Sodium supplementing material and preparation method thereof, positive pole piece and preparation method thereof, electrode assembly, battery and electric device

Abstract

The invention relates to the technical field of batteries, in particular to a sodium supplementing material and a preparation method thereof, a positive pole piece and a preparation method thereof, an electrode assembly, a battery and an electric device. The sodium supplementing material comprises a sodium-containing compound and a reducing agent, and the sodium-containing compound and the reducing agent react in the cycle process (such as a formation stage) of the secondary battery to generate sodium ions and reduction products for sodium supplementing, so that the formation and the stability of a negative electrode SEI are promoted, and the first coulombic efficiency of the battery is improved.

Description

Technical Field

[0001] The present invention relates to the field of battery technology, and in particular to a sodium supplement material and a preparation method thereof, a positive electrode sheet and a preparation method thereof, an electrode assembly, a battery and an electrical device. Background Art

[0002] Sodium secondary batteries have great development prospects in the field of large-scale energy storage due to their abundant sodium reserves. Compared with lithium-ion batteries, the sodium required for sodium-ion batteries has the advantages of low cost and abundant reserves, and has broad application prospects in the field of next-generation energy storage and power batteries.

[0003] There is a problem of sodium loss during the cycle of sodium secondary batteries. Summary of the invention

[0004] The main purpose of the present invention is to provide a sodium supplement material to improve the performance of the battery.

[0005] To achieve the above object, the present invention provides a sodium supplement material, which comprises a sodium-containing compound and a reducing agent.

[0006] The sodium supplement material includes a sodium-containing compound and a reducing agent. During the secondary battery cycle (for example, the formation stage), the sodium-containing compound and the reducing agent react to produce sodium ions and reduction products for sodium supplementation. The generated sodium ions are affected by the electric field force, migrate from the cathode side to the anode surface and participate in the formation and repair of SEI on the negative electrode surface, thereby improving the first coulombic efficiency of the battery. Compared with directly adding a sodium supplement agent to the battery (for example, the sodium supplement agent includes the above-mentioned reduction product), considering that the electrostatic force between the anion and cation of the sodium supplement agent is large, it is not conducive to the migration of sodium ions to the anode, and the sodium supplement effect is not as good as the present application.

[0007] In addition, considering that the sodium supplement will dissolve in the electrolyte, resulting in an increase in the sodium salt concentration in the electrolyte and an increase in the viscosity of the electrolyte, if the sodium supplement is directly added to the battery, the above problems will occur; in the present application, sodium-containing compounds and reducing agents are used, and neither the sodium-containing compounds nor the reducing agents will dissolve in the electrolyte. The reaction between the two during the cycle process produces sodium ions and reduction products, so that the generated sodium ions migrate directly to the anode surface to participate in the formation of SEI, thereby reducing the concentration of sodium salts, so that only part of the reduction products exist in the form of sodium salts. At this time, the concentration of these sodium salts is lower than that of the directly added sodium supplement, thereby weakening the problem of excessive sodium salt concentration in the electrolyte.

[0008] In addition, the reducing agent can also react with the electrolyte to form a film layer on the surface of the positive electrode, which can protect the positive electrode material.

[0009] Furthermore, the reducing agent includes at least one of a non-metallic element and an inorganic sodium salt.

[0010] The reducing agent in the present application includes but is not limited to at least one of a non-metallic element and an inorganic sodium salt.

[0011] Further, the sodium-containing compound includes at least one of sodium fluoride and sodium oxide;

[0012] And / or, the reducing agent includes a non-metallic element, and the non-metallic element includes at least one of silicon, sulfur, arsenic, phosphorus, and boron;

[0013] And / or, the reducing agent includes an inorganic sodium salt, and the inorganic sodium salt includes at least one of sodium sulfite and sodium arsenite.

[0014] The sodium-containing compounds in the present application include but are not limited to sodium fluoride and / or sodium oxide.

[0015] The reducing agent in the present application includes non-metallic elements, and the non-metallic elements include but are not limited to at least one of silicon, sulfur, arsenic, phosphorus, and boron.

[0016] The reducing agent in the present application includes an inorganic sodium salt, and the inorganic sodium salt includes but is not limited to at least one of sodium sulfite and sodium arsenite.

[0017] Considering that directly adding a sodium supplement will lead to an excessively high sodium salt concentration in the electrolyte and an increase in the viscosity of the electrolyte, sodium sulfite and / or sodium arsenite can be used as a sodium supplement among the reducing agents. In order to improve the above problems, preferably, the reducing agent includes at least one of silicon, sulfur, arsenic, phosphorus, and boron.

[0018] Furthermore, the reaction product of the sodium-containing compound and the reducing agent includes one or more of sodium borate, sodium silicate, sodium arsenate, sodium sulfate, sodium tetrafluoroborate, sodium hexafluorosilicate, sodium hexafluoroborate or sodium hexafluoroarsenate.

[0019] The reaction product of the sodium-containing compound and the reducing agent in the present application includes but is not limited to one or more of sodium borate, sodium silicate, sodium arsenate, sodium sulfate, sodium tetrafluoroborate, sodium hexafluorosilicate, sodium hexafluoroborate or sodium hexafluoroarsenate. These reduction products can increase the conductivity of the electrolyte when entering the electrolyte. In particular, sodium hexafluoroborate and sodium hexafluorosilicate are sodium salts commonly used in sodium secondary batteries, have good electrical conductivity, and can increase the conductivity of the electrolyte when entering the electrolyte as reduction products.

[0020] Optionally, the mass ratio of the sodium-containing compound to the reducing agent is in the range of (2 to 6):1, preferably, 3:1.

[0021] Considering that the amount of both the reducing agent and the sodium-containing compound is unreasonable, there will be a problem of residue, which will reduce the energy density of the battery. In order to improve the above problem, the mass ratio of the sodium-containing compound to the reducing agent is in the range of (2 to 6): 1, preferably 3: 1. At this time, after the two are fully reacted, the residual reducing agent and sodium-containing compound are reduced. It is understandable that when the reducing agent and the sodium-containing compound are mixed with the active material, it is inevitable that there will be residual sodium-containing compound and reducing agent. After the above ratio is fully reacted, the residue will be less than 0.1ppm.

[0022] Optionally, the present application also provides a method for preparing the sodium supplement material, comprising:

[0023] The sodium-containing compound is mixed with a reducing agent to obtain a sodium-supplementing material.

[0024] That is, the sodium-supplementing material can be obtained by directly mixing the sodium-containing compound with the reducing agent.

[0025] Optionally, in the step of mixing the sodium-containing compound with the reducing agent, the step further comprises:

[0026] mixing at least one of a sodium-containing compound and a reducing agent with a conductive agent and a dispersant to obtain a mixture;

[0027] The mixture is mixed with at least the other of the sodium-containing compound and the reducing agent to obtain a mixed material.

[0028] Considering that if the sodium-containing compound and the reducing agent are unevenly distributed, on the one hand, it is difficult for the two to react effectively and fully; on the other hand, the uneven distribution of the reducing agent leads to differences in the capacity of each region of the positive electrode active material in the positive electrode plate. During the cycle process, there will be problems of uneven sodium embedding, which affects the stability of the interface. For example, too much sodium is embedded in some places, resulting in enrichment on the surface of the electrode, affecting the battery cycle performance.

[0029] That is, in order to make the reducing agent and the sodium-containing compound mix evenly and distribute evenly, increase the contact area between particles, and avoid particle agglomeration, so that the reducing agent and the sodium-containing compound can fully contact and react, a conductive agent and a dispersant are also added during the mixing process, and the mixing method is not limited. For example, the sodium-containing compound and the reducing agent can be directly mixed with the conductive agent and the dispersant, or the sodium-containing compound can be first mixed with the conductive agent and the dispersant, and then the reducing agent is added for mixing, or the reducing agent can be first mixed with the conductive agent and the dispersant, and then the sodium-containing compound is added for mixing.

[0030] It is understandable that the present application does not limit the types of conductive agents and dispersants. For example, the conductive agent includes one or more of acetylene black, Super P or carbon nanotubes, and the dispersant includes at least one of ethylene glycol, n-propanol, propylene glycol or polyacrylate.

[0031] Optionally, the mass ratio of the sodium-containing compound to the conductive agent and the dispersant is (1 to 2):(10 to 20):(50 to 100).

[0032] In order to achieve uniform dispersion, the mass ratio of the sodium-containing compound to the conductive agent and the dispersant is (1 to 2):(10 to 20):(50 to 100).

[0033] Optionally, during the mixing process, the mixing method includes at least one of ball milling, grinding milling and sand milling, the mixing time is 2 hours to 3 hours, and the rotation speed during the ball milling, grinding milling and sand milling process is 200 rpm to 300 rpm.

[0034] The present application does not limit the mixing method, which includes but is not limited to at least one of ball milling, grinding milling, and sand milling. The mixing time is 2 to 3 hours, and the rotation speed during ball milling, grinding milling, and sand milling is 200 to 300 rpm.

[0035] Optionally, the present application further provides a positive electrode plate, the positive electrode plate comprising the sodium supplement material as described above;

[0036] Alternatively, the sodium-supplementing material comprises the sodium-supplementing material obtained by the preparation method of the sodium-supplementing material.

[0037] Optionally, the positive electrode plate includes a current collector and a positive electrode coating provided on the current collector, and the mass percentage of the mass of the sodium supplement material to the total mass of the positive electrode coating is 1.75% to 3.38%, preferably 2% to 3%.

[0038] In the present application, the mass percentage of the sodium supplement material to the total mass of the positive electrode coating is 1.75% to 3.38%, preferably 2% to 3%. If the above range is met, the battery performance is improved.

[0039] Optionally, the positive electrode plate includes a positive electrode active material, and the mass percentage of the sodium supplement material to the total mass of the positive electrode active material and the sodium supplement material is 2% to 4%, preferably 2.75% to 3.25%.

[0040] The sodium supplement material is mixed in the positive electrode active material, and the mass percentage of the sodium supplement material to the total mass of the positive electrode active material and the sodium supplement material is 2% to 4%, preferably 2.75% to 3.25%. The sodium supplement material in the electrode sheet meets the above range, and a suitable amount of reduction product can be obtained through the reaction for sodium supplementation.

[0041] The sodium-containing compound of the present application will not change the potential of the positive electrode active material, and the product is a stable reduction product that can improve the ionic conductivity of the material. The sodium generated by the reaction can be transferred to the surface of the negative electrode to participate in the formation of SEI, which will not reduce the reversible capacity of the positive electrode, thereby improving the initial efficiency of the sodium secondary battery.

[0042] Optionally, the positive electrode active material includes at least one of Na5FeO4, Na5Fe5O8, Na6CoO4, Na2NiO2, NaCrO2, Na2O, Na2S, Na3P, Na3N, Na2O2, Na2C2O2N2, Na2C2O4, and Prussian blue sodium salt.

[0043] The positive electrode active material in the present application includes but is not limited to at least one of Na5FeO4, Na5Fe5O8, Na6CoO4, Na2NiO2, NaCrO2, Na2O, Na2S, Na3P, Na3N, Na2O2, Na2C2O2N2, Na2C2O4, and Prussian blue sodium salt.

[0044] Optionally, the positive electrode coating comprises at least two active layers, the at least two active layers are stacked and arranged on the same side of the current collector, at least one of the active layers is arranged on the current collector, and at least another of the active layers is arranged on a side of at least one of the active layers away from the current collector;

[0045] The mass percentage of the sodium-replenishing material in at least one of the active layers is defined as W1, and the mass percentage of the sodium-replenishing material in at least another active layer is defined as W2, satisfying W1<W2.

[0046] The positive electrode coating includes at least two active layers, at least one active layer is arranged on the current collector, and at least another active layer is arranged on the side of the at least one active layer away from the current collector, which means that one active layer is closer to the current collector than the other active layer, and the other active layer is closer to the electrolyte, and the mass percentage of the sodium-replenishing material in the other active layer close to the electrolyte is greater than the mass percentage of the sodium-replenishing material in the active layer close to the current collector, so that the mass percentage of the sodium-replenishing material in the active layer from the current collector side to the electrolyte side presents an increasing gradient, which can promote the migration of sodium ions, improve the sodium replenishing performance, and improve the battery performance.

[0047] Optionally, 0≤W1<2%, 2%≤W2≤3%.

[0048] In the present application, 0≤W1<2%, 2%≤W2≤3%. Meeting the above ranges can improve the sodium supplementation performance and the battery performance.

[0049] Optionally, the present application also provides a method for preparing the positive electrode sheet as described above, comprising:

[0050] Mixing a positive electrode active material, a sodium supplement material, a binder, and a solvent to obtain a positive electrode slurry;

[0051] The positive electrode slurry is applied to a current collector and dried to obtain a positive electrode sheet.

[0052] In the process of preparing the positive electrode sheet, the positive electrode active material, the sodium supplement material, the binder and the solvent can be mixed to obtain the positive electrode slurry; the positive electrode slurry is coated on the current collector and dried to obtain the positive electrode sheet.

[0053] Optionally, the step of mixing the positive electrode active material, the sodium supplement material, the binder and the solvent to obtain the positive electrode slurry includes:

[0054] dry-mixing the positive electrode active material with the sodium supplement material;

[0055] A binder and a solvent are added and mixed to obtain a positive electrode slurry.

[0056] In order to improve the uniformity of mixing, the mixing process includes dry mixing the positive electrode active material and the sodium supplement material; adding a binder and a solvent to mix to obtain a positive electrode slurry.

[0057] Optionally, the mass ratio of the active material, the sodium supplement material, the binder and the solvent is (80 to 85): (1.6 to 3.5): (5 to 10): (100 to 150).

[0058] During the mixing process, the mass ratio of the active material, the sodium supplement material, the binder and the solvent is (80 to 85): (1.6 to 3.5): (5 to 10): (100 to 150), which is conducive to the coating of the positive electrode slurry on the current collector.

[0059] Optionally, the present application also provides an electrode assembly, which includes a negative electrode plate, an electrolyte and a positive electrode plate as described, or includes a positive electrode plate obtained by the preparation method of the positive electrode plate as described.

[0060] Optionally, during the battery formation stage, the sodium-containing compound reacts with the reducing agent, and the reaction product of the sodium-containing compound and the reducing agent includes one or more of sodium borate, sodium silicate, sodium arsenate, sodium sulfate, sodium tetrafluoroborate, sodium hexafluorosilicate, sodium hexafluoroborate or sodium hexafluoroarsenate.

[0061] Considering that a layer of SEI film will also form on the surface of the hard carbon negative electrode of the sodium ion battery, which leads to low first efficiency of the entire battery system and increase of irreversible capacity, for this reason, in the battery formation stage, the reaction between the sodium-containing compound and the reducing agent is controlled, and the reaction product of the sodium-containing compound and the reducing agent includes one or more of sodium borate, sodium silicate, sodium arsenate, sodium sulfate, sodium tetrafluoroborate, sodium hexafluorosilicate, sodium hexafluoroborate or sodium hexafluoroarsenate. So as to replenish the loss of sodium in time, improve the first coulomb efficiency of the battery, and extend the cycle life of the battery.

[0062] Optionally, the first charging voltage range of the formation stage is 3.9V to 4.2V;

[0063] And / or, the temperature range of the formation stage is 55°C to 80°C.

[0064] In order to control the reaction between the sodium-containing compound and the reducing agent during the battery formation stage to obtain a reaction product (such as sodium borate, sodium silicate, sodium arsenate, sodium sulfate, sodium tetrafluoroborate, sodium hexafluorosilicate, sodium hexafluoroborate or sodium hexafluoroarsenate, etc.), the first charging voltage range of the formation stage is 3.9V to 4.2V; and / or, the temperature range of the formation stage is 55°C to 80°C.

[0065] The present application also provides a battery, which includes the electrode assembly as described.

[0066] The present application also provides an electrical device, which includes the battery as described above.

[0067] The sodium-supplementing material of the present application includes a sodium-containing compound and a reducing agent. During the secondary battery cycle (e.g., the formation stage), the sodium-containing compound and the reducing agent react to produce sodium ions and reduction products for sodium supplementation, thereby promoting the formation and stabilization of the negative electrode SEI and improving the first coulombic efficiency of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0069] Figure 1 It is a schematic structural diagram of a positive electrode sheet according to an embodiment of the present application;

[0070] Figure 2 It is a schematic diagram of the preparation process of the positive electrode sheet according to one embodiment of the present application;

[0071] Figure 3is a schematic diagram of a secondary battery according to an embodiment of the present application;

[0072] Figure 4 yes Figure 3 An exploded view of a secondary battery according to an embodiment of the present application is shown;

[0073] Figure 5 is a schematic diagram of a battery module according to an embodiment of the present application;

[0074] Figure 6 is a schematic diagram of a battery pack according to an embodiment of the present application;

[0075] Figure 7 yes Figure 6 An exploded view of a battery pack according to an embodiment of the present application is shown;

[0076] Figure 8 FIG. 1 is a schematic diagram of an electric device using a secondary battery according to an embodiment of the present application as a power source.

[0077] Description of Figure Numbers:

[0078] Label name Label name 1 Battery Pack 5 Secondary battery 2 Upper box 51 case 3 Lower box 52 Electrode assembly 4 Battery Module 53 Top cover assembly 100 Positive electrode 20 Conductive layer 30 current collector 40 Cathode coating 41 At least one active layer 42 At least one other active layer

[0079] The realization of the purpose, functional features and advantages of the present invention will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0080] The following will be combined with the drawings in 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.

[0081] Hereinafter, the sodium supplement material and its preparation method, positive electrode plate, electrode assembly, battery and electric device of the present application are specifically disclosed in detail with appropriate reference to the accompanying drawings. However, there are cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following descriptions are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0082] "Scope" disclosed in the present application is limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope limited in this way can be including end values ​​or not including end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following scope can be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0083] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0084] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0085] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0086] If there is no special explanation, the "include" and "comprising" mentioned in this application are open-ended or closed-ended. For example, the "include" and "comprising" may mean that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

[0087] If not specifically stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0088] Sodium secondary batteries have great development prospects in the field of large-scale energy storage due to their abundant sodium reserves. Compared with lithium-ion batteries, the sodium required for sodium-ion batteries has the advantages of low cost and abundant reserves, and has broad application prospects in the field of next-generation energy storage and power batteries.

[0089] There is a problem of sodium loss during the cycle of sodium secondary batteries.

[0090] In order to improve the problem of sodium loss, the present invention provides a sodium supplement material, which includes a sodium-containing compound and a reducing agent.

[0091] Sodium-containing compounds, compounds that include sodium, for example, sodium fluoride. Reducing agents, substances that lose electrons or have electrons deviated in redox reactions, for example, sulfur. Sodium-containing compounds and reducing agents can undergo reduction reactions.

[0092] The sodium supplement material includes a sodium-containing compound and a reducing agent. During the secondary battery cycle (for example, the formation stage), the sodium-containing compound and the reducing agent react to produce sodium ions and reduction products for sodium supplementation. The generated sodium ions are affected by the electric field force, migrate from the cathode side to the anode surface and participate in the formation and repair of SEI on the negative electrode surface, thereby improving the first coulombic efficiency of the battery. Compared with directly adding a sodium supplement agent to the battery (for example, the sodium supplement agent includes the above-mentioned reduction product), considering that the electrostatic force between the anion and cation of the sodium supplement agent is large, it is not conducive to the migration of sodium ions to the anode, and the sodium supplement effect is not as good as the present application.

[0093] In addition, considering that the sodium supplement will dissolve in the electrolyte, resulting in an increase in the sodium salt concentration in the electrolyte and an increase in the viscosity of the electrolyte, if the sodium supplement is directly added to the battery, the above problems will occur; in the present application, sodium-containing compounds and reducing agents are used, and neither the sodium-containing compounds nor the reducing agents will dissolve in the electrolyte. The reaction between the two during the cycle process produces sodium ions and reduction products, so that the generated sodium ions migrate directly to the anode surface to participate in the formation of SEI, thereby reducing the concentration of sodium salts, so that only part of the reduction products exist in the form of sodium salts. At this time, the concentration of these sodium salts is lower than that of the directly added sodium supplement, thereby weakening the problem of excessive sodium salt concentration in the electrolyte.

[0094] In addition, the reducing agent can also react with the electrolyte to form a film layer on the surface of the positive electrode, which can protect the positive electrode material.

[0095] It can be understood that by mixing the sodium-supplementing material into the positive electrode active material, the sodium-containing compound reacts with the reducing agent during the battery cycle (e.g., the formation stage), and the reaction generates a reduction product including a sodium-supplementing effect, which can promote the formation of a more uniform SEI on the negative electrode surface, thereby improving the battery's cycle performance.

[0096] In one embodiment, the reducing agent includes at least one of a non-metallic element and an inorganic sodium salt.

[0097] The reducing agent in the present application includes but is not limited to at least one of a non-metallic element and an inorganic sodium salt.

[0098] Non-metallic elements can act as reducing agents and react with sodium-containing compounds, and inorganic sodium salts can act as reducing agents and react with sodium-containing compounds.

[0099] In one embodiment, the sodium-containing compound includes at least one of sodium fluoride and sodium oxide; and / or the reducing agent includes a non-metallic element, and the non-metallic element includes at least one of silicon, sulfur, arsenic, phosphorus, and boron; and / or the reducing agent includes an inorganic sodium salt, and the inorganic sodium salt includes at least one of sodium sulfite and sodium arsenite.

[0100] The sodium-containing compounds in the present application include but are not limited to sodium fluoride and / or sodium oxide.

[0101] The reducing agent in the present application includes non-metallic elements, and the non-metallic elements include but are not limited to at least one of silicon, sulfur, arsenic, phosphorus, and boron.

[0102] The reducing agent in the present application includes an inorganic sodium salt, and the inorganic sodium salt includes but is not limited to at least one of sodium sulfite and sodium arsenite.

[0103] Considering that directly adding a sodium supplement will lead to an excessively high sodium salt concentration in the electrolyte and an increase in the viscosity of the electrolyte, sodium sulfite and / or sodium arsenite can be used as a sodium supplement among the reducing agents. In order to improve the above problems, preferably, the reducing agent includes at least one of silicon, sulfur, arsenic, phosphorus, and boron.

[0104] For example, part of the reaction equation of the sodium supplement material in the formation stage is as follows.

[0105] The chemical equation for the reaction of sodium oxide and boron is:

[0106] The chemical equation for the reaction of sodium oxide and silicon is:

[0107] The chemical equation for the reaction of sodium oxide and phosphorus is:

[0108] Chemical equation for the reaction of sodium fluoride and boron:

[0109] Chemical equation for the reaction of sodium fluoride and silicon:

[0110] The chemical equation for the reaction of sodium fluoride and phosphorus is:

[0111] In one embodiment, the reaction product of the sodium-containing compound and the reducing agent includes one or more of sodium borate, sodium silicate, sodium arsenate, sodium sulfate, sodium tetrafluoroborate, sodium hexafluorosilicate, sodium hexafluoroborate or sodium hexafluoroarsenate.

[0112] The reaction product of the sodium-containing compound and the reducing agent in the present application includes but is not limited to one or more of sodium borate, sodium silicate, sodium arsenate, sodium sulfate, sodium tetrafluoroborate, sodium hexafluorosilicate, sodium hexafluoroborate or sodium hexafluoroarsenate. These reduction products can increase the conductivity of the electrolyte when entering the electrolyte. In particular, sodium hexafluoroborate and sodium hexafluorosilicate are sodium salts commonly used in sodium secondary batteries, have good electrical conductivity, and can increase the conductivity of the electrolyte when entering the electrolyte as reduction products.

[0113] In one embodiment, the mass ratio of the sodium-containing compound to the reducing agent is in the range of (2 to 6):1, preferably, 3:1.

[0114] Considering that the amount of both the reducing agent and the sodium-containing compound is unreasonable, there will be a problem of residue, which will reduce the energy density of the battery. In order to improve the above problem, the mass ratio of the sodium-containing compound to the reducing agent is in the range of (2 to 6): 1, preferably 3: 1. At this time, after the two are fully reacted, the residual reducing agent and sodium-containing compound are reduced. It is understandable that when the reducing agent and the sodium-containing compound are mixed with the active material, it is inevitable that there will be residual sodium-containing compound and reducing agent. After the above ratio is fully reacted, the residue will be less than 0.1ppm.

[0115] In the above (2 to 6): 1, the values ​​include the minimum and maximum values ​​of the range, and every value between the minimum and maximum values. Specific examples include but are not limited to the point values ​​in the embodiments and 2:1, 3:1, 4:1, 5:1, 6:1, etc., as well as the range values ​​between any two of the above point values.

[0116] In one embodiment, the present application also provides a method for preparing a sodium-supplementing material, comprising: mixing a sodium-containing compound with a reducing agent to obtain a sodium-supplementing material.

[0117] That is, the sodium-supplementing material can be obtained by directly mixing the sodium-containing compound with the reducing agent.

[0118] In one embodiment, the step of mixing the sodium-containing compound with the reducing agent further includes: mixing at least one of the sodium-containing compound and the reducing agent with a conductive agent and a dispersant to obtain a mixture; and mixing the mixture with at least the other of the sodium-containing compound and the reducing agent to obtain a mixed material.

[0119] Considering that if the sodium-containing compound and the reducing agent are unevenly distributed, on the one hand, it is difficult for the two to react effectively and fully; on the other hand, the uneven distribution of the reducing agent leads to differences in the capacity of each region of the positive electrode active material in the positive electrode plate. During the cycle process, there will be problems of uneven sodium embedding, which affects the stability of the interface. For example, too much sodium is embedded in some places, resulting in enrichment on the surface of the electrode, affecting the battery cycle performance.

[0120] That is, in order to make the reducing agent and the sodium-containing compound mix evenly and distribute evenly, increase the contact area between particles, and avoid particle agglomeration, so that the reducing agent and the sodium-containing compound can fully contact and react, a conductive agent and a dispersant are also added during the mixing process, and the mixing method is not limited. For example, the sodium-containing compound and the reducing agent can be directly mixed with the conductive agent and the dispersant, or the sodium-containing compound can be first mixed with the conductive agent and the dispersant, and then the reducing agent is added for mixing, or the reducing agent can be first mixed with the conductive agent and the dispersant, and then the sodium-containing compound is added for mixing.

[0121] It is understandable that the present application does not limit the types of conductive agents and dispersants. For example, the conductive agent includes one or more of acetylene black, Super P or carbon nanotubes, and the dispersant includes at least one of ethylene glycol, n-propanol, propylene glycol or polyacrylate.

[0122] In one embodiment, the mass ratio of the sodium-containing compound to the conductive agent and the dispersant is (1 to 2): (10 to 20): (50 to 100).

[0123] In order to disperse evenly, the mass ratio of the sodium-containing compound to the conductive agent and the dispersant is (1 to 2): (10 to 20): (50 to 100). At the same time, considering that the sodium-supplementing material needs to be mixed in the positive electrode active material, since the conductive agent and the dispersant need to be mixed in the preparation process of the positive electrode active material slurry, the conductive agent and the dispersant are directly added in the preparation process of the sodium-supplementing material, which can simplify the subsequent preparation process of the positive electrode active material slurry, that is, in the process of preparing the sodium-supplementing material, a suitable amount of conductive agent and dispersant are added as needed, so that the conductive agent and the dispersant are mixed in the sodium-supplementing material, so that the conductive agent and the dispersant do not need to be added in the subsequent preparation process of the positive electrode slurry.

[0124] In the above (1 to 2): (10 to 20): (50 to 100), the values ​​include the minimum and maximum values ​​of the range, and every value between the minimum and maximum values. Specific examples include but are not limited to the point values ​​in the embodiments and 1:10:50, 1.5:15:75, 2:20:100, etc., as well as the range values ​​between any two of the above point values.

[0125] In one embodiment, during the mixing process, the mixing method includes at least one of ball milling, grinding milling, and sand milling. The mixing time is 2 hours to 3 hours. The rotation speed during the ball milling, grinding milling, and sand milling process is 200 rpm to 300 rpm.

[0126] The present application does not limit the mixing method, which includes but is not limited to at least one of ball milling, grinding milling, and sand milling. The mixing time is 2 to 3 hours, and the rotation speed during ball milling, grinding milling, and sand milling is 200 to 300 rpm.

[0127] In the above 2h to 3h, the values ​​include the minimum and maximum values ​​of the range, and every value between the minimum and maximum values. Specific examples include but are not limited to the point values ​​in the embodiments and 2h, 2.5h, 3h, etc., and the range values ​​between any two of the above point values.

[0128] In the above-mentioned 200rpm to 300rpm, the values ​​include the minimum and maximum values ​​of the range, and every value between the minimum and maximum values. Specific examples include but are not limited to the point values ​​in the embodiments and 200rpm, 220rpm, 250rpm, 260rpm, 280rpm, 300rpm, etc., as well as the range values ​​between any two of the above-mentioned point values.

[0129] In one embodiment, the present application further provides a positive electrode plate, which includes the sodium-supplementing material as described above; or, includes the sodium-supplementing material obtained by the preparation method of the sodium-supplementing material as described above.

[0130] In one embodiment, the positive electrode plate includes a current collector and a positive electrode coating disposed on the current collector, and the mass percentage of the sodium supplement material to the total mass of the positive electrode coating is 1.75% to 3.38%, preferably 2% to 3%.

[0131] Define the mass of the sodium supplement material as m1, the total mass of the positive electrode coating as M, and the mass percentage of the mass of the sodium supplement material to the total mass of the positive electrode coating as m1 / M×100%.

[0132] In the present application, the mass percentage of the sodium supplement material to the total mass of the positive electrode coating is 1.75% to 3.38%, preferably 2% to 3%. If the above range is met, the battery performance is improved.

[0133] In the above 1.75% to 3.38%, the values ​​include the minimum and maximum values ​​of the range, and every value between the minimum and maximum values. Specific examples include but are not limited to the point values ​​in the embodiments and 1.75%, 1.85%, 2.0%, 2.15%, 2.75%, 3.0%, 3.15%, 3.38%, etc., as well as the range values ​​between any two of the above point values.

[0134] In one embodiment, the positive electrode plate includes a positive electrode active material, and the mass percentage of the sodium supplement material to the total mass of the positive electrode active material and the sodium supplement material is 2% to 4%, preferably, 2.75% to 3.25%.

[0135] The mass of the sodium supplement material is defined as m1 (the mass of the sodium supplement material includes the mass of the sodium-containing compound and the mass of the reducing agent), and the total mass of the positive electrode active material and the sodium supplement material is defined as m2. The mass percentage of the mass of the sodium supplement material to the total mass of the positive electrode active material and the sodium supplement material is m1 / m2×100%.

[0136] The sodium supplement material is mixed in the positive electrode active material, and the mass percentage of the sodium supplement material to the total mass of the positive electrode active material and the sodium supplement material is 2% to 4%, preferably 2.75% to 3.25%. The sodium supplement material in the electrode sheet meets the above range, and a suitable amount of reduction product can be obtained through the reaction for sodium supplementation.

[0137] The sodium-containing compound of the present application will not change the potential of the positive electrode active material, and the product is a stable reduction product that can improve the ionic conductivity of the material. The sodium generated by the reaction can be transferred to the surface of the negative electrode to participate in the formation of SEI, which will not reduce the reversible capacity of the positive electrode, thereby improving the initial efficiency of the sodium secondary battery.

[0138] In the above 2% to 4%, the values ​​include the minimum and maximum values ​​of the range, and every value between the minimum and maximum values. Specific examples include but are not limited to the point values ​​in the embodiments and 2%, 2.5%, 3%, 3.5%, 4%, etc., and the range values ​​between any two of the above point values.

[0139] In one embodiment, the positive electrode active material includes at least one of Na5FeO4, Na5Fe5O8, Na6CoO4, Na2NiO2, NaCrO2, Na2O, Na2S, Na3P, Na3N, Na2O2, Na2C2O2N2, Na2C2O4, and Prussian blue sodium salt.

[0140] Prussian blue sodium salt, Prussian blue sodium salt includes Na p M1Fe(CN)6, wherein p is a number between 1 and 2, and M1 includes at least one of Mn, Fe, Co, Ni and Zn.

[0141] The positive electrode active material in the present application includes but is not limited to at least one of Na5FeO4, Na5Fe5O8, Na6CoO4, Na2NiO2, NaCrO2, Na2O, Na2S, Na3P, Na3N, Na2O2, Na2C2O2N2, Na2C2O4, and Prussian blue sodium salt.

[0142] In one embodiment, the positive electrode coating includes at least two active layers, at least two active layers are stacked on the same side of the current collector, at least one active layer is arranged on the current collector, and at least another active layer is arranged on the side of the at least one active layer away from the current collector; the mass percentage of the sodium-replenishing material in at least one active layer is defined as W1, and the mass percentage of the sodium-replenishing material in at least another active layer is defined as W2, satisfying W1<W2.

[0143] like Figure 1 As shown, it is a schematic diagram of the structure of a positive electrode plate 100, the positive electrode coating 40 includes at least one active layer 41 and at least another active layer 42, at least one active layer 41 is arranged on the current collector 30, and at least another active layer 42 is arranged on the side of at least one active layer 41 away from the current collector.

[0144] The positive electrode coating includes at least two active layers, at least one active layer is arranged on the current collector, and at least another active layer is arranged on the side of the at least one active layer away from the current collector, which means that one active layer is closer to the current collector than the other active layer, and the other active layer is closer to the electrolyte, and the mass percentage of the sodium-replenishing material in the other active layer close to the electrolyte is greater than the mass percentage of the sodium-replenishing material in the active layer close to the current collector, so that the mass percentage of the sodium-replenishing material in the active layer from the current collector side to the electrolyte side presents an increasing gradient, which can promote the migration of sodium ions, improve the sodium replenishing performance, and improve the battery performance.

[0145] In one embodiment, 0%≤W1<2%, 2%≤W2≤3%.

[0146] In the present application, 0%≤W1<2%, 2%≤W2≤3%. Meeting the above ranges can improve the sodium supplementation performance and the battery performance.

[0147] In the above 0%≤W1<2%, the values ​​include the minimum and maximum values ​​of the range, and every value between the minimum and maximum values. Specific examples include but are not limited to the point values ​​in the embodiments and 0%, 0.1%, 0.5%, 1%, 1.5%, 1.9%, etc., and the range values ​​between any two of the above point values.

[0148] In the above 2%≤W2≤3%, the values ​​include the minimum and maximum values ​​of the range, and every value between the minimum and maximum values. Specific examples include but are not limited to the point values ​​in the embodiments and 2%, 2.1%, 2.5%, 3%, etc., and the range values ​​between any two of the above point values.

[0149] In one embodiment, the present application also provides a method for preparing a positive electrode plate as described above, comprising: mixing a positive electrode active material, a sodium supplement material, a binder, and a solvent to obtain a positive electrode slurry; coating the positive electrode slurry on a current collector, and drying to obtain a positive electrode plate.

[0150] like Figure 2 As shown, it is a schematic flow chart of the method for preparing a positive electrode sheet. During the preparation process of the positive electrode sheet, the positive electrode active material, the sodium supplement material, the binder, and the solvent can be mixed to obtain a positive electrode slurry; the positive electrode slurry is coated on the current collector and dried to obtain a positive electrode sheet.

[0151] In one embodiment, the step of mixing the positive electrode active material, the sodium supplement material, the binder, and the solvent to obtain the positive electrode slurry includes: dry mixing the positive electrode active material and the sodium supplement material; adding the binder and the solvent to mix to obtain the positive electrode slurry.

[0152] In order to improve the uniformity of mixing, the mixing process includes dry mixing the positive electrode active material and the sodium supplement material; adding a binder and a solvent to mix to obtain a positive electrode slurry.

[0153] In one embodiment, the mass ratio of the active material, the sodium supplement material, the binder and the solvent is (80 to 85): (1.6 to 3.5): (5 to 10): (100 to 150).

[0154] During the mixing process, the mass ratio of the active material, the sodium supplement material, the binder and the solvent is (80 to 85): (1.6 to 3.5): (5 to 10): (100 to 150), which is conducive to the coating of the positive electrode slurry on the current collector.

[0155] In the above (80 to 85): (1.6 to 3.5): (5 to 10): (100 to 150), the values ​​include the minimum and maximum values ​​of the range, and every value between such minimum and maximum values. Specific examples include but are not limited to the point values ​​in the embodiments and 80: 1.6: 5: 100, 83: 2: 7: 120, 85: 3.5: 10: 150, etc., as well as the range values ​​between any two of the above point values.

[0156] In one embodiment, the present application also provides an electrode assembly, which includes a negative electrode plate, an electrolyte and a positive electrode plate as described above, or includes a positive electrode plate obtained by the preparation method of the positive electrode plate as described above.

[0157] In one embodiment, during the battery formation stage, the sodium-containing compound reacts with a reducing agent, and the reaction product of the sodium-containing compound and the reducing agent includes one or more of sodium borate, sodium silicate, sodium arsenate, sodium sulfate, sodium tetrafluoroborate, sodium hexafluorosilicate, sodium hexafluoroborate or sodium hexafluoroarsenate.

[0158] Considering that a layer of SEI film will also form on the surface of the hard carbon negative electrode of the sodium ion battery, which leads to low first efficiency of the entire battery system and increase of irreversible capacity, for this reason, in the battery formation stage, the reaction between the sodium-containing compound and the reducing agent is controlled, and the reaction product of the sodium-containing compound and the reducing agent includes one or more of sodium borate, sodium silicate, sodium arsenate, sodium sulfate, sodium tetrafluoroborate, sodium hexafluorosilicate, sodium hexafluoroborate or sodium hexafluoroarsenate. So as to replenish the loss of sodium in time, improve the first coulomb efficiency of the battery, and extend the cycle life of the battery.

[0159] In one embodiment, the first charging voltage range of the formation stage is 3.9V to 4.2V; and / or the temperature range of the formation stage is 55° C. to 80° C.

[0160] In order to control the reaction between the sodium-containing compound and the reducing agent during the battery formation stage to obtain a reaction product (such as sodium borate, sodium silicate, sodium arsenate, sodium sulfate, sodium tetrafluoroborate, sodium hexafluorosilicate, sodium hexafluoroborate or sodium hexafluoroarsenate, etc.), the first charging voltage range of the formation stage is 3.9V to 4.2V; and / or, the temperature range of the formation stage is 55°C to 80°C.

[0161] In the above 3.9V to 4.2V, the values ​​include the minimum and maximum values ​​of the range, and every value between the minimum and maximum values. Specific examples include but are not limited to the point values ​​in the embodiments and 3.9V, 4V, 4.1V, 4.2V, etc., and the range values ​​between any two of the above point values.

[0162] In the above-mentioned 55℃ to 80℃, the values ​​include the minimum and maximum values ​​of the range, and every value between the minimum and maximum values. Specific examples include but are not limited to the point values ​​in the embodiments and 55℃, 60℃, 65℃, 70℃, 75℃, 80℃, etc., and the range values ​​between any two of the above-mentioned point values.

[0163] In one embodiment, the present application also provides a battery, which includes the electrode assembly as described above.

[0164] Since the electrode assembly adopts all the technical solutions of all the above embodiments, it has at least all the beneficial effects brought by the technical solutions of the above embodiments, which will not be described one by one here.

[0165] It is understandable that batteries include secondary batteries, battery modules, and battery packs.

[0166] In one embodiment, the present application further provides an electrical device, which includes the battery as described above.

[0167] Since the battery adopts all the technical solutions of all the above embodiments, it has at least all the beneficial effects brought by the technical solutions of the above embodiments, which will not be described one by one here.

[0168] In addition, the battery (secondary battery, battery module, battery pack) and the electric device of the present application will be described below with reference to the drawings as appropriate.

[0169] In one embodiment of the present application, a secondary battery is provided.

[0170] Typically, a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator. During the battery charge and discharge process, active ions are embedded and removed back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is arranged between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing ions to pass through. The separator is the separator improved above in this application.

[0171] The positive electrode plate includes a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector.

[0172] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

[0173] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0174] In some embodiments, the positive electrode film layer may also optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0175] In some embodiments, the positive electrode film layer may further include a conductive agent, for example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0176] In some embodiments, the positive electrode sheet can be prepared in the following manner: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0177] The negative electrode plate includes a negative electrode current collector and a negative electrode film layer arranged on at least one surface of the negative electrode current collector, and the negative electrode film layer includes a negative electrode active material.

[0178] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

[0179] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, a copper foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0180] In some embodiments, the negative electrode active material may adopt the negative electrode active material for the battery known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0181] In some embodiments, the negative electrode film layer may further include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).

[0182] In some embodiments, the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0183] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0184] In some embodiments, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0185] The electrolyte plays a role in conducting ions between the positive electrode and the negative electrode. The present application has no specific restrictions on the type of electrolyte, which can be selected according to needs.

[0186] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0187] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane sulfone, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0188] In some embodiments, the electrolyte may further include additives, such as negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.

[0189] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous structure separator with good chemical stability and mechanical stability can be selected.

[0190] In some embodiments, the material of the diaphragm can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The diaphragm can be a single-layer film or a multi-layer composite film, without particular limitation. When the diaphragm is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0191] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly by a winding process or a lamination process.

[0192] In some embodiments, the secondary battery may include an outer package, which may be used to encapsulate the electrode assembly and the electrolyte.

[0193] In some embodiments, the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0194] The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square or any other shape. Figure 3 The secondary battery 5 is a square structure as an example.

[0195] In some embodiments, reference Figure 4 , the outer package may include a shell 51 and a cover plate 53. Among them, the shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the diaphragm can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0196] In some embodiments, secondary batteries may be assembled into a battery module. The number of secondary batteries contained in the battery module may be one or more, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery module.

[0197] Figure 5 4 is an example of a battery module. Figure 5 In the battery module 4, the plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other manner. Further, the plurality of secondary batteries 5 may be fixed by fasteners.

[0198] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of secondary batteries 5 are received in the receiving space.

[0199] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery pack.

[0200] Figure 6 and Figure 7 1 is a battery pack 1 as an example. Figure 6 and Figure 7 The battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can cover the lower box body 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0201] In addition, the present application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in the present application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.

[0202] As an electrical device, a secondary battery, a battery module or a battery pack can be selected according to its usage requirements.

[0203] Figure 8 The power consumption device is taken as an example. The power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the high power and high energy density requirements of the power consumption device for the secondary battery, a battery pack or a battery module can be used.

[0204] Another example of a device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be light and thin, and a secondary battery may be used as a power source.

[0205] Example

[0206] Example 1

[0207] The sodium-containing compound is sodium fluoride, and the reducing agent is elemental phosphorus, with a mass ratio of 3:1.

[0208] Pretreatment of sodium supplement materials:

[0209] Conductive carbon powder (acetylene black) and sodium-containing compounds are added to a dispersant (ethylene glycol) and ball-milled to obtain a mixture, and then the mixture is ball-milled with a reducing agent. The mass ratio of the sodium-containing compound to the conductive agent and the dispersant is 1.5:15:80. The ball-milling time is 2.5 hours and the rotation speed is 250 rpm.

[0210] Preparation of positive electrode:

[0211] The active material (Na 1.72 MnFe(CN)6), sodium supplement material, binder (PVDF) and solvent (NMP) in a mass ratio of 83:3:7:125. In the mass ratio of the sodium supplement material, 3 includes the mass of the sodium-containing compound and the reducing agent, but does not include the mass of the dispersant and the conductive agent. The active material and the sodium supplement material are pre-dry mixed for 35 minutes, and then the binder and the solvent are added and stirred for 35 minutes to obtain a positive electrode slurry. After the positive electrode slurry is stirred evenly, it is applied to the surface of the aluminum foil to obtain a positive electrode sheet.

[0212] Preparation of negative electrode

[0213] The active material artificial graphite, the conductive agent carbon black, the binder styrene-butadiene rubber (SBR), and the thickener sodium hydroxymethyl cellulose (CMC) are dissolved in the solvent deionized water in a weight ratio of 96.2:0.8:0.8:1.2, and the mixture is evenly mixed to prepare a negative electrode slurry; the negative electrode slurry is evenly coated on the negative electrode current collector copper foil once or multiple times, and the negative electrode sheet is obtained after drying, cold pressing, and slitting.

[0214] Preparation of electrolyte

[0215] In an argon atmosphere glove box (H2O<0.1ppm, O2<0.1ppm), organic solvents ethylene carbonate (EC) / ethyl methyl carbonate (EMC) were mixed evenly in a volume ratio of 3 / 7, 12.5% ​​NaPF6 sodium salt was added and dissolved in the organic solvent, and stirred evenly.

[0216] Isolation film

[0217] Polypropylene film is used as the isolation film.

[0218] Preparation of sodium ion batteries

[0219] The positive electrode sheet, the separator, and the negative electrode sheet of Example 1 are stacked in order, so that the separator is between the positive and negative electrode sheets to play an isolating role, and then wound to obtain a bare cell, and the bare cell is welded with a pole ear, and the bare cell is placed in an aluminum shell, and baked at 100°C to remove water, and then the electrolyte is injected and sealed to obtain an uncharged battery. The uncharged battery is then subjected to the processes of static, hot and cold pressing, formation, shaping, and capacity testing in sequence to obtain the sodium ion battery product of Example 1.

[0220] Example 2

[0221] The sodium-containing compound is sodium oxide, the reducing agent is elemental phosphorus, the mass ratio is 3:1, and the rest is the same as in Example 1.

[0222] Example 3 and Example 4

[0223] The sodium-containing compound is sodium fluoride, and the reducing agent is elemental silicon, with a mass ratio of 3:1 and 6:1 respectively, and the rest is the same as in Example 1.

[0224] Example 5

[0225] The sodium-containing compound is sodium fluoride, the reducing agent is phosphorus, the mass ratio is 3:1, and the rest is the same as in Example 1.

[0226] Example 6

[0227] The sodium-containing compound is sodium fluoride, the reducing agent is phosphorus, the mass ratio is 2:1, and the rest is the same as in Example 1.

[0228] Example 7

[0229] The sodium-containing compound is sodium fluoride, the reducing agent is phosphorus, the mass ratio is 4:1, and the remaining parts are the same as in Example 1.

[0230] Example 8

[0231] The sodium-containing compound is sodium fluoride and sodium oxide, the reducing agent is elemental phosphorus, the mass ratio of sodium fluoride to sodium oxide is 1:1, the ratio of the sodium-containing compound to the reducing agent is 3:1, and the rest is the same as in Example 1.

[0232] Example 9

[0233] The sodium-containing compound is sodium fluoride, the reducing agent is sodium sulfite, the mass ratio of sodium fluoride to sodium sulfite is 3:1, and the rest is the same as in Example 1.

[0234] Comparative Example 1

[0235] No reducing agent was added, and the rest was the same as in Example 1.

[0236] Comparative Example 2

[0237] No reducing agent was added, and the rest was the same as in Example 1.

[0238] Comparative Example 3

[0239] No sodium-containing compound and reducing agent were added, and the rest was the same as in Example 1.

[0240] Table 1 List of Examples

[0241]

[0242]

[0243] Comparative Example 4

[0244] On the basis of Example 5, the sodium supplement material is replaced by the reduction product Na2BO3 in Example 5, wherein the mass of Na2BO3 in Comparative Example 4 is consistent with the mass of Na2BO3 generated by the reaction in Example 5.

[0245] Comparative Example 5

[0246] On the basis of Example 3, the sodium supplement material is replaced by the reduction product Na2SiO3 in Example 3.

[0247] Comparative Example 6

[0248] On the basis of Example 6, the sodium supplement material is replaced by the reduction product Na2PO4 in Example 6.

[0249] Table 2 Example List

[0250]

[0251] Performance Test:

[0252] Battery first performance test steps:

[0253] 1. Let the battery stand; 2. Charge the battery to 4.4V using a constant current of 0.33C and calculate the charging capacity; 3. Let the battery stand; 4. Discharge the battery to 2.5V using a constant current of 0.33C and calculate the discharge capacity; 5. Test the first efficiency of the battery. The calculation formula for the first efficiency is: first efficiency = discharge capacity / charge capacity.

[0254] Cycle life test steps:

[0255] 1. Let the battery stand; 2. Charge the battery to 4.4V using a 0.33C constant current; 3. Let the battery stand; 4. Discharge the battery to 2.5V using a 0.33C constant current; 5. Repeat steps 1-4 until the battery's SOH is less than 80%.

[0256] The test steps of electrolyte conductivity are as follows: using a two-electrode conductivity tester, selecting the same electrodes, placing the electrolyte before and after formation between the two electrodes respectively; turning on the power supply, and passing a small current (at 100mA to 300mA, for example, at 150mA) through the circuit to obtain the conductivity value of the electrolyte.

[0257] It can be seen from the data of the examples and comparative examples in Table 1 that the addition of sodium-containing compounds and reducing agents to the positive electrode sheet improves the initial efficiency and cycle life of the battery. It can be seen from Table 2 that the addition of sodium-containing compounds and reducing agents to the positive electrode sheet significantly improves the conductivity of the electrolyte.

[0258] The above are only preferred embodiments of the present invention, and are not intended to limit the patent scope of the present invention. All equivalent structural changes made using the contents of the present invention's specification and drawings, or directly / indirectly applied in other related technical fields, are included in the patent protection scope of the present invention.

Claims

1. A sodium supplement material, characterized in that: The sodium supplement material comprises a sodium-containing compound and a reducing agent.

2. The sodium supplement material according to claim 1, characterized in that The reducing agent includes at least one of a non-metallic element and an inorganic sodium salt.

3. The sodium supplement material according to claim 1 or 2, characterized in that The sodium-containing compound includes at least one of sodium fluoride and sodium oxide; And / or, the reducing agent includes a non-metallic element, and the non-metallic element includes at least one of silicon, sulfur, arsenic, phosphorus, and boron; And / or, the reducing agent includes an inorganic sodium salt, and the inorganic sodium salt includes at least one of sodium sulfite and sodium arsenite.

4. The sodium supplement material according to any one of claims 1 to 3, characterized in that The reaction product of the sodium-containing compound and the reducing agent includes one or more of sodium borate, sodium silicate, sodium arsenate, sodium sulfate, sodium tetrafluoroborate, sodium hexafluorosilicate, sodium hexafluoroborate or sodium hexafluoroarsenate.

5. The sodium supplement material according to any one of claims 1 to 4, characterized in that The mass ratio of the sodium-containing compound to the reducing agent is in the range of (2 to 6):1, preferably, 3:

1.

6. A method for preparing the sodium supplement material according to any one of claims 1 to 5, characterized in that: include: The sodium-containing compound is mixed with a reducing agent to obtain a sodium-supplementing material.

7. The method for preparing the sodium supplement material according to claim 6, wherein: In the step of mixing the sodium-containing compound with the reducing agent, the method further comprises: mixing at least one of a sodium-containing compound and a reducing agent with a conductive agent and a dispersant to obtain a mixture; The mixture is mixed with at least the other of the sodium-containing compound and the reducing agent to obtain a mixed material.

8. The method for preparing the sodium supplement material according to claim 7, wherein: The mass ratio of the sodium-containing compound to the conductive agent and the dispersant is (1 to 2): (10 to 20): (50 to 100).

9. The method for preparing the sodium supplement material according to any one of claims 6 to 8, characterized in that: In the mixing process, the mixing method includes at least one of ball milling, grinding milling and sand milling, the mixing time is 2 hours to 3 hours, and the rotation speed in the ball milling, grinding milling and sand milling process is 200 rpm to 300 rpm.

10. A positive electrode sheet, characterized in that: The positive electrode plate comprises a sodium supplement material as claimed in any one of claims 1 to 5; Alternatively, the sodium-supplementing material comprises a sodium-supplementing material obtained by the preparation method of the sodium-supplementing material according to any one of claims 6 to 9.

11. The positive electrode sheet according to claim 10, characterized in that: The positive electrode plate includes a current collector and a positive electrode coating disposed on the current collector, and the mass percentage of the mass of the sodium supplement material to the total mass of the positive electrode coating is 1.75% to 3.38%, preferably 2% to 3%.

12. The positive electrode sheet according to claim 10 or 11, characterized in that: The positive electrode plate includes a positive electrode active material, and the mass percentage of the sodium supplement material to the total mass of the positive electrode active material and the sodium supplement material is 2% to 4%, preferably, 2.75% to 3.25%.

13. The positive electrode sheet according to claim 12, characterized in that: The positive electrode active material includes at least one of Na5FeO4, Na5Fe5O8, Na6CoO4, Na2NiO2, NaCrO2, Na2O, Na2S, Na3P, Na3N, Na2O2, Na2C2O2N2, Na2C2O4, and Prussian blue sodium salt.

14. The positive electrode sheet according to any one of claims 11 to 13, characterized in that: The positive electrode coating comprises at least two active layers, the at least two active layers are stacked and arranged on the same side of the current collector, at least one of the active layers is arranged on the current collector, and at least another of the active layers is arranged on a side of at least one of the active layers away from the current collector; The mass percentage of the sodium-replenishing material in at least one of the active layers is defined as W1, and the mass percentage of the sodium-replenishing material in at least another active layer is defined as W2, satisfying W1<W2.

15. The positive electrode sheet according to claim 14, characterized in that: 0≤W1<2%, 2%≤W2≤3%.

16. A method for preparing a positive electrode sheet according to any one of claims 10 to 15, characterized in that: include: Mixing a positive electrode active material, a sodium supplement material, a binder, and a solvent to obtain a positive electrode slurry; The positive electrode slurry is applied to a current collector and dried to obtain a positive electrode sheet.

17. The method for preparing a positive electrode sheet according to claim 16, characterized in that: The step of mixing the positive electrode active material, the sodium supplement material, the binder and the solvent to obtain the positive electrode slurry includes: dry-mixing the positive electrode active material with the sodium supplement material; A binder and a solvent are added and mixed to obtain a positive electrode slurry.

18. The method for preparing a positive electrode sheet according to claim 16 or 17, characterized in that: The mass ratio of the active material, the sodium supplement material, the binder and the solvent is (80 to 85): (1.6 to 3.5): (5 to 10): (100 to 150).

19. An electrode assembly, characterized in that: The electrode assembly comprises a negative electrode sheet, an electrolyte, and a positive electrode sheet as claimed in any one of claims 10 to 15, or comprises a positive electrode sheet obtained by the method for preparing a positive electrode sheet as claimed in any one of claims 16 to 18.

20. The electrode assembly according to claim 19, characterized in that During the battery formation stage, the sodium-containing compound reacts with the reducing agent, and the reaction product of the sodium-containing compound and the reducing agent includes one or more of sodium borate, sodium silicate, sodium arsenate, sodium sulfate, sodium tetrafluoroborate, sodium hexafluorosilicate, sodium hexafluoroborate or sodium hexafluoroarsenate.

21. The electrode assembly according to claim 20, characterized in that The first charging voltage range of the formation stage is 3.9V to 4.2V; And / or, the temperature range of the formation stage is 55°C to 80°C.

22. A battery, characterized in that: The battery comprises the electrode assembly according to any one of claims 19 to 21.

23. An electrical device, characterized in that: The electrical device comprises the battery as claimed in claim 22.

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