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

Abstract

The present application relates to the technical field of batteries, and particularly relates to a sodium supplementing material, a preparation method thereof, a positive electrode sheet, 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. During the cycle process (for example, the formation stage) of the secondary battery, the sodium-containing compound and the reducing agent react to generate sodium ions and a reduction product for supplementing sodium, promote the formation and stability of the negative electrode SEI, and improve the initial coulomb efficiency of the battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a sodium supplementing material, a preparation method thereof, a positive electrode sheet, a preparation method thereof, an electrode assembly, a battery and an electric device. BACKGROUND

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

[0003] There is a problem of sodium loss in the cycle process of sodium secondary batteries. SUMMARY

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

[0005] To achieve the above purpose, the present application provides a sodium supplementing material, which comprises a sodium-containing compound and a reducing agent.

[0006] The sodium supplementing material comprises a sodium-containing compound and a reducing agent. In the cycle process of the secondary battery (such as the formation stage), the sodium-containing compound and the reducing agent react to produce sodium ions and a reducing product for sodium supplementing. The generated sodium ions are affected by the electric field force and migrate from the cathode side to the anode surface and participate in the formation and repair of the SEI on the negative electrode surface, improving the first coulomb efficiency of the battery. Compared with directly adding a sodium supplementing agent (such as a sodium supplementing agent comprising the above-mentioned reducing product) in the battery, the sodium supplementing agent has a larger electrostatic force between its cations and anions, which is not conducive to the migration of sodium ions to the anode, and the sodium supplementing effect is not as good as that of the present application.

[0007] In addition, considering that the sodium supplementing agent will dissolve in the electrolyte, resulting in an increase in the concentration of sodium salt in the electrolyte and an increase in the viscosity of the electrolyte, if the sodium supplementing agent is directly added in the battery, the above problems will occur. In the present application, the sodium-containing compound and the reducing agent are used, neither of which will dissolve in the electrolyte. The reaction of the sodium-containing compound and the reducing agent in the cycle process produces sodium ions and a reducing product, so that the generated sodium ions directly migrate to the anode surface to participate in the formation of SEI, reducing the concentration of sodium salt, so that only part of the reducing product exists in the form of sodium salt. At this time, the concentration of these sodium salts is lower than that of the directly added sodium supplementing agent, which weakens the problem of excessive concentration of sodium salt 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] Further, the reducing agent comprises at least one of a non-metallic element, an inorganic sodium salt.

[0010] The reducing agent in the present application includes, but is not limited to, at least one of non-metallic elements, inorganic sodium salts.

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

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

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

[0014] The sodium-containing compound in the present application includes, but is 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, boron.

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

[0017] In view of the problem that direct addition of sodium supplement will cause the sodium salt concentration in the electrolyte to be too high, and the viscosity of the electrolyte to increase, in the reducing agent, sodium sulfite and / or sodium arsenite can be used as a sodium supplement, and in order to improve the above problem, preferably, the reducing agent includes at least one of silicon, sulfur, arsenic, phosphorus, boron.

[0018] Further, 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 into the electrolyte can improve the conductivity of the electrolyte. In particular, sodium hexafluoroborate and sodium hexafluorosilicate are commonly used sodium salts for sodium secondary batteries, and have good conductivity, and as reduction products into the electrolyte can increase the conductivity of the electrolyte.

[0020] Optionally, the mass ratio of the sodium-containing compound to the reducing agent ranges from 2 to 6:1, and preferably, 3:1.

[0021] In consideration of the unreasonable use of both the reducing agent and the sodium-containing compound, there will be residual problems, which will reduce the energy density of the battery. In order to improve the above problems, the mass ratio range value of the sodium-containing compound to the reducing agent is (2 to 6): 1, preferably 3: 1. At this time, after the full reaction of the two, the residual reducing agent and sodium-containing compound are reduced. It can be understood that the reducing agent and the sodium-containing compound are mixed with the active material, and the sodium-containing compound and the reducing agent will inevitably be residual. After the full reaction by the above ratio, the residue will be less than 0.1 ppm.

[0022] Optionally, the application also provides a preparation method of the sodium supplementing material, comprising:

[0023] mixing the sodium-containing compound with the reducing agent to obtain the sodium supplementing material.

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

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

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

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

[0028] In consideration of the uneven distribution of the sodium-containing compound and the reducing agent, on the one hand, the two cannot effectively and fully react, and on the other hand, the uneven distribution of the reducing agent leads to the difference in capacity of the positive active material in each region of the positive electrode sheet, and there will be the problem of uneven sodium intercalation in the cycle process, which affects the stability of the interface, for example, some places intercalate too much sodium, thereby enriching on the surface of the electrode sheet, affecting the cycle performance of the battery.

[0029] That is, in order to make the mixture of the reducing agent and the sodium-containing compound uniform and evenly distributed, improve the contact area between the particles, and avoid particle agglomeration, so that the reducing agent and the sodium-containing compound fully contact and react, the conductive agent and the dispersing agent are 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 dispersing agent, or the sodium-containing compound can be mixed with the conductive agent and the dispersing agent first, and then the reducing agent is added for mixing, or the reducing agent can be mixed with the conductive agent and the dispersing agent first, and then the sodium-containing compound is added for mixing.

[0030] It can be understood that the type of the conductive agent and the dispersing agent is not limited in the application, for example, the conductive agent includes one or more of acetylene black, Super P or carbon nanotube, and the dispersing agent 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 dispersing agent is (1 to 2):(10 to 20):(50 to 100).

[0032] To disperse uniformly, the mass ratio of the sodium-containing compound to the conductive agent and the dispersing agent is (1 to 2):(10 to 20):(50 to 100).

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

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

[0035] Optionally, the present application also provides a positive electrode tab, which comprises the sodium supplementing material as described.

[0036] Alternatively, the sodium supplementing material is obtained by the preparation method comprising the sodium supplementing material.

[0037] Optionally, the positive electrode tab comprises a current collector and a positive electrode coating arranged on the current collector, and the mass percentage of the mass of the sodium supplementing 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 mass of the sodium supplementing material to the total mass of the positive electrode coating is 1.75% to 3.38%, preferably 2% to 3%, which meets the above range, and the battery performance is improved.

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

[0040] The sodium supplementing material is mixed in the positive electrode active material, and the mass percentage of the mass of the sodium supplementing material to the total mass of the positive electrode active material and the sodium supplementing material is 2% to 4%, preferably 2.75% to 3.25%, and the sodium supplementing material in the tab meets the above range, and the appropriate amount of reduction product can be obtained by reaction for supplementing sodium.

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

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

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

[0044] Optionally, the positive electrode coating comprises at least two active layers, which are 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 active layer is arranged on the side of at least one of the active layers away from the current collector.

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

[0046] The positive electrode coating comprises 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 at least one active layer away from the current collector, which indicates that one active layer is closer to the current collector than another active layer, and another active layer is closer to the electrolyte. The mass percentage of the sodium supplement material in another active layer closer to the electrolyte is greater than the mass percentage of the sodium supplement material in one active layer closer to the current collector, so that the mass percentage of the sodium supplement 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 supplement performance, and improve the battery performance.

[0047] Optionally, 0 < W1 < 2%, and 2% < W2 < 3%.

[0048] In the present application, 0 < W1 < 2%, and 2% < W2 < 3%. Satisfying the above range can improve the sodium supplement performance and improve the battery performance.

[0049] Optionally, the present application also provides a preparation method of the positive electrode tab as described.

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

[0051] Coating the positive slurry to the current collector and drying to obtain the positive electrode sheet.

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

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

[0054] Dry mixing the positive active material and the sodium supplement material;

[0055] Adding the binder and the solvent and mixing to obtain the positive slurry.

[0056] In order to improve the uniformity of the mixing, the mixing process comprises dry mixing the positive active material and the sodium supplement material; adding the binder and the solvent and mixing to obtain the positive 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] In 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 slurry on the current collector.

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

[0060] Optionally, in the battery formation stage, the sodium-containing compound and the reducing agent react, and the reaction product of the sodium-containing compound and the reducing agent comprises 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 SEI film also forms on the surface of the hard carbon anode in sodium-ion batteries, leading to low initial efficiency and increased irreversible capacity, the reaction between sodium-containing compounds and reducing agents is controlled during the battery formation stage. The reaction products of these compounds include one or more of sodium borate, sodium silicate, sodium arsenate, sodium sulfate, sodium tetrafluoroborate, sodium hexafluorosilicate, sodium hexafluoroborate, or sodium hexafluoroarsenate. This ensures timely replenishment of sodium losses, improves the battery's initial coulombic efficiency, and extends its cycle life.

[0062] Optionally, the initial charging voltage during the formation stage ranges from 3.9V to 4.2V;

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

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

[0065] This application also provides a battery that includes the electrode assembly as described above.

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

[0067] The sodium-replenishing material of this application includes a sodium-containing compound and a reducing agent. During secondary battery cycling (e.g., the formation stage), the sodium-containing compound and the reducing agent react to generate sodium ions and reduction products for sodium replenishment, which promotes the formation and stability of the negative electrode SEI and improves the battery's initial coulombic efficiency. Attached Figure Description

[0068] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0069] FIG. 1 This is a schematic diagram of the structure of the positive electrode sheet according to one embodiment of this application;

[0070] FIG. 2 This is a schematic diagram of the preparation process of the positive electrode sheet according to one embodiment of this application;

[0071] FIG. 3is a schematic view of a secondary battery according to an embodiment of the present application.

[0072] FIG. 4 is FIG. 3 is an exploded view of a secondary battery according to an embodiment of the present application.

[0073] FIG. 5 is a schematic view of a battery module according to an embodiment of the present application.

[0074] FIG. 6 is a schematic view of a battery pack according to an embodiment of the present application.

[0075] FIG. 7 is FIG. 6 is an exploded view of a battery pack according to an embodiment of the present application.

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

[0077] Explanation of Reference Signs

[0078] Reference Name Reference Name 1 Battery pack 5 Secondary battery 2 Upper case 51 Housing 3 Lower case 52 Electrode assembly 4 Battery module 53 Top cover assembly 100 Positive electrode tab 20 Conductive layer 30 Current collector 40 Positive electrode coating 41 At least one active layer 42 At least another active layer

[0079] The implementation, functional features and advantages of the present application will be further described with reference to the embodiments in conjunction with the accompanying drawings. DETAILED DESCRIPTION

[0080] The technical solutions in the embodiments of the present application will be apparently and completely described with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by those of ordinary skill in the art without any creative work fall within the scope of protection of the present application.

[0081] Hereinafter, the embodiments of the sodium supplement material and the preparation method thereof, the positive electrode sheet, the electrode assembly, the battery and the electric device according to the present application will be specifically disclosed with appropriate reference to the accompanying drawings. However, there will be cases where unnecessary detailed description is omitted. For example, there will be cases where detailed description of matters known well, repeated description of substantially the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand the present application, and are not intended to limit the subject matter recited in the claims.

[0082] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also expected. Furthermore, if minimum range values ​​1 and 2 are listed, and if maximum range values ​​3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0083] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0084] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0085] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0086] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

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

[0088] Sodium secondary batteries have a promising development prospect in the field of large-scale energy storage due to the abundant reserves of sodium elements. Compared with lithium-ion batteries, sodium-ion batteries have the advantages of low cost and abundant reserves of sodium, and have wide application prospects in the field of next-generation energy storage and power batteries.

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

[0090] In order to improve the problem of sodium loss, a sodium supplement material is provided in the present application, which comprises a sodium-containing compound and a reducing agent.

[0091] The sodium-containing compound includes sodium elements, for example, sodium fluoride. The reducing agent is a substance that loses electrons or has electron deviation in the redox reaction, for example, sulfur. The sodium-containing compound and the reducing agent can undergo a reduction reaction.

[0092] The sodium supplement material comprises a sodium-containing compound and a reducing agent, which react during the cycle process of the secondary battery (for example, the formation stage) to produce sodium ions and a reduction product for sodium supplementation. The generated sodium ions are affected by the electric field force and migrate from the cathode side to the anode surface and participate in the formation and repair of the SEI on the negative electrode surface, improving the first coulomb efficiency of the battery. Compared with directly adding a sodium supplement agent (for example, the sodium supplement agent comprises the above-mentioned reduction product) in the battery, considering that the electrostatic force between the cations and anions 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 that of the present application.

[0093] In addition, considering that the sodium supplement agent will dissolve in the electrolyte, resulting in an increase in the concentration of sodium salt in the electrolyte and an increase in the viscosity of the electrolyte, if the sodium supplement agent is directly added in the battery, the above problems will occur. In the present application, the sodium-containing compound and the reducing agent are used, neither of which will dissolve in the electrolyte. Sodium ions and a reduction product are generated by the reaction of the two during the cycle process, so that the generated sodium ions directly migrate to the anode surface to participate in the formation of SEI, reducing the concentration of sodium salt, so that only part of the reduction product exists in the form of sodium salt. At this time, the concentration of these sodium salts is lower than that of the directly added sodium supplement agent, and the problem of excessive concentration of sodium salt in the electrolyte is weakened.

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

[0095] It is understandable that by mixing sodium-supplementing materials into the positive electrode active material, the sodium-containing compounds react with the reducing agent during battery cycling (e.g., the formation stage) to generate reduction products that include sodium-supplementing effects, 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 this application includes, but is not limited to, at least one of non-metallic elements and inorganic sodium salts.

[0098] Non-metallic elements, as reducing agents, can react with sodium-containing compounds; inorganic sodium salts, as reducing agents, can also 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, which includes at least one of silicon, sulfur, arsenic, phosphorus, and boron; and / or, the reducing agent includes an inorganic sodium salt, which includes at least one of sodium sulfite and sodium arsenite.

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

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

[0102] The reducing agent in this application includes inorganic sodium salts, including but not limited to at least one of sodium sulfite and sodium arsenite.

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

[0104] For example, some of the reaction formulas for sodium supplementation materials during the formation stage are as follows.

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

[0106] Chemical equation for the reaction of sodium oxide and silicon:

[0107] Chemical equation for the reaction of sodium oxide and phosphorus:

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

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

[0110] Chemical equation for the reaction of sodium fluoride and phosphorus:

[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 products of the sodium-containing compounds and reducing agents in this application include, but are 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, when introduced into the electrolyte, can increase the electrolyte's conductivity. In particular, sodium hexafluoroborate and sodium hexafluorosilicate are commonly used sodium salts in sodium secondary batteries and possess excellent conductivity; their introduction into the electrolyte as reduction products can increase the electrolyte's conductivity.

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

[0114] Considering that improper use of both reducing agent and sodium-containing compound can lead to residue issues and reduce battery energy density, to mitigate this problem, the mass ratio of sodium-containing compound to reducing agent is set to (2 to 6):1, preferably 3:1. In this ratio, after sufficient reaction, the residual reducing agent and sodium-containing compound are reduced. It is understood that mixing reducing agent and sodium-containing compound with active materials inevitably results in residual sodium-containing compound and reducing agent; however, after sufficient reaction using the above ratio, the residue will be less than 0.1 ppm.

[0115] In the above (2 to 6):1, the values ​​include the minimum and maximum values ​​of the range, as well as 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, this 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] In other words, sodium-containing compounds can be directly mixed with reducing agents to obtain sodium-supplementing materials.

[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 not distributed evenly, on the one hand, the two are difficult to react effectively and fully, and on the other hand, the uneven distribution of the reducing agent leads to differences in the capacity of different regions of the positive electrode active material in the positive electrode sheet. During cycling, there will be uneven sodium intercalation, which will affect the stability of the interface. For example, excessive sodium intercalation in some places will result in enrichment on the electrode surface, affecting the battery cycle performance.

[0120] In other words, to ensure uniform mixing and distribution of the reducing agent and sodium-containing compound, increase the contact area between particles, and prevent particle agglomeration, so that the reducing agent and sodium-containing compound can fully react, conductive agents and dispersants are added during the mixing process. The mixing method is not limited. For example, the sodium-containing compound and reducing agent can be mixed directly with the conductive agent and dispersant, or the sodium-containing compound can be mixed with the conductive agent and dispersant first, and then the reducing agent can be added. Alternatively, the reducing agent can be mixed with the conductive agent and dispersant first, and then the sodium-containing compound can be added.

[0121] It is understood that this application does not limit the types of conductive agents and dispersants. For example, conductive agents include one or more of acetylene black, Super P or carbon nanotubes, and dispersants include 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 dispersant is (1 to 2):(10 to 20):(50 to 100).

[0123] To ensure uniform dispersion, the mass ratio of sodium-containing compound to conductive agent and dispersant is (1 to 2):(10 to 20):(50 to 100). Furthermore, considering the need to incorporate the sodium-supplementing material into the positive electrode active material, and since conductive agent and dispersant need to be mixed during the preparation of the positive electrode active material slurry, adding the conductive agent and dispersant directly during the preparation of the sodium-supplementing material slurry simplifies the subsequent preparation process. That is, during the preparation of the sodium-supplementing material, an appropriate amount of conductive agent and dispersant is added as needed, so that the conductive agent and dispersant are incorporated into the sodium-supplementing material, eliminating the need to add conductive agent and dispersant during the subsequent preparation 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, as well as 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, the mixing process includes at least one of ball milling, grinding, and sand milling, the mixing time is 2 to 3 hours, and the rotation speed during ball milling, grinding, and sand milling is 200 to 300 rpm.

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

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

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

[0129] In one embodiment, this application also provides a positive electrode sheet, which includes the sodium-supplementing material as described above; or, includes the sodium-supplementing material obtained by the method for preparing the sodium-supplementing material as described above.

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

[0131] Let the mass of the sodium-supplementing material be m1, and the total mass of the positive electrode coating be M. Then, the mass percentage of the sodium-supplementing material to the total mass of the positive electrode coating is m1 / M×100%.

[0132] In this application, the mass percentage of the sodium-supplementing material in the total mass of the positive electrode coating is 1.75% to 3.38%, preferably 2% to 3%. Meeting the above range improves battery performance.

[0133] The values ​​in the range of 1.75% to 3.38% include the minimum and maximum values ​​of the range, as well as 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 sheet includes a positive electrode active material, and the mass percentage of the sodium supplement material is 2% to 4% of the total mass of the positive electrode active material and the sodium supplement material, preferably 2.75% to 3.25%.

[0135] Let m1 be the mass of the sodium-supplementing material (which includes the mass of the sodium-containing compound and the mass of the reducing agent), and m2 be the total mass of the positive electrode active material and the sodium-supplementing material. Then, the mass percentage of the sodium-supplementing material in the total mass of the positive electrode active material and the sodium-supplementing material is m1 / m2×100%.

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

[0137] The sodium-containing compound of this application does 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, without reducing the reversible capacity of the positive electrode, thus improving the first efficiency of the sodium secondary battery.

[0138] The values ​​in the range of 2% to 4% include the minimum and maximum values ​​of the range, as well as 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., as well as 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] Sodium Prussian blue, sodium Prussian blue includes Na p M1Fe(CN)6, where 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 this 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, which are stacked on the same side of the current collector. At least one active layer is disposed on the current collector, and at least another active layer is disposed on the side of the at least one active layer away from the current collector. The mass percentage of sodium-supplementing material in the at least one active layer is defined as W1, and the mass percentage of sodium-supplementing material in the at least another active layer is defined as W2, satisfying W1 < W2.

[0143] like FIG. 1 The diagram shows a schematic of a positive electrode 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 disposed on the current collector 30, and at least another active layer 42 is disposed 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 disposed on the current collector, and at least another active layer is disposed on the side of the at least one active layer away from the current collector. This 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. The mass percentage of sodium-replenishing material in the other active layer closer to the electrolyte is greater than the mass percentage of sodium-replenishing material in the active layer closer to the current collector. This creates a gradient of increasing mass percentage of sodium-replenishing material in the active layers from the current collector side to the electrolyte side, which can promote sodium ion migration, improve sodium replenishment performance, and improve battery performance.

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

[0146] In this application, 0% ≤ W1 < 2%, and 2% ≤ W2 ≤ 3%. Meeting these ranges can improve sodium replenishment performance and thus battery performance.

[0147] In the above 0%≤W1<2%, the values ​​include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments, as well as 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, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments, as well as 2%, 2.1%, 2.5%, 3%, etc., and the range values ​​between any two of the above point values.

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

[0150] like FIG. 2 The diagram shows a flow chart of the preparation method of the positive electrode sheet. In the preparation process of the positive electrode sheet, the positive active material, sodium supplement material, binder and solvent can be mixed to obtain the positive electrode slurry; the positive electrode slurry is coated onto the current collector and dried to obtain the 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 and mixing to obtain the positive electrode slurry.

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

[0153] In one embodiment, the mass ratio of the active material, the sodium-supplementing 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 active material, sodium supplement material, binder and solvent is (80 to 85): (1.6 to 3.5): (5 to 10): (100 to 150), which is beneficial for the coating of 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, as well as every value between the 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, this application also provides an electrode assembly, which includes a negative electrode, an electrolyte, and a positive electrode as described above, or a positive electrode obtained by the method for preparing the positive electrode as described above.

[0157] In one embodiment, during the battery formation stage, a sodium-containing compound reacts with a reducing agent, and the reaction products of the sodium-containing compound and the reducing agent include 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 SEI film also forms on the surface of the hard carbon anode in sodium-ion batteries, leading to low initial efficiency and increased irreversible capacity, the reaction between sodium-containing compounds and reducing agents is controlled during the battery formation stage. The reaction products of these compounds include one or more of sodium borate, sodium silicate, sodium arsenate, sodium sulfate, sodium tetrafluoroborate, sodium hexafluorosilicate, sodium hexafluoroborate, or sodium hexafluoroarsenate. This ensures timely replenishment of sodium losses, improves the battery's initial coulombic efficiency, and extends its cycle life.

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

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

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

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

[0163] In one embodiment, this 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 about by the technical solutions of the above embodiments, which will not be repeated here.

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

[0166] In one embodiment, this application also provides an electrical device, which includes a 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 about by the technical solutions of the above embodiments, which will not be repeated here.

[0168] In addition, the battery (secondary battery, battery module, battery pack) and power supply device of this application will be described below with appropriate reference to the accompanying drawings.

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

[0170] Typically, a secondary battery includes a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits between the electrodes while allowing ions to pass through. The separator described above is the improved separator of this application.

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

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

[0173] In some embodiments, the positive 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 substrate and a metal layer formed on at least one surface of the polymer substrate. 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 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 optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0175] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from 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 by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

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

[0178] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either 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, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate 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 be a negative electrode active material known in the art for use in batteries. 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. Silicon-based materials may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional 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 optionally 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 may optionally include a conductive agent. The conductive agent 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 may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0184] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0185] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not specify any particular type of electrolyte; it can be selected according to requirements.

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

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

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

[0189] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0190] In some embodiments, the diaphragm material can be selected from at least one of glass fiber, nonwoven 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 implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0192] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0193] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0194] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, FIG. 3 This is an example of a square-structured secondary battery 5.

[0195] In some implementations, refer to FIG. 4 The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. The positive electrode, negative electrode, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

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

[0197] FIG. 5 This is battery module 4, used as an example. (See reference...) FIG. 5 In battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

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

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

[0200] FIG. 6 and FIG. 7 This is battery pack 1 as an example. (See reference...) FIG. 6 and FIG. 7 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0201] In addition, this application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., 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.

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

[0203] FIG. 8 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0204] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their 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 supplementation materials:

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

[0210] Preparation of the positive electrode sheet:

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

[0212] Preparation of negative electrode sheet

[0213] The active material artificial graphite, conductive agent carbon black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC) are dissolved in deionized water at a weight ratio of 96.2:0.8:0.8:1.2 and mixed evenly to prepare a negative electrode slurry. The negative electrode slurry is uniformly coated onto the negative electrode current collector copper foil once or multiple times, and then dried, cold-pressed, and slit to obtain the negative electrode sheet.

[0214] Preparation of electrolyte

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

[0216] Separating membrane

[0217] Polypropylene film is used as the separator.

[0218] Preparation of sodium-ion batteries

[0219] In Example 1, the positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The cells are then wound to obtain a bare cell. Tabs are welded to the bare cell, which is then placed in an aluminum casing and baked at 100°C to remove moisture. Electrolyte is then injected and the casing is sealed, resulting in a non-charged battery. This non-charged battery then undergoes a series of processes including settling, hot and cold pressing, formation, shaping, and capacity testing 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 remaining part is the same as in Example 1.

[0222] Examples 3 and 4

[0223] The sodium-containing compound was sodium fluoride, and the reducing agent was elemental silicon, with mass ratios of 3:1 and 6:1, respectively. The remaining portion was 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 remaining part 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 remaining part 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 part is the same as in Example 1.

[0230] Example 8

[0231] The sodium-containing compounds are 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 sodium-containing compounds to reducing agents is 3:1, and the remaining portion 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 remaining portion is the same as in Example 1.

[0234] Comparative Example 1

[0235] Without adding a reducing agent, the remaining portion is the same as in Example 1.

[0236] Comparative Example 2

[0237] Without adding a reducing agent, the remaining portion is the same as in Example 1.

[0238] Comparative Example 3

[0239] No sodium-containing compounds or reducing agents were added; the remainder was the same as in Example 1.

[0240] Table 1 List of Examples

[0241]

[0242]

[0243] Comparative Example 4

[0244] Based on Example 5, the sodium supplement material was replaced with the reduction product Na2BO3 in Example 5, wherein the mass of Na2BO3 in Comparative Example 4 was consistent with the mass of Na2BO3 generated in the reaction in Example 5.

[0245] Comparative Example 5

[0246] Based on Example 3, the sodium-supplementing material was replaced with the reduction product Na2SiO3 in Example 3.

[0247] Comparative Example 6

[0248] Based on Example 6, the sodium-supplementing material was replaced with the reduction product Na2PO4 from Example 6.

[0249] Table 2 List of Examples

[0250]

[0251] Performance testing:

[0252] Battery first-efficiency test steps:

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

[0254] Cyclic life test procedure:

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

[0256] Electrolyte conductivity testing steps: Using a two-electrode conductivity meter, select the same electrodes and place the electrolyte before and after formation between the two electrodes respectively; turn on the power supply, and obtain the electrolyte conductivity value by passing a small current (100mA to 300mA, for example, 150mA) through the circuit.

[0257] As can be seen from the examples and comparative data in Table 1, adding both a sodium-containing compound and a reducing agent to the positive electrode improves both the initial efficiency and cycle life of the battery. Table 2 shows that adding both a sodium-containing compound and a reducing agent to the positive electrode significantly improves the conductivity of the electrolyte.

[0258] The above are merely preferred embodiments of the present invention and do not limit the scope of the patent. Any equivalent structural transformations made using the contents of the specification and drawings of the present invention under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the scope of patent protection of the present invention.

Claims

1. A positive electrode sheet, characterized by, The positive electrode tab comprises a sodium supplement material, the sodium supplement material comprises a sodium-containing compound and a reducing agent; The reducing agent comprises at least one of a non-metallic element, an inorganic sodium salt; The non-metallic element comprises at least one of silicon, sulfur, arsenic, phosphorus, boron; the inorganic sodium salt comprises at least one of sodium sulfite and sodium arsenite; The reaction product of the sodium-containing compound and the reducing agent comprises one or more of sodium borate, sodium silicate, sodium arsenate, sodium sulfate, sodium tetrafluoroborate, sodium hexafluorosilicate, sodium hexafluoroborate, sodium hexafluoroarsenate or sodium hexafluorophosphate.

2. The cathode sheet of claim 1, wherein, The sodium-containing compound comprises at least one of sodium fluoride and sodium oxide.

3. The cathode sheet of claim 1, wherein, The mass ratio of the sodium-containing compound to the reducing agent is (2 to 6):

1.

4. The cathode sheet of claim 3, wherein The mass ratio of the sodium-containing compound to the reducing agent is 3:

1.

5. The cathode sheet of any one of claims 1 to 4, wherein, The positive electrode tab comprises 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 in the total mass of the positive electrode coating is 1.75% to 3.38%.

6. The cathode sheet of claim 5, wherein, The mass percentage of the mass of the sodium supplement material in the total mass of the positive electrode coating is 2% to 3%.

7. The cathode sheet of claim 5, wherein The positive electrode tab comprises a positive electrode active material, and the mass percentage of the mass of the sodium supplement material in the total mass of the positive electrode active material and the sodium supplement material is 2% to 4%.

8. The cathode sheet of claim 7, wherein, The mass percentage of the mass of the sodium supplement material in the total mass of the positive electrode active material and the sodium supplement material is 2.75% to 3.25%.

9. The positive electrode sheet according to claim 7 or 8, wherein The positive electrode active material comprises at least one of Na5FeO4, Na5Fe5O8, Na6CoO4, Na2NiO2, NaCrO2 and prussian blue sodium salt.

10. The cathode sheet of any one of claims 6-8, wherein, The positive electrode coating comprises at least two active layers, the at least two active layers are arranged in a stack on the same side of the current collector, at least one of the active layers is arranged closer to the current collector than at least one other active layer, and the at least one other 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 supplement material in the at least one active layer is defined as W1, and the mass percentage of the sodium supplement material in the at least one other active layer is defined as W2, and W1W2.

11. The cathode electrode of claim 10, wherein 0W1<2%, 2%W2<3%.

12. A method of making the positive electrode sheet according to any one of claims 1 to 11, characterized by, 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 tab.

13. The method of producing a positive electrode sheet according to claim 12, wherein In the step of mixing a positive electrode active material, a sodium supplement material, a binder and a solvent to obtain a positive electrode slurry, comprising: 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.

14. The method of producing a positive electrode sheet according to claim 12, wherein 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).

15. The method of producing a positive electrode sheet according to any one of claims 12 to 14, wherein Comprising preparing a sodium supplement material by the following steps: Mixing a sodium-containing compound and a reducing agent to obtain a sodium supplement material.

16. The method of producing a positive electrode sheet according to claim 15, wherein In the step of mixing a sodium-containing compound and a reducing agent, further comprising: Mixing one of the sodium-containing compound and the reducing agent with a conductive agent and a dispersing agent to obtain a mixture; Mixing the mixture with the other of the sodium-containing compound and the reducing agent to obtain a mixed material.

17. The method of producing a cathode electrode piece according to claim 16, wherein The mass ratio of the sodium-containing compound to the conductive agent and the dispersing agent is (1-2):(10-20):(50-100).

18. The method of producing a positive electrode sheet according to claim 16 or 17, characterized by, The mixing process includes at least one of ball milling, roller milling, and sand milling, and the mixing time is 2-3 hours, and the rotation speed during the ball milling, roller milling, and sand milling is 200-300 rpm.

19. An electrode assembly, characterized by, The electrode assembly includes a negative electrode sheet, an electrolyte, and the positive electrode sheet of any one of claims 1-11, or a positive electrode sheet obtained by the preparation method of any one of claims 12-18.

20. The electrode assembly of claim 19, wherein, 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, sodium hexafluoroarsenate, or sodium hexafluorophosphate.

21. The electrode assembly of claim 20, wherein, The first charge voltage range of the formation stage is 3.9-4.2 V. And / or, the temperature range of the formation stage is 55-80 °C.

22. A battery, characterized by The battery includes the electrode assembly of any one of claims 19-21.

23. An electrical device, comprising: The electric device includes the battery of claim 22.

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