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

Abstract

The application provides a halogen-sulfur composite positive electrode material and a preparation method thereof. The electrochemical capacity of the halogen-sulfur composite positive electrode is contributed by halogen-based positive electrode active material, sulfur-based positive electrode active material and solid electrolyte. The halogen-sulfur composite positive electrode disclosed by the application can simultaneously exert the capacity of halogen-based materials and sulfur-based positive electrode materials, improve the bulk conductivity of sulfur-based positive electrode active material, reduce the size of the positive electrode material, enhance the solid-solid contact between materials, effectively reduce the proportion of inert components such as conductive carbon and non-electrochemical active electrolyte in the positive electrode system, greatly improve the energy density of the positive electrode material, and has a wide application prospect.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of lithium batteries, and particularly relates to a halogen-sulfur-based composite positive electrode material and a preparation method thereof. BACKGROUND

[0002] With the increasingly prominent energy problem, lithium ion batteries based on intercalation compounds have been rapidly developed in recent decades and have been widely applied in the field of portable electronic devices. However, the capacity of the existing lithium ion batteries has reached the theoretical value, which cannot meet the requirements of the rapidly developing electronic industry and the electric vehicle industry, and therefore it is urgent to develop new high-capacity lithium batteries. Lithium-sulfur batteries have become one of the ideal choices for the next 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, and the most serious obstacle is the inherent shuttle effect and the resulting safety problem. In recent years, all-solid-state lithium-sulfur batteries using solid-state electrolytes to replace traditional liquid electrolytes have gradually been considered as a promising solution to these problems. First, the decomposition temperature of the solid-state electrolyte is significantly higher than that of the liquid electrolyte and the separator, thereby improving the thermal stability of the all-solid-state lithium-sulfur battery and reducing the risk of thermal runaway. Second, the all-solid-state lithium-sulfur battery does not produce liquid polysulfides during the charging and discharging cycle, but only needs to convert solid sulfur into solid lithium sulfide and lithium polysulfide, which can effectively avoid the formation of polysulfides, capacity decay and safety hazards caused by the shuttle effect.

[0003] Although the all-solid-state lithium-sulfur battery has reliable safety and can essentially eliminate the shuttle effect, there are still many problems, including large interface impedance caused by poor solid-solid contact and slow redox kinetics caused by high conversion energy barrier. Some previous work has proposed several feasible methods to alleviate the above difficulties, such as adding various conductive carbons and matching new solid-state electrolytes to improve the 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-state electrolyte needs to be added to construct the three-phase interface between the sulfur component, the conductive carbon and the solid-state electrolyte during the preparation of the positive electrode, which significantly increases the tortuosity of the charge transport 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 a redox active component, thus accelerating the reaction kinetics of the all-solid-state lithium-sulfur battery and contributing additional capacity. Halogen-based elemental iodine (I2) can insert into the crystal structure of sulfur-based cathodes, thus increasing the conductivity of composite sulfur-based cathodes. If lithium halide and elemental iodine can be introduced into the conversion-type sulfur-based cathode to replace part of the non-active conductive carbon, the energy density of the all-solid-state lithium-sulfur battery will be further improved.

[0005] The prior art has reported that the electrochemical performance can be improved by compounding metal halides in sulfur-based positive electrode materials. For example, CN118630131A discloses a preparation method of a composite sulfur positive electrode with the introduction of an iodide additive, and the solid-state lithium-sulfur battery positive electrode comprises a sulfur / carbon composite material, a conductive agent, a solid-state electrolyte, a binder and an iodide additive. By introducing the iodide additive into the solid-state lithium-sulfur battery positive electrode, the solid-phase conversion energy barrier of the active material sulfur is significantly reduced, the positive electrode reaction kinetics is promoted, thereby reducing the battery polarization and improving the active material utilization rate, and the capacity and rate performance of the battery are improved. The iodide additive is at least one of LiI, PI3, CaI2, AgI and NaI. CN116018699A discloses a positive electrode mixture for a composite full-solid lithium-sulfur battery, 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 the solid sulfur or its discharge product (A) to form a solid solution, and the halide ions partially replace 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 a solid-state battery, comprising: 30-80 wt% of Li2S, 10-40 wt% of one or more second lithium compounds selected from LiI, LiBr, LiNO3 and LiNO2, and 0-30 wt% of a conductive carbon material. The second lithium compound can form an electron-withdrawing group with high electronegativity during charging, thereby improving 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 catalysis of the decomposition of lithium sulfide and the lithiation of sulfur, and thereby improves the specific capacity of the electrode material. CN110957483A discloses a preparation method of a sulfur composite positive electrode material, comprising the following steps: 1) mixing a lithium ion matrix material and a conductive matrix material, then ball milling to obtain a mixture A; 2) mixing elemental sulfur with the mixture A, then ball milling to obtain a mixture B; 3) under the protection of inert gas, the mixture B is heat treated by a melting diffusion method, and then cooled to obtain a sulfur composite positive electrode material. The 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 of compounding lithium halide such as LiI and sulfur-based positive electrode active material to form a positive electrode, but the above patent's composite positive electrode contains sulfur positive electrode material inherent to the problem of low electron conduction between the bodies, which still needs to add more non-active conductive carbon material to improve the electrical conductivity, and the composite positive electrode material obtained by conventional ball milling method has limited minimum particle size, and the contact between various materials is not tight, the formation of non-conductive interface, void or delamination area limits the effective diffusion of lithium ions, resulting in increased interface impedance and limited utilization of active materials in the electrode. The present application compiles halogen-based substances, including elemental iodine and halogen-based salt LiX (X includes Cl, Br, I), sulfur-based positive electrode and solid electrolyte, and the obtained multi-mechanism energy storage positive electrode not only can fully exert the capacity of these materials, but also effectively solve the problems of low electrical conductivity of active sulfur-based positive electrode and difficulty in obtaining small size positive electrode material to enhance the contact between various materials, which is expected to further improve the energy density of solid-state lithium-sulfur battery. SUMMARY

[0007] To solve the above challenges of high solid-state conversion barrier of full solid-state lithium-sulfur battery leading to slow redox kinetics, low electrical conductivity of active sulfur-based positive electrode inherent to the material, and poor contact between materials caused by large particle size, which leads to difficulty in further improving the capacity of positive electrode material, the present application compiles sulfur-based positive electrode and lithium halide, iodine element to obtain halogen-based sulfur-based composite positive electrode, which not only improves the reaction kinetics, but also fully utilizes the capacity of the three materials, and further improves the energy density of full solid-state lithium-sulfur battery. The present application provides a halogen-based sulfur-based composite positive electrode material, which improves the low electrical conductivity of sulfur-based positive electrode and large particle size through the joint action of halogen-based active material, sulfur-based positive electrode active material and solid electrolyte, effectively reduces the proportion of inert ingredients such as conductive carbon and non-electrochemical active electrolyte in the positive electrode system, improves the energy density of the positive electrode material, and has broad research space and application prospect. The present application provides the following technical solutions to solve the above technical problems:

[0008] A halogen-based sulfur-based composite positive electrode material, comprising the following mass parts of raw materials: 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:

[0009] 1) First, the sulfur-based positive electrode active material and iodine element are subjected to high-speed ball milling and low-temperature heat treatment under vacuum conditions, and then subjected to ball milling and mixing with other materials;

[0010] 2) and lithium halide ball-milling, also high-temperature heat treatment, high-temperature heat treatment, if the material exists sulfide solid electrolyte, need to be carried out in an inert atmosphere;

[0011] Further, the particle size of the iodine sulfide 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 positive electrode material is sulfur, after ball milling, high-temperature heat treatment at a temperature higher than the melting point of sulfur is also required to ensure that it can effectively infiltrate the oxygen-based positive electrode material and the conductive carbon material, and then an effective electron transport network can be built. In high-temperature heat treatment, if the material contains sulfide solid electrolyte, it needs to be carried out in an inert atmosphere.

[0013] The technical idea of the present application is to mix sulfur-based positive electrode active material and lithium halide, iodine, conductive carbon material, sulfide solid electrolyte by ball milling to obtain a composite material. However, there are certain requirements for the order of ball milling, i.e. the ball milling of sulfur-based positive electrode active material and iodine is required first, and the ball milling is high-speed high-energy ball milling (500-800 rpm), and low-temperature heat treatment at a temperature higher than the melting point of iodine sulfide (generally 80-120℃) is required to enable the iodine to fully react with the sulfur-based positive electrode active material to form iodine sulfide, thereby enhancing the bulk conductivity, and then mixed with other materials (one or more of lithium halide, conductive carbon material, and sulfide solid electrolyte). The order of ball milling with lithium halide, conductive carbon material, and sulfide solid electrolyte is not particularly limited, one material can be added, or multiple materials can be added simultaneously for ball milling.

[0014] Further, the high-speed ball milling speed is 500-800 rpm, which is equivalent to high-energy ball milling, the purpose is to make the halogen-based material and the sulfur-based positive electrode material more uniform, the iodine can fully react with the sulfur-based positive electrode, and at the same time the particle size of the positive electrode material can be reduced, the specific surface area can be increased, thereby enhancing the solid-solid contact between the materials, making the material mixing more uniform and compact, and reducing the interface resistance; the low-temperature heat treatment under vacuum is heating at 80-120℃ for 3-5h under a vacuum degree of 1-5mbar; the high-temperature heat treatment is heat treatment at 160-200℃ for 5-10h, except for the ball milling of the material and the halogen-based material, which requires high-energy ball milling, the ball milling speed of other materials is 100-300rpm.

[0015] Further, 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); and 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. The melting point of sulfur is 155°C, and the high-temperature heat treatment is performed at a temperature higher than the melting point of sulfur, so that the sulfur can be effectively infiltrated, and an effective electron transport network can be constructed.

[0016] Further, the sulfide solid electrolyte is selected from at least one of Li2GeS3, Li4GeS4, Li2ZnGeS4, Li 4-2x Zn x GeS4(wherein 0≤x≤1), Li5GaS4, Li 4+x+y (Ge 1-y-x Ga x )S4(wherein 0≤x≤0.2, 0≤y≤1), Li 10 GeP2S 12xy O x F y (wherein 0≤x≤1, 0≤y≤1), Li 2+2x Zn 1-x GeO4(wherein 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=M, Sn, or Si, 0≤x≤2), xLi2S·(100-x)P2S5(wherein x is 50-87.5), Li6PS5X (X=Cl, Br, or I, for example, Li3PS4, Li7P3S 11 , Li 10 GeP2S 12 , Li6PS5Cl).

[0017] The inventors unexpectedly found that in the sulfur-based positive electrode material, the introduced halogen includes lithium halide and elemental iodine, the elemental iodine can be inserted into the crystal structure of the sulfur-based positive electrode, contributing new states within the band gap of sulfur, and the formed iodide not only can introduce electronic conductivity, reduce the slow redox kinetics caused by the intrinsic low conductivity of the sulfur-based positive electrode; and the particle size after the reaction is smaller than that of the traditional sulfur-based positive electrode, 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 the reduction of particle size also facilitates the increase of contact with the solid-state electrolyte and the conductive carbon material, reduces the void problem in the solid-state positive electrode which causes ion blockage, thereby improving the utilization rate of active material. The introduced lithium halide has very high ionic conductivity, which 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 the two halogen-based substances not only enables the capacity of the sulfur-based positive electrode to be more fully developed; on the other hand, part of the halogen-based material can also act as a redox active component, and accordingly contribute some additional capacity, thereby improving the capacity of the positive electrode. However, the order of ball milling needs to be controlled, and the high-speed ball milling of the iodine element is performed first to ensure that it can react with part of the sulfur-based positive electrode, and then lithium halide is introduced for ball milling. The ball milling of the conductive carbon material and the sulfide solid electrolyte needs to be mixed uniformly after the reaction of the sulfur-based positive electrode with 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 the sulfide solid electrolyte already exists in the material, it needs to be heat treated in an inert gas condition, because the stability of the sulfide solid electrolyte in air is very poor and it is extremely sensitive to water and oxygen. Once the sulfide solid electrolyte is introduced, the inert atmosphere environment needs to be controlled.

[0018] In the traditional sulfur-based positive electrode system, because the sulfur-based positive electrode has relatively low electronic and ionic conductivity, it is necessary to add a very high proportion of conductive carbon material and solid-state electrolyte in the sulfur-based positive electrode system to realize effective charge transfer. The halogen-based sulfur-based composite positive electrode material provided by the present application has very high ionic and electronic conductivity, and can reduce the proportion of the content of the conductive carbon and the solid-state electrolyte in the traditional sulfur-based positive electrode material. The conductive carbon material is an inert material and does not contribute to the capacity of the battery. In the sulfur composite positive electrode material, part of the conductive carbon is replaced by the electrochemically active halogen-based positive electrode material. This part of the halogen-based positive electrode material can not only realize the function of transmitting electrons as the original conductive carbon, but also can exert a certain electrochemical capacity, which will further improve the capacity of the battery. Using the halogen-based positive electrode material to replace part of the solid-state electrolyte can further enhance the interfacial transport of lithium ions to solve the main challenge faced by the all-solid-state lithium-sulfur battery, i.e. the slow oxidation-reduction kinetics caused by the high solid-state conversion energy barrier. However, it is necessary to control the ball milling mixing sequence and the ball milling conditions of lithium halide and iodine element, i.e. first ball milling mixing and heating of the sulfur-based positive electrode material and iodine element, and then ball milling mixing of lithium halide, conductive carbon material and solid-state electrolyte. It should be noted that if the material already contains a sulfur-containing solid-state electrolyte, the subsequent operation needs to be carried out under inert gas protection conditions.

[0019] Further, the present application also provides a preparation method of the halogen-based sulfur-based composite positive electrode material, comprising the following steps:

[0020] (S1) mixing the sulfur-based positive electrode material and iodine element, high-speed ball milling under inert atmosphere, and then low-temperature heat treatment under vacuum condition to obtain a precursor I;

[0021] (S2) mixing the precursor I with lithium halide and conductive carbon material, ball milling under inert atmosphere, and then high-temperature heat treatment to obtain a precursor II;

[0022] (S3) ball milling the precursor II and sulfide solid-state electrolyte under inert atmosphere to obtain a halogen-based sulfur-based composite positive electrode.

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

[0024] Further, the high-speed ball milling rotation speed is 500-800 rpm, the low-temperature heat treatment under vacuum condition is heating at 1-5 mabr vacuum degree and 80-120℃ for 3-5h; the high-temperature heat treatment is heat treatment at 160-200℃ for 5-10h; in steps (S2) and (S3), the ball milling rotation speed is 100-300 rpm.

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

[0026] The present application has the following beneficial effects:

[0027] I. By adding halogen-based substances in the conversion-type sulfur-based positive electrode energy storage material, the advantages of two kinds of electrode materials are integrated and the deficiencies are complemented. Iodine can be inserted into the crystal structure of the sulfur-based positive electrode, introducing electronic conductivity and reducing the slow oxidation-reduction kinetics caused by the intrinsic low conductivity of the sulfur-based positive electrode. Moreover, the particle size after the reaction is smaller than that of the traditional sulfur-based positive electrode, and the small particle size can increase the contact with the solid-state electrolyte and the conductive carbon material, reduce the void problem that causes ion blockage in the solid-state positive electrode, thereby improving the electrochemical reaction kinetics of the battery and the utilization rate of the active material.

[0028] II. The halogen-based positive electrode material after energy storage can replace part of the conductive carbon and solid-state electrolyte material that needs to be added in the sulfur-based positive electrode. The conductive carbon material does not have electrochemical activity and is an inert component. By reducing the content of the inert component of the conductive carbon, the halogen-based positive electrode material added can also contribute to a certain capacity, which can effectively improve the energy density of the battery.

[0029] III. The halogen-based material can enhance the interfacial transport of lithium ions, provide abundant catalytic sites for sulfur species, improve the reversibility of the sulfur-based positive electrode, and make the capacity of the sulfur-based positive electrode more fully developed.

[0030] In summary, the halogen-based catalyst sulfur composite positive electrode disclosed in the present application can simultaneously exhibit the advantages of halogen-based positive electrode materials and sulfur-based positive electrode materials, reduce the size of the positive electrode material, enhance the solid-solid contact between materials, effectively reduce the proportion of inert components such as conductive carbon and non-electrochemically active electrolyte in the positive electrode system, greatly improve the energy density of the positive electrode material, and has a wide research space and application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 It is the X-ray diffraction picture of the precursor I applied in the halogen-based sulfur composite positive electrode of Example 1.

[0032] Figure 2 It is the atomic force microscope photo of the halogen-based sulfur composite positive electrode applied in Example 1.

[0033] Figure 3 It is the atomic force microscope photo of the sulfur composite positive electrode without iodine monomer composite in Comparative Example 1.

[0034] Figure 4 It is the scanning electron microscope photo of the halogen-based sulfur composite positive electrode applied in Example 1.

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

[0036] The application is further described below in connection with specific examples, but the application is not limited to the following examples. In the following examples, the experimental methods described are conventional methods unless otherwise specified; the reagents and materials described are commercially available unless otherwise specified. The following specific examples are provided to assist in understanding the halogen-based sulfur composite cathode described in the application.

[0037] Example 1

[0038] (S1) 40 parts by mass of elemental sulfur powder and 8 parts by mass of elemental iodine were mixed, and the mixed material was added to a ball mill tank under argon protection, with a ball-to-material ratio of 100:1, a rotation speed of 600 rpm, and ball milling for 8 h. The mixture after ball milling was transferred to a round-bottom flask, vacuumed to 2 mbar using a joint with a piston, and then heated at 80°C for 3 h to react. After natural cooling, precursor I was obtained.

[0039] (S2) Precursor I and 5 parts by mass of lithium iodide and 8 parts by mass of conductive carbon black Super P powder were mixed, and the mixture was ball milled under argon atmosphere at 300 rpm for 5 h. Then, the mixture was incubated 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 were mixed, and the mixed material was added to a ball mill tank under argon protection, with a ball-to-material ratio of 100:1, a rotation speed of 300 rpm, and ball milling for 18 h to obtain a halogen-based sulfur composite cathode material.

[0041] (S4) Assembly of all-solid-state lithium-sulfur battery: In an argon-protected glove box, 70 mg of sulfide solid electrolyte Li6PS5Cl was poured into a mold, and a pressure of 400 MPa was applied to shape it into a sulfide solid electrolyte Li6PS5Cl ceramic sheet. 4 mg of halogen-based sulfur composite cathode material powder prepared in step S3 above was poured into one side of the pressed double-inorganic composite solid electrolyte ceramic sheet, and a pressure of 500 MPa was applied to make the sulfur cathode and the double-inorganic composite solid electrolyte in close contact. Finally, a lithium-indium alloy ceramic sheet was placed on the other side of the double-inorganic composite solid electrolyte ceramic sheet, and the full battery was tested under a pressure of 100 MPa.

[0042] Figure 1 X-ray diffraction pattern of the precursor I obtained in step S1 of Example 1. The peaks in the blue area in the figure indicate that sulfur and elemental iodine react to form iodine sulfide.

[0043] Figure 2An atomic force microscope photograph of the halogen-based sulfur-based composite positive electrode material prepared in Step S3 of Example 1 is shown. As can be seen from the dotted line frame, the particle size of the iodized sulfur is about 120-150 nm, and the particle size is smaller and the solid-solid contact with the solid electrolyte and the conductive carbon, etc. is more intimate.

[0044] Figure 3 A scanning electron microscope photograph of the halogen-based sulfur-based composite positive electrode material prepared in Step S3 of Example 1 is shown.

[0045] Figure 5 A first cycle cyclic voltammogram of the full solid-state battery using the halogen-based sulfur-based composite positive electrode material in Example 1 is shown.

[0046] Example 2

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

[0048] Example 3

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

[0050] Example 4

[0051] The other conditions are the same as 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 in Example 1, except that the sulfur-based positive electrode material is changed from 40 parts by mass of sulfur elemental powder to 45 parts by mass of Li2S. From the atomic force microscope photograph, the particle size of the iodized sulfur in the composite positive electrode material obtained in Example 5 is 150-190 nm.

[0054] Comparative Example 1

[0055] Other conditions are same as example 1, the difference is to cancel step (S1), that is, not to add iodine element. In step (S2), 40 parts by mass of sulfur element powder and 15 parts by mass of lithium iodide, 8 parts by mass of conductive carbon black Super P powder are mixed.

[0056] Figure 4 The atomic force microscope photo of the sulfur composite cathode prepared in step S3 in 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] Other conditions are same as example 1, the difference is that in step (S1), the ball milling speed is 200 rpm. In the obtained composite cathode material, the particle size of iodized sulfur is about 200-250 nm.

[0059] Comparative Example 3

[0060] (S1) Sulfur-based cathode material and halogen-based material composite: 40 parts by mass of sulfur element powder, 5 parts by mass of lithium iodide, 8 parts by mass of iodine element, 8 parts by mass of conductive carbon black Super P powder are mixed, and the mixed material is added to an argon-protected ball milling tank, the ball-to-material ratio is controlled to be 100:1, the rotating speed is 600 rpm, and the ball milling is carried out for 8 h, then the mixture after ball milling is heated at a temperature of 160°C for 6 hours in an argon atmosphere, to obtain a precursor I;

[0061] (S2) The precursor I and 40 parts by mass of sulfur-containing solid electrolyte Li6PS5Cl are mixed, and the mixed material is added to an argon-protected ball milling tank, the ball-to-material ratio is controlled to be 100:1, the rotating speed is 200 rpm, and the ball milling is carried out for 18 h, to obtain a halogen-based sulfur-based composite cathode material.

[0062] The battery is assembled as in step (S4) of Example 1.

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

[0064] Comparative Example 4

[0065] (S1) 40 parts by mass of sulfur element powder, 5 parts by mass of lithium iodide, 8 parts by mass of conductive carbon black Super P powder are mixed, and the mixed material is added to an argon-protected ball milling tank, the ball-to-material ratio is controlled to be 100:1, the rotating speed is 200 rpm, and the ball milling is carried out for 8 h, and the precursor I is obtained after heat treatment at 170°C for 6 h;

[0066] (S2) precursor I and 8 parts by mass of iodine element were mixed, and ball-milling was performed under an argon atmosphere at 500 rpm for 8 h, and then the mixture was heated at a temperature of 100 DEG C for 6 h under an argon atmosphere to obtain precursor II;

[0067] (S3) precursor II and 40 parts by mass of a sulfur-containing solid electrolyte Li6PS5Cl were mixed, and the mixture was added to a ball-milling tank under an argon atmosphere, a ball-to-material ratio of 100:1 was controlled, a rotation speed was 200 rpm, and ball-milling was performed for 18 h to obtain a halogen-sulfur composite positive electrode material.

[0068] The battery was assembled according to step (S4) of Example 1.

[0069] That is, compared with Example 1, the ball-milling mixing and heating of sulfur element powder and lithium iodide were performed first, and then the ball-milling mixing and heating of iodine element were performed.

[0070] Application Example

[0071] Constant current charge and discharge tests were performed on a multi-channel blue electric tester in a voltage range of 1.5-3 V, and the charge and discharge rates were both 0.2 C, and the ambient temperature was room temperature 25 DEG C.

[0072] The electrochemical performance of the full solid-state batteries using the halogen-sulfur composite positive electrode materials of the above examples and comparative examples is shown in Table 1 below.

[0073] Table 1 Electrochemical performance test results of halogen-sulfur composite positive electrode materials

[0074]

[0075]

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

Claims

1. A halogen-based sulfide-based composite positive electrode material, characterized by, The raw materials include the following quality parts: 35-45 parts of sulfur-based positive active material, 3-5 parts of lithium halide, 6-10 parts of iodine, 5-10 parts of conductive carbon material, 30-50 parts of sulfide solid electrolyte; the iodine reacts with the sulfur-based positive active material to convert into iodized sulfur; The preparation of the halogen-based sulfur-based composite positive material includes the following steps: (S1) mixing the sulfur-based positive material and the iodine, high-speed ball milling in an inert atmosphere, and then low-temperature heat treatment under vacuum conditions to obtain a precursor I; (S2) mixing the precursor I with lithium halide and conductive carbon material, ball milling in an inert atmosphere, and then high-temperature heat treatment to obtain a precursor II; (S3) ball milling the precursor II and the sulfide solid electrolyte in an inert atmosphere to obtain a halogen-based sulfur-based composite positive electrode.

2. The halogen-based sulfido complex cathode material of claim 1, wherein, The particle size of the iodized sulfur particles is 120-200 nm.

3. The halogen-based sulfur-based composite cathode material of claim 1, wherein, The particle size of the iodized sulfur particles is 120-160 nm.

4. The halogen-based sulfur-based composite cathode material of claim 1, wherein, The high-speed ball milling rotation speed is 500-800 rpm, the low-temperature heat treatment under vacuum conditions is heating at 80-120℃ for 3-5 h under a vacuum degree of 1-5 mbar, and the high-temperature heat treatment is heat treatment at 160-200℃ for 5-10 h.

5. The halogen-based sulfur-based composite cathode material of claim 1, wherein, The sulfur-based positive active material is selected from at least one of sulfur, lithium sulfide, iron sulfide, copper sulfide, and molybdenum disulfide; and the conductive carbon material is selected from at least one of carbon nanotubes, conductive carbon black, acetylene black, and Ketjen black.

6. The halogen-based sulfur-based composite cathode material of claim 1, wherein, Li2GeS3, Li4GeS4, Li2ZnGeS4, Li 4-2x Zn x GeS4, wherein 0≤ x ≤1, Li5GaS4, Li 4+x+y (Ge 1-y-x Ga x )S4, wherein 0≤ x ≤0.2, 0≤ y ≤1, Li 10 GeP2S 12xy O x F y , wherein 0≤ x ≤1, 0≤ y ≤1, Li 2+2x Zn 1-x GeO4, wherein 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, wherein x is 50-87.5, Li6PS5X, wherein X = Cl, Br or I, at least one of.

7. The halogen-based sulfido complex cathode material of claim 6, wherein, The sulfide solid electrolyte is selected from at least one of Li3PS4, Li7P3S 11 10 GeP2S 12 , Li6PS5Cl.​ 8. The halogen-based sulfur-based composite cathode material of claim 1, wherein, The inert atmosphere is nitrogen and / or argon.

9. The halogen-based sulfur-based composite cathode material of claim 1, wherein, The high-speed ball milling rotation speed is 500-800 rpm, the low-temperature heat treatment under vacuum conditions is heating at 80-120℃ for 3-5 h under a vacuum degree of 1-5 mbar, and the high-temperature heat treatment is heat treatment at 160-200℃ for 5-10 h; in steps (S2) and (S3), the ball milling rotation speed is 100-300 rpm.

10. A full solid-state lithium-sulfur battery, the positive electrode of which comprises the halogen-based sulfur-based composite positive material according to any one of claims 1-9.

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