CN106785002A - A kind of lithium sulfide system solid electrolyte material containing silver iodide and preparation method thereof - Google Patents

Abstract

The invention discloses a kind of lithium sulfide system solid electrolyte material containing silver iodide and preparation method thereof.Described preparation method is comprised the following steps：1) under the conditions of atmosphere protection, by mass percentage, 35 50% lithium sulfide and the phosphoric sulfide of surplus are weighed, is well mixed, obtain lithium sulphur phosphorus ternary mixture；2) under the conditions of atmosphere protection and safe feux rouges, lithium sulphur phosphorus ternary mixture and the silver iodide equivalent to its quality 2 10% are taken, is placed in ball milling in ball grinder, obtain the amorphous li sulphur phosphate mixture containing silver iodide；3) after the amorphous li sulphur phosphate mixture of gained silver iodide is sealed under the conditions of atmosphere protection and feux rouges, 120 200 DEG C are warming up under the conditions of vacuum or atmosphere protection and are heat-treated, obtained final product.A large amount of atom vacancies that can be used for lithium ion diffusion, and then the effectively ionic conduction performance of lifting lithium sulfide system solid electrolyte can be formed when preparing lithium sulfide system solid electrolyte material using the method for the invention.

Description

A lithium sulfide-based solid electrolyte material containing silver iodide and its preparation method

technical field

The invention relates to a lithium sulfide-based solid electrolyte material, in particular to a silver iodide-containing lithium sulfide-based solid electrolyte material and a preparation method thereof.

Background technique

Lithium-ion batteries with high voltage and high energy density have been widely used in consumer electronics such as laptop computers and mobile phones. In recent years, lithium batteries with high energy density have shown more and more important market prospects as power batteries for electric vehicles, and have been considered as ideal energy conversion devices for the development of the 21st century. A general lithium-ion battery is composed of a positive electrode, a negative electrode, a diaphragm, an organic electrolyte, and a sealed casing. Major safety accidents such as fires caused by flammable organic electrolytes occur from time to time. Although many studies have greatly improved the performance of traditional lithium-ion batteries in terms of material modification and battery structure improvement, the safety problems of lithium-ion batteries containing organic electrolytes in use have not been fundamentally resolved.

Using solid electrolyte materials instead of flammable organic electrolyte solutions is the best way to solve the safety problem of lithium-ion batteries in use. An all-solid lithium-ion battery is usually composed of a positive electrode film, a negative electrode film, and a solid electrolyte film between the positive and negative electrode layers. Because it does not contain flammable organic electrolyte solutions, it has high safety. The simple layered structure can further reduce manufacturing costs and improve production efficiency. At the same time, it can be stacked in series to achieve high voltage and increase the energy density of all solid lithium-ion batteries. Therefore, All-solid lithium-ion batteries have received increasing attention in recent years.

The key material of all solid lithium ion batteries is the all solid electrolyte material with high lithium ion conductivity. In November 2000, in the abstract of the 26th Symposium on Solid State Ionics in Japan (p174), it was reported that a mixture of lithium sulfide (Li ₂ S) and phosphorus sulfide P ₂ S ₅ could form a lithium ion conductor after heat treatment at 200 degrees. As a result, amorphous lithium sulfide-based solid electrolytes have gradually become a hot material in the research and development of all-solid lithium batteries.

The lithium ion solid electrolyte should have the following characteristics: ① the lithium ion in the lithium ion carrier compound should be easily polarized, that is, the binding force is relatively small and easy to migrate; ② the lithium ion density of the lithium ion solid electrolyte should be as high as possible, that is, for lithium Lithium ions that contribute to ion conduction must exist in large quantities; ③The diffusion of lithium ions in the solid electrolyte is through the rapid diffusion of atomic vacancies, structural relaxation and structural defects in the amorphous or quasi-crystalline solid electrolyte matrix, and other ways to introduce A large number of atomic vacancies will promote the rapid diffusion of lithium ions through atomic vacancies, thus possessing high lithium ion conductivity. Lithium sulfide-based materials with high lithium-ion conductivity are suitable for use as solid electrolytes for all-solid-state lithium-ion batteries.

Existing studies have shown that adding other components to lithium sulfide-based solid electrolyte materials can improve ion conductivity. For example, the invention patent with the publication number CN101013761A discloses three types of solid electrolyte material systems for all-solid-state lithium-ion batteries, which are respectively : (A) Li ₂ S+A/I, where A/I is AlI ₃ , ZnI ₂ , ZrI ₄ or LaI ₃ , 0.5≤x≤1.5; (B)yLi ₂ S-mA/I-zB/S , where y+z=9, y from 5.0 to 7.0, m from 0.5 to 3, B/S is SiS ₂ , 0.5P ₂ S ₅ , CeS ₂ or 0.5B ₂ S ₃ ; A/I is AlI ₃ , ZnI ₂ , ZrI ₄ or LaI ₃ ; (C)yLi ₂ S-mA/I-zB/S-nLiI, where y+z=9, y from 5.0 to 7.0, m from 0.5 to 3.0, n from 0.5 to 3.0, A/I is AlI ₃ , ZnI ₂ , ZrI ₄ or LaI ₃ ; B/S is SiS ₂ , 0.5P ₂ S ₅ , CeS ₂ or 0.5B ₂ S ₃ . The preparation method of these three types of solid electrolyte materials is as follows: After the batching is completed, they are placed in a quartz glass tube for vacuum packaging, and then reacted at a high temperature of 500-750° C. for 10-14 hours, then quenched to room temperature, and ground into powder. The structure of the solid electrolyte prepared according to the technical scheme of the invention is amorphous. Although the invention can improve the cation migration ability, the improvement of the ion conductivity of the obtained material is not ideal. 6Li ₂ S-0.5AlI ₃ - Take the 3SiS ₂ -LiI system as an example (y=6, m=0.5, z=3, n=1), this system is mainly a lithium ion conductor at room temperature and higher temperature (≤200°C), and its total conductance at room temperature The highest rate is only 3.80×10 ^-6 S/cm. As another example, CN101013753A also discloses a lithium-sulfur system solid electrolyte material for all-solid-state lithium batteries, which is compounded according to the molar ratio of Li ₂ S:A/S:P ₂ S ₅ =6:0.1-4.0:1.5 In the formula, A/S is the sulfide of Ag, Zn, Al or Zr; the preparation process is to place the ingredients in a quartz glass tube for vacuum packaging, slowly raise the temperature to 450°C for 24 hours, and then raise the temperature to 500°C React at -750°C for 10-14 hours, then quench to room temperature and grind into powder. The improvement of the ionic conductivity of the solid electrolyte obtained by the invention is also not satisfactory, and the total conductivity at room temperature is also 10 ^-6 S/cm. According to the analysis of the applicant, the reasons for the unsatisfactory improvement of the ion conductivity of the solid electrolyte obtained by the above-mentioned invention patent are mainly: (1) the added substance (such as iodide or sulfide, etc.) is a stable hexagonal crystal or orthorhombic crystal, It cannot react with surrounding substances, and cannot introduce more atomic vacancies into the system, and cannot provide more diffusion channels for the diffusion of lithium ions; (2) The content of added substances is too high, on the one hand, it reduces the capacity of lithium ion carriers. On the other hand, high content and stable additives not only do not increase the lithium ion diffusion channels in the solid electrolyte, but hinder the diffusion of lithium ions. Therefore, the ingredients added in the above invention patents did not significantly improve the ion conductivity of the sulfide-based solid electrolyte.

The invention patent with the publication number CN104752756A discloses a method for preparing a silver iodide-based solid electrolyte material with high ionic conductivity. The material is Ag ₂ S:P ₂ S ₅ :AgI=3:1:14 by molar ratio The proportion of silver iodide mixed with a small amount of phosphorus sulfide and silver sulfide after high-energy ball milling made of solid electrolyte using silver ion conduction. Although the solid electrolyte prepared by the method described in the invention has a higher room temperature ion conductivity (up to 10 ^-3 S/cm), the solid electrolyte prepared in the invention is a fast conductor of silver ions, and silver iodide is utilized. By adding a small amount of phosphorus sulfide and combining the amorphization process to facilitate the migration of Ag ⁺ , the silver ion conductivity of the material is improved. Nevertheless, the applicant believes that this invention is a solid electrolyte that does not contain lithium ions but relies on Ag ⁺ to conduct electricity. It does not increase the diffusion channels of lithium ions by generating a large number of new atomic vacancies to improve the sulfide-based solid electrolyte. The effect of lithium ion conductivity; The silver ion conductive solid electrolyte that makes by the described method of this invention is not suitable as solid electrolyte between positive pole and negative pole of all-solid lithium battery, and this is because: under the electric field action when charging and discharging Ag ⁺ migration is not accompanied by electrochemical reactions and thus cannot become a battery. On the other hand, Ag ⁺ migrates to the low-potential interface during charging and discharging, which will form a barrier to the passage of lithium ions and cause a large amount of lithium ions to stay in the silver iodide system. In the solid electrolyte, the consumption of a large amount of lithium ions will make the coulombic efficiency of the battery's initial cycle very low, making it difficult to maintain the charge-discharge cycle.

Contents of the invention

The technical problem to be solved by the present invention is to provide a silver iodide-containing lithium sulfide solid electrolyte material and a preparation method thereof that can form a large number of atomic vacancies that can be used for lithium ion diffusion, thereby effectively improving the ion conductivity of the lithium sulfide solid electrolyte.

The preparation method of the lithium sulfide series solid electrolyte material containing silver iodide of the present invention comprises the following steps:

1) Under atmosphere protection conditions, weigh 35-50% of lithium sulfide and the remainder of phosphorus sulfide by mass percentage, and mix them uniformly to obtain a lithium-sulfur-phosphorus ternary mixture;

2) Under the conditions of atmosphere protection and safe red light, take the lithium-thion-phosphorus ternary mixture and silver iodide equivalent to 2-10% of its mass, and place them in a ball mill jar for ball milling to obtain an amorphous lithium-thion-phosphorus mixture containing silver iodide;

3) The obtained silver iodide amorphous lithium sulfur phosphorus mixture is sealed under atmosphere protection and red light conditions, and then heated to 120-200° C. for heat treatment under vacuum or atmosphere protection conditions to obtain a lithium sulfide-based solid electrolyte material containing silver iodide .

In the present invention, lithium sulfide and phosphorus sulfide are used as a matrix, and silver iodide in a specific proportion is added through high-energy ball milling to achieve the effect that the third component, silver iodide, is uniformly distributed in the matrix while forming an amorphous sulfide mixture; The heat treatment process promotes the silver iodide powder to transform into a body-centered cubic silver iodide with a "rigid skeleton" composed of iodide ions that exists stably at a higher temperature. While the iodide ions stabilize the cubic skeleton, part of the silver ions is combined with the sulfur in the surrounding lithium sulfide. Forming nano-scale silver sulfide, the formed nano-scale silver sulfide can stabilize the solid electrolyte matrix; at the same time, a large number of atomic vacancies suitable for lithium ion diffusion are formed in the body-centered cubic structure dominated by iodine, thereby effectively improving the sulfidation. The effect of lithium-based solid electrolyte ion conductivity is to form part of lithium iodide while forming atomic vacancies; on the other hand, the nano-silver sulfide and lithium iodide formed by the reaction also have the effect of improving ion conductivity.

In step 1) of the above preparation method, the atmosphere protection is usually under the protection of an inert gas, such as conventionally used inert gases such as argon and nitrogen. The specific operation is usually carried out in a glove box with argon protection.

In the step 1) of the above-mentioned preparation method, the existing conventional technology can be used to make lithium sulfide and phosphorus sulfide uniformly mixed, usually by ball milling to make them uniformly mixed, dry ball milling or medium ball milling can be used during ball milling, and carbon dioxide is used during ball milling. For zirconium grinding balls, the ball-to-material ratio is preferably 2:0.5-1 (mass ratio). When using a conventional rolling ball mill, it usually takes 6-10 hours to mix lithium sulfide and phosphorus sulfide uniformly, and it usually takes 25 hours to mix lithium sulfide and phosphorus sulfide uniformly when using a planetary high-energy ball mill.

In step 2) of the above preparation method, the atmosphere protection is usually under the protection of an inert gas, such as conventionally used inert gases such as argon and nitrogen. The specific operation is usually carried out in a glove box with argon protection.

In step 2) of the above preparation method, the silver iodide is preferably silver iodide powder with a particle size of less than 200 mesh. For ball milling, zirconia grinding balls are used, and the ball-to-material ratio is preferably 2:0.5-1 (mass ratio), more preferably 2:0.7 (mass ratio). In this step, the time for ball milling to obtain the amorphous lithium-thion-phosphorus mixture containing silver iodide is usually 30-48h. The mixture is stirred evenly and then placed in a ball milling tank for ball milling. At this time, the ball milling time is controlled at 30-40 hours to realize the complete amorphization of the lithium-thion phosphorus mixture and the full mixing of the silver iodide and the amorphous lithium-thion phosphorus mixture.

In step 3) of the above preparation method, the atmosphere protection is usually under the protection of an inert gas, such as conventionally used inert gases such as argon and nitrogen. The specific sealing operation is usually carried out in a glove box with argon protection.

In step 3) of the above-mentioned preparation method, a heat treatment operation is carried out to promote the transformation of silver iodide into body-centered cubic silver iodide with a "rigid skeleton" formed by iodide ions which is stable at a higher temperature, and at the same time part of the silver ions and the surrounding lithium sulfide The sulfur in the solution combines to form nano-scale silver sulfide (in situ precipitation), which promotes the formation of a large number of atomic vacancies in the body-centered cubic structure dominated by iodine, which can be used as diffusion channels for lithium ions, and at the same time forms part of lithium iodide (in situ Precipitation), so as to prepare lithium sulfur phosphorus iodine multi-component solid electrolyte powder formed by nano-silver sulfide particles. In this step, the heat treatment time is generally greater than or equal to 1 h, preferably 1-5 h; the heat treatment temperature is more preferably 150-180° C., and under this temperature condition, the heat treatment time is preferably 1-3 h.

The present invention also includes the silver iodide-containing lithium sulfide solid electrolyte material prepared by the above method.

Compared with prior art, the present invention is characterized in that:

1. In the present invention, lithium sulfide and phosphorus sulfide are used as the matrix, and silver iodide in a specific proportion is added through high-energy ball milling to achieve the effect that the third component, silver iodide, is evenly distributed in the matrix while forming an amorphous sulfide mixture; After the heat treatment process, the silver iodide powder is transformed into a body-centered cubic crystal silver iodide composed of iodide ions with a "rigid skeleton" that exists at a higher temperature. While the iodide ions stabilize the cubic structure, part of the silver ions and the surrounding lithium sulfide At the same time, a large number of new atomic vacancies suitable for the diffusion of lithium ions are formed in the body-centered cubic structure dominated by iodine, thereby effectively improving the ion conductivity of lithium sulfide-based solid electrolytes. Partial lithium iodide is also formed along with the formation of atomic vacancies.

2, the product nano-silver sulfide and lithium iodide of in-situ precipitation reaction during heat treatment in the method for the present invention, all have ion conductivity, can play the effect of further improving lithium ion conductivity of lithium sulfide series solid electrolyte; The formed Nano-silver sulfide particles can obtain a dispersion strengthening effect, and nano-silver sulfide particles dispersed in the lithium-sulfur-phosphorus ternary mixture can stabilize the microstructure of the lithium-sulfur-based solid electrolyte and inhibit the formation of lithium-sulfur-phosphorus-iodide during charge and discharge. Microstructural changes of multicomponent mixture solid electrolyte powders.

3. In the method of the present invention, a three-stage process combination method is adopted, wherein lithium sulfide and phosphorus sulfide are used as a preliminary mixing process to ensure that the main component lithium sulfide of the solid electrolyte is evenly mixed in phosphorus sulfide to form a lithium-sulfur-phosphorus ternary mixture; and After adding the third component silver iodide, the second high-energy ball milling mixing can ensure the uniform distribution of the added component silver iodide and at the same time realize the amorphization of the lithium sulfur phosphorus ternary mixture to ensure the high lithium ion conductivity of the lithium sulfide solid electrolyte.

detailed description

The present invention will be described in further detail below in conjunction with specific examples to better understand the content of the present invention, but the present invention is not limited to the following examples.

The reagents used in the following examples, such as lithium sulfide (Li ₂ S) and phosphorus sulfide (P ₂ S ₅ ), are chemically pure reagents with a purity of 99.9%.

Example 1

1) Sulfide preparation mixing process:

By mass percent, take by weighing 40% lithium sulfide and 60% phosphorus sulfide in the glove box with argon atmosphere protection of low moisture (≤1ppm), low oxygen content (≤1ppm), and mix with zirconium dioxide After the balls are matched, they are sealed into a ball mill jar, and the mass ratio of the zirconia balls in the jar to the mixture is 2:0.7; the sealed ball mill jars are packed in a planetary high-energy ball mill and pre-mixed by a dry ball mill, and the milling time is After 5 hours, a ternary mixture of lithium sulfur and phosphorus (LiPS mixture for short) was obtained;

2) Second high energy ball milling process:

In a glove box protected by an argon atmosphere with low moisture (≤1ppm) and low oxygen content (≤1ppm) with safe lights (such as red light), silver iodide powder (particle size) equivalent to 2.5% of the above LiPS mixture mass 300 mesh) mixed with LiPS mixture by hand, and the resulting mixed material is mixed with zirconia balls with a diameter of 3-10mm at a mass ratio of 2:0.7, and then sealed into a ball mill jar, sealed, and packed in the sealed ball mill jar Carry out high-energy dry ball milling in the planetary high-energy ball mill ball mill, the ball milling time is 36 hours, obtains the amorphous lithium sulfur phosphorus mixture containing silver iodide;

3) In-situ precipitation reaction process:

The resulting silver iodide-containing amorphous lithium-sulfur phosphorus mixture is sealed in a glove box protected by an argon atmosphere with low moisture (≤1ppm) and low oxygen content (≤1ppm) with safe lights (such as red light) , and then heated to 150° C. for 2 hours under vacuum conditions to obtain a lithium sulfide-based solid electrolyte material containing silver iodide. During heat treatment, silver iodide transforms into a body-centered cubic crystal silver iodide that is stable at higher temperatures and consists of iodide ions with a "rigid skeleton". Part of the silver ions in its structure combine with sulfur in the surrounding lithium sulfide to form nano-scale sulfide Silver, while forming a large number of atomic vacancies in the body-centered cubic structure dominated by iodine, which can be used for lithium ion diffusion channels; The ion-conducting properties of the electrolyte material are further improved.

After the solid electrolyte powder prepared in this example was pressed into a standard sample, the ion conductivity of the sample in this example was measured to be 4.5×10 ^-4 at a room temperature of 25°C by using a CHI660 electrochemical workstation and using AC impedance method S/cm.

comparative example

By mass percent, take by weighing 40% lithium sulfide and 60% phosphorus sulfide in the glove box with argon atmosphere protection of low moisture (≤1ppm), low oxygen content (≤1ppm), and mix with zirconium dioxide After the balls are matched, they are sealed into a ball mill jar, and the mass ratio of the zirconia balls in the jar to the mixture is 2:0.7; the sealed ball mill jars are packed in a planetary high-energy ball mill and pre-mixed by a dry ball mill, and the milling time is After 36 hours, the lithium sulfur phosphorus ternary mixture solid electrolyte powder was obtained.

After the solid electrolyte powder prepared in this comparative example was pressed into a standard sample, the ionic conductivity of the sample of this comparative example was measured to be 8.6×10 ^-6 at a room temperature of 25° C. S/cm.

Example 2

Repeat Example 1, the difference is:

In step 1), the mass percentages of lithium sulfide and phosphorus sulfide are 50% and 50% respectively, and the ball milling time is 10 hours.

After the solid electrolyte powder prepared in this example was pressed into a standard sample, the ion conductivity of the sample in this example was measured to be 8.1×10 ^-4 at a room temperature of 25°C by using a CHI660 electrochemical workstation and using AC impedance method S/cm.

Example 3

Repeat Example 1, the difference is:

In step 1), the mass percentages of lithium sulfide and phosphorus sulfide are respectively 50% and 50%, and the time of ball milling is 2 hours;

In step 2), the particle size of the silver iodide powder is 400 mesh, and the addition amount of the silver iodide powder is equivalent to 5% of the mass of the LiPS mixture;

After the solid electrolyte powder prepared in this example was pressed into a standard sample, the ion conductivity of the sample in this example was measured to be 8.7×10 ^-4 at a room temperature of 25°C by using a CHI660 electrochemical workstation and using AC impedance method S/cm.

Example 4

Repeat Example 1, the difference is:

In step 1), the mass percentages of lithium sulfide and phosphorus sulfide are respectively 50% and 50%, and the time of ball milling is 4 hours;

In step 2), the particle size of the silver iodide powder is 220-260 mesh, the amount of the silver iodide powder added is equivalent to 10% of the mass of the LiPS mixture, and the ball milling time is 40 hours;

In step 3), the heat treatment is carried out in an argon atmosphere, the temperature of the heat treatment is 200° C., and the time of the heat treatment is 1 hour.

After the solid electrolyte powder prepared in this example was pressed into a standard sample, the ion conductivity of the sample in this example was measured to be 7.2×10 ^-4 at a room temperature of 25°C by using a CHI660 electrochemical workstation and using AC impedance method S/cm.

Example 5

Repeat Example 1, the difference is:

In step 1), the mass percentages of lithium sulfide and phosphorus sulfide are respectively 35% and 65%, and the time of ball milling is 6 hours;

In step 2), the particle size of the silver iodide powder is 100-200 mesh, the amount of the silver iodide powder added is equivalent to 2% of the mass of the LiPS mixture, and the ball milling time is 30 hours;

In step 3), the heat treatment is carried out in an argon atmosphere, the heat treatment temperature is 120° C., and the heat treatment time is 5 hours.

After the solid electrolyte powder prepared in this example was pressed into a standard sample, the ion conductivity of the sample in this example was measured to be 2.7×10 ^-4 at a room temperature of 25°C by using a CHI660 electrochemical workstation and using an AC impedance method S/cm.

Claims (7)

1. a kind of preparation method of the lithium sulfide system solid electrolyte material containing silver iodide, comprises the following steps：

1) under the conditions of atmosphere protection, by mass percentage, the lithium sulfide of 35-50% and the phosphoric sulfide of surplus are weighed, is mixed Uniformly, lithium sulphur phosphorus ternary mixture is obtained；

2) under the conditions of atmosphere protection and safe feux rouges, lithium sulphur phosphorus ternary mixture and the iodate equivalent to its quality 2-10% are taken Silver, is placed in ball milling in ball grinder, obtains the amorphous li sulphur phosphate mixture containing silver iodide；

3) after the amorphous li sulphur phosphate mixture of gained silver iodide is sealed under the conditions of atmosphere protection and feux rouges, in vacuum or atmosphere 120-200 DEG C is warming up under protective condition to be heat-treated, that is, obtain the lithium sulfide system solid electrolyte material containing silver iodide.

2. preparation method according to claim 1, it is characterised in that：Step 2) in, the time of ball milling is 30-48h.

3. preparation method according to claim 1, it is characterised in that：Step 2) in, ratio of grinding media to material during ball milling is 2：0.5- 1。

4. preparation method according to claim 1, it is characterised in that：Step 3) in, time of heat treatment be more than or wait In 1h.

5. preparation method according to claim 1, it is characterised in that：Step 3) in, the time of heat treatment is 1-5h.

6. preparation method according to claim 1, it is characterised in that：Step 3) in, the temperature of heat treatment is 150-180 ℃。

7. the lithium sulfide system solid electrolyte material containing silver iodide that any one of claim 1-6 methods are prepared.