A sulfide solid electrolyte, its preparation method and application

Abstract

The present invention provides a sulfide solid electrolyte, a preparation method thereof, and an application. The solid electrolyte includes a core, a transition layer sequentially connected to the core, and a coating layer; the core is Li 7‑ x PS 6‑x Cl x , 0.6 ≤ x ≤ 1.9; the transition layer is Li 7‑y PS 6‑ y Cl y , 0.3 ≤ y ≤ 0.6; the coating layer is Li 7‑z PS 6‑z Cl z , 0 ≤ z ≤ 0.3, and the concentration of Cl element in the coating layer decreases in a gradient from the inner layer to the outer layer. The sulfide solid electrolyte provided by the present invention enables the battery to have a higher charge-discharge capacity, better rate performance, and more excellent cycle performance.

Description

Technical Field

[0001] The present invention relates to the field of lithium-ion batteries, and relates to a sulfide solid electrolyte assembly and a preparation method and application thereof. Background Art

[0002] Since the invention of lithium-ion secondary batteries, they have been widely used in fields such as personal consumer electronics, electric two-wheel vehicles, new energy vehicles, and large-scale energy storage power stations. Due to their characteristics such as rechargeability, relatively high energy density, and long cycle life, people's daily lives have become inseparable from lithium-ion secondary batteries. With the increasing energy consumption of consumer electronics and the increasing demand for the cruising range of electric vehicles, the currently commercialized traditional lithium-ion secondary batteries composed of liquid electrolytes are increasingly unable to meet people's demands for battery energy density and safety performance. To solve the safety performance problems of traditional lithium-ion secondary batteries and improve the energy density of batteries at the same time, new all-solid-state lithium-ion secondary batteries have become a hot spot in battery technology development. All-solid-state batteries have characteristics such as high energy density, non-explosion, and non-combustion, and are recognized as the future development direction of battery technology.

[0003] Compared with traditional liquid lithium-ion secondary batteries, all-solid-state batteries replace the liquid electrolyte and separator with a solid electrolyte. The solid electrolyte is uniformly mixed with the positive electrode material or the negative electrode material on the positive electrode or negative electrode side, playing the role of conducting Li + . At the same time, the solid electrolyte forms a solid electrolyte membrane similar to a separator between the positive electrode and the negative electrode, playing the role of physically isolating the positive and negative electrodes and transporting Li + between the positive and negative electrodes. Thus, it can be seen that the solid electrolyte is an important medium for transporting Li + in the all-solid-state battery system. However, due to the natural phase state properties of the solid electrolyte, it cannot be well infiltrated into the gaps between the positive electrode or negative electrode material particles like a liquid electrolyte. Because it is difficult to form rich, stable, and effective ion transport channels in the all-solid-state battery due to the contact between solids, this battery system faces various problems in terms of electrochemical kinetics such as low charge and discharge capacity, poor first charge and discharge efficiency, poor cycle performance, and unsatisfactory high-rate charge and discharge performance.

[0004] CN113410515A discloses a sulfide solid electrolyte, a preparation method and an application thereof. The sulfide solid electrolyte includes a sulfide electrolyte and a halogen oxidant. The halogen oxidant is incorporated into the surface lattice of the sulfide electrolyte in a lattice doping manner. By incorporating the halogen oxidant into the surface lattice of the sulfide electrolyte in a lattice doping manner, a nanoscale oxidized coating layer can be formed on the surface layer of the sulfide electrolyte. The sulfide solid electrolyte has a high internal ionic conductivity, and at the same time, the surface oxidation state has good stability to the positive electrode, which can improve the contact stability with the positive electrode and enhance the battery cycle performance and life. However, after the halogen oxidant is incorporated into the lattice of the sulfide electrolyte, it will change its ionic transport performance, air stability and other properties, bringing new problems to the solid battery system.

[0005] CN110098432A discloses a preparation method and an application of a carbon fiber-coated solid electrolyte material. The method includes: 1. Weigh polyacrylonitrile powder and dissolve it in dimethylformamide, and stir magnetically until the solution becomes transparent, viscous and homogeneous; 2. Transfer the electrospinning solution into a syringe for electrospinning; 3. Remove the electrospun solid electrolyte sheet, dry it and calcine it in a tube furnace for pre-oxidation; 4. Carbonize the pre-oxidized material under an argon atmosphere to obtain a carbon fiber-coated solid electrolyte material. The surface of the solid electrolyte is coated with carbon fibers by electrospinning. The coating layer is in close contact with the solid electrolyte, which can inhibit the element diffusion and side reactions between the positive electrodes. At the same time, it can also significantly increase the contact area between the positive electrode material and the electrolyte, reduce the interfacial contact resistance, reduce polarization and improve the discharge performance. However, the synthesis process of the coated solid electrolyte material proposed in this invention is complex, the production rate is low, the production capacity is small, the cost is high, and it is difficult to carry out large-scale production.

[0006] CN112448025A discloses a softened solid electrolyte for a lithium-ion battery. In one embodiment, the softened solid electrolyte includes an oxide-based solid electrolyte, wherein at least a part of the oxide anions in the oxide-based solid electrolyte are replaced by replacement anions. In another embodiment, the softened solid electrolyte includes a sulfide-based solid electrolyte, wherein at least a part of the sulfide anions in the sulfide-based solid electrolyte are replaced by replacement anions. When the replacement anions replace the oxide anions, the replacement anions have a larger atomic radius than the oxide anions, and when the replacement anions replace the sulfide anions, the replacement anions have a larger atomic radius than the sulfide anions. Compared with a solid-state battery including the corresponding solid electrolyte but without replacement anions, this replacement-anion-containing solid electrolyte can increase the interfacial contact between the softened solid electrolyte and the electrode. However, after replacement with anions having a larger atomic radius, the crystal structure of the material body will change significantly, thereby affecting various electrochemical properties such as its ionic conductivity.

[0007] Therefore, how to prepare a sulfide solid electrolyte with large-scale production, high ionic conductivity, and stable material properties is an important research direction in this field. Summary of the Invention

[0008] The purpose of the present invention is to provide a sulfide solid electrolyte assembly and its preparation method and application.

[0009] To achieve the purpose of this invention, the following technical solutions are adopted:

[0010] One purpose of the present invention is to provide a sulfide solid electrolyte, which includes a core, a transition layer and a coating layer sequentially connected to the core.

[0011] The core is Li 7-x PS 6-x Cl x , 0.6 ≤ x ≤ 1.9, where the value of x can be 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8 or 1.9, etc., but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0012] The transition layer is Li 7-y PS 6-y Cl y , 0.3 ≤ y ≤ 0.6, where the value of y can be 0.3, 0.4, 0.5 or 0.6, etc., but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0013] The coating layer is Li 7-z PS6-z Cl z ,0 ≤ z ≤ 0.3, where the value of z can be 0, 0.1, 0.2, 0.3, etc., but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable. The concentration of Cl element in the coating layer decreases in a gradient from the inner layer to the outer layer.

[0014] The present invention provides a solid electrolyte material with a gradient decrease in the concentration of Cl element from the center to the outer surface. The concentration of Cl element on the outer surface of the material particles is the lowest, and the hardness of its outer surface is also the lowest. After the solid-state battery is pressure-treated, the solid electrolyte material with a smaller hardness outer surface has a larger contact area with the positive electrode material or negative electrode material particles. Therefore, a richer and more effective ion conduction channel is established between the positive and negative electrode materials and the sulfide solid electrolyte particles. The sulfide solid electrolyte provided by the present invention enables the battery to have a higher charge-discharge capacity, better rate performance, and more excellent cycle performance.

[0015] Since the gradient coating material only exhibits a low Cl element concentration on the outer surface in the present invention, its crystal structure does not show a phenomenon of poor Li + ion transport ability due to the lack of Cl element. The Li 7-x PS 6-x Cl x (0.6 ≤ x ≤ 1.9) solid electrolyte material still has excellent ionic conductivity performance.

[0016] As a preferred technical solution of the present invention, the concentration of Cl element near the inner core in the transition layer is greater than the concentration of Cl element near the coating layer.

[0017] Preferably, the raw materials of the solid electrolyte include LiCl, P2S5, and Li2S.

[0018] The second object of the present invention is to provide a preparation method of the sulfide solid electrolyte as described in the first object. The preparation method includes the following steps:

[0019] (1) First, mix LiCl, P2S5, and Li2S to obtain a raw material precursor, and perform first high-temperature sintering on the raw material precursor, and then naturally cool to obtain a first sintered matrix material;

[0020] (2) Second, mix the first sintered matrix material obtained in step (1), P2S5, and Li2S to obtain a mixed sample, and perform second high-temperature sintering on the mixed sample, and then naturally cool to obtain the sulfide solid electrolyte material.

[0021] In the present invention, by adding a gradient coating layer to the unoptimized Li 7-x PS 6-x Clx (0.6 ≤ x ≤ 1.9) For the base material, additive solid-phase mixing and pyroprocessing sintering processes are carried out. The solid-phase mixing sintering process adopted for the gradient-coated solid electrolyte material involved in the present invention has a simple and easy preparation method, is suitable for large-scale industrial production, and is conducive to improving product consistency.

[0022] In the preparation scheme of the present invention, after the first firing, Li with a certain Cl concentration can be obtained. 7-x PS 6-x Cl x (0.6 ≤ x ≤ 1.9) matrix material. The Cl element content shows a uniform distribution inside and on the surface of the matrix material particles. During the second firing, the surfaces of the matrix material particles are coated with P2S5 and Li2S raw materials. Under the action of thermal diffusion, the Cl atoms in the matrix material gradually diffuse to the surface of the coating layer. At the same time, elements such as Li, P, and S in the P2S5 and Li2S raw materials also diffuse into the matrix material, thereby forming a Cl element concentration gradient from the inside to the outer surface of the material particles. On the outer surface of the concentration-gradient-coated material particles, the Cl element concentration is the smallest, so the hardness of the outer surface of the material particles is also the smallest. This material design can significantly improve the contact between the solid electrolyte material and the positive electrode material or negative electrode material particles, thereby establishing a rich, stable, and effective Li + ion transport channel.

[0023] As a preferred technical solution of the present invention, in the first mixing described in step (1), the molar ratio of LiCl, P2S5, and Li2S is 2m:1:(7 - 2m), 0.6 ≤ m ≤ 1.9, where the value of m can be 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8, 1.9, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0024] As a preferred technical solution of the present invention, the rate of the first mixing described in step (1) is 500 - 700 rpm, where the rate can be 500 rpm, 520 rpm, 540 rpm, 560 rpm, 580 rpm, 600 rpm, 620 rpm, 640 rpm, 660 rpm, 680 rpm, 700 rpm, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0025] Preferably, the time of the first mixing described in step (1) is 20 - 25 min, where the time can be 20 min, 21 min, 22 min, 23 min, 24 min, 25 min, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0026] Preferably, the atmosphere for the first high-temperature sintering in step (1) is an inert atmosphere.

[0027] Preferably, the heating rate for the first high-temperature sintering in step (1) is 4 - 6 °C / min. The heating rate can be 4 °C / min, 5 °C / min, 6 °C / min, etc., but is not limited to the listed values. Other unlisted values within this range are equally applicable.

[0028] Preferably, the constant temperature for the first high-temperature sintering in step (1) is 500 - 600 °C. The constant temperature can be 500 °C, 520 °C, 540 °C, 560 °C, 580 °C, 600 °C, etc., but is not limited to the listed values. Other unlisted values within this range are equally applicable.

[0029] Preferably, the constant temperature holding time for the first high-temperature sintering in step (1) is 5 - 10 h. The constant temperature holding time can be 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, etc., but is not limited to the listed values. Other unlisted values within this range are equally applicable.

[0030] As a preferred technical solution of the present invention, in the second mixing in step (2), the molar ratio of the first sintered matrix material, P2S5, and Li2S is 1:(0.001 - 0.01):(0.001 - 0.1). The molar ratio can be 1:0.001:0.001, 1:0.001:0.1, 1:0.001:0.01, 1:0.01:0.001, 1:0.01:0.01, 1:0.01:0.1, etc., but is not limited to the listed values. Other unlisted values within this range are equally applicable.

[0031] As a preferred technical solution of the present invention, the rate of the second mixing in step (2) is 500 - 700 rpm. The rate can be 500 rpm, 520 rpm, 540 rpm, 560 rpm, 580 rpm, 600 rpm, 620 rpm, 640 rpm, 660 rpm, 680 rpm, 700 rpm, etc., but is not limited to the listed values. Other unlisted values within this range are equally applicable.

[0032] Preferably, the time for the second mixing in step (2) is 20 - 25 min. The time can be 20 min, 21 min, 22 min, 23 min, 24 min, 25 min, etc., but is not limited to the listed values. Other unlisted values within this range are equally applicable.

[0033] Preferably, the atmosphere for the second high-temperature sintering in step (2) is an air atmosphere.

[0034] Preferably, the heating rate of the second high-temperature sintering in step (2) is 15-25 °C / min. The heating rate can be 15 °C / min, 16 °C / min, 17 °C / min, 18 °C / min, 19 °C / min, 20 °C / min, 21 °C / min, 22 °C / min, 23 °C / min, 24 °C / min or 25 °C / min, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0035] Preferably, the constant temperature of the second high-temperature sintering in step (2) is 300-600 °C. The constant temperature can be 300 °C, 330 °C, 360 °C, 390 °C, 420 °C, 450 °C, 480 °C, 510 °C, 540 °C, 570 °C or 600 °C, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0036] Preferably, the constant temperature holding time of the second high-temperature sintering in step (2) is 2-6 h. The constant temperature holding time can be 2 h, 3 h, 4 h, 5 h or 6 h, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0037] As a preferred technical solution of the present invention, the temperature after natural cooling in step (1) is <50 °C. The temperature can be 5 °C, 10 °C, 15 °C, 20 °C, 25 °C, 30 °C, 35 °C, 40 °C, 45 °C or 49 °C, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0038] Preferably, the temperature after natural cooling in step (2) is <50 °C. The temperature can be 5 °C, 10 °C, 15 °C, 20 °C, 25 °C, 30 °C, 35 °C, 40 °C, 45 °C or 49 °C, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0039] As a preferred technical solution of the present invention, the preparation method includes the following steps:

[0040] (1) Mix LiCl, P2S5 and Li2S at a rate of 500-700 rpm for 20-25 min to obtain a raw material precursor. Perform the first high-temperature sintering on the raw material precursor with a heating rate of 4-6 °C / min, a constant temperature of 500-600 °C, and a constant temperature holding time of 5-10 h, and naturally cool to <50 °C to obtain the first sintered matrix material;

[0041] (2) The first sintered matrix material, P2S5, and Li2S described in step (1) are subjected to a second mixing at a rate of 500 - 700 rpm for 20 - 25 min to obtain a mixed sample. The mixed sample is subjected to a second high-temperature sintering with a heating rate of 15 - 25 °C / min, a constant temperature of 300 - 600 °C, and a constant-temperature holding time of 2 - 6 h, and is naturally cooled to <50 °C to obtain the sulfide solid electrolyte material.

[0042] The second object of the present invention is to provide an application of the sulfide solid electrolyte as described in the first object, and the sulfide solid electrolyte is applied to the field of lithium-ion batteries.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] In the solid electrolyte of the present invention, the concentration of Cl element decreases in a gradient from the center to the outer surface. The concentration of Cl element on the outer surface of the material particles is the smallest, and the hardness of its outer surface is also the smallest. After the solid-state battery is subjected to a pressing treatment, the solid electrolyte material with a smaller hardness outer surface has a larger contact area with the positive electrode material or the negative electrode material particles. Therefore, a more abundant and effective ion conduction channel is established between the positive and negative electrode materials and the solid electrolyte particles. The solid electrolyte provided by the present invention enables the battery to have a higher charge-discharge capacity, better rate performance, and more excellent cycle performance. Among them, the first charge-discharge reversible specific capacity can reach more than 180 mAh / g, the 2C rate capacity retention rate can reach more than 80%, and the cycle performance can exceed 150 cycles. Description of the Drawings

[0045] Figure 1 It is the SEM diagram of the sulfide solid electrolyte in Example 1 of the present invention.

[0046] Figure 2 It is the XRD curve of the sulfide solid electrolyte materials in Example 1 and Comparative Example 1 of the present invention.

[0047] Figure 3 It is the charge-discharge curve of the sulfide solid electrolyte in the solid-state battery in Example 1 and Comparative Example 1 of the present invention. Detailed Embodiments

[0048] The technical solutions of the present invention will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations to the present invention.

[0049] Example 1

[0050] This example provides a preparation method of a sulfide solid electrolyte, including the following steps:

[0051] (1) 8.478 g of LiCl, 22.227 g of P2S5 and 22.975 g of Li2S were added to a high-speed mixer and mixed at a rate of 500 rpm for 20 min to obtain a raw material precursor. The raw material precursor was transferred to a ceramic crucible and placed in an atmosphere sintering furnace. Under a nitrogen atmosphere, the raw material precursor was subjected to a first high-temperature sintering with a heating rate of 5 °C / min, a constant temperature of 550 °C, and a constant temperature holding time of 8 h. After the constant temperature sintering was completed, the sample remained in the atmosphere sintering furnace and was naturally cooled to a furnace temperature <50 °C to obtain a first sintered matrix material. The material was taken out of the sintering furnace under the protection of a nitrogen atmosphere;

[0052] (2) 50 g of the first sintered matrix material, 0.04 g of P2S5 and 0.3 g of Li2S obtained in step (1) were added to a high-speed mixer and mixed at a rate of 500 rpm for 20 min to obtain a mixed sample. The mixed sample was poured into a ceramic crucible and placed in an atmosphere sintering furnace. Under a nitrogen atmosphere, the mixed sample was subjected to a second high-temperature sintering with a heating rate of 20 °C / min, a constant temperature of 500 °C, and a constant temperature holding time of 2 h. After the constant temperature holding was completed, the sample remained in the atmosphere sintering furnace and was naturally cooled to a furnace temperature <50 °C to obtain the sulfide solid electrolyte material. The sintered sulfide solid electrolyte material was taken out of the furnace under the protection of a nitrogen atmosphere to complete the sintering.

[0053] In this example, the SEM image of the sulfide solid electrolyte is as Figure 1 shown.

[0054] Example 2

[0055] This example provides a method for preparing a sulfide solid electrolyte, including the following steps:

[0056] (1) 8.478 g of LiCl, 22.227 g of P2S5 and 22.975 g of Li2S were added to a high-speed mixer and mixed at a rate of 700 rpm for 25 min to obtain a raw material precursor. The raw material precursor was transferred to a ceramic crucible and placed in an atmosphere sintering furnace. Under a nitrogen atmosphere, the raw material precursor was subjected to a first high-temperature sintering with a heating rate of 4 °C / min, a constant temperature of 550 °C, and a constant temperature holding time of 8 h. After the constant temperature sintering was completed, the sample remained in the atmosphere sintering furnace and was naturally cooled to a furnace temperature <50 °C to obtain a first sintered matrix material. The material was taken out of the sintering furnace under the protection of a nitrogen atmosphere;

[0057] (2) Add the 50 g of the first sintered matrix material, 0.04 g of P2S5, and 0.3 g of Li2S described in step (1) into a high-speed mixer, perform a second mixing at a rate of 700 rpm for 25 min to obtain a mixed sample. Pour the mixed sample into a ceramic crucible and place it in an atmosphere sintering furnace. Under a nitrogen atmosphere, perform a second high-temperature sintering on the mixed sample with a heating rate of 15 °C / min, a constant temperature of 300 °C, and a constant temperature holding time of 2 h. After the constant temperature holding is completed, the sample remains in the atmosphere sintering furnace and is naturally cooled to a furnace temperature <50 °C to obtain the sulfide solid electrolyte material. Take out the sintered sulfide solid electrolyte material from the furnace under the protection of a nitrogen atmosphere to complete the sintering.

[0058] Example 3

[0059] This example provides a method for preparing a sulfide solid electrolyte, including the following steps:

[0060] (1) Add 8.478 g of LiCl, 22.227 g of P2S5, and 22.975 g of Li2S into a high-speed mixer, perform a first mixing at a rate of 600 rpm for 22 min to obtain a raw material precursor. Transfer the raw material precursor to a ceramic crucible and place it in an atmosphere sintering furnace. Under a nitrogen atmosphere, perform a first high-temperature sintering on the raw material precursor with a heating rate of 6 °C / min, a constant temperature of 550 °C, and a constant temperature holding time of 8 h. After the constant temperature sintering is completed, the sample remains in the atmosphere sintering furnace and is naturally cooled to a furnace temperature <50 °C to obtain the first sintered matrix material. Take out the material from the sintering furnace under the protection of a nitrogen atmosphere;

[0061] (2) Add the 50 g of the first sintered matrix material, 0.04 g of P2S5, and 0.3 g of Li2S described in step (1) into a high-speed mixer, perform a second mixing at a rate of 600 rpm for 25 min to obtain a mixed sample. Pour the mixed sample into a ceramic crucible and place it in an atmosphere sintering furnace. Under a nitrogen atmosphere, perform a second high-temperature sintering on the mixed sample with a heating rate of 25 °C / min, a constant temperature of 600 °C, and a constant temperature holding time of 2 h. After the constant temperature holding is completed, the sample remains in the atmosphere sintering furnace and is naturally cooled to a furnace temperature <50 °C to obtain the sulfide solid electrolyte material. Take out the sintered sulfide solid electrolyte material from the furnace under the protection of a nitrogen atmosphere to complete the sintering.

[0062] Example 4

[0063] This example provides a method for preparing a sulfide solid electrolyte, including the following steps:

[0064] (1) Add 8.478 g of LiCl, 22.227 g of P2S5, and 22.975 g of Li2S to a high-speed mixer. After the first mixing at a rate of 500 rpm for 20 min, a raw material precursor is obtained. Transfer the raw material precursor to a ceramic crucible and place it in an atmosphere sintering furnace. Under a nitrogen atmosphere, perform the first high-temperature sintering on the raw material precursor with a heating rate of 5 °C / min, a constant temperature of 550 °C, and a constant temperature holding time of 8 h. After the constant temperature sintering is completed, the sample remains in the atmosphere sintering furnace and is naturally cooled to a furnace temperature <50 °C to obtain the first sintered matrix material. Take out the material from the sintering furnace under the protection of a nitrogen atmosphere;

[0065] (2) Add 50 g of the first sintered matrix material, 0.08 g of P2S5, and 0.3 g of Li2S obtained in step (1) to a high-speed mixer. After the second mixing at a rate of 500 rpm for 20 min, a mixed sample is obtained. Pour the mixed sample into a ceramic crucible and place it in an atmosphere sintering furnace. Under a nitrogen atmosphere, perform the second high-temperature sintering on the mixed sample with a heating rate of 20 °C / min, a constant temperature of 500 °C, and a constant temperature holding time of 2 h. After the constant temperature holding is completed, the sample remains in the atmosphere sintering furnace and is naturally cooled to a furnace temperature <50 °C to obtain the sulfide solid electrolyte material. Take out the sintered sulfide solid electrolyte material from the furnace under the protection of a nitrogen atmosphere to complete the sintering.

[0066] Example 5

[0067] This example provides a method for preparing a sulfide solid electrolyte, including the following steps:

[0068] (1) Add 8.478 g of LiCl, 22.227 g of P2S5, and 22.975 g of Li2S to a high-speed mixer. After the first mixing at a rate of 500 rpm for 20 min, a raw material precursor is obtained. Transfer the raw material precursor to a ceramic crucible and place it in an atmosphere sintering furnace. Under a nitrogen atmosphere, perform the first high-temperature sintering on the raw material precursor with a heating rate of 5 °C / min, a constant temperature of 550 °C, and a constant temperature holding time of 8 h. After the constant temperature sintering is completed, the sample remains in the atmosphere sintering furnace and is naturally cooled to a furnace temperature <50 °C to obtain the first sintered matrix material. Take out the material from the sintering furnace under the protection of a nitrogen atmosphere;

[0069] (2) Add the 50 g of the first sintered matrix material, 0.04 g of P2S5, and 0.3 g of Li2S described in step (1) to a high-speed mixer, and perform a second mixing at a rate of 500 rpm for 20 min to obtain a mixed sample. Pour the mixed sample into a ceramic crucible and place it in an atmosphere sintering furnace. Under a nitrogen atmosphere, perform a second high-temperature sintering on the mixed sample with a heating rate of 20 °C / min, a constant temperature of 500 °C, and a constant temperature holding time of 4 h. After the constant temperature holding is completed, the sample remains in the atmosphere sintering furnace and is naturally cooled to a furnace temperature <50 °C to obtain the sulfide solid electrolyte material. Take out the sintered sulfide solid electrolyte material from the furnace under the protection of a nitrogen atmosphere to complete the sintering.

[0070] Example 6

[0071] This example provides a method for preparing a sulfide solid electrolyte, which includes the following steps:

[0072] (1) Add 8.478 g of LiCl, 22.227 g of P2S5, and 22.975 g of Li2S to a high-speed mixer, and perform a first mixing at a rate of 500 rpm for 20 min to obtain a raw material precursor. Transfer the raw material precursor to a ceramic crucible and place it in an atmosphere sintering furnace. Under a nitrogen atmosphere, perform a first high-temperature sintering on the raw material precursor with a heating rate of 5 °C / min, a constant temperature of 550 °C, and a constant temperature holding time of 8 h. After the constant temperature sintering is completed, the sample remains in the atmosphere sintering furnace and is naturally cooled to a furnace temperature <50 °C to obtain the first sintered matrix material. Take out the material from the sintering furnace under the protection of a nitrogen atmosphere;

[0073] (2) Add the 50 g of the first sintered matrix material, 0.04 g of P2S5, and 0.3 g of Li2S described in step (1) to a high-speed mixer, and perform a second mixing at a rate of 500 rpm for 20 min to obtain a mixed sample. Pour the mixed sample into a ceramic crucible and place it in an atmosphere sintering furnace. Under a nitrogen atmosphere, perform a second high-temperature sintering on the mixed sample with a heating rate of 20 °C / min, a constant temperature of 400 °C, and a constant temperature holding time of 2 h. After the constant temperature holding is completed, the sample remains in the atmosphere sintering furnace and is naturally cooled to a furnace temperature <50 °C to obtain the sulfide solid electrolyte material. Take out the sintered sulfide solid electrolyte material from the furnace under the protection of a nitrogen atmosphere to complete the sintering.

[0074] Example 7

[0075] In this example, except that 8.478 g of LiCl, 22.227 g of P2S5, and 22.975 g of Li2S in step (1) are replaced with 4.239 g of LiCl, 22.227 g of P2S5, and 27.57 g of Li2S, other conditions are the same as those in Example 1.

[0076] Example 8

[0077] In this example, except that 8.478 g of LiCl, 22.227 g of P2S5 and 22.975 g of Li2S in step (1) are replaced with 16.956 g of LiCl, 22.227 g of P2S5 and 13.785 g of Li2S, other conditions are the same as those in Example 1.

[0078] Comparative Example 1

[0079] This example provides a method for preparing a sulfide solid electrolyte, including the following steps:

[0080] (1) Add 8.478 g of LiCl, 22.227 g of P2S5 and 22.975 g of Li2S into a high-speed mixer, conduct the first mixing at a rate of 500 rpm for 20 min to obtain a raw material precursor, transfer the raw material precursor to a ceramic crucible, and place it in an atmosphere sintering furnace. Under a nitrogen atmosphere, perform the first high-temperature sintering on the raw material precursor with a heating rate of 5 °C / min, a constant temperature of 550 °C, and a constant temperature holding time of 8 h. After the constant temperature sintering is completed, the sample remains in the atmosphere sintering furnace and naturally cools to a furnace temperature <50 °C to obtain a first sintered matrix material, and take out the material from the sintering furnace under the protection of a nitrogen atmosphere;

[0081] (2) Pour the first sintered matrix material in step (1) into a ceramic crucible and place it in an atmosphere sintering furnace. Under a nitrogen atmosphere, perform the second high-temperature sintering on the first sintered matrix material with a heating rate of 20 °C / min, a constant temperature of 500 °C, and a constant temperature holding time of 2 h. After the constant temperature holding is completed, the sample remains in the atmosphere sintering furnace and naturally cools to a furnace temperature <50 °C to obtain the sulfide solid electrolyte material. Take out the sintered sulfide solid electrolyte material from the furnace under the protection of a nitrogen atmosphere to complete the sintering.

[0082] The XRD curves of the sulfide solid electrolytes prepared in Example 1 and this comparative example are as Figure 2 shown, and the charge-discharge curves of the prepared sulfide solid-state batteries are as Figure 3 shown.

[0083] Figure 2 is the XRD curve of the gradient-coated sulfide solid electrolyte material; the gradient-coated optimized solid electrolyte provided by the present invention has the same crystal structure as the unoptimized solid electrolyte material, indicating that the coating of P2S5 and Li2S does not change the crystal structure of the material itself and does not affect the ionic conductivity of the material itself.

[0084] Figure 3Charge and discharge curves of the sulfide solid electrolyte obtained in Example 1 and Comparative Example 1 in a solid-state battery. The sulfide solid electrolyte optimized by gradient coating can provide higher capacity and smaller polarization effect after being assembled into a solid-state battery. This phenomenon can be attributed to its excellent fusion with the cathode material particles, and there are abundant, stable and effective lithium-ion transport channels between the material particles.

[0085] Comparative Example 2

[0086] In this comparative example, except for not adding Li2S in the second mixing of step (2), other conditions are the same as those in Example 1.

[0087] Comparative Example 3

[0088] In this comparative example, except for not adding P2S5 in the second mixing of step (2), other conditions are the same as those in Example 1.

[0089] The sulfide solid electrolytes in Examples 1-8 and Comparative Examples 1-3 were assembled into batteries, and the batteries were tested for ionic conductivity, rate performance and cycling performance. The test results are shown in Table 1.

[0090] The test method for ionic conductivity is as follows: In an argon glove box, weigh 100 mg of the above-mentioned solid electrolyte powder, place it in an insulating outer cylinder, press it into a mold at a pressure of 300 MPa, and use a mold battery to perform an AC impedance spectroscopy test. The test conditions are: the test pressure is 300 MPa, and the frequency is 3.5 MHz - 0.1 Hz. The ionic conductivity of the electrolyte material is calculated from the impedance value and the Arrhenius formula based on the test data.

[0091] The test method for rate performance is as follows: In an argon glove box, assemble a mold battery with an 811 ternary material as the cathode, a Li / In alloy as the anode, and the above-mentioned sulfide solid electrolyte. Use a constant current charge and discharge tester to perform 0.1C constant current charge and discharge and 2C constant current charge and discharge tests on it. The capacity retention percentage obtained by dividing the 2C constant current discharge capacity by the 0.1C constant current discharge capacity is the rate performance.

[0092] The test method for cycling performance is as follows: In an argon glove box, assemble a mold battery with an 811 ternary material as the cathode, a Li / In alloy as the anode, and the above-mentioned sulfide solid electrolyte. Use a constant current charge and discharge tester to perform 1 / 3C constant current charge and discharge tests on it. After 100 constant current charge and discharge cycles, the percentage of the remaining reversible capacity to the first capacity is the cycling performance.

[0093] Table 1

[0094]

[0095] It can be obtained from the above table that:

[0096] (1) The addition of Li2S and P2S5 during the second sintering process has no adverse effect on the ionic conductivity, and at the same time significantly improves the rate performance and cycling performance of the die battery. Therefore, the solid electrolyte proposed by the solution of the present invention can establish a good lithium-ion conduction path between the solid state and the solid surface.

[0097] (2) During the second sintering process, the sintering temperature plays a very important role in achieving the goal of Cl element gradient coating.

[0098] The applicant declares that the above description is only a specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A sulfide solid electrolyte, characterized in that, The sulfide solid electrolyte includes a core, a transition layer sequentially connected to the core, and a coating layer; The kernel is Li 7-x PS 6-x Cl x , 0.6 ≤ x ≤ 1.9; The transition layer is Li 7-y PS 6-y Cl y , 0.3 ≤ y ≤ 0.6, and the concentration of Cl element near the inner core in the transition layer is greater than that near the coating layer; The coating layer is Li 7-z PS 6-z Cl z , 0 ≤ z ≤ 0.3, and the concentration of Cl element in the coating layer decreases in a gradient from the inner layer to the outer layer.

2. The sulfide solid electrolyte according to claim 1, wherein The raw materials of the solid electrolyte include LiCl, P2S5, and Li2S.

3. A method for preparing a sulfide solid electrolyte as described in claim 1 or 2, characterized in that, The preparation method includes the following steps: (1) First mix LiCl, P2S5, and Li2S to obtain a raw material precursor, perform first high-temperature sintering on the raw material precursor, and naturally cool to obtain a first sintered matrix material; (2) Second mix the first sintered matrix material, P2S5, and Li2S in step (1) to obtain a mixed sample, perform second high-temperature sintering on the mixed sample, and naturally cool to obtain the sulfide solid electrolyte material.

4. The preparation method according to claim 3, characterized in that, In the first mixing in step (1), the molar ratio of LiCl, P2S5, and Li2S is 2m:1:(7 - 2m), where 0.6 ≤ m ≤ 1.

9.

5. The preparation method according to claim 3, characterized in that, The rate of the first mixing in step (1) is 500 - 700 rpm.

6. The preparation method according to claim 3, wherein The time of the first mixing in step (1) is 20 - 25 min.

7. The preparation method according to claim 3, wherein The atmosphere of the first high-temperature sintering in step (1) is an inert atmosphere.

8. The preparation method according to claim 3, wherein, The heating rate of the first high-temperature sintering in step (1) is 4 - 6 °C / min.

9. The preparation method according to claim 3, wherein, The constant temperature of the first high-temperature sintering in step (1) is 500 - 600 °C.

10. The preparation method according to claim 3, characterized in that, The constant temperature holding time of the first high-temperature sintering in step (1) is 5 - 10 h.

11. The preparation method according to claim 3, wherein In the second mixing in step (2), the molar ratio of the first sintered matrix material, P2S5, and Li2S is 1:(0.001 - 0.01):(0.001 - 0.1).

12. The preparation method according to claim 3, characterized in that, The rate of the second mixing in step (2) is 500 - 700 rpm.

13. The preparation method according to claim 3, characterized in that, The time of the second mixing in step (2) is 20 - 25 min.

14. The preparation method according to claim 3, wherein The atmosphere of the second high-temperature sintering in step (2) is an air atmosphere.

15. The preparation method according to claim 3, characterized in that, The heating rate of the second high-temperature sintering in step (2) is 15 - 25 °C / min.

16. The preparation method according to claim 3, characterized in that, The constant temperature of the second high-temperature sintering in step (2) is 300 - 600 °C.

17. The preparation method according to claim 3, wherein, The constant temperature holding time of the second high-temperature sintering in step (2) is 2 - 6 h.

18. The preparation method according to claim 3, characterized in that, The temperature after natural cooling in step (1) < 50 °C.

19. The preparation method according to claim 3, wherein, The temperature after natural cooling in step (2) < 50 °C.

20. The preparation method according to claim 3, characterized in that, The preparation method includes the following steps: (1) First mix LiCl, P2S5, and Li2S at a rate of 500 - 700 rpm for 20 - 25 min to obtain a raw material precursor, perform first high-temperature sintering on the raw material precursor with a heating rate of 4 - 6 °C / min, a constant temperature of 500 - 600 °C, and a constant temperature holding time of 5 - 10 h, and naturally cool to < 50 °C to obtain a first sintered matrix material; (2) Second mix the first sintered matrix material, P2S5, and Li2S in step (1) at a rate of 500 - 700 rpm for 20 - 25 min to obtain a mixed sample, perform second high-temperature sintering on the mixed sample with a heating rate of 15 - 25 °C / min, a constant temperature of 300 - 600 °C, and a constant temperature holding time of 2 - 6 h, and naturally cool to < 50 °C to obtain the sulfide solid electrolyte material.

21. Use of a sulfide solid electrolyte as described in claim 1 or 2, characterized in that, The sulfide solid electrolyte is applied in the field of lithium-ion batteries.

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