Solid electrolyte, battery and preparation method of battery

Abstract

The invention provides a solid electrolyte, a battery and a preparation method of the battery. The solid electrolyte comprises a first layer, a garnet electrolyte layer and a second layer which are sequentially stacked; the first layer comprises lithium fluoride and a lithium alloy; the second layer includes an organic material and a lithium salt. When the solid-state electrolyte is used for preparing an all-solid-state battery, the solid-state electrolyte has excellent interface performance with an electrode, and the electrochemical performance of the battery can be remarkably improved.

Description

Technical Field

[0001] The present invention relates to a solid electrolyte, a battery and a method for preparing the battery, and belongs to the technical field of secondary batteries. Background Art

[0002] In a lithium-ion battery prepared by matching a lithium metal anode with an organic electrolyte, during the cycling process of the battery, the lithium metal anode not only easily generates lithium dendrites, but also the lithium metal anode will react with the organic electrolyte, which is not conducive to the safety performance of the battery. In order to avoid the generation of lithium dendrites during the cycling process of the battery and to improve the safety performance of the battery, a solid electrolyte has emerged. Compared with the organic electrolyte, the solid electrolyte has better stability and safety. Therefore, the solid electrolyte can be used to replace the organic electrolyte to prepare an all-solid-state battery.

[0003] Among various types of solid electrolytes, garnet-type solid electrolytes have attracted much attention due to their excellent Li + conductivity, excellent mechanical strength, excellent chemical stability, and a relatively wide electrochemical window. However, when the existing garnet-type solid electrolyte is assembled with a positive electrode sheet and a lithium metal anode to prepare an all-solid-state battery, the garnet-type solid electrolyte is extremely easy to react with moisture and carbon dioxide in the air to generate lithium carbonate, resulting in strong lithium aversion of the garnet-type solid electrolyte, and a large interfacial impedance between the garnet-type solid electrolyte and the lithium metal anode, thereby affecting the comprehensive performance of the battery. Summary of the Invention

[0004] The present invention provides a solid electrolyte, which has excellent interfacial performance with a lithium metal anode when used to prepare an all-solid-state battery, and can significantly improve the electrochemical performance of the battery.

[0005] The present invention provides a battery, which includes the above-mentioned solid electrolyte, and not only has excellent safety performance, but also performs excellently in terms of electrochemical performance.

[0006] The present invention provides a method for preparing a battery, which is used to prepare the above-mentioned battery, and the preparation method is simple to operate and suitable for wide promotion and application.

[0007] The present invention provides a solid electrolyte, wherein the solid electrolyte includes a first layer, a garnet electrolyte layer, and a second layer which are stacked;

[0008] The first layer includes lithium fluoride and a lithium alloy;

[0009] The second layer includes an organic substance and a lithium salt.

[0010] The solid electrolyte as described above, wherein the lithium alloy is selected from at least one of a lithium-sodium alloy, a lithium-aluminum alloy, a lithium-indium alloy, and a lithium-gallium alloy.

[0011] The solid electrolyte as described above, wherein in the first layer, the mass ratio of lithium fluoride to the lithium alloy is (0.5 - 2):1.

[0012] The solid electrolyte as described above, wherein in the second layer, the mass percentage content of the lithium salt is 5 - 50%.

[0013] The solid electrolyte as described above, wherein the organic substance is selected from at least one of poly(propylene carbonate) and succinonitrile.

[0014] The solid electrolyte as described above, wherein the organic substance is obtained by polymerization of a raw material system comprising at least succinonitrile and 1,3,5-trioxane.

[0015] The solid electrolyte as described above, wherein the mass ratio of 1,3,5-trioxane to the succinonitrile is 5:(1 - 5).

[0016] The solid electrolyte as described above, wherein the solid electrolyte further satisfies at least one of the following:

[0017] a) The thickness of the first layer is 50 - 200 nm;

[0018] b) The thickness of the garnet electrolyte layer is 100 - 500 μm;

[0019] c) The thickness of the second layer is 10 - 50 μm.

[0020] The present invention provides a battery, which includes a positive electrode, a lithium metal negative electrode, and the solid electrolyte as described above;

[0021] The solid electrolyte is disposed between the positive electrode and the lithium metal negative electrode, and the first layer is disposed close to the lithium metal negative electrode sheet, and the second layer is disposed close to the positive electrode.

[0022] The present invention provides a method for preparing a battery as described above, which includes:

[0023] Treating the first surface of the garnet electrolyte layer with a first solution, and laminating the lithium metal negative electrode with the first surface;

[0024] Coating a precursor slurry on the second surface of the garnet electrolyte layer, laminating the positive electrode with the second surface, and then polymerizing the precursor slurry;

[0025] Wherein, the first solution includes nitrite and fluoride; the precursor slurry includes 1,3,5-trioxane, succinonitrile, and a lithium salt.

[0026] The present invention also provides another method for preparing the battery as described above, which includes:

[0027] Treat the first surface of the garnet electrolyte layer with a first solution, and stack the lithium metal negative electrode on the first surface;

[0028] Coat a coating slurry on the second surface of the garnet electrolyte layer. After stacking the positive electrode on the second surface, cure the coating slurry;

[0029] Wherein, the first solution includes nitrite and fluoride; the coating slurry includes at least one of poly(propylene carbonate) and succinonitrile, and a lithium salt.

[0030] The solid electrolyte of the present invention includes a first layer, a garnet electrolyte layer, and a second layer which are stacked. The first layer includes lithium fluoride and a lithium alloy, and the second layer includes an organic substance and a lithium salt. Among them, lithium fluoride is one of the main components of the solid electrolyte interphase film, which can effectively inhibit the growth of lithium dendrites. The lithium alloy not only has excellent wettability to the garnet electrolyte layer, but also has excellent lithiophilicity, which helps to improve the interfacial performance between the lithium metal negative electrode and the solid electrolyte, reduce the interfacial impedance between the lithium metal negative electrode and the solid electrolyte, and improve the cycle performance of the battery; the second layer can act as a buffer layer to reduce the interfacial impedance between the positive electrode and the solid electrolyte, and further improve the cycle performance of the battery.

[0031] The battery of the present invention includes the above solid electrolyte, which can not only inhibit the growth of lithium dendrites, but also has excellent interfacial performance between the electrode and the solid electrolyte, with a lower interfacial impedance, and the battery has excellent cycle performance.

[0032] The present invention provides a method for preparing a solid electrolyte for preparing the above solid electrolyte. The preparation method is simple to operate and is suitable for wide promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or related technologies, the following briefly introduces the drawings required to be used in the description of the embodiments of the present invention or related technologies. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0034] Figure 1 It is a schematic diagram of the wettability of molten lithium by the garnet electrolyte layer not treated with the first solution of the present invention;

[0035] Figure 2Schematic diagram of the wettability of the garnet electrolyte layer of the first layer of the present invention with respect to molten lithium;

[0036] Figure 3 Electrochemical performance diagrams of the all-solid-state batteries of Examples 1-3 and Comparative Example 1 of the present invention.

[0037] Explanation of reference numerals:

[0038] 1: Garnet electrolyte layer;

[0039] 2: Molten lithium. Detailed implementation manners

[0040] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0041] The first aspect of the present invention provides a solid electrolyte, wherein the solid electrolyte includes a first layer, a garnet electrolyte layer, and a second layer which are stacked;

[0042] The first layer includes lithium fluoride and a lithium alloy;

[0043] The second layer includes an organic substance and a lithium salt.

[0044] It can be understood that the solid electrolyte of the present invention sequentially includes a first layer, a garnet electrolyte layer, and a second layer along the stacking direction.

[0045] During the assembly process of the battery, the first layer is disposed close to the lithium metal negative electrode, and the second layer is disposed close to the positive electrode. Lithium fluoride in the first layer is the main component of the solid electrolyte interphase film, which can effectively inhibit the growth of lithium dendrites; and the lithium alloy not only has excellent lithium affinity, but also has extremely strong wettability with respect to the garnet electrolyte layer. Therefore, the first layer including the lithium alloy can improve the interfacial performance between the lithium metal negative electrode and the garnet electrolyte layer, reduce the interfacial impedance between the lithium metal negative electrode and the solid electrolyte, and further improve the cycle performance of the battery; the second layer can serve as a buffer layer to reduce the interfacial impedance between the positive electrode and the solid electrolyte, and further improve the cycle performance of the battery.

[0046] The present invention does not particularly limit the garnet electrolyte layer, and it can be any garnet electrolyte layer commonly used in the art. Exemplarily, the garnet electrolyte layer may include at least one of lithium lanthanum zirconate (LLZO), tantalum-doped lithium lanthanum zirconate (LLZTO), niobium-doped lithium lanthanum zirconate (LLZNO), aluminum-doped lithium lanthanum zirconate (LLZAO), and gallium-doped lithium lanthanum zirconate (LLZGO). Further, the garnet electrolyte layer may be an LLZTO layer.

[0047] The present invention does not particularly limit the lithium alloy, and the lithium alloy can be a lithium alloy commonly used in the art. Exemplarily, the lithium alloy is selected from at least one of lithium-sodium alloy, lithium-aluminum alloy, lithium-indium alloy, and lithium-gallium alloy. Further, the lithium alloy is preferably a lithium-sodium alloy.

[0048] It can be understood that in the first layer, lithium fluoride and the lithium alloy are the main components for improving the interfacial performance between the solid electrolyte and the lithium metal anode. Therefore, the present invention can further improve the cycling performance of the battery by specifically selecting the mass ratio of lithium fluoride and the lithium alloy in the first layer. Exemplarily, in some embodiments of the present invention, in the first layer, the mass ratio of lithium fluoride to the lithium alloy is (0.5 - 2):1.

[0049] In some embodiments of the present invention, when the mass percentage content of the lithium salt in the second layer is 5 - 50%, the second layer has excellent lithium-ion transport performance, can further reduce the interfacial impedance between the positive electrode and the solid electrolyte, and improve the cycling performance of the battery.

[0050] The present invention does not particularly limit the type of the organic matter in the second layer, and it can be an organic matter commonly used in the art. In some embodiments of the present invention, the organic matter can be selected from at least one of poly(propylene carbonate) and succinonitrile.

[0051] In the present invention, a coating slurry including poly(propylene carbonate) and a lithium salt can be prepared, and the coating slurry is disposed on the surface of the garnet electrolyte layer away from the first layer, and after curing, a second layer including poly(propylene carbonate) is obtained; a coating slurry including succinonitrile and a lithium salt can also be prepared, and the coating slurry is disposed on the surface of the garnet electrolyte layer away from the first layer, and after curing, a second layer including succinonitrile is obtained; or a coating slurry including poly(propylene carbonate), succinonitrile, and a lithium salt can be prepared, and the coating slurry is disposed on the surface of the garnet electrolyte layer away from the first layer, and after curing, a second layer including poly(propylene carbonate) and succinonitrile is obtained.

[0052] In some other embodiments of the present invention, when the organic matter is polymerized from a raw material system including at least succinonitrile and 1,3,5-trioxane, the second layer can further reduce the interfacial impedance between the positive electrode and the solid electrolyte and improve the electrochemical performance of the battery.

[0053] Further, when the mass ratio of 1,3,5 - trioxane to succinonitrile is 5:(1 - 5), 1,3,5 - trioxane and succinonitrile can match better, improving the cycling performance of the battery. Exemplarily, the mass ratio of 1,3,5 - trioxane to succinonitrile can be 5:1, 5:2, 5:3, 5:4, 5:5 or the range composed of any two of them.

[0054] In some embodiments, a certain mass of lithium salt can be added to the eutectic solution formed by mixing 1,3,5 - trioxane (TXE) and succinonitrile (SN) and stirred to obtain a precursor slurry, and the precursor slurry is subjected to a polymerization reaction to obtain a second layer including an organic substance and a lithium salt. The lithium salt can be lithium difluoroborate (LiDFOB).

[0055] Further, the eutectic solution is obtained by mixing TXE and SN in a certain mass ratio and heating and melting at a certain temperature. Among them, during the heating and melting, the temperature can be 80 - 100 °C, and the time can be 1 - 2 h;

[0056] During stirring, the rotation speed can be 300 rpm - 450 rpm, the time can be 10 min - 30 min, and the temperature can be 80 °C - 100 °C.

[0057] In some embodiments, the mass ratio of the lithium salt to 1,3,5 - trioxane in the precursor slurry can also be selected to improve the lithium - ion transport efficiency of the second layer and reduce the interfacial impedance. For example, the mass ratio of the lithium salt to 1,3,5 - trioxane is 1:(1 - 8).

[0058] Exemplarily, in the precursor slurry, the mass ratio of the lithium salt to 1,3,5 - trioxane can be 1:1, 1:2, 1:2.5, 1:3, 1:4, 1:4.5, 1:5, 1:6, 1:7, 1:8 or the range composed of any two of them.

[0059] In some embodiments of the present invention, in the solid - state electrolyte, when the thickness of the first layer is 50 - 200 nm, the growth of lithium dendrites can be better inhibited, the interfacial performance between the negative electrode sheet and the solid - state electrolyte can be improved, and the energy density of the battery can also be improved;

[0060] When the thickness of the garnet electrolyte layer is 100 - 500 μm, it can promote the transport of lithium ions and improve the electrochemical performance of the battery while improving the energy density of the battery;

[0061] When the thickness of the second layer is 10 - 50 μm, it can further reduce the interfacial impedance between the positive electrode sheet and the solid - state electrolyte and improve the cycling performance of the battery while improving the energy density of the battery.

[0062] A second aspect of the present invention provides a battery, comprising a positive electrode, a lithium metal negative electrode, and the above-mentioned solid electrolyte;

[0063] The solid electrolyte is disposed between the positive electrode and the lithium metal negative electrode, with the first layer disposed closer to the lithium metal negative electrode and the second layer disposed closer to the positive electrode.

[0064] It can be understood that the battery of the present invention may sequentially include a lithium metal negative electrode, a first layer, a garnet electrolyte layer, a second layer, and a positive electrode in the stacking direction.

[0065] The present invention does not particularly limit the positive electrode sheet, and the positive electrode sheet may be a positive electrode sheet commonly used in the art. Exemplarily, the positive electrode sheet may include a positive electrode current collector and a positive electrode active layer provided on at least one surface of the positive electrode current collector, wherein the positive electrode active layer includes a positive electrode active material, a conductive agent, and a binder.

[0066] The positive electrode current collector may be a positive electrode current collector commonly used in the art, for example, it may be aluminum foil;

[0067] The positive electrode active material may be a positive electrode active material commonly used in the art, for example, it may be at least one of lithium iron phosphate (LiFePO4), lithium cobaltate (LiCoO2), lithium manganate (Li2MnO4), ternary materials (lithium nickel cobalt manganese oxide (LiNi 0.6 Co 0.2 Mn 0.2 O2) and lithium nickel cobalt aluminate (LiNi 0.8 Co 0.15 Al 0.05 O2).

[0068] The conductive agent may be a conductive agent commonly used in the art, for example, it may be selected from at least one of super P, acetylene black, Ketjen black, carbon nanotubes, and graphene;

[0069] The binder may be a binder commonly used in the art, for example, it may be at least one of polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR) emulsion, and carboxymethyl cellulose (CMC).

[0070] In some embodiments, the positive electrode active layer may include: LiFePO4 positive electrode powder, polyvinylidene fluoride, and a conductive agent, and based on the total mass of the positive electrode active layer, the mass percentage content of the LiFePO4 positive electrode powder is 80%, the mass percentage content of polyvinylidene fluoride is 10%, and the mass percentage content of the conductive agent is 10%.

[0071] For the battery of the present invention, since the lithium metal negative electrode is disposed adjacent to the first layer in the solid electrolyte, that is, the first layer is disposed at the interface between the lithium metal negative electrode and the solid electrolyte layer, not only can the growth of lithium dendrites be inhibited, but also excellent interfacial properties are achieved between the lithium metal negative electrode and the solid electrolyte, with a low interfacial impedance. This battery has excellent cycling performance; the second layer can serve as a buffer layer to reduce the interfacial impedance between the positive electrode and the solid electrolyte, further improving the cycling performance of the battery. And since the battery of the present invention does not contain an organic electrolyte and is an all-solid-state battery, the battery of the present invention also has excellent safety performance.

[0072] In the present invention, the affinity between the lithium alloy in the first layer and the lithium metal negative electrode is better, so that the interfacial impedance between the lithium metal negative electrode and the first layer is lower, which helps to improve the cycling performance of the battery.

[0073] The third aspect of the present invention provides a method for preparing the above-mentioned solid electrolyte, including:

[0074] Treating one surface of the garnet electrolyte layer with a first solution, and laminating the lithium metal negative electrode with the first surface;

[0075] Coating a precursor slurry on the second surface of the garnet electrolyte layer, and after laminating the positive electrode with the second surface, polymerizing the precursor slurry;

[0076] Wherein, the first solution includes nitrite and fluoride; the precursor slurry includes 1,3,5-trioxane, succinonitrile and a lithium salt.

[0077] In a specific embodiment, one surface of the garnet electrolyte layer is treated with a first solution including nitrite and fluoride. The fluoride reacts with the nitrite to form a metal fluoride compound. Then, the lithium metal negative electrode is laminated with the first surface, and the metal fluoride compound reacts with molten metallic lithium to form lithium fluoride and a lithium alloy, thereby forming a first layer containing lithium fluoride and the lithium alloy, and realizing the adhesion between the lithium metal negative electrode and the solid electrolyte; a precursor slurry including 1,3,5-trioxane, succinonitrile and a lithium salt is disposed between the positive electrode sheet and the garnet electrolyte layer, and the polymerization reaction of the precursor slurry is initiated, thereby in-situ generating a second layer between the positive electrode sheet and the garnet electrolyte layer.

[0078] In the prior art, acid etching is usually used to form a porous structure on the surface of a solid electrolyte to increase the interfacial contact while removing lithium carbonate on the surface of the solid electrolyte, thereby reducing the interfacial resistance between the solid electrolyte and the negative electrode sheet. However, the acid solution not only has uncontrollable etching direction and depth on the solid electrolyte, but also has low efficiency in etching to form a porous structure, and the acid solution is prone to pollution. Therefore, this method cannot achieve large-scale production of solid electrolytes. Compared with the prior art, the present invention uses a first solution containing sodium nitrite and ammonium fluoride to treat the surface of a garnet electrolyte layer, and obtains a lithiumophilic first layer without adding an additional liquid electrolyte or without relying on other complex modification methods, realizing a stable negative electrode interface. This preparation method is simple to operate, highly applicable, and environmentally friendly, and is suitable for large-scale production.

[0079] In the prior art, the interfacial impedance between the positive electrode sheet and the solid electrolyte is mainly reduced by performing a low-temperature sintering treatment on the material system after the composite of the positive electrode active material and the solid electrolyte. However, low-temperature sintering not only easily produces harmful heterophases, but also the re-sintering process takes a long time and generates additional energy consumption. Compared with the prior art, the present invention can make the bonding between the second layer and the positive electrode sheet closer and the integration between the second layer and the garnet electrolyte layer closer by in-situ generating a second layer between the positive electrode sheet and the garnet electrolyte layer, further reducing the interfacial impedance between the positive electrode sheet and the garnet electrolyte layer and improving the cycling performance of the battery.

[0080] In this application, no special limitation is imposed on nitrites, and the nitrites can be nitrites commonly used in the art. Exemplarily, the nitrite can be sodium nitrite.

[0081] In this application, no special limitation is imposed on fluorides, and the fluorides can be fluorides commonly used in the art. Exemplarily, the fluoride can be selected from at least one of lithium fluoride, sodium fluoride, ammonium fluoride, and hydrogen fluoride. Further, the fluoride can be selected from ammonium fluoride and / or hydrogen fluoride.

[0082] In some embodiments, a certain amount of nitrite and fluoride can be weighed and added to a certain volume of an organic solvent, and stirred until completely dissolved to obtain a first solution.

[0083] Further, the mass ratio of nitrite to fluoride can be (1-2):(1-2). Exemplarily, the mass ratio of nitrite to fluoride can be 2:1, 1:1, 1:2, or a range composed of any two of them;

[0084] The organic solvent can be an organic solvent commonly used in the art. Exemplarily, the organic solvent can be selected from at least one of methanol, ethanol, isopropanol, and acetone; when the organic solvent is isopropanol, the volume of isopropanol can be 50 mL;

[0085] Stirring can be carried out at room temperature (15°C to 25°C), the stirring speed can be 200 rpm to 450 rpm, and the stirring time can be 1 h to 2 h.

[0086] In some embodiments, silicon carbide sandpapers with 400 mesh, 800 mesh, 1200 mesh, 2000 mesh, and 5000 mesh can be used in sequence to polish the surface of the garnet electrolyte layer to remove impurities on the surface of the garnet electrolyte layer, obtaining a garnet electrolyte layer with a polished surface; subsequently, a certain volume of the first solution is drop-coated on the garnet electrolyte layer with a polished surface, and through drying treatment, a solid electrolyte containing a first layer is obtained.

[0087] Furthermore, the volume of the first solution drop is 10 - 50 μL;

[0088] The drying treatment can be at least one of natural drying, air-blowing drying, vacuum drying, and desiccant drying; when the drying treatment is vacuum drying, during the drying treatment, the temperature can be 60 - 80°C, and the time can be 12 - 48 h.

[0089] In some embodiments, the surface of the lithium metal negative electrode sheet can be polished to remove impurities in the lithium metal negative electrode sheet, and then the polished lithium metal negative electrode sheet is attached to the surface of the first layer away from the garnet electrolyte layer, heated to melt the lithium metal negative electrode sheet, and then pressurized to closely bond the molten lithium metal negative electrode sheet to the surface of the solid electrolyte;

[0090] After the temperature drops to 80°C and the molten lithium on the negative electrode side solidifies, a certain volume of the precursor solution of the second layer (the volume of the precursor solution can be 20 - 50 μL) is drop-coated on the surface of the garnet solid electrolyte layer away from the negative electrode sheet, and a positive electrode sheet is covered, and then pressurized to closely bond the positive electrode sheet to the surface of the solid electrolyte, obtaining a battery;

[0091] The above battery is encapsulated in a casing, the casing of the battery is sealed with high-voltage silicone grease for batteries, kept warm at 80°C for a certain time and then pressurized with a battery clamp (applying a force of about 20 N) in a vacuum sleeve mold for testing, wherein the heat preservation time can be 30 - 60 min.

[0092] The fourth aspect of the present invention provides a preparation method of the above solid electrolyte, including:

[0093] Using the first solution to treat the first surface of the garnet electrolyte layer, and laminating the lithium metal negative electrode with the first surface layer;

[0094] Coating the coating slurry on the second surface of the garnet electrolyte layer, laminating the positive electrode with the second surface, and then curing the coating slurry;

[0095] Among them, the first solution includes nitrite and fluoride; the coating slurry includes at least one of poly(propylene carbonate) and succinonitrile, and a lithium salt.

[0096] Specifically, the specific operations of treating the first surface of the garnet electrolyte and setting the lithium metal negative electrode can be the same as those in the third aspect of the present invention.

[0097] The specific operations of setting the second layer and the positive electrode include: disposing a coating slurry including 1,3,5-trioxane and / or succinonitrile and a lithium salt on a surface of the garnet electrolyte layer away from the first layer to form a coating layer; laminating one surface of the positive electrode with the coating layer, and after curing, forming a second layer between the positive electrode and the garnet electrolyte layer, and realizing the lamination of the solid electrolyte and the positive electrode.

[0098] Hereinafter, the technical solutions of the present invention will be introduced in detail through specific examples.

[0099] Example 1

[0100] The all-solid-state battery of this example is prepared by a method including the following steps:

[0101] 1) Under dry conditions, the surface of the garnet electrolyte layer is polished successively with 400-mesh, 800-mesh, 1200-mesh, 2000-mesh, and 5000-mesh silicon carbide sandpapers to remove impurities on the surface of the garnet electrolyte layer, and then the surface of the garnet electrolyte layer is polished with a fine sandpaper (7000-mesh) to a thickness of 300 μm, and then quickly transferred to a glove box for storage and standby;

[0102] Weigh 0.4 g of sodium nitrite and 0.2 g of ammonium fluoride and add them to 50 mL of isopropanol, and stir vigorously at 25 °C for 1 h to completely dissolve them to obtain a first solution; then use a pipette to measure 30 μL of the first solution and drop it on the surface of the polished garnet electrolyte layer, and quickly transfer it to a vacuum drying oven and dry it at 70 °C for 24 h to obtain a solid electrolyte containing a first layer;

[0103] Among them, the glove box is an Ar-filled glove box (MBraun, Unilab Pro SP 780), and the oxygen and humidity are <0.1 ppm;

[0104] The first layer includes lithium fluoride and lithium-sodium alloy. In the first layer, the mass ratio of lithium fluoride to lithium-sodium alloy is 0.5:1, the thickness of the first layer is 100 nm, and the thickness of the garnet electrolyte layer is 300 μm;

[0105] 2) After mixing 2.5 g of TXE and 2.5 g of SN, heat them to 80 °C and keep them warm for 10 min to melt to obtain a eutectic solution, and add 0.365 g of LiDFOB to the eutectic solution and stir to obtain a precursor solution;

[0106] 3) Polish the surface of the lithium metal negative electrode sheet with a scalpel to remove the surface impurities of the lithium metal negative electrode sheet, and then attach the polished lithium metal negative electrode sheet to the surface of the first layer and apply a certain pressure to make the lithium metal fit more closely to the first layer;

[0107] Place the positive electrode sheet on the other side of the garnet electrolyte layer, inject the precursor solution between the positive electrode sheet and the garnet electrolyte layer, store it at 80 °C for 40 min to in-situ polymerize the precursor solution, and form a second layer between the positive electrode sheet and the garnet electrolyte layer. Then, naturally cool it to room temperature and directly assemble the battery with a CR2032 coin cell case;

[0108] Among them, the thickness of the second layer is 20 μm;

[0109] The positive electrode sheet includes an aluminum foil and positive electrode active layers provided on two surfaces of the aluminum foil. The positive electrode active layer includes LiFePO4, polyvinylidene fluoride, and conductive carbon black (Super P). Based on the total mass of the positive electrode active layer, the mass percentage content of LiFePO4 is 80%, the mass percentage content of polyvinylidene fluoride is 10%, and the mass percentage content of Super P is 10%.

[0110] Example 2

[0111] The preparation method of the all-solid-state battery in this example is basically the same as that in Example 1, except that:

[0112] In step 1), the mass of sodium nitrite is 0.2 g;

[0113] In the first layer, the mass ratio of lithium fluoride to lithium-sodium alloy is 1:1.

[0114] Example 3

[0115] The preparation method of the all-solid-state battery in this example is basically the same as that in Example 1, except that:

[0116] In step 1), the mass of sodium nitrite is 0.1 g;

[0117] In the first layer, the mass ratio of lithium fluoride to lithium-sodium alloy is 2:1.

[0118] Example 4

[0119] The preparation method of the all-solid-state battery in this example is basically the same as that in Example 1, except that:

[0120] In step 1), the mass of sodium nitrite is 0.5 g;

[0121] In the first layer, the mass ratio of lithium fluoride to lithium-sodium alloy is 0.4:1.

[0122] Example 5

[0123] The preparation method of the all - solid - state battery in this example is basically the same as that in Example 1, except that:

[0124] In step 2), the addition amount of SN is 3 g (i.e., the mass ratio of TXE to SN = 5:6).

[0125] Example 6

[0126] The preparation method of the all - solid - state battery in this example is basically the same as that in Example 1, except that:

[0127] In step 1), the amount of the first solution taken is 5 μL, and the thickness of the first layer is 10 nm.

[0128] Example 7

[0129] The preparation method of the all - solid - state battery in this example is basically the same as that in Example 1, except that:

[0130] In step 2), after mixing 0.3 g of poly(propylene carbonate) with 0.2 g of SN, it is heated to 80 °C and kept warm for 10 min to melt to obtain a eutectic solution. Then 0.3 g of LiDFOB is added to the eutectic solution and stirred to obtain a coating slurry;

[0131] In step 3), the surface of the lithium metal negative electrode sheet is polished with a scalpel to remove the surface impurities of the lithium metal negative electrode sheet. Then the polished lithium metal negative electrode sheet is attached to the surface of the first layer, and a certain pressure is applied to make the lithium metal fit more closely to the first layer;

[0132] The coating slurry is coated on the side of the garnet electrolyte layer away from the first layer. A second layer is set between the positive electrode sheet and the garnet electrolyte layer, and the positive electrode sheet is placed on the other side of the garnet electrolyte layer, and a CR2032 - type coin battery case is directly used to form a battery.

[0133] Comparative Example 1

[0134] The preparation method of the all - solid - state battery in this comparative example is basically the same as that in Example 1, except that:

[0135] In step 1), the polished garnet electrolyte layer is directly used without treating the surface of the garnet electrolyte layer.

[0136] Comparative Example 2

[0137] The preparation method of the all - solid - state battery in this comparative example is basically the same as that in Example 1, except that:

[0138] In step 1), the polished garnet electrolyte layer is directly used without treating the surface of the garnet electrolyte layer.

[0139] In step 3), a scalpel is used to polish the surface of the lithium metal negative electrode sheet to remove surface impurities of the lithium metal negative electrode sheet, and then the polished lithium metal negative electrode sheet is attached to the surface of the garnet electrolyte, and a certain pressure is applied to make the lithium metal adhere to the garnet electrolyte more firmly.

[0140] No second layer is provided between the positive electrode sheet and the garnet electrolyte layer. The positive electrode sheet is placed on the other side of the garnet electrolyte layer, and a CR2032 coin cell case is directly used to form a battery.

[0141] Performance Test

[0142] 1. Wettability Test

[0143] The wettability between molten lithium metal and the garnet solid electrolyte layer not treated with the first solution and the wettability between molten lithium metal and the garnet electrolyte layer containing the first layer are respectively tested. Figure 1 This is a schematic diagram of the wettability of the garnet electrolyte layer not treated with the first solution of the present invention to molten lithium; Figure 2 This is a schematic diagram of the wettability of the garnet electrolyte layer containing the first layer of the present invention to molten lithium. As can be seen from Figure 1 and Figure 2 it can be seen that there is excellent wettability between the garnet electrolyte layer 1 treated with the first solution and molten lithium 2, which helps to improve the interfacial performance between the negative electrode and the solid electrolyte and improve the cycling performance of the battery.

[0144] 2. The following performance tests are carried out on the all-solid-state batteries in the examples and comparative examples;

[0145] The all-solid-state batteries in Examples 1-7 and Comparative Examples 1 and 2 are subjected to a cycling performance test on a blue electrochemical workstation, where the test voltage range is 2.8 - 4.0 V, and a constant current charge-discharge test is carried out at a rate of 0.5C. Figure 3 This is the electrochemical performance curve of the all-solid-state batteries in Examples 1-3 and Comparative Example 1 of the present invention; Table 1 shows the electrochemical performance data of the all-solid-state batteries in Examples 1-7 and Comparative Examples 1 and 2 of the present invention.

[0146] Table 1

[0147]

[0148] As Figure 3As shown in Table 1, the all-solid-state battery in the embodiment of the present invention can stably cycle 120 times, with a capacity retention rate of more than 50% and an average Coulombic efficiency greater than 85%. Further, it can be seen that when the solid electrolyte of the present invention is applied to a battery, after 120 cycles, the discharge specific capacity of the battery is more than 30 mAh / g. However, the battery in Comparative Example 1 has basically no discharge specific capacity after 40 cycles, and the battery in Comparative Example 2 cannot operate normally. This shows that when the solid electrolyte of the present invention is applied to a battery, it can not only reduce the interfacial impedance between the lithium metal negative electrode and the garnet electrolyte layer, but also inhibit the formation of lithium dendrites, effectively improving the cycle performance of the all-solid-state battery.

[0149] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features. These modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A solid electrolyte, characterized in that, The solid electrolyte includes a first layer, a garnet electrolyte layer, and a second layer that are stacked in sequence; The first layer includes lithium fluoride and a lithium alloy; The second layer includes an organic substance and a lithium salt.

2. The solid electrolyte according to claim 1, characterized in that, The lithium alloy is selected from at least one of a lithium-sodium alloy, a lithium-aluminum alloy, a lithium-indium alloy, and a lithium-gallium alloy.

3. The solid electrolyte according to claim 1 or 2, characterized in that, In the first layer, the mass ratio of lithium fluoride to the lithium alloy is (0.5-2):

1.

4. The solid electrolyte according to any one of claims 1-3, characterized in that, In the second layer, the mass percentage content of the lithium salt is 5-50%.

5. The solid electrolyte according to any one of claims 1-4, characterized in that, The organic substance is selected from at least one of poly(propylene carbonate) and succinonitrile.

6. The solid electrolyte according to any one of claims 1-4, characterized in that, The organic substance is obtained by polymerization of a raw material system including at least succinonitrile and 1,3,5-trioxane.

7. The solid electrolyte according to claim 6, characterized in that, The mass ratio of the 1,3,5-trioxane to the succinonitrile is 5:(1-5).

8. The solid electrolyte according to any one of claims 1-7, characterized in that, The solid electrolyte further satisfies at least one of the following: a) The thickness of the first layer is 50-200 nm; b) The thickness of the garnet electrolyte layer is 100-500 μm; c) The thickness of the second layer is 10-50 μm.

9. A battery, characterized in that, Comprising a positive electrode, a lithium metal negative electrode, and the solid electrolyte according to any one of claims 1-7; The solid electrolyte is disposed between the positive electrode and the lithium metal negative electrode, and the first layer is disposed close to the lithium metal negative electrode, and the second layer is disposed close to the positive electrode.

10. A method for preparing the battery according to claim 9, characterized in that, Comprising: Treating a first surface of the garnet electrolyte layer with a first solution, and laminating the lithium metal negative electrode with the first surface; Coating a precursor slurry on a second surface of the garnet electrolyte layer, laminating the positive electrode with the second surface, and then polymerizing the precursor slurry; Wherein, the first solution includes nitrite and fluoride; the precursor slurry includes 1,3,5-trioxane, succinonitrile, and a lithium salt.

11. A method for preparing the battery according to claim 9, characterized in that, Comprising: Treating a first surface of the garnet electrolyte layer with a first solution, and laminating the lithium metal negative electrode with the first surface; Coating a coating slurry on a second surface of the garnet electrolyte layer, laminating the positive electrode with the second surface, and then curing the coating slurry; Wherein, the first solution includes nitrite and fluoride; the coating slurry includes at least one of poly(propylene carbonate) and succinonitrile, and a lithium salt.

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