Sodium ion battery, battery pack and energy storage system

Abstract

The invention provides a sodium ion battery, a battery pack and an energy storage system. The sodium ion battery comprises a positive pole piece and a negative pole piece, wherein the negative electrode piece comprises a negative electrode current collector and a nano coating arranged on the surface of the negative electrode current collector, the nano coating comprises a plurality of sodium-philic carriers, the sodium-philic carriers are sheet-shaped, and the included angle between at least part of the sodium-philic carriers and the negative electrode current collector is greater than 0; a gap is formed between every two adjacent sodium-philic carriers, and a sodium metal layer is deposited on at least part of the surface of each sodium-philic carrier. The negative pole piece in the sodium ion battery has sodium affinity, so that the deposition uniformity of sodium ions in the negative pole piece can be improved, and the cycle performance of the sodium ion battery is further improved.

Description

Technical Field

[0001] The present application relates to the field of batteries, and particularly to a sodium-ion battery, a battery pack, and an energy storage system. Background Art

[0002] Currently, the process of replacing traditional energy with new energy is accelerating day by day, and the installed capacity of lithium-ion batteries has been increasing rapidly year by year. The shortage and price increase of lithium resources have become a constraint on the development of energy storage or power batteries. Sodium resources are abundant and inexpensive, and sodium-ion batteries have many potential advantages, such as good low-temperature performance and safety performance, which have led the industrial community to accelerate the research and production of sodium batteries. However, due to the relatively large atomic size and weight of sodium, the energy density of sodium-ion batteries is generally lower than 160 Wh / Kg. To improve its energy density, the negative electrode of sodium batteries usually uses metallic sodium. However, since sodium metal is very unstable even in dry air and continuously forms a porous structure, it is very difficult to process and manufacture the sodium metal negative electrode. In addition, if the sodium content in the negative electrode is excessive, it will cause a decrease in the energy density of the battery cell. Currently, the problem of excessive sodium is often solved by the method of "no negative electrode material", that is, during the battery assembly stage, no sodium metal or other active substances are provided on the negative electrode side. During the first charge and discharge process, the sodium ions released from the positive electrode are directly deposited on the surface of the negative electrode current collector. Since the sodium metal deposited on the negative electrode side completely comes from the positive electrode and there is no situation of excessive sodium metal, the energy density of the battery cell can be effectively improved. Moreover, this method does not require pre-setting unstable sodium metal on the negative electrode side to reduce the manufacturing difficulty of the sodium metal negative electrode and improve the processing stability. However, during the first charge and discharge process, the deposition / detachment process of sodium ions on the traditional commercial negative electrode current collector foil is uneven and has poor reversibility. And during the subsequent charge and discharge cycles, the uneven sodium deposition is likely to form local high-activity regions, such as dendrites or tip regions. The reaction activity of this part of the region with the electrolyte is relatively high, and side reactions are likely to occur, which will cause the rapid decay of the cycle performance of the sodium-ion battery. Summary of the Invention

[0003] The present application provides a sodium-ion battery, a battery pack, and an energy storage system. The negative electrode plate in the sodium-ion battery can improve the deposition uniformity of sodium ions in the negative electrode plate due to its sodium-philic property, thereby improving the cycle performance of the sodium-ion battery.

[0004] In a first aspect, the present application provides a sodium-ion battery, including a positive electrode plate and a negative electrode plate. Among them, the negative electrode plate includes a negative electrode current collector and a nano-coating provided on the surface of the negative electrode current collector. The nano-coating includes a plurality of sodium-philic carriers, each sodium-philic carrier is in a sheet shape, and the material of the sodium-philic carrier is Sn, Zn, Cu, Co3O4, NiO, Fe3O4, MoO X, at least one of Co2S, NiS, FeS, MoS2, CoP, and NiP; the angle between at least a part of the sodiumophilic carrier and the negative electrode current collector is greater than 0, there is a gap between adjacent sodiumophilic carriers, and a sodium metal layer is deposited on at least a part of the surface of the sodiumophilic carrier.

[0005] For the negative electrode plate of the present application, a nano-coating is provided on the surface of the negative electrode current collector. The nano-coating is a coating mainly formed by the staggered connection of a plurality of sodiumophilic carriers. Each sodiumophilic carrier is sheet-shaped, and the angle between at least a part of the sodiumophilic carrier and the negative electrode current collector is greater than 0, that is, the sodiumophilic carrier and the negative electrode current collector are not parallel, and there is a gap between adjacent sodiumophilic carriers. During the charge and discharge cycle of the sodium-ion battery, due to the sodiumophilic property of the sodiumophilic carrier, the deposition potential of sodium can be reduced, and the deposition of sodium can be induced; at the same time, the gap between the sodiumophilic carriers can improve the transmission of sodium ions, improve the reaction kinetics, so as to form a more uniform sodium metal layer on the surface of each sodiumophilic carrier and the surface of the negative electrode current collector, avoid the formation of tips or dendrites caused by local excessive deposition of sodium, and then reduce the local high-activity area, avoid excessive increase in the local current density, so as to reduce the occurrence of side reactions between sodium metal and the electrolyte, and improve the cycle performance of the sodium-ion battery. The sodium metal layer deposited on the surface of the sodiumophilic carrier and the surface of the negative electrode current collector can be used as the negative electrode active material to realize the adsorption and desorption of sodium ions during the charge and discharge cycle. Therefore, the sodium-ion battery of the present application, while realizing the reduction of the sodium deposition potential and rapid transmission, solves the problem of rapid attenuation of the cycle performance of the sodium-ion battery caused by uneven sodium deposition / detachment, and improves the cycle performance of the sodium-ion battery.

[0006] In an optional implementation manner, the thickness of the nano-coating is greater than or equal to 50 nm and less than 1 μm. The thickness of the nano-coating is at the nanoscale to avoid the reduction of the energy density of the sodium-ion battery caused by too thick nano-coating.

[0007] In an optional implementation manner, the thickness of the nano-coating is 120 - 500 nm. When the thickness of the nano-coating is controlled within the range of 120 - 500 nm, the Coulomb efficiency and cycle stability of the sodium-ion battery can be further improved. When the thickness of the nano-coating is relatively thin, it is not conducive to the improvement of the Coulomb efficiency and cycle performance of the sodium-ion battery. When the thickness of the nano-coating is relatively thick, it is not conducive to the improvement of the energy density of the sodium-ion battery.

[0008] In an optional implementation manner, the thickness of the sodiumophilic carrier is less than or equal to 25 nm. If the thickness of the sodiumophilic carrier is too high, it is not conducive to the lap joint between the sodiumophilic carriers, reduces the lap joint area, and will cause the reduction of pores in the nano-coating, hindering the transmission of sodium ions.

[0009] In some implementations, the material of the sodiumophilic carrier is NiO. The material of the sodiumophilic carrier is selected from materials such as metals, metal oxides, metal sulfides, and metal phosphides. The above materials can effectively reduce the sodium deposition overpotential and uniformly induce the deposition and detachment of sodium.

[0010] In an alternative implementation, the sodiumophilic carrier is connected to the negative electrode current collector. Among them, the sodiumophilic carrier can be formed by in-situ growth on the surface of the negative electrode current collector.

[0011] In an alternative implementation, the included angle between the sodiumophilic carrier and the negative electrode current collector is 30° to 85°. When the included angle between the sodiumophilic carrier and the negative electrode current collector is within the above range, the transmission rate of sodium ions can be increased, the area where sodium ions can be deposited on the sodiumophilic carrier can be increased, the total area of the sodium metal layer can be increased, and thus the energy density of the sodium-ion battery can be increased.

[0012] In an alternative implementation, the areal deposition amount of the sodium metal layer on the surface of the sodiumophilic carrier is 1 - 10 mAh / cm 2 .

[0013] In a second aspect, the present application provides a method for preparing a sodium-ion battery, and the preparation method includes:

[0014] Assembling the positive electrode sheet and the negative electrode sheet to obtain the sodium-ion battery.

[0015] The sodium-ion battery obtained by using the preparation method of the present application can achieve the same technical effects as the sodium-ion battery in the first aspect of the present application, and will not be repeated here.

[0016] In an alternative implementation, the preparation method further includes the preparation of the negative electrode sheet, and the preparation of the negative electrode sheet includes:

[0017] In an electroplating tank, using the negative electrode current collector as the working electrode and placing it in an electrodeposition solution containing sodiumophilic elements for electrodeposition to form a precursor containing sodiumophilic elements on the surface of the negative electrode current collector, obtaining an intermediate composite structure;

[0018] Performing heat treatment on the intermediate composite structure to obtain the negative electrode sheet.

[0019] The production process of the negative electrode current collector is usually prepared by an electrodeposition method. Using the electrodeposition method to prepare a nano-coating on the surface of the negative electrode current collector can facilitate the industrial production of the negative electrode sheet.

[0020] In an alternative implementation, the time of electro-deposition is 10 to 60 s, the temperature of electro-deposition is room temperature, and the concentration of the electro-deposition solution is 0.01 to 0.1 M. By controlling the process parameters of electro-deposition, nano-coatings with different thicknesses can be obtained, and sodium-philic carriers with different thicknesses can be obtained at the same time, so as to regulate the performance of the negative electrode sheet.

[0021] In a third aspect, the present application provides a battery pack, which includes a plurality of batteries, and the plurality of batteries are connected in series or in parallel; the battery is the sodium-ion battery of the first aspect of the present application.

[0022] In a fourth aspect, the present application provides an energy storage system, which includes a power converter and at least one battery pack of the present application; the power converter is used to perform power conversion on the voltage output by the battery pack and output it to the power grid or load, and / or perform power conversion on the voltage output by an external power source and output it to the battery pack.

[0023] For the technical effects that can be achieved in the above third and fourth aspects, reference can be made to the corresponding effect descriptions in the above first aspect, and details will not be repeated here.

[0024] Among them, for the data in the above possible implementation manners of the present application, such as the thickness of the nano-coating, the thickness of the sodium-philic carrier, and the temperature and time of electro-deposition, etc., when measuring, the values within the range of engineering measurement errors should be understood as being within the range defined by the present application. Description of the Drawings

[0025] Figure 1 It is a schematic structural diagram of the sodium-ion battery provided by the embodiment of the present application;

[0026] Figure 2 It is a schematic structural diagram of the negative electrode sheet of an embodiment;

[0027] Figure 3 It is a schematic side view structural diagram of the negative electrode sheet of an embodiment;

[0028] Figure 4 It is an SEM diagram of the nano-coating of Example 1;

[0029] Figure 5 It is a schematic connection structure diagram of an energy storage system.

[0030] Reference Signs:

[0031] 11 - positive electrode sheet; 12 - negative electrode sheet; 13 - separator; 14 - electrolyte; 121 - negative electrode current collector; 122 - nano-coating; 123 - sodium-philic carrier. Detailed Embodiments

[0032] To make the objectives, technical solutions, and advantages of this application clearer, the following will further describe this application in detail with reference to the accompanying drawings.

[0033] The terms used in the following embodiments are only for the purpose of describing specific embodiments and are not intended to limit this application. As used in the specification and appended claims of this application, the singular forms "a", "an", "the above", "the", and "this" are also intended to include expressions such as "one or more", unless the context clearly indicates otherwise.

[0034] Reference to "one embodiment" or "some embodiments" etc. described in this specification means that a specific feature, structure, or characteristic described in connection with that embodiment is included in one or more embodiments of this application. Thus, statements such as "in one embodiment", "in some embodiments", "in other some embodiments", "in still other embodiments" etc. that appear in different places in this specification do not necessarily refer to the same embodiment, but mean "one or more but not all embodiments", unless otherwise specifically emphasized in other ways. The terms "comprise", "include", "have" and their variants mean "including but not limited to", unless otherwise specifically emphasized in other ways.

[0035] Rechargeable batteries have been widely used in energy storage modules for scenarios such as household energy storage, site energy, smart photovoltaics, and data center energy. With the continuous increase in the price of lithium source raw materials, sodium-ion batteries have gradually become a research hotspot. Currently, the negative electrode active material of sodium-ion batteries is usually a sodium metal layer formed during the first charge and discharge process. However, in this structure, due to the uneven deposition of sodium, the sodium-ion cycling performance will rapidly decay during the charge and discharge cycles of sodium-ion batteries. To solve the above problems, the embodiments of this application provide a sodium-ion battery, which sets a sodium-philic nano-coating on the surface of the negative electrode current collector to achieve the purpose of promoting uniform deposition of sodium ions, thereby improving the cycling performance of sodium-ion batteries.

[0036] Figure 1 It is a schematic structural diagram of a sodium-ion battery. As Figure 1 shown, the sodium-ion battery includes a positive electrode plate 11, a negative electrode plate 12, a separator 13, and an electrolyte 14. The separator 13 is disposed between the positive electrode plate 11 and the negative electrode plate 12, and the electrolyte 14 wets the positive electrode plate 11, the separator 13, and the negative electrode plate 12.

[0037] The positive electrode plate 11 includes a positive electrode current collector and a positive electrode material layer. The positive electrode current collector can be a metal foil such as copper foil or aluminum foil. The positive electrode material layer can include a positive electrode active material, a binder, and a conductive agent. The positive electrode active material can be a layered oxide of sodium, Prussian blue, or a polyanion material. The molecular formula of the layered oxide of sodium can be Nam M n O p , wherein, M is selected from at least one of Mn, Ni, Li, Mg, Al, Fe, Co, Cu, Zn, Ca, Sr, Ce, Cr, Ti, Zr, Sn, V, Nb, Sb or Mo, m≥0.44, n≥1, p≥2, and the values of m, n, and p satisfy the charge balance of the chemical formula. The binder can be selected from at least one of polyvinylidene fluoride and modified polyvinylidene fluoride; the modified polyvinylidene fluoride is acrylate-modified polyvinylidene fluoride. Exemplarily, in the positive electrode material layer, the mass ratio of the positive electrode layered oxide is 93% - 99%, the mass ratio of the conductive agent is 0.5% - 5%. The mass ratio of the binder is 1% - 5%. The above compositions of the positive electrode current collector and the positive electrode material layer are only for exemplary illustration, and the embodiments of the present application do not specifically limit the compositions of the positive electrode current collector and the positive electrode material layer.

[0038] The main function of the separator 13 is not only to prevent the positive and negative electrodes from directly contacting and causing a short circuit, but also to provide a porous channel for the transport of sodium ions. The separator can be a polyolefin separator and a glass fiber separator. The polyolefin separator can be, for example, a polyethylene separator or a polypropylene separator, etc. The above is only for exemplary illustration, and the embodiments of the present application do not specifically limit the structure and material composition of the separator.

[0039] The electrolyte 14 is a carrier for the transport of ions in the sodium-ion battery and is usually composed of a sodium salt, a solvent, and an additive. The sodium salt can be, for example, one or more of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium hexafluoroarsenate, sodium perchlorate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide, sodium bis(oxalato)borate, sodium difluoro(oxalato)borate. The solvent can be an aqueous solvent or a non-aqueous solvent, and can be specifically selected according to the types of the sodium salt and the additive. The additive can include, for example, one or more of vinylene carbonate, 1,3-propane sultone, fluoroethylene carbonate, fluoromethyl carbonate, dimethyl sulfate, ethylene methyl sulfate, etc. The above is only for exemplary illustration, and the embodiments of the present application do not specifically limit the composition of the electrolyte.

[0040] Figure 2 This is a schematic structural diagram of a negative electrode sheet of the present application. As Figure 2 shown, the negative electrode sheet 12 includes a negative electrode current collector 121 and a nano-coating 122 provided on the surface of the negative electrode current collector 121. The negative electrode current collector 121 can be, for example, a metal foil such as a copper foil or an aluminum foil. The metal foil can be, for example, at least one of a foam metal foil with a thickness less than 6 μm or a metal mesh with a mesh size greater than 150 meshes.

[0041] Figure 3 This is a schematic side view structural diagram of a negative electrode sheet of an embodiment. Referring together to Figure 2 and Figure 3, the nano - coating 122 may include a sodium - attracting carrier 123, and there are multiple sodium - attracting carriers 123. Among them, the sodium - attracting carrier is a carrier that can attract sodium deposition. The sodium - attracting carrier 123 is connected to the negative - electrode current collector 121. For example, the sodium - attracting carrier 123 can be formed by in - situ growth from the surface of the negative - electrode current collector 121. Among them, the included angle between at least part of the sodium - attracting carriers 123, such as most of the sodium - attracting carriers 123, or all of the sodium - attracting carriers 123, and the negative - electrode current collector 121 is greater than 0. The included angle between the sodium - attracting carrier 123 and the negative - electrode current collector 121 is the included angle between the large surface of the sodium - attracting carrier and the surface of the negative - electrode current collector 121. The sodium - attracting carrier 123 and the negative - electrode current collector 121 are not arranged in parallel, so that a gap can be formed between the sodium - attracting carrier 123 and the negative - electrode current collector 121. The gap formed between the sodium - attracting carrier 123 and the negative - electrode current collector 121 can promote the transport of sodium ions between the sodium - attracting carrier 123 and the negative - electrode current collector 121.

[0042] In some embodiments, the included angle between the sodium - attracting carrier 123 and the negative - electrode current collector 121 is 30° - 85°. The sodium - attracting carrier 123 and the negative - electrode current collector 121 are not parallel and not perpendicular, which can form more pore structures. And the sodium - attracting carrier 123 is not perpendicularly lapped, which can play a role in blocking the growth of sodium dendrites, prevent the formation of sodium dendrites, and thus improve the safety of sodium - ion batteries. Exemplarily, the included angle between the sodium - attracting carrier 123 and the negative - electrode current collector 121 can be 30°, 35°, 40°, 45°, 50°, 55°, 60°, 65°, 70°, 75°, 80°, 85° or any value between the above - mentioned two values.

[0043] Continue to refer to Figure 2 and Figure 3 , the shape of the sodium - attracting carrier 123 can be an irregular shape, but generally it is in a sheet - like structure. That is, the size of the large surface of the sodium - attracting carrier 123 is much larger than the size h in its thickness direction. For example, the distance between the two farthest points on the large surface is more than 20 times the thickness. The thickness of the sodium - attracting carrier 123 is the size in the direction perpendicular to the large surface of the sodium - attracting carrier 123. One side of the sodium - attracting carrier 123 is connected to the negative - electrode current collector 121. The sodium - attracting carriers 123 are either arranged at intervals or connected. When adjacent sodium - attracting carriers 123 are connected, they can be connected through the sides of the sodium - attracting carrier 123 that do not contact the negative - electrode current collector 121.

[0044] When adjacent sodium - attracting carriers 123 are connected, a gap is formed between the sodium - attracting carriers 123. Thus, three - dimensional transport of sodium ions can be realized, avoiding local excessive deposition of sodium.

[0045] The thickness of the sodiumophilic carrier is less than or equal to 25 nm. The above-mentioned nanoscale sodiumophilic carrier can increase the internal specific surface area of the nano-coating, and then more sodium metal can be deposited in the nano-coating with a thinner thickness, increasing the total area of the sodium metal layer, so that the thickness of the nano-coating can be controlled within the nanoscale range to have enough space to deposit a sufficient amount of sodium metal.

[0046] The sodiumophilic carrier 123 is prepared from a sodiumophilic material. Using the sodiumophilic carrier 123 with sodiumophilic characteristics can reduce the deposition potential of Na. The sodiumophilic material has a large affinity for sodium and can attract sodium elements. During the charge-discharge cycle of the sodium-ion battery, due to its sodiumophilic characteristics, the sodiumophilic carrier 123 can reduce the deposition potential of sodium and induce the deposition of sodium, thereby forming a more uniform sodium metal layer on the surface of each sodiumophilic carrier 123 and optionally on the surface of the negative electrode current collector 121, avoiding the formation of tips or dendrites caused by local over-deposition of sodium, and then reducing the formation of local high-activity regions, and improving the cycle performance of the sodium-ion battery. Among them, the material for forming the sodiumophilic carrier 123 can be selected from at least one of Sn, Zn, Cu, Co3O4, NiO, Fe3O4, MoO X 、Co2S, NiS, FeS, MoS2, CoP, NiP. During the first charge-discharge process of the battery, the sodium ions transported from the positive electrode plate to the negative electrode plate are deposited on at least part of the surface of the sodiumophilic carrier 123, such as the entire surface, and optionally on the surface of the negative electrode current collector, such as the entire surface of the negative electrode current collector, to form a sodium metal layer. A part of the sodium metal in this sodium metal layer will be deposited on the surface of the sodiumophilic carrier as irreversible sodium metal, and another part of the sodium metal shuttles between the positive electrode plate and the negative electrode plate during the charge-discharge process. Among them, the irreversible sodium metal no longer acts as an active substance and shuttles between the positive electrode plate and the negative electrode plate during the charge-discharge process. Among them, the formed Na metal layer is not a flat layer, but a sodium metal layer with a curved surface structure deposited along the surface of the sodiumophilic carrier and optionally on the surface of the negative electrode current collector. The sodium metal layer can be a continuous metal layer or a non-fully closed continuous sodium metal layer. The sodium metal layer deposited on the surface of the sodiumophilic carrier and optionally on the surface of the negative electrode current collector can be used as a negative electrode active substance to realize the adsorption and desorption of sodium ions during the charge-discharge cycle. The surface deposition amount of the sodium metal layer on the surface of the sodiumophilic carrier is 1-10 mAh / cm 2 . Therefore, the sodium-ion battery of the present application solves the problem of rapid decay of the cycle performance of the sodium-ion battery caused by uneven sodium deposition / detachment while achieving a reduction in the sodium deposition potential and rapid transmission, and improves the cycle performance of the sodium-ion battery.

[0047] Among them, the thickness of the nano - coating is greater than or equal to 50 nm and less than 1 μm, such as 120 - 500 nm. Among them, the thickness direction of the nano - coating is from the negative current collector to the direction of the nano - coating. The thickness of the nano - coating is at the nanoscale. The nanoscale coating thickness can deposit a sufficient sodium metal layer, ensuring the normal charge - discharge cycle of the sodium - ion battery and reducing the loss of unnecessary energy density.

[0048] The lower limit value of the thickness of the nano - coating can be, for example, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, 150 nm, 180 nm, 200 nm, 210 nm, 220 nm, 240 nm, 260 nm, 260 nm, 280 nm, 300 nm, 320 nm, 340 nm, 350 nm, 380 nm, or 400 nm or a larger value or any value between any two of the above values. The upper limit value of the thickness of the nano - coating can be, for example, 980 nm, 950 nm, 920 nm, 900 nm, 880 nm, 850 nm, 800 nm, 780 nm, 750 nm, 730 nm, 700 nm, 680 nm, 650 nm, 630 nm, 610 nm, 600 nm, 580 nm, 550 nm, 530 nm, 520 nm, 500 nm, 480 nm, 450 nm or a smaller value or any value between any two of the above values.

[0049] The preparation method of the negative electrode sheet of the embodiment of the present application includes the following steps: depositing the nano - coating on at least one side surface of the negative current collector to obtain a negative electrode sheet; assembling the positive electrode sheet and the negative electrode sheet to obtain the sodium - ion battery.

[0050] Exemplarily, the nano - coating can be prepared by one of electro - deposition method, chemical deposition method, magnetron sputtering method, atomic layer deposition method, etc.

[0051] As a specific embodiment, the negative electrode sheet of the embodiment of the present application is prepared by electro - deposition method, specifically including the following steps:

[0052] In an electroplating bath, using the negative current collector as a working electrode and placing it in an electro - deposition solution containing sodium - affinity elements for electro - deposition, a precursor containing sodium - affinity elements is formed on the surface of the negative current collector to obtain an intermediate composite structure; heat - treating the intermediate composite structure to obtain the negative electrode sheet.

[0053] Using the electro - deposition method to prepare the negative electrode sheet can flexibly adjust the coating thickness to the nanoscale, which is beneficial to improving the energy density of the sodium - ion battery, reducing the waste of raw materials of the nano - coating, and can effectively adjust the microstructure of the nano - coating, optimize the micropore structure size of the nano - coating, thereby further optimizing the cycle performance of the sodium - ion battery.

[0054] Among them, in the above method, the electroplating time is 10 - 60 s, the electroplating temperature is room temperature, and the concentration of the electroplating solution is 0.01 - 0.1 M. By adjusting the parameters in the electroplating process, the surface deposition amount of sodium metal can be optimized, thereby flexibly designing the capacity of the battery cell.

[0055] The structure and preparation method of the sodium-ion battery have been explained above. Next, the performance of the sodium ions in this application will be further explained with specific examples.

[0056] Example 1

[0057] 1. Preparation of the composite current collector for the negative electrode sheet:

[0058] Prepare a 0.01 - 0.1 M NiCl₂ electrolyte solution. Use a copper foil as the working electrode, a saturated calomel or AgCl as the reference electrode, and a platinum sheet, nickel sheet or graphite sheet as the counter electrode. Place the working electrode in the electrolyte solution for electroplating for 10 - 60 s to prepare a Ni precursor on the surface of the Cu foil. The Ni precursor is a substance containing Ni, O and H.

[0059] Heat-treat the copper foil deposited with the Ni precursor in the air. The heating temperature is 300 - 350 °C, the heating rate is set at 3 °C / min, and the holding time is set at 3 - 3.5 h. Obtain a NiO / Cu composite current collector, with the copper foil as the negative current collector and the NiO layer as the nano-coating.

[0060] Figure 4 It is a schematic diagram of the microstructure of the nano-coating formed on the surface of the copper foil. As Figure 4 shown, in the nano-coating of this application, NiO is a sodium-philic carrier, and there are pores between the sodium-philic carriers.

[0061] 2. Preparation of the positive electrode sheet

[0062] Disperse O₃-Na[Ni 0.5 Mn 0.5 O₂, polyvinylidene difluoride (PVDF), and conductive carbon black in an N-methylpyrrolidone (NMP) solution in a ratio of 8.2:0.9:0.9 to obtain a positive electrode slurry; coat the positive electrode slurry on the surface of the aluminum foil, and then dry it in vacuum to remove NMP. Roll-press the dried composite electrode sheet to obtain the positive electrode sheet.

[0063] 3. Battery assembly

[0064] A battery was assembled using a composite current collector NiO / Cu, a positive electrode sheet, a glass fiber separator, and an electrolyte. The electrolyte was a 1 M solution of NaPF6 in dimethyl ether.

[0065] Examples 2 - 10 and Comparative Example 1

[0066] Examples 2 - 10 and Comparative Example 1 were respectively a kind of sodium-ion battery. Different from the sodium-ion battery of Example 1, the electrodeposition parameters were different in the preparation process of the composite current collector used for the negative electrode sheet, and the rest was the same as that of Example 1. The metal foil used as the negative current collector was copper foil. Among them, the electrodeposition parameters of different examples and comparative examples are listed in Table 1.

[0067] Table 1

[0068] Sample Electrodeposition time Concentration of electrodeposition solution Thickness of nano - coating Deposition substrate Example 1 10s 0.05M 61nm Copper foil Example 2 30s 0.05M 156nm Copper foil Example 3 50s 0.05M 284nm Copper foil Example 4 100s 0.05M 413nm Copper foil Example 5 150s 0.05M 514nm Copper foil Example 6 210s 0.05M 653nm Copper foil Example 7 50s 0.01M 223nm Copper foil Example 8 50s 0.03M 252nm Copper foil Example 9 50s 0.07M 291nm Copper foil Example 10 50s 0.09M 325nm Copper foil Comparative Example 1 0 / 0 Copper foil

[0069] It can be seen from the data in Table 1 that by controlling parameters such as the electrodeposition time and the concentration of the electrodeposition solution, the thickness of the sodiumophilic carrier in the formed nano-coating can be regulated.

[0070] Comparative Example 2

[0071] Comparative Example 2 was respectively a kind of sodium-ion battery. In this comparative example, a slurry containing NiO particles was coated on the surface of the copper foil, and the coating thickness was 6 μm. The slurry was a suspension containing NiO particles, carboxymethyl cellulose (CMC), polymerized styrene butadiene rubber (SBR), and super-P (SP). After drying, a composite current collector was obtained. The processes of assembling the positive electrode sheet and the battery were the same as those of Example 1.

[0072] Among them, the NiO particles in this comparative example were prepared by a hydrothermal method, that is, nickel nitrate hexahydrate and urea were dissolved in deionized water, the solution was transferred to a hydrothermal autoclave and reacted at 100 °C for 9 h, then the precipitate was collected, rinsed, dried, and calcined in air at 400 °C for 3 h to obtain NiO particles.

[0073] The overpotential, cycling performance, and Coulomb efficiency of the sodium-ion batteries of different examples and comparative examples were respectively tested.

[0074] 1. The process of overpotential test was as follows:

[0075] Using the composite current collectors in different examples and comparative examples as the working electrodes, a symmetric battery was assembled with a Na sheet as the counter electrode. The assembled battery was cycled 5 times at 50 μA / cm 2 , 0.01 - 0.5 V to form a stable film on the surface of the composite current collector. At 1 - 4 mAh / cm 2Sodium metal electrodeposition on the composite current collector is subjected to charge and discharge cycles, and the overpotential is taken as the difference between the deposition platform potential and 0 V in the charge and discharge curves.

[0076] 2. The cycle performance test process is as follows:

[0077] The sodium-ion battery is subjected to a nuclear capacity test at 0.2C at 25°C and then discharged at a constant current to 2V, and left standing for 30 min; it is left standing in an environment of 55°C for 4 hours; the cycle is carried out according to the following steps, and the capacity retention rate after 200 cycles is counted: constant current and constant voltage charging at 0.5C to 3.95V / 0.1C cut-off, left standing for 30 min, and constant current discharge at 0.1C to 2V and left standing for 30 min. After the cycle is completed, the Coulomb efficiency of the sodium-ion battery is tested.

[0078] Table 2

[0079]

[0080] According to the test results of Examples 1 to 6 and Comparative Example 1, when the concentration of the electrodeposition solution is 0.05 M and the electrodeposition time is set to 10 - 210 s, the thickness of the grown nano-coating is between 61 and 653 nm. Compared with the pure copper foil, the sodium-ion deposition overpotential can be effectively reduced, and its capacity retention rate and Coulomb efficiency can be improved.

[0081] From the test data of Examples 1 - 10, when the thickness of the nano-coating is 156 - 413 nm, that is, when the thickness of the nano-coating is less than 500 nm, the cycle efficiency of the sodium-ion battery can reach more than 91%. Especially when it is between 200 and 300 nm, the capacity retention rate of the sodium-ion battery after 200 cycles is 94.3%, and the Coulomb efficiency can reach 99.5%. When the thickness of the nano-coating is less than 200 nm, it is not sufficient to fully play the role of inducing uniform deposition / stripping of sodium ions by the nano-coating. When the nano-coating is too thick, it will reduce the conductivity of the overall negative electrode sheet, thereby affecting the cycle performance of the sodium-ion battery.

[0082] According to the test results of Example 3 and Examples 6 to 9 and Comparative Example 1, when the electrodeposition time is 50 s, the concentration of the electrodeposition solution is 0.01 M - 0.09 M, and the thickness of the grown nano-coating is between 223 and 325 nm. When the thickness of the nano-coating is between 252 - 291 nm, the overpotential drops to 16.3 - 16.9 mv. After the sodium-ion battery is cycled 200 times, the capacity retention rate can reach 94.2% - 94.6%. It shows that changing the concentration of the electrodeposition solution can finely adjust the thickness of the nano-coating, and thus adjust the cycle performance of the sodium-ion battery.

[0083] From the comparison data of Examples 1-10 and Comparative Example 2, it can be seen that the NiO coating prepared by the coating method has a thickness of 8 μm, but its cycle stability and Coulomb efficiency are slightly lower than those of the electrodeposition method. Moreover, the electrodeposition method can achieve better results with a coating thickness of only about 200 nm.

[0084] Based on the same technical purpose, the present application provides a battery pack, which includes a plurality of batteries connected in series or in parallel; the batteries are the sodium-ion batteries of the embodiments of the present application.

[0085] Based on the same technical concept, an embodiment of the present application provides an energy storage system. Figure 5 It is a schematic diagram of the connection structure of an energy storage system. As Figure 5 shown, the energy storage system includes the battery pack of the present application and a power converter. The power converter is used to perform power conversion on the voltage output by the battery pack and then output it to the power grid or an external load, and / or the power converter is used to perform power conversion on the voltage output by an external power source and then output it to the battery pack. Among them, the battery pack can be connected to a photovoltaic module to charge the battery pack by using the photovoltaic module.

[0086] The above are only the specific embodiments of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed in the present application, and all of them should be covered by the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.

Claims

1. A sodium-ion battery, characterized in that, It includes a positive electrode plate and a negative electrode plate; The negative electrode sheet includes a negative electrode current collector and a nano-coating provided on the surface of the negative electrode current collector. The nano-coating includes a plurality of sodium-philic carriers, each of the sodium-philic carriers being sheet-shaped, and the material of the sodium-philic carrier is at least one of Sn, Zn, Cu, Co3O4, NiO, Fe3O4, MoO X , Co2S, NiS, FeS, MoS2, CoP, NiP; The included angle between at least part of the sodium-philic carrier and the negative electrode current collector is greater than 0, there is a gap between adjacent sodium-philic carriers, and a sodium metal layer is deposited on at least part of the surface of the sodium-philic carrier.

2. The sodium-ion battery according to claim 1, characterized in that, The thickness of the nano-coating is greater than or equal to 50 nm and less than 1 μm.

3. The sodium-ion battery according to claim 2, characterized in that, The thickness of the nano-coating is 120 - 500 nm.

4. The sodium-ion battery according to any one of claims 1-3, characterized in that, The thickness of the sodium-philic carrier is less than or equal to 25 nm.

5. The sodium-ion battery according to any one of claims 1-4, characterized in that, The material of the sodium-philic carrier is NiO.

6. The sodium-ion battery according to any one of claims 1-5, characterized in that, The sodium-philic carrier is connected to the negative electrode current collector.

7. The sodium-ion battery according to any one of claims 1-6, characterized in that, The included angle between the sodium-philic carrier and the negative electrode current collector is 30 - 85°.

8. The sodium-ion battery according to any one of claims 1-7, characterized in that, The areal deposition amount of the sodium metal layer on the surface of the sodiumophilic carrier is 1-10 mAh / cm 2 .

9. A battery pack, characterized in that, The battery pack includes a plurality of batteries, and the plurality of batteries are connected in series or in parallel; the battery is a sodium-ion battery as described in any one of claims 1 - 8.

10. An energy storage system, characterized in that, The energy storage system includes a power converter and at least one battery pack as described in claim 9; the power converter is used to perform power conversion on the voltage output by the battery pack and output it to the power grid or load, and / or perform power conversion on the voltage output by an external power source and output it to the battery pack.

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