Composite solid electrolyte and method for preparing the same

Abstract

This invention discloses a composite solid electrolyte and its preparation method, relating to the field of battery technology. The preparation method of the composite solid electrolyte includes the following steps: mixing raw materials for preparing a sulfide solid electrolyte and bismuth iodide, then sintering at a preset temperature for a preset time to obtain a bismuth iodide-doped sulfide solid electrolyte; coating the surface of the bismuth iodide-doped sulfide solid electrolyte with barium titanate to obtain the composite solid electrolyte; the mass of bismuth iodide accounts for 3% to 8% of the total mass of the raw materials for preparing the sulfide solid electrolyte. This invention uses bismuth iodide to dope and modify the sulfide solid electrolyte, improving air stability while enhancing the coating performance of barium titanate and reducing the impact of barium titanate coating on the ionic conductivity of the sulfide solid electrolyte. Simultaneously, barium titanate coating can further improve air stability and mitigate bismuth iodide doping defects, i.e., preventing bismuth iodide from absorbing moisture and preventing iodide ions from being oxidized by air.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a composite solid electrolyte and its preparation method. Background Technology

[0002] Among various solid electrolytes, sulfide solid electrolytes possess excellent mechanical ductility and high ionic conductivity, with room temperature ionic conductivity reaching 10⁻⁶. -3 ~10 -2 While its S / cm ratio is close to or even better than that of liquid electrolytes, the core weakness of sulfide solid electrolytes is their extremely poor chemical stability. Especially when exposed to air (containing components such as O2, H2O, and CO2), they are prone to undergoing multiple irreversible chemical reactions. This not only releases toxic and harmful hydrogen sulfide (H2S) gas, posing safety and environmental hazards, but also causes significant changes in the electrolyte's morphology and mass, destroying its crystal structure and producing a series of harmful side reactions. Ultimately, this greatly degrades its key electrochemical properties such as ionic conductivity and interfacial compatibility.

[0003] Currently, the method to improve the air stability of sulfide solid electrolytes is coating. For example, using barium titanate to coat sulfide solid electrolytes can improve air stability and suppress the release of H2S. However, on the one hand, the coating of barium titanate will reduce the ionic conductivity of the sulfide solid electrolyte; on the other hand, barium titanate has poor wettability with sulfide solid electrolytes, low lattice fit, poor coating performance, and unsatisfactory coating effect.

[0004] Therefore, existing technologies still need to be improved and developed. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the purpose of this invention is to provide a composite solid electrolyte and its preparation method, which aims to solve the problems of reduced ionic conductivity and unsatisfactory coating effect in existing solid electrolytes using barium titanate-coated sulfides.

[0006] The technical solution of the present invention is as follows: In a first aspect, the present invention provides a method for preparing a composite solid electrolyte, comprising the following steps: The raw materials for preparing sulfide solid electrolytes and bismuth iodide are mixed, and then sintered at a preset temperature for a preset time to obtain bismuth iodide-doped sulfide solid electrolytes; the mass of bismuth iodide accounts for 3% to 8% of the total mass of the raw materials for preparing sulfide solid electrolytes; The composite solid electrolyte is obtained by coating barium titanate onto the surface of the bismuth iodide-doped sulfide solid electrolyte.

[0007] Optionally, the raw materials for preparing sulfide solid electrolyte and bismuth iodide are added to a pulverizer for mixing. The parameters of the pulverizer are set as follows: 6 to 10 pulverization cycles, with each pulverization cycle lasting 20 to 40 seconds.

[0008] Optionally, the preset temperature is 440~480 ℃, and the preset time is 14~18 h.

[0009] Optionally, bismuth iodide-doped sulfide solid electrolyte and barium titanate are added to a polishing machine for mixing and coating, thereby coating the surface of the bismuth iodide-doped sulfide solid electrolyte with barium titanate. The parameters of the polishing machine are set as follows: rotation speed 10~50 r / min, time 10~30 min; or, Bismuth iodide-doped sulfide solid electrolyte and barium titanate were added to a ball mill for mixing and coating, thereby coating the surface of the bismuth iodide-doped sulfide solid electrolyte with barium titanate. The parameters of the ball mill were set as follows: rotation speed of 120~150 rpm and time of 0.5~3 h.

[0010] Optionally, in the step of adding bismuth iodide-doped sulfide solid electrolyte and barium titanate into a polishing machine for mixing and coating, the mass of barium titanate accounts for 5% to 20% of the mass of the bismuth iodide-doped sulfide solid electrolyte; Alternatively, in the step of adding bismuth iodide-doped sulfide solid electrolyte and barium titanate into a ball mill for mixing and coating, the mass of barium titanate accounts for 5% to 20% of the mass of the bismuth iodide-doped sulfide solid electrolyte.

[0011] Optionally, the raw materials for preparing the sulfide solid electrolyte include Li2S, P2S5 and LiCl; the mass ratio of Li2S, P2S5 and LiCl is (2~2.2):(0.4~0.6):(1.3~1.5).

[0012] Optionally, the preparation method of the composite solid electrolyte specifically includes the following steps: Li₂S, P₂S₅, LiCl, and bismuth iodide are added to a pulverizer and mixed. The mass ratio of Li₂S, P₂S₅, and LiCl is (2~2.2):(0.4~0.6):(1.3~1.5). The mass of bismuth iodide accounts for 3%~8% of the total mass of Li₂S, P₂S₅, and LiCl. The parameters of the pulverizer are set as follows: 6~10 pulverization cycles, with each pulverization cycle lasting 20~40 seconds. The product obtained in the pulverizer is placed in a muffle furnace and heated to 440-480℃ at a rate of 3-5℃ / min, and sintered at 440-480℃ for 14-18 h to obtain bismuth iodide doped sulfide solid electrolyte. Bismuth iodide-doped sulfide solid electrolyte and barium titanate are added to a polishing machine and mixed and coated to obtain the composite solid electrolyte. The parameters of the polishing machine are set as follows: rotation speed of 10~50 r / min and time of 10~30 min. The mass of barium titanate accounts for 5%~20% of the mass of bismuth iodide-doped sulfide solid electrolyte.

[0013] In a second aspect, the present invention provides a composite solid electrolyte, wherein it is prepared by the preparation method described above.

[0014] Beneficial Effects: This invention first dopes a sulfide solid electrolyte with bismuth iodide, followed by barium titanate coating. Using bismuth iodide to modify the sulfide solid electrolyte improves air stability while enhancing the coating performance of barium titanate and reducing the impact of barium titanate coating on the ionic conductivity of the sulfide solid electrolyte. Simultaneously, barium titanate coating further improves air stability and mitigates defects caused by bismuth iodide doping, preventing moisture absorption and oxidation of iodide ions by air. The combined effect of bismuth iodide doping and barium titanate coating achieves dual modification of the inner and outer layers of the sulfide solid electrolyte, improving its air stability and ensuring high ionic conductivity. Therefore, the composite solid electrolyte provided by this invention exhibits high ionic conductivity, good air stability, and structural stability. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the preparation process of the composite solid electrolyte in an embodiment of the present invention.

[0016] Figure 2 The images show the XRD patterns of BTO@BiI3-LPSC-1 in Example 1 and LPSC-1 in Comparative Example 1.

[0017] Figure 3 In the image, (a) is the SEM image of LPSC-1 in Comparative Example 1, and (b) is the SEM image of BTO@BiI3-LPSC-1 in Example 1.

[0018] Figure 4 The images show the EDS scan results of two different elements of BTO@BiI3-LPSC-1 in Example 1, where (a) is the EDS scan result of Ba and (b) is the EDS scan result of Ti. Detailed Implementation

[0019] This invention provides a composite solid electrolyte and its preparation method. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention.

[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0021] If the embodiments of the present invention involve descriptions such as "first" or "second", such descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated.

[0022] This invention provides a method for preparing a composite solid electrolyte, wherein, as shown in the embodiments, Figure 1 As shown, it includes the following steps: S1. The raw materials for preparing sulfide solid electrolyte (i.e., the raw materials required for preparing undoped sulfide solid electrolyte) and bismuth iodide are mixed, and then sintered at a preset temperature for a preset time to obtain bismuth iodide-doped sulfide solid electrolyte; the mass of bismuth iodide accounts for 3% to 8% of the total mass of the raw materials for preparing sulfide solid electrolyte (for example, it can be 3%, 4%, 5%, 6%, 7% or 8%, etc.; this ratio can enable bismuth iodide doping to better improve ionic conductivity and improve the subsequent barium titanate coating performance); S2. Barium titanate is coated on the surface of the bismuth iodide-doped sulfide solid electrolyte to obtain the composite solid electrolyte.

[0023] The method provided by this invention can achieve uniform doping of bismuth iodide and uniform coating of barium titanate without impairing the performance of sulfide solid electrolytes, and can even improve the performance of sulfide solid electrolytes.

[0024] This invention first dopes a sulfide solid electrolyte with bismuth iodide, then coats it with barium titanate. Specifically, this invention improves the barium titanate coating performance through bismuth iodide doping. The bismuth iodide doping first modifies the sulfide solid electrolyte, passivating the hydrolytic active sites and reducing hydrogen sulfide release. Bismuth iodide doping also improves the interfacial bonding between barium titanate and the sulfide solid electrolyte, thereby improving the uniformity of barium titanate coating. Specifically, the Bi and I atoms on the surface of the bismuth iodide-doped sulfide solid electrolyte core undergo ion interpenetration with the barium titanate shell, improving the lattice compatibility between the barium titanate shell and the sulfide solid electrolyte core. When the barium titanate shell cracks, these atoms migrate in situ to fill the cracks, thus improving the barium titanate coating performance, reducing coating defects, and increasing the stability of the coating layer. Furthermore, using bismuth iodide to dope the sulfide solid electrolyte results in a large bismuth ion radius, increasing the lithium ion (Li) content. +The vacancy in the bismuth iodide-barium electrolyte (BTO) and the high electronegativity of iodide ions enhance ionic conductivity. Therefore, this invention, through bismuth iodide doping, improves air stability while simultaneously enhancing the coating performance of barium titanate and reducing the impact of barium titanate coating on the ionic conductivity of the sulfide solid electrolyte. Furthermore, barium titanate coating further improves air stability because bismuth iodide has limited moisture resistance, and iodide ions are easily oxidized by air. Therefore, barium titanate coating also prevents the aforementioned defects of bismuth iodide doping. In summary, using bismuth iodide for doping modification of the sulfide solid electrolyte improves air stability while enhancing the coating performance of barium titanate and reducing the impact of barium titanate coating on the ionic conductivity of the sulfide solid electrolyte. At the same time, barium titanate coating further enhances air stability and mitigates the defects of bismuth iodide doping, namely, preventing bismuth iodide from absorbing moisture and preventing iodide ions from being oxidized by air. Bismuth iodide doping and barium titanate coating together achieve dual modification of the inner and outer layers of the sulfide solid electrolyte, improving its air stability and ensuring high ionic conductivity. Therefore, the composite solid electrolyte provided by the present invention has high ionic conductivity, good air stability and structural stability.

[0025] In step S1, in some embodiments, the raw materials for preparing the sulfide solid electrolyte and bismuth iodide are added to a pulverizer for mixing. The parameters of the pulverizer are set as follows: the number of pulverizations is 6 to 10 times (for example, 6, 7, 8, 9 or 10 times), and the time for each pulverization is 20 to 40 seconds (for example, 20 seconds, 22 seconds, 25 seconds, 28 seconds, 30 seconds, 32 seconds, 35 seconds, 38 seconds or 40 seconds, etc.).

[0026] In some embodiments, the preset temperature is 440~480 ℃, for example, it can be 440 ℃, 445 ℃, 450 ℃, 455 ℃, 460 ℃, 465 ℃, 470 ℃, 475 ℃ or 480 ℃, etc., and the preset time is 14~18 h, for example, it can be 14 h, 15 h, 16 h, 17 h or 18 h, etc.

[0027] In some embodiments, the raw materials for preparing the sulfide solid electrolyte include Li₂S, P₂S₅, and LiCl; the mass ratio of Li₂S, P₂S₅, and LiCl is (2~2.2):(0.4~0.6):(1.3~1.5), for example, 2:0.4:1.3, 2:0.5:1.3, 2:0.6:1.3, 2:0.4:1.4, 2:0.5:1.4, 2:0.6:1.4, 2:0.4:1.5, 2... :0.5:1.5, 2:0.6:1.5, 2.1:0.4:1.3, 2.1:0.5:1.3, 2.1:0.6:1.3, 2.1:0.4:1.5, 2.1:0.5:1.5, 2.1:0.6:1.5, 2.2:0.4:1.3, 2.2:0.5:1.3, 2.2:0.6:1.3, 2.2:0.4:1.5, 2.2:0.5:1.5 or 2.2:0.6:1.5, etc.

[0028] In step S2, in some embodiments, bismuth iodide-doped sulfide solid electrolyte and barium titanate are added to a polishing machine for mixing and coating, thereby coating the surface of the bismuth iodide-doped sulfide solid electrolyte with barium titanate. The parameters of the polishing machine are set as follows: rotation speed of 10~50 r / min (e.g., 10 r / min, 20 r / min, 30 r / min, 40 r / min, or 50 r / min, etc.), and time of 10~30 min (e.g., 10 min, 15 min, 20 min, 25 min, or 30 min, etc.); or, Bismuth iodide-doped sulfide solid electrolyte and barium titanate are added to a ball mill for mixing and coating, thereby coating the surface of the bismuth iodide-doped sulfide solid electrolyte with barium titanate. The parameters of the ball mill are set as follows: rotation speed of 120~150 rpm and time of 0.5~3 h (e.g., 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h or 3 h, etc.).

[0029] Ball milling coating takes a long time, and prolonged coating can easily damage the bismuth iodide-doped sulfide solid electrolyte. Therefore, this invention prefers to perform coating in a polishing machine. Using a polishing machine can achieve a uniform and high coating amount in a short time. The bismuth iodide-doped sulfide solid electrolyte process has low defects. That is, using a polishing machine for coating can achieve high coating output in a short time, while also achieving high coating uniformity. This saves production costs and shortens working time, enabling large-scale mass production.

[0030] In addition, compared with other coating machines (such as ball mills, which require 0.5 to 3 hours to coat and only a few hundred grams to coat at a time), polishing machines can add more coating materials and only require 10 to 30 minutes, effectively solving the problems of small coating amount and long coating time of other coating machines.

[0031] In some embodiments, in the step of adding bismuth iodide-doped sulfide solid electrolyte and barium titanate into a polishing machine for mixing and coating, the barium titanate accounts for 5% to 20% of the mass of the bismuth iodide-doped sulfide solid electrolyte (for example, it can be 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, or 20%, etc.); or, In the step of adding bismuth iodide-doped sulfide solid electrolyte and barium titanate into a ball mill for mixing and coating, the mass of barium titanate accounts for 5% to 20% of the mass of the bismuth iodide-doped sulfide solid electrolyte (for example, it can be 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, or 20%, etc.).

[0032] In some specific embodiments, the preparation method of the composite solid electrolyte specifically includes the following steps: Li₂S, P₂S₅, LiCl, and bismuth iodide are added to a pulverizer and mixed. The mass ratio of Li₂S, P₂S₅, and LiCl is (2~2.2):(0.4~0.6):(1.3~1.5). The mass of bismuth iodide accounts for 3%~8% of the total mass of Li₂S, P₂S₅, and LiCl. The parameters of the pulverizer are set as follows: 6~10 pulverization cycles, with each pulverization cycle lasting 20~40 seconds. The product obtained in the pulverizer is placed in a muffle furnace and heated to 440-480℃ at a rate of 3-5℃ / min, and sintered at 440-480℃ for 14-18 h to obtain bismuth iodide doped sulfide solid electrolyte. The bismuth iodide-doped sulfide solid electrolyte and barium titanate are added to a polishing machine and mixed and coated to obtain the composite solid electrolyte. The parameters of the polishing machine are set as follows: rotation speed of 10~50 r / min and time of 10~30 min. The mass of barium titanate accounts for 5%~20% of the mass of the bismuth iodide-doped sulfide solid electrolyte (for example, it can be 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19% or 20%, etc.).

[0033] The method provided by this invention can achieve uniform doping of bismuth iodide and uniform coating of barium titanate without impairing the performance of the sulfide solid electrolyte, and can even improve its performance. This invention achieves bismuth iodide doping during the synthesis stage of the sulfide solid electrolyte, followed by barium titanate coating using a polishing machine after sintering. 1500 g of bismuth iodide-doped sulfide solid electrolyte can be coated in 20 minutes (while a ball mill can only coat 200 g in 30 minutes). The polishing process is short, efficient, and yields high coating output. This invention passivates the hydrolytic active sites of the sulfide solid electrolyte through bismuth iodide doping, and then coats it with hydrophobic barium titanate, achieving a dual modification effect on the sulfide solid electrolyte. This effectively improves the air stability of the sulfide solid electrolyte and overcomes the defects of reduced ionic conductivity when coated with barium titanate alone and the defects of bismuth iodide doping alone. This invention achieves the goals of non-destructive uniform coating, high coating efficiency and high yield, and improved air stability. Therefore, the present invention also provides a doping coating process for improving the air stability of sulfide solid electrolytes with high coating amount.

[0034] This invention also provides a composite solid electrolyte, which is prepared using the preparation method described above.

[0035] The composite solid electrolyte comprises a bismuth iodide-doped sulfide solid electrolyte core and a barium titanate shell covering the surface of the bismuth iodide-doped sulfide solid electrolyte core.

[0036] In other words, the composite solid electrolyte provided in this embodiment of the invention includes a core and a shell covering the surface of the core. The core is made of bismuth iodide-doped sulfide solid electrolyte, and the shell is made of barium titanate.

[0037] Specifically, there is ion interpenetration between the bismuth iodide-doped sulfide solid electrolyte core and the barium titanate shell.

[0038] This invention first involves doping a sulfide solid electrolyte with bismuth iodide, followed by barium titanate coating. The use of bismuth iodide to modify the sulfide solid electrolyte improves air stability while simultaneously enhancing the coating performance of barium titanate and reducing the impact of barium titanate coating on the ionic conductivity of the sulfide solid electrolyte. Simultaneously, barium titanate coating further improves air stability and mitigates defects caused by bismuth iodide doping, preventing moisture absorption and oxidation of iodide ions by air. The combined effect of bismuth iodide doping and barium titanate coating achieves dual modification of the inner and outer layers of the sulfide solid electrolyte, improving its air stability while ensuring high ionic conductivity. Therefore, the composite solid electrolyte provided by this invention exhibits high ionic conductivity, good air stability, and structural stability.

[0039] Specifically, bismuth iodide doping can passivate the hydrolysis active sites of sulfide solid electrolytes, reducing hydrogen sulfide release. The Bi and I atoms on the surface of the bismuth iodide-doped sulfide solid electrolyte core undergo ion interpenetration with the barium titanate shell, improving the lattice compatibility between the barium titanate shell and the sulfide solid electrolyte core. When the barium titanate shell cracks, these atoms migrate in situ to fill the cracks, thereby improving the coating performance of barium titanate, reducing coating defects, and increasing the stability of the coating layer. Furthermore, using bismuth iodide to dope sulfide solid electrolytes results in a large bismuth ion radius, increasing the lithium ion (Li) content. + The vacancy in bismuth iodide (BIO) allows for the creation of vacancy sites. Iodide ions, with their high negative charge, enhance ionic conductivity. Therefore, this invention, through bismuth iodide doping, improves air stability while simultaneously enhancing the coating performance of barium titanate and reducing the impact of barium titanate coating on the ionic conductivity of the sulfide solid electrolyte. Furthermore, barium titanate coating further improves air stability because bismuth iodide has limited moisture resistance, and iodide ions are easily oxidized by air. Therefore, barium titanate coating also prevents the aforementioned defects associated with bismuth iodide doping. In summary, bismuth iodide doping and barium titanate coating together achieve dual modification of the inner and outer layers of the sulfide solid electrolyte, improving its air stability and ensuring high ionic conductivity.

[0040] This invention does not limit the specific type of sulfide solid electrolyte. For example, in some embodiments, the sulfide solid electrolyte is a lithium phosphorus sulfur chloride solid electrolyte, that is, the bismuth iodide doped sulfide solid electrolyte core is a bismuth iodide doped lithium phosphorus sulfur chloride solid electrolyte core.

[0041] The present invention will be further described below through specific embodiments.

[0042] In the following embodiments, unless otherwise specified, the raw materials and equipment used are all commercially available products.

[0043] The polishing machine used was a Zhengxing brand polishing machine, which was an 8-inch PU (polyurethane) centerless drum vibrating machine. The powder grinder used was a DFT-100 model, purchased from Shanghai Xinnuo Instrument Group Co., Ltd. The planetary ball mill used was model YXQM-8L, purchased from Shanghai Xinnuo Instrument Group Co., Ltd.

[0044] In the following examples, BTO represents barium titanate (BaTiO3).

[0045] In the following examples, the amount of each raw material used is shown in Table 1.

[0046] Table 1. Usage of each raw material

[0047] Wherein, the doping amount of BiI3 refers to the percentage of BiI3 in the total mass of Li2S, P2S5 and LiCl; the coating amount of BTO refers to the percentage of the mass of BTO added during the preparation process in the total mass of the bismuth iodide-doped sulfide solid electrolyte added.

[0048] Example 1 This embodiment provides a method for preparing a composite solid electrolyte (denoted as BTO@BiI3-LPSC-1), comprising the following steps: (1) Li2S, P2S5, LiCl and BiI3 were added to a pulverizer for mixing and refining. The parameters of the pulverizer were set as follows: 6 pulverization times and 40 s for each pulverization time; wherein, as shown in Example 1 in Table 1, the mass ratio of Li2S, P2S5 and LiCl was 2.0:0.4:1.4, and the mass of BiI3 accounted for 8% of the total mass of Li2S, P2S5 and LiCl; (2) The product synthesized in the pulverizer was placed in a muffle furnace and heated to 460 °C at a rate of 3 °C / min, and then held at this temperature for 17 h to obtain a bismuth iodide-doped sulfide solid electrolyte (i.e., BiI3-doped Li). 6.75 PS5Cl 1.75 ), denoted as BiI3-LPSC-1; (3) BiI3-LPSC-1 and BTO (as shown in Example 1 in Table 1, the mass of BTO is 15% of the mass of BiI3-LPSC-1) were added to a polishing machine for mixing and coating. The parameters of the polishing machine were set as follows: rotation speed of 50 r / min and time of 20 min to obtain a composite solid electrolyte, denoted as BTO@BiI3-LPSC-1.

[0049] Comparative Example 1 This comparative example provides a method for preparing a sulfide solid electrolyte (denoted as LPSC-1), wherein the amount of each raw material is shown in Comparative Example 1 in Table 1. The difference between the preparation method of LPSC-1 in this comparative example and Example 1 is only that: in step (1), BiI3 is not added; in step (2), the final product is a sulfide solid electrolyte, denoted as LPSC-1; and step (3) is not performed.

[0050] Comparative Example 2 This comparative example provides a method for preparing a bismuth iodide-doped sulfide solid electrolyte (denoted as BiI3-LPSC-1). The amount of each raw material is shown in Comparative Example 2 in Table 1. The only difference between the preparation method of BiI3-LPSC-1 in this comparative example and Example 1 is that step (3) is not performed.

[0051] Comparative Example 3 This comparative example provides a method for preparing a BTO-coated sulfide solid electrolyte (referred to as BTO-LPSC-1). The amounts of each raw material are shown in Comparative Example 3 in Table 1. The only difference between the preparation method of BTO-LPSC-1 in this comparative example and Example 1 is that: in step (1), BiI3 is not added; in step (2), the final product is a sulfide solid electrolyte, referred to as LPSC-1; in step (3), the final product is a BTO-coated sulfide solid electrolyte, referred to as BTO-LPSC-1.

[0052] Example 2 This embodiment provides a method for preparing a composite solid electrolyte (denoted as BTO@BiI3-LPSC-2), comprising the following steps: (1) Li2S, P2S5, LiCl and BiI3 were added to a pulverizer for mixing and refining. The parameters of the pulverizer were set as follows: 8 pulverization cycles, each pulverization time was 20 s; wherein, as shown in Example 2 in Table 1, the mass ratio of Li2S, P2S5 and LiCl was 2.2:0.5:1.3, and the mass of BiI3 accounted for 3% of the total mass of Li2S, P2S5 and LiCl; (2) The product synthesized in the pulverizer was placed in a muffle furnace and heated to 480 °C at a rate of 5 °C / min, and then held at this temperature for 14 h to obtain a bismuth iodide-doped sulfide solid electrolyte (i.e., BiI3-doped Li). 5.3 PS 4.5 Cl 1.3 ), denoted as BiI3-LPSC-2; (3) BiI3-LPSC-2 and BTO (as shown in Example 2 in Table 1, the mass of BTO is 5% of the mass of BiI3-LPSC-2) were added to a polishing machine for mixing and coating. The parameters of the polishing machine were set as follows: rotation speed of 30 r / min and time of 30 min. The composite solid electrolyte was obtained and denoted as BTO@BiI3-LPSC-2.

[0053] Comparative Example 4 This comparative example provides a method for preparing a sulfide solid electrolyte (denoted as LPSC-2), wherein the amount of each raw material is shown in Comparative Example 4 in Table 1. The difference between the preparation method of LPSC-2 in this comparative example and Example 2 is only that: in step (1), BiI3 is not added; in step (2), the final product is a sulfide solid electrolyte, denoted as LPSC-2; and step (3) is not performed.

[0054] Comparative Example 5 This comparative example provides a method for preparing a bismuth iodide-doped sulfide solid electrolyte (denoted as BiI3-LPSC-2). The amount of each raw material is shown in Comparative Example 5 in Table 1. The only difference between the preparation method of BiI3-LPSC-2 in this comparative example and Example 2 is that step (3) is not performed.

[0055] Comparative Example 6 This comparative example provides a method for preparing a BTO-coated sulfide solid electrolyte (denoted as BTO-LPSC-2). The amounts of each raw material are shown in Comparative Example 6 in Table 1. The only difference between the preparation method of BTO-LPSC-2 in this comparative example and Example 2 is that: in step (1), BiI3 is not added; in step (2), the final product is a sulfide solid electrolyte, denoted as LPSC-2; in step (3), the final product is a BTO-coated sulfide solid electrolyte, denoted as BTO-LPSC-2.

[0056] Example 3 This embodiment provides a method for preparing a composite solid electrolyte (denoted as BTO@BiI3-LPSC-3), comprising the following steps: (1) Li2S, P2S5, LiCl and BiI3 were added to a pulverizer for mixing and refining. The parameters of the pulverizer were set as follows: 10 pulverization cycles, each pulverization time was 40 s; wherein, as shown in Example 3 in Table 1, the mass ratio of Li2S, P2S5 and LiCl was 2.0:0.5:1.4, and the mass of BiI3 accounted for 8% of the total mass of Li2S, P2S5 and LiCl; (2) The product synthesized in the pulverizer was placed in a muffle furnace and heated to 450 °C at a rate of 4 °C / min, and then held at this temperature for 18 h to obtain a bismuth iodide-doped sulfide solid electrolyte (i.e., BiI3-doped Li). 5.4 PS 4.5 Cl 1.4 ), denoted as BiI3-LPSC-3; (3) BiI3-LPSC-3 and BTO (as shown in Example 3 in Table 1, the mass of BTO is 20% of the mass of BiI3-LPSC-3) were added to a polishing machine for mixing and coating. The parameters of the polishing machine were set as follows: rotation speed of 40 r / min and time of 30 min to obtain a composite solid electrolyte, denoted as BTO@BiI3-LPSC-3.

[0057] Comparative Example 7 This comparative example provides a method for preparing a sulfide solid electrolyte (denoted as LPSC-3), wherein the amount of each raw material is shown in Comparative Example 7 in Table 1. The difference between the preparation method of LPSC-3 in this comparative example and Example 3 is only that: in step (1), BiI3 is not added; in step (2), the final product is a sulfide solid electrolyte, denoted as LPSC-3; and step (3) is not performed.

[0058] Comparative Example 8 This comparative example provides a method for preparing a bismuth iodide-doped sulfide solid electrolyte (denoted as BiI3-LPSC-3). The amount of each raw material is shown in Comparative Example 8 in Table 1. The only difference between the preparation method of BiI3-LPSC-3 in this comparative example and Example 3 is that step (3) is not performed.

[0059] Comparative Example 9 This comparative example provides a method for preparing a BTO-coated sulfide solid electrolyte (denoted as BTO-LPSC-3). The amounts of each raw material are shown in Comparative Example 9 in Table 1. The only difference between the preparation method of BTO-LPSC-3 in this comparative example and Example 1 is that: in step (1), BiI3 is not added; in step (2), the final product is a sulfide solid electrolyte, denoted as LPSC-3; in step (3), the final product is a BTO-coated sulfide solid electrolyte, denoted as BTO-LPSC-3.

[0060] Example 4 This embodiment provides a method for preparing a composite solid electrolyte (denoted as BTO@BiI3-LPSC-4), comprising the following steps: (1) Li2S, P2S5, LiCl and BiI3 were added to a pulverizer for mixing and refining. The parameters of the pulverizer were set as follows: 8 pulverization times and 30 s for each pulverization time; wherein, as shown in Example 4 in Table 1, the mass ratio of Li2S, P2S5 and LiCl was 2.1:0.6:1.5, and the mass of BiI3 accounted for 6% of the total mass of Li2S, P2S5 and LiCl; (2) The product synthesized in the pulverizer was placed in a muffle furnace and heated to 460 °C at a rate of 4 °C / min, and then held at this temperature for 16 h to obtain a bismuth iodide-doped sulfide solid electrolyte (i.e., BiI3-doped Li). 4.75 PS 4.25 Cl 1.25 ), denoted as BiI3-LPSC-4; (3) BiI3-LPSC-4 and BTO (as shown in Example 6 in Table 1, the mass of BTO is 15% of the mass of BiI3-LPSC-4) were added to a polishing machine for mixing and coating. The parameters of the polishing machine were set as follows: rotation speed of 20 r / min and time of 10 min to obtain a composite solid electrolyte, denoted as BTO@BiI3-LPSC-4.

[0061] Comparative Example 10 This comparative example provides a method for preparing a sulfide solid electrolyte (denoted as LPSC-4), wherein the amount of each raw material is shown in Comparative Example 10 in Table 1. The difference between the preparation method of LPSC-4 in this comparative example and Example 4 is only that: in step (1), BiI3 is not added; in step (2), the final product is a sulfide solid electrolyte, denoted as LPSC-4; and step (3) is not performed.

[0062] Comparative Example 11 This comparative example provides a method for preparing a bismuth iodide-doped sulfide solid electrolyte (denoted as BiI3-LPSC-4). The amount of each raw material is shown in Comparative Example 11 in Table 1. The only difference between the preparation method of BiI3-LPSC-4 in this comparative example and Example 4 is that step (3) is not performed.

[0063] Comparative Example 12 This comparative example provides a method for preparing a BTO-coated sulfide solid electrolyte (denoted as BTO-LPSC-4). The amounts of each raw material are shown in Comparative Example 12 in Table 1. The difference between the preparation method of BTO-LPSC-4 in this comparative example and Example 4 is only that: in step (1), BiI3 is not added; in step (2), the final product is a sulfide solid electrolyte, denoted as LPSC-4; and in step (3), the final product is a BTO-coated sulfide solid electrolyte, denoted as BTO-LPSC-4.

[0064] Example 5 This embodiment provides a method for preparing a composite solid electrolyte (denoted as BTO@BiI3-LPSC-5), comprising the following steps: (1) Li2S, P2S5, LiCl and BiI3 were added to a pulverizer for synthesis reaction. The parameters of the pulverizer were set as follows: pulverization times were 6 times and the pulverization time was 20 s each time. As shown in Example 5 in Table 1, the mass ratio of Li2S, P2S5 and LiCl was 2.0:0.5:1.3, and the mass of BiI3 accounted for 8% of the total mass of Li2S, P2S5 and LiCl. (2) The product synthesized in the pulverizer was placed in a muffle furnace and heated to 440 °C at a rate of 3 °C / min, and then held at this temperature for 14 h to obtain a bismuth iodide-doped sulfide solid electrolyte (i.e., BiI3-doped Li). 5.3 PS 4.5 Cl 1.3 ), denoted as BiI3-LPSC-5; (3) BiI3-LPSC and BTO (as shown in Example 5 in Table 1, the mass of BTO is 10% of the mass of BiI3-LPSC-5) were added to a polishing machine for mixing and coating. The parameters of the polishing machine were set as follows: rotation speed of 10 r / min and time of 30 min to obtain a composite solid electrolyte, denoted as BTO@BiI3-LPSC-5.

[0065] Comparative Example 13 This comparative example provides a method for preparing a sulfide solid electrolyte (denoted as LPSC-5), wherein the amount of each raw material is shown in Comparative Example 13 in Table 1. The difference between the preparation method of LPSC-5 in this comparative example and Example 5 is only that: in step (1), BiI3 is not added; in step (2), the final product is a sulfide solid electrolyte, denoted as LPSC-5; and step (3) is not performed.

[0066] Comparative Example 14 This comparative example provides a method for preparing a bismuth iodide-doped sulfide solid electrolyte (denoted as BiI3-LPSC-5). The amount of each raw material is shown in Comparative Example 14 in Table 1. The only difference between the preparation method of BiI3-LPSC-5 in this comparative example and Example 5 is that step (3) is not performed.

[0067] Comparative Example 15 This comparative example provides a method for preparing a BTO-coated sulfide solid electrolyte (referred to as BTO-LPSC-5). The amounts of each raw material are shown in Comparative Example 15 in Table 1. The difference between the preparation method of BTO-LPSC-5 in this comparative example and Example 5 is only that: in step (1), BiI3 is not added; in step (2), the final product is a sulfide solid electrolyte, referred to as LPSC-5; in step (3), the final product is a BTO-coated sulfide solid electrolyte, referred to as BTO-LPSC-5.

[0068] test: 1. X-ray diffraction (XRD) test, the specific steps are as follows: (1) Preparation of powder samples Grinding requirements: The sample is ground until the particle size is uniform (passes through a 200-mesh sieve, particle size ≤75μm) to obtain powder. The powder has no grainy feel when touched and has a texture similar to flour, in order to reduce preferred orientation and enhance the intensity of diffraction peaks.

[0069] Moisture-proof treatment: Sulfides are prone to moisture absorption and decomposition, so samples need to be ground and pressed in an inert gas (such as argon) glove box to avoid oxidation or structural damage.

[0070] Compressing method: The positive pressure method is used to fill the powder into the groove of the glass sample holder and compact it with a glass plate until the surface is flat and flush with the groove to ensure sample uniformity.

[0071] (2) Instrument setup and testing procedures a. Instrument initialization Circulating water system: Ensure water temperature is 17-20℃ and water pressure is 0.3-0.4 MPa to prevent equipment from overheating or being damaged.

[0072] Software startup: Open the PC-based XRD control software (such as Rigaku Ultimate IV or DIFFRAC measurement system), initialize the goniometer, and confirm that the sample chamber door is closed.

[0073] b. Parameter settings Scanning range: The standard wide-angle test range is 5–90°, with a step size of 0.02° and a scanning speed of 5° / min (adjusted according to the crystallinity of the sample).

[0074] Slit width: entrance slit is 0.2–0.6 mm, detector slit is 3–8 mm, optimizing resolution and signal-to-noise ratio.

[0075] X-ray conditions: copper target Kα rays (λ=1.5418 Å), voltage 40 kV, current 30 mA, to ensure clear diffraction peaks.

[0076] c. Sample loading and testing Sample loading procedure: Gently open the sample chamber door, insert the sample holder into the slot, ensuring the sample surface is facing up and centered, gently close the door and confirm that the closing indicator light is on.

[0077] Start the test: Click "Start" to start the scan. Wait for the software to indicate that the scan is complete and save the data (e.g., RAW or TXT format).

[0078] The XRD results of BTO@BiI3-LPSC-1 in Example 1 and LPSC-1 in Comparative Example 1 are as follows: Figure 2 As shown, compared to LPSC-1, BTO@BiI3-LPSC-1 exhibits hybrid peaks of LiBiS2 and BTO at 25~30° and 30~35°, indicating that the modification (i.e., doping and coating) was successful.

[0079] 2. Scanning electron microscopy (SEM) examination, the specific steps are as follows: The BTO@BiI3-LPSC-1 from Example 1 and the LPSC-1 from Comparative Example 1 were dispersed on the surface of the conductive adhesive. Excess powder was gently blown away to ensure that the particles were dispersed and did not agglomerate. After gold sputtering, the samples were loaded, observed and adjusted, and finally, images were acquired. The detection results are as follows: Figure 3 As shown; the EDS (energy dispersive spectroscopy) scan results of Ba and Ti in BTO@BiI3-LPSC-1 are as follows. Figure 4 As shown in the figure. The results above demonstrate that the modification method for sulfide solid electrolytes in this invention does not damage the morphology of the sulfide solid electrolytes, and the doping and coating are uniform.

[0080] 3. Ionic conductivity test, the specific steps are as follows: (1) Sample preparation The electrolytes prepared in each example and comparative example were cold-pressed at 400 MPa to form an electrolyte sheet with a thickness of about 0.5 mm and a diameter of 10 mm.

[0081] (2) Electrochemical impedance spectroscopy (EIS) Clamp the electrolyte sheet with a blocking electrode (such as stainless steel) and apply an AC voltage (amplitude of 10 mV, frequency range of 1 MHz to 0.1 Hz).

[0082] The bulk resistance R is obtained by fitting the semicircular intercept in the high-frequency region using EIS. bulk The low-frequency region reflects the interfacial resistance and the double-layer effect.

[0083] (3) Geometric parameter measurement Thickness (L): The thickness of the electrolyte sheet is measured directly using a micrometer; Area (A): Calculate the effective contact area based on the electrode diameter; According to the formula Calculate the ionic conductivity σ of the corresponding electrolyte.

[0084] The ionic conductivity of the samples in each example and comparative example was tested after being placed in an air environment (temperature 30 ℃, humidity 0.7%, glove box) for 0 h, 2 h, 4 h, 8 h and 24 h respectively. The results are shown in Table 2.

[0085] Table 2. Results of Ion Conductivity Test

[0086] The ionic conductivity at 0 h in air refers to the ionic conductivity test performed directly on the prepared sample. The retention rates of ionic conductivity at 2 h, 4 h, 8 h, and 24 h in air represent the percentages of the ionic conductivity at 2 h, 4 h, 8 h, and 24 h in air compared to the ionic conductivity at 0 h in air. In Table 2, the values ​​in parentheses represent the retention rates of ionic conductivity at different times of air exposure. For example, in Example 1, the retention rate of ionic conductivity after 2 h of electrolyte exposure was 94%.

[0087] As shown in Table 2, the doping modification coating process provided by this invention can effectively improve the air stability and ionic conductivity of sulfide solid electrolytes. Among them, BTO@BiI3-LPSC-5 exhibits the best air stability within 24 h, and its ionic conductivity after 24 h in air is significantly better than that of BTO-LPSC-5 or LPSC-5. This indicates that by doping and modifying sulfide solid electrolytes with bismuth iodide, this invention improves air stability while enhancing the coating performance of barium titanate and reducing the impact of barium titanate coating on the ionic conductivity of sulfide solid electrolytes.

[0088] It should be understood that the application of the present invention is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A method for preparing a composite solid electrolyte, characterized in that, Includes the following steps: The raw materials for preparing sulfide solid electrolytes and bismuth iodide are mixed, and then sintered at a preset temperature for a preset time to obtain bismuth iodide-doped sulfide solid electrolytes; the mass of bismuth iodide accounts for 3% to 8% of the total mass of the raw materials for preparing sulfide solid electrolytes; The composite solid electrolyte is obtained by coating barium titanate onto the surface of the bismuth iodide-doped sulfide solid electrolyte.

2. The method for preparing the composite solid electrolyte according to claim 1, characterized in that, The raw materials for preparing sulfide solid electrolyte and bismuth iodide are added to a pulverizer for mixing. The parameters of the pulverizer are set as follows: 6 to 10 pulverization cycles, with each pulverization cycle lasting 20 to 40 seconds.

3. The method for preparing the composite solid electrolyte according to claim 1, characterized in that, The preset temperature is 440~480 ℃, and the preset time is 14~18 h.

4. The method for preparing the composite solid electrolyte according to claim 1, characterized in that, Bismuth iodide-doped sulfide solid electrolyte and barium titanate were added to a polishing machine for mixing and coating, thereby coating the surface of the bismuth iodide-doped sulfide solid electrolyte with barium titanate. The parameters of the polishing machine were set as follows: rotation speed 10~50 r / min, time 10~30 min; or, Bismuth iodide-doped sulfide solid electrolyte and barium titanate were added to a ball mill for mixing and coating, thereby coating the surface of the bismuth iodide-doped sulfide solid electrolyte with barium titanate. The parameters of the ball mill were set as follows: rotation speed of 120~150 rpm and time of 0.5~3 h.

5. The preparation method according to claim 4, characterized in that, In the step of adding bismuth iodide-doped sulfide solid electrolyte and barium titanate into a polishing machine for mixing and coating, the mass of barium titanate accounts for 5% to 20% of the mass of the bismuth iodide-doped sulfide solid electrolyte; Alternatively, in the step of adding bismuth iodide-doped sulfide solid electrolyte and barium titanate into a ball mill for mixing and coating, the mass of barium titanate accounts for 5% to 20% of the mass of the bismuth iodide-doped sulfide solid electrolyte.

6. The method for preparing the composite solid electrolyte according to claim 1, characterized in that, The raw materials for preparing the sulfide solid electrolyte include Li2S, P2S5 and LiCl; the mass ratio of Li2S, P2S5 and LiCl is (2~2.2):(0.4~0.6):(1.3~1.5).

7. The method for preparing the composite solid electrolyte according to claim 1, characterized in that, The preparation method of the composite solid electrolyte specifically includes the following steps: Li₂S, P₂S₅, LiCl, and bismuth iodide are added to a pulverizer and mixed. The mass ratio of Li₂S, P₂S₅, and LiCl is (2~2.2):(0.4~0.6):(1.3~1.5). The mass of bismuth iodide accounts for 3%~8% of the total mass of Li₂S, P₂S₅, and LiCl. The parameters of the pulverizer are set as follows: 6~10 pulverization cycles, with each pulverization cycle lasting 20~40 seconds. The product obtained in the pulverizer was placed in a muffle furnace and heated to 440-480 °C at a rate of 3-5 °C / min, and sintered at 440-480 °C for 14-18 h to obtain bismuth iodide-doped sulfide solid electrolyte. Bismuth iodide-doped sulfide solid electrolyte and barium titanate are added to a polishing machine and mixed and coated to obtain the composite solid electrolyte. The parameters of the polishing machine are set as follows: rotation speed of 10~50 r / min and time of 10~30 min. The mass of barium titanate accounts for 5%~20% of the mass of bismuth iodide-doped sulfide solid electrolyte.

8. A composite solid electrolyte, characterized in that, It is prepared by the preparation method according to any one of claims 1-7.

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