Halogen-based sulfenyl composite positive electrode material and preparation method thereof

Abstract

The invention provides a halogen-based sulfur-based composite positive electrode material and a preparation method thereof. The electrochemical capacity of a halogen-based sulfur-based composite positive electrode is jointly contributed by a halogen-based positive electrode active material, a sulfur-based positive electrode active material and a solid electrolyte. The halogen sulfur-based composite positive electrode disclosed by the invention can simultaneously exert the capacities of a halogen-based material and a sulfur-based positive electrode material, improve the conductivity of a sulfur-based positive electrode active substance body, reduce the size of the positive electrode material, enhance the solid-solid contact between the materials, effectively reduce the proportion of inert components such as conductive carbon and electrolyte without electrochemical activity in a positive electrode system, and improve the stability of the positive electrode system. The energy density of the positive electrode material can be greatly improved, and the application prospect is wide.

Description

Technical Field

[0001] The present invention belongs to the field of lithium batteries, and in particular relates to a halogen-based sulfur-based composite positive electrode material and a preparation method thereof. Background Art

[0002] As energy issues become increasingly prominent, lithium-ion batteries based on lithium-intercalated compound cathodes have developed rapidly in recent decades and have been widely used in portable electronic devices and other fields. However, the capacity of existing lithium-ion batteries is close to its theoretical value and cannot meet the requirements of the rapidly developing electronics industry and electric vehicles. Therefore, it is urgent to develop new high-capacity lithium batteries. Lithium-sulfur batteries have become one of the ideal choices for the new generation of energy storage devices due to their high theoretical specific capacity, large energy density, abundant sulfur resources, low manufacturing cost and environmental friendliness. However, many challenges still hinder the further development of lithium-sulfur batteries. The most severe obstacle is the inherent shuttle effect and the safety issues caused by it. In recent years, all-solid-state lithium-sulfur batteries that use solid electrolytes instead of traditional liquid electrolytes have gradually been regarded as a promising solution to these problems. First, the decomposition temperature of solid electrolytes is significantly higher than that of liquid electrolytes and diaphragms, which improves the thermal stability of all-solid-state lithium-sulfur batteries and reduces the risk of thermal runaway. Secondly, all-solid-state lithium-sulfur batteries do not produce liquid polysulfides during the charge and discharge cycle. Instead, they only need to convert solid sulfur into solid lithium sulfide and lithium persulfide, which can effectively avoid the formation of polysulfides, capacity decay and safety hazards caused by the shuttle effect.

[0003] Although all-solid-state lithium-sulfur batteries have reliable safety and can essentially eliminate the shuttle effect, there are still many problems, including large interfacial impedance caused by poor solid-solid contact and slow redox kinetics caused by high solid-phase conversion energy barriers. Some preliminary work has proposed several feasible methods to alleviate the above difficulties, such as adding various conductive carbons and matching new solid electrolytes to increase capacity. However, due to the low electronic and ionic conductivity of the conversion-type sulfur-based positive electrode commonly used in all-solid-state lithium-sulfur batteries, a large amount of conductive carbon and solid electrolyte need to be added in the process of preparing the positive electrode to construct a three-phase interface between the sulfur component, conductive carbon and solid electrolyte, which significantly increases the tortuosity of the charge transfer path and limits the further improvement of the energy density of the conversion-type sulfur-based positive electrode.

[0004] Halogen-based catalysts LiX (X includes Cl, Br, I) have high ionic conductivity and can provide abundant catalytic sites for sulfur species. Some LiX can also be oxidized as redox active components, thereby accelerating the reaction kinetics of all-solid-state lithium-sulfur batteries and contributing additional capacity. Halogen-based elemental iodine (I2) can be inserted into the crystal structure of the sulfur-based positive electrode, thereby improving the conductivity of the composite sulfur-based positive electrode. If lithium halides and elemental iodine can be introduced into the conversion-type sulfur-based positive electrode to replace part of the inactive conductive carbon, the energy density of the all-solid-state lithium-sulfur battery will be further improved.

[0005] The prior art has reported on improving electrochemical performance by compounding metal halides in sulfur-based positive electrode materials. For example, CN118630131A discloses a method for preparing a composite sulfur positive electrode introducing an iodide additive, wherein the solid-state lithium-sulfur battery positive electrode includes a sulfur / carbon composite material, a conductive agent, a solid electrolyte, a binder, and an iodide additive. By introducing an iodide additive into the positive electrode of a solid-state lithium-sulfur battery, the solid-phase conversion energy barrier of the active substance sulfur is significantly reduced, and the positive electrode reaction kinetics are promoted, thereby reducing battery polarization and improving the utilization rate of active substances, thereby improving the capacity and rate performance of the battery. The iodide additive is at least one of LiI, PI3, CaI2, AgI, and NaI. CN116018699A discloses a composite all-solid lithium-sulfur battery positive electrode mixture, which contains sulfur or its discharge product (A), phosphorus pentasulfide (B), conductive carbon (C) and lithium halide (D) in a weight ratio of A:B:C:D=40-60:15-35:5-20:16-30. The lithium halide (D) is uniformly mixed with solid sulfur or its discharge product (A) to form a solid solution, and the halide ions are partially replaced with the sulfide ions in the sulfur or its discharge product (A), thereby improving the ionic conductivity of the sulfur or its discharge product (A). CN110838577A discloses a sulfur-based positive electrode active material for solid-state batteries, comprising: 30-80 weight % of Li2S, 10-40 weight % of one or more second lithium compounds selected from LiI, LiBr, LiNO3 and LiNO2, and 0-30 weight % of conductive carbon material. The second lithium compound can form an electron-withdrawing group with high electronegativity during charging, thereby increasing the discharge voltage of the battery. In addition, the introduction of the second lithium compound further improves the ionic conductivity of the positive electrode, improves the catalytic effect on the decomposition of lithium sulfide and the lithiation of sulfur, and thus increases the specific capacity of the electrode material. CN110957483A discloses a method for preparing a sulfur composite positive electrode material, comprising the following steps: 1) mixing a lithium ion matrix material and a conductive matrix material, and then ball milling to obtain a mixture A; 2) mixing elemental sulfur with the mixture A, and then ball milling to obtain a mixture B; 3) heat treating the mixture B by a melt diffusion method under the protection of an inert gas, and then cooling to obtain a sulfur composite positive electrode material. Sulfur is effectively fixed in the lithium ion matrix material and the conductive matrix material, so that the composite sulfur positive electrode has good ionic and electronic conductivity.

[0006] The above patent discloses a method for compounding lithium halides such as LiI and sulfur-based positive electrode active materials to form a positive electrode, but the inherent low electron conduction problem between the bulk of the sulfur positive electrode material contained in the composite positive electrode of the above patent has not been solved, and more inactive conductive carbon materials need to be added to improve the conductivity. In addition, the minimum particle size of the composite positive electrode material obtained by the conventional ball milling method is limited, and the contact between various materials is not close. The formation of non-conductive interfaces, gaps or stratified areas limits the effective diffusion of lithium ions, resulting in increased interface impedance and limited utilization of active materials in the electrode. The present invention combines halogen-based substances, including elemental iodine and halogen-based salts LiX (X includes Cl, Br, I), sulfur-based positive electrodes and solid electrolytes to obtain a multi-mechanism energy storage positive electrode that can not only give full play to the capacity of these materials, but also effectively solve the inherent low conductivity of the active material sulfur-based positive electrode, and the difficulty in obtaining small-sized positive electrode materials to enhance the contact between various materials. The problem is expected to further improve the energy density of solid-state lithium-sulfur batteries. Summary of the invention

[0007] In order to solve the challenges of slow redox kinetics caused by the high solid-phase conversion energy barrier of the above-mentioned all-solid-state lithium-sulfur battery, the inherent low conductivity of the active sulfur-based positive electrode, and the poor contact between materials due to the large particle size, which makes it difficult to further increase the capacity of the positive electrode material, the present invention combines the sulfur-based positive electrode with lithium halide and iodine to obtain a halogen-based sulfur-based composite positive electrode, which can not only improve the reaction kinetics, but also give full play to the capacity of the three materials, and further improve the energy density of the all-solid-state lithium-sulfur battery. The present invention provides a halogen-based sulfur-based composite positive electrode material, which improves the low conductivity and large particle size of the sulfur-based positive electrode body through the joint action of halogen-based active substances, sulfur-based positive electrode active substances, and solid electrolytes, effectively reduces the proportion of inert components such as conductive carbon and electrochemically inactive electrolytes in the positive electrode system, and improves the energy density of the positive electrode material, which has broad research space and application prospects. The present invention provides the following technical solutions to solve the above technical problems:

[0008] A halogen-based sulfur-based composite positive electrode material comprises the following raw materials in parts by mass: 35-45 parts of sulfur-based positive electrode active material, 3-5 parts of lithium halide, 6-10 parts of iodine element, 5-10 parts of conductive carbon material, and 30-50 parts of sulfide solid electrolyte; the halogen-based sulfur-based composite positive electrode material is prepared by mixing the materials uniformly by ball milling, and the following conditions are met:

[0009] 1) firstly subjecting the sulfur-based positive electrode active material and the iodine element to high-speed ball milling and low-temperature heat treatment under vacuum conditions, and then subjecting the subject to ball milling and mixing with other materials; the resulting material is subjecting the subject to ball milling and mixing with one or more of lithium halide, conductive carbon material, and sulfide solid electrolyte;

[0010] 2) After ball milling with lithium halide, high temperature heat treatment is also performed. During the high temperature heat treatment, if there is a sulfide solid electrolyte in the material, it needs to be performed under an inert atmosphere;

[0011] Furthermore, the particle size of sulfur iodide particles in the obtained halogen-based sulfur-based composite positive electrode material is 120-200 nm, preferably 120-160 nm.

[0012] If the selected sulfur-based cathode material is sulfur, after ball milling, it is necessary to perform high-temperature heat treatment at a temperature higher than the melting point of sulfur to ensure that it can effectively infiltrate the oxygen-based cathode material and the conductive carbon material, thereby building an effective electron transport network. During the high-temperature heat treatment, if there is a sulfide solid electrolyte in the material, it needs to be carried out in an inert atmosphere.

[0013] The technical idea of ​​the present invention is to mix sulfur-based positive electrode active material with lithium halide, iodine, conductive carbon material, and sulfide solid electrolyte by ball milling to obtain a composite material. However, there are certain requirements for the order of ball milling mixing, that is, it is necessary to firstly mix sulfur-based positive electrode active material with iodine, and the ball milling is a high-speed high-energy ball milling (500-800rpm), and it is also necessary to perform low-temperature heat treatment at a temperature higher than the melting point of sulfur iodide (generally 80-120°C) so that iodine can fully react with sulfur-based positive electrode active material to be converted into sulfur iodide, enhance the bulk conductivity, and then perform with other materials (one or more of lithium halide, conductive carbon material, and sulfide solid electrolyte). The order of ball milling mixing with lithium halide, conductive carbon material, and sulfide solid electrolyte is not particularly limited, and one material can be put into, or multiple materials can be put into ball milling mixing at the same time.

[0014] Furthermore, the high-speed ball milling speed is 500-800rpm, and high-speed ball milling is equivalent to high-energy ball milling. The purpose is to make the halogen-based substances and sulfur-based positive electrode materials mix more evenly, and the iodine element can fully react with the sulfur-grade positive electrode. At the same time, it can reduce the particle size of the positive electrode material and increase the specific surface area, thereby enhancing the solid-solid contact between the materials, making the materials more evenly mixed and compact, and reducing the interface resistance; low-temperature heat treatment under vacuum conditions is heating at 80-120°C for 3-5h at a vacuum degree of 1-5mbar; high-temperature heat treatment is heat treatment at 160-200°C for 5-10h. Except for the ball milling of materials and halogen-based substances, which requires high-energy ball milling, the ball milling rate for mixing other materials is 100-300rpm.

[0015] Furthermore, the sulfur-based positive electrode active material is selected from at least one of sulfur (S), lithium sulfide (Li2S), iron sulfide (FeS), copper sulfide (CuS), and molybdenum disulfide (MoS2); the conductive carbon material is selected from at least one of carbon nanotubes, conductive carbon black (SuperP), acetylene black, and Ketjen black. Preferably, the sulfur-based positive electrode active material is sulfur. The melting point of sulfur is 155°C. High-temperature heat treatment at a temperature higher than the melting point of sulfur can effectively infiltrate and thus construct an effective electron transport network.

[0016] Furthermore, the sulfide solid electrolyte is selected from Li2GeS3, Li4GeS4, Li2ZnGeS4, Li 4-2x Zn x GeS4 (where 0≤x≤1), Li5GaS4, Li 4+x+y (Ge 1-y-x Ga x )S4 (where 0≤x≤0.2, 0≤y≤1), Li 10 GeP2S 12xy O x F y (where 0≤x≤1, 0≤y≤1), Li 2+2x Zn 1-x GeO4 (where 0≤x≤1), Li 3+z X z Y 1-z O4 (Y=P, As or V; X=Si, Ge or Ti, 0≤z≤1), Li 11-x M 2-x P 1+x S 12 (M=Ge, Sn or Si, 0≤x≤2), xLi2S·(100–x)P2S5 (where x is 50-87.5), Li6PS5X (X=Cl, Br or I, such as Li3PS4, Li7P3S 11 , Li 10 GeP2S 12 , Li6PS5Cl).

[0017] The inventor unexpectedly found that the halogen introduced into the sulfur-based positive electrode material includes lithium halide and iodine, and the iodine can be inserted into the crystal structure of the sulfur-based positive electrode, contributing new states in the band gap of sulfur, and the iodide formed can not only introduce electronic conductivity, but also reduce the slow redox kinetics caused by the intrinsic low conductivity of the sulfur-based positive electrode; and the particle size formed after the reaction is smaller than that of the traditional sulfur-based positive electrode, and the small particles can increase the specific surface area of ​​the active material, reduce the diffusion path of lithium ions in the battery, thereby improving the electrochemical reaction kinetics of the battery, and reduce the particle size. It is also easy to increase the contact with the solid electrolyte and the conductive carbon material, and reduce the gap problem that causes ion blocking in the solid positive electrode, thereby improving the utilization rate of the active material. The introduced lithium halide has a high ionic conductivity, can enhance the interfacial transport of lithium ions, catalyze the conversion of the sulfur-based positive electrode, and further improve the reversibility of the sulfur-based positive electrode. The introduction of two halogen-based substances can not only make the capacity of the sulfur-based positive electrode more fully utilized; on the other hand, some halogen-based materials can also serve as redox active components, correspondingly contributing some additional capacity, thereby increasing the capacity of the positive electrode. However, it is necessary to control the order of ball milling mixing, and the high-speed ball milling mixing with the iodine element should be carried out first to ensure that it can react with part of the sulfur-based positive electrode, and then introduce the lithium halide for ball milling. Conductive carbon materials and sulfide solid electrolytes need to be evenly mixed with the materials by ball milling after the reaction between the sulfur-based positive electrode and the iodine element is completed. It should be noted that since there is a high-temperature heat treatment step after ball milling with lithium halide, if there is already a sulfide solid electrolyte in the material, it needs to be heat treated under inert gas conditions, because the stability of the sulfide solid electrolyte in the air is very poor and it is extremely sensitive to water and oxygen. Once the sulfide solid electrolyte is introduced, the inert atmosphere environment conditions must be controlled.

[0018] In the traditional sulfur-based positive electrode system, since the sulfur-based positive electrode has relatively low electronic and ionic conductivity, it is necessary to add a very high proportion of conductive carbon materials and solid electrolytes to the sulfur-based positive electrode system to achieve effective charge transfer. The halogen-based sulfur-based composite positive electrode material provided by the present invention has very high ionic and electronic conductivity, and can reduce the proportion of conductive carbon and solid electrolyte content in the traditional sulfur-based positive electrode material. Conductive carbon material is an inert material and does not contribute to the capacity of the battery. In the sulfur composite positive electrode material, we replace part of the conductive carbon with an electrochemically active halogen-based positive electrode material. This part of the halogen-based positive electrode material can not only realize the original role of conductive carbon in transmitting electrons, but also play a certain electrochemical capacity, which will further achieve the improvement of battery capacity. Using halogen-based positive electrode materials instead of part of the solid electrolyte can further enhance the interfacial transport of lithium ions to solve the main challenge faced by all-solid-state lithium-sulfur batteries, namely the slow redox kinetics caused by the high solid-phase conversion energy barrier. However, the ball milling mixing order and ball milling conditions of lithium halide and iodine need to be controlled, that is, the sulfur-based cathode material and iodine are first ball milled and heated, and then the lithium halide, conductive carbon material and solid electrolyte are ball milled. It should be noted that if there is already a sulfur-containing solid electrolyte in the material, the subsequent operations need to be carried out under inert gas protection conditions.

[0019] Furthermore, the present invention also provides a method for preparing the halogen-based sulfur-based composite positive electrode material, comprising the following steps:

[0020] (S1) The sulfur-based cathode material and iodine are mixed, ball-milled at high speed under an inert atmosphere, and then heat-treated at low temperature under vacuum conditions to obtain a precursor I;

[0021] (S2) Precursor I is mixed with lithium halide and conductive carbon material, ball-milled under an inert atmosphere, and subjected to high-temperature heat treatment to obtain precursor II;

[0022] (S3) Precursor II and sulfide solid electrolyte are ball milled under an inert atmosphere to obtain a halogen-based sulfur-based composite positive electrode.

[0023] Further, the inert atmosphere is nitrogen and / or argon.

[0024] Furthermore, the high-speed ball milling speed is 500-800 rpm, the low-temperature heat treatment under vacuum conditions is heating at 80-120°C for 3-5 hours at a vacuum degree of 1-5 mabr; the high-temperature heat treatment is heating at 160-200°C for 5-10 hours; in steps (S2) and (S3), the ball milling speed is 100-300 rpm.

[0025] The present invention also provides an all-solid-state lithium-sulfur battery, the positive electrode of which comprises the above-mentioned halogen-sulfur-based composite positive electrode material.

[0026] Beneficial effects of the present invention:

[0027] 1. By adding halogen-based substances to the conversion-type sulfur-based positive electrode energy storage material, the advantages of the two electrode materials are integrated and complement each other. Iodine can be inserted into the crystal structure of the sulfur-based positive electrode, introducing electronic conductivity, alleviating the slow redox kinetics caused by the intrinsic low conductivity of the sulfur-based positive electrode; and the particle size formed after the reaction is smaller than that of the traditional sulfur-based positive electrode. The small particle size can increase the contact with the solid electrolyte and the conductive carbon material, reduce the gap problem that causes ion blockage in the solid positive electrode, and thus improve the electrochemical reaction kinetics of the battery and the utilization rate of the active material.

[0028] 2. The halogen-based positive electrode material after energy storage can replace part of the conductive carbon and solid electrolyte materials that originally need to be added to the sulfur-based positive electrode. The conductive carbon material has no electrochemical activity and is an inert component. The content of the inert component such as conductive carbon can be reduced. The added halogen-based positive electrode material can also contribute a certain capacity, which can effectively improve the energy density of the battery.

[0029] 3. Halogen-based materials will enhance the interfacial transport of lithium ions, provide abundant catalytic sites for sulfur species, improve the reversibility of sulfur-based positive electrodes, and enable the capacity of sulfur-based positive electrodes to be more fully utilized.

[0030] In summary, the halogen-based catalyst sulfur composite positive electrode disclosed in the present invention can simultaneously give play to the advantages of halogen-based positive electrode materials and sulfur-based positive electrode materials, reduce the size of positive electrode materials, enhance the solid-solid contact between materials, effectively reduce the proportion of inert components such as conductive carbon and electrochemically inactive electrolytes in the positive electrode system, greatly improve the energy density of positive electrode materials, and has broad research space and application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is an X-ray diffraction image of the precursor I used in the halogen-based sulfur composite positive electrode in Example 1.

[0032] Figure 2 This is an atomic force microscope photograph of the halogen-based sulfur composite positive electrode used in Example 1.

[0033] Figure 3 This is an atomic force microscope photograph of the sulfur composite positive electrode without iodine element in Comparative Example 1.

[0034] Figure 4 This is a scanning electron microscope photograph of the halogen-based sulfur-based composite positive electrode used in Example 1.

[0035] Figure 5 This is the first cycle cyclic voltammetry curve of the all-solid-state lithium-sulfur battery using the halogen-based sulfur-based composite positive electrode in Example 1. DETAILED DESCRIPTION

[0036] The present invention is further described below in conjunction with specific examples, but the present invention is not limited to the following examples. The experimental methods described in the following examples are conventional methods unless otherwise specified; the reagents and materials described are commercially available unless otherwise specified. The following specific examples are given to help understand the halogen-based catalyst sulfur composite positive electrode described in the present invention.

[0037] Example 1

[0038] (S1) 40 parts by mass of sulfur powder and 8 parts by mass of iodine powder were mixed, and the mixed materials were added into a ball mill protected by argon gas, and the ball-to-material ratio was controlled to 100:1, the rotation speed was 600 rpm, and the ball milling was performed for 8 hours. The ball-milled mixture was transferred to a round-bottom flask, and the vacuum was evacuated to 2 mbar using a joint piston, and then heated at 80° C. for 3 hours to react, and then naturally cooled to obtain a precursor I;

[0039] (S2) Precursor I is mixed with 5 parts by mass of lithium iodide and 8 parts by mass of conductive carbon black Super P powder, ball-milled at 300 rpm for 5 h under an argon atmosphere, and then the mixture is kept at 170° C. for 6 h to obtain Precursor II;

[0040] (S3) Precursor II and 40 parts by mass of sulfur-containing solid electrolyte Li6PS5Cl are mixed, and the mixed material is added into a ball mill protected by argon gas, the ball-to-material ratio is controlled to 100:1, the rotation speed is 300 rpm, and the ball milling is performed for 18 hours to obtain a halogen-based sulfur-based composite positive electrode material.

[0041] (S4) Assembling an all-solid-state lithium-sulfur battery: In an argon-protected glove box, pour 70 mg of sulfide solid electrolyte Li6PS5Cl into a mold and apply a pressure of 400 MPa to shape it to obtain a sulfide solid electrolyte Li6PS5Cl ceramic sheet, pour 4 mg of the halogen-based sulfur-based composite positive electrode material powder prepared in the above step S3 onto one side of the pressed dual inorganic composite solid electrolyte ceramic sheet, apply a pressure of 500 MPa to make the sulfur positive electrode in close contact with the dual inorganic composite solid electrolyte, finally place a lithium indium alloy ceramic sheet on the other side of the dual inorganic composite solid electrolyte ceramic sheet, and test the entire battery under a pressure of 100 MPa.

[0042] Figure 1 This is an X-ray diffraction image of the precursor I obtained in step S1 of Example 1. The peaks in the blue region of the image indicate that sulfur reacts with iodine to obtain sulfur iodide.

[0043] Figure 2This is an atomic force microscope photograph of the halogen-based sulfur-based composite positive electrode material obtained in step S3 of Example 1. It can be seen from the dotted box that the particle size of sulfur iodide is about 120-150nm, which is smaller and has a closer solid-solid contact with the solid electrolyte and conductive carbon.

[0044] Figure 3 This is a scanning electron microscope photograph of the halogen-based sulfur-based composite positive electrode material obtained in step S3 of Example 1.

[0045] Figure 5 This is the first cycle cyclic voltammetry curve of the all-solid-state battery using the halogen-based sulfur-based composite positive electrode material in Example 1.

[0046] Example 2

[0047] The other conditions are the same as those in Example 1, except that the raw materials are changed from 40 parts by mass of sulfur powder, 5 parts by mass of lithium iodide, 8 parts by mass of iodine, 8 parts by mass of conductive carbon material, and 40 parts by mass of sulfide solid electrolyte to: 45 parts by mass of sulfur-based positive electrode active material, 5 parts by mass of lithium iodide, 10 parts by mass of iodine, 10 parts by mass of conductive carbon material, and 50 parts by mass of sulfide solid electrolyte. According to the atomic force microscope photos, the particle size of sulfur iodide in the composite positive electrode material obtained in Example 2 is 130-180nm.

[0048] Example 3

[0049] The other conditions are the same as those in Example 1, except that the raw materials are changed from 40 parts by mass of sulfur powder, 5 parts by mass of lithium iodide, 8 parts by mass of iodine, 8 parts by mass of conductive carbon material, and 40 parts by mass of sulfide solid electrolyte to: 35 parts by mass of sulfur-based positive electrode active material, 3 parts by mass of lithium iodide, 8 parts by mass of iodine, 8 parts by mass of conductive carbon material, and 40 parts by mass of sulfide solid electrolyte. According to the atomic force microscope photos, the particle size of sulfur iodide in the composite positive electrode material obtained in Example 3 is 130-170nm.

[0050] Example 4

[0051] The other conditions are the same as those in Example 1, except that the sulfur-containing solid electrolyte is Li 10 GeP2S 12 .

[0052] Example 5

[0053] The other conditions are the same as those in Example 1, except that the sulfur-based cathode material is changed from 40 parts by mass of sulfur elemental powder to 45 parts by mass of Li2S. The atomic force microscope photographs show that the particle size of sulfur iodide in the composite cathode material obtained in Example 5 is 150-190 nm.

[0054] Comparative Example 1

[0055] Other conditions are the same as those in Example 1, except that step (S1) is omitted, that is, iodine is not added. In step (S2), 40 parts by mass of sulfur powder, 15 parts by mass of lithium iodide, and 8 parts by mass of conductive carbon black Super P powder are mixed.

[0056] Figure 4 This is an atomic force microscope photograph of the sulfur composite positive electrode prepared in step S3 of comparative example 1. Without adding iodine, the particle size of the original sulfur particles used is about 230-260 nm even after high-energy ball milling, which is not conducive to solid-solid contact.

[0057] Comparative Example 2

[0058] The other conditions are the same as those in Example 1, except that in step (S1), the ball milling speed is 200 rpm. In the obtained composite positive electrode material, the particle size of sulfur iodide particles is about 200-250 nm.

[0059] Comparative Example 3

[0060] (S1) Composite of sulfur-based positive electrode material and halogen-based material: 40 parts by mass of sulfur powder, 5 parts by mass of lithium iodide, 8 parts by mass of iodine, and 8 parts by mass of conductive carbon black Super P powder were mixed, and the mixed materials were added to a ball mill protected by argon gas, and the ball-to-material ratio was controlled to 100:1, the rotation speed was 600 rpm, and the ball milling was performed for 8 hours. Then, the ball-milled mixture was kept at a temperature of 160° C. for 6 hours under an argon atmosphere to obtain a precursor I;

[0061] (S2) Precursor I and 40 parts by mass of sulfur-containing solid electrolyte Li6PS5Cl are mixed, and the mixed material is added into a ball mill protected by argon gas, the ball-to-material ratio is controlled to 100:1, the rotation speed is 200 rpm, and the ball milling is performed for 18 hours to obtain a halogen-based sulfur-based composite positive electrode material.

[0062] The battery assembly is the same as step (S4) of Example 1.

[0063] That is, compared with Example 1, in step S1, sulfur powder, lithium iodide, iodine powder and conductive carbon black Super P powder are ball-milled together.

[0064] Comparative Example 4

[0065] (S1) 40 parts by mass of sulfur powder, 5 parts by mass of lithium iodide, and 8 parts by mass of conductive carbon black Super P powder were mixed, and the mixed materials were added into a ball mill protected by argon gas, and the ball-to-material ratio was controlled to be 100:1, the rotation speed was 200 rpm, and the ball milling was performed for 8 hours, and the precursor I was obtained after heat treatment at 170° C. for 6 hours;

[0066] (S2) Precursor I and 8 parts by mass of iodine were mixed, ball-milled at 500 rpm for 8 h under an argon atmosphere, and then heated at 100° C. for 6 h under an argon atmosphere to obtain Precursor II;

[0067] (S3) Precursor II and 40 parts by mass of sulfur-containing solid electrolyte Li6PS5Cl are mixed, and the mixed material is added into a ball mill protected by argon gas, the ball-to-material ratio is controlled to 100:1, the rotation speed is 200 rpm, and the ball milling is performed for 18 hours to obtain a halogen-based sulfur-based composite positive electrode material.

[0068] The battery assembly is the same as step (S4) of Example 1.

[0069] That is, compared with Example 1, the sulfur powder and lithium iodide are firstly subjected to ball milling, mixing and heat treatment, and then the sulfur powder and iodine powder are subjected to ball milling, mixing and heating.

[0070] Application Examples

[0071] In the voltage range of 1.5-3V, constant current charge and discharge tests were carried out on a multi-channel blue electricity tester. The charge and discharge rate was 0.2C and the ambient temperature was room temperature 25℃.

[0072] The electrochemical performance of the all-solid-state battery using the halogen-based sulfur-based composite positive electrode material in the above examples and comparative examples is listed in the following Table 1.

[0073] Table 1 Electrochemical performance test results of halogen-based sulfur-based composite cathode materials

[0074]

[0075]

[0076] In summary, the halogen-based sulfur-based composite positive electrode disclosed in the present invention can simultaneously play the advantages of halogen-based positive electrode materials and sulfur-based positive electrode materials, reduce the size of positive electrode materials, enhance the solid-solid contact between materials, and effectively reduce the proportion of inert components such as conductive carbon and electrochemically inactive electrolytes in the positive electrode system, which can greatly improve the energy density of positive electrode materials and has broad research space and application prospects. However, in order to prepare a halogen-based sulfur-based composite positive electrode with excellent performance, the ball milling sequence of the materials and the ball milling mixing of the iodine element need to be carried out under high-energy ball milling conditions.

Claims

1. A halogen-based sulfur-based composite positive electrode material, characterized in that: The raw materials include the following parts by weight: 35-45 parts of sulfur-based positive electrode active material, 3-5 parts of lithium halide, 6-10 parts of iodine element, 5-10 parts of conductive carbon material, and 30-50 parts of sulfide solid electrolyte; the preparation of the halogen-based sulfur-based composite positive electrode material is to mix the materials uniformly by ball milling, and meet the following conditions: 1) firstly subjecting the sulfur-based positive electrode active material and the iodine element to high-speed ball milling and low-temperature heat treatment under vacuum conditions, and then subjecting the subject to ball milling and mixing with other materials; the resulting material is subjecting the subject to ball milling and mixing with one or more of lithium halide, conductive carbon material, and sulfide solid electrolyte; 2) After ball milling with lithium halide, high-temperature heat treatment is also performed. During the high-temperature heat treatment, if there is a sulfide solid electrolyte in the material, it needs to be carried out under an inert atmosphere.

2. The halogen-based sulfur-based composite positive electrode material according to claim 1, characterized in that: The particle size of sulfur iodide particles in the obtained halogen-based sulfur-based composite positive electrode material is 120-200 nm.

3. The halogen-based sulfur-based composite positive electrode material according to claim 1, characterized in that: The particle size of sulfur iodide particles in the obtained halogen-based sulfur-based composite positive electrode material is 120-160nm.

4. The halogen-based sulfur-based composite positive electrode material according to claim 1, characterized in that: The high-speed ball milling speed is 500-800rpm, the low-temperature heat treatment under vacuum conditions is heating at 80-120°C for 3-5h at a vacuum degree of 1-5mbar, and the high-temperature heat treatment is heating at 160-200°C for 5-10h.

5. The halogen-based sulfur-based composite positive electrode material according to claim 1, characterized in that: The sulfur-based positive electrode active material is selected from at least one of sulfur (S), lithium sulfide (Li2S), iron sulfide (FeS), copper sulfide (CuS), and molybdenum disulfide (MoS2); the conductive carbon material is selected from at least one of carbon nanotubes, conductive carbon black (Super P), acetylene black, and Ketjen black; preferably, the sulfur-based positive electrode active material is sulfur.

6. The halogen-based sulfur-based composite positive electrode material according to claim 1, characterized in that: The sulfide solid electrolyte is selected from Li2GeS3, Li4GeS4, Li2ZnGeS4, Li 4-2x Zn x GeS4 (where 0≤x≤1), Li5GaS4, Li 4+x+y (Ge 1-y- x Ga x )S4 (where 0≤x≤0.2, 0≤y≤1), Li 10 GeP2S 12xy O x F y (where 0≤x≤1, 0≤y≤1), Li 2+2x Zn 1- x GeO4 (where 0≤x≤1), Li 3+z X z Y 1-z O4 (Y=P, As or V; X=Si, Ge or Ti, 0≤z≤1), Li 11-x M 2-x P 1+x S 12 (M=Ge, Sn or Si, 0≤x≤2), xLi2S·(100–x)P2S5 (where x is 50-87.5), Li6PS5X (X=Cl, Br or I, such as Li3PS4, Li7P3S 11 , Li 10 GeP2S 12 , Li6PS5Cl).

7. The method for preparing the halogen-based sulfur-based composite positive electrode material according to any one of claims 1 to 6, characterized in that: The following steps are involved: (S1) The sulfur-based cathode material and iodine are mixed, ball-milled at high speed under an inert atmosphere, and then heat-treated at low temperature under vacuum conditions to obtain a precursor I; (S2) Precursor I is mixed with lithium halide and conductive carbon material, ball-milled under an inert atmosphere, and subjected to high-temperature heat treatment to obtain precursor II; (S3) Precursor II and sulfide solid electrolyte are ball milled under an inert atmosphere to obtain a halogen-based sulfur-based composite positive electrode.

8. The preparation method according to claim 7, characterized in that: The inert atmosphere is nitrogen and / or argon.

9. The preparation method according to claim 7, characterized in that: The high-speed ball milling speed is 500-800 rpm, the low-temperature heat treatment under vacuum conditions is heating at 80-120°C for 3-5 hours at a vacuum degree of 1-5 mabr; the high-temperature heat treatment is heating at 160-200°C for 5-10 hours; in steps (S2) and (S3), the ball milling speed is 100-300 rpm.

10. An all-solid-state lithium-sulfur battery, wherein the positive electrode thereof comprises the halogen-sulfur-based composite positive electrode material according to any one of claims 1 to 6.

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