Sulfide solid electrolyte, preparation method thereof and all-solid-state lithium battery

Abstract

The invention discloses a sulfide solid electrolyte, a preparation method thereof and an all-solid-state lithium battery, and belongs to the technical field of all-solid-state lithium batteries. The method comprises the following steps: carrying out ball milling on raw materials at least comprising lithium sulfide and phosphorus pentasulfide under the ball milling energy of 30-100J / g.hit, then carrying out vacuum ball milling under the ball milling energy of 150-300J / g.hit, putting a ball milling product into a quartz tube, carrying out vacuum sealing, and then sintering. According to the preparation method of the sulfide solid electrolyte, the compaction density of the sulfide solid electrolyte is improved, meanwhile, the ionic conductivity of an electrolyte material is prevented from being greatly reduced, the compaction density can reach 92% or above of the true density, and the ionic conductivity can be maintained to be 3 mS / cm or above.

Description

Technical Field

[0001] The present invention relates to the technical field of all-solid-state lithium batteries, and particularly to a sulfide solid electrolyte, a preparation method thereof, and an all-solid-state lithium battery. Background Art

[0002] The information disclosed in the background art of the present invention is only intended to increase the understanding of the overall background of the present invention, and does not necessarily be regarded as an admission or imply in any form that this information constitutes the prior art already known to those of ordinary skill in the art.

[0003] The solid electrolyte is one of the key materials for all-solid-state batteries. Among them, the sulfide solid electrolyte is considered to be one of the most promising solid electrolytes due to its excellent conductivity and good mechanical properties. However, the true density of the sulfide solid electrolyte is small, and the volume of the same weight of sulfide material is larger than that of the oxide solid electrolyte and the halide electrolyte, which results in a small volume energy density of the sulfide all-solid-state battery. In addition, the sulfide solid electrolyte has a porous structure, resulting in a lower tap density than the true density, further reducing the volume energy density. The prior art usually uses high-energy ball milling to grind raw materials such as lithium sulfide, phosphorus pentasulfide, and lithium chloride to prepare the sulfide solid electrolyte, but there are few reports on improving the tap density of the sulfide solid electrolyte. Therefore, it is very necessary to provide a method for improving the tap density of the sulfide solid electrolyte. Summary of the Invention

[0004] In view of this, the present invention provides a sulfide solid electrolyte, a preparation method thereof, and an all-solid-state lithium battery. The present invention can significantly improve the tap density of the sulfide solid electrolyte without significantly reducing the ionic conductivity, thereby improving the volume energy density of the battery.

[0005] In a first aspect, the present invention provides a preparation method of a sulfide solid electrolyte, comprising the following steps:

[0006] S1. Ball-milling raw materials including at least lithium sulfide and phosphorus pentasulfide at a ball-milling energy of 30 - 100 J / g·hit to obtain a primary ball-milled product;

[0007] S2. Vacuum ball-milling the primary ball-milled product at a ball-milling energy of 150 - 300 J / g·hit to obtain a secondary ball-milled product;

[0008] S3. Placing the secondary ball-milled product in a quartz tube for vacuum sealing, and then sintering.

[0009] Preferably, the raw materials further include LiX, where X is one or more of F, Cl, Br, or I.

[0010] Further, the molar ratio of Li, P, S, and X in the raw materials is controlled to be (5-7):(0.8-1.2):(4-6):(1-2).

[0011] Preferably, in step S1, the ball-milling solvent is selected from one or more of hexane, heptane, pentane, halogenated hexane, halogenated heptane, or halogenated pentane, and the ball-milling time is 4-12 h.

[0012] Preferably, in step S2, the ball-milling solvent is selected from one or more of hexane, heptane, pentane, halogenated hexane, halogenated heptane, or halogenated pentane, the vacuum ball-milling time is 4-12 h, and the vacuum degree is less than 0.1 bar.

[0013] Preferably, in step S3, the vacuum degree of the vacuum sealing is less than 0.1 bar.

[0014] Preferably, the sintering temperature is 300-600 °C, the sintering time is 4-24 h, and the heating rate to the sintering temperature is 1-10 °C / min.

[0015] Preferably, after the sintering step, it further includes a step of grinding the sintered product.

[0016] In a second aspect, the present invention provides a sulfide solid electrolyte prepared by the above preparation method.

[0017] In a third aspect, the present invention provides a all-solid-state lithium battery, including a positive electrode, a solid electrolyte layer, and a negative electrode, and the positive electrode, the solid electrolyte layer, and the negative electrode are stacked in sequence, and the solid electrolyte layer includes the above sulfide solid electrolyte.

[0018] Compared with the prior art, the present invention has achieved the following beneficial effects:

[0019] The present invention adopts a two-stage ball-milling process. First, a lower ball-milling energy is used to ensure uniform mixing of the raw materials, then a higher ball-milling energy is used in combination with vacuum pumping for ball-milling, and finally vacuum tube sealing sintering is combined. This method can not only improve the compaction density of the sulfide solid electrolyte, and the compaction density can reach more than 92% of the true density, but also effectively reduce its porosity, thereby improving the volume energy density of the battery. In addition, while improving the compaction density of the sulfide solid electrolyte, the present invention avoids a significant decrease in the ionic conductivity of the electrolyte material, and the ionic conductivity can be maintained above 3 mS / cm, thus ensuring that the performance of the battery is not affected. The technical solution of the present invention can make the ionic conductivity and compaction density of the all-solid-state battery in a better balance, and has high application value and good application prospects. Specific Embodiments

[0020] It should be noted that the following detailed description is exemplary and is intended to provide further illustration of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention pertains.

[0021] Glossary

[0022] Ball milling energy: Its calculation formula is as follows:

[0023] ΔE = 7.66×10 -2 ×R p 1.2 ×ρ 0.6 ×E 0.4 ×D b ×n p 1.2 / ρ s ;

[0024] Wherein, R p represents the distance from the center of the ball milling tank to the center of the ball mill, ρ and E respectively represent the density and Young's modulus of the ball milling medium used, D b is the diameter of the ball milling medium, n p is the rotational speed of the ball mill, ρ s represents the areal density of the powder wrapped on the surface of the grinding balls and can be obtained by measuring the mass increment of the grinding balls after ball milling. The present invention preferably adjusts the ball milling energy by the rotational speed of the ball mill.

[0025] Compaction density: It refers to the ratio of the mass to the volume of the material in a given container under the condition of applying a certain pressure. Generally speaking, the greater the compaction density, the higher the capacity of the battery can be made, so the compaction density is also regarded as one of the reference indicators of the material energy density.

[0026] True density: It refers to the actual mass of the solid substance per unit volume of the material in the absolutely dense state, that is, the density after removing the internal pores or the voids between particles.

[0027] Ionic conductivity: It refers to the rate and migration ability of ions moving in the electrolyte. In a battery, it affects the concentration and flow rate of ions in the electrolyte, and thus affects the performance and lifespan of the battery.

[0028] The present invention provides a method for preparing a sulfide solid electrolyte, comprising the following steps:

[0029] S1. Ball mill raw materials comprising at least lithium sulfide and phosphorus pentasulfide under a ball milling energy of 30 - 100 J / g·hit to obtain a primary ball mill product;

[0030] S2. Subject the primary ball-milled product to vacuum ball milling at a ball milling energy of 150 - 300 J / g·hit to obtain a secondary ball-milled product;

[0031] S3. Place the secondary ball-milled product in a quartz tube for vacuum sealing, and then perform sintering.

[0032] In the present invention, first, the raw materials of the sulfide solid electrolyte are ball milled through a ball milling step with a low ball milling energy. This ball milling process can make the raw materials fully and evenly mixed. Then, the primary ball-milled product is ball milled under vacuum with a higher ball milling energy. This step makes the material denser and is beneficial to the improvement of the compaction density. Subsequently, it is sealed in a vacuum quartz tube for sintering to obtain a sulfide solid electrolyte with a high compaction density. The present invention finds that the ball milling process has a great influence on the compaction density of the final sulfide solid electrolyte. A suitable ball milling energy can ensure that the finally prepared sulfide solid electrolyte has a high compaction density and the ionic conductivity does not decrease significantly.

[0033] In the present invention, the raw materials further include LiX, where X is one or more of F, Cl, Br, and I, preferably Cl. In the present invention, the molar ratio of Li, P, S, and X in the raw materials is controlled to be (5 - 7):(0.8 - 1.2):(4 - 6):(1 - 2). In one or more embodiments of the present invention, the molar ratio of Li, P, S, and X is 5.5:1:4.5:1.5 or 6:1:5:1.

[0034] In step S1 of the present invention, the ball milling solvent is selected from one or more of hexane, heptane, pentane, halohexane, halooctane, or halopentane, and the ball milling time is 4 - 12 h. The present invention does not impose special restrictions on the ball milling medium, and a commonly used ball milling medium in the art can be adopted.

[0035] In step S2 of the present invention, the ball milling solvent is selected from one or more of hexane, heptane, pentane, halohexane, halooctane, or halopentane, the vacuum ball milling time is 4 - 12 h, more preferably 6 - 10 h; the vacuum degree is less than 0.1 bar, for example, it can be 0.01 bar, 0.02 bar, 0.03 bar, 0.04 bar, 0.05 bar, etc. The present invention does not impose special restrictions on the ball milling medium, and a commonly used ball milling medium in the art can be adopted.

[0036] In the present invention, in step S3, the vacuum degree of the vacuum sealing is less than 0.1 bar, for example, it can be 0.01 bar, 0.02 bar, 0.03 bar, 0.04 bar, 0.05 bar, etc.

[0037] In the present invention, the sintering temperature is 300 to 600 °C, more preferably 400 to 500 °C; the sintering time is 4 to 24 h, more preferably 10 to 15 h; the heating rate for heating to the sintering temperature is 1 to 10 °C / min, more preferably 2 to 5 °C / min.

[0038] After the sintering step in the present invention, a step of grinding the sintered product is further included.

[0039] The present invention provides a sulfide solid electrolyte prepared by the above preparation method. The ionic conductivity of the sulfide solid electrolyte is above 3 mS / cm, and the compaction density is above 92% of the true density.

[0040] The present invention provides an all-solid-state lithium battery, which includes a positive electrode, a solid electrolyte layer, and a negative electrode, and the positive electrode, the solid electrolyte layer, and the negative electrode are stacked in sequence. The solid electrolyte layer includes the above sulfide solid electrolyte.

[0041] The present invention does not impose special restrictions on the materials and preparation methods of the positive electrode and the negative electrode and the preparation method of the solid electrolyte layer. Commonly used materials and preparation methods in the art can be adopted.

[0042] The technical solution of the present invention will be further elaborated below with specific examples.

[0043] Example 1

[0044] This example provides a preparation method of a sulfide solid electrolyte Li 5.5 PS 4.5 Cl 1.5 .

[0045] (1) Weigh 1.72 g of lithium sulfide (37.43 mmol), 2.08 g of phosphorus pentasulfide (9.36 mmol), and 1.19 g of lithium chloride (28.07 mmol) respectively, put them into a high-energy ball mill, set the ball milling energy to 50 J / g·hit, and the ball milling time to 8 hours; the ball milling medium is zirconia balls; the ball milling solvent is heptane.

[0046] (2) Set the ball milling energy to 200 J / g·hit, and at the same time evacuate the ball mill to a vacuum degree of 0.05 bar, and continue ball milling for 8 hours. The ball milling medium is zirconia balls; the ball milling solvent is heptane.

[0047] (3) Collect the milled material, put it into a quartz tube, evacuate it to a vacuum degree of 0.05 bar, and seal it. Put the sealed quartz tube into a tube furnace, set the heating rate to 3 °C / min, heat it to 450 °C, keep it warm for 12 h, and cool it to room temperature with the furnace. Use an agate mortar to grind the sintered material in a glove box to obtain a sulfide solid electrolyte material Li 5.5 PS4.5 Cl 1.5 。

[0048] Example 2

[0049] This example provides a preparation method for the sulfide solid electrolyte Li 6 PS 5 Cl.

[0050] (1) Weigh 2.14 g of lithium sulfide (42.84 mmol), 2.07 g of phosphorus pentasulfide (9.31 mmol), and 0.79 g of lithium chloride (18.64 mmol) respectively, put them into a high-energy ball mill, set the ball milling energy to 50 J / g·hit, and the ball milling time to 8 hours; the ball milling medium is zirconia balls; the ball milling solvent is heptane.

[0051] (2) Set the ball milling energy to 200 J / g·hit, and at the same time evacuate the ball mill to a vacuum degree of 0.05 bar, and continue ball milling for 8 hours; the ball milling medium is zirconia balls; the ball milling solvent is heptane.

[0052] (3) Collect the ground material, load it into a quartz tube, evacuate it to a vacuum degree of 0.05 bar, and seal it. Put the sealed quartz tube into a tube furnace, set the heating rate to 3 °C / min, heat it to 480 °C, keep it warm for 12 h, and cool it to room temperature with the furnace. Use an agate mortar to grind the sintered material in a glove box to obtain a high-compactness sulfide solid electrolyte material Li 6 PS 5 Cl.

[0053] Example 3

[0054] This example is different from Example 2 in that the ball milling energy in step (2) is set to 150 J / g·hit.

[0055] Example 4

[0056] This example is different from Example 2 in that the ball milling energy in step (1) is set to 80 J / g·hit.

[0057] Example 5

[0058] This example is different from Example 2 in that the ball mill is evacuated to a vacuum degree of 0.04 bar in step (2).

[0059] Example 6

[0060] This example is different from Example 2 in that the ball mill is evacuated to a vacuum degree of 0.01 bar in step (2).

[0061] Example 7

[0062] Compared with Example 2, the difference in this example is that in step (2), the ball milling energy is set to 150 J / g·hit, and the ball mill is evacuated to a vacuum degree of 0.01 bar.

[0063] Comparative Example 1

[0064] Compared with Example 1, the difference in this comparative example is that step (1) is not carried out.

[0065] Comparative Example 2

[0066] Compared with Example 1, the difference in this comparative example is that step (2) is not carried out.

[0067] Comparative Example 3

[0068] Compared with Example 2, the difference in this comparative example is that step (1) is not carried out.

[0069] Comparative Example 4

[0070] Compared with Example 2, the difference in this comparative example is that step (2) is not carried out.

[0071] Comparative Example 5

[0072] Compared with Example 2, the difference in this comparative example is that in step (2), the evacuation step is not carried out, that is, ball milling is carried out under normal pressure.

[0073] Comparative Example 6

[0074] Compared with Example 2, the difference in this comparative example is that in step (2), the ball milling energy is set to 350 J / g·hit.

[0075] Test Example

[0076] In the glove box, weigh 150 mg (mass m) of the sulfide solid electrolyte material of the example or comparative example, put it into the inner liner of the mold battery with a cross-sectional area of 0.785 cm 2 , and press it into a sulfide solid electrolyte layer at a pressure of 300 MPa. Use a vernier caliper to measure the thickness L of the compacted electrolyte layer. Subsequently, put 10 mg of conductive carbon on each side of the electrolyte layer, and continue to press it at a pressure of 300 MPa. Put the above-mentioned inner liner of the mold battery into the mold battery to form a symmetric battery. Use an electrochemical workstation to conduct EIS testing and read the impedance value R. Compaction density = m / (0.785×L); Ionic conductivity = L / (0.785×R). The measurement results are shown in Table 1. Li 5.5 PS 4.5 Cl 1.5 The true density of is 1.88 g / cm 3 , Li 6 PS 5The true density of Cl is 1.64 g / cm 3 .

[0077] Table 1 Measurement results of examples and comparative examples

[0078]

[0079] As can be seen from Table 1, the parameter settings (such as ball milling pressure, method, and energy, etc.) have obvious effects on both the compaction density and the ionic conductivity. The first-stage ball milling ensures that the raw materials are evenly mixed and crushed to a certain particle size range, ensuring complete reaction during sintering to obtain a high ionic conductivity. The second-stage ball milling uses a higher grinding energy, which helps to densify the raw material particles (eliminating grain boundaries and pores inside the particles), so as to improve the compaction density of the final product. In the solution of the embodiment of the present invention, the compaction density of the sulfide solid electrolyte can reach more than 92% of the true density, and the highest can reach more than 95%; while the compaction density of the comparative example is lower than 87% of the true density, and even lower than 80% of the true density, with a relatively low compaction density. Moreover, it can be seen that the ionic conductivity of the embodiment of the present invention does not significantly decrease compared with that of the comparative example. It can be seen that the embodiment of the present invention can maintain a high ionic conductivity while significantly increasing the compaction density.

[0080] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a sulfide solid electrolyte, characterized in that: The steps include: S1, ball milling a raw material including at least lithium sulfide and phosphorus pentasulfide at a ball milling energy of 30 to 100 J / g·hit to obtain a primary ball milling product; S2, vacuum ball milling the primary ball milling product at a ball milling energy of 150 to 300 J / g·hit to obtain a secondary ball milling product; S3. Place the secondary ball milling product in a quartz tube for vacuum sealing and then sinter.

2. The preparation method according to claim 1, characterized in that The raw material further comprises LiX, wherein X is one or more of F, Cl, Br or I.

3. The preparation method according to claim 2, characterized in that: The molar ratio of Li, P, S and X in the raw material is controlled to be (5-7): (0.8-1.2): (4-6): (1-2).

4. The preparation method according to claim 1, characterized in that: In step S1, the ball milling solvent is selected from one or more of hexane, heptane, pentane, halogenated hexane, halogenated heptane or halogenated pentane, and the ball milling time is 4 to 12 hours.

5. The preparation method according to claim 1, characterized in that: In step S2, the ball milling solvent is selected from one or more of hexane, heptane, pentane, halogenated hexane, halogenated heptane or halogenated pentane, the vacuum ball milling time is 4 to 12 hours, and the vacuum degree is less than 0.1 bar.

6. The preparation method according to claim 1, characterized in that: In step S3, the vacuum degree of the vacuum seal is less than 0.1 bar.

7. The preparation method according to claim 1, characterized in that: The sintering temperature is 300-600°C, the sintering time is 4-24h, and the heating rate to the sintering temperature is 1-10°C / min.

8. The preparation method according to claim 1, characterized in that: After the sintering step is completed, the method further includes a step of grinding the sintered product.

9. The sulfide solid electrolyte obtained by the preparation method according to any one of claims 1 to 8.

10. An all-solid-state lithium battery, comprising a positive electrode, a solid electrolyte layer and a negative electrode, wherein the positive electrode, the solid electrolyte layer and the negative electrode are stacked in sequence, characterized in that: The solid electrolyte layer includes the sulfide solid electrolyte according to claim 9.

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