Solid-state battery

Abstract

The application provides a solid-state battery, which comprises a negative electrode sheet, the negative electrode sheet comprising a current collector, a first coating layer and a second coating layer, the second coating layer being arranged on at least one side surface of the current collector, and the first coating layer being arranged on the surface of the second coating layer; the first coating layer comprises silicon particles; and the second coating layer comprises silicon particles and lithium alloy particles. The lithium contained in the lithium alloy particles can make up for the active lithium consumed in the formation of an SEI film during the first charging of the solid-state battery, improve the coulomb efficiency of the first cycle of the solid-state battery, and further improve the capacity and energy density of the solid-state battery. The second coating layer comprising the lithium alloy particles and the silicon particles is arranged between the first coating layer and the current collector, so that the second coating layer comprising the lithium alloy particles and the silicon particles is prevented from being directly in contact with a solid-state electrolyte layer, and the reaction and heat release of the two during the assembly of the solid-state battery are avoided, and safety problems are caused.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, and specifically relates to a solid-state battery. Background Technology

[0002] With the increasingly widespread application of batteries, the energy density of existing batteries is far from meeting the needs, making it imperative to improve the energy density of current batteries. Replacing existing batteries with new materials is one way to increase battery energy density. Silicon anodes have a theoretical specific capacity of 3500 mAh / g, nearly ten times that of the current mainstream graphite anodes. Replacing graphite with silicon anodes can significantly improve the energy density of existing batteries.

[0003] However, silicon anodes undergo significant volume changes (~300%) during cycling, leading to silicon particle pulverization, exposing fresh surfaces that come into contact with the liquid electrolyte and form a new SEI film. This process consumes the electrolyte and active lithium, resulting in short battery cycle life and hindering the application of silicon anodes in batteries.

[0004] Using solid electrolytes instead of liquid electrolytes can effectively solve the above problems.

[0005] However, the electrochemical window of existing solid electrolytes (such as oxide electrolytes, sulfide electrolytes and polymer electrolytes) is smaller than the charge and discharge range of the battery. In particular, the electrochemical window of sulfide electrolytes with high ionic conductivity is even narrower. Therefore, during the first charge of the battery, a solid electrolyte layer (SEI film) will form at the interface between the solid electrolyte and the negative electrode. This process consumes the active lithium of the positive electrode, reduces the battery capacity, and the battery energy density decreases accordingly. Summary of the Invention

[0006] To address the problem that during the first charge of a silicon-based solid-state battery, an SEI film forms at the anode / solid electrolyte interface, consuming active lithium from the cathode, reducing the coulombic efficiency of the first cycle, and consequently decreasing the battery's energy density. This invention provides a solid-state battery comprising an anode sheet, which includes a first coating layer and a second coating layer. The first coating layer comprises silicon particles; the second coating layer comprises silicon particles and lithium alloy particles. The lithium contained in the lithium alloy particles can compensate for the active lithium consumed in the formation of the SEI film during the first charge, improving the coulombic efficiency of the first cycle, thereby increasing the battery's capacity and energy density.

[0007] Furthermore, the second coating layer, which includes lithium alloy particles and silicon particles, is located between the first coating layer and the current collector. This structural arrangement can prevent the second coating layer, which includes lithium alloy particles and silicon particles, from directly contacting the solid electrolyte layer, thus preventing them from reacting and generating heat during battery assembly and causing safety issues.

[0008] In addition, the second coating layer, which includes lithium alloy particles and silicon particles, retains the conductive framework structure after compensating for the active lithium consumed in the formation of the SEI film during the first charge of the battery. That is, the second coating layer still exists after lithium replenishment, which can ensure the electronic conduction between the first coating layer and the current collector and avoid problems such as poor electrical contact between the first coating layer and the current collector after the second coating layer disappears.

[0009] The objective of this invention is achieved through the following technical solution:

[0010] A solid-state battery includes a negative electrode sheet, the negative electrode sheet including a current collector, a first coating layer and a second coating layer, the second coating layer being disposed on at least one side surface of the current collector, and the first coating layer being disposed on the surface of the second coating layer; the first coating layer includes silicon particles; the second coating layer includes silicon particles and lithium alloy particles.

[0011] According to an embodiment of the present invention, the lithium alloy particles are selected from at least one of lithium silicon alloy particles, lithium aluminum alloy particles, lithium boron alloy particles, lithium magnesium alloy particles, and mixtures of metallic lithium with at least one of lithium silicon alloy, lithium aluminum alloy, lithium boron alloy, and lithium magnesium alloy.

[0012] In this invention, after the lithium alloy particles are delithiated, they still retain a conductive framework structure, ensuring electronic conduction between the first coating layer and the second coating layer. Moreover, the non-lithium components in the lithium alloy particles become negative electrode materials and participate in the electrode reaction.

[0013] According to an embodiment of the present invention, the particle size Dv50 of the lithium alloy particles is 0.01 μm to 100 μm, for example, 0.01 μm, 0.02 μm, 0.05 μm, 0.1 μm, 0.2 μm, 0.4 μm, 0.5 μm, 0.8 μm, 1 μm, 1.2 μm, 1.5 μm, 1.8 μm, 2 μm, 3 μm, 4 μm, 5 μm, 8 μm, 10 μm, 15 μm, 18 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, or any value within the range of the above two-to-one values.

[0014] According to an embodiment of the present invention, the silicon particles are selected from at least one of elemental silicon particles, silicon-carbon composite material particles, and silicon suboxide particles.

[0015] According to an embodiment of the present invention, the particle size Dv50 of the silicon particles is 0.01 μm to 100 μm, for example, 0.01 μm, 0.02 μm, 0.05 μm, 0.1 μm, 0.2 μm, 0.4 μm, 0.5 μm, 0.8 μm, 1 μm, 1.2 μm, 1.5 μm, 1.8 μm, 2 μm, 3 μm, 4 μm, 5 μm, 8 μm, 10 μm, 15 μm, 18 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, or any point value within the range of the above two-to-one values.

[0016] According to an embodiment of the present invention, the thickness of the first coating layer is 1 μm to 100 μm, for example, 1 μm, 1.2 μm, 1.5 μm, 1.8 μm, 2 μm, 3 μm, 4 μm, 5 μm, 8 μm, 10 μm, 15 μm, 18 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm or any point value within the range of the above two-to-one point values.

[0017] According to an embodiment of the present invention, the thickness of the second coating layer is 1 μm to 100 μm, for example, 1 μm, 1.2 μm, 1.5 μm, 1.8 μm, 2 μm, 3 μm, 4 μm, 5 μm, 8 μm, 10 μm, 15 μm, 18 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm or any point value within the range of the above two-to-one point values.

[0018] According to an embodiment of the present invention, the first coating layer and the solid electrolyte layer are in surface-to-surface contact, which can minimize the contact area between the second coating layer and the solid electrolyte layer, that is, to separate the lithium alloy particles from the solid electrolyte layer, thereby reducing the formation of the SEI layer and reducing the consumption of positive electrode active lithium.

[0019] According to an embodiment of the present invention, the second coating layer includes lithium alloy particles, which can provide a lithium source for the negative electrode, compensate for the lithium consumed by the formation of the SEI film between the negative electrode and the solid electrolyte layer, and improve the first efficiency of the battery.

[0020] According to an embodiment of the present invention, the mass percentage of lithium alloy particles in the second coating layer is 0.1 wt% to 50 wt%. Exemplarily, it can be 0.1 wt%, 0.5 wt%, 1.0 wt%, 5.0 wt%, 10 wt%, 15 wt%, 20 wt%, 30 wt%, 40 wt%, or 50 wt%.

[0021] According to an embodiment of the present invention, the first coating layer further includes a first adhesive.

[0022] According to an embodiment of the present invention, the second coating layer further includes a second adhesive.

[0023] According to an embodiment of the present invention, the first coating layer and the second coating layer do not include conductive agents.

[0024] According to embodiments of the present invention, the first adhesive and the second adhesive may be the same or different, and are independently selected from at least one of polytetrafluoroethylene, polyvinylidene fluoride, styrene-butadiene rubber, polystyrene, sodium carboxymethyl cellulose, styrene-butadiene copolymer, etc.

[0025] According to an embodiment of the present invention, the solid-state battery is a lithium-ion solid-state battery.

[0026] According to an embodiment of the present invention, the solid-state battery further includes a positive electrode and a solid electrolyte layer.

[0027] The positive electrode sheet includes a current collector and a positive electrode active material layer disposed on at least one side surface of the current collector. The positive electrode active material layer includes a positive electrode active material, a solid electrolyte, a conductive agent, and a binder.

[0028] The solid electrolyte layer comprises a solid electrolyte and a binder.

[0029] The positive electrode active material is selected from at least one of lithium iron phosphate, lithium manganese oxide, lithium cobalt oxide, nickel-cobalt-manganese (aluminum) ternary active materials, lithium titanate, lithium manganese iron phosphate, and lithium nickel oxide.

[0030] The solid electrolyte in the solid electrolyte layer may be the same as or different from the solid electrolyte in the positive electrode active material layer, and may be selected independently from sulfide solid electrolytes.

[0031] The sulfide solid electrolyte is selected from Li7P3S. 11 Li 9.6 P3S 12 , Li2S-P2S5, Li2S-P2S5-LiBr, Li2S-P2S5-LiI, Li4GePS4, Li4SiPS4, Li 10 GeP2S 12 Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 At least one of them.

[0032] The conductive agent is selected from at least one of carbon nanotubes, graphene, conductive graphite, acetylene black, conductive carbon fiber, and carbon black.

[0033] The adhesive is selected from at least one of polytetrafluoroethylene, polyvinylidene fluoride, styrene-butadiene rubber, polystyrene, sodium carboxymethyl cellulose, and styrene-butadiene copolymer.

[0034] The beneficial effects of this invention are:

[0035] This invention provides a solid-state battery, comprising a negative electrode sheet, a current collector, a first coating layer, and a second coating layer. The second coating layer is disposed on at least one surface of the current collector, and the first coating layer is disposed on the surface of the second coating layer. The first coating layer comprises silicon particles; the second coating layer comprises silicon particles and lithium alloy particles. The lithium contained in the lithium alloy particles can compensate for the active lithium consumed in the formation of the SEI film during the first charge of the solid-state battery, improving the coulombic efficiency of the first cycle, thereby increasing the capacity and energy density of the solid-state battery. The second coating layer, comprising lithium alloy particles and silicon particles, is positioned between the first coating layer and the current collector. This structural arrangement prevents the second coating layer, comprising lithium alloy particles and silicon particles, from directly contacting the solid electrolyte layer, thus avoiding exothermic reactions between the two during solid-state battery assembly and potential safety issues. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the negative electrode sheet according to a preferred embodiment of the present invention. Detailed Implementation

[0037] The present invention also provides a method for preparing the above-mentioned negative electrode sheet, the method comprising the following steps:

[0038] 1) Prepare a slurry to form a second coating layer, the slurry comprising silicon particles, lithium alloy particles, binder and solvent, and coat the slurry onto the surface of the current collector and dry it to obtain the second coating layer;

[0039] 2) Prepare a slurry to form the first coating layer, the slurry comprising silicon particles, binder and solvent, and coat the slurry onto the surface of the second coating layer and dry it to obtain a negative electrode sheet.

[0040] The present invention also provides a method for preparing the above-mentioned solid-state battery, the method comprising the following steps:

[0041] 1) Prepare a slurry to form a second coating layer, the slurry comprising silicon particles, lithium alloy particles, binder and solvent, and coat the slurry onto the surface of the current collector and dry it to obtain the second coating layer;

[0042] 2) Prepare a slurry to form the first coating layer, the slurry comprising silicon particles, binder and solvent, and coat the slurry onto the surface of the second coating layer and dry it to obtain a negative electrode sheet;

[0043] 3) Prepare a slurry to form a solid electrolyte layer, the slurry comprising a sulfide electrolyte, a binder and a solvent, and coat the slurry onto the surface of a first coating layer and dry it to obtain a solid electrolyte layer;

[0044] 4) The positive electrode active material, binder, sulfide electrolyte and conductive agent are mixed and prepared into a positive electrode by dry method or wet method; wherein the dry method is to directly mix the positive electrode active material, binder, sulfide electrolyte and conductive agent, then press into a sheet and composite with aluminum foil to form a positive electrode; wherein the wet method is to add the positive electrode active material, binder, sulfide electrolyte and conductive agent into a solvent, mix evenly, coat onto the surface of aluminum foil, dry and roll to form a positive electrode sheet;

[0045] 5) Combine the positive electrode sheet prepared in step 4) with the solid electrolyte layer-negative electrode prepared in step 3) and compact it;

[0046] 6) After encapsulation, they are assembled into solid-state batteries.

[0047] The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0048] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0049] In the description of this invention, it should be noted that the terms "first," "second," etc., are used for descriptive purposes only and are not intended to indicate or imply relative importance.

[0050] Example 1

[0051] A. Experimental Group

[0052] 1. Lithium-silicon alloy particles

[0053] In an argon glove box, silicon (Thermo Fisher Chemicals, Dv50 of 1-5 microns) was dried at 100°C for 24 hours to remove moisture. Then, silicon and lithium (Tianjin Zhongneng Lithium Industry Co., Ltd.) were added to a heated stirring tank at a mass ratio of 1:1.2 and stirred at 200°C for 24 hours to allow them to react fully and obtain lithium-silicon alloy particles.

[0054] 2. Negative electrode

[0055] Silicon particles, lithium-silicon alloy particles, and styrene-butadiene copolymer (styrene-butadiene rubber, Shanghai Aladdin Biochemical Technology Co., Ltd.) were added to p-xylene solvent in a ratio of 89:6:5 (mass ratio), mixed evenly, coated onto the surface of copper foil, and dried to obtain a second coating layer. The areal weight of the dried second coating layer was 3.37 mg / cm². 2 .

[0056] Silicon particles and styrene-butadiene copolymer were added to p-xylene solvent at a ratio of 95:5 (mass ratio), mixed thoroughly, and the slurry was coated onto the surface of a second coating layer and dried to obtain a first coating layer. The surface mass of the dried first coating layer was 1.58 mg / cm². 2 .

[0057] 3. Solid electrolyte layer

[0058] sulfide electrolyte (Li7P3S) 11 Shenzhen Kejing) and styrene-butadiene copolymer were added to the solvent p-xylene in a ratio of 95:5 (mass ratio), mixed evenly, and the slurry was coated on the surface of the first coating layer of the negative electrode and dried. The thickness of the solid electrolyte layer after drying was about 22 μm.

[0059] 4. Positive electrode

[0060] Lithium iron phosphate (Defang Nano), conductive agent Super P, and sulfide electrolyte (Li7P3S) were added. 11 The active material and binder, styrene-butadiene copolymer, were added to xylene solvent in a ratio of 92.5:2.5:2.5:2.5 (mass ratio), mixed thoroughly, coated onto aluminum foil, and dried to form the positive electrode. The areal mass of the positive electrode active material layer was approximately 18.2 mg / cm². 2 .

[0061] 5. Solid-state battery composition

[0062] The positive electrode is bonded to the surface of the solid electrolyte layer from step 3 and then rolled. The rolled sheet is then stamped into a 15mm diameter disc, placed into a CR2025 coin cell, and encapsulated to complete the battery assembly.

[0063] 6. First-time effectiveness test

[0064] The initial efficiency test was performed on a Newway battery tester with a test current of 0.05C, a voltage range of 2.75 to 4.2V, and a test temperature of 25℃.

[0065] B. Control Group

[0066] The second coating layer does not include lithium-silicon alloy particles. Instead, silicon particles and styrene-butadiene copolymer are added to p-xylene (Aladdin reagent) solvent in a ratio of 89:5 (mass ratio), mixed thoroughly, coated onto the copper foil surface, and dried to obtain the second coating layer. The areal weight of the dried second coating layer is approximately 3.1 mg / cm². 2 .

[0067] The remaining preparation and testing procedures were the same as those for the experimental group.

[0068] Table 1 shows the first-efficiency test results of the experimental group and the control group in Example 1. It can be seen from the table that the first-efficiency of the experimental group is higher than that of the control group. This is because lithium silicon alloy particles were added to the negative electrode of the experimental group, which made up for the positive electrode active lithium consumed by the formation of the SEI layer in the first cycle process, thus improving the first-efficiency.

[0069] Table 1. Battery first-efficiency test results for the experimental and control groups in Example 1.

[0070] Group First effect experimental group 95％ control group 78％

[0071] Example 2

[0072] The battery preparation process for both the experimental and control groups was the same as in Example 1, except for the preparation of the positive electrode sheet:

[0073] Lithium iron phosphate (Defang Nano), conductive agent Super P, and sulfide electrolyte (Li7P3S) were added. 11 The positive electrode and the binder polytetrafluoroethylene are mixed evenly in a ratio of 92.5:2.5:2.5:2.5 (by mass), and then rolled into sheets using a roller press. The positive electrode sheet is then laminated with aluminum foil, and the positive electrode sheet and aluminum foil are then firmly laminated together using another roller press to form the positive electrode.

[0074] Table 2 shows the first-efficiency test results of the experimental group and the control group of Example 2. As can be seen from Table 2, the first-efficiency of the experimental group battery of Example 2 is higher than that of the control group. This is because lithium silicon alloy particles were added to the negative electrode of the experimental group of Example 2, which made up for the positive electrode active lithium consumed by the formation of SEI film during the first cycle of the battery, thus improving the first-efficiency.

[0075] Table 2. Battery first-efficiency test results for the experimental and control groups in Example 2.

[0076] Group First effect experimental group 96％ control group 80％

[0077] The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A solid-state battery, characterized by, The battery includes a negative electrode sheet and a solid electrolyte layer, the negative electrode sheet includes a current collector, a first coating layer, and a second coating layer, the second coating layer is arranged on at least one side surface of the current collector, and the first coating layer is arranged on a surface of the second coating layer; the first coating layer includes silicon particles; and the second coating layer includes silicon particles and lithium alloy particles. The first coating layer is in contact with the solid electrolyte layer. The first coating layer further includes a first binder, and the second coating layer further includes a second binder. In the second coating layer, the mass percentage content of the lithium alloy particles is 0.1wt%-50wt%.

2. The solid-state battery of claim 1, wherein, The lithium alloy particles are selected from at least one of lithium-silicon alloy particles, lithium-aluminum alloy particles, lithium-boron alloy particles, lithium-magnesium alloy particles, and mixed particles of metallic lithium and at least one of lithium-silicon alloy particles, lithium-aluminum alloy particles, lithium-boron alloy particles, and lithium-magnesium alloy particles.

3. The solid-state battery of claim 1, wherein, The particle size Dv50 of the lithium alloy particles is 0.01μm-100μm. The particle size Dv50 of the silicon particles is 0.01μm-100μm.

4. The solid-state battery of claim 1, wherein, The silicon particles are selected from at least one of elemental silicon particles, silicon-carbon composite material particles, and silicon monoxide particles.

5. The solid-state battery of claim 1, wherein, The thickness of the first coating layer is 1μm-100μm. The thickness of the second coating layer is 1μm-100μm.

6. The solid-state battery according to any one of claims 1 to 5, characterized in that, The solid-state battery further includes a positive electrode sheet. The positive electrode sheet includes a current collector and a positive electrode active material layer arranged on at least one side surface of the current collector, and the positive electrode active material layer includes a positive electrode active material, a solid electrolyte, a conductive agent, and a binder.

7. The solid-state battery of claim 6, wherein, The solid electrolyte layer includes a solid electrolyte and a binder, the solid electrolyte in the positive electrode active material layer and the solid electrolyte layer is the same or different and is independently selected from sulfide solid electrolytes.

8. The solid-state battery of claim 7, wherein, The sulfide solid-state electrolyte is selected from at least one of Li7P3S 11 , Li 9.6 P3S 12 , Li2S-P2S5, Li2S-P2S5-LiBr, Li2S-P2S5-Lii, Li4GePS4, Li4SiPS4, Li 10 GeP2S 12 , Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 .

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