Composite structure of negative electrode and solid electrolyte for battery as well as preparation method and application of composite structure

Abstract

The invention provides a composite structure for a negative electrode and a solid electrolyte of a battery and a preparation method and application of the composite structure, and the composite structure comprises a negative electrode plate which comprises a negative electrode current collector, a negative electrode active material layer located on at least one functional surface of the negative electrode current collector, and first liquid metal; the solid electrolyte is located on the surface of the side, away from the negative electrode current collector, of the negative electrode active material layer, and the solid electrolyte comprises second liquid metal; the solid electrolyte and the negative plate are combined at the interface through metal connection, and the metal connection is solid combination formed by melting the first liquid metal and the second liquid metal and fusing the first liquid metal and the second liquid metal at the interface. According to the invention, the interface connection between the negative plate and the solid electrolyte can be enhanced.

Description

Technical Field

[0001] The present invention relates to the technical field of solid-state batteries, and particularly relates to a composite structure of a negative electrode and a solid electrolyte for a battery, a preparation method thereof, and an application thereof. Background Art

[0002] Since the interface between the solid electrolyte and the negative electrode is a solid-solid contact interface, the contact sites are discontinuous, the contact area is small, and the contact is not tight enough, resulting in a relatively high contact resistance. The current solutions mainly involve directly introducing an interface layer. Although it can induce uniform deposition of lithium metal on the interface or inhibit the nucleation of lithium metal, introducing the interface layer will inevitably increase new interfaces, with a limited improvement effect on the interface contact between the solid electrolyte and the negative electrode, and may even increase the overall resistance of the battery. Moreover, the lithium metal deposited on the interface layer exists in a two-dimensional form, that is, it grows along the direction from the negative electrode to the positive electrode, which is extremely likely to cause dendrite problems. At the same time, the deposited lithium will directly contact the solid electrolyte, consuming part of the solid electrolyte and causing side reactions.

[0003] Therefore, a structure that can improve the interface contact between the solid electrolyte and the negative electrode and avoid introducing a new interface layer has attracted much attention in the field. Summary of the Invention

[0004] The present invention provides a composite structure of a negative electrode and a solid electrolyte for a battery, a preparation method thereof, and an application thereof, which helps to enhance the tight connection between the negative electrode and the solid electrolyte and reduce the interfacial impedance.

[0005] The present invention provides a composite structure of a negative electrode and a solid electrolyte for a battery, comprising: a negative electrode sheet, including a negative electrode current collector and a negative electrode active material layer located on at least one functional surface of the negative electrode current collector, the negative electrode active material layer including a first liquid metal; a solid electrolyte, located on a surface of the negative electrode active material layer away from the negative electrode current collector, the solid electrolyte including a second liquid metal; the solid electrolyte and the negative electrode sheet are metallically connected and combined at the interface, and the metallic connection is a solid combination formed by melting the first liquid metal and the second liquid metal and fusing them at the interface.

[0006] Optionally, the first liquid metal includes one or more of gallium and gallium alloys; and / or, the second liquid metal includes one or more of gallium and gallium alloys.

[0007] Optionally, the negative electrode active material layer includes N layers of negative electrode active material layers, where N ≥ 3; among them, the (n + 1)-th negative electrode active material layer is located on the side of the n-th negative electrode active material layer away from the negative electrode current collector, and 1 ≤ n ≤ N - 1; and / or, the solid electrolyte includes M layers of solid electrolyte layers, where M ≥ 3; among them, the (m + 1)-th solid electrolyte layer is located on the side of the m-th solid electrolyte layer close to the negative electrode active material layer, and 1 ≤ m ≤ M - 1.

[0008] Optionally, part of the first liquid metal is located in the i-th layer of the negative electrode active material layer, and i = N; and / or, part of the second liquid metal is located in the j-th layer of the solid electrolyte layer, and j = M.

[0009] Optionally, the N - 1 layers of negative electrode active material layers away from the negative electrode current collector include a conductive lithiumophilic material, and the conductive lithiumophilic material includes one or more of Al, Cu, Sn, Zn, Pb, Sb, Cd, Au, Bi, Ge, and the particle size of the conductive lithiumophilic material is 10 - 200 nm; and / or, the M - 1 layers of solid electrolyte layers close to the negative electrode active material layer include an insulating lithiumophilic material, and the insulating lithiumophilic material includes one or more of lithium fluoride, lithium nitride, aluminum oxide, zirconium oxide.

[0010] Optionally, the porosity of the first negative electrode active material layer is 0.01% - 5%, the porosity of each layer in the middle negative electrode active material layer is 10% - 20%, the porosity of the i-th negative electrode active material layer is 20% - 40%, and i = N; and / or, the porosity of the first solid electrolyte layer is 0.01% - 5%, the porosity of each layer in the middle solid electrolyte layer is 10% - 20%, the porosity of the j-th solid electrolyte layer is 20% - 40%, and j = M.

[0011] Optionally, the thickness ratio Q1 of the first negative electrode active material layer to the negative electrode active material layer satisfies: 1 / N ≤ Q1 ≤ (4N + 1) / 5N, and the thickness ratio Q2 of each of the remaining N - 1 layers of negative electrode active material layers to the negative electrode active material layer satisfies: 1 / 5N ≤ Q2 ≤ 1 / N; and / or, the thickness ratio Q3 of the first solid electrolyte layer to the solid electrolyte satisfies: 1 / M ≤ Q3 ≤ (4M + 1) / 5M, and the thickness ratio Q4 of each of the remaining M - 1 layers of solid electrolyte layers to the solid electrolyte satisfies: 1 / 5M ≤ Q4 ≤ 1 / M.

[0012] Optionally, the negative electrode active material layer further includes a first interface modifier, and the first interface modifier includes tungsten; and / or, the solid electrolyte further includes a second interface modifier, and the second interface modifier includes tungsten.

[0013] The present invention provides a method for preparing a composite structure of a negative electrode and a solid electrolyte for a battery as described in the above item, comprising: 1) coating a negative electrode paste on at least one functional surface of a negative electrode current collector, and after drying, forming a precursor of a negative electrode active material layer; 2) filling a first liquid metal into some pores on the side of the precursor of the negative electrode active material layer away from the negative electrode current collector; 3) subjecting a solid electrolyte raw material to a pressing treatment to obtain a precursor of a solid electrolyte; 4) filling a second liquid metal into some pores on one side of the precursor of the solid electrolyte; 5) bringing the surface of the precursor of the negative electrode active material layer filled with the first liquid metal into contact with the surface of the precursor of the solid electrolyte filled with the second liquid metal, and then performing a hot pressing treatment to obtain the composite structure of the negative electrode and the solid electrolyte for the battery, wherein the temperature of the hot pressing treatment is 30 to 130 °C and the pressure is 0.1 to 20 MPa.

[0014] Optionally, step 1) includes: separately preparing N portions of negative electrode paste, N≥3, then coating the first portion of negative electrode paste on at least one functional surface of the negative electrode current collector, and after drying, forming a first precursor of a negative electrode active material layer, then coating the second portion of negative electrode paste on the surface of the first precursor of the negative electrode active material layer, and after drying, forming a second precursor of a negative electrode active material layer, and so on, sequentially completing the coating and drying of the N portions of negative electrode paste to form the precursor of the negative electrode active material layer having an N-layer structure; and / or, step 3) includes: separately preparing M portions of solid electrolyte raw material, M≥3, then subjecting the first portion of solid electrolyte raw material to a pressing treatment to form a first precursor of a solid electrolyte layer, then laying the second portion of solid electrolyte raw material on the surface of the first precursor of the solid electrolyte layer, and then performing a pressing treatment to form a second precursor of a solid electrolyte layer, and so on, sequentially completing the pressing treatment of the M portions of solid electrolyte raw material to form the precursor of the solid electrolyte having an M-layer structure.

[0015] Optionally, step 2) includes: filling the first liquid metal into some pores of the i-th layer of the precursor of the negative electrode active material layer, i = N; and / or. Step 4) includes: filling the second liquid metal into some pores of the j-th precursor of the solid electrolyte layer, j = M.

[0016] Optionally, step 1) further includes: after forming the precursor of the second negative electrode active material layer, filling the conductive lithiumophilic material into at least part of the pores of the precursor of the second negative electrode active material layer, and then preparing the precursor of the third negative electrode active material layer. In this way, the conductive lithiumophilic material is sequentially filled into the precursors of the N-1 layer of the negative electrode active material layer far from the negative electrode current collector. The conductive lithiumophilic material includes one or more of Al, Cu, Sn, Zn, Pb, Sb, Cd, Au, Bi, and Ge, and the particle size of the conductive lithiumophilic material is 10-200 nm; and / or, step 3) further includes: after forming the precursor of the second solid electrolyte layer, filling the insulating lithiumophilic material into at least part of the pores of the precursor of the second solid electrolyte layer, and then preparing the precursor of the third solid electrolyte layer. In this way, the insulating lithiumophilic material is sequentially filled into the M-1 layer close to the negative electrode active material layer. The insulating lithiumophilic material includes one or more of lithium fluoride, lithium nitride, aluminum oxide, and zirconium oxide.

[0017] Optionally, the negative electrode slurry of the first negative electrode active material layer includes a negative electrode active material, a binder, and a conductive agent with a mass ratio of (80-99):(0.5-10):(0.5-10); the negative electrode slurry of each layer in the intermediate negative electrode active material layer includes the negative electrode slurry of the first negative electrode active material layer and ammonium bicarbonate, where the mass ratio of the negative electrode active material to ammonium bicarbonate in the negative electrode slurry of the first negative electrode active material layer is (4-25):1; the negative electrode slurry of the i-th negative electrode active material layer includes the negative electrode slurry of the first negative electrode active material layer and ammonium bicarbonate, where the mass ratio of the negative electrode active material to ammonium bicarbonate in the negative electrode slurry of the first negative electrode active material layer is (1-4):1, i = N; and / or, the raw materials of each layer in the intermediate solid electrolyte layer include the raw materials of the first solid electrolyte layer and ammonium bicarbonate, where the mass ratio of the raw materials of the first solid electrolyte layer to ammonium bicarbonate is (4-25):1; the raw materials of the j-th solid electrolyte layer include the raw materials of the first solid electrolyte layer and ammonium bicarbonate, where the mass ratio of the raw materials of the first solid electrolyte layer to ammonium bicarbonate is (1-4):1, j = M.

[0018] Optionally, the ratio P1 of the mass of the first portion of the negative electrode slurry to the sum of the masses of the N portions of the negative electrode slurry satisfies: 1 / N ≤ P1 ≤ (4N + 1) / 5N, and the ratio P2 of the mass of each of the remaining N-1 portions of the negative electrode slurry to the sum of the masses of the N portions of the negative electrode slurry satisfies: 1 / 5N ≤ P2 ≤ 1 / N; and / or, the ratio P3 of the mass of the first portion of the solid electrolyte raw material to the sum of the masses of the M portions of the solid electrolyte raw material satisfies: 1 / M ≤ P3 ≤ (4M + 1) / 5M, and the ratio P4 of the mass of each of the remaining M-1 portions of the solid electrolyte layer raw material to the sum of the masses of the M portions of the solid electrolyte raw material satisfies: 1 / 5M ≤ P4 ≤ 1 / M.

[0019] Optionally, step 2) further includes depositing a first interfacial modifier on partial pores on the side of the negative electrode active material layer precursor away from the negative electrode current collector, and then filling the partial pores on the side of the negative electrode active material layer precursor deposited with the first interfacial modifier with the first liquid metal, wherein the first interfacial modifier includes tungsten; and / or, step 4) further includes: depositing a second interfacial modifier on partial pores on one side of the solid electrolyte precursor, and then filling the partial pores on the side of the solid electrolyte precursor deposited with the second interfacial modifier with the second liquid metal, wherein the second interfacial modifier includes tungsten.

[0020] The present invention provides a battery, which includes the composite structure of the negative electrode and the solid electrolyte for the battery as described above or the composite structure of the negative electrode and the solid electrolyte for the battery obtained by the preparation method as described above.

[0021] The present invention provides a composite structure of a negative electrode and a solid electrolyte for a battery, a preparation method thereof, and an application thereof. By introducing a first liquid metal into the negative electrode sheet and a second liquid metal into the solid electrolyte, the first liquid metal and the second liquid metal are melted and fused at the interface between the solid electrolyte and the negative electrode sheet to form a solid bond, thereby tightly connecting the negative electrode sheet and the solid electrolyte, realizing the integration of the negative electrode sheet and the solid electrolyte, which is beneficial to reducing the interface resistance and also avoiding various problems caused by introducing a new interface layer in the prior art. In addition, the above-mentioned liquid metal can provide strong conductivity in the negative electrode, which is beneficial to reducing the use of conductive agents in the negative electrode material slurry. Description of the Drawings

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required to be used in the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0023] Figure 1 A microstructural schematic diagram of a composite structure of a negative electrode and a solid electrolyte for a battery provided for some embodiments;

[0024] Figure 2 A scanning electron microscope (SEM) image of a three-layer negative electrode active material layer provided for some embodiments;

[0025] Figure 3 A scanning electron microscope (SEM) image and an energy dispersive spectroscopy (EDS) image of the third layer of active material filled with tungsten provided for some embodiments ( Figure 3In Figure A, it is a scanning electron microscope (SEM) image of the surface of the electrode sheet after the third layer of active material is filled with tungsten, and in Figure B, it is an energy dispersive spectroscopy (EDS) image after the third layer of active material is filled with tungsten;

[0026] Figure 4 It is a scanning electron microscope (SEM) image of the third layer of active material filled with liquid metal gallium provided for some embodiments;

[0027] Figure 5 It is a comparison chart of the rate performance of the batteries of some embodiments and comparative examples;

[0028] Figure 6 It is a comparison chart of the cycling performance of the batteries of some embodiments and comparative examples;

[0029] Figure 7 It is a comparison chart of the impedance performance of the batteries of some embodiments and comparative examples;

[0030] Figure 8 It is a microscopic schematic diagram of the composite structure of the negative electrode and the solid electrolyte for the battery provided by the embodiments of the present invention. Detailed Embodiments

[0031] To enable those skilled in the art to better understand the solution of the present invention, the present invention will be further described in detail below. The following specific embodiments are only used to describe the principles and features of the present invention, and the examples are only used to explain the present invention, not to limit the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

[0032] The prior art mainly improves the interfacial contact between the solid electrolyte and the negative electrode by directly introducing an interfacial layer, but the improvement effect on the interfacial contact between the solid electrolyte and the negative electrode is limited, and it may even increase the overall resistance of the battery.

[0033] To overcome the defects in the prior art, the embodiments of the present invention provide a composite structure for the negative electrode and the solid electrolyte of a battery, including: a negative electrode sheet, including a negative electrode current collector and a negative electrode active material layer located on at least one functional surface of the negative electrode current collector, and the negative electrode active material layer includes a first liquid metal; a solid electrolyte, located on the surface of the negative electrode active material layer away from the negative electrode current collector, and the solid electrolyte includes a second liquid metal; the solid electrolyte and the negative electrode sheet are combined by metal connection at the interface, and the metal connection is a solid connection formed by melting the first liquid metal and the second liquid metal and fusing them at the interface.

[0034] According to research and analysis: introducing a first liquid metal into the negative electrode sheet and a second liquid metal into the solid electrolyte, melting the first liquid metal and the second liquid metal and fusing them at the interface between the solid electrolyte and the negative electrode sheet to form a solid bond, thereby tightly connecting the negative electrode sheet and the solid electrolyte, realizing the integration of the negative electrode sheet and the solid electrolyte, which is beneficial to reducing the interface resistance and avoiding various problems caused by introducing a new interface layer in the prior art. In addition, the above-mentioned liquid metal can provide strong conductivity inside the negative electrode, which is beneficial to reducing the use of conductive agents in the negative electrode material slurry.

[0035] Specifically, the above metal connection and combination can be understood as that in the part where the negative electrode sheet and the solid electrolyte are connected, the atoms of the first liquid metal and the second liquid metal are combined together, making the first liquid metal in the negative electrode sheet and the second liquid metal in the solid electrolyte merge into one, thereby strengthening the tight contact connection between the negative electrode sheet and the solid electrolyte, realizing the integration of the negative electrode sheet and the solid electrolyte, and helping to reduce the interface impedance.

[0036] In some embodiments, the first liquid metal includes one or more of gallium and gallium alloys. The above first liquid metal helps to stabilize the negative electrode interface, promote the uniform deposition of lithium, and alleviate the growth of lithium dendrites. For example, at room temperature, liquid metal gallium has a low lithium nucleation energy barrier. Introducing an interface layer of gallium (Ga) on the negative electrode current collector (such as copper foil) can reduce the overpotential of lithium metal nucleation from 112 mV to 64 mV, and it can repair the surface of lithium metal through the reversible phase transformation reaction of gallium solid-liquid, so it can stabilize the negative electrode interface, promote the uniform deposition of lithium, and alleviate the growth of lithium dendrites.

[0037] In some embodiments, the second liquid metal includes one or more of gallium and gallium alloys. These second liquid metals and the first liquid metal are solidly combined as described above, and their synergistic effect helps to increase the contact area of the negative electrode interface and reduce the interface impedance.

[0038] Among them, the gallium alloy can include gallium-indium alloy and / or gallium-indium-tin alloy.

[0039] The types of the above first liquid metal and second liquid metal can be the same or different. Preferably, the types of the first liquid metal and the second liquid metal are the same because due to the principle of like dissolves like, the same type of liquid metals are more uniformly mixed after hot pressing.

[0040] Such as Figure 8As shown, the negative electrode active material layer in the above-mentioned composite structure of the negative electrode and the solid electrolyte for the battery (the symmetric hierarchical porous structure of the negative electrode material and the solid electrolyte) may include N negative electrode active material layers, where N ≥ 3; among them, the (n + 1)-th negative electrode active material layer is located on the side of the n-th negative electrode active material layer away from the negative electrode current collector, 1 ≤ n < n + 1 ≤ N, that is, 1 ≤ n ≤ N - 1.

[0041] In some embodiments, part of the first liquid metal is located in the i-th negative electrode active material layer, and i = N.

[0042] It can be understood that the remaining first liquid metal is located at the interface between the negative electrode sheet and the solid electrolyte layer and is solid-state combined with the second liquid metal, so that the negative electrode sheet and the solid electrolyte are in close contact and connection, realizing the integration of the negative electrode sheet and the solid electrolyte and reducing the interface impedance.

[0043] In some embodiments, the remaining N - 1 negative electrode active material layers away from the negative electrode current collector may include a conductive lithiumophilic material (a metal lithium deposition inducing material). This helps to improve the conductivity within the negative electrode sheet, especially the conductivity (utilization rate) of the negative electrode active material away from the negative electrode current collector (i.e., closer to the solid electrolyte side), helps to solve the concentration polarization problem inside the negative electrode sheet and reduce the degree of concentration polarization, and also helps to induce uniform deposition of metallic lithium and avoid the appearance of lithium dendrites. This conductive lithiumophilic material has properties such as conducting electrons and facilitating the conduction of lithium ions.

[0044] Specifically, the conductive lithiumophilic material may include one or more of Al, Cu, Sn, Zn, Pb, Sb, Cd, Au, Bi, Ge.

[0045] The particle size of the above-mentioned conductive lithiumophilic material may be 10 - 200 nm. A conductive lithiumophilic material with an appropriate particle size helps to reduce the lithium nucleation overpotential, improve the electronic conductivity of the electrode sheet at the same time, and also helps to improve the energy density of the composite structure of the embodiments of the present invention.

[0046] Furthermore, in at least part of the regions of the remaining N - 1 negative electrode active material layers away from the negative electrode current collector, the mass percentage content of the conductive lithiumophilic material may show an increasing trend along the direction away from the negative electrode current collector, for example, gradually increasing, which helps to solve the concentration polarization problem inside the negative electrode sheet and reduce the degree of concentration polarization, and also helps to induce uniform deposition of metallic lithium and avoid the appearance of lithium dendrites.

[0047] Along the direction away from the negative electrode current collector, the porosity of the negative electrode active material layer shows an increasing trend, for example, gradually increasing, which helps metallic lithium to deposit inside the pores of the negative electrode active material layer, and the negative electrode structure will not change significantly due to the precipitation of metallic lithium, ensuring the overall stability of the negative electrode and at the same time suppressing the appearance of lithium dendrites.

[0048] In some embodiments, the porosity of the first negative electrode active material layer is 0.01% to 5%, the porosity of each layer in the intermediate negative electrode active material layer is 10% to 20%, and the porosity of the i-th negative electrode active material layer is 20% to 40%, where i = N. By controlling the porosity to meet the above range, it helps metallic lithium to deposit inside the pores of the third negative electrode active material layer, and the negative electrode structure will not change significantly due to the precipitation of metallic lithium, ensuring the overall stability of the negative electrode and suppressing the emergence of lithium dendrites at the same time.

[0049] The intermediate negative electrode active material layer includes the negative electrode active material layers between the first negative electrode active material layer and the i-th (i = N) negative electrode active material layer. For example, when N = 3, the intermediate negative electrode active material layer includes the second negative electrode active material layer; when N = 4, the intermediate negative electrode active material layer includes the second negative electrode active material layer and the third negative electrode active material layer.

[0050] In some embodiments, the thickness ratio Q1 of the first negative electrode active material layer to the negative electrode active material layer satisfies: 1 / N ≤ Q1 ≤ (4N + 1) / 5N, and the thickness ratio Q2 of each of the remaining N - 1 negative electrode active material layers to the negative electrode active material layer satisfies: 1 / 5N ≤ Q2 ≤ 1 / N. By controlling the thickness to meet the above range, it helps to provide a three-dimensional structure for accommodating lithium deposition without significantly reducing the energy density of the battery, that is, while providing a three-dimensional structure for accommodating lithium deposition, the battery still maintains a high energy density.

[0051] In some embodiments, the negative electrode active material layer further includes a first interface modifier, and the first interface modifier includes tungsten. The first interface modifier is beneficial to reducing the surface tension of the first liquid metal, improving its dispersibility in the negative electrode active material layer, and further helping to improve the fastening property of the connection between the first liquid metal and the second liquid metal, making the negative electrode sheet and the solid electrolyte in close contact and connection, realizing the integration of the negative electrode sheet and the solid electrolyte, and reducing the interface impedance.

[0052] Taking N = 3 as an example, the negative electrode active material layer is further explained as follows.

[0053] As Figure 1 shown, the negative electrode active material layer of the negative electrode sheet includes 3 layers of negative electrode active material layers. Along the direction away from the current collector, they are the first negative electrode active material layer, the second negative electrode active material layer, and the third negative electrode active material layer in sequence.

[0054] Furthermore, in the negative electrode active material layer with N = 3, the second negative electrode active material layer may include the above-mentioned conductive lithiumophilic material. That is, the above-mentioned conductive lithiumophilic material may be located in the second negative electrode active material layer, which helps to enhance the electronic conductivity of the negative electrode active material far from the negative electrode current collector, improve the utilization rate of the negative electrode active material, and at the same time induce excessive metallic lithium to deposit on the surface of the second negative electrode active material layer. And the above-mentioned third negative electrode active material layer includes a first liquid metal, that is, the first liquid metal is located in the above-mentioned third negative electrode active material layer, which can make the negative electrode sheet and the solid electrolyte in close contact and connection, realize the integration of the negative electrode sheet and the solid electrolyte, and reduce the interfacial impedance.

[0055] In addition, the thickness ratio of the above-mentioned first negative electrode active material layer to the negative electrode active material layer may be 1 / 3 to 13 / 15, the thickness ratio of the second negative electrode active material layer to the negative electrode active material layer may be 1 / 15 to 1 / 3, and the thickness ratio of the third negative electrode active material layer to the negative electrode active material layer may be 1 / 15 to 1 / 3. By controlling the thickness to meet the above range, it helps to provide a three-dimensional structure for accommodating lithium deposition while not significantly reducing the energy density of the battery, that is, while providing a three-dimensional structure for accommodating lithium deposition, the battery still maintains a high energy density.

[0056] To avoid internal short circuit of the battery, although the solid electrolyte in the embodiment of the present invention includes a second liquid metal, it can still play a role in blocking the flow of electrons. Specifically, the above-mentioned second liquid metal may be located in a partial area on the side of the solid electrolyte close to the negative electrode sheet. For example, if the thickness of the solid electrolyte along the direction from the solid electrolyte to the negative electrode sheet is set to 1 width, then the second liquid metal may be located in the area corresponding to 1 / 15 to 1 / 3 width on the side of the solid electrolyte close to the negative electrode sheet and is solidly combined with the first liquid metal, thus avoiding the conduction of electrons in the solid electrolyte, and at the same time enabling the negative electrode sheet and the solid electrolyte to be in close contact and connection, realizing the integration of the negative electrode sheet and the solid electrolyte, and reducing the interfacial impedance.

[0057] As Figure 8 shown, the above-mentioned solid electrolyte may include M solid electrolyte layers, M ≥ 3; wherein, the (m + 1)-th solid electrolyte layer is located on the side of the m-th solid electrolyte layer close to the negative electrode active material layer, 1 ≤ m < m + 1 ≤ M, that is, 1 ≤ m ≤ M - 1.

[0058] In some embodiments, part of the second liquid metal is located in the j-th solid electrolyte layer, and j = M. Filling the second liquid metal in the solid electrolyte layer close to the negative electrode active material layer helps to reduce the amount of the second liquid metal used, and at the same time can also realize the integration of the solid electrolyte and the negative electrode and reduce the impedance.

[0059] It is understandable that the remaining second liquid metal is located at the interface between the negative electrode sheet and the solid electrolyte layer and is solid-state combined with the first liquid metal, thereby avoiding the conduction of electrons in the solid electrolyte, enabling the negative electrode sheet and the solid electrolyte to be in close contact and connection, realizing the integration of the negative electrode sheet and the solid electrolyte, and reducing the interface impedance.

[0060] In some embodiments, the remaining M-1 layer solid electrolyte layer near the negative electrode active material layer may include an insulating lithiumophilic material. This helps to improve the ionic conduction rate in the solid electrolyte, solve the problem of slow ion transfer inside the solid-state battery, induce uniform deposition of metallic lithium, and avoid the appearance of lithium dendrites.

[0061] The above-mentioned insulating lithiumophilic material is a material that is insulating to electrons and helps the conduction of lithium ions, that is, the insulating lithiumophilic material has properties such as insulating electrons and facilitating the conduction of lithium ions.

[0062] Specifically, the insulating lithiumophilic material may include one or more of lithium fluoride (LiF), lithium nitride (Li3N), aluminum oxide (Al2O3), and zirconium oxide (ZrO2).

[0063] Furthermore, in at least some regions of the above-mentioned remaining M-1 layer solid electrolyte layer, the mass percentage content of the insulating lithiumophilic material may show an increasing trend in the direction close to the negative electrode sheet, for example, gradually increasing, which helps to improve the ionic conduction rate in the solid electrolyte, induce uniform deposition of metallic lithium, and avoid the appearance of lithium dendrites.

[0064] In the direction close to the negative electrode current collector, the porosity of the solid electrolyte shows an increasing trend, for example, gradually increasing, which helps the flow of liquid metal inside the pores, thereby enhancing the interfacial transport, and at the same time provides a storage space for the appearance of a large number of lithium dendrites, further preventing the dendrites from penetrating the electrolyte.

[0065] In some embodiments, the porosity of the first solid electrolyte layer is 0.01-5%, the porosity of each layer in the middle solid electrolyte layer is 10%-20%, and the porosity of the jth solid electrolyte layer is 20%-40%, where j = M. By controlling the porosity to meet the above range, it helps the flow of liquid metal inside the pores, thereby enhancing the interfacial transport, and at the same time provides a storage space for the appearance of a large number of lithium dendrites, further preventing the dendrites from penetrating the electrolyte.

[0066] The middle solid electrolyte layer includes the solid electrolyte layer between the first solid electrolyte layer and the jth (i = M) solid electrolyte layer. For example, when M = 3, the middle solid electrolyte layer includes the second solid electrolyte layer; when N = 4, the middle solid electrolyte layer includes the second solid electrolyte layer and the third solid electrolyte layer.

[0067] In some embodiments, the ratio Q3 of the thickness of the first solid electrolyte layer to the thickness of the solid electrolyte satisfies: 1 / M ≤ Q3 ≤ (4M + 1) / 5M, and the ratio Q4 of the thickness of each of the remaining M - 1 solid electrolyte layers to the thickness of the solid electrolyte satisfies: 1 / 5M ≤ Q4 ≤ 1 / M. By controlling the thickness to meet the above range, a small amount of solid electrolyte and the negative electrode sheet are integrated, reducing the interfacial impedance of the negative electrode while ensuring the sufficiency of the remaining solid electrolyte.

[0068] In some embodiments, the solid electrolyte further includes a second interface modifier, and the second interface modifier includes tungsten. The second interface modifier is beneficial to reducing the surface tension of the second liquid metal, improving its dispersibility in the negative electrode active material layer, and further contributing to improving the fastening property of the connection between the second liquid metal and the first liquid metal, enabling the negative electrode sheet and the solid electrolyte to be closely contacted and connected, realizing the integration of the negative electrode sheet and the solid electrolyte, and reducing the interfacial impedance.

[0069] Taking M = 3 as an example, the solid electrolyte is further explained as follows.

[0070] As Figure 1 shown, the solid electrolyte includes 3 solid electrolyte layers. Along the direction from the solid electrolyte to the negative electrode active material layer (negative electrode sheet), they are the first solid electrolyte layer, the second solid electrolyte layer, and the third solid electrolyte layer in sequence. Among them, the second solid electrolyte layer may include the above-mentioned insulating lithiumophilic material, that is, the above-mentioned insulating lithiumophilic material may be located in the second solid electrolyte layer, which helps to enhance the lithium ion transfer ability while further hindering electron transport, improving the electrochemical performance and stability of the battery; the above-mentioned third solid electrolyte layer may include the second liquid metal, that is, the second liquid metal is located in the third solid electrolyte layer, which can enable the negative electrode sheet and the solid electrolyte to be closely contacted and connected, realize the integration of the negative electrode sheet and the solid electrolyte, reduce the interfacial impedance, and can also avoid conducting electrons in the solid electrolyte.

[0071] In addition, the ratio of the thickness of the first solid electrolyte layer to the thickness of the solid electrolyte may be 1 / 3 - 13 / 15, the ratio of the thickness of the second solid electrolyte layer to the thickness of the solid electrolyte may be 1 / 15 - 1 / 3, and the ratio of the thickness of the third solid electrolyte layer to the thickness of the solid electrolyte may be 1 / 15 - 1 / 3. By controlling the thickness to meet the above range, a small amount of solid electrolyte (the third solid electrolyte layer) and the negative electrode sheet are integrated, reducing the interfacial impedance of the negative electrode while ensuring the sufficiency of the remaining solid electrolyte.

[0072] In some embodiments, through the symmetric hierarchical porous structure design of the solid electrolyte and the negative electrode sheet, the inner surface of the porous interface structure where the solid electrolyte and the negative electrode sheet are connected is connected by liquid metals (the first liquid metal and the second liquid metal), such as gallium and / or gallium alloy, which can realize the integration of the solid electrolyte and the negative electrode and reduce the adverse effects of solid-solid contact. At the same time, an insulating lithiumophilic material (a non-conductive lithiumophilic material) and a conductive lithiumophilic material are respectively introduced into the solid electrolyte and the negative electrode sheet on both sides of the liquid metal interface. Further, the content of the insulating lithiumophilic material in the hierarchical porous structure of the solid electrolyte shows an increasing trend from the positive electrode side to the negative electrode side, for example, gradually increasing, and the content of the conductive lithiumophilic material in the hierarchical porous structure of the negative electrode shows an increasing trend from the direction close to the current collector to the direction away from the current collector, for example, gradually increasing, which can promote lithium ion conduction, induce uniform lithium deposition inside the three-dimensional space structure of the integrated interface layer and the negative electrode active material layer, and effectively solve the problem of volume expansion caused by the deposition of metallic lithium on the porous current collector with low strength in the prior art, which helps to further improve the safety performance of the battery.

[0073] In addition, after the hierarchical pore structure of the negative electrode introduces a highly conductive liquid metal (such as gallium and / or gallium alloy), there is less negative electrode active material on the side in contact with the solid electrolyte, and the surrounding conductivity is strong, which can improve the utilization rate of the negative electrode active material far from the negative electrode current collector and help to solve the problem of concentration polarization inside the negative electrode material.

[0074] The embodiment of the present invention also provides a preparation method for the composite structure of the negative electrode and the solid electrolyte for the battery as described above, including: 1) Coating the negative electrode slurry on at least one functional surface of the negative electrode current collector, and after drying, forming a precursor of the negative electrode active material layer; 2) Filling the first liquid metal into some pores on the side of the precursor of the negative electrode active material layer away from the negative electrode current collector; 3) Pressing the solid electrolyte raw material to obtain a solid electrolyte precursor; 4) Filling the second liquid metal into some pores on one side of the solid electrolyte precursor; 5) Contacting the surface of the precursor of the negative electrode active material layer filled with the first liquid metal with the surface of the solid electrolyte precursor filled with the second liquid metal, and then performing hot pressing treatment to obtain the composite structure of the negative electrode and the solid electrolyte for the battery, wherein the temperature of the hot pressing treatment is 30-130 °C and the pressure is 0.1-20 MPa.

[0075] According to research and analysis: After filling the first liquid metal into some pores on the side of the precursor of the negative electrode active material layer away from the negative electrode current collector and filling the second liquid metal into some pores on one side of the solid electrolyte precursor respectively, under the action of hot pressing treatment at 30-80 °C, the first liquid metal and the second liquid metal melt and flow between the interfaces of the negative electrode sheet and the solid electrolyte to form a fluid interface layer. After solidification, a solid bonding region connecting the negative electrode sheet and the solid electrolyte can be formed, thereby enhancing the interface connection, tightly connecting the negative electrode sheet and the solid electrolyte, and helping to reduce the interfacial ion transfer impedance.

[0076] In the embodiments of the present invention, the process conditions for forming the precursor of the negative electrode active material layer and the precursor of the solid electrolyte in the above steps 1) and 3) are not particularly limited.

[0077] In step 2), the first liquid metal is filled into some pores on the side of the precursor of the negative electrode active material layer away from the negative electrode current collector, so that the first liquid metal infiltrates but does not completely fill the pores, which is beneficial to reserve space for lithium deposition, and further beneficial to the uniform deposition of lithium inside the three-dimensional space structure of the negative electrode active material layer, improving the safety performance of the battery.

[0078] Similarly, in step 4), the second liquid metal is filled into some pores on one side of the solid electrolyte precursor, so that the second liquid metal infiltrates but does not completely fill the pores, which is beneficial to reserve some three-dimensional space to accommodate a large number of unknown lithium dendrites, further preventing the risk of dendrite penetration through the electrolyte.

[0079] It can be understood that in step 5), at a temperature of 30-130 °C and a pressure of 0.1-20 MPa for the above hot pressing treatment (low-temperature heat preservation), the liquid metal (such as gallium and / or gallium alloy) is in a molten state, so that the liquid metal flows between the interfaces to connect the electrolyte and the negative electrode, and then tightly connects the negative electrode and the solid electrolyte, obtaining a composite structure integrating the negative electrode and the solid electrolyte, which is beneficial to the preparation of an integrated solid-state battery, conducive to solving the interface contact problem and reducing the interfacial ion transfer impedance.

[0080] In addition, the embodiments of the present invention do not limit the time of the above hot pressing treatment, as long as the first liquid metal and the second liquid metal can be melted and mixed with each other and are beneficial to tightly connecting the negative electrode sheet and the solid electrolyte, for example, it can be 10-180 min.

[0081] The above preparation method can obtain a composite structure in which the negative electrode and the solid electrolyte are tightly combined, which is beneficial to reducing the ion conduction impedance.

[0082] In some embodiments, step 1) includes: separately preparing N portions of negative electrode slurries, where N ≥ 3, and then coating the first portion of the negative electrode slurry on at least one functional surface of the negative electrode current collector. After drying, a precursor of the first negative electrode active material layer is formed. Then, the second portion of the negative electrode slurry is coated on the surface of the precursor of the first negative electrode active material layer. After drying, a precursor of the second negative electrode active material layer is formed. In this way, the coating and drying of N portions of negative electrode slurries are sequentially completed to form a precursor of the negative electrode active material layer with an N-layer structure.

[0083] Based on the above precursor of the negative electrode active material layer with an N-layer structure, a negative electrode active material layer with an N-layer structure can be prepared.

[0084] In some embodiments, step 1) further includes: after forming the precursor of the second negative electrode active material layer, filling a conductive lithiumophilic material into at least part of the pores of the precursor of the second negative electrode active material layer, and then preparing the precursor of the third negative electrode active material layer. In this way, the conductive lithiumophilic material is sequentially filled into the N - 1 layers of the precursor of the negative electrode active material layer far from the negative electrode current collector.

[0085] The conductive lithiumophilic material can include one or more of Al, Cu, Sn, Zn, Pb, Sb, Cd, Au, Bi, Ge, and the particle size of the conductive lithiumophilic material is 10 - 200 nm.

[0086] In some embodiments, step 2) includes: filling the first liquid metal into part of the pores of the i-th layer of the precursor of the negative electrode active material layer, where i = N. Filling the first liquid metal into the negative electrode active material layer close to the solid electrolyte helps reduce the amount of the first liquid metal used, and at the same time can also achieve the integration of the solid electrolyte and the negative electrode, reducing the impedance.

[0087] In some embodiments, the negative electrode slurry of the first negative electrode active material layer includes a negative electrode active material, a binder, and a conductive agent in a mass ratio of (80 - 99):(0.5 - 10):(0.5 - 10). This helps form a first negative electrode active material layer with a porosity of 0.01 - 5%.

[0088] Specifically, the negative electrode active material, the binder, and the conductive agent can be stirred and mixed in NMP (N-methylpyrrolidone) (for example, for 12 h) to obtain the negative electrode slurry of the first negative electrode active material layer.

[0089] Both the binder and the conductive agent in the negative electrode sheet can use conventional types in the art, and the embodiments of the present invention do not limit them. For example, the binder (adhesive or thickener) can include one or more of carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), and polyacrylic acid (PAA), and the conductive agent can include one or more of Super P, VGCF, and CNTs.

[0090] Furthermore, the negative electrode slurries of each layer in the intermediate negative electrode active material layer all include the negative electrode slurry of the first negative electrode active material layer and ammonium bicarbonate, where the mass ratio of the negative electrode active material to ammonium bicarbonate in the negative electrode slurry of the first negative electrode active material layer is (4 - 25):1. That is to say, the negative electrode slurries of each layer in the intermediate negative electrode active material layer are all prepared from the negative electrode slurry of the first negative electrode active material layer and ammonium bicarbonate.

[0091] Ammonium bicarbonate can decompose under the condition that the temperature is not lower than 60 °C, which helps to form a precursor of the intermediate negative electrode active material layer with a porosity of 20% - 30%, facilitating the filling of the conductive lithiumophilic material into its pores to form an intermediate negative electrode active material layer with a porosity of 10% - 20%.

[0092] The negative electrode slurry of the i-th layer of the negative electrode active material layer includes the negative electrode slurry of the first negative electrode active material layer and ammonium bicarbonate, where the mass ratio of the negative electrode active material to ammonium bicarbonate in the negative electrode slurry of the first negative electrode active material layer is (1 - 4):1, and i = N. That is to say, the negative electrode slurry of the i-th layer of the negative electrode active material layer is prepared from the negative electrode slurry of the first negative electrode active material layer and ammonium bicarbonate.

[0093] Ammonium bicarbonate can decompose under the condition that the temperature is not lower than 60 °C, which helps to form a precursor of the i(N)-th negative electrode active material layer with a porosity of 30% - 60%, facilitating the filling of the first liquid metal into its pores to form an i(N)-th negative electrode active material layer with a porosity of 20% - 40%.

[0094] In some embodiments, the ratio P1 of the mass of the first portion of the negative electrode slurry to the sum of the masses of the N portions of the negative electrode slurry satisfies: 1 / N ≤ P1 ≤ (4N + 1) / 5N, and the ratio P2 of the mass of the remaining N - 1 portions of the negative electrode slurry to the sum of the masses of the N portions of the negative electrode slurry all satisfies: 1 / 5N≤P2≤1 / N 。

[0095] The above-mentioned first portion of the negative electrode slurry is the negative electrode slurry corresponding to the first layer of the negative electrode active material layer, and the remaining N - 1 portions of the negative electrode slurry are the negative electrode slurries corresponding to the remaining N - 1 layers of the negative electrode active material layer.

[0096] Since the thickness ratios and mass ratios of the above-mentioned layers of the negative electrode active material layer are the same, that is, the ratios are the same. Therefore, by controlling the mass of the N portions of the negative electrode slurry to meet the above range, it helps to prepare N layers of the negative electrode active material layer with thickness ratios that meet the expectations.

[0097] In some embodiments, step 2) further includes depositing the first interfacial modifier on some pores on the side of the negative electrode active material layer precursor away from the negative electrode current collector, and then filling the first liquid metal into some pores on the side of the negative electrode active material layer precursor where the first interfacial modifier is deposited.

[0098] The above-mentioned first interfacial modifier includes a material having a high affinity with the first liquid metal. First, using the first interfacial modifier to cover the inner surface of the pores in the precursor part of the negative electrode active material layer, and then filling the first liquid metal, is beneficial to reducing the surface tension of the first liquid metal, improving its dispersibility in the negative electrode active material layer, and further contributing to improving the fastening of the connection between the first liquid metal and the second liquid metal, enabling the negative electrode sheet and the solid electrolyte to be in close contact and connection, realizing the integration of the negative electrode sheet and the solid electrolyte, and reducing the interfacial impedance.

[0099] Specifically, the above-mentioned first interfacial modifier may include tungsten. Tungsten (W) has a high affinity with the first liquid metal (such as gallium Ga and / or indium). First, using tungsten (W particles of Ga-affinitive material metal) to cover the inner surface of the pores in the precursor part of the negative electrode active material layer, and then filling the first liquid metal, is beneficial to reducing the surface tension of the first liquid metal, improving its dispersibility in the negative electrode active material layer, and further contributing to improving the fastening of the connection between the first liquid metal and the second liquid metal, enabling the negative electrode sheet and the solid electrolyte to be in close contact and connection, realizing the integration of the negative electrode sheet and the solid electrolyte, and reducing the interfacial impedance.

[0100] The particle size of the above-mentioned tungsten (W particles) can be 10 nm - 1 μm, which helps to reduce the surface tension with the liquid metal (such as Ga) and promote the uniform distribution of the liquid metal (such as Ga) on the surface of the negative electrode active material.

[0101] In specific implementation, at least one of thermal evaporation, magnetron sputtering, electron beam sputtering, spraying, solution immersion, and melt infiltration (such as melting at 250 - 270 °C in a vacuum environment) can be used to deposit tungsten on (cover) the pores on the side of the precursor of the negative electrode active material layer away from the negative electrode current collector.

[0102] Taking N = 3 as an example below, the preparation process of the precursor of the negative electrode active material layer is explained as follows.

[0103] The preparation process of the precursor of the negative electrode active material layer with a three-layer structure includes: mixing the negative electrode active material, binder, and conductive agent according to a mass ratio of (80-99):(0.5-10):(0.5-10) to obtain a first negative electrode slurry, coating the first negative electrode slurry on at least one functional surface of the negative electrode current collector, and after drying, forming a first negative electrode active material layer; mixing the first negative electrode slurry and ammonium bicarbonate (NH4HCO3) according to a mass ratio of the negative electrode active material and ammonium bicarbonate in the first negative electrode slurry of (4-25):1 to obtain a second negative electrode slurry, coating the second negative electrode slurry on the surface of the first negative electrode active material layer, and after drying, obtaining a precursor of the second negative electrode active material layer, and then filling at least part of the pores of the precursor of the second negative electrode active material layer with a conductive lithiumophilic material to form a second negative electrode active material layer, where the conductive lithiumophilic material includes one or more of Al, Cu, Sn, Zn, Pb, Sb, Cd, Au, Bi, Ge; mixing the first negative electrode slurry and ammonium bicarbonate according to a mass ratio of the negative electrode active material and ammonium bicarbonate in the first negative electrode slurry of (1-4):1 to obtain a third negative electrode slurry, coating the third negative electrode slurry on the surface of the second negative electrode active material layer, and after drying, forming a precursor of the third negative electrode active material layer, and further obtaining a precursor of the negative electrode active material layer with a three-layer structure.

[0104] It should be noted that in practical applications, the solid contents of the first negative electrode slurry, the second negative electrode slurry, and the third negative electrode slurry can be close to or the same, and all need to meet the conventional coating requirements of negative electrode slurries in the art. Then, on this basis, adjust the mass ratio of the first negative electrode slurry and ammonium bicarbonate (NH4HCO3) to obtain the second negative electrode slurry and the third negative electrode slurry.

[0105] Mixing the first negative electrode slurry and ammonium bicarbonate according to a mass ratio of the negative electrode active material and ammonium bicarbonate in the first negative electrode slurry of (4-25):1 to obtain a second negative electrode slurry, ammonium bicarbonate can decompose under the condition that the temperature is not lower than 60 °C (such as during the drying process), which helps to form a precursor of the second negative electrode active material layer with a porosity of 20%-30%, facilitating the filling of the conductive lithiumophilic material into its pores to form a second negative electrode active material layer with a porosity of 10%-20%. In the embodiments of the present invention, the filling amount of the above-mentioned conductive lithiumophilic material in the second negative electrode active material layer is not particularly limited, that is, the porosity of the second negative electrode active material layer is not particularly limited, but the above-mentioned conductive lithiumophilic material should be evenly dispersed in the second negative electrode active material layer as much as possible, which helps to improve the conductivity in the negative electrode sheet, and further helps to solve the concentration polarization problem inside the negative electrode sheet and reduce the degree of concentration polarization, and also helps to induce uniform deposition of metallic lithium and avoid the appearance of lithium dendrites.

[0106] In specific implementation, at least one of thermal evaporation, magnetron sputtering, electron beam sputtering, spraying, solution immersion, and melt infiltration (such as melting at 250-270 °C in a vacuum environment) can be used to fill at least part of the pores of the precursor of the second negative electrode active material layer with a conductive lithiumophilic material to form the second negative electrode active material layer.

[0107] The time for the process of filling the at least part of the pores of the precursor of the second negative electrode active material layer with the conductive lithiumophilic material should be appropriate to promote the uniform filling of the conductive lithiumophilic material, for example, it can be 10-12 h.

[0108] If the temperature of the material is too high after filling the at least part of the pores of the precursor of the second negative electrode active material layer with the conductive lithiumophilic material, it should be naturally cooled before subsequent operations are carried out.

[0109] After mixing the first negative electrode slurry and ammonium bicarbonate according to the mass ratio of the negative electrode active material to ammonium bicarbonate in the first negative electrode slurry being (1-4):1 to obtain a third negative electrode slurry, and then coating the third negative electrode slurry on the surface of the second negative electrode active material layer (double-layer negative electrode) and drying, ammonium bicarbonate can decompose under the condition of a temperature not lower than 60 °C, which helps to form a precursor of the third negative electrode active material layer with a porosity of 30%-60%, facilitating the filling of the first liquid metal into its pores to form a third negative electrode active material layer with a porosity of 20%-40%.

[0110] The embodiments of the present invention do not particularly limit the above drying conditions. For example, it can be dried at 50-60 °C for 2-3 h and then heated to 120-130 °C and dried for 11-12 h.

[0111] It can be understood that after the above first liquid metal is filled into the negative electrode active material layer, for example, part of the pores of the third negative electrode active material layer, the porosity of the third negative electrode active material layer decreases. For example, it can fill 30%-50% of the original porosity. In some embodiments, the porosity of the third negative electrode active material layer after filling the first liquid metal is 20%-40%.

[0112] In the embodiments of the present invention, the negative electrode current collector can include a copper foil and a carbon-coated copper foil.

[0113] In some embodiments, step 3) includes: respectively preparing M parts of solid electrolyte raw materials, M≥3, then pressing the first part of the solid electrolyte raw materials to form a precursor of the first solid electrolyte layer, then laying the second part of the solid electrolyte raw materials on the surface of the precursor of the first solid electrolyte layer, and then performing pressing treatment to form a precursor of the second solid electrolyte layer. In this way, the pressing treatment of M parts of solid electrolyte raw materials is sequentially completed to form a solid electrolyte precursor with an M-layer structure.

[0114] Based on the above-mentioned solid electrolyte precursor with an M-layer structure, a solid electrolyte layer with an M structure can be prepared.

[0115] In some embodiments, step 3) further includes: after forming the second solid electrolyte layer precursor, filling the at least partial pores of the second solid electrolyte layer precursor with an insulating lithiumophilic material, and then preparing the third solid electrolyte layer precursor. In this way, the insulating lithiumophilic material is sequentially filled in the M-1 layers close to the negative electrode active material layer.

[0116] The insulating lithiumophilic material may include one or more of lithium fluoride, lithium nitride, aluminum oxide, and zirconium oxide.

[0117] In some embodiments, step 4) includes: filling the second liquid metal in the partial pores of the j-th solid electrolyte layer precursor, where j = M. Filling the second liquid metal in the solid electrolyte layer close to the negative electrode active material layer helps reduce the amount of the second liquid metal used, and at the same time can also achieve the integration of the solid electrolyte and the negative electrode, reducing the impedance.

[0118] During the process of pressing the first portion of the solid electrolyte raw material, by controlling the pressure of the pressing process, it is helpful to obtain a first solid electrolyte layer with a porosity of 0.01% to 5%.

[0119] In some embodiments, the raw materials of each layer in the intermediate solid electrolyte layer include the raw materials of the first solid electrolyte layer and ammonium bicarbonate, and the mass ratio of the raw materials of the first solid electrolyte layer to ammonium bicarbonate is (4 to 25):1. That is, each layer in the intermediate solid electrolyte layer is prepared from the raw materials of the first solid electrolyte layer and ammonium bicarbonate.

[0120] Ammonium bicarbonate can decompose under the condition of a temperature not lower than 60°C, which helps to form a precursor of the intermediate solid electrolyte layer with a porosity of 20% to 30%, facilitating the filling of the insulating lithiumophilic material into its pores to form an intermediate solid electrolyte layer with a porosity of 10% to 20%.

[0121] In some embodiments, the j-th portion of the solid electrolyte raw material includes the raw materials of the first solid electrolyte layer and ammonium bicarbonate, where the mass ratio of the raw materials of the first solid electrolyte layer to ammonium bicarbonate is (1 to 4):1, and j = M. That is, the raw materials of the first solid electrolyte layer are prepared from the first portion of the solid electrolyte raw material and ammonium bicarbonate.

[0122] Ammonium bicarbonate can decompose under the condition of a temperature not lower than 60°C, which helps to form a precursor of the j-th (M) solid electrolyte layer with a porosity of 30% to 60%, facilitating the filling of the second liquid metal into its pores to form a j-th (M) solid electrolyte layer with a porosity of 20% to 40%.

[0123] In some embodiments, the ratio P3 of the mass of the first solid electrolyte raw material to the sum of the masses of M solid electrolyte raw materials satisfies: 1 / M ≤ P3 ≤ (4M + 1) / 5M, and the ratio P4 of the mass of the remaining M - 1 solid electrolyte layer raw materials to the sum of the masses of M solid electrolyte raw materials satisfies: 1 / 5M ≤ P4 ≤ 1 / M.

[0124] The first solid electrolyte raw material corresponds to the raw material of the first solid electrolyte layer, and the remaining M - 1 solid electrolyte layer raw materials correspond to the raw materials of the remaining M - 1 solid electrolyte layers.

[0125] Since the thickness ratio and mass ratio of the above-mentioned solid electrolyte layers are the same, that is, the ratio is the same. Therefore, by controlling the mass of N solid electrolyte raw materials to meet the above range, it helps to prepare M solid electrolyte layers with the thickness ratio of each layer meeting the expectation.

[0126] In some embodiments, step 4) further includes: depositing a second interfacial modifier on a part of the pores on one side of the solid electrolyte precursor, and then filling a second liquid metal into a part of the pores on the side of the solid electrolyte precursor where the second interfacial modifier is deposited.

[0127] The above-mentioned second interfacial modifier includes a material having a high affinity with the second liquid metal. First, using this second interfacial modifier to cover the inner surface of a part of the pores in the solid electrolyte precursor layer, and then filling the second liquid metal is beneficial to reducing the surface tension of the second liquid metal, improving its dispersibility in the solid electrolyte layer, and further helping to improve the fastening property of the connection between the second liquid metal and the first liquid metal, enabling the negative electrode sheet and the solid electrolyte to be in close contact and connection, realizing the integration of the negative electrode sheet and the solid electrolyte, and reducing the interfacial impedance.

[0128] Specifically, the above-mentioned second interfacial modifier may include tungsten. Tungsten (W) has a high affinity with the second liquid metal (such as gallium Ga and / or indium). First, using tungsten (metal W particles that are materials affinity with Ga) to cover the inner surface of a part of the pores in the solid electrolyte precursor, and then filling the second liquid metal is beneficial to reducing the surface tension of the second liquid metal, improving its dispersibility in the solid electrolyte, and further helping to improve the fastening property of the connection between the first liquid metal and the second liquid metal, enabling the negative electrode sheet and the solid electrolyte to be in close contact and connection, realizing the integration of the negative electrode sheet and the solid electrolyte, and reducing the interfacial impedance.

[0129] The particle size of the above-mentioned tungsten (metal W particles) can be 10 nm - 1 μm, which helps to reduce the surface tension with the liquid metal (such as Ga) and promote the uniform distribution of the liquid metal (such as Ga) on the surface of the negative electrode active material.

[0130] It is understandable that after the above-mentioned second liquid metal fills some pores of the solid electrolyte layer, the porosity of the part of the solid electrolyte layer filled with the second liquid metal decreases. In some embodiments, the porosity of the part of the solid electrolyte layer after filling with the second liquid metal is 20% to 40%.

[0131] Taking M = 3 as an example, the preparation process of the solid electrolyte precursor is explained as follows.

[0132] The preparation process of the solid electrolyte precursor with a three-layer structure includes: performing a first pressing treatment on the solid electrolyte to obtain a first solid electrolyte layer; mixing the solid electrolyte and ammonium bicarbonate in a mass ratio of (4 to 25):1, and then laying (such as dusting, covering or spreading) on the surface of the first solid electrolyte layer, and then performing a second pressing treatment to obtain a second solid electrolyte layer precursor, and then filling at least part of the pores (channels) of the second solid electrolyte layer precursor with an insulating lithiumophilic material, where the insulating lithiumophilic material includes one or more of lithium fluoride, lithium nitride, aluminum oxide, and zirconium oxide; mixing the solid electrolyte and ammonium bicarbonate in a mass ratio of (1 to 4):1, and then laying (such as dusting, covering or spreading) on the surface of the second solid electrolyte layer, and then performing a third pressing treatment to obtain the solid electrolyte precursor.

[0133] The above method of filling the insulating lithiumophilic material into the second solid electrolyte layer may include: drop-coating a solution containing the insulating lithiumophilic material onto at least part of the pores of the second solid electrolyte layer precursor, and then drying at 100 to 200 °C.

[0134] By controlling the pressure of the first pressing treatment, it is helpful to obtain a first solid electrolyte layer with a porosity of 0.01% to 5%.

[0135] After mixing the solid electrolyte and ammonium bicarbonate in a mass ratio of (4 to 25):1 and laying (such as covering) on the surface of the first solid electrolyte layer, and then performing a second pressing treatment, it is helpful to obtain a second solid electrolyte layer precursor with a porosity of 20% to 30%, and then it is convenient to fill at least part of the pores of the second solid electrolyte layer precursor with the insulating lithiumophilic material to form a second solid electrolyte layer with a porosity of 10% to 20%. In the embodiments of the present invention, the filling amount of the above insulating lithiumophilic material in the second solid electrolyte layer is not particularly limited, that is, the porosity of the second solid electrolyte layer is not particularly limited, but the above insulating lithiumophilic material should be evenly dispersed in the second solid electrolyte layer as much as possible, which helps to improve the ion conduction rate in the solid electrolyte, helps to induce uniform deposition of metallic lithium, and avoids the appearance of lithium dendrites.

[0136] The pressure of the above-mentioned second pressing treatment (which belongs to hot pressing treatment) can be 150-300 MPa, such as 150, 200, 300 MPa or the range composed of any two of them, and the temperature of the second pressing treatment can be 80-200 °C.

[0137] During specific implementation, after the above-mentioned second pressing treatment, the material can be kept warm at 90-100 °C for 10-12 h.

[0138] After mixing the solid electrolyte and ammonium bicarbonate according to the mass ratio of (1-4):1, it is laid (such as covered) on the surface of the second solid electrolyte layer, and then the third pressing treatment is carried out, which helps to form a precursor of the third solid electrolyte layer with a porosity of 30%-60%, facilitating the filling of the second liquid metal into its pores to form a third solid electrolyte layer with a porosity of 20%-40%.

[0139] The pressure of the above-mentioned third pressing treatment (hot pressing treatment) is 150-200 MPa, and the temperature of the third pressing treatment is 80-200 °C, such as 80, 100, 150, 200 °C or the range composed of any two of them.

[0140] In step 5), the process of bringing the surface of the precursor of the negative electrode active material layer filled with the first liquid metal into contact with the surface of the precursor of the solid electrolyte filled with the second liquid metal and then performing hot pressing treatment to obtain a composite structure of the negative electrode and the solid electrolyte for the battery may include: bringing the surface of the precursor of the negative electrode active material layer filled with the first liquid metal into contact with the surface of the precursor of the solid electrolyte filled with the second liquid metal, and then performing the first hot pressing treatment at 110-130 °C, such as 110, 120, 130 °C or the range composed of any two of them and 0.1-20 MPa, such as 0.1, 1, 5, 10, 20 MPa or the range composed of any two of them, and then performing the second hot pressing treatment at 30-70 °C, such as 30, 40, 50, 60, 70 °C or the range composed of any two of them and 0.1-20 MPa, such as 0.1, 1, 5, 10, 20 MPa or the range composed of any two of them, to obtain a composite structure of the negative electrode and the solid electrolyte for the battery.

[0141] It can be understood that the negative electrode active material in the above-mentioned embodiments of the present invention should not react with the liquid metal (such as one or more of gallium, indium, and tin), and specifically may include lithium titanate, Si, SiO x 、graphite, carbon black, graphene, etc.

[0142] The raw materials of the solid electrolyte can be of conventional types in the art, and the embodiments of the present invention do not limit it. For example, it may include sulfide electrolytes, oxide electrolytes, halide electrolytes.

[0143] An embodiment of the present invention provides a battery, which includes the above composite structure or the composite structure obtained by the above preparation method. Based on this composite structure, the above battery has corresponding performance, which will not be elaborated here.

[0144] It can be understood that the above battery further includes a positive electrode sheet or a counter electrode, such as ternary materials, lithium iron phosphate, lithium-rich manganese-based, lithium cobaltate, spinel lithium manganate, metallic lithium sheet, Li-In alloy.

[0145] The positive electrode sheet specifically includes a positive electrode current collector and a positive electrode active layer provided on the surface of the positive electrode current collector.

[0146] When specifically preparing the positive electrode sheet, for example, the positive electrode active material, the conductive agent and the binder can be dispersed in an appropriate amount of N-methylpyrrolidone (NMP) solvent, and sufficiently stirred and mixed to form a uniform positive electrode slurry; the positive electrode slurry is uniformly coated on the positive electrode current collector, and after drying, rolling and slitting, the positive electrode sheet is obtained. In a specific embodiment, the positive electrode active layer includes 70-99 wt% of the positive electrode active material, 0.5-15 wt% of the conductive agent, and 0.5-15 wt% of the binder by mass percentage. Further, it includes 80-98 wt% of the positive electrode active material, 1-10 wt% of the conductive agent, and 1-10 wt% of the binder.

[0147] Among them, the material of the positive electrode current collector can be at least one of aluminum foil and nickel foil; the conductive agent can be selected from at least one of carbon black, acetylene black, graphene, Ketjen black, and carbon fiber; the binder can be selected from at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polymers containing ethylene oxide, polyvinylpyrrolidone, and polyurethane.

[0148] Specifically, the positive electrode sheet, the above-mentioned composite structure of the negative electrode for the battery and the solid electrolyte are laminated and assembled into an all-solid-state battery.

[0149] The present invention will be further described below through specific examples and comparative examples. Unless otherwise specified, the reagents, materials and instruments used below are all conventional reagents, conventional materials and conventional instruments, which can be commercially purchased, and the reagents and materials involved can also be obtained by conventional synthesis methods.

[0150] Example 1

[0151] Preparation of negative electrode sheet

[0152] A binder was prepared by dissolving polyvinylidene fluoride (PVDF) in N-methylpyrrolidone (NMP). Then, conductive carbon black and lithium titanate (LTO) (D50 = 300 nm) were added in sequence, where the mass ratio of lithium titanate:conductive carbon black:PVDF was 8:1:1. After mixing and stirring for 12 h, the first negative electrode slurry was obtained. The first negative electrode slurry was coated on one functional surface of the copper foil and dried at 60 °C for 2 h, and then the temperature was raised to 120 °C and dried for 12 h to form a first negative electrode active material layer with a thickness of about 20 μm.

[0153] The first negative electrode slurry and ammonium bicarbonate (the negative electrode active material in the first negative electrode slurry, i.e., the above lithium titanate:ammonium bicarbonate in a mass ratio of 4:1) were mixed to obtain a second negative electrode slurry. The second negative electrode slurry was coated on the surface of the first negative electrode active material layer. After drying, a precursor of the second negative electrode active material layer with a thickness of 20 μm was obtained. Then, metal Sn particles with a D50 of 50 nm were evenly spread on the surface of the precursor of the second negative electrode active material layer, and the metal Sn was melted at a high temperature of 250 °C in a vacuum environment and completely filled the pores of the precursor of the second negative electrode active material layer. Subsequently, it was naturally cooled to form the second negative electrode active material layer.

[0154] The first negative electrode slurry and ammonium bicarbonate (the negative electrode active material in the first negative electrode slurry, i.e., the above lithium titanate:ammonium bicarbonate in a mass ratio of 4:1) were mixed to obtain a third negative electrode slurry. The third negative electrode slurry was coated on the surface of the second negative electrode active material layer. After drying, a precursor of the third negative electrode active material layer with a thickness of 20 μm was formed to obtain a precursor of the negative electrode active material layer.

[0155] The inner surface of the pores of the precursor of the third negative electrode active material layer was covered with metal W particles with a particle size of 20 nm by magnetron sputtering. Subsequently, liquid metal Ga was filled (infiltrated) into the pores of the precursor of the third negative electrode active material layer, that is, part of the pores on the side of the precursor of the negative electrode active material layer away from the negative electrode current collector, and the filling degree was 50% of the original porosity of the precursor of the third negative electrode active material layer.

[0156] Preparation of solid electrolyte

[0157] 50 mg of sulfide electrolyte Li6PS5Cl was subjected to the first pressing treatment to obtain a first solid electrolyte layer, where the pressure of the first pressing treatment was 1.5 t.

[0158] 50 mg of the sulfide electrolyte Li6PS5Cl and 12.5 mg of NH4HCO3 (mass ratio 4:1) were mixed evenly and then covered on the surface of the first solid electrolyte layer, followed by a second pressing process to obtain a precursor of the second solid electrolyte layer. The process of the second pressing included: hot pressing at 80 °C under a pressure of 200 MPa, then holding at 100 °C for 12 h. Then, a 6 mol / L LiF solution was drop-coated on the surface of the precursor of the second solid electrolyte layer to fill the pores of the precursor of the second solid electrolyte layer, and then dried at 120 °C to form the second solid electrolyte layer.

[0159] 50 mg of the sulfide electrolyte Li6PS5Cl and 50 mg of NH4HCO3 (mass ratio 1:1) were mixed evenly and then covered on the surface of the second solid electrolyte layer, followed by a third pressing process to form a precursor of the third solid electrolyte layer. The temperature of the third pressing was 100 °C and the pressure was 200 MPa.

[0160] The inner surface of the pores of the precursor of the third solid electrolyte layer was covered with metal W particles with a particle size of 20 nm by magnetron sputtering. Subsequently, liquid metal Ga was filled (infiltrated) into the pores of the precursor of the third solid electrolyte layer to form the third solid electrolyte layer, and the filling degree was 50% of the original porosity of the precursor of the third solid electrolyte layer.

[0161] Preparation of the composite structure of the negative electrode and the solid electrolyte for the battery (integrated preparation of the electrolyte and the negative electrode)

[0162] The surface of the negative electrode active material layer filled with Ga (the third negative electrode active material layer) was brought into contact with the surface of the solid electrolyte filled with Ga (the third solid electrolyte layer), and then hot pressing was carried out to obtain the composite structure of the negative electrode and the solid electrolyte for the battery. Among them, the process of the hot pressing included holding at 120 °C under a pressure of 5 MPa for 30 min to make the electrolyte and the negative electrode in close contact, and then adjusting to 60 °C and 0.5 MPa pressure and continuing for 120 min.

[0163] Battery preparation

[0164] The above-mentioned composite structure of the negative electrode and the solid electrolyte for the battery was combined with the Li-In alloy to prepare an all-solid-state battery.

[0165] Example 2

[0166] This example is basically the same as Example 1, the difference is that:

[0167] The thickness of the first negative electrode active material layer was 45 μm (accounting for 3 / 4 of the total thickness of the negative electrode active material layer), and the thicknesses of the second negative electrode active material layer and the third negative electrode active material layer were both 7.5 μm (accounting for 1 / 8 of the total thickness of the negative electrode active material layer).

[0168] Adjust the mass of the sulfide electrolyte Li6PS5Cl in the first solid electrolyte layer to 112.5 mg, and adjust the masses of Li6PS5Cl in the second and third solid electrolyte layers to 18.75 mg each; keep other conditions unchanged.

[0169] Example 3

[0170] This example is basically the same as Example 1, except that:

[0171] After mixing the first negative electrode paste and ammonium bicarbonate (the mass ratio of the negative electrode active material to ammonium bicarbonate in the first negative electrode paste is 25:1), the second negative electrode paste is obtained. After mixing the first negative electrode paste and ammonium bicarbonate (the mass ratio of the negative electrode active material to ammonium bicarbonate is 4:1), the third negative electrode paste is obtained. The mass ratio of the sulfide electrolyte to NH4HCO3 in the second solid electrolyte layer is 25:1, and the mass ratio of the sulfide electrolyte to NH4HCO3 in the third solid electrolyte layer is 4:1; keep other conditions unchanged.

[0172] Example 4

[0173] This example is basically the same as Example 1, except that:

[0174] The thickness of the first negative electrode active material layer is 45 μm (the ratio to the thickness of the solid electrolyte is 3 / 4), and the thicknesses of the second and third negative electrode active material layers are both 7.5 μm (the ratio to the thickness of the solid electrolyte is 1 / 8).

[0175] After mixing the first negative electrode paste and ammonium bicarbonate (the negative electrode active material in the first negative electrode paste is the above-mentioned lithium titanate: ammonium bicarbonate with a mass ratio of 25:1), the second negative electrode paste is obtained. After mixing the first negative electrode paste and ammonium bicarbonate (the negative electrode active material in the first negative electrode paste is the above-mentioned lithium titanate: ammonium bicarbonate with a mass ratio of 4:1), the third negative electrode paste is obtained.

[0176] Adjust the mass of the sulfide electrolyte in the first solid electrolyte layer to 112.5 mg, and adjust the masses of the sulfide electrolyte in the second and third solid electrolyte layers to 18.75 mg each;

[0177] In the second solid electrolyte layer, the mass ratio of the sulfide electrolyte to ammonium bicarbonate is 25:1.

[0178] In the third solid electrolyte layer, the mass ratio of the sulfide electrolyte to ammonium bicarbonate is 4:1; keep other conditions unchanged.

[0179] Example 5

[0180] This example is basically the same as Example 1, except that:

[0181] The thickness of the first negative electrode active material layer is 52 μm (the ratio to the thickness of the solid electrolyte is 13 / 15), and the thicknesses of the second negative electrode active material layer and the third negative electrode active material layer are both 4 μm (the ratio to the thickness of the solid electrolyte is 1 / 15).

[0182] After mixing the first negative electrode slurry and ammonium bicarbonate (the negative electrode active material in the first negative electrode slurry, i.e., the above-mentioned lithium titanate: ammonium bicarbonate is in a mass ratio of 15:1), the second negative electrode slurry is obtained. After mixing the first negative electrode slurry and ammonium bicarbonate (the negative electrode active material in the first negative electrode slurry, i.e., the above-mentioned lithium titanate: ammonium bicarbonate is in a mass ratio of 2:1), the third negative electrode slurry is obtained.

[0183] The mass of the sulfide electrolyte in the first solid electrolyte layer is adjusted to 100 mg, and the masses of the sulfide electrolytes in the second solid electrolyte layer and the third solid electrolyte layer are both adjusted to 25 mg.

[0184] In the second solid electrolyte layer, the mass ratio of the sulfide electrolyte to ammonium bicarbonate is 15:1.

[0185] In the third solid electrolyte layer, the mass ratio of the sulfide electrolyte to ammonium bicarbonate is 2:1; other conditions remain unchanged.

[0186] Example 6

[0187] This example is basically the same as Example 1, except that:

[0188] During the preparation of the negative electrode sheet, 1) ammonium bicarbonate is not added to both the second negative electrode active slurry and the third negative electrode active slurry; 2) metal Sn is not filled in the second negative electrode active material layer.

[0189] During the preparation of the solid electrolyte, 1) ammonium bicarbonate is not added to both the second solid electrolyte layer and the third solid electrolyte layer; 2) LiF solution is not filled in the second solid electrolyte layer.

[0190] Other conditions remain unchanged.

[0191] Example 7

[0192] This example is basically the same as Example 1, except that:

[0193] The thickness of the first negative electrode active material layer is 52 μm (the ratio to the thickness of the solid electrolyte is 13 / 15), and the thicknesses of the second negative electrode active material layer and the third negative electrode active material layer are both 4 μm (the ratio to the thickness of the solid electrolyte is 1 / 15).

[0194] After mixing the first negative electrode slurry and ammonium bicarbonate (the negative electrode active material in the first negative electrode slurry, i.e., the above-mentioned lithium titanate: ammonium bicarbonate, in a mass ratio of 1:1), the second negative electrode slurry is obtained. After mixing the first negative electrode slurry and ammonium bicarbonate (the negative electrode active material in the first negative electrode slurry, i.e., the above-mentioned lithium titanate: ammonium bicarbonate, in a mass ratio of 4:1), the third negative electrode slurry is obtained.

[0195] Adjust the mass of the sulfide electrolyte in the first solid electrolyte layer to 100 mg, and adjust the mass of the sulfide electrolyte in the second and third solid electrolyte layers to 25 mg each;

[0196] In the second solid electrolyte layer, the mass ratio of the sulfide electrolyte to ammonium bicarbonate is 1:1.

[0197] In the third solid electrolyte layer, the mass ratio of the sulfide electrolyte to ammonium bicarbonate is 4:1; other conditions remain unchanged.

[0198] Example 8

[0199] This example is basically the same as Example 1, except that:

[0200] Replace metallic gallium with a gallium-indium alloy (the mass ratio of the two is 1:1);

[0201] Replace Sn with Cu;

[0202] Replace LiF with lithium nitride;

[0203] Other conditions remain unchanged.

[0204] Example 9

[0205] This example is basically the same as Example 1, except that:

[0206] The negative electrode active material layer includes 4 layers of negative electrode active material layers, and the solid electrolyte includes 4 layers of solid electrolyte layers. That is, on the basis of Example 1, the first negative electrode slurry and ammonium bicarbonate are mixed according to the mass ratio of the negative electrode active material in the first negative electrode slurry, i.e., the above-mentioned lithium titanate: ammonium bicarbonate, of 1:2 to obtain a fourth negative electrode slurry. The fourth negative electrode slurry is coated on the surface of the third negative electrode active material layer and dried to form a fourth active material layer with a thickness of 1 / 10 of the first active material layer, obtaining a precursor of the negative electrode active material layer. The sulfide electrolyte Li6PS5Cl and ammonium bicarbonate are mixed according to the mass ratio of 1:2 and then covered on the surface of the third solid electrolyte layer. After pressing treatment, a fourth solid electrolyte layer with a thickness of 1 / 10 of the first solid electrolyte layer is formed, obtaining a precursor of the solid electrolyte. Then, the same amount of metal Ga is introduced into the fourth solid electrolyte layer and the fourth negative electrode active material layer according to the method of Example 1. Then, a composite structure of the negative electrode and the solid electrolyte for the battery and the battery are prepared according to the method of Example 1. Other conditions remain unchanged.

[0207] Example 10

[0208] This example is basically the same as Example 1, with the difference being:

[0209] In the preparation of the first negative electrode slurry: the mass ratio of lithium titanate: conductive carbon black: PVDF is 8:2:1, that is, the content of the conductive agent carbon black in the negative electrode sheet is increased;

[0210] Other conditions remain unchanged.

[0211] Example 11

[0212] This example is basically the same as Example 1, with the difference being:

[0213] No metal Sn particles are added to the second negative electrode active material layer. Specifically, the preparation process of the second negative electrode active material layer includes mixing the first negative electrode slurry and ammonium bicarbonate (the mass ratio of the negative electrode active material in the first negative electrode slurry, i.e., the above-mentioned lithium titanate: ammonium bicarbonate, is 4:1) to obtain a second negative electrode slurry. The second negative electrode slurry is coated on the surface of the first negative electrode active material layer and dried to obtain a second negative electrode active material layer with a thickness of 20 μm. Other conditions remain unchanged.

[0214] Example 12

[0215] This example is basically the same as Example 1, with the difference being:

[0216] The LiF solution is not added to the second solid electrolyte layer. Specifically, the preparation process of the second solid electrolyte layer includes mixing 50 mg of sulfide electrolyte Li6PS5Cl and 12.5 mg of NH4HCO3 (mass ratio 4:1) evenly and then covering the surface of the first solid electrolyte layer, followed by a second pressing process to obtain the second solid electrolyte layer. The second pressing process includes: hot pressing at 80 °C under a pressure of 200 MPa and then holding at 100 °C for 12 h; other conditions remain unchanged.

[0217] Example 13

[0218] This example is basically the same as Example 1, except that:

[0219] After obtaining the precursor of the negative electrode active material layer, instead of using metal W particles, liquid metal Ga is directly filled. Specifically, liquid metal Ga is filled in (infiltrated into) the pores of the third precursor of the negative electrode active material layer, that is, in some of the pores on the side of the precursor of the negative electrode active material layer away from the negative electrode current collector, and the filling degree is 50% of the original porosity of the third precursor of the negative electrode active material layer;

[0220] Other conditions remain unchanged.

[0221] Example 14

[0222] This example is basically the same as Example 1, except that:

[0223] After obtaining the precursor of the third solid electrolyte layer, liquid metal Ga is directly filled in (infiltrated into) the pores of the third solid electrolyte layer precursor. Specifically, liquid metal Ga is filled in (infiltrated into) the pores of the third solid electrolyte layer precursor to form the third solid electrolyte layer, and the filling degree is 50% of the original porosity of the third solid electrolyte layer precursor;

[0224] Other conditions remain unchanged.

[0225] Example 15

[0226] This example is basically the same as Example 1, except that:

[0227] The negative electrode active material layer includes four layers of negative electrode active material layers, and the solid electrolyte includes four layers of solid electrolyte layers. That is, on the basis of Example 1, the first negative electrode slurry and ammonium bicarbonate are mixed according to the mass ratio of the negative electrode active material in the first negative electrode slurry, i.e., the above-mentioned lithium titanate: ammonium bicarbonate, being 4:1 to obtain a fourth negative electrode slurry. The fourth negative electrode slurry is coated on the surface of the third negative electrode active material layer and dried to form a fourth active material layer with the same thickness as the first active material layer, obtaining a precursor of the negative electrode active material layer; the sulfide electrolyte Li6PS5Cl and ammonium bicarbonate are mixed according to a mass ratio of 4:1 and then covered on the surface of the third solid electrolyte layer, and after pressing treatment, a fourth solid electrolyte layer with the same thickness as the first solid electrolyte layer is formed, obtaining a precursor of the solid electrolyte; then, the same amount of metal Ga is introduced into the fourth solid electrolyte layer and the fourth negative electrode active material layer according to the method of Example 1; then, a composite structure of the negative electrode and the solid electrolyte for the battery and the battery are prepared according to the method of Example 1; other conditions remain unchanged.

[0228] Example 16

[0229] This example is basically the same as Example 15, the differences being:

[0230] Adjust the ratio of the mass of the first portion of the negative electrode slurry to the sum of the masses of the 4 portions of the negative electrode slurry to be 17 / 20, and the ratios of the masses of the remaining 3 portions of the negative electrode slurry to the sum of the masses of the 4 portions of the negative electrode slurry are all 1 / 20, so that the ratio of the thickness of the first negative electrode active material layer to the negative electrode active material layer is 17 / 20, and the ratios of the thicknesses of the remaining 3 layers of the negative electrode active material layer to the negative electrode active material layer are all 1 / 20 respectively;

[0231] Adjust the ratio of the mass of the first portion of the solid electrolyte raw material to the sum of the masses of the 4 portions of the solid electrolyte raw material to be 17 / 20, and the ratios of the masses of the remaining 3 portions of the solid electrolyte raw material to the sum of the masses of the 4 portions of the solid electrolyte raw material are all 1 / 20, so that the ratio of the thickness of the first solid electrolyte layer to the solid electrolyte is 17 / 20, and the ratios of the thicknesses of the remaining 3 layers of the solid electrolyte layer to the solid electrolyte are all 1 / 20 respectively;

[0232] Other conditions remain unchanged.

[0233] Example 17

[0234] This example is basically the same as Example 15, the differences being:

[0235] Adjust the ratio of the mass of the first portion of the negative electrode slurry to the sum of the masses of the 4 portions of the negative electrode slurry to 19 / 20, and the ratios of the masses of the remaining 3 portions of the negative electrode slurry to the sum of the masses of the 4 portions of the negative electrode slurry are all 1 / 60, so that the thickness ratio of the first negative electrode active material layer to the negative electrode active material layer is 19 / 20, and the thickness ratios of the remaining 3 layers of the negative electrode active material layer to the negative electrode active material layer are all 1 / 60;

[0236] Adjust the ratio of the mass of the first portion of the solid electrolyte raw material to the sum of the masses of the 4 portions of the solid electrolyte raw material to 19 / 20, and the ratios of the masses of the remaining 3 portions of the solid electrolyte raw material to the sum of the masses of the 4 portions of the solid electrolyte raw material are all 1 / 60, so that the thickness ratio of the first solid electrolyte layer to the solid electrolyte is 19 / 20, and the thickness ratios of the remaining 3 layers of the solid electrolyte layer to the solid electrolyte are all 1 / 60;

[0237] Keep other conditions unchanged.

[0238] Comparative Example 1

[0239] This comparative example is basically the same as Example 1, the differences are as follows:

[0240] Liquid metal Ga is not introduced into the third solid electrolyte layer and the third negative electrode active material layer; keep other conditions unchanged.

[0241] Comparative Example 2

[0242] This comparative example is basically the same as Example 1, the differences are as follows:

[0243] The thickness of the first negative electrode active material layer is 52 μm (the thickness ratio to the solid electrolyte is 13 / 15), and the thicknesses of the second negative electrode active material layer and the third negative electrode active material layer are both 4 μm (the thickness ratio to the solid electrolyte is 1 / 15),

[0244] After mixing the first negative electrode slurry and ammonium bicarbonate (the negative electrode active material in the first negative electrode slurry, i.e., the above-mentioned lithium titanate: ammonium bicarbonate is in a mass ratio of 15:1), the second negative electrode slurry is obtained. After mixing the first negative electrode slurry and ammonium bicarbonate (the negative electrode active material in the first negative electrode slurry, i.e., the above-mentioned lithium titanate: ammonium bicarbonate is in a mass ratio of 2:1), the third negative electrode slurry is obtained.

[0245] Adjust the mass of the sulfide electrolyte in the first solid electrolyte layer to 100 mg, and adjust the masses of the sulfide electrolytes in the second solid electrolyte layer and the third solid electrolyte layer to 25 mg each;

[0246] In the second solid electrolyte layer, the mass ratio of the sulfide electrolyte to ammonium bicarbonate is 15:1,

[0247] In the third solid electrolyte layer, the mass ratio of the sulfide electrolyte to ammonium bicarbonate is 2:1;

[0248] No liquid metal Ga is introduced into the third solid electrolyte layer and the third negative electrode active material layer;

[0249] Other conditions remain unchanged.

[0250] Test Examples

[0251] Test the rate performance, cycle performance, and impedance of the batteries of the above-mentioned examples and comparative examples:

[0252] Rate performance (10C / 1C): First, at room temperature, the battery is activated by charging and discharging at 0.1C for the first cycle, and then the rate tests are carried out by charging and discharging at 1C / 2C / 5C / 10C respectively (the results are shown in Figure 5 );

[0253] Capacity retention rate (%) after 500 cycles at 4C: First, at room temperature, the battery is activated by charging and discharging at 0.1C for the first cycle, and then the cycle test is carried out by charging and discharging at 4C (the results are shown in Figure 6 );

[0254] Impedance: After the battery is cycled 500 times, it is charged to 50% SOC for electrochemical impedance spectroscopy test (EIS test), and the test frequency range is 50 mHz - 1 MHz (the results Figure 7 );

[0255] The porosity of each negative electrode active material layer / solid electrolyte layer is detected by the gas adsorption method;

[0256] The thickness ratio of each negative electrode active material layer to the negative electrode active material layer, and the thickness ratio of each solid electrolyte layer to the solid electrolyte: Detected using a micrometer.

[0257] Test Results

[0258] Table 1

[0259]

[0260]

[0261] Table 2 Thickness ratio of each negative electrode active material layer to the negative electrode active material layer, thickness ratio of each solid electrolyte layer to the solid electrolyte

[0262]

[0263] Table 3 Electrochemical Performance

[0264]

[0265]

[0266] Analyze Tables 1, 2, and 3:

[0267] The data of Examples 1-5, Example 8, Example 10, Example 15, Example 16, and Comparative Examples 1-2 show that each negative electrode active material layer and solid electrolyte layer have appropriate thickness and porosity, which is beneficial to improving the rate performance and cycling performance of the battery and reducing the impedance. Among them, appropriately increasing the porosity is beneficial to introducing an appropriate amount of conductive lithiumophilic material or insulating lithiumophilic material in the negative electrode active material layer or solid electrolyte layer, which is beneficial to enhancing the rate performance and cycling performance and reducing the impedance. Moreover, appropriately increasing the porosity makes the negative electrode active material layer have more pores, which can accommodate more metal lithium deposition and relieve the swelling of the negative electrode active material layer.

[0268] The data of Example 1, Example 6, Example 11, and Example 12 show that appropriately increasing the porosity is beneficial to introducing an appropriate amount of conductive lithiumophilic material or insulating lithiumophilic material in the negative electrode active material layer or solid electrolyte layer, which is beneficial to enhancing the rate performance and cycling performance and reducing the impedance.

[0269] The data of Example 1 and Example 7 show that along the direction away from the negative electrode current collector, the porosity of the negative electrode active material layer shows an increasing trend, which helps to enhance the rate performance and cycling performance and reduce the impedance. The reason is that along the direction away from the negative electrode current collector, the increasing porosity of the negative electrode active material layer helps metal lithium to deposit better inside the pores of the negative electrode active material layer, and the negative electrode structure will not change significantly due to the precipitation of metal lithium, ensuring the overall stability of the negative electrode and suppressing the emergence of lithium dendrites. In addition, along the direction close to the negative electrode current collector, the porosity of the solid electrolyte shows an increasing trend, which also helps to enhance the rate performance and cycling performance and reduce the impedance. The reason is that along the direction close to the negative electrode current collector, the increasing porosity of the solid electrolyte helps the flow of liquid metal inside the pores, thereby enhancing the interfacial transport and providing storage space for the emergence of a large number of lithium dendrites, further preventing dendrites from penetrating the electrolyte;

[0270] The data of Example 9, Example 15, and Example 17 show that in the four-layer negative electrode active material layer or four-layer solid electrolyte layer, adjusting the thickness ratio of each layer within an appropriate range helps to enhance the rate performance and cycling performance and reduce the impedance;

[0271] The data of Example 10 show that more conductive agents will enhance the side reactions of sulfide electrolytes, thus affecting the cycling performance of the battery. In addition, due to the introduction of liquid metal Ga, the reduction of conductive agents has no obvious adverse effect on the impedance of the battery.

[0272] In addition, Figure 1This is a microscopic schematic diagram of the three-layer negative electrode active material layer provided by the embodiments of the present invention, serving as a schematic model for the pore design of the layered structure of the three-layer negative electrode active material layer (electrode material) provided by this embodiment;

[0273] Figure 2 This is an SEM image of the three-layer negative electrode active material (including lithium titanate LTO) layer provided by the embodiments of the present invention, Figure 2 near the current collector at the lower part, from Figure 2 it can be seen that the pores of the negative electrode active material show an increasing trend in the direction from the position near the current collector to the position far from the current collector;

[0274] Figure 3 This is an SEM image (left) and an EDS image (right) of the surface of the electrode sheet after the third-layer active material is filled with tungsten provided by the embodiments of the present invention, Figure 3 where A is the scanning electron microscope (SEM) image of the surface of the electrode sheet after the third-layer active material is filled with tungsten, and B is the energy dispersive spectrum (EDS) of the third-layer active material filled with tungsten. It can be seen that the surface of the electrode sheet is loose, indicating a relatively high porosity. The EDS image shows that the metal tungsten W is evenly distributed in the electrode sheet;

[0275] Figure 4 This is an SEM image of the third-layer active material filled with liquid metal gallium provided by the embodiments of the present invention. It can be seen that the liquid metal (liquid state metal) can infiltrate the inside of the electrode sheet and completely cover the surface of the negative electrode particles;

[0276] Figure 5 This is a comparison chart of the rate performance of the batteries of the embodiments and comparative examples of the present invention, proving that the electrode sheets and solid electrolytes with appropriate porosity and thickness distribution can provide high ion and electron conduction rates while taking into account the capacity, which is beneficial to the improvement of the rate performance;

[0277] Figure 6 This is a comparison chart of the cycle performance of the batteries of the embodiments and comparative examples of the present invention, proving that the electrode sheets and solid electrolytes with appropriate porosity and thickness distribution can maintain the structural stability while taking into account the capacity, showing good cycle performance;

[0278] Figure 7 This is a comparison chart of the impedance performance of the batteries of the embodiments and comparative examples of the present invention. By comparing the impedance data, it can be proved that the introduction of liquid metal Ga can significantly reduce the impedance of the electrode sheet, which is beneficial to the performance of the battery.

[0279] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A composite structure for the negative electrode and solid electrolyte of a battery, characterized in that, Comprising: A negative electrode sheet, including a negative electrode current collector and a negative electrode active material layer located on at least one functional surface of the negative electrode current collector, the negative electrode active material layer including a first liquid metal; A solid electrolyte, located on the surface of the negative electrode active material layer away from the negative electrode current collector, the solid electrolyte including a second liquid metal; The solid electrolyte and the negative electrode sheet are combined by metal connection at the interface, and the metal connection is a solid connection formed by melting the first liquid metal and the second liquid metal and fusing them at the interface.

2. The composite structure for the negative electrode and solid electrolyte of a battery according to claim 1, characterized in that, The first liquid metal includes one or more of gallium and gallium alloys; And / or, the second liquid metal includes one or more of gallium and gallium alloys.

3. The composite structure for the negative electrode and solid electrolyte of a battery according to claim 1 or 2, characterized in that, The negative electrode active material layer includes N layers of negative electrode active material layers, N≥3; wherein, the (n + 1)th negative electrode active material layer is located on the side of the nth negative electrode active material layer away from the negative electrode current collector, 1≤n≤N - 1; And / or, the solid electrolyte includes M layers of solid electrolyte layers, M≥3; wherein, the (m + 1)th solid electrolyte layer is located on the side of the mth solid electrolyte layer close to the negative electrode active material layer, 1≤m≤M - 1.

4. The composite structure for the negative electrode and the solid electrolyte of a battery according to claim 3, wherein Part of the first liquid metal is located in the ith layer of the negative electrode active material layer, and i = N; And / or, part of the second liquid metal is located in the jth layer of the solid electrolyte layer, and j = M.

5. The composite structure for the negative electrode and solid electrolyte of a battery according to claim 3 or 4, characterized in that, The N - 1 layers of negative electrode active material layers away from the negative electrode current collector include a conductive lithiumophilic material, the conductive lithiumophilic material includes one or more of Al, Cu, Sn, Zn, Pb, Sb, Cd, Au, Bi, Ge, and the particle size of the conductive lithiumophilic material is 10 - 200nm; And / or, the M - 1 layers of solid electrolyte layers close to the negative electrode active material layer include an insulating lithiumophilic material, the insulating lithiumophilic material includes one or more of lithium fluoride, lithium nitride, aluminum oxide, and zirconium oxide.

6. The composite structure for the negative electrode and solid electrolyte of a battery according to claim 4, characterized in that, The porosity of the first negative electrode active material layer is 0.01% - 5%, the porosity of each layer in the middle negative electrode active material layer is 10% - 20%, and the porosity of the ith negative electrode active material layer is 20% - 40%, i = N; And / or, the porosity of the first solid electrolyte layer is 0.01% - 5%, the porosity of each layer in the middle solid electrolyte layer is 10% - 20%, and the porosity of the jth solid electrolyte layer is 20% - 40%, j = M.

7. The composite structure of the negative electrode and the solid electrolyte for a battery according to any one of claims 3 - 6, wherein The ratio Q1 of the thickness of the first negative electrode active material layer to the thickness of the negative electrode active material layer satisfies: 1 / N≤Q1≤(4N + 1) / 5N, and the ratio Q2 of the thickness of each of the remaining N - 1 layers of the negative electrode active material layer to the thickness of the negative electrode active material layer satisfies: 1 / 5N≤Q2≤1 / N; And / or, the ratio Q3 of the thickness of the first solid electrolyte layer to the thickness of the solid electrolyte satisfies: 1 / M≤Q3≤(4M + 1) / 5M, and the ratio Q4 of the thickness of each of the remaining M - 1 layers of the solid electrolyte layer to the thickness of the solid electrolyte satisfies: 1 / 5M≤Q4≤1 / M.

8. The composite structure of the negative electrode and the solid electrolyte for a battery according to any one of claims 1-7, characterized in that the negative electrode active material layer further comprises a first interfacial modifier, and the first interfacial modifier comprises tungsten; and / or, the solid electrolyte further comprises a second interfacial modifier, and the second interfacial modifier comprises tungsten.

9. A method for preparing a composite structure of a negative electrode and a solid electrolyte for a battery according to any one of claims 1-8, characterized in that, Comprising: 1) Coating a negative electrode slurry on at least one functional surface of a negative electrode current collector, and after drying, forming a precursor of a negative electrode active material layer; 2) Filling a first liquid metal into some pores on the side of the precursor of the negative electrode active material layer away from the negative electrode current collector; 3) Performing a pressing treatment on a solid electrolyte raw material to obtain a solid electrolyte precursor; 4) Filling a second liquid metal into some pores on one side of the solid electrolyte precursor; 5) Contacting the surface of the precursor of the negative electrode active material layer filled with the first liquid metal with the surface of the solid electrolyte precursor filled with the second liquid metal, and then performing a hot pressing treatment to obtain the composite structure of the negative electrode and the solid electrolyte for the battery, wherein the temperature of the hot pressing treatment is 30-130 °C and the pressure is 0.1-20 MPa.

10. The preparation method according to claim 9, characterized in that step 1) comprises: separately preparing N portions of negative electrode slurries, N≥3, then coating the first portion of the negative electrode slurry on at least one functional surface of the negative electrode current collector, and after drying, forming a first precursor of the negative electrode active material layer, then coating the second portion of the negative electrode slurry on the surface of the first precursor of the negative electrode active material layer, and after drying, forming a second precursor of the negative electrode active material layer, and so on, successively completing the coating and drying of the N portions of the negative electrode slurries to form the precursor of the negative electrode active material layer having an N-layer structure; and / or, step 3) comprises: separately preparing M portions of solid electrolyte raw materials, M≥3, then performing a pressing treatment on the first portion of the solid electrolyte raw material to form a first precursor of the solid electrolyte layer, then laying the second portion of the solid electrolyte raw material on the surface of the first precursor of the solid electrolyte layer, and then performing a pressing treatment to form a second precursor of the solid electrolyte layer, and so on, successively completing the pressing treatment of the M portions of the solid electrolyte raw materials to form the solid electrolyte precursor having an M-layer structure.

11. The preparation method according to claim 10, characterized in that step 2) comprises: filling the first liquid metal into some pores of the i-th layer of the precursor of the negative electrode active material layer, i = N; and / or, step 4) comprises: filling the second liquid metal into some pores of the j-th solid electrolyte layer precursor, j = M.

12. The preparation method according to claim 10 or 11, characterized in that Step 1) further includes: after forming the precursor of the second negative electrode active material layer, filling at least part of the pores of the precursor of the second negative electrode active material layer with a conductive lithiophilic material, and then preparing the precursor of the third negative electrode active material layer. In this way, the conductive lithiophilic material is sequentially filled into the precursors of the N-1 layer of negative electrode active material layers away from the negative electrode current collector. The conductive lithiophilic material includes one or more of Al, Cu, Sn, Zn, Pb, Sb, Cd, Au, Bi, and Ge, and the particle size of the conductive lithiophilic material is 10-200 nm; And / or, Step 3) further includes: after forming the precursor of the second solid electrolyte layer, filling at least part of the pores of the precursor of the second solid electrolyte layer with an insulating lithiophilic material, and then preparing the precursor of the third solid electrolyte layer. In this way, the insulating lithiophilic material is sequentially filled into the precursors of the M-1 layer close to the negative electrode active material layer. The insulating lithiophilic material includes one or more of lithium fluoride, lithium nitride, aluminum oxide, and zirconium oxide.

13. The preparation method according to claim 11, wherein The negative electrode slurry of the first negative electrode active material layer includes a negative electrode active material, a binder, and a conductive agent with a mass ratio of (80-99):(0.5-10):(0.5-10); the negative electrode slurry of each layer in the intermediate negative electrode active material layer includes the negative electrode slurry of the first negative electrode active material layer and ammonium bicarbonate, where the mass ratio of the negative electrode active material to ammonium bicarbonate in the negative electrode slurry of the first negative electrode active material layer is (4-25):1; the negative electrode slurry of the i-th negative electrode active material layer includes the negative electrode slurry of the first negative electrode active material layer and ammonium bicarbonate, where the mass ratio of the negative electrode active material to ammonium bicarbonate in the negative electrode slurry of the first negative electrode active material layer is (1-4):1, i = N; And / or, the raw materials of each layer in the intermediate solid electrolyte layer include the raw materials of the first solid electrolyte layer and ammonium bicarbonate, where the mass ratio of the raw materials of the first solid electrolyte layer to ammonium bicarbonate is (4-25):1; the raw materials of the j-th solid electrolyte layer include the raw materials of the first solid electrolyte layer and ammonium bicarbonate, where the mass ratio of the raw materials of the first solid electrolyte layer to ammonium bicarbonate is (1-4):1, j = M.

14. The preparation method according to any one of claims 10-13, wherein The ratio P1 of the mass of the first portion of the negative electrode slurry to the sum of the masses of the N portions of the negative electrode slurry satisfies: 1 / N ≤ P1 ≤ (4N + 1) / 5N, and the ratio P2 of the mass of each of the remaining N-1 portions of the negative electrode slurry to the sum of the masses of the N portions of the negative electrode slurry satisfies: 1 / 5N ≤ P2 ≤ 1 / N; And / or, the ratio P3 of the mass of the first portion of the solid electrolyte raw material to the sum of the masses of the M portions of the solid electrolyte raw material satisfies: 1 / M ≤ P3 ≤ (4M + 1) / 5M, and the ratio P4 of the mass of each of the remaining M-1 portions of the solid electrolyte layer raw material to the sum of the masses of the M portions of the solid electrolyte raw material satisfies: 1 / 5M ≤ P4 ≤ 1 / M.

15. The preparation method according to any one of claims 9-14, characterized in that, Step 2) further includes depositing a first interfacial modifier on partial pores on the side of the negative electrode active material layer precursor away from the negative electrode current collector, and then filling the partial pores on the side of the negative electrode active material layer precursor deposited with the first interfacial modifier with the first liquid metal, wherein the first interfacial modifier includes tungsten; And / or, step 4) further includes: depositing a second interfacial modifier on partial pores on one side of the solid electrolyte precursor, and then filling the partial pores on the side of the solid electrolyte precursor deposited with the second interfacial modifier with the second liquid metal, wherein the second interfacial modifier includes tungsten.

16. A battery, characterized in that, The battery includes the composite structure of the negative electrode and the solid electrolyte for a battery according to any one of claims 1-8 or the composite structure of the negative electrode and the solid electrolyte for a battery obtained by the preparation method according to any one of claims 9-15.

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