Negative electrode sheet, sodium-ion battery and electric device

Abstract

The present application relates to the technical field of sodium-ion batteries. Particularly disclosed are a negative electrode sheet, a sodium-ion battery and an electric device. The negative electrode sheet comprises a negative electrode current collector and a carbon coating, wherein the carbon coating is arranged on at least part of the surface of the negative electrode current collector, and comprises a carbon material, a solid electrolyte and a polymer binder; and holes are formed in the surface of the carbon coating far away from the negative electrode current collector and extend in the thickness direction of the carbon coating, and the depths of the holes are less than the thickness of the carbon coating.

Description

Negative electrode sheet, sodium ion battery and electrical equipment

[0001] Priority information

[0002] This application requests the priority and rights of the Chinese patent application filed with the State Intellectual Property Office of China on March 8, 2024, with patent application number 202410268840.X and application name “Negative electrode sheet, sodium ion battery and electrical equipment”, all contents of which are incorporated by reference into this application. Technical Field

[0003] The present application belongs to the technical field of sodium ion batteries, and specifically relates to a negative electrode sheet, a sodium ion battery, and an electrical device. Background Art

[0004] As the application of lithium-ion batteries in the energy storage market gradually expands, the world will rapidly enter the TWh era. Supply chain security in this TWh era has become an unavoidable issue, especially as the shortage of lithium resources has begun to become prominent. Sodium-ion batteries, however, are gradually gaining attention due to their high raw material abundance and low cost. However, due to the higher reduction potential and larger relative molecular weight of metallic sodium compared to metallic lithium, the energy density of sodium-ion batteries, which operate on similar principles, is significantly lower than that of lithium-ion batteries. Furthermore, the larger ionic radius of sodium ions results in greater volume expansion when they are inserted into and removed from the positive and negative electrode materials, resulting in a decrease in the battery's cyclic reversibility. The low energy density and rapid cyclic decay significantly restrict their application and promotion.

[0005] To improve the energy density of battery cells, "anode-free" sodium metal batteries have become the ultimate goal. However, the negative electrode side of anode-free batteries has poor liquid absorption and retention capabilities, resulting in accelerated cycle degradation of the battery cells. Summary of the Invention

[0006] The present application aims to solve at least one of the technical problems in the related art to a certain extent. To this end, the purpose of the present application is to propose a negative electrode sheet, a sodium ion battery and an electrical device. The present application can effectively reduce the contact angle between the electrolyte and the surface of the negative electrode sheet by setting holes on the surface of the negative electrode sheet, and at the same time increase the roughness of the surface of the negative electrode sheet, so that the sodium metal layer deposited on the surface of the negative electrode sheet can have a strong bonding force with the surface of the negative electrode sheet. In addition, the electric field on the surface of the negative electrode sheet can be adjusted to improve the uniformity and density of the deposition of sodium metal on the surface of the negative electrode sheet. In addition, the solid electrolyte in the carbon coating can further enhance the affinity of the carbon coating with the electrolyte, thereby enhancing the wetting ability of the negative electrode side and the ion migration rate.

[0007] In one aspect of the present application, a negative electrode sheet is provided. According to an embodiment of the present application, the negative electrode sheet includes:

[0008] negative electrode current collector;

[0009] A carbon coating is provided 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; a 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, and the depth of the pores is less than the thickness of the carbon coating.

[0010] According to the negative electrode sheet of the embodiment of the present application, by setting holes on the surface of the negative electrode sheet, the contact angle between the electrolyte and the surface of the negative electrode sheet can be effectively reduced, thereby ensuring the rapid infiltration of the electrolyte on the surface of the negative electrode sheet, greatly improving the liquid absorption and retention capacity of the negative electrode sheet, and reducing the ion transfer impedance on the negative electrode side. At the same time, by setting holes on the surface of the negative electrode sheet, the roughness of the surface of the negative electrode sheet is increased, so that the sodium metal layer deposited on the surface of the negative electrode sheet can have a strong bonding force with the surface of the negative electrode sheet, thereby effectively avoiding the phenomenon of peeling and pulverization of the sodium deposition layer during the cycle, and avoiding irreversible capacity loss. In addition, the electric field on the surface of the negative electrode sheet can also be adjusted to improve the uniformity and density of the deposition of sodium metal on the surface of the negative electrode sheet. In addition, the solid electrolyte in the carbon coating can further enhance the affinity of the carbon coating with the electrolyte, thereby enhancing the wetting ability and ion migration rate of the negative electrode side.

[0011] In a second aspect of the present application, a sodium-ion battery is provided. According to an embodiment of the present application, the sodium-ion battery comprises a negative electrode sheet according to the above embodiment, thereby effectively improving the cycle performance of the sodium-ion battery.

[0012] In a third aspect of the present application, an electrical device is provided. According to an embodiment of the present application, the electrical device comprises a sodium-ion battery as described above. Thus, the electrical device has all the advantages of the sodium-ion battery, which will not be further elaborated here.

[0013] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become obvious from the description below, or will be learned through practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The above and / or additional aspects and advantages of the present application will become apparent and readily understood from the description of the embodiments with reference to the following drawings, in which:

[0015] FIG1 is a schematic structural diagram of a negative electrode sheet according to an embodiment of the present application.

[0016] Reference numerals: 1-negative electrode current collector, 2-carbon coating, 3-pore. DETAILED DESCRIPTION

[0017] The embodiments of the present application are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present application, and should not be understood as limiting the present application.

[0018] In one aspect, the present application provides a negative electrode sheet. According to an embodiment of the present application, referring to FIG1 , the negative electrode sheet comprises: a negative electrode current collector 1; a carbon coating 2 disposed on at least a portion of the surface of the negative electrode current collector 1, the carbon coating 2 comprising a carbon material, a solid electrolyte, and a polymer binder; and pores 3 are provided on the surface of the carbon coating 2 distal from the negative electrode current collector 1. The pores 3 extend along the thickness direction (i.e., the Y direction) of the carbon coating 2, and the depth of the pores 3 is less than the thickness of the carbon coating 2. Thus, by providing pores on the surface of the negative electrode sheet, the present application can effectively reduce the contact angle between the electrolyte and the surface of the negative electrode sheet, thereby ensuring rapid electrolyte infiltration on the surface of the negative electrode sheet, significantly improving the liquid absorption and retention capacity of the negative electrode sheet, and reducing the ion transfer impedance on the negative electrode side. Furthermore, by providing pores on the surface of the negative electrode sheet, the surface roughness of the negative electrode sheet is increased, allowing the sodium metal layer deposited on the surface of the negative electrode sheet to have a strong bond with the surface of the negative electrode sheet, thereby effectively preventing the sodium deposit from flaking and pulverizing during cycling, thereby 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. Furthermore, 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.

[0019] It should be noted that, in FIG1 , the Y direction represents the thickness direction of the negative electrode sheet, and the X direction represents the width direction of the negative electrode sheet.

[0020] The following is a detailed description of the principle by which the negative electrode sheet proposed in this application can achieve the above beneficial effects:

[0021] In related technologies, the negative electrode side of a negative electrode-free sodium ion battery is generally made of metal foil or modified foil, so the negative electrode side has poor liquid absorption and retention capabilities. At the same time, in order to stabilize the negative electrode interface, the battery cell is usually subjected to electrical performance testing under a large external pressure. During the cycle, due to the weak liquid absorption capacity of the negative electrode side itself, coupled with the extrusion effect of the electrolyte caused by the volume expansion of the cycle, the amount of electrolyte on the negative electrode side will become lower and lower as the cycle progresses, which in turn leads to greater polarization of the battery cell and accelerated cycle attenuation of the battery cell.

[0022] In addition, in the related art, because the surface of the negative electrode sheet is too smooth, the sodium metal layer deposited on the surface of the negative electrode sheet is prone to peeling and powdering during the cycle process, losing contact with the conductive network and causing electrical insulation, thereby affecting the capacity and cycle life of the battery cell.

[0023] In order to solve this technical problem, the present application provides a carbon coating on at least part of the surface of the negative electrode current collector, and provides holes (i.e., straight holes) extending in the thickness direction of the carbon coating on the surface of the carbon coating, and the depth of the holes is less than the thickness of the carbon coating (i.e., the holes do not penetrate the carbon coating), which can effectively reduce the contact angle between the electrolyte and the surface of the negative electrode sheet, so that the contact angle θ between the surface of the negative electrode sheet and the electrolyte can be within the range of 0°≤θ≤10° (or even within the range of 0°≤θ≤5°), thereby ensuring the rapid infiltration of the electrolyte on the surface of the negative electrode sheet, greatly improving the liquid absorption and retention capacity of the negative electrode sheet, and reducing the ion transfer impedance on the negative electrode side. When the negative electrode sheet is used in a sodium ion battery, it can effectively improve the cycle performance of the sodium ion battery. At the same time, by providing holes on the surface of the carbon coating, the roughness of the surface of the negative electrode sheet is increased, so that the roughness of the negative electrode surface can be within the range of 0.4μm≤Ra≤3.2μm (or even within the range of 2.4μm≤Ra≤3.2μm), so that the sodium metal layer deposited on the surface of the negative electrode sheet can 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 deposited layer during the cycle process, avoiding irreversible capacity loss. In addition, by providing holes on the surface of the carbon coating, the electric field on the surface of the negative electrode sheet can be adjusted, improving the uniformity and density of the deposition of sodium metal on the surface of the negative electrode sheet.

[0024] 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.

[0025] According to some specific embodiments of the present application, the hole depth is h2, and the thickness of the carbon coating is h1, satisfying 40% ≤ h2 / h1 ≤ 80%. By limiting the hole depth to this range, the contact angle between the electrolyte and the negative electrode sheet surface can be further effectively reduced, while further effectively ensuring that the roughness of the negative electrode sheet surface is increased. The inventors have discovered that if the hole depth is too small, that is, the drilling depth is insufficient, it will lead to insufficient electrolyte absorption and storage, affecting the cycle performance of the sodium-ion battery; if the hole depth is too large, that is, too close to the negative electrode current collector, it is easy to cause foil leakage, thereby affecting the metal deposition at that location.

[0026] According to some specific embodiments of the present application, the diameter of the pores may be 1 μm to 3 μm, and the density of the pores on the surface of the carbon coating may be 1000 / mm 2 ~3000 pieces / mm2 By limiting the pore diameter and the pore density on the surface of the carbon coating to the above range, the contact angle between the electrolyte and the surface of the negative electrode can be further effectively reduced, while further effectively ensuring that the roughness of the surface of the negative electrode is increased.

[0027] In the embodiment of the present application, the contact angle between the electrolyte and the surface of the negative electrode sheet can be effectively reduced by setting holes in the surface of the negative electrode sheet and by adding solid electrolyte to the carbon coating. Under the joint action of these two conditions, the contact angle θ between the surface of the negative electrode sheet and the electrolyte can be within the range of 0°≤θ≤10° (even within the range of 0°≤θ≤5°), thereby ensuring the rapid infiltration of the electrolyte into the surface of the negative electrode sheet, greatly improving the liquid absorption and retention capacity of the negative electrode sheet, and reducing the ion transfer impedance on the negative electrode side.

[0028] It should be noted that the contact angle refers to the tangent of the gas-liquid interface at the intersection of the gas, liquid and solid phases. The angle θ between this tangent on the liquid side and the solid-liquid boundary line is a measure of the degree of wettability.

[0029] In the embodiment of the present application, by setting holes on the surface of the negative electrode sheet, the roughness of the surface of the negative electrode sheet can be effectively increased, so that the roughness of the surface of the negative electrode sheet can be within the range of 0.4μm≤Ra≤3.2μm (even within the range of 2.4μm≤Ra≤3.2μm), so that the sodium metal layer deposited on the surface of the negative electrode sheet can have a strong bonding force with the surface of the negative electrode sheet, thereby effectively avoiding the peeling and pulverization of the sodium deposition layer during the cycle process, and avoiding irreversible capacity loss.

[0030] In the embodiment of the present application, the thickness h1 of the carbon coating layer is not greater than 5 μm.

[0031] According to some specific embodiments of the present application, the mass ratio of the carbon material, solid electrolyte, and polymer binder can be (60-80):(0.5-10):(10-30). By limiting the mass ratio of the carbon material, solid electrolyte, and polymer binder to the above range, the conductivity of the negative electrode side can be further effectively improved, and the affinity of the carbon coating with the electrolyte can be further effectively improved, thereby further improving the wettability of the negative electrode side and the ion migration rate.

[0032] According to further specific embodiments of the present application, the carbon material is a one-dimensional carbon material compounded with at least one selected from a zero-dimensional carbon material, a two-dimensional carbon material, and a three-dimensional carbon material, with the one-dimensional carbon material comprising 60wt%-90wt% based on 100% of the total mass of the carbon material. Thus, by mixing carbon materials of different dimensions, the carbon coating can form a three-dimensional structure, further facilitating internal liquid retention in the carbon coating and facilitating the deposition of sodium metal within the carbon coating, thereby reducing the deposition volume of sodium metal on the surface of the negative electrode sheet and minimizing volume expansion.

[0033] 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 within the entire 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 compounding of carbon fibers and acetylene black is preferred.

[0034] 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.

[0035] 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, polyacrylate, polyacrylonitrile, polyacrylic acid, sodium polyacrylate, carboxymethyl cellulose, sodium alginate, gum arabic, xanthan gum, and guar gum.

[0036] According to some other specific embodiments of the present application, a laser method can be used to form pores on the surface of the carbon coating, thereby further effectively ensuring a reduction in the contact angle between the electrolyte and the surface of the negative electrode sheet, and at the same time further effectively ensuring an increase in the surface roughness of the negative electrode sheet.

[0037] The preparation method of the above-mentioned negative electrode sheet includes:

[0038] 1) The carbon material, solid electrolyte and polymer binder are mixed uniformly according to a preset ratio, a solvent is added and stirred uniformly to form a slurry, which is then coated on the negative electrode current collector, dried and set aside.

[0039] 2) A laser method is used to form holes (i.e., straight holes) on the surface of the carbon coating to obtain the negative electrode sheet of the present application.

[0040] In a second aspect of the present application, a sodium-ion battery is provided. According to an embodiment of the present application, the sodium-ion battery comprises a negative electrode sheet according to the above embodiment, thereby effectively improving the cycle performance of the sodium-ion battery.

[0041] In particular, the above-mentioned sodium ion battery can be a negative electrode-free sodium ion battery. A negative electrode-free sodium ion battery refers to: sodium is removed from the positive electrode material and deposited in situ on the negative electrode current collector (in this application, it is deposited on the carbon coating on the surface of the negative electrode current collector). No negative electrode active material is added during the production and manufacturing process, and only the negative electrode current collector is used as the nominal negative electrode. However, this negative electrode current collector does not have the function of 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). The metal layer formed on the negative electrode current collector is the true negative electrode.

[0042] Specifically, the negative electrode-free sodium-ion battery includes a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte, with the separator being disposed between the positive and negative electrode sheets. The specific material of the separator is not particularly limited. As some specific examples, the separator includes at least one of a PP separator, a PE separator, a single-sided ceramic separator, a double-sided ceramic separator, a non-woven fabric separator, and a glass fiber separator.

[0043] The positive electrode sheet includes a positive electrode current collector and a positive electrode material layer formed on the positive electrode current collector. The positive electrode material layer includes a positive electrode active material, a positive electrode binder, and a positive electrode conductor.

[0044] For sodium ion batteries, the positive electrode active material may include but is not limited to one or more of transition metal oxides, polyanionic compounds, organic polymers, and Prussian blue materials. In sodium transition metal oxides, the transition metal may be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. For example, the sodium transition metal oxide is Na 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 / 3 Mn 1 / 3 ]O2.

[0045] The polyanionic compound is a compound having sodium ions, transition metal ions and tetrahedral (YO4) n- A class of compounds with anionic units, 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- valence state, such as Na3V2(PO4)3.

[0046] The above-mentioned Prussian blue compounds are sodium ions, transition metal ions and cyanide ions (CN - ) is a class of compounds whose general chemical formula can be expressed as Na x M1[M2(CN)6], wherein 0<x≤2, M1 and M2 are at least one of Ni, Cu, Fe, Mn, Co and Zn respectively.

[0047] The specific material of the positive electrode binder is 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).

[0048] The specific material of the positive electrode conductive agent is 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, and the like.

[0049] In the embodiments of the present application, the specific material of the positive electrode current collector is not particularly limited. As some specific examples, the positive electrode current collector may include but is not limited to at least one of aluminum foil, carbon-coated aluminum foil, and stainless steel foil.

[0050] In the embodiment of the present application, the above-mentioned electrolyte includes an electrolyte salt and an organic solvent, wherein 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.

[0051] 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(oxalatoborate) (NaB(C2O4)2), and sodium difluorooxalatoborate (NaBF2C2O4).

[0052] 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).

[0053] The sodium-ion batteries of the present application may include battery cell forms, battery module forms, and battery pack forms. In some embodiments, battery cells can be assembled into battery modules, and the number of battery cells contained in the battery module can be one or more, and the specific number can be selected by those skilled in the art based on the application and capacity of the battery module. In some embodiments, battery modules can also be assembled into battery packs, and the number of battery modules contained in the battery pack can be one or more, and the specific number can be selected by those skilled in the art based on the application and capacity of the battery pack.

[0054] In a third aspect of the present application, an electrical device is provided. According to an embodiment of the present application, the electrical device comprises a sodium-ion battery as described above. Thus, the electrical device has all the advantages of a sodium-ion battery, which will not be further elaborated here.

[0055] Specifically, the electrical devices may include, but are not limited to, mobile phones, tablets, laptop computers, electric toys, electric tools, battery-powered vehicles, electric cars, ships, spacecraft, etc. Electric toys may include fixed or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. Spacecraft may include airplanes, rockets, space shuttles, and spacecraft, etc.

[0056] The following examples of the present application are described in detail. It should be noted that the following examples are illustrative and are intended only to explain the present application and are not to be construed as limiting the present application. In addition, unless otherwise expressly stated, all reagents used in the following examples are commercially available or can be synthesized according to methods described herein or known methods. Reaction conditions not listed are also readily available to those skilled in the art.

[0057] Example 1

[0058] This embodiment provides a sodium ion battery, the preparation method of which includes:

[0059] (1) Preparation of negative electrode sheet:

[0060] First, carbon nanotubes, polyacrylate (a binder), and β″-Al2O3 were dispersed in the solvent NMP and mixed evenly to create a carbon coating slurry. The mass ratio of carbon nanotubes, polyacrylate, and β″-Al2O3 was 70:25:5. This carbon coating slurry was then applied to the negative electrode current collector aluminum foil. After drying, cold pressing, slitting, and cutting, it was set aside. The carbon coating thickness was 5 μm.

[0061] Then, a laser method is used to form straight holes with a diameter of 2 μm on the surface of the carbon coating. The density of the holes on the surface of the carbon coating is 2000 / mm 2 , the depth of the straight hole is 3 μm, and the negative electrode sheet of the present application is obtained.

[0062] (2) Preparation of positive electrode sheet:

[0063] 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 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, and then the positive electrode sheet is obtained after roller pressing and slitting.

[0064] (3) Preparation of diaphragm:

[0065] A polyethylene film with a thickness of 17 μm was used as the separator.

[0066] (4) Preparation of electrolyte:

[0067] 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, and the volume ratio of diethylene glycol dimethyl ether to tetraethylene glycol dimethyl ether was 1:1.

[0068] (5) Preparation of sodium ion batteries:

[0069] The positive electrode sheet, negative electrode sheet and separator prepared above are stacked in order so that the separator is between the positive and negative electrode sheets, and then wound to obtain a bare battery cell. The bare battery cell is placed in an aluminum-plastic film soft package, and after drying, the electrolyte is injected. After vacuum packaging, standing, formation, shaping and other processes, a soft-pack sodium ion battery is obtained.

[0070] Example 2

[0071] The difference between Example 2 and Example 1 is that:

[0072] The laser method is used to form straight holes with a diameter of 1 μm on the surface of the carbon coating. The density of the holes on the surface of the carbon coating is 3000 / mm 2, the depth of the straight hole is 4μm.

[0073] The rest of the contents are the same as those in Example 1.

[0074] Example 3

[0075] The only difference between Example 3 and Example 1 is that:

[0076] The laser method is used to form straight holes with a diameter of 3 μm on the surface of the carbon coating. The density of the holes on the surface of the carbon coating is 1000 / mm 2 , the depth of the straight hole is 2μm.

[0077] The rest of the contents are the same as those in Example 1.

[0078] Example 4

[0079] The only difference between Example 4 and Example 1 is that:

[0080] Example 4 uses Na3Zr2Si2PO 12 Replace β″-Al2O3.

[0081] The rest of the contents are the same as those in Example 1.

[0082] Example 5

[0083] The only difference between Example 5 and Example 1 is that:

[0084] Example 5 Using Na 3.25 La 0.25 Zr 0.5 Si2PO 12 Replace β″-Al2O3.

[0085] The rest of the contents are the same as those in Example 1.

[0086] Example 6

[0087] The only difference between Example 6 and Example 1 is that:

[0088] The mass ratio of carbon nanotubes, polyacrylate and β″-Al2O3 is 70:28:2.

[0089] The rest of the contents are the same as those in Example 1.

[0090] Example 7

[0091] The only difference between Example 7 and Example 1 is that:

[0092] The mass ratio of carbon nanotubes, polyacrylate and β″-Al2O3 is 70:20:10.

[0093] The rest of the contents are the same as those in Example 1.

[0094] Example 8

[0095] The only difference between Example 8 and Example 1 is that:

[0096] In this embodiment, the carbon nanotubes in the carbon coating slurry are replaced by a mixture of carbon nanotubes and acetylene black, wherein the mass ratio of the carbon nanotubes to the acetylene black is 80:20.

[0097] The rest of the contents are the same as those in Example 1.

[0098] Example 9

[0099] The only difference between Example 9 and Example 1 is that:

[0100] In this embodiment, the carbon nanotubes in the carbon coating slurry are replaced with a composite of carbon nanotubes and graphene, wherein the mass ratio of the carbon nanotubes to the graphene is 70:30.

[0101] The rest of the contents are the same as those in Example 1.

[0102] Example 10

[0103] The only difference between Example 10 and Example 1 is that:

[0104] In this embodiment, the carbon nanotubes in the carbon coating slurry are replaced by a mixture of carbon nanotubes and mesocarbon microspheres, wherein the mass ratio of the carbon nanotubes to the mesocarbon microspheres is 60:40.

[0105] The rest of the contents are the same as those in Example 1.

[0106] Example 11

[0107] The only difference between Example 11 and Example 4 is that:

[0108] In this embodiment, the carbon nanotubes in the carbon coating slurry are replaced by a mixture of carbon fibers and acetylene black, wherein the mass ratio of the carbon fibers to the acetylene black is 80:20.

[0109] The rest of the contents are the same as those in Example 4.

[0110] Comparative Example 1

[0111] The difference between Comparative Example 1 and Example 1 is only that:

[0112] (1) Preparation of negative electrode sheet:

[0113] No straight pores were formed on the surface of the carbon coating.

[0114] The rest of the contents are the same as those in Example 1.

[0115] Comparative Example 2

[0116] The difference between Comparative Example 2 and Example 1 is only that:

[0117] (1) Preparation of negative electrode sheet:

[0118] No β″-Al2O3 was added to the carbon coating slurry.

[0119] The rest of the contents are the same as those in Example 1.

[0120] The contact angles between the negative electrode surfaces prepared in Examples 1-11 and Comparative Examples 1-2 and the electrolyte were tested, and the specific testing methods are as follows:

[0121] 1) Place the negative electrode sample on the contact angle meter's sample stage and adjust it appropriately to ensure the negative electrode sample surface is level with the liquid in the syringe. 2) Use the syringe to slowly inject the electrolyte onto the negative electrode sample surface, taking care not to allow the liquid to flow or spread across the surface. 3) Use the device's camera to capture a photo of the droplet on the negative electrode sample surface, including both the front and side views, to obtain complete contact angle information. 4) Measure the contact angle using the ruler tool in the contact angle measurement software. For improved accuracy, perform multiple measurements and take the average. The test results are shown in Table 1.

[0122] The surface roughness of the negative electrode sheets of Examples 1-11 and Comparative Examples 1-2 was tested respectively. The specific testing methods are as follows:

[0123] The surface roughness of the cut negative electrode sheet was calculated using the ISO 25178 standard, which complies with international microscopic surface geometry measurement standards, to obtain the Ra parameter. The test results are shown in Table 1.

[0124] The bonding strength between the sodium metal layer deposited on the surface of the negative electrode sheet of Examples 1-11 and Comparative Examples 1-2 and the surface of the negative electrode sheet was tested respectively. The specific testing method is as follows:

[0125] Adhesive tapes with different adhesive strengths (wrinkled adhesive, yellow adhesive, and blue adhesive) were purchased, with the adhesive strength of blue adhesive > yellow adhesive > wrinkled adhesive. Fully charged battery cells were disassembled in a glove box, and adhesive tapes with different adhesive strengths were adhered to the surface of the negative electrode deposition layer. A 2kg small wheel was used to roll back and forth three times, and a peel test was performed using a small tensile testing machine to determine the condition of the sodium metal layer adhered to the tape. The test results are shown in Table 1.

[0126] The cycle performance of the sodium ion batteries prepared in Examples 1-11 and Comparative Examples 1-2 was tested respectively, and the specific test methods are as follows:

[0127] Using a flat test fixture, a preload of 0.25 MPa was applied to the battery cell. Cycling tests were performed at room temperature using a 0.5P / 0.5P rate, with the charge and discharge voltage range controlled between 2.5V and 3.5V. The number of cycles required to achieve 90% capacity loss was recorded. The test results are shown in Table 1.

[0128] Table 1

[0129] As can be seen from Table 1, compared with Comparative Example 1, the contact angle between the negative electrode sheet and the electrolyte of Examples 1-11 is significantly reduced, the roughness of the surface of the negative electrode sheet is significantly increased, the adhesion performance between the sodium metal layer deposited on the surface of the negative electrode sheet and the surface of the negative electrode sheet is significantly improved, and the cycle performance of the battery is significantly improved. It can be seen that by providing holes on the surface of the negative electrode sheet, the contact angle between the negative electrode sheet and the electrolyte can be significantly reduced, the roughness of the surface of the negative electrode sheet can be significantly increased, the adhesion performance between the sodium metal layer deposited on the surface of the negative electrode sheet and the surface of the negative electrode sheet can be significantly improved, and the cycle performance of the battery can be significantly improved.

[0130] It can also be seen from Table 1 that compared with Comparative Example 2, the contact angle between the negative electrode sheet and the electrolyte of Examples 1-11 is significantly reduced and the cycle performance of the battery is significantly improved. It can be seen that adding a solid electrolyte to the carbon coating can effectively reduce the contact angle between the negative electrode sheet and the electrolyte and effectively improve the cycle performance of the battery.

[0131] It can also be seen from Table 1 that compared with Example 1, the contact angle between the negative electrode sheet of Examples 8-10 and the electrolyte is reduced and the cycle performance of the battery is improved. It can be seen that the use of a compound of one-dimensional carbon material carbon nanotubes and zero-dimensional carbon material acetylene black, a compound of one-dimensional carbon material carbon nanotubes and two-dimensional carbon material graphene, or a compound of one-dimensional carbon material carbon nanotubes and three-dimensional carbon material mesophase carbon microspheres improves the affinity of the carbon coating with the electrolyte and improves the cycle performance of the battery.

[0132] It can also be seen from Table 1 that compared with Example 4, the contact angle between the negative electrode sheet of Example 11 and the electrolyte is significantly reduced, and the cycle performance of the battery is significantly improved. It can be seen that the use of a one-dimensional carbon material carbon fiber and a zero-dimensional carbon material acetylene black compound significantly improves the affinity between the carbon coating and the electrolyte, and significantly improves the cycle performance of the battery. In addition, the comprehensive performance of Example 11 is the best, which shows that when the solid electrolyte uses Na3Zr2Si2PO 12 Moreover, when the carbon material is a combination of one-dimensional carbon material carbon fiber and zero-dimensional carbon material acetylene black, the overall performance of the battery is the best.

[0133] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0134] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limitations on the present application. Ordinary technicians in this field can change, modify, replace and modify the above embodiments within the scope of the present application.

Claims

1. A negative electrode sheet, wherein: include: negative electrode current collector; A carbon coating is provided 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; a 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, and the depth of the pores is less than the thickness of the carbon coating.

2. The negative electrode sheet according to claim 1, wherein: The depth of the hole is h2, and the thickness of the carbon coating is h1, satisfying 40%≤h2 / h1≤80%.

3. The negative electrode sheet according to claim 1 or 2, wherein: The diameter of the pore is 1 μm to 3 μm; And / or, the density of the pores on the surface of the carbon coating is 1000 / mm 2 ~3000 pieces / mm 2 .

4. The negative electrode sheet according to any one of claims 1 to 3, wherein The contact angle θ between the surface of the negative electrode sheet and the electrolyte satisfies 0°≤θ≤10°.

5. The negative electrode sheet according to any one of claims 1 to 4, wherein The roughness Ra of the surface of the negative electrode sheet satisfies 0.4 μm≤Ra≤3.2 μm.

6. The negative electrode sheet according to any one of claims 2 to 5, wherein: The thickness h1 of the carbon coating is not greater than 5 μm.

7. The negative electrode sheet according to any one of claims 1 to 6, wherein: The mass ratio of the carbon material, the solid electrolyte and the polymer binder is (60-80):(0.5-10):(10-30).

8. The negative electrode sheet according to any one of claims 1 to 7, wherein The carbon material is compounded by a one-dimensional carbon material and at least one selected from a zero-dimensional carbon material, a two-dimensional carbon material and a three-dimensional carbon material.

9. The negative electrode sheet according to any one of claims 1 to 8, wherein The solid electrolyte includes β″-Al2O3, Na3Zr2Si2PO 12 、Na 3+x La x Zr 2x Si2PO 12 、Na3PS4、Na 11 Sn2PS4、Na7P3S 11 At least one of which 0 <x≤0.5。 10. The negative electrode sheet according to claim 8, wherein: The one-dimensional carbon material includes at least one of carbon nanotubes and carbon fibers; and / or, the zero-dimensional carbon material comprises at least one of acetylene black, furnace black, Ketjen black and carbon quantum dots; and / or, the two-dimensional carbon material comprises at least one of graphene and multilayer graphite sheets; And / or, the three-dimensional carbon material includes at least one of mesocarbon microbeads, natural graphite, artificial graphite, hard carbon, and porous activated carbon.

11. The negative electrode sheet according to any one of claims 1 to 10, wherein 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.

12. The negative electrode sheet according to any one of claims 1 to 11, wherein The pores are formed on the surface of the carbon coating by using a laser method.

13. A sodium ion battery, wherein: The negative electrode sheet comprises the negative electrode sheet according to any one of claims 1 to 12.

14. An electrical device, wherein: A sodium ion battery according to claim 13.

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