Sodium-ion battery negative electrode and preparation method and application thereof

Abstract

The invention provides a sodium ion battery negative electrode as well as a preparation method and application thereof. The negative electrode comprises a first negative electrode pole piece structure or a second negative electrode pole piece structure containing a porous structure, the first negative electrode pole piece structure containing the porous structure comprises a porous current collector, and the second negative electrode pole piece structure containing the porous structure comprises a negative electrode current collector and a porous modification layer located on the surface of at least one side of the negative electrode current collector; and the thickness change of the negative pole piece in a 0-100% charge state is between 0 and 5.0 percent. According to the sodium ion battery negative electrode provided by the invention, the change of the thickness of the electrode in the charging and discharging process of the battery is inhibited through the physical confinement of the porous structure of the negative electrode end on sodium metal and the synergistic effect of related electrochemical reactions; therefore, the problems of volume expansion and short cycle life caused by deposition / stripping of sodium metal on the surface of the negative electrode current collector in the non-negative electrode secondary sodium battery are solved, and the service life and the stability of the battery are improved while the high energy density is maintained.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of sodium ion batteries, and relates to a sodium ion battery negative electrode and a preparation method and application thereof. BACKGROUND

[0002] Among numerous battery technologies, lithium ion batteries, as green and environmentally friendly energy storage devices, have been widely used in electronic markets, new energy vehicles and other energy storage fields due to their high energy density, long cycle life, safety and no pollution, which greatly improves the production and living standards of human beings. However, the global reserves of lithium resources are limited, and the content of lithium element in the earth's crust is only 0.0065%. With the rapid increase in demand for batteries with the development of new energy vehicles, the bottleneck of resources gradually appears, and the high cost limits the large-scale application and sustainable development of lithium ion batteries. Under this background, sodium ion batteries with many advantages show sustainability and economy, making them one of the focuses of research and development of new generation battery technologies.

[0003] CN211017288U discloses a sodium ion battery cell, which comprises: a sodium ion battery cell comprising: a sodium ion battery positive electrode sheet, a sodium ion battery negative electrode sheet and a separator; wherein the sodium ion battery positive electrode sheet, the separator and the sodium ion battery negative electrode sheet are connected in the order of sodium ion battery positive electrode sheet / separator / sodium ion battery negative electrode sheet / separator, and the interface adhesion formed by hot pressing is provided at the interface between the sodium ion battery positive electrode sheet and the separator and the interface between the sodium ion battery negative electrode sheet and the separator; in the sodium ion battery positive electrode sheet, the positive electrode active material coating is arranged on the front and back surfaces of the positive electrode current collector, and the positive electrode modification coating is arranged on the outer surface of the positive electrode active material coating; in the sodium ion battery negative electrode sheet, the negative electrode active material coating is arranged on the front and back surfaces of the negative electrode current collector, and the negative electrode modification coating is arranged on the outer surface of the negative electrode active material coating.

[0004] Due to the relatively large atomic size and weight of sodium, the energy density of the current sodium ion battery is generally lower than that of the lithium battery. Therefore, how to improve the energy density of the sodium ion battery is a technical problem to be solved for the current sodium ion battery. One of the solutions is to use ultra-thin sodium metal to manufacture high-energy sodium metal batteries. However, due to the softness and high viscosity of the metal sodium, it is difficult to process and mold, and it is difficult to produce ultra-thin sodium metal negative electrodes. In addition, the poor air stability of sodium metal is not conducive to large-scale manufacturing. The anode-free sodium battery can solve the above problems, wherein the anode-free means that the negative electrode does not need active materials, conductive agents, adhesives and other substances, and only the current collector is needed to assemble the battery. The sodium metal of the negative electrode is formed in situ electrochemically during the first charging process, and the active sodium ions come entirely from the positive electrode material. The anode-free sodium battery not only simplifies the manufacturing process, but also reduces the mass of the negative electrode and improves the energy density of the full battery.

[0005] Without the protection of a stable host material on the negative side, the deposition / stripping of sodium metal on the negative side can cause changes in the volume of the battery, leading to battery swelling, especially under long-term use or high-intensity conditions. The swelling of the battery not only affects the appearance, but also can cause damage to the internal components of the battery, leading to a decrease in cycle life, and even serious safety problems such as battery leakage / short circuit. The cycle life and safety of the metal lithium battery without a negative electrode are facing great challenges. In addition, for some specific fields such as aerospace / medical devices, there are strict requirements for the size and weight of the battery, and the swelling problem of the battery is more prominent. Therefore, the research on low-swelling batteries has become one of the hotspots in the field of battery technology. Low-swelling batteries not only can improve the stability and safety of the battery, but also can prolong the service life of the battery, reduce maintenance costs, and promote the popularization and development of electric vehicles / portable electronic devices and other products. However, to realize the commercial application of low-swelling batteries, many technical problems need to be solved, including challenges in material selection / structure design / production process / electrolyte optimization, etc.

[0006] Therefore, how to solve the problem of volume expansion of sodium metal in the sodium secondary battery without a negative electrode is an urgent consideration. SUMMARY

[0007] In view of the deficiencies in the prior art, the purpose of the present application is to provide a sodium ion battery negative electrode and a preparation method and use thereof. The sodium ion battery negative electrode provided by the present application inhibits the change in electrode thickness during the charging and discharging process of the battery through the synergistic effect of the physical confinement of sodium metal by the porous structure at the negative end and the related electrochemical reaction, thereby solving the problems of volume expansion and low cycle life caused by the deposition / stripping of sodium metal on the surface of the negative current collector in the secondary sodium battery without a negative electrode, thereby maintaining high energy density while improving the service life and stability of the battery.

[0008] To achieve this purpose, the present application adopts the following technical solutions:

[0009] In a first aspect, the present application provides a sodium ion battery negative electrode, which comprises a first negative electrode sheet structure comprising a porous structure or a second negative electrode sheet structure comprising a porous structure, the first negative electrode sheet structure comprising a porous current collector, and the second negative electrode sheet structure comprising a negative current collector and a porous modification layer on at least one side surface of the negative current collector;

[0010] The thickness change of the negative electrode sheet under 0-100% state of charge is between 0-5.0%, for example, the thickness change can be 0%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5%, etc., but is not limited to the listed values, and other values not listed in this range are also applicable.

[0011] It should be noted that the porous structure of the negative electrode provided by the present application is derived from the pore structure of the material itself (such as porous carbon material, porous current collector material) and the porous structure obtained by the structure layer (such as the pore structure retained after the slurry coating and drying).

[0012] The sodium ion battery negative electrode provided by the present application can inhibit the change of the electrode thickness during the charging and discharging of the battery through the synergistic effect of the physical confinement of the sodium metal by the porous structure of the negative electrode end (the presence of the porous current collector or the porous modification layer) and the related electrochemical reaction; during the charging of the battery, the sodium metal is deposited in the porous structure of the porous current collector or the porous modification layer, and the negative electrode side porous framework hardly expands, and during the discharging, the sodium metal is dissolved from the porous interior, and the negative electrode side porous framework does not shrink, thereby solving the problems of volume expansion and low cycle life caused by the deposition / detachment of the sodium metal on the surface of the negative electrode current collector in the secondary sodium battery without negative electrode, thereby maintaining the high energy density while improving the service life and stability of the battery.

[0013] In the present application, if the negative electrode does not contain a porous structure, the problem of the change of the battery volume caused by the deposition / dissolution of the sodium metal during the charging and discharging of the battery cannot be solved.

[0014] Preferably, the pore volume in the porous structure is greater than the volume of the sodium metal to be deposited.

[0015] In the present application, the volume of the sodium metal is obtained by the calculated ratio of the theoretical capacity of the battery / volume specific capacity of the sodium metal.

[0016] Preferably, the pore volume in the porous structure is 0.1-2 mL / g, such as 0.1 mL / g, 0.2 mL / g, 0.3 mL / g, 0.4 mL / g, 0.5 mL / g, 0.6 mL / g, 0.7 mL / g, 0.8 mL / g, 0.9 mL / g, 1 mL / g, 1.1 mL / g, 1.2 mL / g, 1.3 mL / g, 1.4 mL / g, 1.5 mL / g, 1.6 mL / g, 1.7 mL / g, 1.8 mL / g, 1.9 mL / g or 2 mL / g, and preferably 0.3-1 mL / g, but is not limited to the listed values, and other values not listed in the range are also applicable.

[0017] In the present application, the pore volume in the porous structure is further regulated to 0.3-1 mL / g, which is more conducive to balancing the mass / volume energy density, cycle stability, service life and battery expansion rate of the battery; if less than 0.3 mL / g, it will affect the regulation of the expansion rate and the service life during the charging and discharging of the battery, and if the pore volume is too large, more than 1 mL / g, it will reduce the mass / volume energy density of the battery.

[0018] It should be noted that the porous structure in the present application is adaptively regulated according to different structure layers; if it is a porous current collector structure, a current collector foil with a preferred pore volume can be selected; and if it is a porous modification layer structure, the pore volume size in the modification layer can be regulated by adjusting the coating load, the solid content of the slurry, and the particle size / pore size / density of the carbon skeleton and functional materials in the porous modification layer.

[0019] Preferably, the porous current collector comprises any one or a combination of at least two of foamed nickel, foamed nickel alloy, foamed copper, foamed copper alloy, foamed aluminum, foamed aluminum alloy, foamed iron, foamed iron alloy, foamed zinc, foamed zinc alloy, copper mesh, copper alloy mesh, aluminum mesh, aluminum alloy mesh, titanium mesh, titanium alloy mesh, stainless steel mesh, stainless steel alloy mesh, nickel mesh, nickel alloy mesh, foamed carbon, carbon aerogel, carbon cloth, carbon paper, or carbon felt, preferably any one or a combination of at least two of foamed copper, stainless steel mesh, aluminum mesh, or foamed carbon.

[0020] In the present application, the porous current collector is used as the negative electrode of the sodium ion battery, and foamed copper, stainless steel mesh, aluminum mesh, or foamed carbon is selected, which can better regulate the volume change during sodium metal deposition in the battery charging and discharging process.

[0021] Preferably, the material in the porous modification layer comprises a carbon material and / or a non-carbon material, preferably at least a carbon material.

[0022] Preferably, the porous modification layer further comprises a binder.

[0023] The present application does not specially limit the type of binder, and any type of binder used in the preparation of battery electrode sheets is applicable to the present application, and the binder includes but is not limited to any one or a combination of at least two of polyacrylic acid, lithium polyacrylate, sodium polyacrylate, potassium polyacrylate, sodium carboxymethyl cellulose, polyvinylidene fluoride, sodium alginate, butadiene styrene rubber, guar gum, xanthan gum, tragacanth gum, gum arabic, polyacrylonitrile, or acrylonitrile multi-polymer.

[0024] Preferably, the negative electrode current collector comprises any one or a combination of at least two of copper foil, aluminum foil, stainless steel foil, or Ti foil.

[0025] Preferably, the carbon material comprises any one or a combination of at least two of activated carbon, hard carbon, graphite, soft carbon, carbon nanotube, carbon fiber, mesoporous carbon, or porous carbon.

[0026] Preferably, the non-carbon material comprises any one or a combination of at least two of a metal, an alloy, or a metal compound.

[0027] It should be noted that the types of compounds in the metal compounds in the present application include, but are not limited to, at least one of halides, sulfides, oxides, nitrides, selenides or hydrides, and more preferably halides and phosphides.

[0028] Preferably, the metal elements in the metal and alloy each independently include any one or a combination of at least two of Sn, Bi, Ge or Zn.

[0029] When the porous modification layer contains metal (or alloy) and its compound, the carbon material can reduce the sodium deposition overpotential, promote the uniform deposition of sodium metal, and reduce the volume expansion caused by sodium deposition; if it is pure metal and metal (or alloy) and its compound, the regulation of the volume change of the battery during sodium deposition / dissolution cannot be achieved.

[0030] It should be noted that when the porous modification layer contains carbon material, non-carbon material and binder, the mass ratio is 99:0:1 to 1:1:1, and adaptive selection and adjustment can be made within this numerical range.

[0031] In a second aspect, the present application provides a preparation method of the sodium ion battery negative electrode according to the first aspect, and the preparation method comprises the following steps:

[0032] The first negative electrode sheet structure containing a porous structure is used as the negative electrode, or the second negative electrode sheet structure containing a porous structure is used as the negative electrode, to obtain the sodium ion battery negative electrode.

[0033] Preferably, the preparation of the second negative electrode sheet structure containing a porous structure comprises compounding the porous modification layer on at least one side of the surface of the negative electrode current collector.

[0034] Preferably, the compounding method comprises any one or a combination of at least two of coating, magnetron sputtering, spin coating, electron beam evaporation, thermal evaporation or 3D printing.

[0035] It should be noted that according to the type of material in the porous modification layer, a person skilled in the art can adaptively select the compounding method, such as slurry coating method.

[0036] When the slurry coating method is used, after the porous modification layer is coated, it can be directly dried to obtain the porous modification layer, without the need for further treatment means such as rolling.

[0037] In a third aspect, the present application further provides a sodium ion battery, which comprises the sodium ion battery negative electrode according to the first aspect.

[0038] Preferably, the capacity of the sodium-ion battery negative electrode is 0-20% of the capacity of the sodium-ion battery, such as 0%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, or 20%, etc., but not limited to the listed values, and other unlisted values within the range are also applicable.

[0039] It should be noted that the sodium-ion battery provided by the present application, in addition to the negative electrode defined above, also includes a positive electrode, a separator and an electrolyte, other structures and the assembly method of the battery, which are all conventional technical solutions for those skilled in the art, and the present application is applicable within a reasonable range.

[0040] The remaining structures and preparation methods in the sodium battery and the assembly method of the sodium battery are all conventional technical means, which are not specially limited and can be adaptively selected and adjusted by those skilled in the art according to actual needs.

[0041] Optionally, the positive electrode sheet contains a positive electrode active material, a conductive agent and a binder, the positive electrode active material includes but is not limited to Prussian blue compounds, polyanion compounds or layered transition metal oxides, etc.; the polyanion compound is selected from one or more of sodium vanadium phosphate, sodium iron phosphate, sodium iron pyrophosphate phosphate, sodium manganese phosphate, sodium vanadium fluorophosphate, sodium iron fluorophosphate, sodium manganese acid iron, sodium nickel manganese acid; the chemical formula of the layered transition metal oxide is Na x MO2, M is selected from any one or a combination of at least two of Fe, Co, Ni, Mn, Cr or Ti;

[0042] Optionally, the separator includes but is not limited to at least one of polyethylene, polypropylene, polyvinylidene fluoride or aramid;

[0043] Optionally, the electrolyte is composed of an organic solvent and an electrolyte sodium salt, the organic solvent is selected from one or more of ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, propylene carbonate, methyl acetate, ethyl propionate, fluoroethylene carbonate, diethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, methyl tert-butyl ether; the electrolyte sodium salt is selected from one or more of sodium hexafluorophosphate, sodium bisfluorosulfonylimide, sodium bis-trifluoromethanesulfonylimide, sodium triflate, sodium tetrafluoroborate, sodium difluorophosphate, sodium perchlorate.

[0044] Compared with the prior art, the present application has the following beneficial effects:

[0045] The sodium ion battery negative electrode provided by the application inhibits the change of electrode thickness in the battery charging and discharging process through the synergistic effect of the physical confinement of sodium metal by the porous structure (the presence of the porous current collector or the porous modification layer) at the negative electrode end and the related electrochemical reaction; when the battery is charged, the sodium metal is deposited inside the porous structure of the porous current collector or the porous modification layer, and the negative electrode side porous framework hardly expands, and when the battery is discharged, the sodium metal is dissolved from the porous interior, and the negative electrode side porous framework does not shrink, thereby solving the problems of volume expansion and low cycle life caused by the deposition / exfoliation of sodium metal on the surface of the negative electrode current collector in the secondary sodium battery without negative electrode, thereby maintaining high energy density while improving the service life and stability of the battery. DETAILED DESCRIPTION

[0046] The technical solutions of the application will be further described below through specific examples. Those skilled in the art should understand that the examples are only used to help understand the application and should not be regarded as specific limitations on the application.

[0047] Example 1

[0048] The example provides a sodium ion battery negative electrode, which comprises an aluminum foil current collector and a porous modification layer on the surfaces of the aluminum foil current collector; the porous modification layer comprises activated carbon, a binder polyacrylic acid (PAA) and sodium carboxymethyl cellulose CMC.

[0049] The preparation method of the negative electrode is as follows:

[0050] The activated carbon, the binder polyacrylic acid (PAA) and the sodium carboxymethyl cellulose CMC are mixed in a mass ratio of 95:4:1, then deionized water is added as a solvent, and a negative electrode slurry with a solid content of 45% is prepared and uniformly stirred; the negative electrode slurry is uniformly coated on one surface of the negative electrode current collector aluminum foil with a thickness of 12 μm, and the coating load on the surface of the current collector is 0.15 mg / cm 2 ; 80°C drying is performed to obtain a negative electrode sheet coated with negative electrode slurry on one side, and then the above steps are repeated on the other surface of the negative electrode sheet to obtain a negative electrode sheet coated with negative electrode slurry on both sides; after the coating is completed, the negative electrode sheet is cut into a specification of 58 mm x 45 mm for use, and the negative electrode sheet is not subjected to rolling operation, and the pore volume of the negative electrode sheet is measured to be 0.5 mL / g.

[0051] Example 2

[0052] The difference between the example and example 1 is that the porous modification layer in the example comprises activated carbon, Zn powder, a binder polyacrylic acid (PAA) and a dispersant sodium carboxymethyl cellulose CMC.

[0053] The mass ratio of the activated carbon, Zn powder, binder polyacrylic acid (PAA) and dispersant sodium carboxymethyl cellulose (CMC) in the preparation method is 92:5:2:1, and the pore volume of the porous modification layer is 0.45 mL / g

[0054] The remaining preparation method and parameters remain the same as in Example 1.

[0055] Example 3

[0056] The difference between this example and Example 1 is that the pore volume of the porous modification layer in this example is 0.3 mL / g.

[0057] The remaining preparation method and parameters remain the same as in Example 1.

[0058] Example 4

[0059] The difference between this example and Example 1 is that the pore volume of the coating layer of the porous modification layer in this example is 1.0 mL / g.

[0060] The remaining preparation method and parameters remain the same as in Example 1.

[0061] Example 5

[0062] The difference between this example and Example 1 is that the activated carbon is replaced by Zn powder in this example, and the pore volume in the porous modification layer is 0.08 mL / g.

[0063] The remaining preparation method and parameters remain the same as in Example 1.

[0064] Example 6

[0065] The difference between this example and Example 1 is that the negative electrode in this example is a foam copper, i.e., the foam copper is directly used as the negative electrode.

[0066] Example 7

[0067] The difference between this example and Example 1 is that the pore volume of the negative electrode sheet in this example is 0.1 mL / g.

[0068] The remaining preparation method and parameters remain the same as in Example 1.

[0069] Example 8

[0070] The difference between this example and Example 1 is that the pore volume of the negative electrode sheet in this example is 2 mL / g.

[0071] The remaining preparation method and parameters remain the same as in Example 1.

[0072] Comparative Example 1

[0073] The difference between this comparative example and Example 1 is that the negative electrode in this comparative example is a pure aluminum foil.

[0074] Comparative Example 2

[0075] The difference between this comparative example and Example 1 is that the porous modification layer (substantially non-porous structure) in this comparative example is binder polyacrylic acid (PAA) and sodium carboxymethyl cellulose CMC.

[0076] The preparation method is as follows:

[0077] The binder polyacrylic acid (PAA) and sodium carboxymethyl cellulose CMC are mixed in a mass ratio of 7:3, then deionized water is added as a solvent to prepare a negative electrode slurry with a solid content of 40%, and the negative electrode slurry is uniformly coated on one surface of a negative electrode current collector aluminum foil with a thickness of 12 μm. The mass of the negative electrode active material on the negative electrode tab is 0.3 mg / cm 2 , and dried at 80°C to obtain a negative electrode tab coated with a single side of negative electrode slurry. Then, the above steps are repeated on the other surface of the negative electrode tab to obtain a negative electrode tab coated with a double side of negative electrode slurry. After coating, the negative electrode tab is cold-pressed and cut into a specification of 58 mm x 45 mm for use. The negative electrode tab is not subjected to roll pressing operation, and the pore volume of the negative electrode tab is measured to be 0.06 mL / g.

[0078] The sodium-ion battery negative electrode provided by Examples 1-8 and Comparative Examples 1-2 is prepared into a sodium-ion battery:

[0079] Preparation of positive electrode tab

[0080] The positive electrode active material sodium pyrophosphate, the conductive agent Super P, and the binder polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 97:1.0:2.0, N-methyl pyrrolidone (NMP) is added as a solvent to prepare a slurry with a solid content of 75%, and the positive electrode slurry is uniformly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 12 μm. The mass of the positive electrode active material on the positive electrode tab is 20.0 mg / cm2, and the positive electrode tab is dried at 90°C to obtain a positive electrode tab coated with a single side of positive electrode slurry. Then, the above steps are repeated on the other surface of the positive electrode tab to obtain a positive electrode tab coated with a double side of positive electrode slurry. After coating, the positive electrode tab is cold-pressed and cut into a specification of 56 mm x 43 mm for use. The tap density of the positive electrode tab is 2.0 g / cm 3 ;

[0081] Preparation of electrolyte

[0082] In a glove box under dry argon atmosphere, organic solvents ethylene glycol dimethyl ether, diethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether were mixed in a volume ratio of 1:1:2, then sodium salt sodium hexafluorophosphate (NaPF6) was added to the organic solvent to dissolve and mix uniformly, to obtain an electrolyte with a concentration of 1 mol / L of sodium salt;

[0083] Preparation of the separator

[0084] A polyethylene (PE) film with a thickness of 15 μm (provided by Celgard) was used;

[0085] Preparation of the packaging material

[0086] A 113 μm aluminum-plastic composite film provided by DNP was used;

[0087] Preparation of the sodium battery with less negative electrode

[0088] The positive electrode sheet, the separator and the negative electrode sheet prepared above were stacked in order, with the separator between the positive electrode sheet and the negative electrode sheet to play a separating role, and were wound to obtain an electrode assembly. The electrode assembly was loaded into the packaging shell formed by the packaging material of the application, and was dehydrated at 80°C, injected with the prepared electrolyte, and subjected to vacuum packaging, standing, formation, shaping and other processes to obtain a secondary battery.

[0089] The sodium ion batteries provided by Examples 1-8 and Comparative Examples 1-2 were subjected to performance tests under the following test conditions:

[0090] (a) At room temperature (25°C), the battery was charged at a current of 0.2 C to 3.6 V to obtain the charge capacity of the battery, then was left for 5 minutes, and was discharged at a current of 0.2 C to 1.5 V to obtain the discharge capacity of the battery;

[0091] (b) The initial efficiency of the battery was obtained by dividing the first discharge capacity of the battery by the first charge capacity;

[0092] (c) The energy density of the battery = battery capacity x average voltage of the battery ÷ battery mass = battery energy ÷ (mass of the positive electrode + mass of the negative electrode + mass of the separator + mass of the electrolyte);

[0093] (d) Regarding the cycle life of the battery, at room temperature (25°C), the battery was subjected to constant current charge and discharge test at a current of 0.2 C in the voltage range of 1.5-3.6 V for 3 times of pre-cycle, then was subjected to constant current charge and discharge cycle test at a current of 0.5 C in the voltage range of 1.5-3.6 V, and when the battery capacity was lower than 80% of the first discharge capacity (0.5 C), the cycle life of the battery was considered to be terminated.

[0094] The test results are shown in Table 1.

[0095] Table 1

[0096]

[0097]

[0098] From Table 1, it can be seen that:

[0099] From the data results of Examples 1-4 and Example 6, it can be seen that the sodium ion battery negative electrode provided by the present application, the sodium ion battery negative electrode provided by the present application, the sodium metal physical confinement and the synergistic effect of the related electrochemical reaction to inhibit the change of the electrode thickness in the battery charging and discharging process, solve the problem of volume expansion and low cycle life caused by the deposition / peeling of sodium metal on the surface of the negative electrode current collector in the negative electrode-free secondary sodium battery, thereby maintaining high energy density while improving the service life and stability of the battery.

[0100] From the data results of Examples 1, 2 and 5, it can be seen that if the porous modification layer does not contain carbon materials, the alloy expansion problem will occur when pure metal (alloy) is used as the supporting material, which will greatly increase the expansion rate of the thickness change of the negative electrode end at full charge.

[0101] From the data results of Examples 1 and Examples 3 and 4, Examples 7-8, it can be seen that if the pore volume in the porous structure is too large, it is not conducive to the improvement of the battery coulomb efficiency and energy density, and if the pore volume is too small, it will also lead to limited space for accommodating the deposited sodium metal, which is not conducive to effectively inhibiting the battery expansion and improving the service life of the battery.

[0102] From the data results of Examples 1 and Comparative Examples 1-2, it can be seen that if the negative electrode does not contain a porous structure, the problem of uniform deposition of sodium metal and large volume change during battery charging and discharging cannot be solved, which is not conducive to the energy density and cycle life of the battery.

[0103] In summary, the sodium ion battery negative electrode provided by the present application, through the synergistic effect of the physical confinement of sodium metal and the related electrochemical reaction of the porous structure (the existence of the porous current collector or the porous modification layer) of the negative electrode end to inhibit the change of the electrode thickness during the battery charging and discharging process; during battery charging, sodium metal is deposited in the porous structure of the porous current collector or the porous modification layer, and the negative electrode side porous skeleton hardly expands, and during discharging, sodium metal is dissolved from the porous interior, and the negative electrode side porous skeleton does not shrink, thereby solving the problem of volume expansion and low cycle life caused by the deposition / peeling of sodium metal on the surface of the negative electrode current collector in the negative electrode-free secondary sodium battery, thereby maintaining high energy density while improving the service life and stability of the battery.

[0104] The applicant states that the above description is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto, and it should be understood by those skilled in the art that any changes or replacements within the technical scope disclosed by the present application can be easily thought out by those skilled in the art, and all of them fall within the protection scope and disclosure scope of the present application.

Claims

1. A sodium-ion battery anode, characterized in that, The negative electrode comprises a first negative electrode tab structure comprising a porous current collector or a second negative electrode tab structure comprising a negative electrode current collector and a porous modification layer on at least one side surface of the negative electrode current collector; The thickness change of the negative electrode tab is between 0-5.0% at 0-100% state of charge.

2. The sodium-ion battery anode of claim 1, wherein, The pore volume in the porous structure is larger than the volume of the sodium metal to be deposited.

3. The sodium-ion battery anode according to claim 1 or 2, c h a r a c t e r i z e d in that The pore volume in the porous structure is 0.1-2 mL / g, preferably 0.3-1 mL / g.

4. The sodium-ion battery anode of any one of claims 1-3, wherein, The porous current collector comprises any one or a combination of at least two of foamed nickel, foamed nickel alloy, foamed copper, foamed copper alloy, foamed aluminum, foamed aluminum alloy, foamed iron, foamed iron alloy, foamed zinc, foamed zinc alloy, copper mesh, copper alloy mesh, aluminum mesh, aluminum alloy mesh, titanium mesh, titanium alloy mesh, stainless steel mesh, stainless steel alloy mesh, nickel mesh, nickel alloy mesh, foamed carbon, carbon aerogel, carbon cloth, carbon paper or carbon felt, preferably any one or a combination of at least two of foamed copper, stainless steel mesh, aluminum mesh or foamed carbon.

5. The sodium-ion battery anode of any one of claims 1-4, wherein, The material in the porous modification layer comprises a carbon material and / or a non-carbon material, preferably at least a carbon material; Preferably, the porous modification layer further comprises a binder; Preferably, the negative electrode current collector comprises any one or a combination of at least two of copper foil, aluminum foil, stainless steel foil or Ti foil.

6. The sodium-ion battery anode of claim 5, wherein, The carbon material comprises any one or a combination of at least two of activated carbon, hard carbon, graphite, soft carbon, carbon nanotube, carbon fiber, mesoporous carbon or porous carbon. Preferably, the non-carbon material comprises any one or a combination of at least two of a metal, an alloy or a metal compound. Preferably, the metal elements in the metal and alloy each independently comprise any one or a combination of at least two of Sn, Bi, Ge or Zn.

7. A method of producing a sodium-ion battery anode as claimed in any one of claims 1-6, characterized in that, The preparation method comprises the following steps: The sodium ion battery negative electrode is obtained by using the first negative electrode tab structure comprising a porous structure as the negative electrode or the second negative electrode tab structure comprising a porous structure as the negative electrode.

8. The preparation method according to claim 7, characterized in that The preparation of the second negative electrode tab structure comprising a porous structure comprises compounding a porous modification layer on at least one side surface of the negative electrode current collector; Preferably, the compounding method comprises any one or a combination of at least two of coating, magnetron sputtering, spin coating, electron beam evaporation, thermal evaporation or 3D printing.

9. A sodium-ion battery, characterized in that, The sodium ion battery comprises the sodium ion battery negative electrode according to any one of claims 1-6.

10. The sodium-ion battery of claim 9, wherein, The capacity of the sodium ion battery negative electrode is 0-20% of the capacity of the sodium ion battery.

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