A lithium-sulfur-phosphorus-chloro-bromine solid electrolyte, its preparation method, and an all-solid-state battery

Abstract

This invention belongs to the field of solid-state battery technology. It provides a lithium-sulfur-phosphorus-chloro-bromine solid-state electrolyte, its preparation method, and an all-solid-state battery. The preparation method includes the following steps: mixing lithium sulfide and phosphorus sulfide and then ball-milling to obtain a lithium-sulfur-phosphorus ternary mixture; in a protective gas atmosphere, mixing the lithium-sulfur-phosphorus ternary mixture, lithium chloride, and lithium bromide and then ball-milling to obtain a lithium-sulfur-phosphorus-chloro-bromine mixture; and in a protective gas atmosphere, heat-treating the lithium-sulfur-phosphorus-chloro-bromine mixture to obtain the lithium-sulfur-phosphorus-chloro-bromine solid-state electrolyte. The lithium-sulfur-phosphorus-chloro-bromine solid-state electrolyte provided by this invention not only improves electrochemical stability but also maintains high ionic conductivity.

Description

Technical Field

[0001] This invention relates to the field of solid-state battery technology, and in particular to a lithium-sulfur-phosphorus-chlorobromine solid electrolyte, its preparation method, and an all-solid-state battery. Background Technology

[0002] All-solid-state lithium batteries are the next generation of power batteries that can meet the potential applications of electric vehicles, and all-solid-state battery technology is a battery technology with great application prospects. All-solid-state lithium-ion batteries are composed of a positive electrode, an electrolyte film, and a negative electrode film. Among them, the solid electrolyte material is the core material of all-solid-state batteries and also the key material for all-solid-state battery material research.

[0003] Solid-state electrolyte materials with high lithium-ion conductivity are crucial for the fabrication of all-solid-state batteries. Sulfide-based solid-state electrolytes possess high ionic conductivity comparable to liquid electrolytes and exhibit superior processing performance compared to oxide solid-state electrolytes, making them the preferred electrolyte material for all-solid-state battery development. However, sulfide solid-state electrolytes still face challenges such as an insufficiently wide electrochemical stability window and low air stability, leading to the generation of toxic sulfide gases upon contact with a water atmosphere. To address these issues, the crystal structure needs to be improved through: ① introducing doping elements into the matrix crystal structure to increase the proportion of highly stable functional groups; ② introducing a highly stable coating layer onto the electrolyte powder surface to suppress contact reactions between the powder surface and the external atmosphere. These two methods will improve the reaction characteristics of sulfide electrolytes and simultaneously expand their electrochemical stability window.

[0004] Existing research has shown that doping lithium sulfide-based solid electrolyte materials with other components can improve the air sensitivity of sulfide solid electrolytes. For example, Chinese invention patent application CN120191894A discloses a method for preparing sulfide electrolytes by doping lithium sulfide with oxygen, antimony, and nitrogen. This invention discloses: ① using lithium oxide or antimony trioxide as the oxygen source, with a molar ratio of oxygen to lithium sulfide of 0.05-0.15:1; ② using antimony trioxide or antimony chloride as the antimony source, with a molar ratio of antimony to lithium sulfide of 0.05-0.15:1; ③ using ammonia or urea as the nitrogen source, with a molar ratio of nitrogen to lithium sulfide of 0.05-0.15:1. The sulfide solid electrolyte prepared by mixing the doped and modified lithium sulfide with phosphorus pentasulfide and lithium chloride and then heat-treating has a maximum ionic conductivity of 3.80 mS / cm, while the chemical stability of the electrolyte material is also improved. For example, Chinese patent application CN120413768A also discloses a surface-coated sulfide solid electrolyte and its preparation method. The method involves ① applying a sulfide electrolyte, such as a previously prepared Li... 5.5 PS 4.5The electrolyte powder is mixed with the first solvent, and then the nanoparticles with oxygen-containing functional groups are mixed with the second solvent. The mixture obtained from steps ① and ② is then blended and vacuum dried to prepare a sulfide-coated electrolyte with a maximum ionic conductivity of 3.3 mS / cm. The first and second solvents in this preparation process are p-xylene, butyl acetate, etc., and the nanoparticles with oxygen-containing functional groups are one or more of nano-alumina, lithium aluminum titanium phosphate, and nano-lithium phosphate.

[0005] Although various invention patents have been published, the ionic conductivity and chemical stability of surface-treated sulfide solid electrolytes still cannot meet the requirements for the development of all-solid-state batteries. The main reasons are: (1) The original compounds of dopants are mostly stable oxides or chlorides, which have insufficient reactivity with sulfides in the electrolyte preparation process, resulting in insufficient introduction of atomic vacancies into the crystal structure of sulfide electrolytes, limiting the lithium-ion diffusion channels and causing a decrease in lithium-ion conductivity; (2) The content of additives is too high, causing the sulfide electrolyte to generate impurity phases, which hinders the diffusion of lithium ions. The method of coating sulfide electrolyte powder with solution has inherent defects. Since sulfide electrolytes have different degrees of surface reaction with most solvents, the solvent reaction before the coating layer is formed has already damaged the surface ionic conductivity of sulfide solid electrolytes. Therefore, how to provide a sulfide solid electrolyte material containing trace amounts of additive elements that are conducive to expanding lithium-ion diffusion channels and can form a lithium phosphate coating layer in situ during the growth of sulfide solid electrolyte powder particles has become an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0006] In view of this, the present invention provides a lithium-sulfur-phosphorus-chloro-bromine solid electrolyte, a method for preparing the same, and an all-solid-state battery. Its purpose is to solve the technical problems of poor ion conductivity found in existing sulfide solid electrolytes.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing a lithium-sulfur-phosphorus-chlorobromine solid electrolyte, comprising the following steps: S1. Lithium sulfide and phosphorus sulfide are mixed and then ball-milled to obtain a lithium-sulfur-phosphorus ternary mixture; S2. In a protective gas atmosphere, a lithium-sulfur-phosphorus ternary mixture, lithium chloride, and lithium bromide are mixed and then ball-milled to obtain a lithium-sulfur-phosphorus-chlorine-bromine mixture; S3. In a protective gas atmosphere, a mixture of lithium, sulfur, phosphorus, chlorine, and bromine is heat-treated to obtain a lithium-sulfur-phosphorus-chlorine-bromine solid electrolyte.

[0008] Furthermore, in step S1, the mass ratio of lithium sulfide to phosphorus sulfide is 4~6:4~6.

[0009] Furthermore, in step S1, the ball milling time is 1 to 5 hours.

[0010] Furthermore, in step S2, the total mass of lithium chloride and lithium bromide is 45% of the mass of the lithium-sulfur-phosphorus ternary mixture; the lithium chloride and lithium bromide are in any proportion and neither is zero.

[0011] Furthermore, in step S2, the ball milling time is 5 to 30 hours.

[0012] Furthermore, in step S2, lithium chloride and lithium bromide undergo pretreatment before use. The pretreatment steps are as follows: Lithium chloride and lithium bromide are dissolved and dried sequentially to obtain a mixture of lithium chloride and lithium bromide powder.

[0013] Furthermore, in step S3, the heat treatment temperature is 450~500℃, and the heat treatment time is 1~6h.

[0014] Furthermore, the protective gas mentioned in steps S2 and S3 is either argon or nitrogen.

[0015] This invention provides a lithium-sulfur-phosphorus-chlorobromine solid electrolyte prepared by the above-mentioned method.

[0016] The present invention also provides an all-solid-state battery comprising the above-described lithium-sulfur-phosphorus-chlorobromine solid electrolyte.

[0017] As can be seen from the above technical solution, compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention employs two independent processes. First, lithium sulfide and phosphorus sulfide are used as matrix materials and ball-milled to obtain a lithium-sulfur-phosphorus ternary mixture. Then, a specific proportion of pretreated lithium chloride and lithium bromide are added, and after high-energy ball milling, a lithium-sulfur-phosphorus-chloro-bromine solid electrolyte is formed through heat treatment.

[0018] 2. The pretreatment of lithium chloride and lithium bromide in this invention enables trace amounts of lithium chloride and lithium bromide hydrates to form on the surface of lithium chloride and lithium bromide particles. During the heat treatment process, a lithium phosphate layer that stabilizes the surface structure of the lithium-sulfur-phosphorus solid electrolyte powder can be formed, thereby achieving the purpose of suppressing changes in the surface structure of the lithium-sulfur-phosphorus-chloride-bromine solid electrolyte powder during the charging and discharging process.

[0019] 3. In the preparation process of lithium-sulfur-phosphorus-chlorobromine solid electrolyte, the present invention adopts a two-stage process combination method. The pre-mixing process of lithium sulfide and phosphorus sulfide can ensure that the main component of solid electrolyte, lithium sulfide, is uniformly mixed in phosphorus sulfide to form a lithium-sulfur-phosphorus ternary mixture. The addition of pretreated lithium chloride and lithium bromide, followed by a second rapid ball milling and mixing, can ensure the uniform distribution of the added components while achieving the high lithium-ion conductivity of the lithium-sulfur-phosphorus-chlorobromine solid electrolyte. Attached Figure Description

[0020] Figure 1 XRD comparison diagrams of the formation of lithium phosphate in Examples 1-5 and the comparative example; Figure 2 Comparison of electrochemical impedance spectroscopy (EIS) of the solid electrolytes prepared in Examples 1-5 and the comparative examples; Figure 3 This is a CV curve measured after combining a solid electrolyte with single-sided lithium in Example 1; Figure 4 The CV curves were measured after solid electrolytes were combined with single-sided lithium as a comparative example. Figure 5 The graph shows the rate performance of the all-solid-state battery assembled with a solid electrolyte in Example 1. Detailed Implementation

[0021] This invention provides a method for preparing a lithium-sulfur-phosphorus-chlorobromine solid electrolyte, comprising the following steps: S1. Lithium sulfide and phosphorus sulfide are mixed and then ball-milled to obtain a lithium-sulfur-phosphorus ternary mixture; S2. In a protective gas atmosphere, a lithium-sulfur-phosphorus ternary mixture, lithium chloride, and lithium bromide are mixed and then ball-milled to obtain a lithium-sulfur-phosphorus-chlorine-bromine mixture; S3. In a protective gas atmosphere, a mixture of lithium, sulfur, phosphorus, chlorine, and bromine is heat-treated to obtain a lithium-sulfur-phosphorus-chlorine-bromine solid electrolyte.

[0022] In this invention, in step S1, the mass ratio of lithium sulfide to phosphorus sulfide is 4~6:4~6, preferably 5:5.

[0023] In this invention, the ball milling time in step S1 is 1 to 5 hours, preferably 2 to 4 hours, and more preferably 3 hours.

[0024] In this invention, during step S1, the mass ratio of zirconium dioxide balls to the mixture is preferably 12:1 during the ball milling process.

[0025] In this invention, in step S2, the total mass of lithium chloride and lithium bromide is 45% of the mass of the lithium-sulfur-phosphorus ternary mixture; the lithium chloride and lithium bromide are in any proportion and neither is zero, and the preferred mass ratio of lithium chloride to lithium bromide is 20:25.

[0026] In this invention, the ball milling time in step S2 is 5~30h, preferably 10~25h, and more preferably 15~20h.

[0027] In this invention, during step S1, the mass ratio of zirconium dioxide balls to the mixture is preferably 12:1 during the ball milling process.

[0028] In this invention, in step S2, lithium chloride and lithium bromide are pretreated before use. The pretreatment step is as follows: Lithium chloride and lithium bromide are dissolved and dried sequentially to obtain a mixture of lithium chloride and lithium bromide powder.

[0029] In this invention, lithium chloride and lithium bromide are dissolved in ethanol; the drying and crystallization temperature is 70~90℃, preferably 75~85℃, more preferably 80℃; the drying and crystallization time is 2~5h, preferably 3~4h. The preferred particle size of the lithium bromide is 200 mesh.

[0030] In this invention, in step S3, the heat treatment temperature is 450~500℃, preferably 470℃; the heat treatment time is 1~6h, preferably 2~5h, and more preferably 3~4h.

[0031] In this invention, the protective gas mentioned in steps S2 and S3 is either argon or nitrogen.

[0032] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0033] Example 1 S1. Weigh 40% lithium sulfide and 60% phosphorus sulfide by mass percentage, and mix them in a glove box with argon atmosphere protection in a low water and oxygen environment (water content ≤ 1 ppm, oxygen content ≤ 1 ppm). Then, load the mixture and zirconia balls into a ball mill jar, wherein the mass ratio of zirconia balls to mixture is 12:1. The sealed ball mill jar is placed in a planetary high-energy ball mill, and premixed ball milling is performed using the dry ball milling method for 5 hours to obtain a lithium-sulfur-phosphorus ternary mixture. S2. In an argon-protected glove box with water and oxygen content ≤1 ppm, take 20% lithium chloride and 25% lithium bromide powder (particle size 200 mesh) equivalent to the mass of the lithium-sulfur-phosphorus ternary mixture, dissolve them in analytical grade ethanol (concentration >99%), dry and crystallize at 80℃ for 3 hours, then mix with the lithium-sulfur-phosphorus ternary mixture. Subsequently, mix the resulting mixture with zirconia balls of 3~10 mm diameter at a ball-to-material mass ratio of 12:1, seal it in a ball mill jar, and seal it. Place the sealed jar in a planetary high-energy ball mill for high-energy dry ball milling for 25 hours to obtain a lithium-sulfur-phosphorus-chlorine-bromine mixture.

[0034] S3. The lithium-sulfur-phosphorus-chlorine-bromine mixture is sealed in an argon-protected glove box with water and oxygen content ≤1 ppm, and then heat-treated at 470℃ for 2 hours under argon conditions to obtain the lithium-sulfur-phosphorus-chlorine-bromine solid electrolyte.

[0035] Example 2 Similar to Example 1, except that the ball milling time in step S2 is 5 hours and the heat treatment time in step S3 is 4 hours.

[0036] Example 3 Similar to Example 1, except that in step S1, the mass percentages of lithium sulfide and phosphorus sulfide are 50% and 50% respectively, and the ball milling time is 4 hours; in step S2, the mass ratio of lithium chloride to lithium bromide is 35:10, and the ball milling time is 25 hours.

[0037] Example 4 Similar to Example 1, except that in step S1, the mass percentages of lithium sulfide and phosphorus sulfide are 50% and 50% respectively, and the ball milling time is 1 hour; in step S2, the mass ratio of lithium chloride to lithium bromide is 35:10, and the ball milling time is 28 hours; in step S3, the heat treatment temperature is 500°C and the time is 1 hour.

[0038] Example 5 Similar to Example 1, except that in step S1, the mass percentages of lithium sulfide and phosphorus sulfide are 60% and 40% respectively, and the ball milling time is 3 hours; in step S2, the mass ratio of lithium chloride to lithium bromide is 15:30, and the ball milling time is 30 hours; in step S3, the heat treatment temperature is 450°C and the time is 3 hours.

[0039] Comparative Example Same as Example 1, except that the pretreatment steps of lithium chloride and lithium bromide are omitted.

[0040] The technical solution provided by this invention promotes the rapid crystallization of lithium-sulfur-phosphorus-chlorine solid electrolyte particles. Simultaneously, it utilizes the aqueous atmosphere released from hydrate decomposition to react with the lithium-sulfur-phosphorus mixture, constructing an electrochemically stable lithium phosphate layer on the surface of the lithium-sulfur-phosphorus-chlorine-bromine solid electrolyte powder particles. The formation of lithium phosphate can be found in [reference needed]. Figure 1 The XRD analysis results show that the lithium phosphate layer generated by the technical solution of this invention can suppress the surface structure changes of electrolyte powder during charging and discharging, improve its electrochemical stability, and maintain high ionic conductivity.

[0041] After pressing the solid electrolytes prepared in Examples 1-5 and the comparative examples into standard samples, the electrochemical impedance spectroscopy was measured using an electrochemical impedance spectroscopy method on a Biologic electrochemical workstation, as shown below. Figure 2 As shown, the calculated ionic conductivity of the sample from Example 1 at room temperature (25°C) is 7.4 × 10⁻⁶. -3 S / cm, the ionic conductivity of the sample in Example 2 is 6.2 × 10⁻⁶. -3 S / cm, the ionic conductivity of the sample in Example 3 was 4.8 × 10⁻⁶. -3 S / cm, the ionic conductivity of the sample in Example 4 is 5.2 × 10⁻⁶. -3 S / cm, the ionic conductivity of the sample in Example 5 was 4.3 × 10⁻⁶. -3 The ionic conductivity of the comparative sample is 5.5 × 10⁻⁶ S / cm. -3 S / cm.

[0042] Figure 3 The CV curve of the solid electrolyte composite with single-sided lithium in Example 1 is shown. The complete cycle curve indicates that the electrochemical stability of the electrolyte powder has been improved.

[0043] Figure 4 This is a CV curve measured after combining a solid electrolyte with single-sided lithium, as a comparative example. Figure 4 It can be seen that the reduction peak current increases sharply after 0V, indicating that the electrolyte is conductive and has insufficient electrochemical stability.

[0044] Using the lithium-sulfur-phosphorus-chloro-bromine solid electrolyte powder prepared in Example 1, an all-solid-state battery was assembled using a mold battery method, with Li(Ni) as the positive electrode. 0.7 Co 0.2 Mn 0.1 O2 and 30 wt% electrolyte powder are mixed and pressed into tablets. The electrolyte film is formed by pressing the electrolyte powder synthesized in Example 1. The negative electrode is a lithium-indium alloy. The tablets are formed under a pressure of 300 MPa and subjected to charge-discharge tests. Figure 5 The results of the charge and discharge rates for this solid-state battery are as follows. Figure 5This diagram illustrates the relationship between rate performance and coulombic efficiency of solid-state batteries. The horizontal axis represents the number of charge-discharge cycles, the left vertical axis corresponds to specific capacity, and the right vertical axis corresponds to coulombic efficiency. At different charge-discharge rates (0.1C, 0.2C, 0.5C, 1C, 2C), the change in specific capacity with the number of cycles is represented by circles (charging) and triangles (discharging); while the coulombic efficiency data (squares) shows that within 30 cycles, the coulombic efficiency remains stable at around 100% at all rates. Figure 5 It can be seen that the assembled all-solid-state battery has excellent performance, with a positive electrode discharge specific capacity of more than 170 mAh / g under 0.1C conditions and a positive electrode discharge specific capacity of more than 110 mAh / g under 2C rate conditions.

[0045] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a lithium-sulfur-phosphorus-chlorobromine solid electrolyte, characterized in that, Includes the following steps: S1. Lithium sulfide and phosphorus sulfide are mixed and then ball-milled to obtain a lithium-sulfur-phosphorus ternary mixture; S2. In a protective gas atmosphere, a lithium-sulfur-phosphorus ternary mixture, lithium chloride, and lithium bromide are mixed and then ball-milled to obtain a lithium-sulfur-phosphorus-chlorine-bromine mixture; S3. In a protective gas atmosphere, a lithium-sulfur-phosphorus-chlorine-bromine mixture is heat-treated to obtain a lithium-sulfur-phosphorus-chlorine-bromine solid electrolyte. In S1, the mass ratio of lithium sulfide to phosphorus sulfide is 4~6:4~6; In step S1, the ball milling time is 1~5 hours; In S2, the total mass of lithium chloride and lithium bromide is 45% of the mass of the lithium-sulfur-phosphorus ternary mixture; the lithium chloride and lithium bromide are in any proportion and neither is zero. In step S2, the ball milling time is 5~30h; In step S2, lithium chloride and lithium bromide are pretreated before use. The pretreatment steps are as follows: Lithium chloride and lithium bromide are dissolved and dried sequentially to obtain a mixture powder of lithium chloride and lithium bromide. In step S3, the heat treatment temperature is 450~500℃ and the heat treatment time is 1~6h.

2. The method for preparing the lithium-sulfur-phosphorus-chlorobromine solid electrolyte according to claim 1, characterized in that, The protective gases mentioned in S2 and S3 are both argon or nitrogen.

3. The lithium-sulfur-phosphorus-chlorobromine solid electrolyte prepared by the method described in claim 1 or 2.

4. An all-solid-state battery, characterized in that, The all-solid-state battery comprises the lithium-sulfur-phosphorus-chlorobromine solid electrolyte as described in claim 3.

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