Negative electrode, sodium-ion battery and electrical equipment

Abstract

This application discloses a negative electrode sheet, a sodium-ion battery, and an electrical device. The negative electrode sheet includes a negative electrode current collector and a carbon coating. The carbon coating is disposed on at least a portion of the surface of the negative electrode current collector. The carbon coating includes a carbon material, a solid electrolyte, and a polymer binder. A hole is provided on the surface of the carbon coating away from the negative electrode current collector, and the hole extends along the thickness direction of the carbon coating. The depth of the hole is less than the thickness of the carbon coating.

Description

Technical Field

[0001] This application belongs to the field of sodium-ion battery technology, specifically relating to a negative electrode, a sodium-ion battery, and an electrical device. Background Technology

[0002] As the application of lithium-ion batteries in the energy storage market gradually expands, the world is rapidly entering the TWh era. Supply chain security in the TWh era has become an unavoidable topic, especially with the increasing prominence of lithium resource shortages. Sodium-ion batteries, due to their high raw material abundance and low cost, are gradually gaining attention. However, because metallic sodium has a higher reduction potential and a larger relative molecular mass than metallic lithium, the energy density of sodium-ion batteries, which operate on a similar principle, is significantly lower than that of lithium-ion batteries. Furthermore, the larger ionic radius of sodium ions results in greater volume expansion during insertion and extraction in the positive and negative electrode materials, leading to decreased cycle reversibility. Low energy density and rapid cycle decay significantly restrict their widespread application.

[0003] To improve the energy density of battery cells, "negative electrode-free" sodium metal batteries have become the ultimate goal for increasing energy density. However, negative electrode-free cells have poor liquid absorption and retention capabilities on the negative electrode side, leading to accelerated cell cycle degradation. Summary of the Invention

[0004] This application aims to at least partially address one of the technical problems in related technologies. Therefore, the purpose of this application is to provide a negative electrode, a sodium-ion battery, and an electrical device. By creating holes on the surface of the negative electrode, this application effectively reduces the contact angle between the electrolyte and the negative electrode surface, while also increasing the surface roughness of the negative electrode, allowing the sodium metal layer deposited on the negative electrode surface to have a stronger bond with the surface. Furthermore, it can adjust the electric field on the negative electrode surface, improving the uniformity and density of sodium metal deposition on the negative electrode surface. In addition, the solid electrolyte in the carbon coating can further enhance the affinity between the carbon coating and the electrolyte, thereby improving the wetting ability and ion migration rate on the negative electrode side.

[0005] In one aspect of this application, a negative electrode is provided. According to an embodiment of this application, the negative electrode comprises:

[0006] Negative electrode current collector;

[0007] A carbon coating is disposed on at least a portion of the surface of the negative electrode current collector, the carbon coating comprising a carbon material, a solid electrolyte, and a polymer binder; the surface of the carbon coating away from the negative electrode current collector is provided with pores, and the pores extend along the thickness direction of the carbon coating, the depth of the pores being less than the thickness of the carbon coating.

[0008] According to the embodiments of this application, the negative electrode sheet, by providing holes on its surface, effectively reduces the contact angle between the electrolyte and the negative electrode sheet surface, thereby ensuring rapid wetting of the electrolyte on the negative electrode sheet surface, significantly improving the liquid absorption and retention capacity of the negative electrode sheet, and reducing the ion transport impedance on the negative electrode side. Simultaneously, by providing holes on the surface of the negative electrode sheet, the surface roughness is increased, allowing the sodium metal layer deposited on the negative electrode sheet surface to have a strong bonding force, effectively preventing the sodium deposition layer from peeling off or pulverizing during cycling, thus avoiding irreversible capacity loss. Furthermore, it can also adjust the electric field on the negative electrode sheet surface, improving the uniformity and density of sodium metal deposition on the negative electrode sheet surface. In addition, the solid electrolyte in the carbon coating can further enhance the affinity between the carbon coating and the electrolyte, thereby improving the wetting ability and ion migration rate on the negative electrode side.

[0009] In addition, the negative electrode sheet according to the above embodiments of this application may also have the following additional technical features:

[0010] In some embodiments of this application, the depth of the hole is h2, and the thickness of the carbon coating is h1, satisfying 40% ≤ h2 / h1 ≤ 80%.

[0011] In some embodiments of this application, the diameter of the pores is 1 μm to 3 μm; and / or, the density of the pores on the carbon coating surface is 1000 pores / mm². 2 ~3000 pieces / mm 2 .

[0012] In some embodiments of this application, the contact angle θ between the surface of the negative electrode and the electrolyte satisfies 0°≤θ≤10°.

[0013] In some embodiments of this application, the surface roughness Ra of the negative electrode sheet satisfies 0.4μm≤Ra≤3.2μm.

[0014] In some embodiments of this application, the thickness h1 of the carbon coating is not greater than 5 μm.

[0015] In some embodiments of this application, the mass ratio of the carbon material, the solid electrolyte, and the polymer binder is (60-80):(0.5-10):(10-30).

[0016] In some embodiments of this application, the carbon material is a composite of one-dimensional carbon material and at least one selected from zero-dimensional carbon material, two-dimensional carbon material and three-dimensional carbon material.

[0017] In some embodiments of this application, the solid electrolyte includes β″-Al2O3 and Na3Zr2Si2PO4. 12 Na 3+x La x Zr 2x Si2PO 12 Na3PS4, Na 11 Sn2PS4, Na7P3S 11 At least one of them, wherein 0 <x≤0.5。

[0018] In some embodiments of this application, the one-dimensional carbon material includes at least one of carbon nanotubes and carbon fibers; and / or, the zero-dimensional carbon material includes at least one of acetylene black, furnace black, Ketjen black, and carbon quantum dots; and / or, the two-dimensional carbon material includes at least one of graphene and multilayer graphite sheets; and / or, the three-dimensional carbon material includes at least one of mesophase carbon microspheres, natural graphite, artificial graphite, hard carbon, and porous activated carbon.

[0019] In some embodiments of this application, the polymer binder includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, styrene-butadiene rubber, polyacrylate, polyacrylonitrile, polyacrylic acid, sodium polyacrylate, carboxymethyl cellulose, sodium alginate, gum arabic, xanthan gum, and guar gum.

[0020] In some embodiments of this application, the holes are formed on the surface of the carbon coating using a laser method.

[0021] In a second aspect, this application proposes a sodium-ion battery. According to an embodiment of this application, the sodium-ion battery has the negative electrode sheet described in the above embodiments. This effectively improves the cycle performance of the sodium-ion battery.

[0022] In a third aspect, this application proposes an electrical device. According to an embodiment of this application, the electrical device has a sodium-ion battery as described above. Therefore, the electrical device possesses all the advantages of the sodium-ion battery, which will not be elaborated further here.

[0023] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0024] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0025] Figure 1 This is a schematic diagram of the negative electrode sheet according to an embodiment of this application.

[0026] Figure label:

[0027] 1-Negative current collector, 2-Carbon coating, 3-Pore. Detailed Implementation

[0028] The embodiments of this application are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application.

[0029] In one aspect of this application, a negative electrode is provided. According to an embodiment of this application, refer to the appendix... Figure 1 The negative electrode includes: a negative current collector 1; a carbon coating 2, which is disposed on at least a portion of the surface of the negative current collector 1, and comprises carbon material, a solid electrolyte, and a polymer binder; a hole 3 is provided on the surface of the carbon coating 2 away from the negative current collector 1, and the hole 3 extends along the thickness direction (i.e., the Y direction) of the carbon coating 2, and the depth of the hole 3 is less than the thickness of the carbon coating 2. Therefore, by providing holes on the surface of the negative electrode, this application can effectively reduce the contact angle between the electrolyte and the surface of the negative electrode, thereby ensuring rapid wetting of the electrolyte on the surface of the negative electrode, significantly improving the liquid absorption and retention capacity of the negative electrode, and reducing the ion transport impedance on the negative electrode side. Simultaneously, by providing holes on the surface of the negative electrode, the surface roughness of the negative electrode is increased, allowing the sodium metal layer deposited on the surface of the negative electrode to have a strong bonding force with the surface of the negative electrode, thereby effectively preventing the sodium deposition layer from peeling off and pulverizing during cycling, and avoiding irreversible capacity loss. Furthermore, it can adjust the electric field on the surface of the negative electrode, improving the uniformity and density of sodium metal deposition on the negative electrode surface. In addition, the solid electrolyte in the carbon coating can further enhance the affinity between the carbon coating and the electrolyte, thereby improving the wetting ability and ion migration rate on the negative electrode side.

[0030] It should be noted that, in the appendix Figure 1 In the diagram, the Y direction represents the thickness direction of the negative electrode, and the X direction represents the width direction of the negative electrode.

[0031] The principle by which the negative electrode proposed in this application achieves the above-mentioned beneficial effects will be explained in detail below:

[0032] In related technologies, the negative electrode side of a non-negative electrode sodium-ion battery is generally made of metal foil or modified foil, resulting in poor liquid absorption and retention capacity. At the same time, in order to stabilize the negative electrode interface, the battery cell is usually tested for electrical performance under high external pressure. During cycling, due to the weak liquid absorption capacity of the negative electrode side itself, coupled with the squeezing effect of the electrolyte on the cycling volume expansion, the amount of electrolyte on the negative electrode side will decrease as the cycle progresses, which in turn leads to greater polarization of the battery cell and accelerated cycle degradation.

[0033] In addition, in related technologies, because the surface of the negative electrode is too smooth, the sodium metal layer deposited on the surface of the negative electrode is prone to peeling and pulverization during cycling, which leads to loss of contact with the conductive network and electrical insulation, thereby affecting the capacity and cycle life of the battery cell.

[0034] To address this technical problem, this application provides a carbon coating on at least a portion of the surface of the negative electrode current collector, and creates holes (i.e., straight holes) extending along the thickness direction of the carbon coating on its surface. The depth of these holes is less than the thickness of the carbon coating (i.e., the holes do not penetrate the carbon coating). This effectively reduces the contact angle between the electrolyte and the negative electrode surface, ensuring that the contact angle θ between the negative electrode surface and the electrolyte is within the range of 0°≤θ≤10° (or even 0°≤θ≤5°). This ensures rapid wetting of the electrolyte on the negative electrode surface, significantly improving the negative electrode's liquid absorption and retention capacity and reducing the ion transport impedance on the negative electrode side. When this negative electrode is used in sodium-ion batteries, it effectively improves the cycle performance of the sodium-ion battery. Meanwhile, by creating pores on the surface of the carbon coating, the surface roughness of the negative electrode is increased, allowing it to remain within the range of 0.4μm≤Ra≤3.2μm (or even 2.4μm≤Ra≤3.2μm). This ensures a strong bond between the sodium metal layer deposited on the negative electrode surface and the electrode itself, effectively preventing peeling and pulverization of the sodium deposition layer during cycling and avoiding irreversible capacity loss. Furthermore, creating pores on the carbon coating surface also adjusts the electric field on the negative electrode surface, improving the uniformity and density of sodium metal deposition.

[0035] In addition, the carbon coating contains carbon materials, solid electrolytes, and polymer binders. The design of the carbon coating improves the conductivity of the negative electrode side. At the same time, the solid electrolyte in the carbon coating can further enhance the affinity between the carbon coating and the electrolyte, thereby improving the wetting ability and ion migration rate of the negative electrode side.

[0036] According to some specific embodiments of this application, the depth of the hole is h2, and the thickness of the carbon coating is h1, satisfying 40% ≤ h2 / h1 ≤ 80%. By limiting the hole depth within the above range, the contact angle between the electrolyte and the negative electrode surface can be further effectively reduced, while the surface roughness of the negative electrode can be further effectively increased. The inventors have found that if the hole depth is too small, i.e., the drilling depth is insufficient, it will lead to insufficient electrolyte absorption, affecting the cycle performance of the sodium-ion battery; if the hole depth is too large, i.e., too close to the negative electrode current collector, it is easy to cause foil leakage, thereby affecting the metal deposition at that location.

[0037] According to some specific embodiments of this application, the diameter of the pores can be 1μm to 3μm, and the density of pores on the carbon coating surface can be 1000 pores / mm². 2 ~3000 pieces / mm2 By limiting the diameter of the holes and the density of the holes on the carbon coating surface to the above range, it is possible to further ensure a reduction in the contact angle between the electrolyte and the negative electrode surface, and at the same time, to further ensure an increase in the roughness of the negative electrode surface.

[0038] In the embodiments of this application, the contact angle between the electrolyte and the surface of the negative electrode can be effectively reduced by setting holes on the surface of the negative electrode and by adding solid electrolyte to the carbon coating. Under the combined effect of these two conditions, the contact angle θ between the surface of the negative electrode and the electrolyte can be in the range of 0°≤θ≤10° (or even 0°≤θ≤5°), thereby ensuring rapid wetting of the electrolyte on the surface of the negative electrode, greatly improving the liquid absorption and retention capacity of the negative electrode, and reducing the ion transport impedance on the negative electrode side.

[0039] It should be noted that the contact angle refers to the tangent line drawn at the gas-liquid interface at the junction of the gas, liquid, and solid phases. The angle θ between this tangent line on the liquid side and the solid-liquid interface line is a measure of the degree of wetting.

[0040] In the embodiments of this application, by setting holes on the surface of the negative electrode sheet, the surface roughness of the negative electrode sheet can be effectively increased, so that the surface roughness of the negative electrode sheet can be in the range of 0.4μm≤Ra≤3.2μm (or even in the range of 2.4μm≤Ra≤3.2μm). This allows the sodium metal layer deposited on the surface of the negative electrode sheet to have a strong bonding force with the surface of the negative electrode sheet, thereby effectively avoiding the phenomenon of peeling and powdering of the sodium deposition layer during cycling, and avoiding irreversible capacity loss.

[0041] In the embodiments of this application, the thickness h1 of the carbon coating is no greater than 5 μm.

[0042] According to some specific embodiments of this application, the mass ratio of carbon material, solid electrolyte, and polymer binder can be (60-80):(0.5-10):(10-30). By limiting the mass ratio of carbon material, solid electrolyte, and polymer binder within the above range, the conductivity of the negative electrode side can be further improved, the affinity between the carbon coating and the electrolyte can be further improved, thereby further enhancing the wetting ability and ion migration rate of the negative electrode side.

[0043] According to some specific embodiments of this application, the carbon material is a blend of one-dimensional carbon material and at least one selected from zero-dimensional carbon material, two-dimensional carbon material, and three-dimensional carbon material, with the total mass of carbon material being 100% and the content of one-dimensional carbon material being 60wt%-90wt%. Thus, by using a mixture of carbon materials of different dimensions, the carbon coating can construct a three-dimensional structure, which further facilitates the internal liquid retention of the carbon coating and the deposition of sodium metal within the carbon coating, thereby reducing the deposition volume of sodium metal on the surface of the negative electrode and minimizing volume expansion.

[0044] Among them, the one-dimensional carbon materials include, but are not limited to, at least one of carbon nanotubes and carbon fibers, preferably carbon fibers, which play a framework role throughout the coating. The zero-dimensional carbon materials include, but are not limited to, at least one of acetylene black, furnace black, Ketjen black, and carbon quantum dots. The two-dimensional carbon materials include, but are not limited to, at least one of graphene and multi-layer graphite flakes. The three-dimensional carbon materials include, but are not limited to, at least one of mesophase carbon microspheres, natural graphite, artificial graphite, hard carbon, and porous activated carbon. The compound of carbon fiber and acetylene black is preferred.

[0045] In the embodiments of the present application, the specific types of the above-mentioned solid electrolytes are not particularly limited, and those skilled in the art can select according to actual needs. Oxide solid electrolytes can be selected, such as β″-Al2O3, NZSP type, NLZSP type (Na3Zr2Si2PO 12 、Na 3+x La x Zr 2x Si2PO 12 (0 < x ≤ 0.5), etc. Sulfide solid electrolytes can also be selected, such as Na3PS4, Na 11 Sn2PS4, Na7P3S 11 , etc. Halide solid electrolytes can also be selected, such as Na3MX6, etc. Anti-perovskite solid electrolytes can also be selected, such as X3BA, etc. Borohydride solid electrolytes can also be selected, such as Na2(B n H n ), etc. At least one of Na3Zr2Si2PO 12 、Na 3+x La x Zr 2x Si2PO 12 (0 < x ≤ 0.5) is preferred.

[0046] In the embodiments of the present application, the specific types of the above-mentioned polymer binders are not particularly limited, and those skilled in the art can select according to actual needs. As some specific examples, the polymer binder can include at least one of polyvinylidene fluoride PVDF, polytetrafluoroethylene PTFE, styrene-butadiene rubber type, polyacrylate type, polyacrylonitrile type, polyacrylic acid type, sodium polyacrylate, carboxymethyl cellulose, sodium alginate, gum arabic, xanthan gum, and guar gum.

[0047] According to some other specific embodiments of the present application, holes can be formed on the surface of the carbon coating by means of laser, thereby further effectively ensuring the reduction of the contact angle between the electrolyte and the surface of the negative electrode sheet, and at the same time further effectively ensuring the increase of the surface roughness of the negative electrode sheet.

[0048] The preparation method of the above-mentioned negative electrode sheet includes:

[0049] 1) Mix the carbon material, solid electrolyte and polymer binder evenly according to the preset ratio, add solvent and stir evenly to form a slurry, then coat it onto the negative electrode current collector, dry it and set it aside.

[0050] 2) A hole (i.e. a straight hole) is formed on the surface of the carbon coating by using a laser method to obtain the negative electrode of this application.

[0051] In a second aspect, this application proposes a sodium-ion battery. According to an embodiment of this application, the sodium-ion battery has the negative electrode sheet described in the above embodiments. This effectively improves the cycle performance of the sodium-ion battery.

[0052] In particular, the aforementioned sodium-ion battery can be a negative electrode-free sodium-ion battery, which refers to a battery in which sodium is removed from the positive electrode material and deposited in situ onto the negative electrode current collector (in this application, it is deposited onto the carbon coating on the surface of the negative electrode current collector). No negative electrode active material is added during the manufacturing process; only the negative electrode current collector is used as the nominal negative electrode. However, this negative electrode current collector does not function as a negative electrode. Only after the first charge is completed, the metal in the positive electrode material migrates to the surface of the negative electrode current collector (in this application, it migrates to the carbon coating on the surface of the negative electrode current collector), and the metal layer formed on the negative electrode current collector is the true negative electrode.

[0053] Specifically, a negative electrode-free sodium-ion battery includes a positive electrode, a separator, a negative electrode, and an electrolyte, with the separator disposed between the positive and negative electrode. The specific material of the separator is not particularly limited; as some specific examples, the separator includes at least one of PP separator, PE separator, single-sided ceramic separator, double-sided ceramic separator, non-woven fabric separator, and glass fiber separator.

[0054] The positive electrode sheet includes a positive current collector and a positive electrode material layer formed on the positive current collector. The positive electrode material layer includes a positive electrode active material, a positive electrode binder, and a positive electrode conductive agent.

[0055] For sodium-ion batteries, the positive electrode active material can be one or more of the following, including but not limited to transition metal oxides, polyanionic compounds, organic polymers, and Prussian blue-based materials. In sodium transition metal oxides, the transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; for example, Na is a sodium transition metal oxide. x MO2, where M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr, and Cu, 0 < x ≤ 1, for example Na[Ni 1 / 3 Fe 1 / 3Mn 1 / 3 O2.

[0056] The aforementioned polyanionic compounds possess sodium ion, transition metal ion, and tetrahedral (YO4) structures. n A class of compounds with an anionic unit, wherein the transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be at least one of P, S, and Si; n represents (YO4). n The valence state, for example, Na3V2(PO4)3.

[0057] The aforementioned Prussian blue compounds are a class of compounds containing sodium ions, transition metal ions, and cyanide ions (CN), and their general chemical formula can be represented as Na. x M1[M2(CN)6], where 0 < x ≤ 2, and M1 and M2 are at least one of Ni, Cu, Fe, Mn, Co and Zn, respectively.

[0058] The specific materials of the above-mentioned positive electrode binder are not particularly limited. As some specific examples, the positive electrode binder may include, but is not limited to, one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylonitrile (PAN), and polyacrylic acid (PAA).

[0059] The specific materials of the aforementioned positive electrode conductive agent are not particularly limited. As some specific examples, the positive electrode conductive agent may include, but is not limited to, one or more of acetylene black, conductive carbon black, carbon nanotubes, carbon fibers, graphene, etc.

[0060] In the embodiments of this application, the specific material of the positive current collector is not particularly limited. As some specific examples, the positive current collector may include, but is not limited to, at least one of aluminum foil, carbon-coated aluminum foil, and stainless steel foil.

[0061] In the embodiments of this application, the electrolyte includes an electrolyte salt and an organic solvent. The specific types and compositions of the electrolyte salt and the organic solvent are conventional choices in the battery field and can be selected according to actual needs.

[0062] In some embodiments, the electrolyte salt may include, but is not limited to, at least one of: sodium hexafluorophosphate (NaPF6), sodium tetrafluoroborate (NaBF4), sodium perchlorate (NaClO4), sodium bis(trifluoromethanesulfonyl)imide (NaN(CF3SO2)2), sodium bis(fluorosulfonyl)imide (NaN(SO2F)2), sodium bis(oxalateborate)borate (NaB(C2O4)2), and sodium difluorooxalateborate (NaBF2C2O4).

[0063] In some embodiments, the organic solvent may include, but is not limited to, at least one of: ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), fluoroethylene carbonate (FEC), diethylene glycol dimethyl ether (DEGDME), ethylene glycol dimethyl ether (DME), 1,3-dioxolane (DOL), and tetraethylene glycol dimethyl ether (TEGDME).

[0064] The sodium-ion battery of this application may be in the form of a single battery cell, a battery module, or a battery pack. In some embodiments, the single battery cells may be assembled into a battery module, and the number of single battery cells contained in the battery module may be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module. In some embodiments, the battery modules may also be assembled into a battery pack, and the number of battery modules contained in the battery pack may be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0065] In a third aspect, this application proposes an electrical device. According to an embodiment of this application, the electrical device has the sodium-ion battery described above. Thus, the electrical device possesses all the advantages of a sodium-ion battery, which will not be elaborated further here.

[0066] Specifically, the aforementioned electrical equipment can include, but is not limited to, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Among them, electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc., and spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0067] The embodiments of this application are described in detail below. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. In addition, unless otherwise specified, all reagents used in the following embodiments are commercially available or can be synthesized according to the methods described herein or known methods. For reaction conditions not listed, they are also readily available to those skilled in the art.

[0068] Example 1

[0069] This embodiment provides a sodium-ion battery, the preparation method of which includes:

[0070] (1) Preparation of negative electrode:

[0071] First, carbon nanotubes, polyacrylate binder, and β″-Al2O3 are dispersed in NMP solvent and mixed evenly to obtain a carbon coating slurry. The mass ratio of carbon nanotubes, polyacrylate, and β″-Al2O3 is 70:25:5. The carbon coating slurry is coated onto the negative electrode current collector aluminum foil, and after drying, cold pressing, slitting, and cutting, it is ready for use. The thickness of the carbon coating is 5 μm.

[0072] Then, a laser method was used to form straight holes with a diameter of 2 μm on the surface of the carbon coating, with a hole density of 2000 holes / mm on the carbon coating surface. 2 The depth of the straight hole is 3μm, thus obtaining the negative electrode sheet of this application.

[0073] (2) Preparation of the positive electrode:

[0074] The positive electrode active material (Na4Fe3(PO4)2P2O7), conductive agent (Super-P), and binder (PVDF) are mixed in a mass ratio of 96:2:2. The mixed powder is placed in a vacuum mixer, N-methylpyrrolidone (NMP) is added, and the mixture is stirred evenly to obtain a positive electrode slurry. The positive electrode slurry is evenly coated on the opposite two sides of the positive electrode current collector aluminum foil. The positive electrode current collector coated with the positive electrode slurry is transferred to an oven for drying. After rolling and slitting, the positive electrode sheet is obtained.

[0075] (3) Preparation of the diaphragm:

[0076] A polyethylene film with a thickness of 17μm is used as the diaphragm.

[0077] (4) Electrolyte preparation:

[0078] Dry sodium salt NaPF6 was added to a mixed solvent of diethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether to prepare an electrolyte with a concentration of 1 mol / L. The volume ratio of diethylene glycol dimethyl ether to tetraethylene glycol dimethyl ether was 1:1.

[0079] (5) Sodium-ion battery preparation:

[0080] The positive electrode, negative electrode and separator prepared above are stacked in sequence, with the separator between the positive and negative electrode sheets, and then wound to obtain a bare cell. The bare cell is then placed in an aluminum-plastic film soft pack, dried and injected with electrolyte. After vacuum sealing, standing, formation and shaping processes, a soft pack sodium-ion battery is obtained.

[0081] Example 2

[0082] The only difference between Example 2 and Example 1 is that:

[0083] A laser method was used to form straight holes with a diameter of 1 μm on the surface of the carbon coating, with a hole density of 3000 holes / mm² on the carbon coating surface. 2The depth of the straight hole is 4μm.

[0084] All other contents are the same as in Example 1.

[0085] Example 3

[0086] The only difference between Example 3 and Example 1 is that:

[0087] A laser method was used to form straight holes with a diameter of 3 μm on the surface of the carbon coating, with a hole density of 1000 holes / mm² on the carbon coating surface. 2 The depth of the straight hole is 2μm.

[0088] All other contents are the same as in Example 1.

[0089] Example 4

[0090] The only difference between Example 4 and Example 1 is that:

[0091] Example 4 uses Na3Zr2Si2PO 12 Replace β″-Al2O3.

[0092] All other contents are the same as in Example 1.

[0093] Example 5

[0094] The only difference between Example 5 and Example 1 is that:

[0095] Example 5 uses Na 3.25 La 0.25 Zr 0.5 Si2PO 12 Replace β″-Al2O3.

[0096] All other contents are the same as in Example 1.

[0097] Example 6

[0098] The only difference between Example 6 and Example 1 is that:

[0099] The mass ratio of carbon nanotubes, polyacrylate, and β″-Al2O3 is 70:28:2.

[0100] All other contents are the same as in Example 1.

[0101] Example 7

[0102] The only difference between Example 7 and Example 1 is that:

[0103] The mass ratio of carbon nanotubes, polyacrylate, and β″-Al2O3 is 70:20:10.

[0104] All other contents are the same as in Example 1.

[0105] Example 8

[0106] The only difference between Example 8 and Example 1 is that:

[0107] In this embodiment, the carbon nanotubes in the carbon coating slurry are replaced with a mixture of carbon nanotubes and acetylene black, wherein the mass ratio of carbon nanotubes to acetylene black is 80:20.

[0108] All other contents are the same as in Example 1.

[0109] Example 9

[0110] The only difference between Example 9 and Example 1 is that:

[0111] In this embodiment, the carbon nanotubes in the carbon coating slurry are replaced with a mixture of carbon nanotubes and graphene, wherein the mass ratio of carbon nanotubes to graphene is 70:30.

[0112] All other contents are the same as in Example 1.

[0113] Example 10

[0114] The only difference between Example 10 and Example 1 is that:

[0115] In this embodiment, the carbon nanotubes in the carbon coating slurry are replaced with a mixture of carbon nanotubes and mesophase carbon microspheres, wherein the mass ratio of carbon nanotubes to mesophase carbon microspheres is 60:40.

[0116] All other contents are the same as in Example 1.

[0117] Example 11

[0118] The only difference between Example 11 and Example 4 is that:

[0119] In this embodiment, the carbon nanotubes in the carbon coating slurry are replaced with a mixture of carbon fiber and acetylene black, wherein the mass ratio of carbon fiber to acetylene black is 80:20.

[0120] Everything else is the same as in Example 4.

[0121] Comparative Example 1

[0122] The only difference between Comparative Example 1 and Example 1 is that:

[0123] (1) Preparation of negative electrode:

[0124] Straight holes were not formed on the surface of the carbon coating.

[0125] All other contents are the same as in Example 1.

[0126] Comparative Example 2

[0127] The only difference between Comparative Example 2 and Example 1 is that:

[0128] (1) Preparation of negative electrode:

[0129] β″-Al2O3 was not added to the carbon coating slurry.

[0130] All other contents are the same as in Example 1.

[0131] The contact angles between the negative electrode surfaces and the electrolyte prepared in Examples 1-11 and Comparative Examples 1-2 were tested, and the specific testing methods are as follows:

[0132] 1) Place the negative electrode sample on the sample stage of the contact angle measuring instrument and make appropriate adjustments to ensure that the surface of the negative electrode sample is horizontal with the liquid in the syringe; 2) Slowly inject the electrolyte into the surface of the negative electrode sample using the syringe, taking care not to allow the liquid to flow or spread on the surface of the negative electrode; 3) Take a picture of the droplet on the surface of the negative electrode sample using the device's camera, including the front and side of the droplet, to obtain complete contact angle information; 4) Measure the contact angle using the ruler tool of the contact angle measurement software. To improve accuracy, take multiple measurements and average the results. The test results are shown in Table 1.

[0133] The surface roughness of the negative electrode sheets in Examples 1-11 and Comparative Examples 1-2 was tested, and the specific test methods are as follows:

[0134] The prepared negative electrode sheet was subjected to surface roughness calculation using the ISO 25178 standard, which conforms to the international standard for microscopic surface geometry metrology, to obtain the Ra parameter. The test results are shown in Table 1.

[0135] The adhesion between the sodium metal layer deposited on the surface of the negative electrode and the surface of the negative electrode in Examples 1-11 and Comparative Examples 1-2 was tested, and the specific test methods are as follows:

[0136] Different adhesive tapes (wrinkle tape, yellow tape, and blue tape) with different adhesion strengths were purchased. The adhesion strength of the tapes was blue tape > yellow tape > wrinkle tape. Fully charged cells were disassembled in a glove box. Tapes with different adhesion strengths were applied to the surface of the negative electrode deposition layer. A 2kg roller was used to roll the tape back and forth three times. A small tensile tester was used to perform a peel test to determine the condition of the sodium metal layer adhered to the tape. The test results are shown in Table 1.

[0137] The cycle performance of the sodium-ion batteries prepared in Examples 1-11 and Comparative Examples 1-2 was tested, and the specific test methods are as follows:

[0138] Using a flat plate test fixture, a preload of 0.25 MPa was applied to the battery cell. Cyclic tests were performed at 0.5P / 0.5P rate under normal temperature conditions, with the charge / discharge voltage range controlled between 2.5V and 3.5V. The number of cycles when the cycle capacity loss reached 90% was recorded. The test results are shown in Table 1.

[0139] Table 1

[0140]

[0141]

[0142] As can be seen from Table 1, compared with Comparative Example 1, the contact angle between the negative electrode and the electrolyte in Examples 1-11 is significantly reduced, the surface roughness of the negative electrode is significantly increased, the adhesion between the sodium metal layer deposited on the surface of the negative electrode and the surface of the negative electrode is significantly improved, and the cycle performance of the battery is significantly improved. It can be seen that by setting holes on the surface of the negative electrode, the contact angle between the negative electrode and the electrolyte can be significantly reduced, the surface roughness of the negative electrode can be significantly increased, the adhesion between the sodium metal layer deposited on the surface of the negative electrode and the surface of the negative electrode can be significantly improved, and the cycle performance of the battery can be significantly improved.

[0143] As can be seen from Table 1, compared with Comparative Example 2, the contact angle between the negative electrode and the electrolyte in Examples 1-11 was significantly reduced and the cycle performance of the battery was significantly improved. It can be seen that adding solid electrolyte to carbon coating can effectively reduce the contact angle between negative electrode and electrolyte and effectively improve the cycle performance of battery.

[0144] As can be seen from Table 1, compared with Example 1, the contact angle between the negative electrode and the electrolyte in Examples 8-10 was reduced and the cycle performance of the battery was improved. It can be seen that the use of one-dimensional carbon nanotubes combined with zero-dimensional carbon acetylene black, one-dimensional carbon nanotubes combined with two-dimensional carbon graphene, or one-dimensional carbon nanotubes combined with three-dimensional carbon mesophase carbon microspheres improved the affinity between the carbon coating and the electrolyte and improved the cycle performance of the battery.

[0145] As can be seen from Table 1, compared with Example 4, the contact angle between the negative electrode and the electrolyte in Example 11 was significantly reduced, and the cycle performance of the battery was significantly improved. This demonstrates that the combination of one-dimensional carbon fiber and zero-dimensional carbon acetylene black significantly enhances the affinity between the carbon coating and the electrolyte, and also significantly improves the battery's cycle performance. Furthermore, Example 11 exhibits the best overall performance, indicating that the use of Na3Zr2Si2PO4 as the solid electrolyte demonstrates superior performance. 12 Furthermore, the battery exhibits the best overall performance when the carbon material is a combination of one-dimensional carbon fiber and zero-dimensional carbon acetylene black.

[0146] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0147] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A negative electrode sheet, characterized in that, include: Negative electrode current collector; A carbon coating is disposed on at least a portion of the surface of the negative electrode current collector, the carbon coating comprising a carbon material, a solid electrolyte, and a polymer binder; the surface of the carbon coating away from the negative electrode current collector is provided with pores, and the pores extend along the thickness direction of the carbon coating, the depth of the pores being less than the thickness of the carbon coating; The depth of the hole is h2, and the thickness of the carbon coating is h1, satisfying 40% ≤ h2 / h1 ≤ 80%; The diameter of the pores is 1µm to 3µm; the density of the pores on the carbon coating surface is 1000 pores / mm. 2 ~3000 pieces / mm 2 .

2. The negative electrode sheet according to claim 1, characterized in that, The contact angle θ between the surface of the negative electrode and the electrolyte satisfies 0°≤θ≤10°.

3. The negative electrode sheet according to claim 1, characterized in that, The surface roughness Ra of the negative electrode sheet satisfies 0.4μm≤Ra≤3.2μm.

4. The negative electrode sheet according to claim 1, characterized in that, The thickness h1 of the carbon coating is no greater than 5 μm.

5. The negative electrode sheet according to any one of claims 1 to 4, characterized in that, The mass ratio of the carbon material, the solid electrolyte, and the polymer binder is (60~80):(0.5~10):(10~30).

6. The negative electrode sheet according to any one of claims 1 to 4, characterized in that, The carbon material is a compound of one-dimensional carbon material and at least one selected from zero-dimensional carbon material, two-dimensional carbon material and three-dimensional carbon material.

7. The negative electrode sheet according to any one of claims 1 to 4, characterized in that, The solid electrolyte includes β′′-Al2O3 and Na3Zr2Si2PO4. 12 Na 3+x La x Zr 2x Si2PO 12 Na3PS4, Na 11 Sn2PS4, Na7P3S 11 At least one of them, wherein 0 <x≤0.5。 8. The negative electrode sheet according to claim 6, characterized in that, The one-dimensional carbon material includes at least one of carbon nanotubes and carbon fibers; And / or, the zero-dimensional carbon material includes at least one of acetylene black, furnace black, Ketjen black and carbon quantum dots; And / or, the two-dimensional carbon material includes at least one of graphene and multilayer graphite sheets; And / or, the three-dimensional carbon material includes at least one of mesophase carbon microspheres, natural graphite, artificial graphite, hard carbon, and porous activated carbon.

9. The negative electrode sheet according to any one of claims 1 to 4, characterized in that, The polymer binder includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, styrene-butadiene rubber, polyacrylate, polyacrylonitrile, polyacrylic acid, sodium polyacrylate, carboxymethyl cellulose, sodium alginate, gum arabic, xanthan gum, and guar gum.

10. The negative electrode sheet according to any one of claims 1 to 4, characterized in that, The pores are formed on the surface of the carbon coating using a laser method.

11. A sodium-ion battery, characterized in that, The negative electrode sheet includes any one of claims 1 to 10.

12. An electrical appliance, characterized in that, The sodium-ion battery as described in claim 11.

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