Buffer layer for sulfide solid-state battery as well as preparation method and application of buffer layer

Abstract

The invention provides a buffer layer for a sulfide solid-state battery and a preparation method and application thereof, and the preparation method comprises the following steps: carrying out acid etching treatment on Ti3AlC2 powder, and carrying out first ultrasonic dispersion treatment to obtain two-dimensional nanosheet powder; mixing a sulfide electrolyte raw material, a lithium salt dopant and the two-dimensional nanosheet powder, performing second ultrasonic treatment to obtain a dispersion liquid, and mixing the dispersion liquid with a binder to obtain composite slurry; and coating the composite slurry on the surface of a substrate, and drying to obtain the buffer layer for the sulfide solid-state battery. The two-dimensional nanosheet powder and the sulfide electrolyte are prepared into the composite slurry, then the composite slurry is coated to prepare the buffer layer, and the buffer layer is arranged between the electrode plate of the solid-state battery and the solid-state electrolyte, so that the interface impedance can be effectively reduced, excellent ionic conductivity is achieved, and the cycle capacity retention rate of the solid-state battery can be further improved.

Description

Technical Field

[0001] This invention belongs to the field of solid-state battery technology, and relates to a buffer layer for sulfide solid-state batteries, its preparation method and application. Background Technology

[0002] In solid-state lithium batteries using sulfides as solid electrolytes, the interface between the electrode and the electrolyte is a solid-solid interface. Since the solid phase is non-wetting, the solid-solid interface will form a very high contact resistance, poor interfacial compatibility, and weak lithium-ion transport capability. At the same time, the volume expansion and contraction of the electrode material during charging and discharging makes the interface easy to separate, resulting in a large gap between the solid electrolyte and the electrode, forming a serious poor contact problem and affecting the performance of the solid-state lithium battery.

[0003] CN110034275A discloses a buffer layer for a sulfide solid-state battery, comprising a polymer material and ethylene carbonate, which is formed in situ on the electrode sheet by means of a buffer layer solution. The presence of the polymer can improve the poor physical contact between the electrode and the electrolyte caused by the volume deformation of the positive electrode material during charging and discharging.

[0004] CN118073661A discloses a method for constructing a lithium-rich buffer layer using a pre-discharge strategy and its application in all-solid-state batteries. The lithium-rich buffer layer is located between the lithium anode and the solid electrolyte, and the buffer layer is mainly composed of 2D functional carbon-based materials.

[0005] The interface effect between the buffer layer and the electrode plates or solid electrolyte in the solid-state battery described above is strong, resulting in low ionic conductivity and affecting the performance of the solid-state battery. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a buffer layer for sulfide solid-state batteries, its preparation method, and its application. The present invention prepares a buffer layer by coating a composite slurry made of two-dimensional nanosheet powder and sulfide electrolyte. The buffer layer, placed between the electrode sheet and the solid electrolyte of the solid-state battery, can not only effectively reduce the interfacial impedance but also has excellent ionic conductivity, thereby improving the cycle capacity retention rate of the solid-state battery.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a method for preparing a buffer layer for a sulfide solid-state battery, the method comprising the following steps:

[0009] After acid etching, Ti3AlC2 powder was subjected to a first ultrasonic dispersion treatment to obtain two-dimensional nanosheet powder.

[0010] After mixing sulfide electrolyte raw materials, lithium salt dopant and two-dimensional nanosheet powder, a dispersion was obtained by second ultrasonic treatment. The dispersion was then mixed with a binder to obtain a composite slurry.

[0011] The composite slurry is coated onto the substrate surface and dried to obtain the buffer layer for the sulfide solid-state battery.

[0012] This invention pre-prepares two-dimensional nanosheet powder, then mixes the two-dimensional nanosheet powder with sulfide electrolyte raw materials, adds a binder to form a composite slurry, and then coats it to form a buffer layer for sulfide solid-state batteries. The sulfide electrolyte in the buffer layer and the sulfide points in the sulfide solid-state battery directly belong to the same sulfide system and have highly similar chemical compositions. No chemical reaction occurs at the interface when they come into contact. Compared with the traditional LiNbO3 buffer layer, it can effectively reduce the interface impedance. The two-dimensional nanosheet powder can block excessive metal diffusion, and the lithium salt dopant can improve the ionic conductivity of the sulfide electrolyte through lattice defect regulation, thereby improving the cycle capacity retention rate of the solid-state battery.

[0013] Preferably, the acid solution used in the acid etching treatment includes a hydrofluoric acid solution.

[0014] Preferably, the mass concentration of the hydrofluoric acid solution is 30% to 50%, for example: 30%, 35%, 40%, 45% or 50%, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0015] Preferably, the mass-to-volume ratio of the Ti3AlC2 powder to the hydrofluoric acid solution is 1g:(20~30)mL, for example: 1g:20mL, 1g:22mL, 1g:25mL, 1g:28mL or 1g:30mL, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0016] Preferably, the acid etching process includes stirring dispersion and static etching.

[0017] Preferably, the stirring and dispersion time is 10 min to 20 min, for example: 10 min, 12 min, 15 min, 18 min or 20 min, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0018] Preferably, the static etching time is 20h~24h, for example: 20h, 21h, 22h, 23h or 24h, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0019] This invention uses Ti3AlC2 powder to make two-dimensional nanosheet powder. The two-dimensional sheet structure in the two-dimensional nanosheet powder can overlap with each other, providing excellent mechanical strength and toughness for the buffer layer, and can more effectively suppress the puncture of lithium dendrites.

[0020] Preferably, the acid etching treatment is followed by centrifugation and washing.

[0021] Preferably, the dispersant used in the first ultrasonic dispersion treatment includes deionized water.

[0022] Preferably, the solid-liquid mass-volume ratio of the first ultrasonic dispersion treatment is 1g:(40~50)mL, for example: 1g:40mL, 1g:42mL, 1g:45mL, 1g:48mL or 1g:50mL, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0023] Preferably, the time for the first ultrasonic dispersion treatment is 30 min to 40 min, for example: 30 min, 32 min, 35 min, 38 min or 40 min, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0024] Preferably, after the first ultrasonic dispersion treatment, the mixture is centrifuged, the supernatant is collected, and then vacuum dried.

[0025] Preferably, the centrifugation time is 10 min to 20 min, for example: 10 min, 12 min, 15 min, 18 min or 20 min, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0026] Preferably, the sulfide electrolyte raw material includes Li2S and P2S5.

[0027] Preferably, the lithium salt dopant includes LiI.

[0028] Preferably, the molar ratio of Li2S to P2S5 is (2.9~3.1):(1~1.1), for example: 2.9:1, 3:1, 2.9:1.05, 3:1.02 or 3.1:1.1, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0029] Preferably, the molar ratio of the theoretically synthesized sulfide electrolyte raw material to the lithium element in the lithium salt dopant is (1.8~2.2):1, for example: 1.8:1, 1.9:1, 2:1, 2.1:1 or 2.2:1, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0030] The theoretical molar amount of sulfide electrolyte synthesized from the sulfide electrolyte raw materials of this invention is the molar amount of sulfide electrolyte completely converted into sulfide electrolyte, calculated based on the amount of sulfide electrolyte raw materials fed. For example, if 3 mol of Li2S and 1 mol of P2S5 are added, the molar amount of Li3PS4 sulfide electrolyte synthesized is 2 mol. The molar ratio of the theoretically synthesized sulfide electrolyte from the sulfide electrolyte raw materials to the lithium element in the lithium salt dopant is 2:1, so the molar amount of lithium iodide is 1 mol.

[0031] Preferably, the total mass ratio of the sulfide electrolyte raw material and the lithium salt dopant to the two-dimensional nanosheet powder is 100:(0.5~1), for example: 100:0.5, 100:0.6, 100:0.7, 100:0.8, 100:0.9 or 100:1, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0032] Preferably, the mixture of sulfide electrolyte raw material, lithium salt dopant and two-dimensional nanosheet powder is subjected to ball milling.

[0033] Preferably, the ball milling speed is 300 rpm to 400 rpm, for example: 300 rpm, 320 rpm, 350 rpm, 380 rpm or 400 rpm, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0034] Preferably, the ball milling time is 2h to 3h, for example: 2h, 2.2h, 2.5h, 2.8h or 3h, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0035] During the ball milling process described in this invention, the sulfide electrolyte raw material can react to generate the corresponding sulfide electrolyte.

[0036] Preferably, the dispersant used in the second ultrasonic treatment includes n-heptane.

[0037] Preferably, the duration of the second ultrasonic treatment is 10 min to 20 min, for example: 10 min, 12 min, 15 min, 18 min or 20 min, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0038] This invention effectively breaks up the agglomeration of nanosheets through a two-step ultrasonic treatment, dispersing them into monolayers and allowing them to fully and uniformly contact the sulfide electrolyte particles. This maximizes the effective composite interface, reduces interfacial impedance, and forms a continuous and efficient ion transport channel.

[0039] Preferably, the adhesive comprises polyisobutylene.

[0040] Preferably, the amount of binder added is 1% to 2% based on the mass of the dispersion, for example: 1%, 1.2%, 1.5%, 1.8% or 2%.

[0041] Preferably, the solid content of the composite slurry is 15% to 20%, for example: 15%, 16%, 17%, 18%, 19% or 20%, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0042] Preferably, the substrate includes electrode plates.

[0043] Preferably, the dry atmosphere comprises argon.

[0044] Preferably, the drying temperature is 70℃~80℃, for example: 70℃, 72℃, 75℃, 78℃ or 80℃, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0045] Preferably, the drying time is 3h to 4h, for example: 3, 3.2, 3.5, 3.8 or 4, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0046] In a second aspect, the present invention provides a buffer layer for a sulfide solid-state battery, the buffer layer for a sulfide solid-state battery being prepared by the preparation method described in the first aspect.

[0047] In the buffer layer for sulfide solid-state batteries described in this invention, the two-dimensional nanosheets have good interfacial compatibility with the sulfide electrolyte, resulting in fewer side reactions. This effectively prevents the diffusion of transition metals while avoiding the generation of high-resistivity byproducts, thus significantly improving the cycle stability of the solid-state battery.

[0048] Preferably, the thickness of the buffer layer for the sulfide solid-state battery is 1μm to 2μm, for example: 1μm, 1.2μm, 1.5μm, 1.8μm or 2μm, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0049] Thirdly, the present invention provides a solid-state battery, the solid-state battery comprising electrode plates, a solid electrolyte, and a buffer layer for a sulfide solid-state battery as described in the second aspect.

[0050] The buffer layer for the sulfide solid-state battery is disposed between the electrode plates and the solid electrolyte.

[0051] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0052] Compared with the prior art, the present invention has the following beneficial effects:

[0053] (1) The present invention forms a buffer layer by coating a composite slurry made of two-dimensional nanosheet powder and sulfide electrolyte. The buffer layer is placed between the electrode sheet and the solid electrolyte of the solid battery, which can not only effectively reduce the interfacial impedance, but also has excellent ionic conductivity, thereby improving the cycle capacity retention rate of the solid battery.

[0054] (2) The NCM811 solid-state battery prepared by the buffer layer of the sulfide solid-state battery described in this invention has an initial discharge specific capacity of more than 165.8 mAh / g, an interface impedance of less than 177.3 Ω, and a capacity retention rate of more than 92.8% after 100 cycles at 0.5C. By adjusting the preparation conditions, the NCM811 solid-state battery prepared by the buffer layer of the sulfide solid-state battery can achieve an initial discharge specific capacity of more than 172.8 mAh / g, an interface impedance of less than 138.3 Ω, and a capacity retention rate of more than 96% after 100 cycles at 0.5C. Detailed Implementation

[0055] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0056] The "range" disclosed in this invention can be defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific range. This type of range definition can include or exclude endpoints; any endpoint can be independently included or excluded, and they can be arbitrarily combined, meaning any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~120 and 80~110 are listed for specific parameters, it is understood that ranges of 60~110 and 80~120 are also expected. Furthermore, if minimum range values ​​1 and 2 are listed, and maximum range values ​​3, 4, and 5 are also listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this invention, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0" and "5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer ≥2, it is equivalent to listing integers such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For instance, when a parameter is described as an integer selected from "2~10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0057] In this invention, "a combination of at least two" refers to a quantity greater than or equal to two, unless otherwise specified. For example, "any combination of one or at least two" means one or more or more items. It can be understood that when referring to "a combination of at least two," it refers to any suitable combination of multiple items, that is, a combination of "at least two" items carried out in a manner that does not conflict with and enables the implementation of this invention.

[0058] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0059] The term "embodiment" as used in this invention means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described in this invention can be combined with other embodiments.

[0060] Those skilled in the art will understand that the order in which the steps are written in the methods of the various embodiments does not imply a strict execution order. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, but are preferably performed sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), meaning that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0061] In this invention, open-ended technical features or solutions described using terms such as "comprising" do not exclude additional members beyond those listed unless otherwise specified. They can be considered as providing both closed-ended features or solutions comprised of the listed members and open-ended features or solutions that include additional members beyond the listed members. For example, A includes a1, a2, and a3. Unless otherwise specified, it may also include other members or exclude additional members. This can be considered as providing both technical features or solutions where "A is composed of a1, a2, and a3" or "A is selected from a1, a2, and a3," and technical features or solutions where "A includes not only a1, a2, and a3, but also other members."

[0062] In this invention, unless otherwise specified, the features or solutions corresponding to "and / or" include any one of two or more of the related listed items, as well as any and all combinations of the related listed items. These arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. For example, "A and / or B" represents a group consisting of A, B, and "a combination of A and B". "Containing A and / or B" can mean "containing A, containing B, and containing A and B", or "containing A, containing B, or containing A and B", and can be appropriately understood according to the context.

[0063] In this invention, the terms "first aspect," "second aspect," "third aspect," "fourth aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," "fourth," etc., serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on the quantity.

[0064] In this invention, "optional" means that something is optional, that is, it refers to any one of the two parallel solutions of "having" or "not having". If there are multiple "optional" options in a technical solution, unless otherwise specified, and there are no contradictions or mutual constraints, then each "optional" option is independent.

[0065] In this invention, "room temperature" generally refers to 4℃~35℃, and can refer to 20℃±5℃. In some embodiments of this invention, room temperature refers to 20℃~30℃.

[0066] The electrode plates used in the embodiments and comparative examples of the present invention include positive electrode plates and negative electrode plates, wherein the positive electrode plate is prepared by the following method:

[0067] Prepare aluminum foil, mix the positive electrode active material NCM811, conductive carbon black and binder solution dissolved in N-methylpyrrolidone in the formula amount to obtain positive electrode active layer paste, then use a coating machine to coat the positive electrode active layer paste on the outer surface of aluminum foil, dry to obtain positive electrode;

[0068] The negative electrode is a lithium metal sheet.

[0069] Example 1

[0070] This embodiment provides a buffer layer for sulfide solid-state batteries, which is prepared by the following method:

[0071] Ti3AlC2 powder was added to 40%HF solution at a solid-liquid mass-volume ratio of 1g:25mL, stirred and dispersed for 15min, then allowed to stand for etching for 22h. After centrifugation and washing, the obtained solid material was dispersed in deionized water at a solid-liquid mass-volume ratio of 1g:45mL, ultrasonicated for 35min, then centrifuged for 15min, the supernatant was collected and vacuum dried to obtain two-dimensional nanosheet powder.

[0072] Li₂S, P₂S₅, and LiI were mixed in a molar ratio of 5.8:2:1 (the molar ratio of the theoretically synthesized sulfide electrolyte raw material to the lithium element in the lithium salt dopant is 1.9:1). Two-dimensional nanosheet powder was then added, and the mixture was ball-milled at 350 rpm for 2.5 h to obtain a composite powder. The total mass ratio of Li₂S, P₂S₅, and LiI to the two-dimensional nanosheet powder was 100:0.5. The obtained composite powder was dispersed in n-heptane and ultrasonically dispersed for 15 min to obtain a dispersion. 1% (by mass) of polyisobutylene was added to the dispersion to obtain a composite slurry with a solid content of 15%.

[0073] The composite slurry was coated onto the surface of the electrode sheet and dried at 75°C under an argon atmosphere for 3.5 hours to obtain the buffer layer for the sulfide solid-state battery.

[0074] Example 2

[0075] This embodiment provides a buffer layer for sulfide solid-state batteries, which is prepared by the following method:

[0076] Ti3AlC2 powder was added to 30% HF solution at a solid-liquid mass-volume ratio of 1g:30mL, stirred and dispersed for 20min, then allowed to stand for etching for 24h. After centrifugation and washing, the obtained solid material was dispersed in deionized water at a solid-liquid mass-volume ratio of 1g:50mL, ultrasonicated for 40min, then centrifuged for 20min, the supernatant was collected and vacuum dried to obtain two-dimensional nanosheet powder.

[0077] Li₂S, P₂S₅, and LiI were mixed in a molar ratio of 6:2:1 (the molar ratio of the theoretically synthesized sulfide electrolyte raw material to the lithium element in the lithium salt dopant is 2:1). Two-dimensional nanosheet powder was then added, and the mixture was ball-milled at 400 rpm for 2 hours to obtain a composite powder. The total mass ratio of Li₂S, P₂S₅, and LiI to the two-dimensional nanosheet powder was 100:0.8. The obtained composite powder was dispersed in n-heptane and ultrasonically dispersed for 10 minutes to obtain a dispersion. 1.5% (by mass) of polyisobutylene was added to the dispersion to obtain a composite slurry with a solid content of 18%.

[0078] The composite slurry was coated onto the surface of the electrode sheet and dried at 70°C under an argon atmosphere for 4 hours to obtain the buffer layer for the sulfide solid-state battery.

[0079] Example 3

[0080] This embodiment provides a buffer layer for sulfide solid-state batteries, which is prepared by the following method:

[0081] Ti3AlC2 powder was added to 40%HF solution at a solid-liquid mass-volume ratio of 1g:20mL, stirred and dispersed for 10min, then allowed to stand for etching for 20h. After centrifugation and washing, the obtained solid material was dispersed in deionized water at a solid-liquid mass-volume ratio of 1g:40mL, ultrasonicated for 30min, then centrifuged for 10min, the supernatant was collected and vacuum dried to obtain two-dimensional nanosheet powder.

[0082] Li₂S, P₂S₅, and LiI were mixed in a molar ratio of 6.2:2.2:1 (the molar ratio of the theoretically synthesized sulfide electrolyte raw material to the lithium element in the lithium salt dopant is 2.1:1). Two-dimensional nanosheet powder was then added, and the mixture was ball-milled at 300 rpm for 3 hours to obtain a composite powder. The total mass ratio of Li₂S, P₂S₅, and LiI to the two-dimensional nanosheet powder was 100:1. The obtained composite powder was dispersed in n-heptane and ultrasonically dispersed for 20 minutes to obtain a dispersion. 2% (by mass) of polyisobutylene was added to the dispersion to obtain a composite slurry with a solid content of 20%.

[0083] The composite slurry was coated onto the surface of the electrode sheet and dried at 80°C under an argon atmosphere for 3 hours to obtain the buffer layer for the sulfide solid-state battery.

[0084] Example 4

[0085] The only difference between this embodiment and Embodiment 1 is that the mass concentration of the hydrofluoric acid solution used is 20%, while the other conditions and parameters are exactly the same as in Embodiment 1.

[0086] Example 5

[0087] The only difference between this embodiment and Embodiment 1 is that the mass concentration of the hydrofluoric acid solution used is 60%, while the other conditions and parameters are exactly the same as in Embodiment 1.

[0088] Example 6

[0089] The only difference between this embodiment and Example 1 is that, according to the theoretical synthesis of sulfide electrolyte raw materials, the molar ratio of the sulfide electrolyte to the lithium element in the lithium salt dopant is 1.5:1, and LiI is added. All other conditions and parameters are exactly the same as in Example 1.

[0090] Example 7

[0091] The only difference between this embodiment and Embodiment 1 is that, according to the theoretical synthesis of sulfide electrolyte raw materials, the molar ratio of the sulfide electrolyte to the lithium element in the lithium salt dopant is 2.5:1, and LiI is added. All other conditions and parameters are exactly the same as in Embodiment 1.

[0092] Comparative Example 1

[0093] The only difference between this comparative example and Example 1 is that lithium iodide is not added; all other conditions and parameters are exactly the same as in Example 1.

[0094] Comparative Example 2

[0095] The only difference between this comparative example and Example 1 is that two-dimensional nanosheet powder is not added; all other conditions and parameters are exactly the same as in Example 1.

[0096] Comparative Example 3

[0097] The only difference between this comparative example and Example 1 is that the Ti3AlC2 powder is not acid-etched; all other conditions and parameters are exactly the same as in Example 1.

[0098] Comparative Example 4

[0099] This comparative example uses conventional lithium niobate as a buffer layer.

[0100] Performance testing:

[0101] The electrodes coated with a buffer layer for solid-state batteries obtained in the examples and comparative examples were arranged in the following order: positive electrode - buffer layer for solid-state batteries - solid-state electrolyte (Li). 5.5 PS 4.5 Cl 1.5 The solid-state battery is assembled using a buffer layer-negative electrode structure, and the solid-state battery is tested. The test results are shown in Table 1.

[0102] Table 1

[0103] First discharge specific capacity (mAh / g) Interface impedance (Ω) Capacity retention rate (%) after 100 cycles at 0.5C Example 1 174.5 166.0 96.0 Example 2 174.8 162.2 96.3 Example 3 172.8 168.3 96.7 Example 4 168.2 175.5 93.6 Example 5 169.8 177.3 92.8 Example 6 168.5 161.2 93.8 Example 7 165.8 172.6 96.5 Comparative Example 1 155.2 202.6 90.2 Comparative Example 2 162.2 186.3 87.8 Comparative Example 3 163.8 185.2 82.5 Comparative Example 4 158.6 198.6 92.8

[0104] As shown in Table 1, and based on Examples 1-7, the NCM811 solid-state battery prepared with the sulfide solid-state battery buffer layer of the present invention can achieve an initial discharge specific capacity of over 165.8 mAh / g, an interface impedance of less than 177.3 Ω, and a capacity retention rate of over 92.8% after 100 cycles at 0.5C. By adjusting the preparation conditions, the NCM811 solid-state battery prepared with the sulfide solid-state battery buffer layer can achieve an initial discharge specific capacity of over 172.8 mAh / g, an interface impedance of less than 138.3 Ω, and a capacity retention rate of over 96% after 100 cycles at 0.5C.

[0105] A comparison of Examples 1 and 4-5 shows that the mass concentration of the hydrofluoric acid solution used in the acid etching process of the buffer layer for sulfide solid-state batteries described in this invention affects its performance. Controlling the mass concentration of the hydrofluoric acid solution to 30%~50% results in a buffer layer with better performance. If the mass concentration of the hydrofluoric acid solution is too low, it cannot fully remove the Al atomic layers between the layers, leading to incomplete conversion of some Ti3AlC2. The resulting nanosheets are stacked nanosheets with uneven chemical and electrochemical properties, causing instability at the battery interface. If the mass concentration of the hydrofluoric acid solution is too high, it will destroy the two-dimensional layered structure, etching the Ti atoms in the framework, causing the nanosheets to become thinner, generate numerous pores, or even fragment. When the nanosheets with damaged structures are made into a buffer layer, they may not be able to form a dense, continuous film, thus reducing their physical isolation and buffering effect.

[0106] A comparison of Examples 1 and 6-7 shows that the amount of lithium salt dopant added during the preparation of the buffer layer for the sulfide solid-state battery described in this invention affects its performance. Controlling the molar ratio of the theoretically synthesized sulfide electrolyte raw material to the lithium element in the lithium salt dopant at (1.8~2.2):1 results in a buffer layer with better performance. If the amount of lithium salt dopant added is too low, it cannot effectively improve the lithium-ion migration ability of the buffer layer, and the buffer layer will become a bottleneck for ion transport, increasing the overall internal resistance of the battery. If the amount of lithium salt dopant added is too high, excessive lithium salt will occupy too much volume in the buffer layer, potentially disrupting the continuous ion conduction network, leading to a decrease in overall ionic conductivity and cycle performance.

[0107] As can be seen from the comparison between Example 1 and Comparative Example 1, the lithium salt dopant in the buffer layer of the sulfide solid-state battery of the present invention can improve the ionic conductivity of the sulfide electrolyte through lattice defect regulation, thereby improving the cycle capacity retention rate of the solid-state battery.

[0108] As can be seen from the comparison of Example 1 and Comparative Examples 2-3, the present invention obtains two-dimensional nanosheet powder by acid etching of Ti3AlC2 powder. Ti3AlC2 itself has good metallic conductivity. In the buffer layer, it can provide a three-dimensional electronic conductive network, which helps to balance the electric field distribution inside the electrode and reduce interfacial polarization. After etching and ultrasonic treatment, the functional groups (-O, -OH) on the surface of the nanosheets have strong interactions with lithium ions, which can promote the adsorption and surface migration of lithium ions. When combined with sulfide electrolyte and lithium salt, a continuous ion-electron mixed conductive network can be formed, resulting in a buffer layer with a two-dimensional structure, excellent mixed conductivity, and good mechanical properties.

[0109] As can be seen from the comparison between Example 1 and Comparative Example 4, although the conventional lithium niobate buffer layer can block the diffusion of transition metals, it has poor compatibility with the sulfide electrolyte interface and is prone to generating Li2O, which leads to increased impedance. The sulfide solid-state battery buffer layer described in this invention can effectively reduce the interface impedance and significantly improve the performance of the solid-state battery.

[0110] The applicant declares that the above description is only a specific embodiment 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 conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing a buffer layer for a sulfide solid-state battery, characterized in that, The preparation method includes the following steps: After acid etching, Ti3AlC2 powder was subjected to a first ultrasonic dispersion treatment to obtain two-dimensional nanosheet powder. After mixing sulfide electrolyte raw materials, lithium salt dopant and two-dimensional nanosheet powder, a dispersion was obtained by second ultrasonic treatment. The dispersion was then mixed with a binder to obtain a composite slurry. The composite slurry is coated onto the substrate surface and dried to obtain the buffer layer for the sulfide solid-state battery.

2. The preparation method according to claim 1, characterized in that, The acid solution used in the acid etching treatment includes hydrofluoric acid solution; Preferably, the mass concentration of the hydrofluoric acid solution is 30% to 50%; Preferably, the mass-to-volume ratio of the Ti3AlC2 powder to the hydrofluoric acid solution is 1 g:(20~30) mL.

3. The preparation method according to claim 1 or 2, characterized in that, The acid etching process includes stirring and dispersion followed by static etching. Preferably, the stirring and dispersion time is 10 min to 20 min; Preferably, the static etching time is 20h~24h; Preferably, the acid etching treatment is followed by centrifugation and washing.

4. The preparation method according to any one of claims 1-3, characterized in that, The dispersant used in the first ultrasonic dispersion treatment includes deionized water; Preferably, the solid-liquid mass-to-volume ratio of the first ultrasonic dispersion treatment is 1g:(40~50)mL; Preferably, the time for the first ultrasonic dispersion treatment is 30 min to 40 min; Preferably, after the first ultrasonic dispersion treatment, the mixture is centrifuged, the supernatant is collected, and then vacuum dried. Preferably, the centrifugation time is 10 min to 20 min.

5. The preparation method according to any one of claims 1-4, characterized in that, The sulfide electrolyte raw materials include Li2S and P2S5; Preferably, the lithium salt dopant includes LiI; Preferably, the molar ratio of Li2S to P2S5 is (2.9~3.1):(1~1.1); Preferably, the molar ratio of the theoretically synthesized sulfide electrolyte raw material to the lithium element in the lithium salt dopant is (1.8~2.2):1; Preferably, the total mass ratio of the sulfide electrolyte raw material and the lithium salt dopant to the two-dimensional nanosheet powder is 100:(0.5~1); Preferably, the mixture of sulfide electrolyte raw material, lithium salt dopant and two-dimensional nanosheet powder is subjected to ball milling. Preferably, the ball milling speed is 300 rpm to 400 rpm; Preferably, the ball milling process takes 2 to 3 hours.

6. The preparation method according to any one of claims 1-5, characterized in that, The dispersant used in the second ultrasonic treatment includes n-heptane; Preferably, the second ultrasonic treatment time is 10 min to 20 min; Preferably, the adhesive comprises polyisobutylene; Preferably, the amount of binder added is 1% to 2% based on the mass of the dispersion (100%). Preferably, the solid content of the composite slurry is 15% to 20%.

7. The preparation method according to any one of claims 1-6, characterized in that, The substrate includes electrode plates; Preferably, the dry atmosphere includes argon; Preferably, the drying temperature is 70℃~80℃; Preferably, the drying time is 3 to 4 hours.

8. A buffer layer for a sulfide solid-state battery, characterized in that, The buffer layer for the sulfide solid-state battery is prepared by the preparation method according to any one of claims 1-7.

9. The buffer layer for a sulfide solid-state battery as described in claim 8, characterized in that, The thickness of the buffer layer for the sulfide solid-state battery is 1μm~2μm.

10. A solid-state battery, characterized in that, The solid-state battery includes electrode plates, a solid electrolyte, and a buffer layer for a sulfide solid-state battery as described in claim 8 or 9. The buffer layer for the sulfide solid-state battery is disposed between the electrode plates and the solid electrolyte.