Preparation method of composite positive electrode material and application of composite positive electrode material in all-solid-state lithium-sulfur battery

Abstract

The invention discloses a composite positive electrode material applied to an all-solid-state lithium-sulfur battery. The composite positive electrode material comprises elemental sulfur as an active substance, and a high-temperature and high-ionic-conductivity sulfide solid electrolyte as an ionic conductive agent for conducting lithium ions; and the conductive carbon material is used as an electronic conductive agent for conducting electrons. The mass ratio of the elemental sulfur to the conductive carbon material to the sulfide solid electrolyte can be 1: 1: 2. The volume expansion of the active substance sulfur in the obtained composite positive electrode is small, the ion / electron path in the composite positive electrode is excellent, and the assembled all-solid-state battery is high in safety, good in cycle stability and high in energy density and power density.

Description

Technical Field

[0001] The present invention belongs to the field of lithium-ion battery materials, and in particular relates to a composite positive electrode material used in all-solid-state lithium-sulfur batteries. Background Art

[0002] Lithium-sulfur batteries have the advantages of high theoretical capacity (1675mAh / g), energy density (2600Wh / kg) and environmental protection, and are considered to be one of the most attractive candidates for the next generation of energy storage devices. However, the practical application of liquid lithium-sulfur batteries still has some thorny issues: sulfur and the final discharge product (Li 2 S 2 and Li 2 S) Poor electronic and ionic conductivity limits the specific capacity and rate performance of lithium-sulfur batteries; polysulfide intermediates Li 2 S n (4<n<8) dissolution into the electrolyte and the subsequent "shuttle effect" caused; volume expansion of sulfur during cycling; safety hazards caused by the formation of lithium dendrites. These problems all lead to poor chemical properties of liquid lithium-sulfur batteries, including rapid capacity decay, low coulombic efficiency, and poor rate performance.

[0003] In order to solve the problems of liquid lithium-sulfur batteries, all-solid-state lithium-sulfur batteries have been proposed, which can completely inhibit the dissolution of polysulfides, thereby eliminating the "shuttle effect" of polysulfides. In addition, with the help of solid-state design, the formation and leakage of lithium dendrites can be greatly suppressed. However, the use of solid-state electrolytes brings new problems, such as large interfacial resistance and stress and strain between electrodes and electrolytes. Therefore, constructing a stable solid-solid interface to minimize stress / strain and form robust electron and ion paths is crucial to achieving excellent electrochemical performance. Summary of the invention

[0004] The present invention aims to solve the problems existing in the prior art and provides a composite positive electrode material for an all-solid-state lithium-sulfur battery. The all-solid-state lithium-sulfur battery prepared by using the composite positive electrode material has the characteristics of high safety, good chemical stability, high energy density, high power density, etc.

[0005] The composite positive electrode material for all-solid-state lithium-sulfur batteries provided by the present invention comprises a positive electrode active material, a solid electrolyte, and a conductive agent. The positive electrode active material refers to elemental sulfur, and the conductive agent comprises a conductive carbon material.

[0006] According to the composite positive electrode material of the embodiment of the present invention, sulfur releases a higher capacity as an active material. The conductive carbon material promotes the conduction of electrons in the composite positive electrode. This new composite positive electrode has a simple structure and can alleviate the volume expansion of the active material sulfur in the composite positive electrode. The all-solid-state lithium-ion battery assembled using the composite positive electrode material has a long cycle life, high energy density and power density, and good safety.

[0007] In the above-mentioned composite positive electrode material, the mass ratio between the elemental sulfur, the conductive carbon material, and the sulfide solid electrolyte can be 3:2:5, and the most preferred mass ratio is 1:1:2. Therefore, the composite positive electrode material has a small volume expansion during the cycle, the internal ion / electron conductivity of the composite positive electrode is high, and the utilization rate of the active material is high.

[0008] The conductive carbon material in the present invention is selected from at least one of superP, acetylene black, VGCF, conductive carbon black, graphitized carbon nanotubes, carbon nanotubes, functionalized carbon nanotubes, reduced graphene oxide, and conductive graphite. According to a preferred embodiment of the present invention, the conductive carbon material is carbon nanotubes. As a result, the electronic conductivity in the composite positive electrode is good.

[0009] The invention provides a method for preparing the composite positive electrode material.

[0010] The method for preparing the composite positive electrode material provided by the present invention comprises the following steps: The first step is to dry-mill and mix the elemental sulfur and the conductive carbon material according to the mass ratio; Then, the elemental sulfur / conductive carbon composite obtained above and the sulfide electrolyte are mixed by dry ball milling according to the mass ratio.

[0011] The ball milling speed is 500 pm, the ball milling time is 6 hours, and the ball milling is performed under an inert atmosphere.

[0012] As a result, elemental sulfur, conductive carbon, and sulfide electrolyte are evenly distributed and tightly combined, thereby improving the effective ion / electronic conductivity of the composite positive electrode, thereby improving the utilization rate of the active material sulfur in the composite positive electrode, improving the interfacial reaction kinetics, and reducing the volume expansion of the positive electrode, thereby improving the cycle life, energy density, and power density of the battery.

[0013] A second aspect of the present invention provides an all-solid-state lithium battery.

[0014] The solid-state lithium-sulfur battery provided by the present invention comprises: a positive electrode layer, wherein the positive electrode layer comprises the aforementioned composite positive electrode material Material, solid electrolyte layer, negative electrode layer; The negative electrode layer is one of a graphite-based negative electrode, a silicon-carbon-based negative electrode, a silicon-based negative electrode, a lithium-indium alloy, a lithium-indium alloy, a silver-carbon negative electrode, a lithium metal, and a lithium-aluminum alloy. Thus, the all-solid-state battery has a high capacity and good electrochemical activity.

[0015] The composite positive electrode material applied for releases a higher capacity with elemental sulfur as the active substance. At the same time, the selected sulfide solid electrolyte itself has high high-temperature lithium ion conductivity, which promotes the conduction of lithium ions in the composite positive electrode. The conductive carbon material promotes the conduction of electrons in the composite positive electrode. This new composite positive electrode has a simple structure and can alleviate the volume expansion of the active substance sulfur in the composite positive electrode. The all-solid-state lithium-ion battery assembled using the composite positive electrode material has excellent rate performance and good cycle stability, long cycle life, high energy density and power density, and good safety.

[0016] In addition, the study found that elemental sulfur has poor affinity with sulfide solid electrolytes. The elemental sulfur and the conductive material are first ball-milled, and the conductive material and elemental sulfur are evenly dispersed after ball milling, and then ball-milled with the sulfide electrolyte, which significantly improves the performance of the positive electrode material.

Claims

1. A composite positive electrode material for a solid-state lithium-sulfur battery, comprising a positive electrode active material, an ion conductor, and a conductive agent, wherein the positive electrode active material comprises elemental sulfur as an active substance, the ion conductor comprises a sulfide electrolyte, and the conductive agent comprises a conductive carbon material.

2. A method for preparing a vapor-deposited sulfur cathode composite material, characterized in that Sulfur enters the pores in the form of gas, which includes the following steps: S1, dry-milling and mixing the elemental sulfur and the conductive carbon material according to the mass ratio; S2. The ball-milled material is sealed in a tube and placed in a tube furnace. After evacuation, it is heated to 300°C and kept warm for 5 hours, and then naturally cooled to room temperature to obtain an elemental sulfur / conductive carbon composite material.

3. S3, then dry-milling and mixing the elemental sulfur / conductive carbon composite obtained above and the sulfide electrolyte according to the mass ratio.

4. The composite positive electrode material according to claim 2, characterized in that: The mass ratio of the elemental sulfur, the conductive carbon material and the sulfide solid electrolyte may be 3:2:5; Preferably, the mass ratio of the elemental sulfur, the conductive carbon material and the sulfide solid electrolyte may be 1:1:

2.

5. The composite positive electrode material according to claim 2, characterized in that: The conductive carbon material is selected from at least one of super-P, acetylene black, VGCF, conductive carbon black, carbon nanotubes, reduced graphene oxide, and conductive graphite.

6. An all-solid-state lithium-sulfur battery, characterized in that: The invention comprises a lithium negative electrode sheet, a sulfide electrolyte and a sulfur positive electrode, wherein the sulfur positive electrode contains the sulfur-containing positive electrode composite material according to claim 2.

7. The all-solid-state lithium-sulfur battery according to claim 5, characterized in that: The all-solid-state lithium battery according to claim 5 is characterized in that: the material of the negative electrode layer is selected from at least one of the following: lithium metal, lithium-indium alloy and lithium-aluminum alloy; The solid electrolyte layer comprises the sulfide ceramic electrolyte described in claim 3.

8. The all-solid-state lithium battery according to claim 5 or 6, characterized in that: The pressure of the positive electrode layer is 5t, and the pressure of the solid electrolyte layer is 1t.