Solid-state electrolyte sheet and preparation method and application thereof

Abstract

The application discloses a kind of solid electrolyte sheet and its preparation method and application, belong to battery material technical field.The preparation of the solid electrolyte sheet includes: after oxide solid electrolyte and first binder glue solution are mixed, grinding is carried out, compaction, sintering, and first solid electrolyte sheet body is obtained;Carbon layer is deposited on the surface of first solid electrolyte sheet body, then carbon-containing slurry is coated, and dried;Molecular formula of oxide solid electrolyte is M x Li7La3Zr2O 12 , 0 < x ≤ 0.2, M includes at least one of Ta, Nb and Sb.The M element is doped in the above-mentioned solid electrolyte sheet, which can improve the lithium ion conductivity;By depositing carbon layer and coating carbon-containing slurry, the solid-solid contact problem of the solid electrolyte sheet can be effectively improved, the electrolyte volume strain is relieved, which is beneficial to reduce the interface impedance and improve the interface conductivity.

Description

Technical Field

[0001] The present invention relates to the technical field of battery materials, and in particular to a solid electrolyte sheet and a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries (LIBs) play an important role as energy storage devices in the field of new energy, especially in the fields of portable electronic devices and new energy electric vehicles. Lithium-ion batteries ensure people's energy needs in life and work. However, with the development of new energy devices, traditional lithium-ion batteries can no longer meet people's requirements for future energy storage devices. Current commercial batteries use flammable organic liquid electrolytes, which are prone to electrolyte leakage and environmental pollution, lithium dendrites piercing the diaphragm and causing internal short circuits, and there are safety issues such as fire and even explosion. Traditional lithium-ion batteries find it difficult to achieve high energy density while ensuring safety. The development of lithium-ion batteries with both high energy density and high safety is of great significance to the development of new energy devices.

[0003] Replacing organic electrolytes with solid electrolytes is considered to be the ultimate solution to the above problems, because solid electrolytes (SSE) can fundamentally change the behavior of lithium deposition and allow the direct use of lithium metal as the negative electrode. Researchers believe that the application of solid electrolytes in lithium-ion batteries is very promising. Among inorganic solid lithium-ion conductors, cubic garnet structured Li7La3Zr2O 12 (LLZO) oxide solid electrolytes are the most widely used.

[0004] But the oxide-type solid electrolyte Li7La3Zr2O 12 The actual application of solid-state batteries mainly has the problem of solid-solid interface contact, which is mainly manifested in the interface contact between LLZO and the negative electrode and the interface contact between LLZO and the positive electrode. The above-mentioned interface problems between the positive electrode and the solid electrolyte mainly include the ion transfer impedance caused by the point contact between the positive electrode and the solid electrolyte and the increase in local deformation of the electrode due to interface stress. In addition, LLZO is easily reacted with water and CO2 in the air when exposed to air, forming a Li2CO3 passivation layer on the surface. The presence of the Li2CO3 passivation layer makes it difficult for Li metal and LLZO to come into close contact, resulting in high interface impedance, affecting battery performance, and traditional methods such as polishing cannot completely remove Li2CO3.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The purpose of the present invention is to provide a solid electrolyte sheet and its preparation method and application, so as to solve or improve the above technical problems.

[0007] In a first aspect, the present invention provides a method for preparing a solid electrolyte sheet, comprising the following steps: mixing an oxide solid electrolyte with a first binder paste, grinding the mixture, and then pressing the mixture to obtain a ceramic sheet green body; sintering the ceramic sheet green body a second time to obtain a first solid electrolyte sheet body;

[0008] Depositing a carbon layer on the surface of the first solid electrolyte sheet body to obtain a second solid electrolyte sheet body; applying a slurry obtained by mixing carbon powder and a second binder glue solution to the surface of the second solid electrolyte sheet body and drying;

[0009] The molecular formula of the oxide solid electrolyte is M x Li7La3Zr2O 12 , wherein 0<x≤0.2, M comprises at least one of Ta, Nb and Sb;

[0010] The first adhesive solution is obtained by mixing a first adhesive and a first solvent, wherein the first adhesive is PVB, the first solvent is NMP, and the concentration of the first adhesive in the first adhesive solution is 3wt% to 5wt%;

[0011] The second binder glue solution is obtained by mixing a second binder and a second solvent. The second binder is polyvinylidene fluoride, the second solvent is NMP, and the concentration of the second binder in the second binder glue solution is 3 wt % to 5 wt %.

[0012] In an optional embodiment, the preparation of the oxide solid electrolyte comprises: mixing the oxide of the M element, La2O3, ZrO2 and the lithium source according to M x Li7La3Zr2O 12 The oxide precursor is ball-milled in a stoichiometric ratio to obtain an oxide precursor; the oxide precursor is sintered for the first time to obtain M x Li7La3Zr2O 12 .

[0013] In an optional embodiment, the actual amount of the lithium source used is 1.12 to 1.17 times the theoretical amount;

[0014] And / or, the first sintering is performed at 850° C. to 950° C. for 9 h to 15 h.

[0015] In an optional embodiment, before ball milling, the oxide of element M, La2O3, and ZrO2 are pre-calcined to remove impurities.

[0016] In an optional embodiment, the pre-calcination is carried out at 800° C. to 900° C. for 8 h to 12 h.

[0017] In an optional embodiment, the pressing is performed at 14 MPa to 16 MPa for 3 to 5 minutes.

[0018] In an optional embodiment, the second sintering is performed at 1100° C. to 1300° C. for 8 h to 10 h.

[0019] In an optional embodiment, depositing the carbon layer includes: under furnace gas atmosphere conditions, raising the temperature of the deposition chamber to 300°C~350°C, and keeping it warm for 1h~3h; then raising the temperature in the deposition chamber to 400°C~500°C, and raising the temperature of the gas inlet chamber to 800°C~1000°C; introducing organic gas into the gas inlet chamber, and depositing for 30min~60min.

[0020] In an optional embodiment, the deposition is performed by chemical vapor deposition.

[0021] In an optional embodiment, the coating is performed by screen printing;

[0022] and / or, the mass ratio of carbon powder to the second binder glue is 1.0:7 to 2.5:7;

[0023] And / or, drying is performed at 90° C. to 110° C. for 10 h to 14 h.

[0024] In a second aspect, the present invention provides a solid electrolyte sheet prepared by the preparation method of any one of the aforementioned embodiments;

[0025] The solid electrolyte sheet includes a second solid electrolyte sheet body having a carbon layer and a carbon-containing coating layer arranged on the surface of the second solid electrolyte sheet body.

[0026] In a third aspect, the present invention provides a battery comprising the solid electrolyte sheet according to the aforementioned embodiment.

[0027] The beneficial effects of the present invention include:

[0028] The solid electrolyte sheet provided by the present invention can stabilize the phase structure of the material and improve the lithium ion conductivity by doping with the M element; the cooperation between the carbon layer and the coating layer can effectively improve the solid-solid contact problem of the solid electrolyte sheet, alleviate the electrolyte volume strain, and help reduce the interface impedance and improve the interface conductivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0030] Figure 1 The Ta obtained by the first sintering in Example 1 0.1 SEM image of LLZO powder;

[0031] Figure 2 This is a cross-sectional SEM image of the first solid electrolyte sheet body obtained by the second sintering in Example 1;

[0032] Figure 3 This is a cross-sectional XRD pattern of the first solid electrolyte sheet body obtained by the second sintering in Example 1;

[0033] Figure 4 This is a SEM image of the interface between the second solid electrolyte sheet body and the carbon layer of the solid electrolyte in Example 1. DETAILED DESCRIPTION

[0034] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, all are conventional products that can be purchased commercially.

[0035] The solid electrolyte sheet provided by the present invention and its preparation method and application are described in detail below.

[0036] The present invention provides a method for preparing a solid electrolyte sheet, comprising the following steps:

[0037] The oxide solid electrolyte and the first binder paste are mixed and ground, and then pressed to obtain a ceramic sheet green body; the ceramic sheet green body is subjected to a second sintering to obtain a first solid electrolyte sheet body;

[0038] A carbon layer is deposited on the surface of the first solid electrolyte sheet body to obtain a second solid electrolyte sheet body; a slurry obtained by mixing carbon powder and a second binder glue is coated on the surface of the second solid electrolyte sheet body and dried.

[0039] In the present invention, the molecular formula of the oxide solid electrolyte is M x Li7La3Zr2O 12 (M x LLZO), wherein 0<x≤0.2, and M includes at least one of Ta, Nb and Sb.

[0040] The present invention adopts at least one of Ta, Nb and Sb as a doping element to dope Li7La3Zr2O 12 In (LLZO), the valence state of the above-mentioned doping elements is relatively high, which can achieve zirconium doping, which is beneficial to increase the holes of lithium ions and improve the conductivity of lithium ions.

[0041] In some optional embodiments, the preparation of the oxide solid electrolyte comprises: mixing oxides of M elements, La2O3, ZrO2 and a lithium source according to M x Li7La3Zr2O 12 The oxides of M elements, La2O3 and ZrO2 are mixed in stoichiometric ratio to obtain an oxide precursor; the oxide precursor is sintered for the first time to obtain M x LLZO.

[0042] The amount of oxides of M elements, La2O3 and ZrO2 is matched with the molecular formula of the oxide solid electrolyte, that is, the molar ratio of M, La and Zr is x:3:2.

[0043] Exemplarily, the oxide of Ta can be Ta2O5, the oxide of Nb can be Nb2O5, and the oxide of Sb can be Sb2O3.

[0044] In some optional embodiments, before ball milling, the oxides of M elements, La2O3 and ZrO2 can be pre-calcined to remove impurities.

[0045] The pre-calcination can be performed at 800-900℃ for 8-12h.

[0046] Exemplarily, the pre-calcination temperature can be 800℃, 820℃, 850℃, 880℃ or 900℃, or other values in the range of 800-900℃.

[0047] The pre-calcination time can be 8h, 9h, 10h, 11h or 12h, or other values in the range of 8-12h.

[0048] In the present application, the actual amount of lithium source is 1.12-1.17 times the theoretical amount, such as 1.12 times, 1.15 times or 1.17 times, or other values in the range of 1.12-1.17 times. The theoretical amount of lithium source refers to the molar ratio of Li to La in the lithium source being 7:3.

[0049] By setting the actual amount of lithium source in the above range, the volatilization of lithium during sintering can be compensated.

[0050] In some optional embodiments, the ball milling can be continuous ball milling for 12h using a planetary ball mill, the solvent used in the ball milling process can be isopropyl alcohol, and the mass ratio of the ball milling raw material to the grinding ball during ball milling can be 1:5, so that the material is more easily ground.

[0051] In some optional embodiments, the first sintering can be performed at 850-950℃ for 9-15h.

[0052] Illustratively, the temperature of the first sintering may be 850°C, 860°C, 870°C, 880°C, 890°C, 900°C, 910°C, 920°C, 930°C, 940°C or 950°C, or other values ​​within the range of 850°C to 950°C.

[0053] The time of the first sintering can be 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours or 15 hours, or other values ​​within the range of 9 hours to 15 hours.

[0054] If the temperature of the first sintering is too low or the time is too short, the corresponding cubic phase cannot be obtained; if the temperature of the first sintering is too high or the time is too long, it will lead to the formation of impurity phase.

[0055] Furthermore, the material after the first sintering can be ground, and the ground powder D 50 It can be 10μm to 20μm.

[0056] Furthermore, the ground oxide solid electrolyte powder is mixed with the first binder solution and then ground again until the first solvent is completely evaporated.

[0057] The first adhesive solution is obtained by mixing a first adhesive with a first solvent, wherein the first adhesive may be PVB, the first solvent may be NMP, and the concentration of the first adhesive in the first adhesive solution may be 3wt% to 5wt%, preferably 4wt%.

[0058] In some optional embodiments, the compression can be performed at 14 MPa to 16 MPa for 3 to 5 minutes. This process can be performed using a powder tablet press.

[0059] Illustratively, the pressing pressure may be 14 MPa, 14.5 MPa, 15 MPa, 15.5 MPa, or 16 MPa, or other values ​​within the range of 14 MPa to 16 MPa.

[0060] If the pressing pressure is too high, the electrolyte sheet will be in too tight contact with the mold and the ceramic sheet green body cannot be easily removed.

[0061] The pressing time can be 3 min, 3.5 min, 4 min, 4.5 min or 5 min, etc., or other values ​​within the range of 3 min to 5 min.

[0062] In some optional embodiments, the second sintering may be performed at 1100° C. to 1300° C. for 8 h to 10 h.

[0063] For example, the temperature of the second sintering may be 1100°C, 1150°C, 1200°C, 1250°C or 1300°C, or other values ​​within the range of 1100°C to 1300°C.

[0064] The second sintering time can be 8 hours, 8.5 hours, 9 hours, 9.5 hours or 10 hours, etc., or other values ​​within the range of 8 hours to 10 hours.

[0065] If the temperature of the second sintering is too low or the time is too short, the density of the sintered material will not be sufficient.

[0066] The second sintering can be performed by placing the ceramic green sheet into a corundum crucible in a muffle furnace.

[0067] In some preferred embodiments, the first solid electrolyte sheet body may be surface treated before the carbon layer is deposited.

[0068] Illustratively, the surface treatment may include: mirror-polishing the first solid electrolyte sheet body using 80-mesh, 1200-mesh, 1500-mesh, and 2000-mesh silicon carbide sandpaper on a polishing machine, followed by ultrasonic cleaning with ethanol to remove surface impurities.

[0069] In some optional embodiments, the carbon layer is deposited by chemical vapor deposition, including: under furnace gas atmosphere conditions, raising the temperature of the deposition chamber to 300°C to 350°C (such as 300°C, 310°C, 320°C, 330°C, 340°C or 350°C, etc.), and keeping it warm for 1h to 3h (such as 1h, 1.5h, 2h, 2.5h or 3h, etc.). This process can remove the surface impurity passivation layer (reduce the amount of Li2CO3) and reduce the interface impedance. Then, the temperature in the deposition chamber is raised to 400°C~500°C (such as 400°C, 450°C or 500°C), and the temperature of the gas inlet chamber is raised to 800°C~1000°C (such as 800°C, 850°C, 900°C, 950°C or 1000°C); organic gas is introduced into the gas inlet chamber, and deposition is carried out for 5min~30min (such as 5min, 10min, 15min, 20min, 25min or 30min, etc.).

[0070] The organic gas may include methane, acetylene or propane.

[0071] The amount of organic gas introduced can be 20 mL / min to 50 mL / min, such as 20 mL / min, 30 mL / min, 40 mL / min or 50 mL / min.

[0072] In some optional embodiments, the coating is performed by screen printing. The flexible coating layer prepared by screen printing can improve the wettability of the electrolyte sheet and the lithium metal, transform the rigid contact into a flexible contact, and relieve the interfacial stress.

[0073] The second binder solution is obtained by mixing a second binder with a second solvent. The second binder may be polyvinylidene fluoride, and the second solvent may be NMP. The concentration of the second binder in the second binder solution may be 3 wt% to 5 wt%, preferably 4 wt%. The mass ratio of the carbon powder to the second binder solution may be 1.0:7 to 2.5:7, such as 1.0:7, 2:7, or 2.5:7, or other values ​​within the range of 1.0:7 to 2.5:7 may also be used.

[0074] Drying can be carried out at 90°C to 110°C (such as 90°C, 95°C, 100°C, 105°C or 110°C, etc.) for 10h to 14h (such as 10h, 11h, 12h, 13h or 14h, etc.).

[0075] The thickness of the coating layer obtained after drying may be 10 μm to 20 μm.

[0076] The deposited carbon layer is a pure carbon layer, and the coating layer obtained by coating is a mixed layer of carbon and polymer. Therefore, the carbon layer and the coating layer together form a gradient distribution of carbon.

[0077] Combining chemical vapor deposition with screen printing, the thin carbon layer deposited using chemical vapor deposition improves both the adhesion of the carbon layer to the surface of the first solid electrolyte sheet and the surface stability of the first solid electrolyte sheet. By uniformly coating the polymer and carbon powder onto the surface of the second solid electrolyte sheet using screen printing, the coating layer and the carbon layer are tightly bonded, effectively improving the solid-solid contact of the electrolyte sheet, achieving flexible gradient contact, alleviating electrolyte volume strain, and further increasing interfacial impedance and conductivity.

[0078] As mentioned above, the present invention can stabilize the cubic phase structure of LLZO and improve the ionic conductivity of the electrolyte by doping the M element into the oxide solid electrolyte; by sequentially arranging a carbon layer and a carbon-containing coating layer on the surface of the first solid electrolyte sheet body, it can solve the interface problems between the oxide electrolyte and lithium metal and between the oxide electrolyte and the positive electrode.

[0079] Correspondingly, the present invention also provides a solid electrolyte sheet, which is prepared by the above preparation method.

[0080] The solid electrolyte sheet comprises a second solid electrolyte sheet body having a carbon layer and a carbon-containing coating layer arranged on the surface of the second solid electrolyte sheet body.

[0081] The solid electrolyte sheet has high lithium ion conductivity and can effectively improve the solid-solid contact problem of the solid electrolyte sheet, alleviate the electrolyte volume strain, and is conducive to reducing interface impedance and improving interface conductivity.

[0082] In addition, the present invention also provides a battery comprising the above-mentioned solid electrolyte sheet.

[0083] The features and performance of the present invention are further described in detail below with reference to the embodiments.

[0084] Example 1

[0085] This embodiment provides a solid electrolyte sheet, the preparation method of which includes:

[0086] S1: Preparation of oxide solid electrolyte Ta 0.1 LLZO.

[0087] S11: Pre-calcining Ta2O5, La2O3, and ZrO2 at 850°C for 10 hours to remove impurities.

[0088] S12: The Ta2O5, La2O3, and ZrO2 after impurities are removed are ball-milled with a lithium source in a planetary ball mill in the presence of isopropyl alcohol and grinding beads for 12 hours to obtain an oxide precursor.

[0089] The molar ratio of Ta, La and Zr is 0.1:3:2, and the molar ratio of Li to La in the lithium source is 8.05:3 (the actual amount of the lithium source is 1.15 times the theoretical amount).

[0090] S12: The oxide precursor was first sintered at 900 ° C for 12 hours and then ground to obtain Ta 0.1 LLZO powder (D 50 is 14.5μm).

[0091] Combine Figure 1 , Ta obtained in this step 0.1 LLZO powder has round particles and a clean surface.

[0092] S2: preparing ceramic green sheets.

[0093] PVB glue (concentration of 4wt%, solvent is NMP) was added to the above Ta 0.1 The LLZO powder was mixed and ground until the NMP was completely volatilized, and then pressed in a powder tablet press at a pressure of 15 MPa for 4 minutes to obtain a ceramic green sheet.

[0094] S3: preparing a first solid electrolyte sheet body.

[0095] The ceramic sheet green body was placed in a corundum crucible and sintered for a second time at 1200° C. for 9 h in a muffle furnace to obtain a first solid electrolyte sheet body.

[0096] Combine Figure 2 The first solid electrolyte sheet obtained in this step has a dense cross-section, which is conducive to lithium ion migration; Figure 3 , sharp diffraction peaks can be clearly observed, indicating that the crystallinity of the synthesized first solid electrolyte sheet is high. In addition, compared with the standard card, the first solid electrolyte sheet is in a cubic phase, which is conducive to the performance of lithium ion conductivity.

[0097] S4: Depositing a carbon layer.

[0098] S41: The first solid electrolyte sheet body is mirror-polished using 80-mesh, 1200-mesh, 1500-mesh, and 2000-mesh silicon carbide sandpaper on a polishing machine, and then ultrasonically cleaned with ethanol to remove surface impurities.

[0099] S42: Place the first solid electrolyte sheet body after removing surface impurities in a chemical vapor deposition deposition chamber. Under nitrogen conditions, raise the temperature of the deposition chamber to 320°C and maintain it for 2 hours. Subsequently, raise the temperature in the deposition chamber to 450°C, and raise the temperature of the gas inlet chamber to 900°C; introduce acetylene into the gas inlet chamber (at a rate of 40 mL / min) and deposit for 18 minutes. After the reaction is completed, stop the introduction of organic gas and naturally cool to room temperature to obtain a second solid electrolyte sheet body with a carbon layer.

[0100] S5: Apply the coating layer.

[0101] S51: mixing carbon powder and PVDF glue (concentration of 4 wt %, solvent of NMP) in a slurry machine at a rotation speed of 2000 rpm for 15 minutes to obtain a coating slurry.

[0102] The mass ratio of carbon powder to PVDF glue is 1.5:7.

[0103] S52: In a glove box, the slurry is applied to the carbon layer surface of the second solid electrolyte sheet body by screen printing, and then vacuum dried at 100°C for 12 hours to obtain a solid electrolyte sheet with a coating layer (thickness of about 14.1 μm).

[0104] Combine Figure 4 It can be seen that the carbon layer is in close contact with the second solid electrolyte sheet body and is flexible, which is conducive to alleviating the rigid contact between the electrolyte sheet and the electrode.

[0105] Example 2

[0106] This embodiment provides a solid electrolyte sheet, the preparation method of which includes:

[0107] S1: Preparation of oxide solid electrolyte Nb 0.1 LLZO.

[0108] S11: Pre-calcining Nb2O5, La2O3, and ZrO2 at 800°C for 12 hours to remove impurities.

[0109] S12: The Nb2O5, La2O3, and ZrO2 after impurities are removed are continuously ball-milled with a lithium source in a planetary ball mill in the presence of isopropyl alcohol and grinding beads for 12 hours to obtain an oxide precursor.

[0110] The molar ratio of Nb, La and Zr is 0.1:3:2, and the molar ratio of Li to La in the lithium source is 7.84:3 (the actual amount of the lithium source is 1.12 times the theoretical amount).

[0111] S12: The oxide precursor was first sintered at 850 ° C for 15 h and then ground to obtain Nb 0.1 LLZO powder (D 50 is 14.3μm).

[0112] S2: preparing ceramic green sheets.

[0113] PVB glue (concentration of 4wt%, solvent is NMP) was added to the above Nb 0.1 The LLZO powder was mixed and ground until the NMP was completely volatilized, and then pressed in a powder tablet press at a pressure of 14 MPa for 5 minutes to obtain a ceramic green sheet.

[0114] S3: preparing a first solid electrolyte sheet body.

[0115] The ceramic sheet green body was placed in a corundum crucible and sintered for a second time at 1100° C. for 10 h in a muffle furnace to obtain a first solid electrolyte sheet body.

[0116] S4: Depositing a carbon layer.

[0117] S41: The first solid electrolyte sheet body is mirror-polished using 80-mesh, 1200-mesh, 1500-mesh, and 2000-mesh silicon carbide sandpaper on a polishing machine, and then ultrasonically cleaned with ethanol to remove surface impurities.

[0118] S42: Place the first solid electrolyte sheet body from which surface impurities have been removed into a deposition chamber of chemical vapor deposition. Under nitrogen conditions, raise the temperature of the deposition chamber to 300°C and maintain it for 3 hours. Subsequently, raise the temperature in the deposition chamber to 400°C, and raise the temperature of the gas inlet chamber to 800°C; introduce acetylene into the gas inlet chamber (at a rate of 20 mL / min) and deposit for 30 minutes. After the reaction is complete, stop introducing the organic gas, and naturally cool to room temperature to obtain a second solid electrolyte sheet body having a carbon layer.

[0119] S5: Apply the coating layer.

[0120] S51: Carbon powder and PVDF glue (with a concentration of 4 wt % and a solvent of NMP) were mixed in a slurry machine at a rotation speed of 2000 rpm for 15 minutes to obtain a coating slurry.

[0121] The mass ratio of carbon powder to PVDF glue is 2.5:7.

[0122] S52: In a glove box, the slurry is applied to the carbon layer surface of the second solid electrolyte sheet body by screen printing, and then vacuum dried at 90°C for 14 hours to obtain a solid electrolyte sheet with a coating layer (thickness of about 18.3 μm).

[0123] Example 3

[0124] This embodiment provides a solid electrolyte sheet, the preparation method of which includes:

[0125] S1: Preparation of oxide solid electrolyte Sb 0.1 LLZO.

[0126] S11: Pre-calcining Sb2O3, La2O3, and ZrO2 at 900°C for 8 hours to remove impurities.

[0127] S12: The impurity-removed Sb2O3, La2O3, and ZrO2 are continuously ball-milled with a lithium source in a planetary ball mill in the presence of isopropyl alcohol and milling beads for 12 hours to obtain an oxide precursor.

[0128] The molar ratio of Sb, La and Zr is 0.1:3:2, and the molar ratio of Li to La in the lithium source is 8.19:3 (the actual amount of the lithium source is 1.17 times the theoretical amount).

[0129] S12: The oxide precursor was first sintered at 950 ° C for 9 hours and then ground to obtain Sb 0.1 LLZO powder (D 50 is 15.2μm).

[0130] S2: preparing ceramic green sheets.

[0131] PVB glue (concentration of 4wt%, solvent is NMP) was added to the above Sb 0.1 The LLZO powder was mixed and ground until the NMP was completely volatilized, and then pressed in a powder tablet press at a pressure of 16 MPa for 3 minutes to obtain a ceramic green sheet.

[0132] S3: preparing a first solid electrolyte sheet body.

[0133] The ceramic sheet green body was placed in a corundum crucible and sintered for a second time at 1300° C. for 8 h in a muffle furnace to obtain a first solid electrolyte sheet body.

[0134] S4: Depositing a carbon layer.

[0135] S41: The first solid electrolyte sheet body is mirror-polished using 80-mesh, 1200-mesh, 1500-mesh, and 2000-mesh silicon carbide sandpaper on a polishing machine, and then ultrasonically cleaned with ethanol to remove surface impurities.

[0136] S42: Place the first solid electrolyte sheet body, from which surface impurities have been removed, into a deposition chamber for chemical vapor deposition. Under nitrogen conditions, raise the temperature of the deposition chamber to 350°C and maintain it for 1 hour. Subsequently, raise the temperature in the deposition chamber to 500°C, and raise the temperature of the gas inlet chamber to 1000°C; introduce methane into the gas inlet chamber (at a rate of 50 mL / min) and deposit for 5 minutes. After the reaction is complete, stop introducing the organic gas, and naturally cool to room temperature to obtain a second solid electrolyte sheet body having a carbon layer.

[0137] S5: Apply the coating layer.

[0138] S51: Carbon powder and PVDF glue (with a concentration of 4 wt % and a solvent of NMP) were mixed in a slurry machine at a rotation speed of 2000 rpm for 15 minutes to obtain a coating slurry.

[0139] Among them, the mass ratio of carbon powder to PVDF glue is 1.0:7

[0140] S52: In a glove box, the slurry is applied to the carbon layer surface of the second solid electrolyte sheet body by screen printing, and then vacuum dried at 110°C for 10 hours to obtain a solid electrolyte sheet with a coating layer (thickness of about 11.2 μm).

[0141] Example 4

[0142] The difference between this embodiment and embodiment 1 is that the chemical formula of the oxide solid electrolyte in S1 is Ta 0.2 LLZO.

[0143] Comparative Example 1

[0144] The difference between this comparative example and Example 1 is that the temperature of the first sintering is 800°C.

[0145] Comparative Example 2

[0146] The difference between this comparative example and Example 1 is that the temperature of the first sintering is 1000°C.

[0147] Comparative Example 3

[0148] The difference between this comparative example and Example 1 is that the temperature of the second sintering is 1000°C.

[0149] Comparative Example 4

[0150] The difference between this comparative example and Example 1 is that the temperature of the second sintering is 1400°C.

[0151] Comparative Example 5

[0152] The difference between this comparative example and Example 1 is that Ta is not doped in the oxide solid electrolyte, and the solid electrolyte sheet has no coating layer (ie, the S5 operation is not performed).

[0153] Comparative Example 6

[0154] The difference between this comparative example and Example 1 is that Ta is replaced by an equal amount of Rb.

[0155] Comparative Example 7

[0156] The difference between this comparative example and Example 1 is that Ta is replaced by an equal amount of Ca.

[0157] Comparative Example 8

[0158] The difference between this comparative example and Example 1 is that the amount of Ta incorporated into the oxide solid electrolyte is increased, wherein the molar ratio of Ta, La and Zr is 1:3:2.

[0159] Comparative Example 9

[0160] The difference between this comparative example and Example 1 is that the solid electrolyte sheet has no carbon layer and coating layer (ie, S4 and S5 operations are not performed).

[0161] Comparative Example 10

[0162] The difference between this comparative example and Example 1 is that the solid electrolyte sheet has no carbon layer (ie, the S4 operation is not performed).

[0163] Comparative Example 11

[0164] The difference between this comparative example and Example 4 is that the solid electrolyte sheet has no coating layer (ie, the S5 operation is not performed).

[0165] Comparative Example 12

[0166] This comparative example differs from Example 1 in that, in S42, the first solid electrolyte sheet, after surface impurities have been removed, is directly placed in a chemical vapor deposition (CVD) chamber. Under nitrogen conditions, the temperature in the deposition chamber is raised to 450°C, and the temperature in the gas inlet chamber is raised to 900°C. Acetylene is then introduced into the gas inlet chamber, and deposition proceeds for 18 minutes. After the reaction is complete, the organic gas introduction is stopped, and the sheet is allowed to cool naturally to room temperature.

[0167] Comparative Example 13

[0168] This comparative example differs from Example 1 in that, in S42, acetylene was introduced into the gas inlet chamber (at a rate of 5 mL / min) for 5 minutes of deposition. After the reaction was complete, the introduction of the organic gas was stopped, and the reaction mixture was allowed to cool naturally to room temperature, yielding a second solid electrolyte sheet having a carbon layer.

[0169] Comparative Example 14

[0170] This comparative example differs from Example 1 in that, in S42, acetylene was introduced into the gas inlet chamber (at a rate of 100 mL / min) for 30 minutes of deposition. After the reaction was complete, the introduction of the organic gas was stopped, and the reaction mixture was allowed to cool naturally to room temperature, yielding a second solid electrolyte sheet having a carbon layer.

[0171] Comparative Example 15

[0172] The difference between this comparative example and Example 1 is that the thickness of the coating layer is 5 μm.

[0173] Comparative Example 16

[0174] The difference between this comparative example and Example 1 is that the thickness of the coating layer is 30 μm.

[0175] Test example

[0176] The performance of the solid electrolyte sheets prepared in Examples 1 to 4 and Comparative Examples 1 to 16 was compared in the following manner. The results are shown in Tables 1 and 2.

[0177] Ionic conductivity test:

[0178] The blocking electrode of the test device is a stainless steel electrode. The test principle is to apply a small amplitude sinusoidal AC signal to the solid electrolyte sheet and measure the ratio of the output AC signal voltage to current (this ratio is the impedance of the system) as the frequency of the sinusoidal wave changes. According to the formula The conductivity of the solid electrolyte can be calculated, where σ is the conductivity to be measured, d is the thickness of the sample to be measured, S is the surface area of ​​the sample to be measured in contact with the blocking electrode, and R is the impedance measured by EIS.

[0179] Interface resistance and critical current density (CCD) test:

[0180] Assembling a symmetrical lithium cell: A lithium sheet was attached to both sides of the solid electrolyte sheet provided by each group to form a sandwich structure. The symmetrical lithium cell was then assembled in a glove box. The interfacial resistance and critical current density were then measured. The interfacial resistance was characterized using AC impedance spectroscopy (AIS) with a sweep frequency of 10 mV from a high frequency of 10,000 kHz to a low frequency of 10 Hz.

[0181] The critical current density (CCD) is 0.12 mA / cm at 30°C. 2 ~1.12mA / cm 2 Constant current circulation within the range, the interval of increasing current is 0.02mA / cm 2 .

[0182] Table 1 Test results

[0183]

[0184]

[0185] Table 2 Test results

[0186] <![CDATA[界面电阻(kΩ·cm 2 )]]> <![CDATA[CCD(mA / cm 2 )]]> Example 1 0.89 0.80 Example 2 0.92 0.78 Example 3 0.90 0.76 Example 4 0.91 0.76 Comparative Example 9 8.79 0.28 Comparative Example 10 6.01 0.34 Comparative Example 11 4.63 0.40 Comparative Example 12 2.98 0.48 Comparative Example 13 0.98 0.56 Comparative Example 14 0.92 0.54 Comparative Example 15 0.90 0.62 Comparative Example 16 0.91 0.60

[0187] From Table 1 and Table 2, we can see the following results:

[0188] The results of Examples 1-4 and Comparative Examples 1-4 show that the first sintering temperature was too low, resulting in some raw material residue in the powder; the first sintering temperature was too high, resulting in a hard material after sintering, which was not conducive to subsequent grinding. Therefore, lithium ion conductivity testing was not easily possible in both cases. The second sintering temperature was too low, resulting in significant pores in the electrolyte sheet, preventing lithium ions from easily migrating between particles; and the second sintering temperature was too high, resulting in lithium ion overflow and a lithium-deficient structure that hindered lithium ion migration.

[0189] The results of Examples 1-4 and Comparative Examples 5-8 show that doping is beneficial for improving lithium-ion conductivity, but different doping elements have a certain impact on the lithium-ion conductivity of LLZO. Ta, Nb, and Sb are high-valent elements. Their particles increase lithium-ion vacancies, lowering the energy barrier for lithium-ion migration and achieving high lithium-ion conductivity. The amount of doping elements must be controlled within an appropriate range; excessive levels are detrimental to the optimal lithium-ion conductivity.

[0190] As can be seen from the results of the example 1 and the comparative examples 9-16, before carbon deposition, heating in a nitrogen atmosphere can remove surface impurities, reduce interface impedance and improve tolerance to high current density. The carbon layer is uniformly deposited by chemical vapor deposition, which improves the adhesion of the carbon layer to the surface of the LLZO electrolyte sheet, and the surface coating treatment is performed on the treated LLZO electrolyte sheet to improve the surface stability; then the polymer composite material is uniformly coated on the surface of the electrolyte sheet to be closely combined with the carbon layer, which effectively improves the solid-solid contact problem of the electrolyte sheet, realizes flexible gradient contact, relieves the volume strain of the electrolyte, further reduces the interface impedance and improves the interface conductivity.

[0191] In summary, the solid electrolyte sheet provided by the present application can stabilize the phase structure of the material by doping M elements, improve the lithium ion conductivity, effectively improve the solid-solid contact problem of the solid electrolyte sheet by the cooperation of the carbon layer and the coating layer, relieve the volume strain of the electrolyte, which is conducive to reducing the interface impedance and improving the interface conductivity.

[0192] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a solid electrolyte sheet, characterized in that: The following steps are involved: The oxide solid electrolyte and the first binder paste are mixed and ground, and then pressed to obtain a ceramic sheet green body; the ceramic sheet green body is subjected to a second sintering to obtain a first solid electrolyte sheet body; Depositing a carbon layer on the surface of the first solid electrolyte sheet body to obtain a second solid electrolyte sheet body; applying a slurry obtained by mixing carbon powder and a second binder glue solution to the surface of the second solid electrolyte sheet body and drying; The molecular formula of the oxide solid electrolyte is M x Li7La3Zr2O 12 , wherein 0<x≤0.2, M comprises at least one of Ta, Nb and Sb; The first binder glue solution is obtained by mixing a first binder and a first solvent, the first binder is PVB, the first solvent is NMP, and the concentration of the first binder in the first binder glue solution is 3wt% to 5wt%; The second binder glue solution is obtained by mixing a second binder and a second solvent, the second binder is polyvinylidene fluoride, the second solvent is NMP, and the concentration of the second binder in the second binder glue solution is 3wt%-5wt%.

2. The preparation method according to claim 1, characterized in that The preparation of the oxide solid electrolyte comprises the following steps: the oxide of the M element, La2O3, ZrO2 and the lithium source are mixed according to the M x Li7La3Zr2O 12 The oxide precursor is subjected to a first sintering to obtain M x Li7La3Zr2O 12 .

3. The preparation method according to claim 2, characterized in that The actual amount of the lithium source used is 1.12 to 1.17 times the theoretical amount; And / or, the first sintering is performed at 850° C. to 950° C. for 9 h to 15 h.

4. The preparation method according to claim 2 or 3, characterized in that Before ball milling, the oxides of element M, La2O3, and ZrO2 are pre-calcined to remove impurities; The pre-calcination is carried out at 800°C to 900°C for 8h to 12h.

5. The preparation method according to claim 1, characterized in that The pressing is carried out at 14 MPa to 16 MPa for 3 to 5 minutes.

6. The preparation method according to claim 1, characterized in that The second sintering is carried out at 1100℃~1300℃ for 8h~10h.

7. The preparation method according to claim 1, characterized in that Depositing a carbon layer includes: under furnace gas atmosphere conditions, raising the temperature of the deposition chamber to 300°C~350°C and keeping it warm for 1h~3h; then raising the temperature in the deposition chamber to 400°C~500°C, and raising the temperature of the gas inlet chamber to 800°C~1000°C; introducing organic gas into the gas inlet chamber and depositing for 30min~60min.

8. The preparation method according to claim 7, characterized in that The deposition is carried out by chemical vapor deposition.

9. The preparation method according to claim 1, characterized in that The coating is carried out by screen printing; and / or, the mass ratio of the carbon powder to the second binder glue is 1.0:7 to 2.5:7; And / or, drying is performed at 90° C. to 110° C. for 10 h to 14 h.

10. A solid electrolyte sheet, characterized in that: Prepared by the preparation method according to any one of claims 1 to 9; The solid electrolyte sheet includes a second solid electrolyte sheet body having a carbon layer and a carbon-containing coating layer disposed on a surface of the second solid electrolyte sheet body.

11. A battery, characterized in that: The battery comprises the solid electrolyte sheet according to claim 10.

Images