A composite negative electrode sheet, a preparation method thereof, and a all-solid-state lithium-ion battery

Abstract

The present invention relates to the technical field of lithium batteries, and specifically discloses a composite negative electrode sheet, a preparation method thereof, and a all-solid-state lithium-ion battery. The composite negative electrode sheet sequentially includes a current collector layer, a negative electrode layer 1, a negative electrode layer 2, and an electrolyte layer from bottom to top; the thickness of the negative electrode layer 1 is 30 to 50 μm; the thickness of the negative electrode layer 2 is 10 to 50 μm and the thickness of the negative electrode layer 2 is less than that of the negative electrode layer 1. By preparing a thicker negative electrode layer 1 on the side close to the current collector layer and using a negative electrode active material and an electrolyte with smaller particle sizes, the present invention ensures that the composite negative electrode can have a higher density; a thinner negative electrode layer 2 is prepared on the side close to the electrolyte layer, and a negative electrode active material and an electrolyte with larger particle sizes are used to make it have a higher porosity; the electrolyte layer uses an electrolyte with smaller particle sizes so that it can better embed into the voids of the negative electrode layer 2, thereby obtaining a composite negative electrode sheet with a higher density and better interface contact between the negative electrode layer and the electrolyte layer.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and particularly relates to a composite negative electrode sheet, a preparation method thereof, and a all-solid-state lithium-ion battery. Background Art

[0002] The high energy density, excellent cycle stability, low self-discharge, and weak memory effect of lithium-ion batteries have made them an important part of the mobile electronic product and new energy electric vehicle markets. With the continuous research and update in the battery field, the highest energy density of lithium-ion batteries can already exceed 400 Wh / kg.

[0003] However, traditional lithium-ion batteries still have unstable safety hazards such as easy leakage and combustion. Therefore, safer solid-state batteries have begun to enter the public eye as the most promising new generation of batteries. In order to achieve high-performance solid-state battery products, developing solid electrolytes with excellent electrochemical properties is the key to solid-state batteries. With the continuous development of new solid electrolyte materials, the efficient design of their electrodes greatly affects the electrochemical performance of solid-state batteries.

[0004] Therefore, it is necessary to provide a composite negative electrode sheet, a preparation method thereof, and a all-solid-state lithium-ion battery to solve the difficulty of high densification of the solid-state battery electrode sheet and improve the contact performance at the interface between the negative electrode and the electrolyte layer. Summary of the Invention

[0005] The present invention aims to solve at least one of the technical problems existing in the above-mentioned prior art. Therefore, the present invention provides a composite negative electrode sheet, a preparation method thereof, and a all-solid-state lithium-ion battery to solve the difficulty of high densification of the solid-state battery electrode sheet and improve the contact performance at the interface between the negative electrode and the electrolyte layer.

[0006] The first aspect of the present invention provides a composite negative electrode sheet.

[0007] Specifically, the composite negative electrode sheet sequentially includes a current collector layer, a negative electrode layer 1, a negative electrode layer 2, and an electrolyte layer from bottom to top;

[0008] The thickness of the negative electrode layer 1 is 30-50 μm;

[0009] The thickness of the negative electrode layer 2 is 10-50 μm and the thickness of the negative electrode layer 2 is less than that of the negative electrode layer 1.

[0010] Preferably, the thickness of the negative electrode layer 1 is 35-45 μm.

[0011] More preferably, the thickness of the negative electrode layer 1 is 40 μm.

[0012] Preferably, the thickness of the negative electrode layer 2 is 20-40 μm.

[0013] More preferably, the thickness of the negative electrode layer 2 is 30 μm.

[0014] Preferably, the thickness of the electrolyte layer is 10 - 50 μm.

[0015] Even more preferably, the thickness of the electrolyte layer is 10 - 30 μm.

[0016] Preferably, the current collector layer is a metal foil.

[0017] More preferably, the metal foil is any one of aluminum foil, copper foil, nickel foil, iron foil, and stainless steel.

[0018] Even more preferably, the aluminum foil is carbon-coated aluminum foil.

[0019] Preferably, the material of the negative electrode layer 1 includes negative electrode active material A, electrolyte A, conductive agent A, and binder A; the material of the negative electrode layer 2 includes negative electrode active material B, electrolyte B, conductive agent B, and binder B; the material of the electrolyte layer includes electrolyte C and binder C; wherein the types of the negative electrode active material A and the negative electrode active material B are the same but the particle size is different; the types of the electrolyte A, the electrolyte B, and the electrolyte C are the same but the particle size is different; the types of the conductive agent A and the conductive agent B are the same but the addition amount is different; the types of the binder A, the binder B, and the binder C are the same but the addition amount is different.

[0020] More preferably, the negative electrode active material A includes graphite.

[0021] More preferably, the negative electrode active material B includes graphite.

[0022] More preferably, the electrolyte A includes a sulfide electrolyte.

[0023] More preferably, the electrolyte B includes a sulfide electrolyte.

[0024] More preferably, the electrolyte C includes a sulfide electrolyte.

[0025] Even more preferably, the sulfide electrolyte includes at least one of Li3PS4, Li4P2S6, or Li 7-a PS 6-a Y a where Y is at least one of Cl, Br, and I, and the value of a is 0.5 - 2. This type of electrolyte material is relatively soft, and the contact performance of the solid-solid interface can be improved by external physical pressure.

[0026] Preferably, the Li 7-a PS 6-a Y ais at least one of Li6PS5Cl, Li6PS5Br, and Li6PS5I.

[0027] More preferably, the conductive agent A includes vapor-grown carbon fiber (VGCF).

[0028] More preferably, the conductive agent B includes vapor-grown carbon fiber (VGCF).

[0029] More preferably, the binder A includes hydrogenated styrene-butadiene block copolymer (SEBS).

[0030] More preferably, the binder B includes hydrogenated styrene-butadiene block copolymer (SEBS).

[0031] More preferably, the binder C includes hydrogenated styrene-butadiene block copolymer (SEBS).

[0032] Preferably, the mass ratio of the negative electrode active material A to the electrolyte A, the conductive agent A, and the binder A is 60-90:10-40:1-5:1.

[0033] More preferably, the mass ratio of the negative electrode active material A to the electrolyte A, the conductive agent A, and the binder A is 65-75:25-35:1-5:1.

[0034] Even more preferably, the mass ratio of the negative electrode active material A to the electrolyte A, the conductive agent A, and the binder A is 70:30:1:1.

[0035] Preferably, the mass ratio of the negative electrode active material B to the electrolyte B, the conductive agent B, and the binder B is 30-45:5-20:0.5-2.5:1.

[0036] More preferably, the mass ratio of the negative electrode active material B to the electrolyte B, the conductive agent B, and the binder B is 35-45:10-15:0.5-1:1.

[0037] Even more preferably, the mass ratio of the negative electrode active material B to the electrolyte B, the conductive agent B, and the binder B is 40:10:0.5:1.

[0038] Preferably, the ratio of D50 of the negative electrode active material A to D50 of the negative electrode active material B is 1:1.2-5.

[0039] More preferably, the ratio of D50 of the negative electrode active material A to D50 of the negative electrode active material B is 1:2-3.

[0040] Even more preferably, the ratio of D50 of the negative electrode active material A to D50 of the negative electrode active material B is 1:2.

[0041] Preferably, the ratio of the D50 of electrolyte A to the D50 of electrolyte B is 1:1.2 to 5.

[0042] More preferably, the ratio of the D50 of electrolyte A to the D50 of electrolyte B is 1:2 to 3.

[0043] Even more preferably, the ratio of the D50 of electrolyte A to the D50 of electrolyte B is 1:2.

[0044] Preferably, the ratio of the D50 of electrolyte B to the D50 of electrolyte C is 1.2 to 5:1.

[0045] More preferably, the ratio of the D50 of electrolyte B to the D50 of electrolyte C is 2 to 3:1.

[0046] Even more preferably, the ratio of the D50 of electrolyte B to the D50 of electrolyte C is 2:1. Smaller electrolyte particles can be better embedded into the negative electrode layer 2.

[0047] Preferably, the mass ratio of electrolyte C to binder C is 95 to 99.5:0.5 to 5.

[0048] More preferably, the mass ratio of electrolyte C to binder C is 99 to 99.5:0.5 to 1.

[0049] Even more preferably, the mass ratio of electrolyte C to binder C is 99:1.

[0050] The second aspect of the present invention provides a method for preparing a composite negative electrode sheet.

[0051] Specifically, it includes the following steps:

[0052] S1, Weigh the materials of the negative electrode layer 1, mix and disperse them to obtain the coating slurry 1;

[0053] S2, Coat the coating slurry 1 on the current collector layer and dry it to obtain the negative electrode layer 1;

[0054] S3, Weigh the materials of the negative electrode layer 2, mix and disperse them to obtain the coating slurry 2;

[0055] S4, Coat the coating slurry 2 on the negative electrode layer 1 and dry it to obtain the negative electrode layer 2;

[0056] S5, Weigh the materials of the electrolyte layer, mix and disperse them to obtain the coating slurry 3;

[0057] S6, Coat the coating slurry 3 on the negative electrode layer 2 and dry it to obtain the composite negative electrode sheet.

[0058] The third aspect of the present invention provides an all-solid-state lithium-ion battery.

[0059] Specifically, the all-solid-state lithium-ion battery includes the composite negative electrode sheet provided by the first aspect.

[0060] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0061] In the present invention, the thickness and particle size of the material are designed in combination in the interlayer direction: a thicker negative electrode layer 1 is prepared on the side close to the current collector layer, and a negative electrode active material and an electrolyte with smaller particle size are used to ensure a higher density of the composite negative electrode; a thinner negative electrode layer 2 is prepared on the side close to the electrolyte layer, and a negative electrode active material and an electrolyte with larger particle size are used to make it have a higher porosity; an electrolyte with smaller particle size is used in the electrolyte layer to better embed into the voids of the negative electrode layer 2, so as to obtain a composite negative electrode sheet with a higher density and better interfacial contact between the negative electrode layer and the electrolyte layer. Description of the Drawings

[0062] Figure 1 It is a schematic structural diagram of the composite negative electrode sheet of Embodiment 1 of the present invention;

[0063] Figure 2 It is a graph of the impedance test results of Embodiment 1 of the present invention and Comparative Example 1. Detailed Embodiments

[0064] In order to make those skilled in the art more clearly understand the technical solutions described in the present invention, the following embodiments are listed for illustration. It should be noted that the following embodiments do not limit the scope of protection required by the present invention.

[0065] The raw materials, reagents or devices used in the following embodiments can be obtained from conventional commercial channels or can be obtained by existing known methods without special instructions.

[0066] Embodiment 1

[0067] A composite negative electrode sheet, its preparation method and an all-solid-state lithium-ion battery.

[0068] The preparation process of the composite negative electrode sheet includes the following steps:

[0069] S1, Weigh the materials for the negative electrode layer 1, where the mass ratio of each material is negative electrode active material (graphite): electrolyte (Li3PS4): vapor-grown carbon fiber (VGCF): hydrogenated styrene-butadiene block copolymer (SEBS) = 70:30:1:1. First, premix graphite, Li3PS4 and VGCF, then add xylene solvent for kneading. Control the solid content at 35% during the early kneading. After kneading is completed, add 5% of SEBS glue solution to disperse the materials to obtain the coating slurry 1.

[0070] S2. Use a scraper to apply the coating slurry 1 on the carbon-coated aluminum foil with a thickness of 12 μm. The coated electrode sheet is placed under vacuum conditions and dried at 60 °C to obtain the negative electrode layer 1 with a thickness of 40 μm.

[0071] S3. Weigh the materials for the negative electrode layer 2. The negative electrode active material and electrolyte used in the negative electrode layer 2 are the same as those in the negative electrode layer 1 in terms of materials, but the particle sizes of both the negative electrode active material and electrolyte used in the negative electrode layer 2 are larger than those of the materials in the negative electrode layer 1. Specifically, the ratio of the D50 of the negative electrode active material in the negative electrode layer 1 to the D50 of the negative electrode active material in the negative electrode layer 2 is 1:2. The ratio of the D50 of the electrolyte in the negative electrode layer 1 to the D50 of the electrolyte in the negative electrode layer 2 is 1:2. The mass ratio of each material is negative electrode active material (graphite): electrolyte (Li3PS4): conductive agent (VGCF): binder (SEBS) = 40:10:0.5:1. First, premix graphite, Li3PS4, and VGCF, and then add xylene solvent for kneading. Control the solid content at 45% during the initial kneading. After kneading is completed, add 5% of the SEBS glue solution to disperse the materials to obtain the coating slurry 2.

[0072] S4. Use a 60-μm scraper to apply the coating slurry 2 on the negative electrode layer 1, control the thickness of the negative electrode layer 2 to be 30 μm, and the coated electrode sheet is placed under vacuum conditions and dried at 60 °C to obtain the negative electrode layer 2.

[0073] S5. Weigh the materials for the electrolyte layer. The particle size of the electrolyte in the electrolyte layer is smaller than that of the electrolyte in the negative electrode layer 2. Specifically, the ratio of the D50 of the electrolyte in the negative electrode layer 2 to the D50 of the electrolyte in the electrolyte layer is 2:1. The mass ratio of each material in the electrolyte layer is Li3PS4:SEBS = 99:1. First, add 8% of the SEBS glue solution to Li3PS4, control the initial solid content at 65%, and perform low-speed premix kneading. After kneading is completed, add xylene solvent to disperse the materials, which can reduce the initial solid content and adjust the viscosity to 60% for facilitating the subsequent coating of the electrolyte layer to obtain the coating slurry 3.

[0074] S6. Apply the coating slurry 3 on the negative electrode layer 2, control the thickness to be 20 μm, and after coating is completed, place it under vacuum conditions and dry at 60 °C to obtain the composite negative electrode sheet.

[0075] All-solid-state lithium-ion battery:

[0076] The positive electrode is a ternary positive electrode, the electrolyte layer is a sulfide electrolyte, the negative electrode is a composite negative electrode sheet, and a single-layer solid-state soft-pack assembly is carried out to obtain an all-solid-state lithium-ion battery.

[0077] Comparative Example 1

[0078] Composite negative electrode sheet, its preparation method and all-solid-state lithium-ion battery.

[0079] The preparation process of the composite negative electrode sheet includes the following steps:

[0080] S1, Weigh the materials for the negative electrode layer. The mass ratio of each material is negative electrode active material (graphite): electrolyte (Li3PS4): vapor-grown carbon fiber (VGCF): hydrogenated styrene-butadiene block copolymer (SEBS) = 70:30:1:1. First, premix graphite, Li3PS4, and VGCF, and then add xylene solvent for kneading. Control the solid content at 40% during the initial kneading. After kneading is completed, add 5% of SEBS glue solution to disperse the materials, and obtain the coating slurry for the negative electrode layer.

[0081] S2, Use a scraper to coat the coating slurry for the negative electrode layer on the aluminum foil coated with carbon with a thickness of 12 μm. The coated electrode sheet is placed under vacuum conditions and dried at 60 °C to obtain the negative electrode layer.

[0082] S3, Weigh the materials for the electrolyte layer. The particle size of the electrolyte in the electrolyte layer is smaller than that of the electrolyte in the negative electrode layer. Specifically, the ratio of D50 of the electrolyte in the negative electrode layer to D50 of the electrolyte in the electrolyte layer is 2:1. The mass ratio of each material in the electrolyte layer is Li3PS4:SEBS = 99:1. First, add 8% of SEBS glue solution to Li3PS4, control the initial solid content at 65%, and perform low-speed premix kneading. After kneading is completed, add xylene solvent to disperse the materials, which can reduce the initial solid content and adjust the viscosity to 60% at the same time, and obtain the coating slurry for the electrolyte layer.

[0083] S4, Coat the coating slurry for the electrolyte layer on the negative electrode layer, control the thickness at 20 μm, and place it under vacuum conditions and dry at 60 °C after coating to obtain the composite negative electrode sheet.

[0084] All-solid-state lithium-ion battery:

[0085] The positive electrode is a ternary positive electrode, the electrolyte layer is a sulfide electrolyte, and the negative electrode is the composite negative electrode sheet prepared in Comparative Example 1. Single-layer solid-state soft-pack assembly is carried out to obtain the all-solid-state lithium-ion battery.

[0086] Comparative Example 2

[0087] Composite negative electrode sheet, its preparation method and all-solid-state lithium-ion battery.

[0088] The difference between the preparation process of the composite negative electrode sheet in Comparative Example 2 and that in Example 1 is that the thickness of the negative electrode layer 2 in Comparative Example 2 is greater than that of the negative electrode layer 1. The thickness of the negative electrode layer 1 is 20 μm, and the thickness of the negative electrode layer 2 is 30 μm.

[0089] All-solid-state lithium-ion battery:

[0090] The positive electrode is a ternary positive electrode, the electrolyte layer is a sulfide electrolyte, and the negative electrode is a composite negative electrode sheet prepared in Comparative Example 2. A single-layer solid-state soft-pack assembly is carried out to obtain an all-solid-state lithium-ion battery.

[0091] Comparative Example 3

[0092] Composite negative electrode sheet, its preparation method and all-solid-state lithium-ion battery.

[0093] The difference between the preparation process of the composite negative electrode sheet and that of Example 1 is that the thickness of the negative electrode layer 2 in Comparative Example 3 is equal to the thickness of the negative electrode layer 1, where the thickness of the negative electrode layer 1 is 30 μm and the thickness of the negative electrode layer 2 is 30 μm.

[0094] All-solid-state lithium-ion battery:

[0095] The positive electrode is a ternary positive electrode, the electrolyte layer is a sulfide electrolyte, and the negative electrode is a composite negative electrode sheet prepared in Comparative Example 3. A single-layer solid-state soft-pack assembly is carried out to obtain an all-solid-state lithium-ion battery.

[0096] Battery impedance performance test:

[0097] The test method refers to electrochemical impedance spectroscopy, and the test results are as Figure 2 shown. The impedance of the all-solid-state lithium-ion battery prepared in Example 1 of the present invention is lower, and the impedance of the all-solid-state lithium-ion battery prepared in Comparative Example 1 of the present invention is higher. The impedance of the all-solid-state lithium-ion batteries prepared in Comparative Examples 2 to 3 is also higher than that in Example 1.

[0098] The preferred specific embodiments of the present invention have been described in detail above. It should be understood that those of ordinary skill in the art can make many modifications and variations based on the concept of the present invention without creative work. Therefore, any technical solutions obtained by those skilled in the art in the technical field of the present invention through logical analysis, reasoning or limited experiments based on the concept of the present invention on the basis of the prior art, such as any modifications, equivalent replacements, improvements, etc., should be within the protection scope determined by the claims.

Claims

1. A composite negative electrode sheet, characterized in that: The composite negative electrode sheet includes, from bottom to top, a current collector layer, a negative electrode layer 1, a negative electrode layer 2, and an electrolyte layer; The thickness of the negative electrode layer 1 is 30 to 50 μm; The thickness of the negative electrode layer 2 is 10-50 μm and the thickness of the negative electrode layer 2 is less than that of the negative electrode layer 1; The materials of the negative electrode layer 1 include negative electrode active material A, electrolyte A, conductive agent A, and binder A; the materials of the negative electrode layer 2 include negative electrode active material B, electrolyte B, conductive agent B, and binder B; the materials of the electrolyte layer include electrolyte C and binder C; wherein the negative electrode active material A and the negative electrode active material B are of the same type and have different particle sizes; the electrolyte A, electrolyte B, and electrolyte C are of the same type and have different particle sizes; the conductive agent A and the conductive agent B are of the same type and have different addition amounts; the binder A, binder B, and binder C are of the same type and have different addition amounts; The ratio of D50 of the negative electrode active material A to D50 of the negative electrode active material B is 1:1.2-5; The ratio of D50 of electrolyte A to D50 of electrolyte B is 1:1.2-5; The ratio of D50 of the electrolyte B to D50 of the electrolyte C is 1.2 to 5:

1.

2. The composite negative electrode sheet according to claim 1, characterized in that: The mass ratio of the negative electrode active material A to the electrolyte A, the conductive agent A and the binder A is 60-90:10-40:1-5:

1.

3. The composite negative electrode sheet according to claim 1, characterized in that: The mass ratio of the negative electrode active material B to the electrolyte B, the conductive agent B, and the binder B is 30-45:5-20:0.5-2.5:

1.

4. The composite negative electrode sheet according to claim 1, characterized in that: The mass ratio of the electrolyte C to the binder C is 95-99.5:0.5-5.

5. The method for preparing the composite negative electrode sheet according to any one of claims 1 to 4, characterized in that: The following steps are involved: S1, weighing materials for negative electrode layer 1, mixing and dispersing to prepare coating slurry 1; S2, coating the coating slurry 1 on the current collector layer, and drying to obtain the negative electrode layer 1; S3, weighing the materials of the negative electrode layer 2, mixing and dispersing them to prepare a coating slurry 2; S4, coating the coating slurry 2 on the negative electrode layer 1, and drying to obtain the negative electrode layer 2; S5, weighing the materials for the electrolyte layer, mixing and dispersing them to prepare a coating slurry 3; S6, coating the coating slurry 3 on the negative electrode layer 2, and drying it to obtain a composite negative electrode sheet.

6. An all-solid-state lithium-ion battery, characterized in that: The all-solid-state lithium-ion battery comprises the composite negative electrode sheet according to any one of claims 1 to 4.

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