Solid electrolyte, battery and preparation method thereof, and electric equipment

Abstract

The invention relates to a solid electrolyte, a battery, a preparation method of the battery and electric equipment, and belongs to the technical field of batteries. The solid electrolyte comprises an electrolyte layer and an inorganic composite interface layer arranged on at least one side of the electrolyte layer, the electrolyte layer comprises a sulfide solid electrolyte, and the inorganic composite interface layer comprises LiF and Li2S. And the problem of side reaction of a negative electrode interface can be effectively improved.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a solid electrolyte, a battery, a method for preparing the same, and an electrical device thereof. Background Technology

[0002] Among numerous solid electrolytes, sulfide solid electrolytes stand out due to their high ionic conductivity (10⁻⁶ Ω·cm). -3 ~10 -2 It has the characteristics of low S / cm, low Young's modulus, and good processing performance, and has commercial prospects.

[0003] However, sulfide solid-state batteries still face several pressing issues: sulfide solid electrolytes, typically LPSCl, have a narrow electrochemical window (1.08~2.24V). When using lithium metal or silicon-based anodes, irreversible redox reactions occur at the interface between the solid electrolyte and the anode during charge and discharge. Furthermore, the reaction byproducts cannot further prevent these reactions, leading to continuous degradation of battery performance. The theoretical volume change rates during charge and discharge are approximately 300% and 100%, respectively. To ensure solid-solid interface contact in sulfide solid-state batteries, pressures exceeding 10 MPa are required during charge and discharge to guarantee normal battery performance, hindering the commercialization of sulfide solid-state batteries. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present application aims to provide a solid electrolyte, a battery, and a method for preparing the same. This can effectively mitigate the problem of side reactions occurring at the negative electrode interface.

[0005] In a first aspect, embodiments of this application provide a solid electrolyte, including an electrolyte layer and an inorganic composite interface layer disposed on at least one side of the electrolyte layer. The electrolyte layer includes a sulfide solid electrolyte, and the inorganic composite interface layer includes LiF and Li2S.

[0006] This application employs an inorganic composite interface layer comprising LiF and Li2S on at least one side of the surface of a sulfide solid electrolyte. LiF has high mechanical strength but low ionic conductivity, while Li2S has low mechanical strength but high ionic conductivity. Together, they form a dense interface layer with suitable mechanical strength and maintaining a certain suitable ionic conductivity. Furthermore, the interface rich in LiF and Li2S exhibits excellent chemical stability, thereby effectively improving the problem of side reactions at the negative electrode interface, reducing interfacial impedance, improving the solid-solid interface contact between the negative electrode and the electrolyte, and reducing the operating pressure of the battery.

[0007] In some embodiments of this application, the sulfide solid electrolyte includes at least one of Li6PS5X, LiGePS, LiSiPS, and LiSnPS; wherein X is at least one of F, Cl, Br, and I.

[0008] This application employs a suitable sulfide solid electrolyte to facilitate the formation of a high-performance sulfide solid battery.

[0009] In some embodiments of this application, the density of the inorganic composite interface layer is between 98% and 100%. The inorganic composite interface layer of this application has a high density, which can effectively coat the surface of the electrolyte layer and the negative electrode sheet, thereby effectively improving the problem of side reactions occurring at the interface between the solid electrolyte and the negative electrode.

[0010] In some embodiments of this application, the thickness of the inorganic composite interface layer is between 30 nm and 150 nm.

[0011] The inorganic composite interface layer formed in situ in this application has a smaller thickness, which can reduce interface impedance, improve solid-solid interface contact between the negative electrode and the electrolyte, and reduce the operating pressure of the battery.

[0012] Secondly, embodiments of this application provide a battery, including a positive electrode, a negative electrode, and a solid electrolyte provided in the first aspect.

[0013] This application provides a battery including the above-mentioned solid electrolyte. The solid electrolyte can effectively improve the problem of side reactions occurring at the negative electrode interface, and the battery including the solid electrolyte has good electrochemical performance.

[0014] In some embodiments of this application, the negative electrode is a lithium metal negative electrode or a silicon-based negative electrode. When the negative electrode is a lithium metal negative electrode or a silicon-based negative electrode, an irreversible redox reaction will occur at the interface between the solid electrolyte and the negative electrode during charging and discharging. The solid electrolyte of this application has an inorganic composite interface layer containing LiF and Li2S formed in situ on at least one side of its surface, so as to improve the problem of redox reaction at the interface between the solid electrolyte and the lithium metal negative electrode or the silicon-based negative electrode.

[0015] In some embodiments of this application, the inorganic composite interface layer is located between the solid electrolyte and the negative electrode.

[0016] The inorganic composite interface layer of this application is located between the solid electrolyte and the negative electrode, thereby contacting the surfaces of the solid electrolyte and the negative electrode, effectively improving the problem of side reactions at the interface between the solid electrolyte and the negative electrode, and improving the solid-solid interface contact between the negative electrode and the electrolyte, thus reducing the operating pressure of the battery.

[0017] Thirdly, embodiments of this application provide a method for preparing a battery as provided in the second aspect, comprising: adding a mixed additive to a sulfide solid-state pouch cell and allowing it to stand and wet; densifying and forming the wetted cell to form an inorganic composite interface layer containing LiF and Li2S in situ on at least one side surface of the sulfide solid electrolyte; and drying to obtain a battery; wherein the mixed additive includes a fluorinated ether diluent, a fluorinated sacrificial agent, and a lithium salt.

[0018] This application employs a mixed additive comprising fluorinated ether diluent, fluorinated sacrificial agent, and lithium salt to impregnate a sulfide solid-state pouch cell, and performs an initial charge at a low rate to form a dense inorganic composite interface layer containing LiF and Li2S on at least one side of the sulfide solid electrolyte in situ. This effectively mitigates the problem of side reactions at the interface between the solid electrolyte and the negative electrode. Simultaneously, the in-situ formed interface layer has a small thickness, suitable mechanical strength, and maintains a certain suitable ionic conductivity, which can reduce interface impedance, provide uniform lithium-ion flux, improve the solid-solid interface contact between the negative electrode and the electrolyte, and reduce the operating pressure of the battery. Furthermore, the mixed additive comprising fluorinated ether diluent, fluorinated sacrificial agent, and lithium salt exhibits excellent compatibility with the sulfide solid electrolyte.

[0019] In some embodiments of this application, the mixed additive consists of a fluorinated ether diluent, a fluorinated sacrificial agent, and a lithium salt, and the amount of the mixed additive added is 1~4 g / Ah.

[0020] This application employs a mixed additive consisting of a fluorinated ether diluent, a fluorinated sacrificial agent, and a lithium salt, which is added to a sulfide solid-state pouch cell for impregnation. The initial charge is performed at a low rate, resulting in excellent compatibility with the sulfide solid-state electrolyte and the in-situ formation of a high-density inorganic composite interface layer containing LiF and Li₂S on at least one side of the sulfide solid-state electrolyte surface. Furthermore, the use of an appropriate amount of the mixed additive for in-situ formation of the inorganic composite interface layer ensures thorough impregnation of the cell and facilitates the densification process of the battery, resulting in a dense inorganic composite interface layer.

[0021] In some embodiments of this application, battery formation is performed during the first charge at a charging rate of 0.05 to 0.2C.

[0022] This application uses a low initial charging rate, which facilitates the full decomposition of the fluorinated sacrificial agent during the reaction, thereby forming a high-density inorganic composite interface layer.

[0023] Fourthly, embodiments of this application provide an electrical device, including the battery as provided in the second aspect.

[0024] This application provides an electrical device including a battery provided in the second aspect, which can effectively improve the problem of side reactions occurring at the negative electrode interface and improve the solid-solid interface contact between the negative electrode and the electrolyte, thereby reducing the operating pressure of the battery. Attached Figure Description

[0025] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 The XPS (X-ray photoelectron spectroscopy) test results of the Li6PS5Cl powder provided in Test Example 1 of this application are shown in the figure.

[0027] Figure 2 The image shows the EIS (electrochemical impedance spectroscopy) impedance test results of the battery provided in Example 1 of this application.

[0028] Figure 3 The graph shows the EIS impedance test results of the battery provided in Comparative Example 1 of this application.

[0029] Figure 4 The XPS F 1s spectrum of the inorganic composite interface layer of the battery provided in Embodiment 1 of this application.

[0030] Figure 5 The XPS F 1s spectrum of the inorganic composite interface layer of the battery provided in Comparative Example 1 of this application.

[0031] Figure 6 The XPS 2p spectrum of the inorganic composite interface layer of the battery provided in Embodiment 1 of this application is shown.

[0032] Figure 7 XPS s 2p spectrum of the inorganic composite interface layer of the battery provided in Comparative Example 1 of this application. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0034] To address the issue of side reactions occurring at the negative electrode interface in current sulfide solid-state batteries, this application provides a solid electrolyte comprising an electrolyte layer and an inorganic composite interface layer disposed on at least one side of the electrolyte layer. The electrolyte layer comprises a sulfide solid electrolyte, and the inorganic composite interface layer comprises LiF and Li2S.

[0035] Because sulfide solid electrolytes have a narrow electrochemical window, interfacial side reactions occur at the negative electrode interface during charge and discharge, causing a continuous increase in the negative electrode interface resistance, resulting in a continuous increase in the battery's internal resistance and ultimately battery failure. This application provides an inorganic composite interface layer containing LiF and Li2S on at least one side of the sulfide solid electrolyte surface. LiF has high mechanical strength and is relatively hard, but its ionic conductivity is low. Li2S has low mechanical strength and is relatively soft, but its ionic conductivity is high. The harder LiF and the softer Li2S work together to form a dense interface layer with suitable mechanical strength, effectively coating the sulfide solid electrolyte and preventing further occurrence of negative electrode interface side reactions during charge and discharge. Furthermore, the interface rich in LiF and Li2S exhibits excellent chemical stability, thus effectively improving the problem of negative electrode interface side reactions. Additionally, the low ionic conductivity of LiF and the high ionic conductivity of Li2S work together to maintain a suitable ionic conductivity. Simultaneously, the interface layer has suitable mechanical strength, which can reduce interfacial impedance, improve the solid-solid interface contact between the negative electrode and the electrolyte, and reduce the battery's operating stress.

[0036] In some embodiments, XPS can be used to detect an inorganic composite interface layer containing LiF and Li2S in the solid electrolyte.

[0037] In some embodiments of this application, the sulfide solid electrolyte includes at least one of Li6PS5X (lithium-silver-germanium sulfide electrolyte), LiGePS (lithium-germanium-phosphorus-sulfide), LiSiPS (lithium-silicon-phosphorus-sulfide), and LiSnPS (lithium-tin-phosphorus-sulfide); wherein X is at least one of F (fluorine), Cl (chlorine), Br (bromine), and I (iodine). Using a suitable sulfide solid electrolyte facilitates the formation of high-performance sulfide solid-state batteries.

[0038] In some embodiments of this application, the electrolyte layer further includes an adhesive. As an example, the adhesive may be, but is not limited to, at least one of polyvinylidene fluoride, SEBS (hydrogenated styrene-butadiene block copolymer), and PIB (polyisobutylene).

[0039] In some embodiments of this application, the density of the inorganic composite interface layer is between 98% and 100%. For example, it is 98%, 98.1%, 98.2%, 98.3%, 98.4%, 98.5%, 98.6%, 98.7%, 98.8%, 98.9%, 99%, 99.1%, 99.2%, 99.3%, 99.4%, 99.5%, 99.6%, 99.7%, 99.8%, 99.9%, and 100%. The high density of the inorganic composite interface layer allows for effective coating of the electrolyte layer and the surface of the negative electrode, thereby effectively mitigating the problem of side reactions occurring at the interface between the solid electrolyte and the negative electrode.

[0040] In some embodiments of this application, the thickness of the inorganic composite interface layer is no greater than 30 nm and 150 nm. Examples include 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, 95 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 142 nm, 145 nm, 148 nm, and 150 nm. The smaller thickness of the in-situ formed inorganic composite interface layer can reduce interfacial impedance, improve the solid-solid interface contact between the negative electrode and the electrolyte, and reduce the operating stress of the battery.

[0041] Secondly, embodiments of this application provide a battery, including a positive electrode, a negative electrode, and the aforementioned solid electrolyte.

[0042] In some embodiments of this application, the inorganic composite interface layer is located between the solid electrolyte and the negative electrode. This inorganic composite interface layer contacts the surfaces of both the solid electrolyte and the negative electrode, effectively mitigating the problem of side reactions at the solid electrolyte-negative electrode interface, while also improving the solid-solid interface contact between the negative electrode and the electrolyte, thus reducing the operating stress of the battery.

[0043] In some embodiments of this application, the negative electrode is a lithium metal negative electrode or a silicon-based negative electrode. When the negative electrode is a lithium metal negative electrode or a silicon-based negative electrode, an irreversible redox reaction occurs at the interface between the solid electrolyte and the negative electrode during charging and discharging. However, the electrolyte layer of this application has an inorganic composite interface layer containing LiF and Li2S formed in situ on at least one side surface, thereby improving the problem of redox reaction occurring at the interface between the solid electrolyte and the lithium metal negative electrode or the silicon-based negative electrode.

[0044] In some embodiments of this application, the negative electrode sheet consists of a negative current collector and a negative electrode coating. As an example, the negative current collector may be, but is not limited to, a pure metal foil, an alloy foil, or a foil composite of metal and a polymer compound; specifically, the metal foil may be, but is not limited to, copper foil. The negative electrode coating includes a negative electrode active material, a conductive agent, and a binder. As an example, the negative electrode active material may be, but is not limited to, lithium (Li) metal, silicon (Si), Li-Si alloy, or silicon-carbon; the conductive agent may be, but is not limited to, at least one of carbon nanofibers, vapor-grown carbon fiber (VGCF), Super P (superconducting carbon black), acetylene black, KS6 (large-particle graphite powder conductive agent), CNT (carbon nanotubes), or graphene; the binder may be, but is not limited to, one of SBR (styrene-butadiene rubber), ABR (acrylonitrile-butadiene copolymer), BR (cis-butadiene rubber), NBR (nitrile rubber), SEBS (hydrogenated styrene-butadiene block copolymer), or PIB (polyisobutylene). It should be noted that when silicon or silicon-carbon is used as the negative electrode active material, the negative electrode coating also includes an electrolyte. The electrolyte may be, but is not limited to, at least one of Li6PS5X (where X is at least one of F, Cl, Br, and I), LiGePS, LiSiPS, and LiSnPS.

[0045] In some embodiments of this application, the positive electrode sheet consists of a positive current collector and a positive electrode coating. Exemplarily, the positive current collector may be, but is not limited to, a metal foil or a foil composite of metal and a polymer compound; specifically, the metal foil may be, but is not limited to, aluminum foil. The positive electrode coating includes a positive electrode active material, a conductive agent, a binder, and an electrolyte. Exemplarily, the positive electrode active material may be, but is not limited to, at least one of lithium nickel cobalt manganese oxide (NCM), lithium nickel cobalt aluminum oxide, and lithium-rich manganese-based materials; specifically, lithium nickel cobalt manganese oxide may be NCM811 (with a nickel-cobalt-manganese ratio of 8:1:1). The conductive agent may be, but is not limited to, at least one of vapor-grown carbon fiber, carbon nanofiber, Super P, acetylene black, KS6, CNT, or graphene. The binder may be, but is not limited to, one of polyvinylidene fluoride, SEBS, and PIB. The electrolyte may be, but is not limited to, at least one of Li6PS5X (X being at least one of F, Cl, Br, and I), LiGePS, LiSiPS, and LiSnPS.

[0046] Thirdly, embodiments of this application provide a method for preparing the above-mentioned battery, comprising: A mixed additive is added to a sulfide solid-state soft-pack bare cell and allowed to stand and soak. After soaking, the cell is densified and formed so that the mixed additive forms an inorganic composite interface layer containing LiF and Li2S in situ on at least one side of the sulfide solid electrolyte. Then it is dried to obtain a battery. The mixed additive includes a fluorinated ether diluent, a fluorinated sacrificial agent and a lithium salt.

[0047] A mixed additive comprising fluorinated ether diluent, fluorinated sacrificial agent, and lithium salt is employed, exhibiting excellent compatibility with sulfide solid electrolytes. This additive is incorporated into sulfide solid soft-pack bare cells and subjected to initial charging at low rates. During charging, the fluorinated sacrificial agent reacts with at least one side of the sulfide solid electrolyte at the negative electrode interface, forming a dense inorganic composite interface layer containing LiF and Li₂S in situ. This inorganic composite interface layer effectively coats the sulfide solid electrolyte, effectively suppressing further side reactions at the negative electrode interface during charging and discharging, thereby effectively improving the problem of side reactions between the solid electrolyte and the negative electrode interface. Simultaneously, it reduces interface impedance, provides uniform lithium-ion flux, improves the solid-solid interface contact between the negative electrode and the electrolyte, and reduces the battery's operating stress.

[0048] As an example, the initial charge rate can be, but is not limited to, any one of 0.05 C, 0.06 C, 0.07 C, 0.08 C, 0.09 C, 0.1 C, 0.11 C, 0.12 C, 0.13 C, 0.14 C, 0.15 C, 0.16 C, 0.17 C, 0.18 C, 0.19 C, or 0.2 C, or a range between any two. Using a low initial charge rate facilitates the complete decomposition of the fluorinated sacrificial agent during the reaction, thereby forming a high-density inorganic composite interface layer.

[0049] In some embodiments of this application, the mixed additive comprises a fluorinated ether diluent, a fluorinated sacrificial agent, and a lithium salt. Exemplarily, the fluorinated ether diluent may be, but is not limited to, at least one of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (HFE), 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, bis(2,2,2-trifluoroethyl) ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, and tris(trifluoroethoxy)methane. The fluorinated sacrificial agent may be, but is not limited to, at least one of fluoroethylene carbonate (FEC), hexafluoroglutaric anhydride, heptafluorobutyric anhydride, tetrafluorosuccinic anhydride, perfluoropropionic anhydride, difluoroacetic anhydride, and trifluoroacetic anhydride. The lithium salt can be, but is not limited to, at least one of LiPF6 (lithium hexafluorophosphate), LiPO2F2 (lithium difluorophosphate), LiTFSI (lithium bis(trifluoromethanesulfonyl)imide), and LiFSI (lithium bisfluorosulfonylimide). By employing a suitable fluorinated ether diluent, a suitable fluorinated sacrificial agent, and a suitable lithium salt, the fluorinated sacrificial agent reacts in situ with at least one side of the sulfide solid electrolyte at the negative electrode interface to form an inorganic composite interface layer containing LiF and Li2S. However, the oxygen-containing functional groups of the fluorinated sacrificial agent are reactive with the sulfide solid electrolyte. The fluorinated ether diluent is inert to the sulfide and has no effect on the ionic conductivity of the sulfide after contact. Adding the fluorinated ether diluent can help suppress the reactivity of the fluorinated sacrificial agent with the sulfide electrolyte. Simultaneously, the lithium salt has the function of conducting lithium ions, which can give the inorganic composite interface layer a uniform lithium ion flux.

[0050] In some embodiments of this application, the mass ratio of fluorinated ether diluent, fluorinated sacrificial agent, and lithium salt is 55-90 : 5-30 : 5-25. Using a suitable mass ratio can suppress the reactivity of the fluorinated sacrificial agent with the sulfide electrolyte, achieving good compatibility with the sulfide solid electrolyte and enabling the in-situ formation of a dense inorganic composite interface layer. Preferably, the mass ratio of fluorinated ether diluent, fluorinated sacrificial agent, and lithium salt is 75-85 : 5-20 : 5-15; more preferably, it is 75-85 : 5-15 : 5-15. As an example, the mass ratio of fluorinated ether diluent to fluorinated sacrificial agent may be, but is not limited to, 75:5, 75:6, 75:7, 75:8, 75:9, 75:10, 75:11, 75:12, 75:13, 75:14, 75:15, 80:5, 80:6, 80:7, 80:8, 80:9, 80:10, 80:11, 80:12, 80:13, 80:14, 80:15, 85:5, 85:6, 85:7, 85:8, 85:9, 85:10, 85:11, 85: 12, 85: 13, 85: 14, 85: 15. Further employing more suitable mass ratios can further suppress the reactivity of fluorinated sacrificial agents with sulfide electrolytes, exhibiting excellent compatibility with sulfide solid electrolytes.

[0051] In some embodiments of this application, the amount of the mixed additive added is 1~4 g / Ah; preferably 1.5~2.5 g / Ah. As an example, the amount of the mixed additive added can be, but is not limited to, any one of 1.5 g / Ah, 1.6 g / Ah, 1.7 g / Ah, 1.8 g / Ah, 1.9 g / Ah, 2.0 g / Ah, 2.1 g / Ah, 2.2 g / Ah, 2.3 g / Ah, 2.4 g / Ah, or 2.5 g / Ah, or a range between any two. Using an appropriate amount of the mixed additive to form an inorganic composite interface layer in situ can both fully wet the battery cell and facilitate the densification treatment of the battery, thereby forming a dense inorganic composite interface layer.

[0052] In some embodiments of this application, the mixture is immersed at 25-60 °C and left to stand for 6-36 h. Preferably, it is immersed at 35-45 °C and left to stand for 10-24 h. Using appropriate temperature and immersion time improves the immersion effect of the mixed additives and reduces the chance of reaction between the fluorinated sacrificial agent and the sulfide electrolyte.

[0053] In some embodiments of this application, cell densification includes isostatic pressing at 25–60 °C and 100–500 MPa for a holding time of 3–30 min. Preferably, cell densification is performed at 35–45 °C and 300–450 MPa for a holding time of 5–15 min. Using suitable conditions for densification achieves a high degree of densification while reducing the chance of reaction between the fluorinated sacrificial agent and the sulfide electrolyte.

[0054] In some embodiments of this application, battery formation includes: initial charging to (65%~75%) SOC (State of Charge) using a pressurized formation machine at 5~20 MPa and 45~55 °C in an environment with a relative humidity of 0.19%~0.58%. Using a suitable relative humidity environment during battery formation reduces the reaction between ambient moisture and the sulfide solid electrolyte in the cell, thus minimizing its impact on battery performance and reducing production energy consumption. Selecting a suitable formation pressure ensures sufficient contact between the inorganic composite interface layer formed by the decomposition products of the mixed additives and the sulfide solid electrolyte and negative electrode interface.

[0055] In some embodiments of this application, the preparation method of the positive electrode sheet includes: mixing a positive electrode active material, an electrolyte, a conductive agent, a binder, and a solvent to form a positive electrode slurry; coating the positive electrode slurry onto at least one side of a positive electrode current collector; and drying to obtain the positive electrode sheet. The mass ratio of the positive electrode active material, electrolyte, conductive agent, and binder is 60-85 : 10-30 : 1-6 : 1-6, and n-dodecane is added to adjust the solid content of the positive electrode slurry to 50%-70%. The electrolyte is a sulfide solid electrolyte. It should be noted that commercially available positive electrode sheets can also be used directly.

[0056] In some embodiments of this application, the method for preparing the negative electrode sheet includes: mixing a negative electrode active material, a conductive agent, a binder, and a solvent to form a negative electrode slurry; coating the negative electrode slurry onto at least one side of a negative electrode current collector; and drying to obtain the negative electrode sheet. Specifically, the negative electrode slurry is coated on both sides of the negative electrode current collector. The mass ratio of the negative electrode active material, conductive agent, and binder is 60-85: 1-6: 1-6, and n-dodecane is added to adjust the solid content of the negative electrode slurry to 40%-60%. If an electrolyte is included, the mass ratio of the electrolyte is 10-30. The electrolyte is a sulfide solid electrolyte. It should be noted that commercially available negative electrode sheets can also be used directly.

[0057] In some embodiments of this application, the method for preparing the electrolyte layer includes: mixing a sulfide solid electrolyte, a binder, and a solvent to form an electrolyte slurry; coating the electrolyte slurry onto at least one side of a substrate (release film or aluminum foil); and drying to obtain the electrolyte layer. Specifically, the electrolyte slurry is coated onto one side of the substrate. The mass ratio of the sulfide solid electrolyte to the binder is 90-99.5:0.5-10, and n-dodecane is added to adjust the solid content of the electrolyte slurry to 40%-60%. It should be noted that commercially available electrolyte layers can also be used directly.

[0058] In some embodiments of this application, the method for preparing a sulfide solid-state pouch cell includes: placing a double-sided negative electrode sheet between two single-sided sulfide solid electrolyte layers and rolling it to form a composite negative electrode sheet; stacking and welding the positive electrode sheet and the composite negative electrode sheet, and then encapsulating them, keeping one side open after encapsulation, and drying them to obtain a sulfide solid-state pouch cell. It should be noted that commercially available sulfide solid-state pouch cells can also be used directly.

[0059] Fourthly, embodiments of this application provide an electrical device, which includes the aforementioned battery. The electrical device can be a vehicle, aircraft, robot, computer, mobile phone, or other similar product.

[0060] The features and performance of this application will be further described in detail below with reference to the embodiments.

[0061] Example 1 This embodiment provides a method for preparing a battery, including: S1. Using n-dodecane as a solvent, NCM811, Li6PS5Cl, VGCF, and SEBS are mixed in a mass ratio of 75:20:3:2 to form a positive electrode slurry. n-Dodecane is added to adjust the solid content of the positive electrode slurry to 60%. The positive electrode slurry is coated onto both sides of an aluminum foil and dried to obtain a positive electrode sheet. Using n-dodecane as a solvent, Si, Li6PS5Cl, VGCF, and SEBS are mixed in a mass ratio of 75:20:3:2 to form a negative electrode slurry. n-Dodecane is added to adjust the solid content of the negative electrode slurry to 50%. The negative electrode slurry is coated onto both sides of a copper foil and dried to obtain a negative electrode sheet. S2, using n-dodecane as a solvent, Li6PS5Cl and SEBS are mixed at a mass ratio of 95:5 to form an electrolyte slurry, and n-dodecane is added to adjust the solid content of the electrolyte slurry to 50%. The electrolyte slurry is coated on one side of a PET release film and dried to obtain a solid electrolyte. S3, the double-sided negative electrode sheet prepared in S1 is placed between two layers of single-sided solid electrolyte prepared in S2, and the solid electrolyte is transferred to the negative electrode sheet by multi-stage rolling to obtain a composite negative electrode sheet; S4. The positive electrode sheet prepared in S1 and the composite negative electrode sheet prepared in S3 are stacked, the tabs are welded, and the aluminum-plastic film is sealed with one side of the aluminum-plastic film open. The film is then placed in a vacuum oven and dried in a vacuum oven at 80 °C for 12 h to obtain a solid soft-pack bare cell. S5, HFE, FEC, and LiTFSI are uniformly mixed in a mass ratio of 75:10:15 to form a mixed additive. The mixed additive is added to the solid soft-pack bare cell prepared in S4 through one open side, with an addition amount of 2 g / Ah. The solid soft-pack bare cell is then sealed and allowed to stand at 40 ℃ for 20 h for impregnation. S6. After the cell has been impregnated, it is subjected to isostatic pressing at 40 ℃ and 350 MPa for 10 min. The cell air bag is opened and placed in an environment with a relative humidity of 0.35%. The cell is then charged to 70% SOC at 15 MPa and 50 ℃ using a pressurized formation machine. The charging rate is 0.1 C. This allows the mixed additives to form an inorganic composite interface layer containing LiF and Li2S in situ on the surface of both solid electrolyte layers near the negative electrode. S7. The battery tabs that have been formed are insulated and placed in a vacuum oven at 50 °C for 20 h to remove residual liquid components; then sealed to obtain the battery.

[0062] Example 2 This embodiment provides a method for preparing a battery, including: S1. Using n-dodecane as a solvent, NCM811, Li6PS5Cl, VGCF, and SEBS are mixed in a mass ratio of 60:28:6:6 to form a positive electrode slurry. n-Dodecane is added to adjust the solid content of the positive electrode slurry to 65%. The positive electrode slurry is coated onto both sides of an aluminum foil and dried to obtain a positive electrode sheet. Using n-dodecane as a solvent, Si, Li6PS5Cl, VGCF, and SEBS are mixed in a mass ratio of 60:28:6:6 to form a negative electrode slurry. n-Dodecane is added to adjust the solid content of the negative electrode slurry to 60%. The negative electrode slurry is coated onto both sides of a copper foil and dried to obtain a negative electrode sheet. S2, using n-dodecane as a solvent, Li6PS5Cl and SEBS are mixed at a mass ratio of 98:2 to form an electrolyte slurry, and n-dodecane is added to adjust the solid content of the electrolyte slurry to 60%. The electrolyte slurry is coated on one side of a PET release film and dried to obtain a solid electrolyte. S3, the double-sided negative electrode sheet prepared in S1 is placed between two layers of single-sided solid electrolyte prepared in S2, and the solid electrolyte is transferred to the negative electrode sheet by multi-stage rolling to obtain a composite negative electrode sheet; S4. The positive electrode sheet prepared in S1 and the composite negative electrode sheet prepared in S3 are stacked, the tabs are welded, and the aluminum-plastic film is sealed with one side of the aluminum-plastic film open. The film is then placed in a vacuum oven and dried under vacuum at 60 ℃ for 24 h to obtain a solid soft-pack bare cell. S5, HFE, FEC, and LiTFSI are uniformly mixed in a mass ratio of 85:5:10 to form a mixed additive. The mixed additive is added to the solid soft-pack bare cell prepared in S4 through one open side, with an addition amount of 2.5 g / Ah. The solid soft-pack bare cell is then sealed and left to stand at 35 ℃ for 24 h for impregnation. S6. After the cell has been impregnated, it is subjected to isostatic pressing at 45 ℃ and 300 MPa for 15 min. The cell air bag is opened and placed in an environment with a relative humidity of 0.5%. The cell is then charged to 65% SOC at 20 MPa and 45 ℃ using a pressurized formation machine. The charging rate is 0.05 C. This allows the mixed additives to form an inorganic composite interface layer containing LiF and Li2S in situ on the surface of both solid electrolyte layers near the negative electrode. S7. The battery tabs that have been formed are insulated and placed in a vacuum oven at 45 °C for 24 h to dry and remove residual liquid components; then sealed to obtain the battery.

[0063] Example 3 This embodiment provides a method for preparing a battery, which differs from Embodiment 2 in that: HFE, FEC, and LiTFSI are uniformly mixed in a mass ratio of 80:12:8 to form a mixed additive, and the amount added is 1.5 g / Ah; the initial charging rate is 0.15C.

[0064] Example 4 This embodiment provides a method for preparing a battery, which differs from Embodiment 2 in that: HFE, FEC, and LiTFSI are uniformly mixed in a mass ratio of 78:17:5 to form a mixed additive, with an addition amount of 1.8 g / Ah; the initial charging rate is 0.2 C.

[0065] Example 5 This embodiment provides a method for preparing a battery, which differs from Embodiment 2 in that HFE, FEC, and LiTFSI are uniformly mixed in a mass ratio of 70:25:5 to form a mixed additive.

[0066] Example 6 This embodiment provides a method for preparing a battery, which differs from Embodiment 2 in that it uses a 0.5 C charging rate for the first charge.

[0067] Comparative Example 1 This comparative example provides a method for preparing a battery, which differs from Example 2 in that: the mixed additives are HFE and LiTFSI, which are uniformly mixed at a mass ratio of 85:15; and an inorganic composite interface layer containing Li2S is formed in situ on the surface of both electrolyte layers near the negative electrode.

[0068] Comparative Example 2 This comparative example provides a method for preparing a battery, including... S1. Using n-dodecane as a solvent, NCM811, Li6PS5Cl, VGCF, and SEBS are mixed in a mass ratio of 60:28:6:6 to form a positive electrode slurry. n-Dodecane is added to adjust the solid content of the positive electrode slurry to 65%. The positive electrode slurry is coated onto aluminum foil and dried to obtain a positive electrode sheet. Using n-dodecane as a solvent, Si, Li6PS5Cl, VGCF, and SEBS are mixed in a mass ratio of 60:28:6:6 to form a negative electrode slurry. n-Dodecane is added to adjust the solid content of the negative electrode slurry to 60%. The negative electrode slurry is coated onto both sides of a copper foil and dried to obtain a negative electrode sheet. S2, using n-dodecane as a solvent, Li6PS5Cl and SEBS are mixed at a mass ratio of 98:2 to form an electrolyte slurry, and n-dodecane is added to adjust the solid content of the electrolyte slurry to 60%. The electrolyte slurry is coated on one side of the release film and dried to obtain an electrolyte layer; a LiF interface layer with a thickness of 995 nm is coated on one side of the electrolyte layer. S3, the double-sided negative electrode sheet prepared in S1 is placed between two single-sided electrolyte layers prepared in S2, and the electrolyte layers are transferred to the negative electrode sheet by multi-stage rolling to obtain a composite negative electrode sheet; S4. The positive electrode sheet prepared in S1 and the composite negative electrode sheet prepared in S3 are stacked, the tabs are welded, and the aluminum-plastic film is sealed with one side of the aluminum-plastic film open. The film is then placed in a vacuum oven and dried under vacuum at 60 ℃ for 24 h to obtain a solid soft-pack bare cell. S5, solid-state soft-pack bare cells are subjected to isostatic pressing at 45 ℃ and 300 MPa for 15 min; the cell air bag is opened and placed in an environment with a relative humidity of 0.5%, and a pressure formation machine is used to perform the first charge to 65% SOC at 20 MPa and 45 ℃, with a charging rate of 0.05 C; the formed battery tabs are insulated and sealed to obtain the battery.

[0069] The preparation methods of the batteries provided in Examples 1-6 and Comparative Examples 1-2 are shown in Table 1.

[0070] Table 1. Battery preparation methods

[0071] Note: " / " in the table indicates that the content is not included.

[0072] Experimental Example 1 This test case verifies the compatibility of the mixed additives provided in Example 1 and Comparative Example 1 with Li6PS5Cl. The specific method is as follows: Li6PS5Cl powder was soaked in the mixed additives provided in Example 1 and Comparative Example 1 for 24 hours, and the solvent was removed. The ionic conductivity of the untreated Li6PS5Cl powder and the treated Li6PS5Cl powder were tested, and XPS tests were performed. The results are shown in Table 2 and... Figure 1 As shown.

[0073] Ionic conductivity testing method: The Li6PS5Cl powder to be tested is loaded into a mold battery and pressed into a powder cake. Electrochemical impedance spectroscopy is tested using an electrochemical workstation with a scanning frequency of 10~100kHz and an amplitude of 10mV to obtain the electrochemical impedance spectrum. The bulk resistance R of the electrolyte can then be obtained. The ionic conductivity σ is calculated using the formula σ = L / (R×S), where L is the thickness of the solid electrolyte powder cake, R is the bulk resistance of the solid electrolyte, and S is the area of ​​the solid electrolyte powder cake.

[0074] Table 2 Ionic conductivity of Li6PS5Cl

[0075] As shown in Table 2, after soaking Li6PS5Cl powder in the mixed additives used in Example 1 and Comparative Example 1 for 24 h, the ionic conductivity of the powder was basically consistent with that of the untreated Li6PS5Cl powder. This indicates that the mixed additives used in Example 1 and Comparative Example 1 have good compatibility with Li6PS5Cl and do not affect the ionic conductivity of Li6PS5Cl.

[0076] Depend on Figure 1 The results show that, as can be seen from the S 2p characteristic peak, after soaking Li6PS5Cl powder in the mixed additive used in Example 1 and Comparative Example 1 for 24 h, the characteristic peak position is consistent with the characteristic peak position of untreated Li6PS5Cl, indicating that the mixed additive used in Example 1 and Comparative Example 1 has good compatibility with Li6PS5Cl and does not react with Li6PS5Cl.

[0077] Experimental Example 2 This experiment tested the electrochemical performance of the batteries provided in Examples 1-6 and Comparative Examples 1-2. The results are shown in Table 3. The specific methods are as follows: (1) Initial charge capacity: At room temperature (25 °C), a pressure of 5 MPa was applied to each battery sample provided in Examples 1 to 6 and a pressure of 50 MPa was applied to each battery sample provided in Comparative Examples 1 to 2. The battery samples were charged at a constant current of 0.1 C to the cutoff voltage of 4.3 V, and then charged at a constant voltage of 4.3 V to the cutoff current of 0.05 C to obtain the initial charge capacity.

[0078] (2) Initial discharge capacity: At room temperature (25 °C), a pressure of 5 MPa was applied to each battery sample provided in Examples 1 to 6 and a pressure of 50 MPa was applied to each battery sample provided in Comparative Examples 1 to 2. The fully charged battery samples were discharged at a constant current of 0.1 C to a cutoff voltage of 2.5 V to obtain the initial discharge capacity.

[0079] (3) First effect: First effect = first discharge capacity / first charge capacity × 100%.

[0080] (4) Cycle capacity retention: At room temperature (25 °C), a pressure of 5 MPa was applied to each battery sample provided in Examples 1 to 6, and a pressure of 50 MPa was applied to each battery sample provided in Comparative Examples 1 to 2. The battery samples were charged at a current of 0.1 C to the charging cutoff voltage of 4.3 V, then switched to constant voltage charging to the cutoff current of 0.05 C, and allowed to stand for 0.5 h. The battery samples were then discharged at a current of 0.1 C to the cutoff voltage of 2.5 V, and allowed to stand for 0.5 h before entering the next charge-discharge cycle. This process was repeated for a total of 50 charge-discharge cycles. Cycle capacity retention = (discharge capacity of the 50th cycle / first discharge capacity) × 100%.

[0081] Table 3 Electrochemical performance of solid-state batteries

[0082] As shown in Table 3, compared with the results of Examples 1-4 and Comparative Example 1, the initial charge capacity and initial discharge capacity of the battery provided in Comparative Example 1 were reduced to some extent, and the capacity retention rate after 50 cycles at 0.1 C was significantly reduced. Because the battery provided in Comparative Example 1 only used a mixed additive of HFE and LiTFSI for cell wetting, the in-situ formed inorganic composite interface layer contained only Li2S and not LiF, resulting in an unstable interface and continuous side reactions, leading to lower battery capacity and poor cycle performance. Comparing Examples 2 and 5, the initial charge capacity, initial discharge capacity, and cycle performance of the battery provided in Example 5 were all reduced to some extent. This was because the amount of fluorinated ether diluent added in Example 5 was reduced, while the amount of fluorinated sacrificial agent added was increased. The fluorinated ether diluent reduced the inhibition of the fluorinated sacrificial agent's reactivity with the sulfide electrolyte to some extent, thus reducing the overall capacity of the battery. Compared to Examples 2 and 6, the battery provided in Example 6 exhibits reduced initial charge capacity, initial discharge capacity, and cycle performance to some extent. This is because the initial charge rate in Example 6 was excessively high, potentially reducing the complete decomposition of the fluorinated sacrificial agent during formation and consequently decreasing the density of the formed inorganic composite interface layer. This resulted in a reduction in the overall capacity of the battery. In contrast to Examples 2 and Comparative Example 2, the battery provided in Comparative Example 2 showed significantly reduced initial discharge capacity and cycle performance. This is because Comparative Example 2 used a coating-formed (non-in-situ) interface layer, resulting in numerous pores and low density. Furthermore, the low ionic conductivity of LiF itself affected lithium-ion transport during charge and discharge. The larger thickness of the non-in-situ formed interface layer increased its interfacial impedance, leading to lower capacity and poorer cycle performance.

[0083] In addition, all batteries provided in Examples 1 to 6 were tested at an operating pressure of 5 MPa, while all batteries provided in Comparative Examples 1 to 2 were tested at an operating pressure of 50 MPa. However, the electrochemical performance of the batteries provided in Comparative Examples 1 to 2 was still relatively low; that is, the batteries provided in this application can operate at lower pressures.

[0084] The battery provided in this application has an inorganic composite interface layer containing LiF and Li2S between the sulfide solid electrolyte and the negative electrode. This effectively improves the problem of side reactions at the interface between the solid electrolyte and the negative electrode, while also improving the solid-solid interface contact between the negative electrode and the electrolyte, thus reducing the operating stress of the battery. The solid-state battery provided exhibits a high capacity retention rate.

[0085] Experimental Example 3 This experimental example performs electrochemical impedance spectroscopy (EIS) tests on the batteries provided in Example 1 and Comparative Example 1, using the following specific methods: EIS Impedance Testing Method: After the first charge-discharge cycle of the sulfide solid-state battery, a pressure of 5 MPa was applied, and the battery was charged at a current of 0.1C to the charging cutoff voltage of 4.3V. Electrochemical impedance spectroscopy (EIS) was then performed using an electrochemical workstation with a scanning frequency of 10 mHz to 100 kHz and an amplitude of 10 mV. The resulting EIS spectra are shown in the figure. The figures are obtained immediately after full charging and after being placed in a 60℃ incubator for 100 h, 150 h, and 200 h, respectively. The stability of the interface was determined by the impedance changes. Results are as follows: Figure 2 , Figure 3 As shown.

[0086] Depend on Figure 2 and Figure 3 The results show that, Figure 2 The EIS impedance test results of the battery provided in Example 1 are shown in the figure. The impedance after being placed in a 60°C oven for 100h, 150h and 200h respectively did not change significantly from the initial impedance, indicating that the interface of the solid battery provided in Example 1 is stable. Figure 3 The graph shows the EIS impedance test results of the solid-state battery provided in Comparative Example 1. The impedance of the battery after being placed in a 60℃ oven for 100h, 150h and 200h increases with time. The impedance continues to increase, indicating that the interface of the solid-state battery provided in Comparative Example 1 is unstable and side reactions continue to occur.

[0087] The battery provided in this application has an inorganic composite interface layer containing LiF and Li2S between the sulfide solid electrolyte and the negative electrode, which can prevent further occurrence of negative electrode interface side reactions during charging and discharging, and effectively improve the problem of side reactions occurring at the solid electrolyte and negative electrode interface.

[0088] Test Example 4 In this experimental example, after the batteries provided in Example 1 and Comparative Example 1 underwent 50 charge-discharge cycles in Experiment 2, each solid-state battery sample was disassembled. XPS characterization was performed on the inorganic composite interface layer formed in situ on the side of the electrolyte layer near the negative electrode. The results are as follows: Figures 4-7 As shown.

[0089] Depend on Figures 4-7 The results show that, Figure 4 The XPS F 1s spectrum of the inorganic composite interface layer of the battery provided in Example 1 is shown. Figure 5 The XPS F 1s spectrum of the inorganic composite interface layer of the battery provided in Comparative Example 1 is compared. Figure 4 and Figure 5 It can be seen that the inorganic composite interface layer of the battery provided in Example 1 is rich in LiF, while the inorganic composite interface layer of the battery provided in Comparative Example 1 does not contain LiF.

[0090] Figure 6The XPS s 2p spectrum of the inorganic composite interface layer of the battery provided in Example 1 is shown. Figure 7 XPS s 2p spectra of the inorganic composite interface layer of the battery provided in Comparative Example 1 are compared. Figure 6 and Figure 7 It can be seen that the PS4 in the inorganic composite interface layer of the battery provided in Example 1 3- The peak area ratio with Li2S is 94.5:5.5, while the inorganic composite interface layer of the battery provided in Comparative Example 1 has PS4. 3- The peak area ratio of Li2S is 72.6:27.4, indicating that the battery provided in Comparative Example 1 only uses a mixed additive of HFE and LiTFSI to wet the cell. The inorganic composite interface layer formed in situ does not contain LiF, and its Li2S content is higher than that of the inorganic composite interface layer of the battery provided in Example 1. Combined with the result of the EIS impedance continuously increasing in Experiment 3, it indicates that the interface of the battery provided in Comparative Example 1 is unstable and side reactions continue to occur.

[0091] Experimental Example 5 This experiment investigated the density of the inorganic composite interface layer in the batteries provided in Examples 1-4, Example 6, and Comparative Example 2. Synchrotron X-ray tomography was used, combined with 3D modeling analysis, to obtain the density of the inorganic composite interface layer. The results are shown in Table 4.

[0092] Table 4 Density of Inorganic Composite Interface Layer

[0093] As shown in Table 4, the density of the in-situ formed inorganic composite interface layer in the batteries provided in Examples 1-4 is greater than 98%, corresponding to their excellent electrochemical performance. However, compared to Examples 2 and 6, the density of the in-situ formed inorganic composite interface layer in the battery provided in Example 6 is somewhat lower. This is because the initial charging rate of the battery in Example 6 was too high, which may have reduced the complete decomposition of the fluorine-containing sacrificial agent during the reaction, thus reducing the density of the formed inorganic composite interface layer. Furthermore, compared to Example 2 and Comparative Example 2, the density of the LiF interface layer in the battery provided in Comparative Example 2 is only 75.1%. This is because Comparative Example 2 uses a coating-formed (non-in-situ formed) interface layer, which has more pores and thus lower density.

[0094] Experimental Example 6 This experiment measured the thickness of the inorganic composite interface layer in the batteries provided in Example 6 and Comparative Example 2. The thickness of the inorganic composite interface layer was characterized using SEM. The results are shown in Table 5.

[0095] Table 5 Thickness of Inorganic Composite Interface Layer

[0096] As shown in Table 5, the inorganic composite interface layer thickness in the batteries provided in Example 6 and Comparative Example 2 is smaller than that in Example 6. This is because the inorganic composite interface layer in this application is formed in situ, resulting in a smaller thickness. In contrast, Comparative Example 2 uses coating to form (non-in situ) the interface layer, resulting in a larger thickness. A thicker interface layer increases the interface impedance, leading to lower battery capacity and poor cycle performance.

[0097] The embodiments described above are some, but not all, of the embodiments of this application. The detailed description of the embodiments of this application is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

Claims

1. A solid electrolyte, characterized in that, It includes an electrolyte layer and an inorganic composite interface layer disposed on at least one side of the electrolyte layer, wherein the electrolyte layer includes a sulfide solid electrolyte and the inorganic composite interface layer includes LiF and Li2S.

2. The solid electrolyte according to claim 1, characterized in that, The sulfide solid electrolyte includes at least one of Li6PS5X, LiGePS, LiSiPS, and LiSnPS; wherein X is at least one of F, Cl, Br, and I.

3. The solid electrolyte according to claim 1, characterized in that, The density of the inorganic composite interface layer is between 98% and 100%.

4. The solid electrolyte according to claim 1, characterized in that, The thickness of the inorganic composite interface layer is between 30 nm and 150 nm.

5. A battery, characterized in that, It includes a positive electrode, a negative electrode, and a solid electrolyte as described in any one of claims 1 to 4.

6. The battery according to claim 5, characterized in that, The negative electrode is a lithium metal negative electrode or a silicon-based negative electrode.

7. The battery according to claim 6, characterized in that, The inorganic composite interface layer is located between the solid electrolyte and the negative electrode.

8. A method for preparing a battery as described in any one of claims 1 to 7, characterized in that, include: A mixed additive is added to a sulfide solid electrolyte bare cell and allowed to stand and soak. After soaking, the cell is densified and formed so that the mixed additive forms an inorganic composite interface layer containing LiF and Li2S in situ on at least one side of the sulfide solid electrolyte. The cell is then dried to obtain a battery. The mixed additive includes a fluorinated ether diluent, a fluorinated sacrificial agent, and a lithium salt.

9. The method for preparing a battery according to claim 8, characterized in that, The mixed additive consists of a fluorinated ether diluent, a fluorinated sacrificial agent, and a lithium salt, and the amount of the mixed additive added is 1~4 g / Ah.

10. The method for preparing a battery according to claim 8, characterized in that, Battery formation is performed during the first charge at a charging rate of 0.05~0.2C.

11. An electrical appliance, characterized in that, Includes the battery as described in any one of claims 5 to 7.

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