Solid-state battery and preparation method thereof

Abstract

The invention provides a solid-state battery and a preparation method thereof, and aims to solve the technical problem that lithium titanium aluminum phosphate is easily reduced by metal lithium. The solid-state battery comprises a positive pole piece and a negative pole piece which are oppositely arranged, and a solid-state electrolyte layer positioned between the positive pole piece and the negative pole piece, and the solid-state electrolyte layer contains lithium titanium aluminum phosphate; the solid-state battery further comprises an interface protection layer located between the solid-state electrolyte layer and the negative pole piece, and the interface protection layer is a mixed layer containing lithium salt and a first conductive agent. According to the solid-state battery provided by the embodiment of the invention, the solid-state electrolyte layer and the negative pole piece are separated by using the interface protection layer, so that the risk that lithium titanium aluminum phosphate is reduced due to direct contact between lithium metal on the negative pole piece and lithium titanium aluminum phosphate in the solid-state electrolyte layer is reduced.

Description

Technical Field

[0001] This application relates to the technical field of batteries, and particularly to a solid-state battery and a preparation method thereof. Background Art

[0002] Oxide solid electrolytes have high application value due to their high mechanical strength, good thermal stability, wide electrochemical window and relatively moderate cost. Among oxide solid electrolytes, lithium aluminum titanium phosphate (LATP) is widely used in solid-state batteries due to its stable electrochemical window, high ionic conductivity and high air stability. However, LATP has a relatively fatal drawback that it is easily reduced by metallic lithium, which damages the bulk structure of LATP and affects the performance of solid-state batteries. This drawback of LATP severely restricts its large-scale application. Summary of the Invention

[0003] Embodiments of this application provide a solid-state battery and a preparation method thereof, which can solve the technical problem that LATP is easily reduced by metallic lithium.

[0004] In a first aspect, embodiments of this application provide a solid-state battery, including a positive electrode sheet and a negative electrode sheet arranged oppositely, and a solid electrolyte layer located between the positive electrode sheet and the negative electrode sheet, where the solid electrolyte layer contains LATP; the solid-state battery further includes an interface protection layer located between the solid electrolyte layer and the negative electrode sheet, and the interface protection layer is a mixed layer containing a lithium salt and a first conductive agent.

[0005] In one embodiment, the interface protection layer further contains a first binder. Based on the total mass of the interface protection layer, the content of the lithium salt is 4wt% - 12wt%, the content of the first conductive agent is 40wt% - 70wt%; the content of the first binder is 20wt% - 48wt%.

[0006] In one embodiment, in the interface protection layer, the mass ratio of the lithium salt, the first conductive agent and the first binder is (8 - 10):(58 - 62):(25 - 30).

[0007] In one embodiment, the interface protection layer further includes a first dispersant. Based on the total mass of the interface protection layer, the content of the first dispersant is 3wt% - 5wt%.

[0008] In one embodiment, the first dispersant includes at least one of sodium carboxymethyl cellulose, sodium dodecyl sulfonate, sodium carboxylate, potassium carboxylate, carboxamide, and polyacrylate.

[0009] In one embodiment, the first conductive agent includes at least one of conductive carbon black, acetylene black, Ketjen black, carbon nanotubes, and graphene; and / or, the lithium salt includes at least one of lithium hexafluorophosphate, lithium nitrate, lithium nitrite, lithium chloride, and lithium bis(oxalato)borate; and / or, the first binder includes at least one of polyacrylic acid, polyethylene oxide, and polyacrylamide.

[0010] In one embodiment, the lithium titanium aluminum phosphate is granular, the D50 particle size of the lithium titanium aluminum phosphate is less than 2.0 μm, the D90 particle size is less than 5.0 μm, and the D99 particle size is less than 8.0 μm.

[0011] In one embodiment, the solid electrolyte layer further includes a second binder and a second dispersant. Based on the total mass of the solid electrolyte layer, the content of the lithium titanium aluminum phosphate is 60 wt% to 80 wt%, the content of the second binder is 4 wt% to 30 wt%, and the content of the second dispersant is 10 wt% to 36 wt%.

[0012] In one embodiment, the thickness of the interface protection layer is 0.1 μm to 3 μm.

[0013] In one embodiment, the thickness of the interface protection layer is 0.1 μm to 2 μm.

[0014] In one embodiment, the thickness of the solid electrolyte layer is 6 μm to 10 μm.

[0015] In one embodiment, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer. The negative electrode active material layer is disposed on the negative electrode current collector. The interface protection layer and the solid electrolyte layer are located on a side of the negative electrode active material layer away from the negative electrode current collector, and the interface protection layer is located between the negative electrode active material layer and the solid electrolyte layer.

[0016] In one embodiment, the negative electrode active material layer includes a negative electrode active material, a third binder, a second conductive agent, and a third dispersant.

[0017] In one embodiment, the negative electrode sheet contains metallic lithium.

[0018] In a second aspect, an embodiment of the present application provides a method for manufacturing a solid-state battery for manufacturing the solid-state battery as described above, including:

[0019] Providing a negative electrode sheet, preparing an interface protection layer on the surface of the negative electrode sheet, and preparing a solid electrolyte layer on a surface of the interface protection layer away from the negative electrode sheet to obtain a first multi-layer structure;

[0020] Provide a positive electrode plate, stack the positive electrode plate with the first multi-layer structure, and make the positive electrode plate located on the side of the solid electrolyte layer away from the interface protection layer to obtain a solid-state battery.

[0021] In a third aspect, an embodiment of the present application provides a method for manufacturing a solid-state battery for manufacturing the solid-state battery as described above, including:

[0022] Provide a negative electrode plate, and prepare an interface protection layer on the surface of the negative electrode plate to obtain a second multi-layer structure;

[0023] Provide a separator, and prepare solid electrolyte layers on both side surfaces of the separator to obtain a third multi-layer structure;

[0024] Provide a positive electrode plate, stack the positive electrode plate, the third multi-layer structure and the second multi-layer structure in sequence, and make the third multi-layer structure located between the positive electrode plate and the interface protection layer to obtain a solid-state battery.

[0025] Advantages of the embodiments of the present application:

[0026] In the solid-state battery provided by the embodiments of the present application, the positive electrode plate, the solid electrolyte layer, the interface protection layer and the negative electrode plate are distributed in sequence. Among them, the solid electrolyte layer separates the positive electrode plate and the negative electrode plate, reducing the risk of short circuit caused by the contact between the positive electrode plate and the negative electrode plate; further, the interface protection layer separates the solid electrolyte layer from the negative electrode plate, thereby reducing the risk of the reduction of lithium titanium aluminum phosphate in the solid electrolyte layer caused by the direct contact between metallic lithium on the negative electrode plate and lithium titanium aluminum phosphate in the solid electrolyte layer. Description of the Drawings

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present application. For those skilled in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0028] Figure 1 It is a schematic cross-sectional structure diagram of a solid-state battery provided by an embodiment of the present application;

[0029] Figure 2 It is a preparation flow chart of a solid-state battery provided by an embodiment of the present application;

[0030] Figure 3 It is another preparation flow chart of a solid-state battery provided by an embodiment of the present application.

[0031] Explanation of the reference numerals:

[0032] 10. Solid-state battery;

[0033] 1. Positive electrode sheet; 11. Positive current collector; 12. Positive active material layer;

[0034] 2. Negative electrode sheet; 21. Negative current collector; 22. Negative active material layer;

[0035] 3. Solid electrolyte layer;

[0036] 4. Interface protection layer;

[0037] 5. Separator;

[0038] 101. First multi-layer structure; 102. Second multi-layer structure; 103. Third multi-layer structure. Detailed implementation manners

[0039] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a 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 efforts belong to the scope of protection of the present application.

[0040] In addition, it should be understood that the specific implementation manners described herein are only used to illustrate and explain the present application, and are not used to limit the present application. In the present application, unless otherwise stated, the orientation words such as "upper" and "lower" generally refer to the upper and lower in the actual use or working state of the device, specifically the drawing direction in the accompanying drawings; while "inner" and "outer" refer to the outline of the device.

[0041] The terms "first" and "second" are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of the described features. In the description of the present application, the meaning of "a plurality" is two or more, unless otherwise specifically defined.

[0042] In the description of the present application, it should be noted that unless otherwise clearly defined and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection; it may be a mechanical connection, an electrical connection, or a communication with each other; it may be directly connected, or indirectly connected through an intermediate medium, and may be the internal communication of two components or the interaction relationship between two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to specific situations.

[0043] The term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, such that a process, method, article or apparatus comprising a series of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article or apparatus. Without further limitation, an element qualified by the statement "comprising an..." does not exclude the presence of additional identical elements in the process, method, article or apparatus comprising the element.

[0044] In the description of the embodiments of the present application, words such as "example" or "for example" are used to represent examples, explanations or descriptions. Any embodiment or design solution described as "for example" or "for instance" in the embodiments of the present application is not construed as being more preferred or having more advantages than another embodiment or design solution. The use of words such as "example" or "for example" is intended to present relative concepts in a clear manner.

[0045] To facilitate the understanding of the solution of the present application, the spline curves and arrows used for the reference numerals in the drawings are described herein: For the components indicated by the spline curves without arrows, they are solid components, that is, components having a solid structure; for the components indicated by the spline curves with arrows, they are virtual components, that is, components without a solid structure.

[0046] In a first aspect, please refer to Figure 1 , an embodiment of the present application provides a solid-state battery 10, including a positive electrode plate 1 and a negative electrode plate 2 disposed opposite to each other, and a solid electrolyte layer 3 located between the positive electrode plate 1 and the negative electrode plate 2, the solid electrolyte layer 3 containing lithium titanium aluminum phosphate; the solid-state battery 10 further includes an interface protection layer 4 located between the solid electrolyte layer 3 and the negative electrode plate 2, and the interface protection layer 4 is a mixed layer containing a lithium salt and a first conductive agent.

[0047] The solid-state battery 10 is specifically a lithium-ion battery. Here, the solid-state battery 10 can be a fully solid-state battery or a semi-solid-state battery. A semi-solid-state battery refers to a battery in which either side electrode does not contain a liquid electrolyte and the other side electrode contains a liquid electrolyte, or the mass or volume of the solid electrolyte in the battery cell accounts for more than half of the total mass or total volume of the electrolyte in the battery cell. A fully solid-state battery completely uses a solid electrolyte to replace the electrolyte solution.

[0048] Lithium titanium aluminum phosphate Li 1+x Al x Ti 2-x(PO4)3 (abbreviated as LATP) belongs to the NASICON-structured solid electrolytes, which have the advantages of high ionic conductivity, high environmental stability (towards water and air), easy synthesis, and low cost. However, in lithium-ion batteries, the reduction potential of the negative electrode is the reduction potential of metallic lithium, and the standard electrode potential of metallic lithium is -3.04 V (relative to the standard hydrogen electrode, SHE). That is to say, when lithium ions are embedded in the negative electrode material, its reduction potential is close to -3.04 V. Due to the extremely low reduction potential of metallic lithium, a serious side reaction will occur when lithium titanium phosphate and metallic lithium come into contact, resulting in the reduction of tetravalent titanium ions (i.e., Ti 4+ ) in lithium titanium phosphate to trivalent titanium ions (i.e., Ti 3+ ), which will damage the structure of lithium titanium phosphate and affect the transport of lithium ions.

[0049] It should be noted here that the source of metallic lithium on the negative electrode plate 2 includes the metallic lithium added during the preparation of the negative electrode plate 2. As an example, the negative electrode plate 2 is a metallic lithium negative electrode prepared using metallic lithium or a lithium alloy; the source of metallic lithium on the negative electrode plate 2 can also include the metallic lithium deposited on the negative electrode plate 2 during the charge and discharge process of the solid-state battery 10. As an example, during the charging process of the solid-state battery 10, lithium ions on the positive electrode plate 1 are transferred to the negative electrode plate 2 and undergo a reduction reaction to generate metallic lithium. That is to say, regardless of whether metallic lithium is added during the preparation of the negative electrode plate 2, as the charging of the solid-state battery 10 proceeds, there is always a risk of the existence of metallic lithium on the negative electrode plate 2, that is, there is a risk of lithium titanium phosphate in the solid electrolyte layer 3 being reduced by metallic lithium.

[0050] In the solid-state battery 10 provided by the embodiments of the present application, the positive electrode plate 1, the solid electrolyte layer 3, the interface protection layer 4, and the negative electrode plate 2 are distributed in sequence. Among them, the solid electrolyte layer 3 separates the positive electrode plate 1 and the negative electrode plate 2, reducing the risk of short circuit caused by the contact between the positive electrode plate 1 and the negative electrode plate 2; further, the interface protection layer 4 separates the solid electrolyte layer 3 from the negative electrode plate 2, thereby reducing the risk of direct contact between the metallic lithium on the negative electrode plate 2 and the lithium titanium phosphate in the solid electrolyte layer 3 resulting in the reduction of lithium titanium phosphate.

[0051] At the same time, the interface protection layer 4 is a mixed layer containing a lithium salt and a first conductive agent. In this way, the lithium salt can construct an ion transport channel in the interface protection layer 4, that is, make the interface protection layer 4 have ion conductivity, while the first conductive agent can construct an electron transport channel in the interface protection layer 4, that is, make the interface protection layer 4 have electron conductivity. That is to say, the interface protection layer 4 has the function of conducting both ions and electrons. Compared with other single interface protection layers, the interface protection layer 4 has a lower interface impedance, thereby effectively reducing the internal resistance of the solid-state battery 10 and further improving the cycle performance of the solid-state battery 10.

[0052] It was also found that in the solid-state battery 10 provided in the embodiment of the present application, due to the provision of the interface protection layer 4, when the solid-state battery 10 is subjected to mechanical damage such as needle puncture or impact by a heavy object, the interface protection layer 4 can reduce the risk of fire in the solid-state battery 10. This is because the interface protection layer 4 increases the contact resistance between the positive electrode plate 1 and the negative electrode plate 2 during a short circuit, reducing the short-circuit current, thereby reducing the short-circuit heat, and improving the safety of the solid-state battery 10.

[0053] In some embodiments, the interface protection layer 4 further comprises a first binder. Based on the total mass of the interface protection layer 4 , the content of the lithium salt is 4 wt % to 12 wt %, the content of the first conductive agent is 40 wt % to 70 wt %; and the content of the first binder is 20 wt % to 48 wt %.

[0054] A first binder is added to the interface protective layer 4. The first binder can bond the lithium salt and the first conductive agent together. The higher the content of the first binder in the interface protective layer 4, the stronger the cohesion of the interface protective layer 4, which is more conducive to improving the structural stability of the interface protective layer 4 itself, thereby promoting the formation of continuous and stable ion transmission channels and electron transmission channels in the interface protective layer 4. However, the first binder is usually an organic high molecular polymer, which has poor ability to conduct electrons and ions. If the content of the first binder is too high, it will lead to an increase in the internal resistance of the solid-state battery 10.

[0055] It can be understood that in the interface protective layer 4, the higher the content of lithium salt, the more ion transmission channels in the interface protective layer 4, and the better the ion conductivity of the interface protective layer 4. In the interface protective layer 4, the higher the content of the first conductive agent, the more electron transmission channels in the interface protective layer 4, and the better the electronic conductivity of the interface protective layer 4.

[0056] Since the content of the lithium salt, the first conductive agent, and the first binder in the interface protective layer 4 is in a trade-off relationship, an increase in the content of one substance will inevitably lead to a decrease in the content of the other substances. Therefore, by controlling the content of the lithium salt, the first conductive agent, and the first binder in the interface protective layer 4 to the above ratio, the three interact to make the interface protective layer 4 have both excellent ionic conductivity and electronic conductivity, reducing the ohmic polarization of the solid-state battery 10. It is also found that under this formula, the safety of the solid-state battery 10 is further improved.

[0057] As an example, based on the total mass of the interface protection layer 4, the content of the lithium salt is 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt% or 12 wt%. In the interface protection layer 4, if the content of the lithium salt is too low, the ionic conductivity of the interface protection layer 4 will be reduced, which will further increase the internal resistance of the solid-state battery 10; the internal resistance of the solid-state battery 10 is determined by the synergistic effect of the electronic conductivity and ionic conductivity of the interface protection layer 4. When the content of the lithium salt is too high, it will cause redundancy in the ionic conductivity of the interface protection layer 4. When the electronic conductivity of the interface protection layer 4 is not effectively improved, it is difficult to effectively improve the internal resistance of the solid-state battery 10. Optionally, the lithium salt includes at least one of lithium hexafluorophosphate, lithium nitrate, lithium nitrite, lithium chloride and lithium bis(oxalato)borate.

[0058] As an example, based on the total mass of the interface protection layer 4, the content of the first conductive agent is 40 wt%, 45 wt%, 48 wt%, 50 wt%, 55 wt%, 58 wt%, 60 wt%, 65 wt%, 68 wt% or 70 wt%. If the content of the first conductive agent in the interface protection layer 4 is too low, the conductivity of the interface protection layer 4 will be reduced, resulting in an increase in the internal resistance of the interface protection layer 4; however, the content of the first conductive agent in the interface protection layer 4 should not be too high either, because too high a content of the first conductive agent will cause a decrease in other components in the interface protection layer 4. For example, a decrease in the content of the lithium salt will cause the ionic conductivity of the interface protection layer 4 to deteriorate. The internal resistance of the solid-state battery 10 is determined by the synergistic effect of the electronic conductivity and ionic conductivity of the interface protection layer 4. A deterioration in the ionic conductivity of the interface protection layer 4 will cause an increase in the internal resistance of the solid-state battery 10; and a decrease in the content of the first binder will not only reduce the dispersion effect of the first conductive agent in the interface protection layer 4, resulting in poor conductive electron performance of the interface protection layer 4, but also cause a decline in the mechanical properties of the interface protection layer 4. Therefore, controlling the content of the first conductive agent in the interface protection layer 4 is beneficial to reducing the internal resistance of the interface protection layer 4 and improving the mechanical properties. Optionally, the first conductive agent includes at least one of conductive carbon black, acetylene black, Ketjen black, carbon nanotubes and graphene.

[0059] As an example, based on the total mass of the interface protection layer 4, the content of the first binder is 20 wt%, 25 wt%, 30 wt%, 32 wt%, 35 wt%, 34 wt%, 40 wt%, 45 wt% or 48 wt%. In the interface protection layer 4, if the content of the first binder is too low, the mechanical properties of the interface protection layer 4 will decline, affecting the puncture passing rate and heavy object impact passing rate of the solid-state battery 10; while if the content of the first binder is too high, it will cause an increase in the internal resistance of the interface protection layer 4 and the cycle performance of the solid-state battery 10 will deteriorate. Optionally, the first binder includes at least one of polyacrylic acid, polyethylene oxide, and polyacrylamide.

[0060] As can be seen from the above, there are mutual influences and synergistic effects among the contents of the first binder, the first conductive agent, and the lithium salt in the interface protective layer 4, and the three together determine the cycle performance, the puncture passing rate, and the heavy object impact passing rate of the solid-state battery 10.

[0061] In one embodiment, in the interface protective layer 4, the mass ratio of the lithium salt, the first conductive agent, and the first binder is (8 - 10):(58 - 62):(25 - 30). At this ratio, the contents of the first binder, the first conductive agent, and the lithium salt in the interface protective layer 4 can be effectively coordinated, so that the cycle performance, the puncture passing rate, and the heavy object impact passing rate of the solid-state battery 10 are all effectively improved. As an example, in the interface protective layer 4, the mass ratio of the lithium salt, the first conductive agent, and the first binder is 8:58:30, 10:60:26, or 9:62:25.

[0062] In some embodiments, the interface protective layer 4 further includes a first dispersant, and based on the total mass of the interface protective layer 4, the content of the first dispersant is 3 wt% - 5 wt%.

[0063] Since when preparing the interface protective layer 4, it is usually necessary to first add the lithium salt, the first conductive agent, and the first binder into the first solvent to prepare an interface protective layer slurry, and then perform a film-forming treatment on the interface protective layer slurry to obtain the interface protective layer 4. In order to improve the dispersion effect of each material, especially the first conductive agent in the first solvent, a first dispersant is also added to the first solvent. The first dispersant can promote the dispersion of each material in the first solvent, and thus is beneficial to improving the dispersion and continuity of the electron transport channel and the ion transport channel in the interface protective layer 4, and reducing the ohmic polarization of the solid-state battery 10.

[0064] As an example, based on the total mass of the interface protective layer 4, the content of the first dispersant is 3.0 wt%, 3.5 wt%, 4.0 wt%, 4.5 wt%, or 5.0 wt%. Optionally, the first dispersant includes at least one of sodium carboxymethyl cellulose, sodium dodecyl sulfonate, sodium carboxylate, potassium carboxylate, carboxamide, and polyacrylate.

[0065] As an example, the first solvent includes at least one of water, ethanol, N-methylpyrrolidone (NMP), dimethyl carbonate (DMC), and dimethyl sulfoxide (DMSO).

[0066] In some embodiments, lithium titanium aluminum phosphate is in a granular form, the D50 particle size of lithium titanium aluminum phosphate is less than 2.0 μm, the D90 particle size is less than 5.0 μm, and the D99 particle size is less than 8.0 μm.

[0067] The particle size of lithium aluminum titanium phosphate will affect the dispersion effect of lithium aluminum titanium phosphate in the solid electrolyte layer 3. Generally, the larger the particle size of lithium aluminum titanium phosphate, the worse the dispersion effect; the smaller the particle size of lithium aluminum titanium phosphate, the better the dispersion effect, which is more conducive to improving the transport effect of lithium ions in the solid electrolyte layer 3.

[0068] As an example, the D50 particle size of lithium aluminum titanium phosphate is 0.5μm, 0.7μm, 0.9μm, 1.1μm, 1.3μm, 1.5μm, 1.7μm or 1.9μm.

[0069] As an example, the D90 particle size of lithium aluminum titanium phosphate is 1.0μm, 1.5μm, 2.0μm, 2.5μm, 3.0μm, 3.5μm, 4.0μm, 4.5μm or 4.9μm.

[0070] As an example, the D99 particle size of lithium aluminum titanium phosphate is 1.0μm, 2.0μm, 3.0μm, 4.0μm, 5.0μm, 6.0μm, 7.0μm, 7.5μm or 7.9μm.

[0071] In some embodiments, the solid electrolyte layer 3 further includes a second binder and a second dispersant. Based on the total mass of the solid electrolyte layer 3, the content of lithium aluminum titanium phosphate is 60wt% - 80wt%, the content of the second binder is 4wt% - 30wt%, and the content of the second dispersant is 10wt% - 36wt%.

[0072] It should be noted here that the second binder and the first binder may be the same or different. The second dispersant and the first dispersant may be the same or different.

[0073] As an example, based on the total mass of the solid electrolyte layer 3, the content of lithium aluminum titanium phosphate is 60wt%, 65wt%, 70wt%, 75wt% or 80wt%.

[0074] As an example, based on the total mass of the solid electrolyte layer 3, the content of the second binder is 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, 15wt%, 20wt%, 25wt% or 30wt%.

[0075] As an example, based on the total mass of the solid electrolyte layer 3, the content of the second dispersant is 10wt%, 12wt%, 14wt%, 16wt%, 18wt%, 20wt%, 22wt%, 24wt%, 26wt%, 28wt%, 30wt%, 32wt%, 34wt% or 36wt%.

[0076] In some embodiments, the thickness of the interface protective layer 4 is 0.1 μm to 3 μm. The thickness of the interface protective layer 4 affects the isolation effect of the interface protective layer 4. The thicker the interface protective layer 4, the lower the risk of direct contact between the metallic lithium on the negative electrode sheet 2 and the lithium titanium aluminum phosphate in the solid electrolyte layer 3. However, if the interface protective layer 4 is too thick, the ohmic polarization of the solid-state battery 10 will increase. As an example, the thickness of the interface protective layer 4 is 0.1 μm, 0.5 μm, 1.0 μm, 1.5 μm, 2.0 μm, 2.5 μm, or 3.0 μm.

[0077] In some embodiments, the thickness of the interface protective layer 4 is 0.1 μm to 2 μm. When the thickness of the interface protective layer 4 is less than 2 μm, increasing the thickness of the interface protective layer 4 will improve the film-forming quality of the interface protective layer 4, thereby enhancing the conduction ability of the interface protective layer 4, and instead reducing the internal resistance of the interface protective layer 4 and optimizing the cycling performance of the solid-state battery 10. As an example, the thickness of the interface protective layer 4 is 0.1 μm, 0.2 μm, 0.4 μm, 0.6 μm, 0.8 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, or 2.0 μm. Optionally, the thickness of the interface protective layer 4 is 1 μm to 2 μm. In this range, the interface protective layer 4 has both low internal resistance and good mechanical strength, so that the cycling performance of the solid-state battery 10 is good and the puncture passing rate and heavy object impact passing rate of the solid-state battery 10 are guaranteed.

[0078] In some embodiments, the thickness of the solid electrolyte layer 3 is 6 μm to 10 μm. The thickness of the solid electrolyte layer 3 affects the isolation effect of the solid electrolyte layer 3. The thicker the solid electrolyte layer 3, the lower the risk of short circuit caused by contact between the negative electrode sheet 2 and the positive electrode sheet 1. However, if the solid electrolyte layer 3 is too thick, the ohmic polarization of the solid-state battery 10 will increase. As an example, the thickness of the solid electrolyte layer 3 is 6 μm, 6.5 μm, 7.0 μm, 7.5 μm, 8.0 μm, 8.5 μm, 9.0 μm, 9.5 μm, or 10.0 μm.

[0079] In some embodiments, the negative electrode sheet 2 includes a negative electrode current collector 21 and a negative electrode active material layer 22. The negative electrode active material layer 22 is disposed on the negative electrode current collector 21. The interface protective layer 4 and the solid electrolyte layer 3 are located on the side of the negative electrode active material layer 22 away from the negative electrode current collector 21, and the interface protective layer 4 is located between the negative electrode active material layer 22 and the solid electrolyte layer 3. That is to say, the negative electrode current collector 21, the negative electrode active material layer 22, the interface protective layer 4, and the solid electrolyte layer 3 are arranged in sequence. The interface protective layer 4 isolates the negative electrode active material layer 22 and the solid electrolyte layer 3, which can reduce the risk of reduction of lithium titanium aluminum phosphate by metallic lithium due to contact between the metallic lithium embedded in the negative electrode active material layer 22 and the lithium titanium aluminum phosphate in the solid electrolyte layer 3 during the charging process of the solid-state battery 10.

[0080] In some embodiments, the negative electrode active material layer 22 includes a negative electrode active material, a third binder, a second conductive agent, and a third dispersant.

[0081] It should be noted here that the third binder and the first binder may be the same or different. The third binder and the second binder may be the same or different. The second conductive agent and the first conductive agent may be the same or different. The third dispersant and the first dispersant may be the same or different. The third dispersant and the second dispersant may be the same or different.

[0082] As an example, in the negative electrode active material layer 22, the mass ratio of the negative electrode active material, the third binder, the second conductive agent, and the third dispersant is 96:2.0:0.8:1.2.

[0083] In some embodiments, the negative electrode sheet 2 contains metallic lithium. As an example, the negative electrode sheet 2 is a metallic lithium negative electrode directly prepared from metallic lithium or a lithium alloy. The interface protection layer 4 is between the negative electrode sheet 2 and the solid electrolyte layer 3, which can reduce the risk that the metallic lithium in the negative electrode sheet 2 contacts with the lithium titanium aluminum phosphate in the solid electrolyte layer 3 during the charging process of the solid-state battery 10, resulting in the reduction of lithium titanium aluminum phosphate by metallic lithium.

[0084] In some embodiments, the positive electrode sheet 1 includes a positive electrode current collector 11 and a positive electrode active material layer 12. The positive electrode active material layer 12 is disposed on the positive electrode current collector 11, and the solid electrolyte layer 3 is located on the side of the positive electrode active material layer 12 away from the positive electrode current collector 11. As an example, the positive electrode active material layer 12 includes a positive electrode active material, a fourth binder, a third conductive agent, and a fourth dispersant.

[0085] Second, please refer to Figure 2 Figs. (a) to (e) in, an embodiment of the present application provides a method for manufacturing a solid-state battery 10 for manufacturing the solid-state battery 10 as above, including:

[0086] Providing a negative electrode sheet 2, preparing an interface protection layer 4 on the surface of the negative electrode sheet 2, and preparing a solid electrolyte layer 3 on the surface of the interface protection layer 4 facing away from the negative electrode sheet 2 to obtain a first multi-layer structure 101;

[0087] Providing a positive electrode sheet 1, stacking the positive electrode sheet 1 and the first multi-layer structure 101, and making the positive electrode sheet 1 located on the side of the solid electrolyte layer 3 away from the interface protection layer 4 to obtain the solid-state battery 10.

[0088] The preparation method of the solid-state battery 10 provided by the embodiments of the present application obtains the first multi-layer structure 101 by sequentially disposing an interface protection layer 4 and a solid electrolyte layer 3 on the negative electrode sheet 2, and then combines the obtained first multi-layer structure 101 with the positive electrode sheet 1 to obtain the solid-state battery 10. This preparation method is simple and easy to operate.

[0089] In some embodiments, the preparation process of the first multi-layer structure 101 includes: Please refer to Figure 2 Figure (a) therein, provide a negative electrode current collector 21 and a negative electrode slurry, and the negative electrode slurry includes a negative electrode active material, a third binder, a second conductive agent, and a third dispersant; Please refer to Figure 2 Figure (b) therein, perform a film-forming treatment on both side surfaces of the negative electrode current collector 21 with the negative electrode slurry to obtain a negative electrode active material layer 22; provide an interface protection layer slurry, and the interface protection layer slurry includes a lithium salt, a first conductive agent, a first binder, and a first dispersant; Please refer to Figure 2 Figure (c) therein, perform a film-forming treatment on the side surface of the negative electrode active material layer 22 facing away from the negative electrode current collector 21 with the interface protection layer slurry to obtain the interface protection layer 4; provide a solid electrolyte slurry, and the solid electrolyte slurry includes a solid electrolyte LATP, a second binder, and a second dispersant; Please refer to Figure 2 Figure (d) therein, perform a film-forming treatment on the side surface of the interface protection layer 4 facing away from the negative electrode active material layer 22 with the solid electrolyte slurry to obtain the solid electrolyte layer 3, and further obtain the first multi-layer structure 101.

[0090] In a third aspect, please refer to Figure 3 Figures (a) to (f) therein, the embodiments of the present application provide a preparation method of a solid-state battery 10 for preparing the solid-state battery 10 as above, including:

[0091] Provide a negative electrode sheet 2, and prepare an interface protection layer 4 on the surface of the negative electrode sheet 2 to obtain a second multi-layer structure 102;

[0092] Provide a separator 5, and prepare solid electrolyte layers 3 on both side surfaces of the separator 5 to obtain a third multi-layer structure 103;

[0093] Provide a positive electrode sheet 1, stack the positive electrode sheet 1, the third multi-layer structure 103, and the second multi-layer structure 102 in sequence, and make the third multi-layer structure 103 located between the positive electrode sheet 1 and the interface protection layer 4 to obtain the solid-state battery 10.

[0094] The preparation method of the solid-state battery 10 provided by the embodiments of the present application obtains the second multi-layer structure 102 by setting an interface protection layer 4 on the negative electrode sheet 2; obtains the third multi-layer structure 103 by setting a solid electrolyte layer 3 on the separator 5; and then combines the obtained second multi-layer structure 102 and third multi-layer structure 103 with the positive electrode sheet 1 to obtain the solid-state battery 10. This preparation method is simple and easy to operate.

[0095] As an example, the preparation process of the second multi-layer structure 102 includes: Please refer to Figure 3 Figure (a) in, provide a negative current collector 21 and a negative electrode paste, the negative electrode paste contains a negative active material, a third binder, a second conductive agent, and a third dispersant; Please refer to Figure 3 Figure (b) in, perform a film-forming treatment on both side surfaces of the negative current collector 21 with the negative electrode paste to obtain a negative active material layer 22; provide an interface protection layer paste, the interface protection layer paste contains a lithium salt, a first conductive agent, a first binder, and a first dispersant; Please refer to Figure 3 Figure (c) in, perform a film-forming treatment on the side surface of the negative active material layer 22 facing away from the negative current collector 21 with the interface protection layer paste to obtain the interface protection layer 4, and thus obtain the second multi-layer structure 102.

[0096] As an example, Please refer to Figure 3 , the preparation process of the third multi-layer structure 103 includes: Please refer to Figure 3 Figure (d) in, provide a separator 5 and a solid electrolyte paste, the solid electrolyte paste contains a solid electrolyte LATP, a second binder, and a second dispersant; Please refer to Figure 3 Figure (e) in, perform a film-forming treatment on both side surfaces of the separator 5 with the solid electrolyte paste to obtain the solid electrolyte layer 3, and thus obtain the third multi-layer structure 103.

[0097] As an example, the separator 5 includes one of a polyethylene (PE) film and a polypropylene (PP) film.

[0098] The following is described in conjunction with specific embodiments.

[0099] Example 1

[0100] This example provides a solid-state battery, and the preparation process of the solid-state battery includes:

[0101] S1. Preparation of the negative electrode sheet: The negative electrode active material (graphite), the second conductive agent (conductive carbon black), the third dispersant (carboxymethyl cellulose, CMC), and the third binder (styrene-butadiene rubber, SBR) are configured according to a mass ratio of 96:0.8:1.2:2.0. Then, the second solvent (ethylene carbonate) is added, and a negative electrode slurry with a solid content of 50 wt% is formulated. The above negative electrode slurry is coated on both sides of the copper foil and baked at 120 °C for 15 minutes to complete drying, so that the negative electrode slurry is cured to form a negative electrode active material layer. Then, the negative electrode active material layer is roll-pressed to obtain the negative electrode sheet.

[0102] S2. Preparation of the interface protection layer: The first conductive agent (conductive carbon black), the lithium salt (lithium hexafluorophosphate), the first dispersant (CMC), and the first binder (polyacrylic acid) are configured according to a mass percentage of 68:8:4:20. Then, the first solvent (water) is added, and an interface protection layer slurry with a solid content of 15 wt% is formulated. The above interface protection layer slurry is coated on the surface of the negative electrode active material layer and baked at 120 °C for 5 minutes to complete drying, so that the interface protection layer slurry is cured to form an interface protection layer, where the thickness of the interface protection layer is 2 μm.

[0103] S3. Preparation of the solid electrolyte layer: The solid electrolyte (LATP), the second dispersant (CMC), and the second binder (polyacrylic acid) are configured according to a mass percentage of 60:4:36. Then, the solvent (water) is added, and a solid electrolyte slurry with a solid content of 25 wt% is formulated. The above solid electrolyte slurry is coated on the surface of the interface protection layer and baked at 120 °C for 5 minutes to complete drying, so that the solid electrolyte slurry is cured to form a solid electrolyte layer, and thus the first multi-layer structure is obtained, where the thickness of the solid electrolyte layer is 8 μm.

[0104] S4. Preparation of the positive electrode sheet: The third conductive agent, conductive carbon black, and carbon nanotubes are added to the fourth binder, polyvinylidene fluoride (PVDF) colloidal solution, and stirred evenly. Then, the positive electrode active material, lithium cobaltate, is added and stirred evenly to prepare a positive electrode slurry. The positive electrode slurry is coated on the surface of the aluminum foil, and after baking, the positive electrode slurry is cured to form a positive electrode active material layer; in the positive electrode active material layer, the content of lithium cobaltate is 97 wt%, the content of PVDF is 1.6 wt%, and the total content of conductive carbon black and carbon nanotubes is 1.4 wt% (where the mass ratio of conductive carbon black to carbon nanotubes is 1:1); the positive electrode active material layer is roll-pressed to obtain the positive electrode sheet.

[0105] S5. Preparation of the solid-state battery: After the positive electrode sheet and the negative electrode sheet are cut into square sizes, they are stacked layer by layer, and then a small amount of electrolyte (lithium hexafluorophosphate) is injected, encapsulated, hot-pressed and formed, second-sealed and evacuated, and divided into capacities and then taken off the production line to obtain the solid-state battery.

[0106] Example 2

[0107] The difference from Example 1 is as follows:

[0108] S2. Prepare the interfacial protective layer: The first conductive agent (conductive carbon black), lithium salt (lithium hexafluorophosphate), first dispersant (CMC), and first binder (polyacrylic acid) are configured according to a mass percentage of 58:8:4:30, and then the first solvent (water) is added to formulate an interfacial protective layer slurry with a solid content of 8 wt%. The above interfacial protective layer slurry is coated on the surface of the negative electrode active material layer and baked at 120 °C for 5 minutes to complete drying, so that the interfacial protective layer slurry is cured to form an interfacial protective layer, where the thickness of the interfacial protective layer is 0.1 μm.

[0109] Others are the same as in Example 1.

[0110] Example 3

[0111] The difference from Example 1 is as follows:

[0112] S2. Prepare the interfacial protective layer: The first conductive agent (conductive carbon black), lithium salt (lithium hexafluorophosphate), first dispersant (CMC), and first binder (polyacrylic acid) are configured according to a mass percentage of 58:8:4:30, and then the first solvent (water) is added to formulate an interfacial protective layer slurry with a solid content of 11 wt%. The above interfacial protective layer slurry is coated on the surface of the negative electrode active material layer and baked at 120 °C for 5 minutes to complete drying, so that the interfacial protective layer slurry is cured to form an interfacial protective layer, where the thickness of the interfacial protective layer is 0.5 μm.

[0113] Others are the same as in Example 1.

[0114] Example 4

[0115] The difference from Example 1 is as follows:

[0116] S2. Prepare the interfacial protective layer: The first conductive agent (conductive carbon black), lithium salt (lithium hexafluorophosphate), first dispersant (CMC), and first binder (polyacrylic acid) are configured according to a mass percentage of 58:8:4:30, and then the first solvent (water) is added to formulate an interfacial protective layer slurry with a solid content of 13 wt%. The above interfacial protective layer slurry is coated on the surface of the negative electrode active material layer and baked at 120 °C for 5 minutes to complete drying, so that the interfacial protective layer slurry is cured to form an interfacial protective layer, where the thickness of the interfacial protective layer is 1 μm.

[0117] Others are the same as in Example 1.

[0118] Example 5

[0119] The difference from Example 1 is as follows:

[0120] S2. Prepare the interfacial protective layer: Configure the first conductive agent (conductive carbon black), lithium salt (lithium hexafluorophosphate), first dispersant (CMC), and first binder (polyacrylic acid) according to a mass percentage of 58:8:4:30, then add the first solvent (water) to formulate an interfacial protective layer slurry with a solid content of 15 wt%. Coat the above interfacial protective layer slurry on the surface of the negative electrode active material layer and bake it at 120°C for 5 minutes to complete drying, so that the interfacial protective layer slurry cures to form an interfacial protective layer, where the thickness of the interfacial protective layer is 2 μm.

[0121] Others are the same as in Example 1.

[0122] Example 6

[0123] The difference from Example 1 is:

[0124] S2. Prepare the interfacial protective layer: Configure the first conductive agent (conductive carbon black), lithium salt (lithium hexafluorophosphate), first dispersant (CMC), and first binder (polyacrylic acid) according to a mass percentage of 58:8:4:30, then add the first solvent (water) to formulate an interfacial protective layer slurry with a solid content of 17 wt%. Coat the above interfacial protective layer slurry on the surface of the negative electrode active material layer and bake it at 120°C for 5 minutes to complete drying, so that the interfacial protective layer slurry cures to form an interfacial protective layer, where the thickness of the interfacial protective layer is 3 μm.

[0125] Others are the same as in Example 1.

[0126] Example 7

[0127] The difference from Example 1 is:

[0128] S2. Prepare the interfacial protective layer: Configure the first conductive agent (conductive carbon black), lithium salt (lithium hexafluorophosphate), first dispersant (CMC), and first binder (polyacrylic acid) according to a mass percentage of 58:8:4:30, then add the first solvent (water) to formulate an interfacial protective layer slurry with a solid content of 15 wt%. Coat the above interfacial protective layer slurry on the surface of the negative electrode active material layer and bake it at 120°C for 5 minutes to complete drying, so that the interfacial protective layer slurry cures to form an interfacial protective layer, where the thickness of the interfacial protective layer is 3 μm.

[0129] S3. Preparation of the solid electrolyte layer: The solid electrolyte (LATP), the second dispersant (CMC), and the second binder (polyacrylic acid) are configured according to a mass percentage of 60:4:36, and then a solvent (water) is added to prepare a solid electrolyte slurry with a solid content of 20 wt%. The above solid electrolyte slurry is coated on the surface of the interface protection layer and baked at 120 °C for 5 minutes to complete drying, so that the solid electrolyte slurry is cured to form a solid electrolyte layer, thereby obtaining the first multi-layer structure. Among them, the thickness of the solid electrolyte layer is 6 μm.

[0130] Others are the same as in Example 1.

[0131] Example 8

[0132] The difference from Example 1 is that:

[0133] S2. Preparation of the interface protection layer: The first conductive agent (conductive carbon black), the lithium salt (lithium hexafluorophosphate), the first dispersant (CMC), and the first binder (polyacrylic acid) are configured according to a mass percentage of 58:4:4:34, and then a first solvent (water) is added to prepare an interface protection layer slurry with a solid content of 15 wt%. The above interface protection layer slurry is coated on the surface of the negative electrode active material layer and baked at 120 °C for 5 minutes to complete drying, so that the interface protection layer slurry is cured to form an interface protection layer. Among them, the thickness of the interface protection layer is 2 μm.

[0134] Others are the same as in Example 1.

[0135] Example 9

[0136] The difference from Example 1 is that:

[0137] S2. Preparation of the interface protection layer: The first conductive agent (conductive carbon black), the lithium salt (lithium hexafluorophosphate), the first dispersant (CMC), and the first binder (polyacrylic acid) are configured according to a mass percentage of 48:8:4:40, and then a first solvent (water) is added to prepare an interface protection layer slurry with a solid content of 15 wt%. The above interface protection layer slurry is coated on the surface of the negative electrode active material layer and baked at 120 °C for 5 minutes to complete drying, so that the interface protection layer slurry is cured to form an interface protection layer. Among them, the thickness of the interface protection layer is 2 μm.

[0138] Others are the same as in Example 1.

[0139] Example 10

[0140] The difference from Example 1 is that:

[0141] S2. Preparation of the interfacial protective layer: The first conductive agent (conductive carbon black), lithium salt (lithium hexafluorophosphate), first dispersant (CMC), and first binder (polyacrylic acid) are configured according to a mass percentage of 40:8:4:48, and then the first solvent (water) is added to formulate an interfacial protective layer slurry with a solid content of 15 wt%. The above interfacial protective layer slurry is coated on the surface of the negative electrode active material layer and baked at 120 °C for 5 minutes to complete drying, so that the interfacial protective layer slurry is cured to form an interfacial protective layer, wherein the thickness of the interfacial protective layer is 2 μm.

[0142] Others are the same as in Example 1.

[0143] Example 11

[0144] The difference from Example 1 is that:

[0145] S2. Preparation of the interfacial protective layer: The first conductive agent (conductive carbon black), lithium salt (lithium hexafluorophosphate), first dispersant (CMC), and first binder (polyacrylic acid) are configured according to a mass percentage of 70:8:4:18, and then the first solvent (water) is added to formulate an interfacial protective layer slurry with a solid content of 15 wt%. The above interfacial protective layer slurry is coated on the surface of the negative electrode active material layer and baked at 120 °C for 5 minutes to complete drying, so that the interfacial protective layer slurry is cured to form an interfacial protective layer, wherein the thickness of the interfacial protective layer is 2 μm.

[0146] Others are the same as in Example 1.

[0147] Example 12

[0148] The difference from Example 1 is that:

[0149] S2. Preparation of the interfacial protective layer: The first conductive agent (conductive carbon black), lithium salt (lithium hexafluorophosphate), first dispersant (CMC), and first binder (polyacrylic acid) are configured according to a mass percentage of 55:8:4:33, and then the first solvent (water) is added to formulate an interfacial protective layer slurry with a solid content of 15 wt%. The above interfacial protective layer slurry is coated on the surface of the negative electrode active material layer and baked at 120 °C for 5 minutes to complete drying, so that the interfacial protective layer slurry is cured to form an interfacial protective layer, wherein the thickness of the interfacial protective layer is 2 μm.

[0150] Others are the same as in Example 1.

[0151] Example 13

[0152] The difference from Example 1 is that:

[0153] S2. Preparation of the interfacial protective layer: The first conductive agent (conductive carbon black), lithium salt (lithium hexafluorophosphate), first dispersant (CMC), and first binder (polyacrylic acid) are configured according to a mass percentage of 65:8:4:23, and then the first solvent (water) is added to formulate an interfacial protective layer slurry with a solid content of 15 wt%. The above interfacial protective layer slurry is coated on the surface of the negative electrode active material layer and baked at 120 °C for 5 minutes to complete drying, so that the interfacial protective layer slurry is cured to form an interfacial protective layer, wherein the thickness of the interfacial protective layer is 2 μm.

[0154] Others are the same as in Example 1.

[0155] Example 14

[0156] The difference from Example 1 is that:

[0157] S2. Preparation of the interfacial protective layer: The first conductive agent (conductive carbon black), lithium salt (lithium hexafluorophosphate), first dispersant (CMC), and first binder (polyacrylic acid) are configured according to a mass percentage of 58:6:4:32, and then the first solvent (water) is added to formulate an interfacial protective layer slurry with a solid content of 15 wt%. The above interfacial protective layer slurry is coated on the surface of the negative electrode active material layer and baked at 120 °C for 5 minutes to complete drying, so that the interfacial protective layer slurry is cured to form an interfacial protective layer, wherein the thickness of the interfacial protective layer is 2 μm.

[0158] Others are the same as in Example 1.

[0159] Example 15

[0160] The difference from Example 1 is that:

[0161] S2. Preparation of the interfacial protective layer: The first conductive agent (conductive carbon black), lithium salt (lithium hexafluorophosphate), first dispersant (CMC), and first binder (polyacrylic acid) are configured according to a mass percentage of 58:10:4:28, and then the first solvent (water) is added to formulate an interfacial protective layer slurry with a solid content of 15 wt%. The above interfacial protective layer slurry is coated on the surface of the negative electrode active material layer and baked at 120 °C for 5 minutes to complete drying, so that the interfacial protective layer slurry is cured to form an interfacial protective layer, wherein the thickness of the interfacial protective layer is 2 μm.

[0162] Others are the same as in Example 1.

[0163] Example 16

[0164] The difference from Example 1 is that:

[0165] S2. Preparation of the interfacial protective layer: The first conductive agent (conductive carbon black), lithium salt (lithium hexafluorophosphate), first dispersant (CMC), and first binder (polyacrylic acid) are configured according to a mass percentage of 58:12:4:26, and then the first solvent (water) is added to formulate an interfacial protective layer slurry with a solid content of 15 wt%. The above interfacial protective layer slurry is coated on the surface of the negative electrode active material layer and baked at 120 °C for 5 minutes to complete drying, so that the interfacial protective layer slurry is cured to form an interfacial protective layer, wherein the thickness of the interfacial protective layer is 2 μm.

[0166] Others are the same as in Example 1.

[0167] Example 17

[0168] The difference from Example 1 is as follows:

[0169] S2. Preparation of the interfacial protective layer: The first conductive agent (conductive carbon black), lithium salt (lithium hexafluorophosphate), first dispersant (CMC), and first binder (polyacrylic acid) are configured according to a mass percentage of 58:7:4:31, and then the first solvent (water) is added to formulate an interfacial protective layer slurry with a solid content of 15 wt%. The above interfacial protective layer slurry is coated on the surface of the negative electrode active material layer and baked at 120 °C for 5 minutes to complete drying, so that the interfacial protective layer slurry is cured to form an interfacial protective layer, wherein the thickness of the interfacial protective layer is 2 μm.

[0170] Others are the same as in Example 1.

[0171] Example 18

[0172] The difference from Example 1 is as follows:

[0173] S2. Preparation of the interfacial protective layer: The first conductive agent (conductive carbon black), lithium salt (lithium hexafluorophosphate), first dispersant (CMC), and first binder (polyacrylic acid) are configured according to a mass percentage of 58:11:4:27, and then the first solvent (water) is added to formulate an interfacial protective layer slurry with a solid content of 15 wt%. The above interfacial protective layer slurry is coated on the surface of the negative electrode active material layer and baked at 120 °C for 5 minutes to complete drying, so that the interfacial protective layer slurry is cured to form an interfacial protective layer, wherein the thickness of the interfacial protective layer is 2 μm.

[0174] Others are the same as in Example 1.

[0175] Example 19

[0176] The difference from Example 1 is as follows:

[0177] S2. Preparation of the interfacial protective layer: The first conductive agent (conductive carbon black), lithium salt (lithium hexafluorophosphate), the first dispersant (CMC), and the first binder (polyacrylic acid) are configured according to a mass percentage of 58:8:4:30, and then the first solvent (water) is added to formulate an interfacial protective layer slurry with a solid content of 15 wt%. The above interfacial protective layer slurry is coated on the surface of the negative electrode active material layer and baked at 120 °C for 5 minutes to complete drying, so that the interfacial protective layer slurry is cured to form an interfacial protective layer, where the thickness of the interfacial protective layer is 2 μm.

[0178] S3. Preparation of the solid electrolyte layer: The solid electrolyte (LATP), the second dispersant (CMC), and the second binder (polyacrylic acid) are configured according to a mass percentage of 60:4:36, and then the solvent (water) is added to formulate a solid electrolyte slurry with a solid content of 30 wt%. The above solid electrolyte slurry is coated on the surface of the interfacial protective layer and baked at 120 °C for 5 minutes to complete drying, so that the solid electrolyte slurry is cured to form a solid electrolyte layer, thereby obtaining the first multilayer structure, where the thickness of the solid electrolyte layer is 10 μm.

[0179] Others are the same as in Example 1.

[0180] Example 20

[0181] The difference from Example 1 is:

[0182] S2. Preparation of the interfacial protective layer: The first conductive agent (conductive carbon black), lithium salt (lithium hexafluorophosphate), the first dispersant (CMC), and the first binder (polyacrylic acid) are configured according to a mass percentage of 60:10:4:26, and then the first solvent (water) is added to formulate an interfacial protective layer slurry with a solid content of 15 wt%. The above interfacial protective layer slurry is coated on the surface of the negative electrode active material layer and baked at 120 °C for 5 minutes to complete drying, so that the interfacial protective layer slurry is cured to form an interfacial protective layer, where the thickness of the interfacial protective layer is 2 μm.

[0183] Others are the same as in Example 1.

[0184] Example 21

[0185] The difference from Example 1 is:

[0186] S2. Preparation of the interface protection layer: The first conductive agent (conductive carbon black), lithium salt (lithium hexafluorophosphate), first dispersant (CMC), and first binder (polyacrylic acid) are configured according to a mass percentage of 62:9:4:25, and then the first solvent (water) is added to formulate an interface protection layer slurry with a solid content of 15 wt%. The above interface protection layer slurry is coated on the surface of the negative electrode active material layer and baked at 120 °C for 5 minutes to complete drying, so that the interface protection layer slurry is cured to form an interface protection layer, wherein the thickness of the interface protection layer is 2 μm.

[0187] Others are the same as in Example 1.

[0188] Comparative Example 1

[0189] The difference from Example 5 is that: The interface protection layer is cancelled. Others are the same as in Example 5.

[0190] Comparative Example 2

[0191] The difference from Example 5 is that:

[0192] S2. Preparation of the interface protection layer: The first conductive agent (conductive carbon black), first dispersant (CMC), and first binder (polyacrylic acid) are configured according to a mass percentage of 66:4:30, and then the first solvent (water) is added to formulate an interface protection layer slurry with a solid content of 15 wt%. The above interface protection layer slurry is coated on the surface of the negative electrode active material layer and baked at 120 °C for 5 minutes to complete drying, so that the interface protection layer slurry is cured to form an interface protection layer, wherein the thickness of the interface protection layer is 2 μm.

[0193] Others are the same as in Example 5.

[0194] Comparative Example 3

[0195] The difference from Example 5 is that:

[0196] S2. Preparation of the interface protection layer: The lithium salt (lithium hexafluorophosphate), first dispersant (CMC), and first binder (polyacrylic acid) are configured according to a mass percentage of 66:4:30, and then the first solvent (water) is added to formulate an interface protection layer slurry with a solid content of 15 wt%. The above interface protection layer slurry is coated on the surface of the negative electrode active material layer and baked at 120 °C for 5 minutes to complete drying, so that the interface protection layer slurry is cured to form an interface protection layer, wherein the thickness of the interface protection layer is 2 μm.

[0197] Others are the same as in Example 5.

[0198] Partial experimental parameters of each example and comparative example are recorded in Table 1.

[0199] Table 1

[0200]

[0201]

[0202] The following tests were performed on the solid-state batteries provided in each example and comparative example:

[0203] 1. Internal resistance test: The solid-state battery was first charged at a constant current of 0.5C until the cut-off voltage, and then charged at a constant voltage until the cut-off current of 0.05C. Then, the internal resistance of the solid-state battery was measured using a voltage internal resistance meter and recorded in Table 2.

[0204] 2. Penetration test: The solid-state battery was first charged at a constant current of 0.5C until the cut-off voltage, and then charged at a constant voltage until the cut-off current of 0.05C. After the fully charged solid-state battery was placed in an environment at 45°C for 30 minutes, it was immediately taken out for testing. Specifically, a cell penetration testing machine was used, and a steel nail with a diameter of 3 mm was passed through the middle of the front of the solid-state battery at a rate of 150 mm / s and kept for 6 hours. If the solid-state battery did not catch fire or explode, it was considered qualified. For each example or comparative example, 10 solid-state batteries were tested, and the number of qualified solid-state batteries N1 was recorded. N1 / 10 was used as the penetration pass rate, and the results were recorded in Table 2.

[0205] 3. Heavy object impact test: The solid-state battery was first charged at a constant current of 0.5C until the cut-off voltage, and then charged at a constant voltage until the cut-off current of 0.05C. At an ambient temperature of 25 ± 3°C, the fully charged solid-state battery was placed on a horizontal ground, and an iron rod with a diameter of 15.8 ± 0.2 mm was placed horizontally at the center of the solid-state battery. Then, a 9.1 ± 0.1 Kg weight was freely dropped from a height of 610 ± 25 mm to impact the solid-state battery fixed on the horizontal ground and kept for 6 hours. If the solid-state battery did not catch fire or explode, it was considered qualified. For each example or comparative example, 10 solid-state batteries were tested, and the number of qualified solid-state batteries N2 was recorded. N2 / 10 was used as the penetration pass rate, and the results were recorded in Table 2.

[0206] 4. Cycle performance test: At 25°C, the solid-state battery was subjected to a 0.5C (charge) / 0.7C (discharge) cycle test. The calculation method of the capacity retention rate was the capacity after 300 cycles divided by the initial capacity to obtain the capacity retention rate after cycling. The test results were recorded in Table 2.

[0207] Table 2

[0208]

[0209]

[0210] The differences between Example 11, Example 1, Example 13, Example 5, Example 12, Example 9 and Example 10 lie in the contents of the first conductive agent and the first binder in the interface protective layer. Through comparison, it can be seen that as the content of the first conductive agent in the interface protective layer decreases (70wt%, 68wt%, 65wt%, 58wt%, 55wt%, 48wt%, 40wt%), the content of the first binder increases (18wt%, 20wt%, 23wt%, 30wt%, 33wt%, 40wt%, 48wt%). Instead, the internal resistance of the solid-state battery decreases, the puncture passing rate and the heavy object impact passing rate of the solid-state battery increase, and the capacity retention rate of the solid-state battery decreases. This is because when the content of the first conductive agent in the interface protective layer is relatively high (not less than 40wt%), appropriately increasing the content of the first binder can actually promote the dispersion of the first conductive agent, thereby reducing the internal resistance of the solid-state battery. However, increasing the content of the first binder is not conducive to the transfer of lithium ions, so the capacity retention rate of the solid-state battery decreases. In addition, increasing the content of the first binder can improve the mechanical properties of the interface protective layer, thereby improving the puncture passing rate and the heavy object impact passing rate of the solid-state battery.

[0211] The differences between Example 2, Example 3, Example 4, Example 5 and Example 6 lie in the thickness of the interface protective layer. Through comparison, it can be seen that as the thickness of the interface protective layer gradually increases (0.1μm, 0.5μm, 1μm, 2μm, 3μm), the internal resistance of the solid-state battery first decreases and then increases, the puncture passing rate and the heavy object impact passing rate of the solid-state battery both increase, and the capacity retention rate of the solid-state battery first remains flat and then decreases. Theoretically, the greater the thickness of the interface protective layer, the greater the internal resistance. However, the greater the thickness of the interface protective layer, the stronger the conduction ability of the interface protective layer, indicating that when the thickness of the interface protective layer is between 0.1μm and 2μm, the conduction ability of the interface protective layer is the main factor. Then, as the thickness of the interface protective layer increases, the thickness gradually becomes the main factor, and at this time the internal resistance increases, resulting in a decrease in the capacity retention rate of the solid-state battery. Increasing the thickness of the interface protective layer can improve the mechanical properties of the interface protective layer, thereby improving the puncture passing rate and the heavy object impact passing rate of the solid-state battery.

[0212] Examples 16, 18, 15, 5, 17, 14 and 8 differ in the contents of lithium salt and the first binder in the interface protective layer. Through comparison, it can be seen that as the content of lithium salt in the interface protective layer decreases (12wt%, 11wt%, 10wt%, 8wt%, 7wt%, 6wt%, 4wt%), the content of the first binder increases (26wt%, 27wt%, 28wt%, 30wt%, 31wt%, 32wt%, 34wt%). The internal resistance of the solid-state battery first slightly decreases and then increases. The puncture passing rate and the heavy object impact passing rate of the solid-state battery have little difference, and the capacity retention rate of the solid-state battery decreases. It can be seen that reducing the content of lithium salt in the interface protective layer can increase the internal resistance of the solid-state battery, and the content of lithium element in the interface protective layer decreases, so that the capacity retention rate of the solid-state battery decreases.

[0213] Examples 7, 5 and 19 differ in the thickness of the solid electrolyte layer. Through comparison, it can be seen that as the thickness of the solid electrolyte layer gradually increases (6μm, 8μm, 10μm), the internal resistance of the solid-state battery increases, the puncture passing rate and the heavy object impact passing rate of the solid-state battery both increase, and the capacity retention rate of the solid-state battery first increases and then decreases. However, increasing the thickness of the solid electrolyte layer will increase the internal resistance of the solid-state battery, resulting in a decrease in the capacity retention rate. However, after the thickness of the solid electrolyte layer increases, the mechanical strength of the solid electrolyte layer is improved, and the puncture passing rate and the heavy object impact passing rate of the solid-state battery can also be increased.

[0214] The difference between Examples 1 to 21 and Comparative Example 1 is that the interface protective layer is cancelled in Comparative Example 1. Through comparison, it can be seen that by setting an interface protective layer between the solid electrolyte layer and the negative electrode active material layer, the puncture passing rate, the heavy object impact passing rate and the capacity retention rate of the solid-state battery can be effectively improved. This is because on the one hand, the interface protective layer can separate the solid electrolyte layer from the negative electrode plate, thereby reducing the risk of direct contact between metallic lithium on the negative electrode plate and lithium titanium aluminum phosphate in the solid electrolyte layer, which causes lithium titanium aluminum phosphate to be reduced, and improving the stability of the solid electrolyte layer. On the other hand, the interface protective layer has both ion conductivity and electron conductivity, and this interface protective layer has a lower interface impedance, so that the capacity retention rate of the solid-state battery is improved. In addition, the interface protective layer can also increase the contact resistance when the positive electrode plate and the negative electrode plate are short-circuited, thereby improving the puncture passing rate and the heavy object impact passing rate of the solid-state battery.

[0215] The difference between Example 5 and Comparative Example 2 is that no lithium salt is added to the interface protective layer in Comparative Example 2, and the difference between Example 5 and Comparative Example 3 is that no first conductive agent is added to the interface protective layer in Comparative Example 2. It can be seen from the comparison that although the puncture passing rate and the heavy object impact passing rate of the three are not very different, when the interface protective layer contains both lithium salt and the first conductive agent, the internal resistance of the solid-state battery is lower, indicating that there is a synergistic effect between the lithium salt and the first conductive agent, and the two cooperate with each other to make the interface protective layer have a lower interfacial impedance, thereby reducing the internal resistance of the solid-state battery and improving the cycle performance.

[0216] In addition, further comparing Examples 4, 5, 20 and 21 with other examples, it can be found that the cycle performance of the solid-state batteries in Examples 4, 5, 20 and 21 reaches the optimum. This shows that when the mass ratio of the lithium salt, the first conductive agent and the first binder is (8-10):(58-62):(25-30), the components cooperate with each other to make the interface protective layer have both a lower interfacial impedance and a better isolation effect, thereby improving the cycle performance of the solid-state battery. In addition, compared with Example 4, the puncture passing rate and the heavy object impact passing rate of the solid-state battery in Example 5 are higher because the thickness of the interface protective layer in Example 5 is larger. Increasing the thickness of the interface protective layer can improve the mechanical properties of the interface protective layer, and further improve the puncture passing rate and the heavy object impact passing rate of the solid-state battery.

[0217] The embodiments of the present application have been introduced in detail above. Specific examples are used in this article to elaborate on the principle and implementation manner of the present application. The description of the above embodiments is only used to help understand the method and its core idea of the present application; at the same time, for those skilled in the art, according to the idea of the present application, there will be changes in the specific implementation manner and application scope. In summary, the content of this specification should not be construed as a limitation to the present application.

Claims

1. A solid-state battery, characterized in that, It includes a relatively arranged positive electrode plate and a negative electrode plate, and a solid electrolyte layer located between the positive electrode plate and the negative electrode plate, and the solid electrolyte layer contains lithium titanium aluminum phosphate; the solid-state battery further includes an interface protection layer located between the solid electrolyte layer and the negative electrode plate, and the interface protection layer is a mixed layer containing a lithium salt and a first conductive agent.

2. The solid-state battery according to claim 1, characterized in that, The interface protection layer further contains a first binder. Based on the total mass of the interface protection layer, the content of the lithium salt is 4wt% to 12wt%, the content of the first conductive agent is 40wt% to 70wt%; the content of the first binder is 20wt% to 48wt%.

3. The solid-state battery according to claim 2, characterized in that, In the interface protection layer, the mass ratio of the lithium salt, the first conductive agent and the first binder is (8 to 10):(58 to 62):(25 to 30).

4. The solid-state battery according to claim 2, wherein The interface protection layer further includes a first dispersant. Based on the total mass of the interface protection layer, the content of the first dispersant is 3wt% to 5wt%.

5. The solid-state battery according to claim 4, characterized in that, The first dispersant includes at least one of sodium carboxymethyl cellulose, sodium dodecyl sulfonate, sodium carboxylate, potassium carboxylate, carboxamide, and polyacrylate.

6. The solid-state battery according to any one of claims 1 to 5, characterized in that, The first conductive agent includes at least one of conductive carbon black, acetylene black, Ketjen black, carbon nanotubes, and graphene; and / or, the lithium salt includes at least one of lithium hexafluorophosphate, lithium nitrate, lithium nitrite, lithium chloride, and lithium bis(oxalato)borate; and / or, the first binder includes at least one of polyacrylic acid, polyethylene oxide, and polyacrylamide.

7. The solid-state battery according to any one of claims 1 to 5, characterized in that, The lithium titanium aluminum phosphate is granular, the D50 particle size of the lithium titanium aluminum phosphate is less than 2.0μm, the D90 particle size is less than 5.0μm, and the D99 particle size is less than 8.0μm.

8. The solid-state battery according to any one of claims 1 to 5, characterized in that, The solid electrolyte layer further contains a second binder and a second dispersant. Based on the total mass of the solid electrolyte layer, the content of the lithium titanium aluminum phosphate is 60wt% to 80wt%, the content of the second binder is 4wt% to 30wt%, and the content of the second dispersant is 10wt% to 36wt%.

9. The solid-state battery according to any one of claims 1 to 5, characterized in that, The thickness of the interface protection layer is 0.1μm to 3μm; and / or, the thickness of the solid electrolyte layer is 6μm to 10μm.

10. The solid-state battery according to claim 9, characterized in that, The thickness of the interface protection layer is 0.1μm to 2μm.

11. The solid-state battery according to any one of claims 1 to 5, characterized in that, The negative electrode plate includes a negative electrode current collector and a negative electrode active material layer. The negative electrode active material layer is disposed on the negative electrode current collector. The interface protection layer and the solid electrolyte layer are located on the side of the negative electrode active material layer away from the negative electrode current collector, and the interface protection layer is located between the negative electrode active material layer and the solid electrolyte layer.

12. The solid-state battery according to claim 11, characterized in that, The negative electrode active material layer contains a negative electrode active material, a third binder, a second conductive agent, and a third dispersant.

13. The solid-state battery according to any one of claims 1 to 5, characterized in that, The negative electrode plate contains metallic lithium.

14. A method for preparing a solid-state battery, for preparing the solid-state battery according to any one of claims 1 to 13, characterized in that, It includes: Providing a negative electrode plate, preparing an interface protection layer on the surface of the negative electrode plate, and preparing a solid electrolyte layer on the surface of the interface protection layer away from the negative electrode plate to obtain a first multi-layer structure; Provide a positive electrode sheet, stack the positive electrode sheet with the first multilayer structure, and make the positive electrode sheet located on the side of the solid electrolyte layer away from the interface protection layer to obtain a solid-state battery.

15. A method for preparing a solid-state battery, for preparing the solid-state battery according to any one of claims 1 to 13, characterized in that, It includes: Provide a negative electrode sheet, and prepare an interface protection layer on the surface of the negative electrode sheet to obtain a second multilayer structure; Provide a separator, and prepare solid electrolyte layers on both side surfaces of the separator to obtain a third multilayer structure; Provide a positive electrode sheet, stack the positive electrode sheet, the third multilayer structure and the second multilayer structure in sequence, and make the third multilayer structure located between the positive electrode sheet and the interface protection layer to obtain a solid-state battery.

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