Composite current collector, preparation method and application thereof, and negative-electrode-free sodium ion battery

Abstract

The invention provides a composite current collector, a preparation method and application thereof, and a negative-electrode-free sodium ion battery. The composite current collector comprises a current collector body, and a metal layer, an inorganic sodium salt layer and an organic sodium salt layer which are located on the surface of the current collector body and are sequentially stacked, the metal layer can reduce energy barriers of sodium metal separated out on the surface of a negative electrode, so that the sodium metal is uniformly separated out on the surface of the current collector body, and sodium dendrites and holes in the charging and discharging process are reduced; meanwhile, the inorganic sodium salt layer and the organic sodium salt layer are sequentially formed on the surface of the metal layer, so that the effects of protecting newly-separated sodium metal and reducing side reactions of the sodium metal are achieved, and the cycle performance of the sodium ion battery cell is improved; the metal layer, the inorganic sodium salt layer and the organic sodium salt layer in the composite current collector have a mutual synergistic effect, the cycle performance of the sodium ion battery can be further improved through the combined effect of the metal layer, the inorganic sodium salt layer and the organic sodium salt layer, and if one or two layers are lacked, the cycle performance of the sodium ion battery can be reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion batteries, and in particular to a composite current collector, a preparation method and application thereof, and a negative electrode-free sodium ion battery. Background Art

[0002] Sodium-ion batteries have a significant cost advantage in large-scale energy storage applications because sodium is more abundant in the earth's crust and is more abundant and cheaper than lithium resources. At the same time, sodium-ion batteries have excellent low-temperature performance, which makes them more environmentally adaptable than lithium-ion batteries. Compared with lithium-ion batteries, the cost of sodium salt electrolytes is lower than that of lithium salt electrolytes, and at the same concentration, the conductivity of sodium salts may be higher, which helps to improve battery performance.

[0003] The energy density of sodium-ion batteries is slightly lower than that of lithium-ion batteries. In order to improve the energy density of sodium-ion batteries, negative electrode-free sodium-ion batteries came into being. The negative electrode of the negative electrode-free sodium-ion battery will directly precipitate sodium metal, and the activity of sodium metal is higher than that of lithium metal, and its reaction tendency with the electrolyte is stronger. The side reaction of metallic sodium and the electrolyte greatly affects the cycle performance of the battery. In addition, negative electrode-free sodium-ion batteries also have the problems of dendrites and holes like negative electrode-free lithium-ion batteries. Based on the defects of the current negative electrode-free sodium-ion batteries, it is necessary to improve them. Summary of the invention

[0004] The present invention provides a composite current collector and a preparation method and application thereof, and a negative electrode-free sodium ion battery, so as to solve or at least partially solve the defects existing in the prior art.

[0005] In a first aspect, the present invention provides a composite current collector, comprising:

[0006] A current collector having a metal layer on its surface;

[0007] an inorganic sodium salt layer, which is located on the surface of the metal layer;

[0008] The organic sodium salt layer is located on the surface of the inorganic sodium salt layer.

[0009] Preferably, the material of the metal layer includes at least one of zinc, cadmium, gallium, indium and tin; and / or the material of the inorganic sodium salt layer includes at least one of NaF, Na3PO4, Na2CO3 and Na2SO4;

[0010] And / or, the material of the organic sodium salt layer includes at least one of sodium oxalate, sodium butyrate, sodium malonate, sodium succinate, sodium benzoate, sodium phthalate, n-butyl sodium, isobutyl sodium, tert-butyl sodium, and sec-butyl sodium;

[0011] And / or, the current collector includes any one of copper foil, aluminum foil, nickel foil, composite copper foil, composite aluminum foil and composite nickel foil.

[0012] Preferably, the thickness of the current collector is 2 to 15 μm;

[0013] And / or, the thickness of the metal layer is 10 nm to 3 μm;

[0014] And / or, the thickness of the inorganic sodium salt layer is 0.1 to 10 μm;

[0015] And / or, the thickness of the organic sodium salt layer is 0.1-50 μm.

[0016] In a second aspect, the present invention further provides a method for preparing the composite current collector, comprising the following steps:

[0017] preparing a metal layer on the surface of the current collector;

[0018] preparing an inorganic sodium salt layer on the surface of the metal layer;

[0019] An organic sodium salt layer is prepared on the surface of the inorganic sodium salt layer.

[0020] Preferably, the preparation method of the metal layer includes any one of magnetron sputtering, chemical vapor deposition, vacuum evaporation and ion plating.

[0021] Preferably, preparing an inorganic sodium salt layer on the surface of the metal layer specifically comprises:

[0022] adding an inorganic sodium salt into water to obtain an inorganic sodium salt solution;

[0023] coating the inorganic sodium salt solution on the surface of the metal layer and drying it to obtain an inorganic sodium salt layer;

[0024] The inorganic sodium salt includes at least one of NaF, Na3PO4, Na2CO3, and Na2SO4.

[0025] Preferably, preparing an organic sodium salt layer on the surface of the inorganic sodium salt layer specifically comprises:

[0026] adding an organic sodium salt into a solvent to obtain an organic sodium salt solution;

[0027] coating the organic sodium salt solution on the surface of the inorganic sodium salt layer and drying to obtain an organic sodium salt layer;

[0028] The organic sodium salt includes at least one of sodium oxalate, sodium butyrate, sodium malonate, sodium succinate, sodium benzoate, sodium phthalate, n-butyl sodium, isobutyl sodium, tert-butyl sodium and sec-butyl sodium.

[0029] Preferably, the solvent includes at least one of water, methanol, ethanol, NMP, acetone, n-heptane, cyclohexane, benzene, toluene, xylene, carbon tetrachloride, dichloromethane and chloroform.

[0030] In a third aspect, the present invention further provides an application of the composite current collector or the composite current collector prepared by the preparation method in the preparation of a negative electrode-free sodium ion battery.

[0031] In a fourth aspect, the present invention further provides a negative electrode-free sodium ion battery, comprising a positive electrode plate, an electrolyte, a separator, and the composite current collector or the composite current collector prepared by the preparation method.

[0032] The composite current collector, preparation method and application thereof, and negative electrode-free sodium ion battery of the present invention have the following beneficial effects compared with the prior art:

[0033] 1. The composite current collector of the present invention comprises a current collector, and a metal layer, an inorganic sodium salt layer, and an organic sodium salt layer, which are located on the surface of the current collector and are stacked in sequence, wherein the metal layer can reduce the energy barrier for the precipitation of sodium metal on the surface of the negative electrode (i.e., the current collector), so that the sodium metal is uniformly precipitated on the surface of the current collector (such as aluminum foil or copper foil), and the sodium dendrites and holes during the charge and discharge process are reduced; at the same time, the present invention forms an inorganic sodium salt layer and an organic sodium salt layer on the surface of the metal layer in sequence, which plays a role in protecting the newly precipitated sodium metal, reducing the side reactions of the sodium metal, and improving the cycle performance of the sodium ion battery core; in the composite current collector of the present invention, there is a mutual synergistic effect between the metal layer, the inorganic sodium salt layer, and the organic sodium salt layer, and the three work together to further improve the cycle performance of the sodium ion battery, and the lack of one or two layers will lead to a decrease in the cycle performance of the sodium ion battery;

[0034] 2. The preparation method of the composite current collector of the present invention prepares a metal layer on the surface of the current collector (such as aluminum foil or copper foil), thereby reducing the surface energy of the first precipitation of sodium metal on the current collector, making it easier to form a uniform sodium metal layer; further, an inorganic sodium salt layer and an organic sodium salt layer are formed on the surface of the metal layer, and the inorganic sodium salt layer and the organic sodium salt layer isolate the contact between the sodium metal and the electrolyte, reduce the occurrence of side reactions, and improve the cycle performance of the battery cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the prior art descriptions. Obviously, the drawings described below are only some embodiments of the present invention, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0036] Figure 1The charging curves of the negative electrode-free sodium ion batteries in Example 2 and Comparative Examples 1 to 3 at 2.7-4.0V and 0.1C. DETAILED DESCRIPTION

[0037] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] The following are described in detail. It should be noted that the order of description of the following embodiments is not intended to limit the preferred order of the embodiments. In addition, in the description of the present application, the term "including" means "including but not limited to". Various embodiments of the present invention may exist in the form of a range; it should be understood that the description in the form of a range is only for convenience and simplicity, and should not be understood as a rigid limitation on the scope of the present invention; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single values ​​within the range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the numbered ranges, such as 1, 2, 3, 4, 5 and 6, which apply regardless of the range. In addition, whenever a numerical range is indicated in this article, it is meant to include any quoted numbers (fractions or integers) within the indicated range.

[0039] The present invention provides a composite current collector, comprising:

[0040] A current collector having a metal layer on its surface;

[0041] an inorganic sodium salt layer, which is located on the surface of the metal layer;

[0042] The organic sodium salt layer is located on the surface of the inorganic sodium salt layer.

[0043] The composite current collector of the present invention comprises a current collector, and a metal layer, an inorganic sodium salt layer, and an organic sodium salt layer which are located on the surface of the current collector and are stacked in sequence, wherein the metal layer can reduce the energy barrier for the precipitation of sodium metal on the surface of the negative electrode (i.e., the current collector), so that the sodium metal is uniformly precipitated on the surface of the current collector (such as aluminum foil or copper foil), and the sodium dendrites and holes in the charge and discharge process are reduced; at the same time, the present invention sequentially forms an inorganic sodium salt layer and an organic sodium salt layer on the surface of the metal layer, which plays a role in protecting the newly precipitated sodium metal, reducing the side reactions of the sodium metal, and improving the cycle performance of the sodium ion battery cell.

[0044] In some embodiments, the material of the metal layer includes but is not limited to at least one of zinc, cadmium, gallium, indium, and tin; the thickness of the metal layer is 10 nm to 10 μm, that is, the thickness of the metal layer is from nanometer level to micrometer level.

[0045] In some embodiments, the material of the inorganic sodium salt layer includes but is not limited to at least one of NaF, Na3PO4, Na2CO3, and Na2SO4.

[0046] In some embodiments, the material of the organic sodium salt layer includes but is not limited to at least one of sodium oxalate, sodium butyrate, sodium malonate, sodium succinate, sodium benzoate, sodium phthalate, n-butyl sodium, isobutyl sodium, tert-butyl sodium, and sec-butyl sodium.

[0047] In some embodiments, the current collector includes, but is not limited to, any one of a copper foil, an aluminum foil, a nickel foil, a composite copper foil, a composite aluminum foil, and a composite nickel foil.

[0048] In some embodiments, the thickness of the current collector is 2 to 15 μm.

[0049] In some embodiments, the thickness of the metal layer is 10 nm to 3 μm.

[0050] In some embodiments, the thickness of the inorganic sodium salt layer is 0.1-3 μm.

[0051] In some embodiments, the thickness of the organic sodium salt layer is 0.1-50 μm.

[0052] Based on the same inventive concept, the present invention also provides a method for preparing the above-mentioned composite current collector, comprising the following steps:

[0053] S1. Preparing a metal layer on the surface of the current collector;

[0054] S2, preparing an inorganic sodium salt layer on the surface of the metal layer;

[0055] S3. Preparing an organic sodium salt layer on the surface of the inorganic sodium salt layer.

[0056] In some embodiments, the preparation method of the metal layer includes any one of magnetron sputtering, chemical vapor deposition, vacuum evaporation, ion plating or other sputtering coating methods.

[0057] In some embodiments, a metal layer is prepared on the surface of the current collector by magnetron sputtering, which specifically includes the following steps:

[0058] The current collector was polished with 2000-grit sandpaper, cleaned with ethanol, dried, and then ultrasonically cleaned with acetone for 15 minutes and dried. The dried current collector was fixed to the sample holder and vacuumed to 5×10 -4After the deposition temperature reaches 0.2 Pa, 30 mL / min of high-purity argon gas is introduced for etching and cleaning for 10 min. After that, the deposition gas pressure is adjusted to 0.2 Pa, the sputtering current is controlled to 1 A, and the sputtering time is 10 to 30 min, and a metal layer can be prepared on the surface of the current collector.

[0059] In some embodiments, an inorganic sodium salt layer is prepared on the surface of the metal layer, specifically comprising:

[0060] adding an inorganic sodium salt into water to obtain an inorganic sodium salt solution;

[0061] coating the inorganic sodium salt solution on the surface of the metal layer and drying it to obtain an inorganic sodium salt layer;

[0062] The inorganic sodium salt includes at least one of NaF, Na3PO4, Na2CO3, and Na2SO4.

[0063] In some embodiments, an organic sodium salt layer is prepared on the surface of an inorganic sodium salt layer, specifically comprising:

[0064] adding an organic sodium salt into a solvent to obtain an organic sodium salt solution;

[0065] coating the organic sodium salt solution on the surface of the inorganic sodium salt layer and drying to obtain an organic sodium salt layer;

[0066] The organic sodium salt includes at least one of sodium oxalate, sodium butyrate, sodium malonate, sodium succinate, sodium benzoate, sodium phthalate, n-butyl sodium, isobutyl sodium, tert-butyl sodium, and sec-butyl sodium.

[0067] In some embodiments, the solvent includes, but is not limited to, water, methanol, ethanol, NMP, acetone, n-heptane, cyclohexane, benzene, toluene, xylene, carbon tetrachloride, dichloromethane, chloroform, and the like.

[0068] In some embodiments, the mass concentration of the inorganic sodium salt solution is 2-50%.

[0069] In some embodiments, the mass concentration of the organic sodium salt solution is 1-30%.

[0070] The preparation method of the composite current collector of the present invention prepares a metal layer on the surface of the current collector (such as aluminum foil or copper foil), thereby reducing the surface energy of the first precipitation of sodium metal on the current collector, making it easier to form a uniform sodium metal layer; further, an inorganic sodium salt layer and an organic sodium salt layer are formed on the surface of the metal layer, and the inorganic sodium salt layer and the organic sodium salt layer isolate the contact between the sodium metal and the electrolyte, reduce the occurrence of side reactions, and improve the cycle performance of the battery cell.

[0071] Based on the same inventive concept, the present invention also provides an application of the above-mentioned composite current collector or the composite current collector prepared by the above-mentioned preparation method in the preparation of a negative electrode-free sodium ion battery.

[0072] Based on the same inventive concept, the present invention also provides a negative electrode-free sodium ion battery, comprising a positive electrode plate, an electrolyte, a diaphragm (or a solid electrolyte plate), and the above-mentioned composite current collector or a composite current collector prepared by the above-mentioned preparation method.

[0073] Specifically, the positive electrode sheet, electrolyte, and separator are all conventional positive electrode sheets, electrolytes, and separators in the art.

[0074] In some embodiments, the positive electrode plate includes a positive electrode active material, a conductive agent and a binder; the positive electrode active material includes any one of sodium titanium copper iron manganate, sodium nickel iron manganate, sodium iron manganate, sodium manganate, sodium vanadium phosphate, sodium vanadium fluorophosphate, Prussian blue, Prussian white, sodium iron phosphate, sodium iron pyrophosphate, sodium iron pyrophosphate and sodium iron manganese pyrophosphate; the conductive agent includes any one or more of conductive carbon black, conductive graphite, graphene, carbon nanotubes, acetylene black, Ketjen black or Super P Li; the binder includes at least one of PVDF (polyvinylidene fluoride), PTFE (polytetrafluoroethylene), CMC (sodium carboxymethyl cellulose), SBR (styrene butadiene rubber emulsion), PAN (polyacrylonitrile), PAA (polyacrylic acid), etc.

[0075] In some embodiments, the mass ratio of the positive electrode active material, the conductive agent, and the binder is (90-98.6):(0.01-5):(0.1-5).

[0076] In some embodiments, the preparation method of the positive electrode plate is: adding the positive electrode active material, the conductive agent, and the binder to the positive electrode solvent, mixing, and obtaining the positive electrode slurry; coating the positive electrode slurry on the positive electrode collector (such as aluminum foil or copper foil), drying, and obtaining the positive electrode plate; wherein the positive electrode solvent includes but is not limited to at least one of NMP (N-methylpyrrolidone), water, etc.; the mass ratio of the positive electrode active material, the conductive agent, the binder and the positive electrode solvent is (90~98.6):(0.01~5):(0.1~5):(40~100).

[0077] In some embodiments, the electrolyte includes a sodium salt and an organic solvent; the sodium salt is any one or more of sodium hexafluorophosphate, sodium perchlorate, sodium trifluoromethanesulfonate, sodium tetrafluoroborate, sodium bis(fluorosulfonyl)imide and sodium bis(trifluoromethylsulfonyl)imide; the organic solvent is any one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, diethylene glycol dimethyl ether, 1,3-cyclopentanediol, ethylene glycol dimethyl ether and triethylene glycol dimethyl ether.

[0078] The following further illustrates the composite current collector of the present application, its preparation method and application, and the negative electrode-free sodium ion battery with specific examples. This section further illustrates the content of the present invention in conjunction with specific examples, but should not be construed as limiting the present invention. Unless otherwise specified, the technical means used in the examples are conventional means known to those skilled in the art. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the art.

[0079] Example 1

[0080] The present application embodiment provides a composite current collector, including:

[0081] A current collector having a metal layer on its surface;

[0082] an inorganic sodium salt layer, which is located on the surface of the metal layer;

[0083] an organic sodium salt layer, which is located on the surface of the inorganic sodium salt layer;

[0084] The current collector is aluminum foil, and the thickness of the current collector is 12 μm;

[0085] The metal layer is zinc, and the average thickness of the metal layer is 30nm;

[0086] The material of the inorganic sodium salt layer is NaF, and the average thickness of the inorganic sodium salt layer is 5 μm;

[0087] The material of the organic sodium salt layer is sodium oxalate, and the average thickness of the organic sodium salt layer is 20 μm.

[0088] The preparation method of the composite current collector comprises the following steps:

[0089] S1. A 12 μm thick aluminum foil was polished with 2000 grit sandpaper, cleaned and dried with ethanol, and then ultrasonically cleaned with acetone for 15 minutes and dried. The dried aluminum foil was fixed to the sample holder and vacuumed to 5×10 -4 After the aluminum foil reaches 0.0400 Pa, 30 mL / min high-purity argon gas is introduced for etching and cleaning for 10 min. After that, the deposition gas pressure is adjusted to 0.2 Pa, the sputtering current is controlled to 1 A, and the sputtering time is 20 min. Then, a zinc layer with an average thickness of 30 nm can be deposited on the aluminum foil.

[0090] S2, adding NaF into water to obtain a NaF solution with a mass concentration of 3.5%;

[0091] The NaF solution is coated on the surface of the metal zinc layer and dried to obtain a NaF layer with an average thickness of 5 μm;

[0092] S3, adding sodium oxalate to water to obtain a sodium oxalate solution with a mass concentration of 3.5%;

[0093] The sodium oxalate solution was coated on the surface of the NaF layer and dried to obtain a sodium oxalate layer with an average thickness of 20 μm.

[0094] Example 2

[0095] A negative electrode-free sodium ion battery, comprising: a positive electrode plate, an electrolyte, a separator and the composite current collector of embodiment 1;

[0096] The method for preparing the positive electrode sheet includes:

[0097] The positive electrode active material, the conductive agent and the binder are added to the positive electrode solvent and mixed to obtain a positive electrode slurry; the positive electrode slurry is coated on an aluminum foil with a thickness of 12 μm and dried to obtain a positive electrode sheet;

[0098] The positive electrode active material is sodium titanium copper iron manganese oxide Na 0.8 Ti 0.1 Cu 0.2 Fe 0.3 Mn 0.4 O2, the conductive agent is carbon nanotubes and SP (i.e. Super P Li), the binder is PVDF, and the cathode solvent is NMP;

[0099] The mass ratio of the positive electrode active material, the conductive agent carbon nanotubes, the conductive agent SP, the binder, and the positive electrode solvent is 96.5:1.0:1.0:1.5:60;

[0100] The electrolyte includes a solvent, a sodium salt and an additive; the solvent includes EC (ethylene carbonate), PC (propylene carbonate) and EMC (ethyl methyl carbonate), and the volume ratio of EC, PC and EMC is 4:5:1; the sodium salt is sodium hexafluorophosphate, and the concentration of the sodium salt in the electrolyte is 1 mol / L; the additives include PS (1,3-propane sultone) and FEC (fluoroethylene carbonate), and the mass fraction of PS in the electrolyte is 0.5% and the mass fraction of FEC is 1.5%;

[0101] The separator is a PE separator with a thickness of 7 μm.

[0102] The positive electrode sheet, separator, composite current collector and separator are stacked or wound in sequence and then loaded into a shell to make a dry battery cell; the dry battery cell is dried and injected with electrolyte, and then after formation, sealing and capacity separation, a finished battery cell is made to obtain a negative electrode-free sodium ion battery.

[0103] Comparative Example 1

[0104] This comparative example provides a negative electrode-free sodium ion battery, comprising: a positive electrode plate, an electrolyte, a separator and a negative electrode plate;

[0105] Among them, the negative electrode sheet is an aluminum foil with a thickness of 12μm;

[0106] The preparation method of the positive electrode sheet is the same as that of Example 2;

[0107] The electrolyte includes a solvent, a sodium salt and an additive; the solvent includes EC (ethylene carbonate), PC (propylene carbonate) and EMC (ethyl methyl carbonate), and the volume ratio of EC, PC and EMC is 4:5:1; the sodium salt is sodium hexafluorophosphate, and the concentration of the sodium salt in the electrolyte is 1 mol / L; the additives include PS (1,3-propane sultone) and FEC (fluoroethylene carbonate), and the mass fraction of PS in the electrolyte is 0.5% and the mass fraction of FEC is 1.5%;

[0108] The separator is a PE separator with a thickness of 7 μm.

[0109] The positive electrode sheet, separator, negative electrode sheet and separator are stacked or wound in sequence and then loaded into a shell to make a dry battery cell; the dry battery cell is dried and injected with electrolyte, and then after formation, sealing and capacity separation, a finished battery cell is made to obtain a negative electrode-free sodium ion battery.

[0110] Comparative Example 2

[0111] This comparative example provides a negative electrode-free sodium ion battery, comprising: a positive electrode plate, an electrolyte, a separator and a negative electrode plate;

[0112] The preparation method of the negative electrode sheet is as follows:

[0113] A 12 μm thick aluminum foil was polished with 2000 grit sandpaper, cleaned and dried with ethanol, and then ultrasonically cleaned with acetone for 15 minutes and dried. The dried aluminum foil was fixed to the sample holder and vacuumed to 5×10 -4 After the aluminum foil reaches 0.0400 Pa, 30 mL / min high-purity argon gas is introduced for etching and cleaning for 10 minutes; then, the deposition gas pressure is adjusted to 0.2 Pa, the sputtering current is controlled to 1 A, and the sputtering time is 20 minutes, so that a zinc layer with an average thickness of 30 nm can be deposited on the aluminum foil to obtain the negative electrode sheet;

[0114] The preparation method of the positive electrode sheet is the same as that of Example 2;

[0115] The electrolyte includes a solvent, a sodium salt and an additive; the solvent includes EC (ethylene carbonate), PC (propylene carbonate) and EMC (ethyl methyl carbonate), and the volume ratio of EC, PC and EMC is 4:5:1; the sodium salt is sodium hexafluorophosphate, and the concentration of the sodium salt in the electrolyte is 1 mol / L; the additives include PS (1,3-propane sultone) and FEC (fluoroethylene carbonate), and the mass fraction of PS in the electrolyte is 0.5% and the mass fraction of FEC is 1.5%;

[0116] The separator is a PE separator with a thickness of 7 μm.

[0117] The positive electrode sheet, separator, negative electrode sheet and separator are stacked or wound in sequence and then loaded into a shell to make a dry battery cell; the dry battery cell is dried and injected with electrolyte, and then after formation, sealing and capacity separation, a finished battery cell is made to obtain a negative electrode-free sodium ion battery.

[0118] Comparative Example 3

[0119] This comparative example provides a negative electrode-free sodium ion battery, comprising: a positive electrode plate, an electrolyte, a separator and a negative electrode plate;

[0120] The method for preparing the negative electrode sheet comprises:

[0121] NaF is added into water to obtain a NaF solution with a mass concentration of 3.5%; the NaF solution is coated on the surface of an aluminum foil with a thickness of 12 μm, and dried to obtain a NaF layer with an average thickness of 5 μm;

[0122] Adding sodium oxalate into water to obtain a sodium oxalate solution with a mass concentration of 3.5%;

[0123] The sodium oxalate solution is coated on the surface of the NaF layer and dried to obtain a sodium oxalate layer with an average thickness of 20 μm, thus preparing a negative electrode sheet;

[0124] The preparation method of the positive electrode sheet is the same as that of Example 2;

[0125] The electrolyte includes a solvent, a sodium salt and an additive; the solvent includes EC (ethylene carbonate), PC (propylene carbonate) and EMC (ethyl methyl carbonate), and the volume ratio of EC, PC and EMC is 4:5:1; the sodium salt is sodium hexafluorophosphate, and the concentration of the sodium salt in the electrolyte is 1 mol / L; the additives include PS (1,3-propane sultone) and FEC (fluoroethylene carbonate), and the mass fraction of PS in the electrolyte is 0.5% and the mass fraction of FEC is 1.5%;

[0126] The separator is a PE separator with a thickness of 7 μm.

[0127] The positive electrode sheet, separator, negative electrode sheet and separator are stacked or wound in sequence and then loaded into a shell to make a dry battery cell; the dry battery cell is dried and injected with electrolyte, and then after formation, sealing and capacity separation, a finished battery cell is made to obtain a negative electrode-free sodium ion battery.

[0128] Performance Testing

[0129] According to the methods in Example 2 and Comparative Examples 1 to 3, negative electrode-free sodium ion batteries were obtained respectively. The charging curves of different negative electrode-free sodium ion batteries at 2.7-4.0V and 0.1C were as follows: Figure 1 .

[0130] from Figure 1It can be seen that the negative electrode-free sodium ion battery in Example 2 has a lower voltage when charged at 0.1C than the negative electrode-free sodium ion batteries in Comparative Examples 1 to 3, indicating that the battery polarization is smaller.

[0131] Negative electrode-free sodium ion batteries were obtained according to the methods in Example 2 and Comparative Examples 1 to 3, and the charging gram capacity (mAh / g) and the average charging voltage (V) of different negative electrode-free sodium ion batteries were tested. The results are shown in Table 1 below.

[0132] Table 1 - Charged gram capacity and average voltage of sodium ion batteries without negative electrode in Example 2 and Comparative Examples 1 to 3

[0133] Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Charging capacity (mAh / g) 112.67 111.52 111.89 111.06 Average charging voltage (V) 3.547 3.550 3.551 3.551

[0134] It can be seen from Table 1 that the negative electrode-free sodium ion battery in Example 2 has a lower average charging voltage and a higher charging capacity when charged at 0.1C than the negative electrode-free sodium ion batteries in Comparative Examples 1 to 3.

[0135] Negative electrode sodium ion batteries were obtained according to the methods in Example 2 and Comparative Examples 1 to 3, and the capacity retention rates of different negative electrode-free sodium ion batteries at different cycles of 0.2C charging and 0.5C discharging were tested. The results are shown in Table 2 below.

[0136] Table 2 - Capacity retention rate of negative electrode-free sodium ion batteries in Example 2 and Comparative Examples 1 to 3

[0137]

[0138]

[0139] As can be seen from Table 2, the negative electrode-free sodium ion battery in Example 2 has a higher capacity retention rate after multiple cycles of 0.2C charging and 0.5C discharging than the negative electrode-free sodium ion batteries in Comparative Examples 1 to 3, and the sodium ion battery cycle performance is greatly improved. Among them, after 39 and 31 cycles respectively, the battery produced gas and bulged after Comparative Example 1 and Comparative Example 3, and the cycle test ended early.

[0140] There is a synergistic effect between the metal layer, the inorganic sodium salt layer and the organic sodium salt layer in the composite current collector of the present invention. The three layers working together can further improve the cycle performance of the sodium ion battery. The lack of one or two layers will lead to a decrease in the cycle performance of the sodium ion battery.

[0141] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A composite current collector, characterized in that: include: A current collector having a metal layer on its surface; an inorganic sodium salt layer, which is located on the surface of the metal layer; The organic sodium salt layer is located on the surface of the inorganic sodium salt layer.

2. The composite current collector according to claim 1, characterized in that: The material of the metal layer includes at least one of zinc, cadmium, gallium, indium and tin; And / or, the material of the inorganic sodium salt layer includes at least one of NaF, Na3PO4, Na2CO3, and Na2SO4; And / or, the material of the organic sodium salt layer includes at least one of sodium oxalate, sodium butyrate, sodium malonate, sodium succinate, sodium benzoate, sodium phthalate, n-butyl sodium, isobutyl sodium, tert-butyl sodium, and sec-butyl sodium; And / or, the current collector includes any one of copper foil, aluminum foil, nickel foil, composite copper foil, composite aluminum foil and composite nickel foil.

3. The composite current collector according to claim 1, characterized in that: The thickness of the current collector is 2 to 15 μm; And / or, the thickness of the metal layer is 10 nm to 3 μm; And / or, the thickness of the inorganic sodium salt layer is 0.1 to 10 μm; And / or, the thickness of the organic sodium salt layer is 0.1-50 μm.

4. A method for preparing a composite current collector according to any one of claims 1 to 3, characterized in that: The steps include: preparing a metal layer on the surface of the current collector; preparing an inorganic sodium salt layer on the surface of the metal layer; An organic sodium salt layer is prepared on the surface of the inorganic sodium salt layer.

5. The method for preparing the composite current collector according to claim 4, characterized in that: The preparation method of the metal layer includes any one of magnetron sputtering, chemical vapor deposition, vacuum evaporation and ion plating.

6. The method for preparing the composite current collector according to claim 4, characterized in that: Preparing an inorganic sodium salt layer on the surface of the metal layer specifically comprises: adding an inorganic sodium salt into water to obtain an inorganic sodium salt solution; coating the inorganic sodium salt solution on the surface of the metal layer and drying it to obtain an inorganic sodium salt layer; The inorganic sodium salt includes at least one of NaF, Na3PO4, Na2CO3, and Na2SO4.

7. The method for preparing the composite current collector according to claim 6, characterized in that: The organic sodium salt layer is prepared on the surface of the inorganic sodium salt layer, specifically comprising: adding an organic sodium salt into a solvent to obtain an organic sodium salt solution; coating the organic sodium salt solution on the surface of the inorganic sodium salt layer and drying to obtain an organic sodium salt layer; The organic sodium salt includes at least one of sodium oxalate, sodium butyrate, sodium malonate, sodium succinate, sodium benzoate, sodium phthalate, n-butyl sodium, isobutyl sodium, tert-butyl sodium and sec-butyl sodium.

8. The method for preparing the composite current collector according to claim 7, characterized in that: The solvent includes at least one of water, methanol, ethanol, NMP, acetone, n-heptane, cyclohexane, benzene, toluene, xylene, carbon tetrachloride, dichloromethane and chloroform.

9. Use of the composite current collector according to any one of claims 1 to 3 or the composite current collector prepared by the preparation method according to any one of claims 4 to 8 in preparing a negative electrode-free sodium ion battery.

10. A negative electrode-free sodium ion battery, characterized in that: The invention comprises a positive electrode sheet, an electrolyte, a separator and a composite current collector as claimed in any one of claims 1 to 3 or a composite current collector prepared by the preparation method as claimed in any one of claims 4 to 8.

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