with the metal sulfide. As a result, the doped substances inside the obtained material are unevenly dispersed and the electrochemical performance is poor.

[0019] Preferably, in step (2), the solid content after mixing is 20 - 60%;

[0020] And / or, the heat treatment conditions are: the heating temperature is 300 - 700 °C; the heat preservation time is 1 - 5 h; the heating rate is 2 - 5 °C / min; more preferably, the heating temperature is 400 - 700 °C;

[0021] And / or, the drying treatment conditions are as follows: the heating temperature is 30 to 100 °C; the drying time is 0.5 to 3 h.

[0022] Preferably, in step (2), the size of the prepared composite cathode material is ≤100 nm, and the thickness of the carbon coating layer is 1 to 10 nm.

[0023] Preferably, in step (3), the electrode composite material includes a composite cathode material, a sulfide solid electrolyte, and conductive carbon.

[0024] More preferably, the sulfide solid electrolyte is at least one of Li6PS5Cl, Li7P3S 11 、Li 10 GeP2S 12 ;

[0025] And / or, the conductive carbon is at least one of multi-walled carbon nanotubes (WMCNTs), acetylene black (AB), and activated carbon (AC);

[0026] And / or, the mass ratio of the composite cathode material, the sulfide solid electrolyte, and the conductive carbon is (50 to 90):(10 to 40):(0 to 10), more preferably 5:4:1;

[0027] And / or, the composite cathode material, the sulfide solid electrolyte, and the conductive carbon are ball-milled and mixed to obtain the electrode composite material, and the ball-milling parameters are: the ball-milling speed is 100 to 500 rpm, and the ball-milling time is 2 to 16 h.

[0028] Preferably, in step (3), for the in-situ electrochemical reduction reaction, the steps are as follows: the assembled battery is subjected to a discharging treatment on a battery rack, and the cut-off discharging voltage is 0.5 V; more preferably, the discharging treatment is carried out at a current density of 20 mA / g to 100 mA / g, and more preferably 50 mA / g.

[0029] Preferably, in step (3), the elemental metal atoms include at least one of manganese, iron, cobalt, nickel, molybdenum, titanium, vanadium, zinc, and chromium.

[0030] Preferably, the size of the carbon-coated metal atom-doped lithium sulfide nanoparticles is ≤100 nm; the thickness of the carbon coating layer is 1 to 10 nm, and the metal atom doping content accounts for 15 to 24 wt.% of the composite cathode material.

[0031] Further preferably, the preparation method includes the following steps:

[0032] (1) Ball-milling and mixing: In a glove box filled with argon and with the humidity and oxygen concentration both less than 0.01 ppm, a certain amount of lithium source and metal sulfide are weighed, and the two are sealed in a ball-milling jar and ball-milled on a ball mill at a certain speed for several hours;

[0033] (2) Heat treatment: In a glove box, the material obtained after ball milling in step (1) is mixed with carbon disulfide, magnetically stirred for 10 min, and then sealed in a quartz tube for heat treatment. After the reaction is completed, drying treatment is carried out to volatilize the excess carbon disulfide, and a lithium sulfide nanocomposite cathode material with carbon-coated and internally doped metal sulfide is obtained.

[0034] (3) In-situ electrochemical reduction reaction:

[0035] In a glove box, the composite cathode material obtained in step (2) is ball milled with a sulfide solid electrolyte and conductive carbon spheres for several hours to obtain an electrode composite material. Subsequently, a carbon-coated aluminum foil, the electrode composite material, the sulfide solid electrolyte, and a lithium sheet are successively cold-pressed and assembled into a all-solid-state lithium-sulfur battery, and then electrochemical discharge is carried out on a battery rack to obtain a lithium sulfide nanocomposite cathode material with internally doped elemental metal atoms through an in-situ electrochemical reduction reaction.

[0036] The present invention also provides a lithium sulfide nanocomposite cathode material with high reaction kinetics prepared by the above preparation method.

[0037] The present invention also provides an application of a lithium sulfide nanocomposite cathode material with high reaction kinetics prepared by the above preparation method in the field of all-solid-state lithium-sulfur batteries.

[0038] Preferably, the application includes a sulfide all-solid-state lithium-sulfur battery, and the all-solid-state lithium-sulfur battery includes the above-mentioned lithium sulfide nanocomposite cathode material with high reaction kinetics.

[0039] The present invention aims to solve the deficiencies of lithium sulfide cathode materials in terms of ionic and electronic conductivity, reduce the activation barrier of lithium sulfide cathode materials, improve the redox kinetics of batteries, and thus improve the rate performance and cycle capacity of batteries. The present invention adopts an in-situ synthesis method to prepare a lithium sulfide nanocomposite cathode material, and the obtained composite material has abundant metal atom crystals embedded in the lithium sulfide matrix and a uniform amorphous carbon coating on the surface. The finally obtained lithium sulfide nanocomposite cathode material exhibits a high reversible capacity and excellent rate performance. The present invention has the characteristics of uniform coating and simple process, is suitable for large-scale production, and has broad application prospects in the field of all-solid-state lithium-sulfur batteries.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] 1. The preparation method of a lithium sulfide nano-composite cathode material with high reaction kinetics provided by the present invention is all generated through in-situ reactions. The present invention is not only simple to operate, but also the obtained composite material has the characteristics of complete doping and uniform coating. The lithium sulfide composite cathode material generated by the reaction has a nano-scale size. At the same time, due to in-situ growth, the carbon coating in the present invention has a more stable interface. Meanwhile, the coated carbon can inhibit the volume change generated by lithium sulfide during charge and discharge, and the carbon coating layer is still intact after cycling without falling off, further improving the stability.

[0042] 2. Existing technologies all perform single modification on lithium sulfide cathode materials, including nanostructure design, core-shell encapsulation, and redox mediator catalysis. The present invention combines the comprehensive advantages of the above three strategies to in-situ synthesize a lithium sulfide nano-composite cathode material with high reaction kinetics. Moreover, the present invention does not simply combine the three strategies, but through precise design of raw materials, thereby realizing the in-situ synthesis method and successfully obtaining a composite material with complete and uniform doping and uniform coating.

[0043] 3. The modified composite material has relatively excellent ionic and electronic conductivity, improves the redox reaction kinetics of the lithium sulfide cathode, and has good rate performance. Moreover, by introducing metal atoms, the activation energy barrier of the lithium sulfide cathode material is also reduced, and there is a small polarization voltage during charge and discharge. Brief Description of the Drawings

[0044] Figure 1 is the XRD pattern of the lithium sulfide nano-composite cathode material with high reaction kinetics in Example 1 of the present invention;

[0045] Figure 2 is the SEM image of the lithium sulfide nano-composite cathode material with high reaction kinetics in Example 1 of the present invention;

[0046] Figure 3 is the TEM image of the lithium sulfide nano-composite cathode material with high reaction kinetics in Example 1 of the present invention;

[0047] Figure 4 is the comparison chart of the first charge-discharge curves of two materials in Example 1 and Comparative Example 1 of the present invention at a current density of 100 mA g -1 ;

[0048] Figure 5 is the cycle capacity chart of two materials in Example 1 and Comparative Example 1 of the present invention at different current densities;

[0049] Figure 6 is the differential capacity curve chart of the first cycle of two materials in Example 1 and Comparative Example 1 of the present invention at a current density of 50 mA g -1 ; Detailed Description of the Invention

[0050] To better clarify and understand the purpose, technical solution and advantages of the present invention, the following will further clearly, completely and detailedly describe the technical solution and implementation manner of the present invention through specific embodiments and in combination with the drawings. It should be noted that the embodiments described in the present invention are implemented on the premise of the technical solution of the present invention, and the detailed implementation manners and specific operation processes are given, but they are only part of the embodiments of the present invention, rather than all the embodiments. The specific implementation manners described are only for explaining and interpreting the present invention, and do not limit the present invention. Based on the embodiments in the present invention, all other implementation manners obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0051] In the embodiments of the present invention, the experimental methods and conditions used are conventional methods and conventional conditions unless otherwise specified. The materials, reagents or instruments used in the embodiments can be obtained from commercial channels or prepared by conventional methods unless otherwise specified. The reaction conditions reflected in the content of the present invention can all achieve the described reactions and obtain the products with the expected effects. Due to space limitations, some embodiments are listed below to further illustrate the advantages of the technical solution of the present invention.

[0052] Example 1

[0053] (1) Ball milling and mixing

[0054] In a glove box filled with argon and with humidity and oxygen concentration both less than 0.01 ppm, 0.258 g of lithium hydride (LiH) and 1 g of cobalt disulfide (CoS2) were weighed, and the two were sealed in a ball milling jar with a ball-to-material ratio of 10:1. Ball milling was carried out on a ball mill at a speed of 500 rpm for 12 h;

[0055] (2) Heat treatment

[0056] In the glove box, the material obtained after ball milling in step (1) was mixed with carbon disulfide with a solid content of 40%, magnetically stirred for 10 min, then loaded into a quartz tube for encapsulation, and kept at 500 °C for 2 h with a heating rate of 2 °C / min. After the reaction, drying treatment was carried out at 30 °C for 2 h to volatilize the excess carbon disulfide, and a lithium sulfide nanocomposite cathode material (Li2S@Co x S y -C) doped with 23 wt.% metal sulfide inside was obtained, and the particle size of the composite cathode material was 30 - 70 nm;

[0057] (3) In-situ electrochemical reduction reaction

[0058] In the glove box, the composite cathode material (Li2S@Co x Sy -C) was ball milled with sulfide solid electrolyte (Li6PS5Cl) and multi-walled carbon nanotubes (WMCNTs) at a mass ratio of 5:4:1 for 12 h at a rotation speed of 500 rpm to obtain an electrode composite material. Subsequently, carbon-coated aluminum foil, the electrode composite material, sulfide solid electrolyte (Li6PS5Cl), and lithium foil were successively cold-pressed to assemble a all-solid-state lithium-sulfur battery, and then the battery was placed on a battery rack at a current density of 50 mAg -1 to perform electrochemical discharge. The cut-off discharge voltage was 0.5 V, and a lithium sulfide nanocomposite cathode material (Li2S@Co-C) internally doped with 15 wt.% elemental cobalt atoms was obtained through in-situ electrochemical reduction reaction. The particle size of this material was 30 - 70 nm, and the thickness of the carbon coating layer was 3 - 10 nm.

[0059] Example 2

[0060] (1) Ball milling and mixing

[0061] In a glove box filled with argon with both humidity and oxygen concentration less than 0.01 ppm, 0.175 g of lithium powder (Li) and 1 g of cobalt sulfide (CoS) were weighed and sealed in a ball milling jar. The ball-to-powder ratio was 10:1, and ball milling was carried out on a ball mill at a rotation speed of 100 rpm for 20 h;

[0062] (2) Heat treatment

[0063] In the glove box, the material obtained after ball milling in step (1) was mixed with carbon disulfide with a solid content of 20%, and magnetic stirring was carried out for 10 min. Then it was loaded into a quartz tube for encapsulation and kept at 400 °C for 5 h with a heating rate of 2 °C / min. After the reaction ended, drying treatment was carried out at 50 °C for 1 h to volatilize the excess carbon disulfide, and a lithium sulfide nanocomposite cathode material (Li2S@Co x S y -C) internally doped with 36 wt.% metal sulfide was obtained, and the particle size of the composite cathode material was 30 - 70 nm;

[0064] (3) In-situ electrochemical reduction reaction

[0065] In the glove box, the composite cathode material (Li2S@Co x S y -C) obtained in step (2) was ball milled with sulfide solid electrolyte (Li7P3S 11 ) and acetylene black (AB) at a mass ratio of 5:4:1 for 12 h at a rotation speed of 300 rpm to obtain an electrode composite material. Subsequently, carbon-coated aluminum foil, the electrode composite material, sulfide solid electrolyte (Li7P3S 11 ) and lithium foil were successively cold-pressed to assemble a all-solid-state lithium-sulfur battery, and then the battery was placed on a battery rack at a current density of 50 mAg -1Electrochemical discharge is carried out at a current density, and the cut-off discharge voltage is 0.5 V. A lithium sulfide nano-composite cathode material (Li2S@Co-C) with 24 wt.% elemental cobalt atoms doped inside is obtained through an in-situ electrochemical reduction reaction. The particle size of this material is 30 - 70 nm, and the thickness of the carbon coating layer is 1 - 8 nm.

[0066] Example 3

[0067] (1) Ball milling and mixing

[0068] In a glove box filled with argon, with both humidity and oxygen concentration less than 0.01 ppm, weigh 0.265 g of lithium hydride (LiH) and 1 g of iron disulfide (FeS2), seal the two in a ball milling jar with a ball-to-material ratio of 10:1, and ball mill at a speed of 700 rpm on a ball mill for 4 h;

[0069] (2) Heat treatment

[0070] In the glove box, mix the material obtained after ball milling in step (1) with carbon disulfide, with a solid content of 40%, stir magnetically for 10 min, then load it into a quartz tube for encapsulation, keep it at 300 °C for 5 h, and the heating rate is 2 °C / min. After the reaction ends, perform a drying treatment at 100 °C for 3 h to volatilize the excess carbon disulfide, and a lithium sulfide nano-composite cathode material (Li2S@Fe x S y -C) doped with 23 wt.% metal sulfide inside is obtained, and the particle size of the composite cathode material is 20 - 60 nm;

[0071] (3) In-situ electrochemical reduction reaction

[0072] In the glove box, mix the composite cathode material (Li2S@Fe x S y -C) obtained in step (2) with a sulfide solid electrolyte (Li6PS5Cl) and multi-walled carbon nanotubes (WMCNTs) in a mass ratio of 5:4:1 and ball mill at a speed of 100 rpm for 16 h to obtain an electrode composite material. Subsequently, successively cold press and assemble a full solid-state lithium-sulfur battery with a carbon-coated aluminum foil, the electrode composite material, the sulfide solid electrolyte (Li6PS5Cl), and a lithium sheet. Then, perform electrochemical discharge on the battery rack at a current density of 50 mAg -1 Electrochemical discharge is carried out at a current density, and the cut-off discharge voltage is 0.5 V. A lithium sulfide nano-composite cathode material (Li2S@Fe-C) with 16 wt.% elemental iron atoms doped inside is obtained through an in-situ electrochemical reduction reaction. The particle size of this material is 20 - 60 nm, and the thickness of the carbon coating layer is 1 - 8 nm.

[0073] Example 4

[0074] (1) Ball milling and mixing

[0075] In a glove box filled with argon, where the humidity and oxygen concentration are both less than 0.01 ppm, weigh 0.282 g of lithium hydride (LiH) and 1 g of nickel disulfide (NiS2). Seal the two in a ball milling jar with a ball-to-material ratio of 10:1, and ball mill at 500 rpm for 12 h on a ball mill.

[0076] (2) Heat treatment

[0077] In the glove box, mix the material obtained after ball milling in step (1) with carbon disulfide with a solid content of 30%. Stir magnetically for 10 min, then load it into a quartz tube for encapsulation, keep it at 400 °C for 3 h with a heating rate of 2 °C / min. After the reaction, conduct a drying treatment at 100 °C for 0.5 h to volatilize the excess carbon disulfide, and thus obtain a lithium sulfide nanocomposite cathode material (Li2S@Ni x S y -C) doped with 23 wt.% metal sulfide inside, and the particle size of the composite cathode material is 30 - 90 nm;

[0078] (3) In-situ electrochemical reduction reaction

[0079] In the glove box, mix the composite cathode material (Li2S@Ni x S y -C) obtained in step (2) with a sulfide solid electrolyte (Li 10 GeP2S 12 ) and activated carbon (AC) in a mass ratio of 5:4:1, and ball mill at 500 rpm for 2 h to obtain an electrode composite material. Subsequently, successively cold press and assemble a full solid-state lithium-sulfur battery with carbon-coated aluminum foil, the electrode composite material, the sulfide solid electrolyte (Li 10 GeP2S 12 ) and a lithium sheet. Then, conduct an electrochemical discharge at a current density of 50 mAg -1 until the cut-off discharge voltage is 0.5 V, and obtain a lithium sulfide nanocomposite cathode material (Li2S@Ni-C) doped with 15 wt.% elemental nickel atoms inside through an in-situ electrochemical reduction reaction. The particle size of this material is 30 - 90 nm, and the thickness of the carbon coating layer is 4 - 10 nm.

[0080] Example 5

[0081] (1) Ball milling and mixing

[0082] In a glove box filled with argon, where the humidity and oxygen concentration are both less than 0.01 ppm, weigh 0.183 g of lithium powder (Li), 0.5 g of manganese sulfide (MnS), and 0.5 g of titanium sulfide (TiS). Seal the three in a ball milling jar with a ball-to-material ratio of 10:1, and ball mill at 400 rpm for 10 h on a ball mill;

[0083] (2) Heat treatment

[0084] In the glove box, mix the material obtained after ball milling in step (1) with carbon disulfide, with a solid content of 20%. Stir magnetically for 10 min, then load it into a quartz tube for encapsulation, keep it at 650 °C for 2 h, and the heating rate is 5 °C / min. After the reaction is completed, conduct a drying treatment at 60 °C for 2 h to volatilize the excess carbon disulfide, and the lithium sulfide nanocomposite cathode material (Li2S@Mn x S y @Ti x S y -C) doped with 30 wt.% metal sulfide inside is obtained. The particle size of the composite cathode material is 30 - 80 nm;

[0085] (3) In-situ electrochemical reduction reaction

[0086] In the glove box, mix the composite cathode material (Li2S@Mn x S y @Ti x S y -C) obtained in step (2) with a sulfide solid electrolyte (Li6PS5Cl) and multi-walled carbon nanotubes (WMCNTs) in a mass ratio of 5:4:1 and ball mill at 300 rpm for 8 h to obtain an electrode composite material. Subsequently, successively cold press and assemble a full solid-state lithium-sulfur battery with carbon-coated aluminum foil, the electrode composite material, the sulfide solid electrolyte (Li6PS5Cl), and a lithium sheet. Then, conduct an electrochemical discharge on a battery rack at a current density of 50 mAg -1 The lithium sulfide nanocomposite cathode material (Li2S@Mn@Ti-C) doped with 18 wt.% elemental manganese atoms and elemental titanium atoms inside is obtained through an in-situ electrochemical reduction reaction. The particle size of this material is 30 - 80 nm, and the thickness of the carbon coating layer is 3 - 9 nm.

[0087] Example 6

[0088] (1) Ball milling and mixing

[0089] In a glove box filled with argon, where the humidity and oxygen concentration are both less than 0.01 ppm, weigh 0.166 g of lithium hydride (LiH), 0.5 g of copper sulfide (CuS), and 0.5 g of titanium disulfide (TiS2). Seal the three in a ball milling jar with a ball-to-material ratio of 10:1, and ball mill at 500 rpm on a ball mill for 10 h;

[0090] (2) Heat treatment

[0091] In the glove box, mix the material obtained after ball milling in step (1) with carbon disulfide, with a solid content of 60%. Stir magnetically for 10 min, then load it into a quartz tube for encapsulation, keep it at 700 °C for 1 h, and the heating rate is 5 °C / min. After the reaction, perform a drying treatment at 60 °C for 2 h to volatilize the excess carbon disulfide, and obtain a lithium sulfide nanocomposite cathode material (Li2S@Cu x S y @Ti x S y -C) doped with 30 wt.% metal sulfide inside, and the particle size of the composite cathode material is 20 - 90 nm;

[0092] (3) In-situ electrochemical reduction reaction

[0093] In the glove box, mix the composite cathode material (Li2S@Cu x S y @Ti x S y -C) obtained in step (2) with a sulfide solid electrolyte (Li 10 GeP2S 12 ) and acetylene black (AB) in a mass ratio of 5:4:1, and ball mill at 500 rpm for 6 h to obtain an electrode composite material. Subsequently, successively cold press and assemble a full solid-state lithium-sulfur battery with carbon-coated aluminum foil, the electrode composite material, the sulfide solid electrolyte (Li 10 GeP2S 12 ) and a lithium sheet. Then, perform electrochemical discharge on a battery rack at a current density of 50 mAg -1 until the cut-off discharge voltage is 0.5 V, and obtain a lithium sulfide nanocomposite cathode material (Li2S@Cu@Ti-C) doped with 15 wt.% elemental copper atoms and elemental titanium atoms inside through an in-situ electrochemical reduction reaction. The particle size of this material is 20 - 90 nm, and the thickness of the carbon coating layer is 3 - 10 nm.

[0094] Example 7

[0095] On the basis of Example 1, cobalt disulfide, a metal sulfide, is replaced with at least one of manganese disulfide (MnS2), molybdenum disulfide (MoS2), titanium disulfide (TiS2), vanadium disulfide (VS2), zinc disulfide (ZnS2), chromium disulfide (CrS2), iron sulfide (FeS), nickel sulfide (NiS), molybdenum sulfide (MoS), vanadium sulfide (VS), zinc sulfide (ZnS), and chromium sulfide (CrS). The feeding relationship between the metal sulfide and the lithium source is the same as that in Example 1, and other conditions are the same as those in Example 1, obtaining a corresponding lithium sulfide nano-composite cathode material doped with elemental metal atoms inside. The particle size of the material is 10 - 90 nm, and the thickness of the carbon coating layer is 1 - 10 nm.

[0096] Comparative Example 1

[0097] A lithium sulfide cathode material without any treatment is used. The particle size of this material is 2 - 4 μm.

[0098] Comparative Example 2

[0099] Ball milling treatment: In a glove box filled with argon with a humidity and oxygen concentration both less than 0.01 ppm, 0.77 g of lithium sulfide (Li2S), 0.15 g of cobalt powder (Co), and 0.08 g of acetylene black (AB) are weighed. The three are sealed in a ball milling tank with a ball-to-material ratio of 10:1 and ball milled on a ball mill at a speed of 500 rpm for 12 h; obtaining a lithium sulfide composite cathode material (Li2S@Co-C) with 15 wt.% elemental cobalt atoms mixed inside. The particle size of this material is 1 - 2 μm.

[0100] Comparative Example 3

[0101] Heating treatment: In a glove box filled with argon with a humidity and oxygen concentration both less than 0.01 ppm, 1 g of lithium hydride (LiH) is mixed with carbon disulfide with a solid content of 60%, and magnetically stirred for 10 min. Then it is loaded into a quartz tube for encapsulation and kept at 500 °C for 2 h with a heating rate of 2 °C / min. After the reaction, it is dried at 60 °C for 2 h to volatilize the excess carbon disulfide, obtaining a carbon-coated lithium sulfide composite cathode material (Li2S-C). The particle size of this material is 0.5 - 1 μm, and the thickness of the carbon coating layer is 1 - 10 nm.

[0102] Comparative Example 4

[0103] (1) Ball milling and mixing

[0104] In a glove box filled with argon with a humidity and oxygen concentration both less than 0.01 ppm, 0.166 g of lithium hydride (LiH) and 0.1 g of nickel disulfide (NiS2) are weighed. The two are sealed in a ball milling tank with a ball-to-material ratio of 10:1 and ball milled on a ball mill at a speed of 500 rpm for 10 h;

[0105] (2) Heat treatment

[0106] In a glove box, the material obtained after ball milling in step (1) is loaded into a quartz tube for encapsulation, kept at 500 °C for 4 h, and the heating rate is 5 °C / min. Thus, a lithium sulfide composite cathode material (Li2S@Ni) with 36 wt.% elemental nickel doped inside is obtained, and the particle size of the composite cathode material is 0.5 - 1 μm.

[0107] Comparative Example 5

[0108] (1) Grinding and mixing

[0109] In a glove box filled with argon with a humidity and oxygen concentration both less than 0.01 ppm, 0.166 g of lithium hydride (LiH) and 0.1 g of vanadium disulfide (VS2) are weighed, and the two are mixed in a mortar and ground for 1 h;

[0110] (2) Heat treatment

[0111] In the glove box, the material obtained after grinding in step (1) is mixed with carbon disulfide with a solid content of 60%, magnetically stirred for 10 min, then loaded into a quartz tube for encapsulation, kept at 400 °C for 2 h, and the heating rate is 2 °C / min. After the reaction, drying treatment is carried out at 60 °C for 2 h to volatilize the excess carbon disulfide, thus obtaining a lithium sulfide composite cathode material (Li2S@V x S y -C) with 23 wt.% metal sulfide doped inside, and the particle size of the composite cathode material is 0.5 - 1 μm;

[0112] (3) In-situ electrochemical reduction reaction

[0113] In the glove box, the composite cathode material (Li2S@V x S y -C) obtained in step (2) is ball milled with a sulfide solid electrolyte (Li 10 GeP2S 12 ) and activated carbon (AC) at a mass ratio of 5:4:1 at a rotation speed of 500 rpm for 2 h to obtain an electrode composite material. Subsequently, carbon-coated aluminum foil, the electrode composite material, the sulfide solid electrolyte (Li 10 GeP2S 12 ) and lithium foil are successively cold-pressed to assemble a all-solid-state lithium-sulfur battery, and then at a current density of 50 mAg -1Electrochemical discharge is carried out at a current density, and the cut-off discharge voltage is 0.5 V. Through in-situ electrochemical reduction reaction, a lithium sulfide nano-composite cathode material (Li2S@VS2@V-C) doped with elemental vanadium atoms (V) and vanadium disulfide (VS2) inside is obtained. The particle size of this material is 0.5 - 1 μm, and the thickness of the carbon coating layer is 2 - 10 nm.

[0114] Test example: Battery assembly and performance test

[0115] All-solid-state lithium-sulfur battery assembly: The electrode composite material is composed of a composite cathode material (Li2S@M x S y -C, M is a metal atom), a sulfide solid electrolyte, and conductive carbon, and is obtained by ball-milling and mixing in a mass ratio of 5:4:1. In a glove box with humidity and oxygen concentration lower than 0.01 ppm and filled with argon for protection, 120 mg of the sulfide solid electrolyte is placed in a PTFE mold with a diameter of 12 mm and compressed into a thin sheet under a pressure of 20 MPa. Then, 5 - 10 mg of the electrode composite material is evenly applied on the carbon-coated aluminum foil, placed on the upper surface of the mold, and a pressure of 10 MPa is applied. Finally, a lithium foil with a diameter of 10 mm is placed on the back of the mold, and the assembly is cold-pressed under a pressure of 10 MPa.

[0116] The assembled battery above is placed on a Neware battery tester. First, an in-situ electrochemical reduction reaction is carried out, and discharge treatment is carried out at a current density of 50 mAg -1 until the battery is discharged to 0.5 V, converting the metal sulfide into a metal element and a lithium sulfide cathode. Subsequently, the charge-discharge test voltage range of the battery is 1.5 - 3.8 V to activate the lithium sulfide cathode, and then the charge-discharge test is carried out in the voltage range of 1.5 - 3 V. The current density of the first cycle of the test is 50 mAg -1 for 3 activation cycles, and then a charge-discharge cycle is carried out at a current density of 200 mAg -1 . The current density for the rate test is 100 mAg -1 、200 mA g -1 、500 mAg -1 、1000 mAg -1 、100 mAg -1 .

[0117] The battery performance is prepared and measured according to the above method, and the results are shown in Table 1.

[0118] Table 1 Comparison of the electrochemical performance of lithium sulfide nano-composite cathode materials with different high reaction kinetics

[0119]

[0120] The material is tested under the test conditions of the test example and all meet: at 50 mAg-1 The initial discharge specific capacity is not less than 800 mAh g at the current density -1 , the initial Coulombic efficiency is not less than 90%, and at 200 mA g -1 the initial discharge specific capacity is not less than 700 mAh g at the current density -1 , the discharge specific capacity is not less than 500 mAh g after 100 cycles -1 , and the cycle capacity retention rate is not less than 80%. In contrast, for the batteries tested in the comparative examples, at 50 mA g -1 the initial discharge specific capacities are all lower than 800 mAh g at the current density -1 , the Coulombic efficiencies are all lower than 85%, and in addition, at 200 mA g -1 the discharge specific capacities are low at the current density, and the capacity retention rates are all lower than 70% after 100 cycles.

[0121] The lithium sulfide nanocomposite cathode material doped with elemental cobalt atoms in Example 1 can exhibit discharge specific capacities of 992.26 mAh g -1 , 857.65 mAh g -1 , 678.62 mAh g -1 at the current densities of 100 mA g -1 , 200 mA g -1 , 500 mA g -1 respectively. Even at a high current density of 1000 mA g -1 , the battery capacity is still as high as 511.62 mAh g -1 . The performances of Examples 2 - 6 have the same trend as that of Example 1. In Comparative Example 1, the battery capacities at different current densities are all lower than those of the examples, and the Coulombic efficiency is low. In Comparative Examples 2 - 4, both the capacity performance and the capacity retention rate are lower than those of the examples.

[0122] According to Figure 6 the differential capacity curve, it can be seen that the material in Comparative Example 1 has a higher polarization voltage, a low peak intensity, and poor reaction kinetics. While the differential capacity curve of Example 1 has a sharper peak, indicating that there is a fast redox reaction during the cycle and it has high reaction kinetics. Therefore, the lithium sulfide nanocomposite cathode material with carbon coating and metal atom doping has a perfect coating structure, and the internal metal atoms are doped evenly, which significantly improves the overall conductivity of the material, enhances the reaction kinetics of the battery composite cathode material, and has excellent rate performance.

[0123] The above - described embodiments are only the preferred solutions of the present invention, and do not impose any form of limitation on the present invention. Without exceeding the technical solutions recorded in the claims, there are other variations and modifications, and these changes and improvements all fall within the scope of the present invention claimed.

Claims

1. A preparation method of a lithium sulfide nano-composite cathode material with high reaction kinetics, characterized in that, It includes the following steps: (1) Mixing: fully mix a lithium source and a metal sulfide to obtain a mixed material; (2) Heat treatment: mix the mixed material with carbon disulfide and then heat it. After the reaction ends, perform a drying treatment to obtain a lithium sulfide nanocomposite cathode material with metal sulfide doped inside; (3) In-situ electrochemical reduction reaction: assemble a all-solid-state lithium-sulfur battery with the composite cathode material as the active substance, and then perform an electrochemical discharge to obtain a lithium sulfide nanocomposite cathode material with elemental metal atoms doped inside through an in-situ electrochemical reduction reaction.

2. The preparation method of a lithium sulfide nano-composite cathode material with high reaction kinetics according to claim 1, characterized in that In step (1), the lithium source is at least one of lithium and lithium hydride; and / or, the metal sulfide is at least one of manganese disulfide, iron disulfide, cobalt disulfide, nickel disulfide, molybdenum disulfide, titanium disulfide, vanadium disulfide, zinc disulfide, chromium disulfide, copper sulfide, manganese sulfide, iron sulfide, cobalt sulfide, nickel sulfide, molybdenum sulfide, titanium sulfide, vanadium sulfide, zinc sulfide, chromium sulfide; and / or, the molar ratio of the lithium source to the metal sulfide is 2-8:

1.

3. The preparation method of a lithium sulfide nano-composite cathode material with high reaction kinetics according to claim 1, characterized in that, In step (1), perform full mixing by ball milling. The ball milling mixing conditions are: the ball milling rotation speed is 100-700 rpm, and the ball milling time is 4-20 h.

4. The preparation method of a lithium sulfide nano-composite cathode material with high reaction kinetics according to claim 3, characterized in that, The ball milling rotation speed is 300-600 rpm, and the ball milling time is 8-16 h.

5. The preparation method of a lithium sulfide nano-composite cathode material with high reaction kinetics according to claim 1, characterized in that, In step (2), the solid content after mixing is 20-60%; and / or, the heat treatment conditions are: the heating temperature is 300-700 °C; the heat preservation time is 1-5 h; the heating rate is 2-5 °C / min; and / or, the drying treatment conditions are: the heating temperature is 30-100 °C; the drying time is 0.5-3 h.

6. The preparation method of a lithium sulfide nanocomposite cathode material with high reaction kinetics according to claim 1, wherein, In step (3), the electrode composite material includes a composite cathode material, a sulfide solid electrolyte, and conductive carbon, where: the sulfide solid electrolyte is Li6PS5Cl, Li7P3S 11 , Li 10 GeP2S 12 at least one; and / or, the conductive carbon is at least one of multi-walled carbon nanotubes, acetylene black, and activated carbon; and / or, the mass ratio of the composite cathode material, the sulfide solid electrolyte, and the conductive carbon is (50-90):(10-40):(0-10).

7. The preparation method of a lithium sulfide nano-composite cathode material with high reaction kinetics according to claim 1, characterized in that, In step (3), for the in-situ electrochemical reduction reaction, the cut-off discharge voltage is 0.5 V, and / or perform a discharge treatment at a current density of 20 mA / g - 100 mA / g.

8. The preparation method of a lithium sulfide nano-composite cathode material with high reaction kinetics according to claim 1, characterized in that, The obtained lithium sulfide nanoparticles have a size ≤100 nm; the carbon coating layer has a thickness of 1-10 nm, and the metal atom doping content accounts for 15-24 wt.% of the composite cathode material.

9. A lithium sulfide nanocomposite cathode material with high reaction kinetics prepared by the preparation method according to any one of claims 1-8.

10. Application of a lithium sulfide nanocomposite cathode material with high reaction kinetics prepared by the preparation method according to any one of claims 1-8 in the field of all-solid-state lithium-sulfur batteries.

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