Composite electrolyte and preparation method thereof, positive plate and solid-state battery

Abstract

The invention provides a composite electrolyte and a preparation method thereof, a positive plate and a solid-state battery, and belongs to the technical field of solid-state batteries, the composite electrolyte comprises a solid-state electrolyte and a coating layer coating the surface of the solid-state electrolyte, and the coating layer is formed by polymerizing a compound with a five-membered ring and alkaline lithium salt on the surface of the solid-state electrolyte. The alkaline lithium salt comprises lithium hydroxide and / or lithium carbonate. According to the composite electrolyte provided by the invention, the coating layer comprises the polymer formed by polymerizing the compound with the five-membered ring and the alkaline lithium salt, so that on one hand, the solid electrolyte can be well protected through the coating layer, the stability of the solid electrolyte is improved, and on the other hand, the solid electrolyte can be effectively protected while coating is realized. The alkaline lithium salt on the surface of the solid electrolyte is consumed, the influence of the alkaline lithium salt on the performance of the solid electrolyte is reduced, and the performance of the composite electrolyte is ensured.

Description

Technical Field

[0001] The present application relates to the technical field of solid-state batteries, and in particular to a composite electrolyte and a preparation method thereof, a positive electrode sheet, and a solid-state battery. Background Art

[0002] Garnet-type solid electrolytes, such as lithium lanthanum zirconium oxide (LLZO) and lithium lanthanum zirconium tantalum oxide (LLZTO), have high room-temperature ionic conductivity, a wide electrochemical window, and good chemical stability. They are compatible with a variety of high-voltage cathodes and primary lithium metal anodes, enabling batteries to achieve high energy density. Garnet-type solid electrolytes also offer advantages such as high temperature resistance, non-flammability, and environmental friendliness, making them one of the most promising solid electrolytes.

[0003] To improve the interfacial stability of solid electrolytes, a coating is applied to their surface. Related technologies typically use materials such as oxides or polymers to directly coat solid electrolytes. However, this type of coating fails to remove residual alkaline lithium compounds, such as lithium hydroxide, from the surface of the solid electrolyte, resulting in poor coating stability and impacting the performance of the solid electrolyte. Summary of the Invention

[0004] The present application provides a composite electrolyte and a preparation method thereof, a positive electrode sheet and a solid-state battery, which can ensure the stability of the composite electrolyte and improve the performance of the composite electrolyte.

[0005] In a first aspect, the present application provides a composite electrolyte comprising a solid electrolyte and a coating layer coated on the surface of the solid electrolyte;

[0006] The coating layer includes a polymer formed by polymerizing a compound having a five-membered ring and an alkaline lithium compound on the surface of the solid electrolyte, and the alkaline lithium compound includes lithium hydroxide and / or lithium carbonate.

[0007] In some embodiments, the solid-state electrolyte includes at least one of lithium lanthanum zirconium oxy and lithium lanthanum zirconium tantalum oxy.

[0008] In some embodiments, the molecular chain of the polymer includes at least one of an ethylene carbonate ring-opening group, a propylene carbonate ring-opening group, a fluoroethylene carbonate ring-opening group, a 2-methyltetrahydrofuran ring-opening group, a 1,3-dioxolane ring-opening group, a maleic anhydride ring-opening group, a vinylene carbonate ring-opening group, a tetrahydrofuran ring-opening group, and a 4-methyl-1,3-dioxolane ring-opening group.

[0009] In some embodiments, the polymer molecular chain includes 1,3-dioxolane ring-opening groups and maleic anhydride ring-opening groups.

[0010] In some embodiments, the molecular chain of the polymer includes a vinylene carbonate ring-opening group, and the compound having a five-membered ring structure also includes at least one of an ethylene carbonate ring-opening group, a propylene carbonate ring-opening group, a fluoroethylene carbonate ring-opening group, a 2-methyltetrahydrofuran ring-opening group, a 1,3-dioxolane ring-opening group, a maleic anhydride ring-opening group, a tetrahydrofuran ring-opening group and a 4-methyl-1,3-dioxolane ring-opening group.

[0011] In some embodiments, the coating layer further includes a lithium salt.

[0012] In some embodiments, the lithium salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(oxalatoborate), lithium bis(fluorosulfonyl imide), and lithium bis(trifluoromethanesulfonyl imide).

[0013] In some embodiments, the lithium salt includes at least one of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide.

[0014] In some embodiments, the composite electrolyte has a compacted density of 3.0 g / cm at 200 MPa. 3 -4.8g / cm 3 .

[0015] In a second aspect, the present application provides a method for preparing a composite electrolyte, comprising:

[0016] Providing a reaction solution; wherein the reaction solution includes a first solvent and a compound having a five-membered ring structure;

[0017] Mixing a solid electrolyte with a reaction solution to form a first mixed solution; wherein lithium hydroxide and / or lithium carbonate exists on the surface of the solid electrolyte;

[0018] The lithium hydroxide and / or lithium carbonate in the first mixed solution is polymerized with the compound having a five-membered ring structure to obtain a composite electrolyte.

[0019] In some embodiments, the solid-state electrolyte includes at least one of lithium lanthanum zirconium oxy and lithium lanthanum zirconium tantalum oxy.

[0020] In some embodiments, the compound having a five-membered ring structure includes at least one of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, 2-methyltetrahydrofuran, 1,3-dioxolane, maleic anhydride, vinylene carbonate, tetrahydrofuran, and 4-methyl-1,3-dioxolane.

[0021] In some embodiments, the first solvent includes at least one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dimethoxymethane, and ethylene glycol dimethyl ether.

[0022] In some embodiments, the reaction solution further includes a lithium salt.

[0023] In some embodiments, the concentration of the lithium salt in the reaction solution is 0.5 mol / L-3 mol / L.

[0024] In some embodiments, in the first mixed solution, the mass ratio of the solid electrolyte to the reaction solution is (1.5-3):1;

[0025] And / or, the solid content in the first mixed liquid is 60%-70%.

[0026] In some embodiments, reacting the lithium hydroxide and / or lithium carbonate in the first mixed solution with the compound having a five-membered ring structure comprises:

[0027] The lithium hydroxide and / or lithium carbonate in the first mixed solution is reacted with the compound having a five-membered ring structure at a temperature of 45° C. to 80° C. for 12 to 48 hours.

[0028] In a third aspect, the present application provides a positive electrode sheet comprising the composite electrolyte as described above, and / or a composite electrolyte prepared by the composite electrolyte preparation method as described above.

[0029] In a fourth aspect, the present application provides a solid-state battery, comprising the above-described positive electrode sheet, and / or the above-described electrolyte.

[0030] In the present application, the composite electrolyte includes a solid electrolyte and a coating layer coated on the surface of the solid electrolyte, wherein the coating layer includes a polymer formed by polymerization of a compound having a five-membered ring and an alkaline lithium compound on the surface of the solid electrolyte, and the alkaline lithium compound includes lithium hydroxide and / or lithium carbonate. By reacting the compound having a five-membered ring with the alkaline lithium compound on the surface of the solid electrolyte to form a coating layer, the solid electrolyte can be effectively coated by the coating layer, thereby improving the stability of the solid electrolyte, while consuming the alkaline lithium compound on the surface of the solid electrolyte and reducing the effect of the alkaline lithium compound on the performance of the solid electrolyte. That is, the composite electrolyte provided by the present application includes a polymer formed by polymerization of a compound having a five-membered ring and an alkaline lithium compound through the coating layer. On the one hand, the solid electrolyte can be well protected by the coating layer, thereby improving the stability of the solid electrolyte. On the other hand, while achieving the coating, the alkaline lithium compound on the surface of the solid electrolyte can be consumed, thereby reducing the effect of the alkaline lithium compound on the performance of the solid electrolyte and ensuring the performance of the composite electrolyte. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0032] Figure 1 is a transmission scanning electron micrograph of the composite electrolyte in Example 1 of the present application;

[0033] Figure 2 This is a picture of the solution prepared from the uncoated lithium lanthanum zirconium tantalum oxide, PVDF binder, and NMP solvent in Comparative Example 1;

[0034] Figure 3 This is a picture of the composite electrolyte, PVDF binder, and NMP solvent prepared into a solution in Example 1. DETAILED DESCRIPTION

[0035] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without making creative work are within the scope of protection of this application. In addition, it should be understood that the specific embodiments described herein are only used to illustrate and explain the present application and are not used to limit the present application.

[0036] Garnet-type solid electrolytes are typically produced using a solid-phase sintering method. To reduce the sintering temperature, lithium hydroxide is used as a lithium source, which can easily lead to residual lithium hydroxide on the surface of the garnet-type solid electrolyte. When preparing composite electrolytes, residual lithium hydroxide on the surface can easily react with the binder polyvinylidene fluoride (PVDF) or the solvent, resulting in a "gel" phenomenon that significantly affects performance.

[0037] In the first aspect, the embodiments of the present application provide a composite electrolyte, comprising a solid electrolyte and a coating layer coated on the surface of the solid electrolyte, wherein the coating layer comprises a polymer formed by polymerization of a compound having a five-membered ring and an alkaline lithium compound on the surface of the solid electrolyte, and the alkaline lithium compound comprises lithium hydroxide and / or lithium carbonate. By reacting the compound having a five-membered ring with the alkaline lithium compound on the surface of the solid electrolyte to form a coating layer, the solid electrolyte can be effectively coated by the coating layer, thereby improving the stability of the solid electrolyte, while consuming the alkaline lithium compound on the surface of the solid electrolyte and reducing the effect of the alkaline lithium compound on the performance of the solid electrolyte. That is, the composite electrolyte provided by the present application comprises a polymer formed by polymerization of a compound having a five-membered ring and an alkaline lithium compound through the coating layer. On the one hand, the solid electrolyte can be well protected by the coating layer, thereby improving the stability of the solid electrolyte. On the other hand, the alkaline lithium compound on the surface of the solid electrolyte can be consumed while achieving the coating, thereby reducing the effect of the alkaline lithium compound on the performance of the solid electrolyte and ensuring the performance of the composite electrolyte.

[0038] In some embodiments, the solid-state electrolyte includes at least one of lithium lanthanum zirconium oxy and lithium lanthanum zirconium tantalum oxy.

[0039] Lithium lanthanum zirconium oxide (LLZO) and lithium lanthanum zirconium tantalum oxide (LLZTO) have high room temperature ionic conductivity, wide electrochemical window, good chemical stability, can adapt to a variety of high voltage positive electrodes and lithium metal negative electrodes, so that the battery can achieve high energy density, and has the advantages of high temperature resistance, non-flammability and environmental friendliness. However, in the large-scale production of lithium lanthanum zirconium oxide (LLZO) and lithium lanthanum zirconium tantalum oxide (LLZTO), a solid phase sintering method is usually adopted. In order to reduce the sintering temperature, an excess of lithium hydroxide (LiOH) is added as a lithium source during the sintering process, resulting in residual lithium hydroxide on the surface of the sintered LLZO and LLZTO, and lithium hydroxide will further generate lithium carbonate when it encounters air. The composite electrolyte provided in the embodiment of the present application can remove impurities on the surface of LLZO and LLZTO by polymerizing the residual lithium hydroxide and / or lithium carbonate impurities on the surface of LLZO and LLZTO with a compound having a five-membered ring structure to form a coating layer, while being able to form a coating layer on the surface of LLZO and LLZTO.

[0040] In some embodiments, the molecular chain of the polymer includes at least one of an ethylene carbonate ring-opening group, a propylene carbonate ring-opening group, a fluoroethylene carbonate ring-opening group, a 2-methyltetrahydrofuran ring-opening group, a 1,3-dioxolane ring-opening group, a maleic anhydride ring-opening group, a vinylene carbonate ring-opening group, a tetrahydrofuran ring-opening group, and a 4-methyl-1,3-dioxolane ring-opening group.

[0041] It is understood that a ring-opening group refers to a group formed after a compound having a five-membered ring is opened. For example, an ethylene carbonate ring-opening group refers to a group formed after ethylene carbonate is opened. Among them, after a compound having a five-membered ring is opened, due to different opening positions, a ring-opening group with certain structural differences may be formed, and all of these groups fall within the scope of protection of the ring-opening group in the embodiments of the present application.

[0042] When a compound with a five-membered ring exists on the surface of a solid electrolyte, it will trigger a ring-opening reaction, thereby obtaining a ring-opening product. The ring-opening product has poor stability and can further polymerize with lithium hydroxide, lithium carbonate, and other unsaturated compounds or ring-opening products to form a stable polymer. The formation of a stable polymer consumes lithium hydroxide and / or lithium carbonate while forming a polymer film on the surface of the solid electrolyte. The molecular chain of the polymer includes at least one of an ethylene carbonate ring-opening group, a propylene carbonate ring-opening group, a fluoroethylene carbonate ring-opening group, a 2-methyltetrahydrofuran ring-opening group, a 1,3-dioxolane ring-opening group, a maleic anhydride ring-opening group, a vinylene carbonate ring-opening group, a tetrahydrofuran ring-opening group, and a 4-methyl-1,3-dioxolane ring-opening group.

[0043] Illustratively, the polymer includes a 1,3-dioxolane ring-opening group and a maleic anhydride ring-opening group in its molecular chain.

[0044] Among them, the five-membered ring structure in 1,3-dioxolane contains two oxygen atoms, forming a more active epoxy structure, which has high activity in the ring-opening reaction and can ensure the efficiency of the reaction. In addition, the ring-opening reaction of 1,3-dioxolane can be carried out under relatively mild conditions, reducing the difficulty of the process. Maleic anhydride has two unsaturated double bonds and two carbonyl groups, has high reaction activity, and can also undergo ring-opening reactions under relatively mild conditions. In addition, the 1,3-dioxolane ring-opening group and the maleic anhydride ring-opening group can further polymerize to form a stable polymer, thereby forming a stable coating layer on the surface of the solid electrolyte to obtain a composite electrolyte with a stable structure.

[0045] Illustratively, the molecular chain of the polymer includes a vinylene carbonate ring-opening group, and the molecular chain of the polymer also includes at least one of an ethylene carbonate ring-opening group, a propylene carbonate ring-opening group, a fluoroethylene carbonate ring-opening group, a 2-methyltetrahydrofuran ring-opening group, a 1,3-dioxolane ring-opening group, a maleic anhydride ring-opening group, a tetrahydrofuran ring-opening group and a 4-methyl-1,3-dioxolane ring-opening group.

[0046] That is to say, the molecular chain of the polymer includes vinylene carbonate ring-opening groups and also includes any one or more other ring-opening groups.

[0047] Vinylene carbonate has active carbon-carbon double bond, has higher reactivity, can under comparatively mild condition, ring-opening reaction.Simultaneously, the vinylene carbonate ring-opening group that obtains after the vinylene carbonate ring-opening can form high molecular weight polymers such as polycarbonate, polyether carbonate, forms close polymer coating on solid electrolyte surface.Cooperate with other ring-opening groups through the vinylene carbonate ring-opening group, introduce different functional groups and chain segment, can improve the performance of polymer.Those skilled in the art can select as needed, for example, introduce the group that improves heat resistance, the group of corrosion resistance or the group that improves mechanical strength etc.

[0048] In some embodiments, the coating layer further includes a lithium salt. Adding the lithium salt to the coating layer helps to form a conductive network in the coating layer, thereby improving the ionic conductivity of the composite electrolyte.

[0049] In some embodiments, the lithium salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(oxalatoborate), lithium bis(fluorosulfonyl imide), and lithium bis(trifluoromethanesulfonyl imide).

[0050] In some embodiments, the lithium salt includes at least one of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide.

[0051] Lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide have higher electrical conductivity and are easily dissociated in the polymer layer, thereby ensuring the formation of a high conductivity structure in the coating layer on the surface of the solid electrolyte.

[0052] In some embodiments, the composite electrolyte has a compacted density of 3.0 g / cm at 200 MPa. 3 -4.8g / cm 3 By setting the compaction density of the composite electrolyte within the above range, good ion conductivity, mechanical strength, and contact performance between the electrolyte and other materials can be ensured, thereby ensuring cycle life.

[0053] Specifically, the composite electrolyte provided in the embodiment of the present application includes a solid electrolyte and a polymer coating layer coated on the surface of the solid electrolyte. The solid electrolyte has a large true density, high particle hardness, and high ionic conductivity, while the coating layer has a low true density, a soft texture, and low ionic conductivity. The embodiment of the present application controls the compaction density of the composite electrolyte at 200 MPa to be 2.0 g / cm 3 -4.8g / cm 3 , the thickness of the coating layer can be controlled within a certain range, which can ensure good contact performance and maintain high ionic conductivity, thereby ensuring the long cycle performance of the battery.

[0054] In a second aspect, the present invention also provides a method for preparing a composite electrolyte, comprising:

[0055] Providing a reaction solution; wherein the reaction solution includes a first solvent and a compound having a five-membered ring structure;

[0056] Mixing a solid electrolyte with a reaction solution to form a first mixed solution; wherein lithium hydroxide and / or lithium carbonate exists on the surface of the solid electrolyte;

[0057] The lithium hydroxide and / or lithium carbonate in the first mixed solution is polymerized with the compound having a five-membered ring structure to obtain a composite electrolyte.

[0058] Among them, the structural stability of the compound with a five-membered ring structure in the reaction solution is low. When the reaction solution is mixed with a solid electrolyte having lithium hydroxide and / or lithium carbonate, the five-membered ring structure can undergo a ring-opening reaction and initiate polymerization of the ring-opening groups in the reaction solution. While consuming the lithium hydroxide and / or lithium carbonate in the solid electrolyte, a polymer coating is formed on the surface of the solid electrolyte to obtain a composite electrolyte. That is, the preparation method of the composite electrolyte provided in the embodiment of the present application can eliminate the alkaline lithium compound in the solid electrolyte and can form a polymer coating on the surface of the solid electrolyte, thereby ensuring the stability of the obtained composite electrolyte and reducing the process difficulty and coating cost.

[0059] In some embodiments, the solid-state electrolyte includes at least one of lithium lanthanum zirconium oxy and lithium lanthanum zirconium tantalum oxy.

[0060] Lithium lanthanum zirconium oxide (LLZO) and lithium lanthanum zirconium tantalum oxide (LLZTO) have high room-temperature ionic conductivity, a wide electrochemical window, and good chemical stability. They can be adapted to a variety of high-voltage positive electrodes and lithium metal negative electrodes, enabling the battery to achieve high energy density. They also have the advantages of high temperature resistance, non-flammability, and environmental friendliness. However, in the large-scale production of lithium lanthanum zirconium oxide (LLZO) and lithium lanthanum zirconium tantalum oxide (LLZTO), a solid-phase sintering method is usually used. In order to reduce the sintering temperature, an excess of lithium hydroxide (LiOH) is added as a lithium source during the sintering process, resulting in residual lithium hydroxide on the surface of the sintered LLZO and LLZTO. When the lithium hydroxide encounters air, it will further generate lithium carbonate. The preparation method of the composite electrolyte provided in the embodiments of the present application can cause the lithium hydroxide and / or lithium carbonate impurities remaining on the surfaces of LLZO and LLZTO to induce a ring-opening reaction in a compound having a five-membered ring structure, thereby causing a polymerization reaction. The lithium hydroxide and / or lithium carbonate can participate in the copolymerization reaction, while removing impurities and forming a polymer coating film on the surfaces of LLZO and LLZTO to obtain a structurally stable composite electrolyte.

[0061] In some embodiments, the compound having a five-membered ring structure includes at least one of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, 2-methyltetrahydrofuran, 1,3-dioxolane, maleic anhydride, vinylene carbonate, tetrahydrofuran, and 4-methyl-1,3-dioxolane.

[0062] All of the above substances have a five-membered ring structure. When lithium hydroxide impurities exist in the solid electrolyte, lithium hydroxide can trigger a ring-opening reaction in the five-membered ring structure. The product after ring opening has poor stability and can further polymerize with lithium hydroxide, lithium carbonate and other unsaturated compounds or ring-opening groups to form a stable polymer, consuming lithium hydroxide and / or lithium carbonate while forming a polymer film on the surface of the solid electrolyte.

[0063] In some embodiments, the first solvent includes at least one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dimethoxymethane, and ethylene glycol dimethyl ether.

[0064] The solvent provided in the embodiments of the present application has good solubility for compounds having a five-membered ring structure and good dispersion properties for solid electrolytes, which can ensure that the lithium hydroxide impurities on the solid electrolyte and the compounds having a five-membered ring structure react fully.

[0065] In some embodiments, the reaction solution also includes a lithium salt. Adding the lithium salt to the reaction solution allows the lithium salt and lithium hydroxide to work synergistically, helping to improve the efficiency of the ring-opening reaction of the compound having a five-membered ring structure and forming a uniform polymer coating on the surface of the solid electrolyte. Furthermore, a portion of the lithium salt in the reaction solution is distributed in the polymer coating, forming a conductive network and improving the ionic conductivity of the solid electrolyte.

[0066] In some embodiments, the concentration of the lithium salt in the reaction solution is 0.5 mol / L-3 mol / L. When the concentration of the lithium salt is set within this range, on the one hand, the synergistic effect of the lithium salt and lithium hydroxide is ensured, the efficiency of the ring-opening reaction and polymerization reaction of the compound having a five-membered ring structure is improved, and a uniform polymer coating layer is formed. On the other hand, the concentration of the lithium salt in the polymer layer is ensured, the conductivity is improved, and the cost can be controlled within an appropriate range.

[0067] In some embodiments, in the first mixed solution, the mass ratio of the solid electrolyte to the reaction solution is (1.5-3): 1. By setting the mass ratio of the solid electrolyte to the reaction solution within the above range, the lithium hydroxide impurity in the solid electrolyte can be consumed, and a polymer coating layer of uniform thickness can be formed on the surface of the solid electrolyte.

[0068] In some embodiments, the solid content of the first mixed solution is 60%-70%. By setting the first mixed solution within the above range, a polymer coating layer with a uniform thickness and appropriate thickness can be formed on the surface of the solid electrolyte, thereby ensuring the performance of the composite electrolyte.

[0069] In some embodiments, reacting the lithium hydroxide and / or lithium carbonate in the first mixed solution with the compound having a five-membered ring structure comprises:

[0070] The lithium hydroxide and / or lithium carbonate in the first mixed solution is reacted with the compound having a five-membered ring structure at a temperature of 45° C. to 80° C. for 12 to 48 hours.

[0071] By carrying out the reaction at a temperature of 45°C-80°C, the efficiency of the ring-opening reaction and polymerization reaction can be guaranteed, and the occurrence of side reactions can be reduced, so that a stable polymer coating can be formed on the surface of the solid electrolyte. By setting the reaction time to 12h-48h, sufficient reaction can be ensured and lithium hydroxide impurities can be consumed.

[0072] In a third aspect, an embodiment of the present application provides a positive electrode sheet comprising the composite electrolyte as described above, and / or a composite electrolyte prepared by the composite electrolyte preparation method as described above.

[0073] In some embodiments, the positive electrode active material includes at least one of a ternary material, lithium iron phosphate, and lithium cobalt oxide.

[0074] In some embodiments, the conductive agent includes at least one of conductive carbon black, conductive graphite, carbon fibers, and carbon nanotubes.

[0075] In some embodiments, the binder includes polyvinylidene fluoride and its derivatives.

[0076] Specifically, during the production of the positive electrode sheet, the positive electrode active material, composite electrolyte, conductive agent, and binder are first ground and then mixed with a second solvent to produce a positive electrode slurry. The positive electrode slurry is then evenly coated on the surface of the positive electrode current collector. After drying, rolling, and punching, the positive electrode sheet is obtained. The second solvent can be N-methylpyrrolidone, and the diameter of the positive electrode sheet can be 10 mm.

[0077] The positive electrode sheet provided in the embodiments of the present application, using the composite electrolyte described above, can reduce the "gelling" phenomenon during the preparation of the positive electrode slurry, thereby reducing the difficulty of preparing the positive electrode sheet. Furthermore, the electrolyte has a polymer coating layer, which can improve the stability and interface performance of the positive electrode sheet.

[0078] In a fourth aspect, an embodiment of the present application provides a solid-state battery comprising the positive electrode sheet as described above.

[0079] The solid-state battery provided in the embodiment of the present application also has the beneficial effects of the above-mentioned method for preparing the composite electrolyte, which will not be described in detail here.

[0080] The following examples are further described in conjunction with specific embodiments. It should be understood that these embodiments are intended to illustrate the present invention only and are not intended to limit the scope of the present invention. The experimental methods in the following examples where specific conditions are not specified are generally based on the conditions recommended by the manufacturer.

[0081] Example 1

[0082] (1) 1.75 g of 1,3-dioxolane, 0.35 g of maleic anhydride, 1.13 g of lithium bis(trifluoromethanesulfonyl)imide, and 1.77 g of dimethoxymethane were mixed to obtain a reaction solution;

[0083] (2) adding 10 g of lithium lanthanum zirconium tantalum oxide to the reaction solution to obtain a first mixed solution;

[0084] (3) reacting the first mixed solution at a speed of 200 rpm and a temperature of 60° C. for 24 h, then filtering the solution, and then drying the filtered solution to obtain a composite electrolyte;

[0085] (4) mixing the high nickel positive electrode material, the composite electrolyte obtained in step (3), conductive carbon black and polyvinylidene fluoride in a mass ratio of 70:25:3:2, grinding and mixing with N-methylpyrrolidone, and stirring evenly to obtain a positive electrode slurry;

[0086] (5) The positive electrode slurry is evenly coated on the surface of the positive electrode current collector, and after drying, rolling, and punching, a positive electrode sheet with a diameter of 10 mm is obtained;

[0087] (6) 100 mg of the composite electrolyte obtained in step (3) was added to the model and cold pressed at a pressure of 400 MPa for 5 min in a tablet press to obtain an electrolyte sheet;

[0088] (7) The positive electrode sheet was attached to one side of the electrolyte sheet and cold pressed at a pressure of 400 MPa for 5 minutes in a sheet press. Then, a lithium metal sheet with a thickness of 0.15 mm and a diameter of 10 mm was attached to the other side of the electrolyte sheet and cold pressed at a pressure of 400 MPa for 5 minutes in a sheet press to obtain a solid-state battery.

[0089] Example 2

[0090] The difference between this embodiment and embodiment 1 is that 1.05 g of vinylene carbonate and 1.05 g of tetrahydrofuran are used to replace 1.75 g of 1,3-dioxolane and 0.35 g of maleic anhydride in embodiment 1, and other conditions remain the same as in embodiment 1.

[0091] Example 3

[0092] The difference between this embodiment and embodiment 1 is that the mass of 1,3-dioxolane is 0.42 g, the mass of maleic anhydride is 0.8 g, and other conditions are consistent with those in embodiment 1.

[0093] Example 4

[0094] The difference between this embodiment and embodiment 1 is that the mass of 1,3-dioxolane is 8.4 g, the mass of maleic anhydride is 1.6 g, and other conditions are consistent with those in embodiment 1.

[0095] Example 5

[0096] The difference between this embodiment and embodiment 1 is that lithium bis(trifluoromethanesulfonyl imide) is not added to the reaction solution, and other conditions are the same as those in embodiment 1.

[0097] Example 6

[0098] The difference between this embodiment and embodiment 1 is that the same mass of lithium hexafluorophosphate is used in the reaction solution instead of lithium bis(trifluoromethanesulfonyl)imide, and other conditions are the same as those in embodiment 1.

[0099] Example 7

[0100] The difference between this embodiment and embodiment 1 is that the amount of lithium bis(trifluoromethanesulfonyl)imide added to the reaction solution is 0.565 g, and other conditions are consistent with those of embodiment 1.

[0101] Example 8

[0102] The difference between this embodiment and embodiment 1 is that the amount of lithium bis(trifluoromethanesulfonyl)imide added to the reaction solution is 3.39 g, and other conditions are consistent with those in embodiment 1.

[0103] Comparative Example 1

[0104] The difference between this comparative example and Example 1 is that uncoated lithium lanthanum zirconium tantalum oxide is directly used to prepare the solid-state battery, and the other conditions are consistent with Example 1.

[0105] in, Figure 1 : is a transmission electron microscope image of the composite electrolyte prepared in Example 1. Figure 1 It can be seen that a polymer coating layer with a thickness of 10 μm-20 μm is formed on the surface of the solid electrolyte.

[0106] Experimental Example 1

[0107] In an argon glove box, 0.2g of the composite electrolyte prepared in Example 1 and the uncoated lithium lanthanum zirconium tantalum oxide in Comparative Example 1 were added to a mortar, and then 0.1g of polyvinylidene fluoride was added to the mortar and ground and mixed evenly. The ground powder was poured into a glass bottle, 5g of N-methylpyrrolidone was added, and stirred at 600 rpm at 60°C. The results are shown in the figure. Figure 2 and Figure 3 As shown:

[0108] in, Figure 2 This is a photo of the uncoated lithium lanthanum zirconium tantalum oxide after stirring in Comparative Example 1. Figure 3 This is a photo of the composite electrolyte after stirring in Example 1. Figure 2 and Figure 3 It can be seen that the uncoated lithium lanthanum zirconium tantalum oxide appears black after being mixed with polyvinylidene fluoride and N-methylpyrrolidone. This is mainly due to the reaction of residual lithium hydroxide on the surface of the uncoated lithium lanthanum zirconium tantalum oxide with polyvinylidene fluoride, causing the solution to gel and discolor. However, after mixing the composite electrolyte with polyvinylidene fluoride and N-methylpyrrolidone, it disperses normally and does not show discoloration or gelation. This is mainly due to the elimination of residual lithium hydroxide on the surface of the solid electrolyte, which prevents the residual lithium hydroxide from reacting with other substances.

[0109] Experimental Example 2

[0110] The first-week discharge specific capacity and capacity retention rate of the solid-state batteries in Examples 1-8 and Comparative Example 1 were tested. The test results are shown in Table 1:

[0111] Table 1 Comparison of solid-state battery performance in Examples 1-8 and Comparative Example 1

[0112]

[0113]

[0114] As can be seen from Table 1, the first-week discharge specific capacity and capacity retention of the solid-state batteries in Examples 1-8 are better than those in Comparative Example 1. Compared with Comparative Example 1, Examples 1-8 have a polymer coating on the solid electrolyte, which improves the stability of the solid electrolyte, slows down the attenuation, and improves the capacity retention.

[0115] In addition, by comparing Examples 1-8, it can be found that: in Example 1, the compound having a five-membered ring includes 1,3-dioxolane and maleic anhydride, and the ratio of 1,3-dioxolane and maleic anhydride to lithium bis(trifluoromethanesulfonyl)imide and dimethoxymethane is within the preferred range, the thickness of the formed coating layer is appropriate, and the ionic conductivity is excellent; Example 2 uses vinylene carbonate and tetrahydrofuran to replace 1,3-dioxolane and maleic anhydride in Example 1, which can also achieve good results. In Example 3, the proportion of compounds with five-membered rings is low, the alkaline lithium compounds on the surface of the solid electrolyte are incomplete, and the formed coating layer is thin, which will lead to a decrease in the first effect and the cycle capacity retention rate compared with Examples 1-2; in Example 4, the proportion of compounds with five-membered rings is high, and a thicker coating layer will be formed, which will lead to a relatively lower first effect, but can improve the cycle stability; in Example 5, no lithium salt is added, which will lead to a low ionic conductivity of the formed coating layer, affecting the first-week capacity, but has little effect on the cycle capacity retention rate; in Example 6, lithium hexafluorophosphate is used to replace the lithium bis(trifluoromethanesulfonyl)imide in Example 1, resulting in a decrease in the cycle capacity retention rate compared with Example 1; in Example 7, the proportion of lithium salt added is low, and the ionic conductivity of the coating layer is reduced compared with Example 1; in Example 8, the proportion of lithium salt added is high, which will also lead to its performance being reduced compared with Example 1.

[0116] Experimental Example 3

[0117] The composite electrolyte in Example 1 and the uncoated lithium lanthanum zirconium tantalum oxide in Comparative Example 1 were spread flat in culture dishes, and the culture dishes were opened and placed in a constant temperature and humidity chamber with a humidity of 40%. The ionic conductivity was measured at the initial stage, 10 h, 24 h, 72 h, and 168 h.

[0118] Among them, the test method of ionic conductivity is: take 200mg of electrolyte powder and put it into a model battery with a diameter of d=10mm, cold press the powder at 400MPa for more than 5min, and after completing the pressing, test the electrolyte thickness L. Aluminum foil with a diameter of 10mm is attached to both sides of the electrolyte powder, and the model battery is encapsulated. The electrolyte impedance R is tested by electrochemical AC impedance spectroscopy, and the ionic conductivity of the electrolyte is obtained according to the ionic conductivity calculation formula σ=L / (R·S), where σ is the ionic conductivity of the electrolyte, L is the thickness of the pressed electrolyte sheet, S is the cross-sectional area of ​​the electrolyte sheet, and R is the electrolyte impedance measured by AC impedance spectroscopy. The results are shown in Table 2:

[0119] Table 2 Comparison of air stability tests of solid electrolytes in Example 1 and Comparative Example 1

[0120]

[0121] As can be seen from Table 2, the ionic conductivity of the uncoated lithium lanthanum zirconium tantalum oxide in Comparative Example 1 decays rapidly in humid air, while the ionic conductivity decay rate of the composite electrolyte in Example 1 is significantly reduced. This is mainly due to the polymer layer coating the surface of the solid electrolyte in Example 1, which significantly improves the stability of the solid electrolyte.

[0122] Experimental Example 4

[0123] The compaction density of the composite electrolytes in Examples 1-8 and the uncoated lithium lanthanum zirconium tantalum oxide in Comparative Example 1 was tested. The test method was as follows: a certain weight m of the electrolyte samples in Examples 1-8 and Comparative Example 1 was weighed and placed into a powder compaction density measuring instrument. The powder compaction density measuring instrument has a built-in mold with a radius r. The instrument can also measure the thickness h of the powder under different pressures. The powder compaction density ρ = m / (πr2h). Table 3 shows the powder compaction density test results of different examples and comparative examples at a pressure of 200 MPa:

[0124] Table 3 Compacted density test results of different embodiments and comparative examples

[0125]

[0126]

[0127] The true density of lithium lanthanum zirconium tantalum oxide is generally 5.0g / cm 3 The true density of the polymer in the polymer layer is generally less than 1.5g / cm 3 . It can be seen from Table 3 that the lithium lanthanum zirconium tantalum oxide in Comparative Example 1 has not been coated, and the compaction density is close to the true density of lithium lanthanum zirconium tantalum oxide. Since the polymer layer is coated on the surface of the lithium lanthanum zirconium tantalum oxide in Example 1 and Example 2, the compaction density is reduced. In Example 3, the proportion of compounds with a five-membered ring structure is low, resulting in a low coverage rate of the polymer layer and a relatively high compaction density. In Example 4, the proportion of compounds with a five-membered ring structure is high, resulting in a high coverage rate of the polymer layer and a relatively low compaction density. In Example 5, no lithium salt is added, and the reaction efficiency is low, resulting in a low coverage rate and a high compaction density. In Example 6, the ionic conductivity of the lithium salt is low, and the effect of promoting coating is poor, resulting in a low coverage rate and a high compaction density. In Example 7, the concentration of lithium salt is low, resulting in a low coverage rate and a high compaction density. In Example 8, the concentration of lithium salt is high, resulting in a high coverage rate and a low compaction density.

[0128] The above is a detailed introduction to the embodiments of the present application. Specific examples are used herein to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the method and core idea of ​​the present application. At the same time, for those skilled in the art, based on the ideas of the present application, there may be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as a limitation on the present application.

Claims

1. A composite electrolyte, characterized in that It includes a solid electrolyte and a coating layer coated on the surface of the solid electrolyte; The coating layer includes a polymer formed by polymerizing a compound having a five-membered ring and an alkaline lithium compound on the surface of the solid electrolyte, and the alkaline lithium compound includes lithium hydroxide and / or lithium carbonate.

2. The composite electrolyte according to claim 1, characterized in that The solid electrolyte includes at least one of lithium lanthanum zirconium oxide and lithium lanthanum zirconium tantalum oxide.

3. The composite electrolyte according to claim 1, characterized in that The molecular chain of the polymer includes at least one of an ethylene carbonate ring-opening group, a propylene carbonate ring-opening group, a fluoroethylene carbonate ring-opening group, a 2-methyltetrahydrofuran ring-opening group, a 1,3-dioxolane ring-opening group, a maleic anhydride ring-opening group, a vinylene carbonate ring-opening group, a tetrahydrofuran ring-opening group and a 4-methyl-1,3-dioxolane ring-opening group.

4. The composite electrolyte according to claim 3, characterized in that The polymer comprises a 1,3-dioxolane ring-opening group and a maleic anhydride ring-opening group in the molecular chain.

5. The composite electrolyte according to claim 3, characterized in that The molecular chain of the polymer includes a vinylene carbonate ring-opening group, and the molecular chain of the polymer also includes at least one of an ethylene carbonate ring-opening group, a propylene carbonate ring-opening group, a fluoroethylene carbonate ring-opening group, a 2-methyltetrahydrofuran ring-opening group, a 1,3-dioxolane ring-opening group, a maleic anhydride ring-opening group, a tetrahydrofuran ring-opening group and a 4-methyl-1,3-dioxolane ring-opening group.

6. The composite electrolyte according to any one of claims 1 to 5, characterized in that The coating layer also includes lithium salt.

7. The composite electrolyte according to claim 6, characterized in that The lithium salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(oxalatoborate), lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide.

8. The composite electrolyte according to claim 7, characterized in that The lithium salt includes at least one of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide.

9. The composite electrolyte according to any one of claims 1 to 5 or 7 to 8, characterized in that The compacted density of the composite electrolyte at 200 MPa is 32.0 g / cm 3 -4.8g / cm 3 .

10. A method for preparing a composite electrolyte, characterized in that: include: Providing a reaction solution; wherein the reaction solution comprises a first solvent and a compound having a five-membered ring structure; Mixing a solid electrolyte with the reaction solution to form a first mixed solution; wherein lithium hydroxide and / or lithium carbonate exists on the surface of the solid electrolyte; The lithium hydroxide and / or the lithium carbonate in the first mixed solution is polymerized with the compound having a five-membered ring structure to obtain a composite electrolyte.

11. The method for preparing a composite electrolyte according to claim 10, characterized in that: The solid electrolyte includes at least one of lithium lanthanum zirconium oxide and lithium lanthanum zirconium tantalum oxide.

12. The method for preparing a composite electrolyte according to claim 10, characterized in that: The compound having a five-membered ring structure includes at least one of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, 2-methyltetrahydrofuran, 1,3-dioxolane, maleic anhydride, vinylene carbonate, tetrahydrofuran and 4-methyl-1,3-dioxolane.

13. The method for preparing a composite electrolyte according to claim 10, characterized in that: The first solvent includes at least one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dimethoxymethane and ethylene glycol dimethyl ether.

14. The method for preparing a composite electrolyte according to any one of claims 10 to 13, characterized in that: The reaction solution also includes a lithium salt.

15. The method for preparing a composite electrolyte according to claim 14, characterized in that: In the reaction solution, the concentration of the lithium salt is 0.5 mol / L-3 mol / L.

16. The method for preparing a composite electrolyte according to claim 10, characterized in that: In the first mixed solution, the mass ratio of the solid electrolyte to the reaction solution is (1.5-3):1; And / or, the solid content of the first mixed liquid is 60%-70%.

17. The method for preparing a composite electrolyte according to claim 10, characterized in that: The step of reacting the lithium hydroxide and / or the lithium carbonate in the first mixed solution with the compound having a five-membered ring structure comprises: The lithium hydroxide and / or the lithium carbonate in the first mixed solution is reacted with the compound having a five-membered ring structure at a temperature of 45° C. to 80° C. for 12 to 48 hours.

18. A positive electrode sheet, characterized in that: The invention comprises the composite electrolyte according to any one of claims 1 to 9, and / or a composite electrolyte prepared by the method for preparing the composite electrolyte according to any one of claims 10 to 17.

19. A solid-state battery, characterized in that: Comprising the positive electrode sheet as claimed in claim 18.

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