Positive electrode material, positive electrode sheet, battery monomer, sodium-ion battery and electric device

Abstract

The embodiment of the application discloses a kind of to provide a kind of positive electrode material, positive electrode sheet, battery cell, sodium ion battery and electric device.The positive electrode material includes positive electrode active material and additive, additive includes inorganic salt that can react with basic sodium salt in positive electrode active material;The mass content a of additive in positive electrode active material satisfies: 0.05%≤a≤2.0%.The positive electrode material is applied to sodium ion battery, and the influence of basic sodium salt on the performance of sodium ion battery can be effectively improved, and the cycle performance and capacity retention of sodium ion battery are improved.

Description

Technical Field

[0001] This application relates to the field of batteries, and more specifically, to a positive electrode material, a positive electrode sheet, a battery cell, a sodium-ion battery, and an electrical device. Background Technology

[0002] With the rapid development of society and the economy, energy and the environment have become increasingly important concerns. Among these, sodium-ion batteries, which are rich in elements, have been extensively researched and developed in recent years and are widely used in energy storage, electronic products, and other fields.

[0003] The positive electrode active material is one of the key factors affecting the performance of sodium-ion batteries. During the preparation of positive electrode active materials for sodium-ion batteries, alkaline sodium salts, or residual alkali, are inevitably left on the surface of the material. Residual alkali has a significant impact on the performance of the positive electrode active material and can cause side reactions and gas generation during the cycling process of sodium-ion batteries, adversely affecting the capacity retention and cycle performance. Therefore, how to mitigate the impact of residual alkali on the performance of sodium-ion batteries has become an urgent technical problem to be solved. Summary of the Invention

[0004] This application addresses the aforementioned technical problems and aims to provide a positive electrode material, a positive electrode sheet, a battery cell, a sodium-ion battery, and an electrical device. The application of this positive electrode material in a sodium-ion battery can effectively mitigate the impact of alkaline sodium salts on the performance of the sodium-ion battery, thereby improving its cycle performance and capacity retention.

[0005] In a first aspect, a positive electrode material is provided, comprising a positive electrode active material and an additive, wherein the additive comprises an inorganic salt capable of reacting with an alkaline sodium salt in the positive electrode active material, and the mass content 'a' of the additive in the positive electrode material satisfies: 0.05% ≤ a ≤ 2.0%.

[0006] In the embodiments of this application, an additive capable of reacting with alkaline sodium salts is introduced into the cathode material. When this cathode material is applied in a sodium-ion battery, the additive can react with the alkaline sodium salts during the battery's electrochemical process, consuming the alkaline sodium salts in the cathode active material. This improves the problem of gas generation by alkaline sodium salts during sodium-ion battery cycling, thus helping to improve the cycle performance of the sodium-ion battery. Simultaneously, by controlling the content of alkaline sodium salts within a suitable range, the impact of the additives on the energy density of the sodium-ion battery can be reduced while improving the gas generation problem.

[0007] In one possible implementation, the average volumetric particle size Dv50 of the additive satisfies: Dv50≤9μm; alternatively, 2μm≤Dv50≤5μm.

[0008] In the embodiments of this application, by controlling the average volume particle size of the additive within a suitable range, the additive can react more fully with the alkaline sodium salt in the positive electrode active material during the electrochemical process.

[0009] In one possible implementation, the additive includes at least one of pyrophosphate, phosphate, oxalate, and borate; optionally, the additive includes pyrophosphate.

[0010] In one possible implementation, the pyrophosphate includes magnesium pyrophosphate, calcium pyrophosphate, iron pyrophosphate, copper pyrophosphate, and potassium pyrophosphate; optionally, the pyrophosphate includes calcium pyrophosphate.

[0011] In one possible implementation, the phosphate includes at least one of calcium hydrogen phosphate, magnesium hydrogen phosphate, and potassium hydrogen phosphate.

[0012] In the embodiments of this application, by selecting pyrophosphate and phosphate as additives, it is possible to improve gas production while helping to form an SEI membrane with high ionic conductivity.

[0013] In one possible implementation, the positive electrode active material includes at least one of a polyanionic compound, a transition metal oxide, and a Prussian blue compound; optionally, the positive electrode active material includes at least one of a polyanionic compound and a transition metal oxide.

[0014] In one possible implementation, the mass content b of the alkaline sodium salt in the positive electrode active material satisfies: 0.01% ≤ b ≤ 1.5%.

[0015] In one possible implementation, the mass content c of the positive electrode active material in the positive electrode material satisfies: 90% ≤ c ≤ 98%.

[0016] In one possible implementation, the transition metal oxide comprises: NaFe 0.33 Mn 0.33 Ni 0.33 O2, NaFe 0.2 Mn 0.4 Ni 0.4 At least one of O2.

[0017] In a second aspect, a positive electrode sheet is provided, comprising a positive current collector and a positive electrode film layer, the positive electrode film layer being disposed on at least one side of the surface of the positive current collector; the positive electrode film layer comprising the positive electrode material in any possible implementation of the first aspect.

[0018] In one possible implementation, the positive electrode film layer further includes at least one of sodium calcium pyrophosphate, sodium magnesium pyrophosphate, and sodium potassium pyrophosphate.

[0019] Thirdly, a battery cell is provided, the battery cell including the positive electrode sheet in any possible implementation of the second aspect.

[0020] In one possible implementation, the internal pressure P of the battery cell after 1000 cycles satisfies: P≤0.4MPa.

[0021] In one possible implementation, the DC internal resistance DCR of the battery cell satisfies: 0.5mΩ≤DCR≤5mΩ, or optionally 0.5mΩ≤DCR≤3mΩ.

[0022] Fourthly, a sodium-ion battery is provided, the sodium-ion battery comprising a single cell in any possible implementation of the third aspect.

[0023] Fifthly, an electrical device is provided, the electrical device comprising a sodium-ion battery in any possible implementation of the fourth aspect. Attached Figure Description

[0024] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0025] Figure 1 This is a schematic diagram of a sodium-ion battery cell according to an embodiment of this application.

[0026] Figure 2 This is a schematic diagram of a sodium-ion battery module according to an embodiment of this application.

[0027] Figure 3 This is a schematic diagram of a sodium-ion battery according to an embodiment of this application.

[0028] Figure 4 This is another schematic diagram of a sodium-ion battery according to an embodiment of this application. Detailed Implementation

[0029] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the positive electrode material, positive electrode sheet, sodium-ion battery, and power application device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0030] 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 included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 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.

[0031] In the description of this application, it should be noted that, unless otherwise stated, "a plurality of" means two or more; the terms "upper," "lower," "left," "right," "inner," "outer," etc., indicating orientation or positional relationships are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this application. Furthermore, the terms "first," "second," "third," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0032] 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.

[0033] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0034] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0035] Unless otherwise specified, the following terms have the following meanings. Any undefined terms have their technically accepted meanings.

[0036] If mentioned, "alkaline sodium salt" refers to sodium salts that are alkaline in solution, such as sodium hydroxide, sodium carbonate, and sodium bicarbonate.

[0037] If mentioned, "residual alkali" refers to alkaline substances left behind or generated in or on the surface of a material. For example, residual alkaline precursors or alkaline substances generated by side reactions during the material preparation process.

[0038] As mentioned, "polyanionic compounds" refer to a class of compounds containing tetrahedral or octahedral anionic units. Based on the type of anion, they can be classified into various different systems. Examples include phosphate systems, pyrophosphate systems, fluoropyrophosphate systems, sulfate systems, and mixed anionic systems.

[0039] As mentioned, "transition metal oxides" refer to compounds composed of sodium and oxides containing transition metal elements, such as one or more of Fe, Co, Ni, Cu, Zn, V, Cr, and Mn. Structurally, sodium transition metal oxides can have layered structures, tunnel structures, etc.

[0040] If mentioned, "Prussian blue compounds" refers to a series of compounds containing ferricyanide structures.

[0041] Typically, a battery cell includes a positive electrode, a negative electrode, an electrolyte, and a separator. During the charging and discharging process, active ions move back and forth between the positive and negative electrodes, inserting and extracting. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily prevents short circuits while allowing active ions to pass through. In some embodiments, this battery cell is also referred to as a secondary battery.

[0042] During the charging process of a sodium-ion battery, sodium ions are released from the positive electrode active material, move and embed into the negative electrode material; while during the discharging process, sodium ions are released from the negative electrode material, move and embed into the positive electrode active material.

[0043] It should be understood that the “intercalation” process described in this application refers to the process by which sodium ions are intercalated in the positive electrode active material and the negative electrode material due to an electrochemical reaction, and the “deintercalation” and “deintercalation” processes described in this application refer to the process by which sodium ions are deintercalated in the positive electrode active material and the negative electrode material due to an electrochemical reaction.

[0044] Similar to lithium-ion batteries, the cathode material is one of the key factors limiting the performance of sodium-ion batteries. Currently, during the preparation of cathode active materials, alkaline sodium salts are inevitably left or generated on the surface of the active material, meaning residual alkali exists in the active material. During the cycling process of sodium-ion batteries, these alkaline sodium salts undergo side reactions, producing gas, which damages the structure of the cathode material and affects the cycle performance of the sodium-ion battery. This gas generation problem is particularly significant in high-energy-density sodium-ion batteries.

[0045] Typically, after preparing the positive electrode active material, residual alkali can be removed by treating it through steps such as sintering and acid washing. This process is complex, and to avoid affecting the positive electrode active material, the removal of residual alkali is limited; it cannot completely remove it. With the increase in sodium-ion energy density, positive electrode active materials with residual alkali can no longer meet the application requirements of high-energy-density sodium-ion batteries.

[0046] In view of this, this application provides a cathode material in which an additive that can react with alkaline sodium salt in the cathode active material is introduced, and the content of the additive is controlled within a suitable range. When applied to a sodium-ion battery, it can fully react with alkaline sodium salt in residual alkali, and consume alkaline sodium salt in the cathode active material without affecting the energy density of the sodium-ion battery. This improves the problem of gas generation by alkaline sodium salt during sodium-ion cycling, and effectively enhances the cycle performance and capacity retention of the sodium-ion battery.

[0047] First, embodiments of this application provide a positive electrode material, including a positive electrode active material and an additive. The additive includes an inorganic salt that can react with an alkaline sodium salt in the positive electrode active material. The mass content 'a' of the additive in the positive electrode material satisfies: 0.05% ≤ a ≤ 2.0%.

[0048] Specifically, the mass content 'a' of the additive in the cathode material can be 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, or 2.0%, or a value within the range obtained by any combination of the above two values.

[0049] It should be understood that in some other examples, "mass content" can also be expressed as "mass percentage". The mass content of the additive in the cathode material can be controlled by adjusting the amount of additive added.

[0050] In the cathode material provided in this application, the additive can react with the alkaline sodium salt in the cathode active material, thereby consuming the alkaline sodium salt during the cycling process of the sodium-ion battery and mitigating the adverse effects of gas generation from the alkaline sodium salt on the cycle performance and capacity of the sodium-ion battery. Simultaneously, the mass content of the additive is controlled within a suitable range. On the one hand, if the mass content of the additive is too high, the excess additive is detrimental to improving the energy density of the sodium-ion battery; on the other hand, if the mass content of the additive is too low, it is not conducive to the sufficient reaction between the additive and the alkaline sodium salt. Therefore, by controlling the mass content of the additive in the cathode material within a suitable range, the gas generation problem of alkaline sodium salt can be effectively improved while reducing the impact of the additive on the energy density of the sodium-ion battery, enabling this cathode material to be used in high-energy-density sodium-ion batteries.

[0051] In one embodiment, the average volumetric particle size Dv50 of the additive satisfies: Dv50≤9μm; optionally, 2μm≤Dv50≤5μm.

[0052] Specifically, because the additive can react with alkaline sodium salts, it can consume the alkaline sodium salts in the positive electrode active material when applied to sodium-ion batteries. The average particle size of the additive is controlled within the range of 9 μm or less, allowing it to fully penetrate the structure of the positive electrode active material and react effectively with the alkaline sodium salts. This method is more efficient at removing alkaline sodium salts compared to treating the positive electrode active material. Therefore, by introducing an inorganic salt with a specific average particle size that can react with alkaline sodium salts into the positive electrode material, the alkaline sodium salts are more fully consumed when the positive electrode material is used in sodium-ion batteries. This effectively mitigates the problem of alkaline sodium salts generating gas that damages the positive electrode material structure and affects battery cycle life, thereby improving the cycle performance and capacity retention of sodium-ion batteries.

[0053] The average volumetric particle size Dv50 of the additive can be 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, or a value within the range obtained by any combination of the above two values.

[0054] In one embodiment, the additive includes at least one of pyrophosphate, phosphate, oxalate, and borate; optionally, the additive includes pyrophosphate.

[0055] Specifically, pyrophosphate, phosphate, oxalate, and borate can all be introduced into the cathode material as at least some of the additives. When pyrophosphate is included as an additive, the reaction between the additive and pyrophosphate helps to form an SEI film with high ionic conductivity on the surface of the cathode film, further improving the cycle performance of the sodium-ion battery.

[0056] In one embodiment, the pyrophosphate includes magnesium pyrophosphate, calcium pyrophosphate, iron pyrophosphate, copper pyrophosphate, and potassium pyrophosphate; optionally, the pyrophosphate includes calcium pyrophosphate. In another embodiment, the phosphate includes calcium hydrogen phosphate, magnesium hydrogen phosphate, and potassium hydrogen phosphate.

[0057] Specifically, basic sodium salts are typically sodium carbonate and sodium hydroxide. Phosphates and pyrophosphates can react with sodium carbonate and sodium hydroxide, thus consuming basic sodium salts. Taking calcium phosphate as an example, calcium phosphate reacts with sodium carbonate and sodium hydroxide, thereby consuming basic sodium salts. Furthermore, calcium phosphate can decompose to produce calcium pyrophosphate, which can then react with sodium carbonate and sodium hydroxide, further consuming basic sodium salts. The specific reactions are as follows:

[0058] 2CaHPO4+Na2CO3→2NaCaPO4+H2O+CO2

[0059] 2CaHPO4 + 2NaOH → 2NaCaPO4 + 2H2O

[0060] 4CaHPO4→2CaP2O7+2H2O

[0061] Ca₂P₂O₇ + Na₂CO₃ → 2NaCaPO₄ + CO₂

[0062] Ca₂P₂O₇ + NaOH → 2NaCaPO₄ + 2H₂O

[0063] Therefore, pyrophosphate and phosphate can effectively consume alkaline sodium salts. In particular, hydrogen phosphate can react with alkaline sodium salts, and the resulting pyrophosphate can further consume them. Compared to the gases generated by side reactions of residual alkali during battery cycling, the small amount of gas (such as CO2) generated during the process of consuming residual alkali with additives can be discharged during formation, and its impact on battery cycle stability is negligible.

[0064] In one embodiment, the positive electrode active material includes at least one of a polyanionic compound, a transition metal oxide, and a Prussian blue compound; optionally, the positive electrode active material includes at least one of a polyanionic compound and a transition metal oxide.

[0065] Specifically, since alkaline sodium salts are more likely to remain or be generated during the preparation of polyanionic compounds and transition metal oxides, the cathode material provided in this application has a more significant improvement on the adverse effects of alkaline sodium salts when the cathode active material includes polyanionic compounds and / or transition metal oxides.

[0066] In one embodiment, the transition metal oxide includes: NaFe 0.33 Mn 0.33 Ni 0.33 O2, NaFe 0.2 Mn 0.4 Ni 0.4 At least one of O2.

[0067] It should be understood that in the embodiments of this application, the cathode material may be selected from the compounds of the above types, but this application is not limited to this.

[0068] In one embodiment, the mass content b of the alkaline sodium salt in the positive electrode active material satisfies: 0.01% ≤ b ≤ 1.5%.

[0069] Specifically, the mass content b of alkaline sodium salt in the positive electrode active material can be: 0.01%, 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, or a value within the range obtained by any combination of the above two values.

[0070] In one embodiment, the mass content c of the positive electrode active material in the positive electrode material satisfies: 90% ≤ c ≤ 98%.

[0071] Specifically, the mass content c of the positive electrode active material in the positive electrode material can be: 90%, 90.5%, 91%, 91.5%, 92%, 92.5%, 93%, 93.5%, 94%, 94.5%, 95%, 95.5%, 96%, 96.5%, 97%, 97.5%, 98%, or a value within the range obtained by any combination of the above two values.

[0072] In one embodiment, the positive electrode material also includes other substances such as conductive agents and binders.

[0073] Next, we will provide a detailed introduction to the electrode materials, positive electrode, negative electrode, separator, and electrolyte in sodium-ion batteries.

[0074] [Positive electrode plate]

[0075] The positive electrode sheet includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector. The positive electrode film layer includes a positive electrode material, and the positive electrode material includes a positive electrode active material.

[0076] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer can be disposed on either or both of the two opposite surfaces of the positive current collector.

[0077] Optionally, the positive current collector can be a metal foil or a composite current collector. For example, aluminum foil can 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 can 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.).

[0078] Optionally, the positive electrode active material may include positive electrode active materials known in the art for sodium-ion batteries. As mentioned above, the positive electrode active material may include one or more of polyanionic compounds, transition metal oxides, and Prussian blue compounds. As an example, polyanionic compounds may be compounds having sodium ions, transition metal ions, and tetrahedral anionic units, such as sodium iron phosphate (NaFePO4) and sodium vanadium phosphate (Na3V2(PO4)3). Transition metal oxides may be transition metal oxides having sodium ions, such as sodium copper iron manganate and sodium iron nickel manganate. Prussian blue compounds may be compounds having sodium ions, transition metal ions, and cyanide ions. However, this application is not limited to these materials, and other materials that can be used as positive electrode active materials for sodium-ion batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more materials.

[0079] Optionally, the adhesive 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.

[0080] Optionally, 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.

[0081] 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, additives, conductive agents, binders and any other components, in a solvent (e.g., NMP) to form a positive electrode slurry; coating the positive electrode slurry onto a positive current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0082] [Negative electrode plate]

[0083] A negative electrode typically includes a negative current collector, or includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, wherein the negative electrode film layer includes a negative electrode material, and the negative electrode material includes a negative electrode active material.

[0084] 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 can be disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0085] Optionally, the negative electrode current collector can be a metal foil or a composite current collector. For example, copper foil can 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 can 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.).

[0086] Optionally, the negative electrode active material can be any negative electrode active material known in the art for use in sodium-ion batteries. For example, the negative electrode active material may include at least one of the following materials: natural graphite, artificial graphite, mesophase microcarbon spheres (MCMB), hard carbon, and soft carbon. As another example, in sodium metal batteries, the negative electrode active material may include at least one of the following materials: sodium metal, carbon-based materials or metals deposited with sodium metal, alloy materials, composite materials containing sodium metal, alloy materials containing sodium metal, etc. However, this application is not limited to these materials, and other materials that can be used as negative electrode active materials for sodium-ion batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more materials.

[0087] In one embodiment, the sodium-ion battery can be a sodium metal battery, meaning the negative electrode of the sodium-ion battery is the negative current collector. In other words, the negative current collector directly serves as the negative electrode of the battery, and this type of sodium-ion battery can also be called a "negative electrode-free battery." During charging, sodium ions released from the positive electrode deposit onto the negative current collector to form a sodium metal negative electrode, in which sodium metal is the negative electrode active material. In other embodiments, for the normal use of the negative electrode or to facilitate the deposition of sodium metal on the negative current collector, a conductive film layer can be disposed on the negative current collector.

[0088] Optionally, the negative electrode material may also include a conductive agent, which may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0089] Optionally, the negative electrode material also includes an adhesive, which 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.

[0090] The aforementioned negative electrode sheet can be prepared using conventional methods in the art. For example, copper foil or copper foil with a conductive film layer disposed on at least one surface of the copper foil can be used as the negative electrode sheet. The conductive film layer can be disposed on at least one surface of the negative electrode current collector by methods such as physical vapor deposition (PVD), spin coating, electroplating, and chemical vapor deposition (CVD).

[0091] For example, the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, can be dispersed in a solvent to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0092] [Electrolytes]

[0093] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0094] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0095] Optionally, the electrolyte salts include NaPF6, NaBCl4, NaSO3CF3, and Na(CH3)C6H4SO3, etc.

[0096] Optionally, the solvent includes carbonate or ether solvents. Carbonate solvents include cyclic ethylene carbonate (EC), propylene carbonate (PC), fluoroethylene carbonate (FEC), and chain-like dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), etc.; ether solvents include ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, tetrahydrofuran, 1,3-dioxane, etc.

[0097] Optionally, the electrolyte may also include electrolyte additives. For example, electrolyte 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.

[0098] [Isolation Component]

[0099] In some embodiments, the sodium-ion battery also includes a separator. This application does not impose any particular limitation on the type of separator; for example, the separator can be a separator membrane. The separator membrane can be any known porous structure separator membrane with good chemical and mechanical stability.

[0100] Optionally, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0101] In some embodiments, the above-mentioned positive electrode, negative electrode and separator can be fabricated into an electrode assembly by a winding process or a stacking process.

[0102] In some embodiments, the battery cell may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte described above.

[0103] In some embodiments, the outer packaging of the battery cell can be a rigid shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the battery cell can also be a flexible package, such as a pouch. The material of the flexible package can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0104] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 This is an example of a sodium-ion battery cell 100 with a square structure.

[0105] In one embodiment, the internal pressure P of a single battery cell 100 after 1000 cycles satisfies: P≤0.4MPa.

[0106] Figure 2 This is a sample sodium-ion battery module 200. (See reference...) Figure 2 In the battery module 200, multiple battery cells 100 can be arranged sequentially along the length of the battery module 200. Of course, they can also be arranged in any other manner. Furthermore, the multiple battery cells 100 can be fixed in place using fasteners.

[0107] Alternatively, in one embodiment, the battery module 200 may further include a housing with a receiving space in which a plurality of battery cells 100 are received.

[0108] Optionally, in one embodiment, the battery module 200 can also be assembled into a sodium-ion battery. The sodium-ion battery may contain one or more battery modules 200, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery.

[0109] Figure 3 and Figure 4 This is an example of a sodium-ion battery 300. (See reference...) Figure 3 and Figure 4 The sodium-ion battery 300 may include a battery case and multiple battery modules 200 disposed within the battery case. The battery case includes an upper casing 301 and a lower casing 302, with the upper casing 301 covering the lower casing 302 to form a closed space for accommodating the battery modules 200. The multiple battery modules 200 may be arranged in any manner within the battery case.

[0110] It should be understood that in some embodiments, the sodium-ion battery 300 described above is also referred to as a sodium-ion battery pack. The individual battery cells 100 can be first assembled into a battery module 200, and the sodium-ion battery 300 is composed of the battery module 200. Alternatively, the sodium-ion battery 300 can be directly assembled from the individual battery cells 100, omitting the intermediate form of the battery module 200.

[0111] In addition, this application also provides an electrical device, which includes at least one of the following: a sodium-ion battery cell 100, a sodium-ion battery module 200, or a sodium-ion battery 300 provided in this application. The battery cell 100, battery module 200, or sodium-ion battery 300 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.

[0112] As an electrical device, the number of battery cells 100, battery modules 200, or sodium-ion batteries 300 can be selected according to its usage requirements.

[0113] This is an example of an electrical device. The device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the secondary battery for this device, a sodium-ion battery 300 or a battery module 200 can be used.

[0114] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell (100) as their power source.

[0115] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0116] [Examples 1-12 and Comparative Examples 1-2]

[0117] Example 1

[0118] (1) Preparation of positive electrode sheet

[0119] NaFe, the positive electrode active material 0.33 Mn 0.33 Ni 0.33 O2, magnesium pyrophosphate (with a Dv50 of 3μm), carbon black (as a conductive agent), and polyvinylidene fluoride (PVDF) (as a binder) are mixed thoroughly in an appropriate amount of NMP at a mass ratio of 94:1:3:2 to form a positive electrode slurry. The positive electrode slurry is then coated onto a positive electrode current collector aluminum foil, and after drying and rolling, a positive electrode sheet is obtained.

[0120] In the embodiments and comparative examples of this application, the thickness h of the positive electrode film layer on the positive current collector is in the range of 100 μm to 180 μm; per 1540.25 mm 2 The loading of positive electrode active material on the positive electrode sheet ranges from 260 mg to 350 mg; under a pressure of 3T, the powder compaction density of the positive electrode sheet is 2.6 g / cm³. 3 ~3.2g / cm 3 Within the range.

[0121] Among them, for the positive electrode active material NaFe 0.33 Mn 0.33 Ni 0.33 O2 was tested, and the mass content of alkaline sodium salt was b = 0.7%.

[0122] (2) Preparation of negative electrode sheet

[0123] Carbon nanotubes and sodium alginate were added to deionized water and stirred to form a uniform slurry. The slurry was coated onto a copper foil with a thickness of 8 μm. After drying and cold pressing, a negative electrode sheet without a negative electrode was obtained.

[0124] Alternatively, the "negative electrode" sheet that has been dried and cold-pressed can be cut and assembled with the positive electrode sheet and separator into a battery cell. The assembled battery cell can be charged to 3.8V at a constant current of 0.5C, thereby pre-depositing sodium metal on the electrode sheet. After the battery cell is fully charged, the fully charged electrode sheet can be removed from the glove box and used as the negative electrode sheet.

[0125] (3) Assembly of sodium-ion battery cells

[0126] The positive electrode, PE separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes. After stacking, an electrode assembly is formed. The electrode assembly is then placed in a packaging shell, and a 1 mol / L NaPF6 electrolyte is added. After encapsulation, formation, and settling, a sodium-ion battery cell is obtained.

[0127] Therefore, in Example 1, the Dv50 of the additive in the positive electrode material is 3 μm, the mass content of the additive in the positive electrode material is a = 1.0%, and the mass content of the positive electrode active material in the positive electrode material is c = 94.0%.

[0128] Example 2

[0129] Compared with Example 1, in Example 2, c = 93.0% and a = 1.5%.

[0130] Example 3

[0131] Compared to Example 1, in Example 3, c = 94.9% and a = 1.8%.

[0132] Example 4

[0133] Compared to Example 1, in Example 4, a = 0.1%.

[0134] Example 5

[0135] Compared to Example 1, in Example 5, a = 2.0%.

[0136] Example 6

[0137] Compared to Example 1, in Example 6, Dv50 = 5 μm.

[0138] Example 7

[0139] Compared to Example 1, in Example 7, Dv50 = 2 μm.

[0140] Example 8

[0141] Compared to Example 1, in Example 8, Dv50 = 1 μm.

[0142] Example 9

[0143] Compared with Example 1, in Example 9, calcium pyrophosphate with a Dv50 of 3 μm was selected as the additive.

[0144] Example 10

[0145] Compared with Example 1, in Example 10, dicalcium phosphate with a Dv50 of 3 μm was selected as the additive.

[0146] Example 11

[0147] Compared with Example 1, in Example 11, calcium borate with a Dv50 of 3 μm was selected as the additive.

[0148] Example 12

[0149] Compared to Example 1, in Example 12, the positive electrode active material is NaFe. 0.2 Mn 0.4 Ni 0.4 O2, with magnesium pyrophosphate as the additive.

[0150] Comparative Example 1

[0151] Compared to Example 1, no additives were used in the cathode material of Comparative Example 1.

[0152] Comparative Example 2

[0153] Compared to Example 1, in the cathode material of Comparative Example 2, the mass content of magnesium pyrophosphate in the cathode material is a = 0.02%.

[0154] Table 1 Product parameters of the examples and comparative examples

[0155] Positive electrode active material c additive a Dv50(μm) Example 1 <![CDATA[NaFe 0.33 Mr 0.33 Ni 0.33 O2]]> 94.0％ Magnesium pyrophosphate 1.00％ 3 Example 2 <![CDATA[NaFe 0.33 Mr 0.33 Ni 0.33 O2]]> 90％ Magnesium pyrophosphate 1.50％ 3 Example 3 <![CDATA[NaFe 0.33 Mr 0.33 Ni 0.33 O2]]> 98％ Magnesium pyrophosphate 1.80％ 3 Example 4 <![CDATA[NaFe 0.33 Mr 0.33 Ni 0.33 O2]]> 94.0％ Magnesium pyrophosphate 0.10％ 3 Example 5 <![CDATA[NaFe 0.33 Mr 0.33 Ni 0.33 O2]]> 94.0％ Magnesium pyrophosphate 2.00％ 3 Example 6 <![CDATA[NaFe 0.33 Mr 0.33 Ni 0.33 O2]]> 94.0％ Magnesium pyrophosphate 1.00％ 5 Example 7 <![CDATA[NaFe 0.33 Mr 0.33 Ni 0.33 O2]]> 94.0％ Magnesium pyrophosphate 1.00％ 2 Example 8 <![CDATA[NaFe 0.33 Mr 0.33 Ni 0.33 O2]]> 94.0％ Magnesium pyrophosphate 1.00％ 1 Example 9 <![CDATA[NaFe 0.33 Mr 0.33 Ni 0.33 O2]]> 94.0％ Calcium pyrophosphate 1.00％ 3 Example 10 <![CDATA[NaFe 0.33 Mr 0.33 Ni 0.33 O2]]> 94.0％ Calcium hydrogen phosphate 1.00％ 3 Example 11 <![CDATA[NaFe 0.33 Mr 0.33 Ni 0.33 O2]]> 94.0％ Calcium borate 1.00％ 3 Example 12 <![CDATA[NaFe 0.2 Mr 0.4 Ni 0.4 O2]]> 94.0％ Magnesium pyrophosphate 1.00％ 3 Comparative Example 1 <![CDATA[NaFe 0.33 Mr 0.33 Ni 0.33 O2]]> 94.0％ / / / Comparative Example 2 <![CDATA[NaFe 0.33 Mr 0.33 Ni 0.33 O2]]> 94.0％ Magnesium pyrophosphate 0.02％ 3

[0156] In Table 1, “a” represents the mass content of additives in the cathode material, “c” represents the mass content of cathode active material in the cathode material, and “Dv50” represents the average volume particle size of the additives.

[0157] The performance test results of the sodium-ion batteries in the above embodiments and comparative examples are detailed in Table 2.

[0158] Table 2. Battery performance test results for different embodiments and comparative examples.

[0159]

[0160]

[0161] In Table 2, "Number of cycles from 1.5V to 3.9V" indicates the number of cycles of the sodium-ion battery within the charge-discharge voltage range of 1.5V to 3.9V, and "DCR" indicates the DC internal resistance of the sodium-ion battery after 1000 cycles.

[0162] Comparative analysis of Examples 1-12 and Comparative Examples 1-2 shows that the sodium-ion batteries in Examples 1-12 all have a higher number of cycle times than those in Comparative Examples 1-2. This indicates that introducing additives that can react with alkaline sodium salts into the cathode material can improve the gas generation problem of alkaline sodium salts during sodium-ion battery cycling, thereby effectively improving the cycle performance of sodium-ion batteries. The DCR of the batteries in Examples 1-12 after 1000 cycles is lower than that of Comparative Examples 1-2.

[0163] A comparison of the data from Examples 1-3 shows that as the mass content (c) of the positive electrode active material in the positive electrode material increases, the mass content (a) of the additives in the positive electrode material can be increased accordingly, allowing the alkaline sodium salt in the positive electrode active material to react fully with the additives. In Examples 1-5, as the mass content of the additives increases, magnesium pyrophosphate reacts fully with the alkaline sodium salt, and the reaction products can participate in the formation of the SEI film during the cycling process of the sodium-ion battery, thereby forming an SEI film with high ion conductivity. This improves the cycle performance of the sodium-ion battery while reducing its DCR.

[0164] A comparison of data from Examples 1 and 6-8 shows that the smaller the average particle size of the additive, the better the cycle performance of the sodium-ion battery. The possible mechanism is that a smaller average particle size allows for a more complete reaction with the alkaline sodium salt, resulting in better improvement of gas generation during cycling and thus better cycle performance of the sodium-ion battery.

[0165] According to the data from Examples 9-11, in addition to phosphates, calcium hydrogen phosphate and calcium borate can also be used as additives, which can achieve similar effects to pyrophosphates and improve the cycle performance of sodium-ion batteries.

[0166] Example 12 provides another example of a positive electrode active material, illustrating that the improvement of the gas generation problem of alkaline sodium salts by additives is applicable to different positive electrode active materials.

[0167] Next, the testing methods for the physical parameters and performance parameters involved in the embodiments of this application will be introduced.

[0168] 1. Test method for average volumetric particle size (Dv50)

[0169] The average volumetric particle size of the material can be tested using a Malvern 2000 (MasterSizer 2000) laser particle size analyzer. Take an appropriate amount of the sample to be tested (the sample concentration should be 8-12% opacity), add 20 ml of deionized water, and simultaneously incubate for 5 minutes (53 kHz / 120 W) to ensure complete dispersion of the sample. Then, measure the sample according to the standard GB / T19077-2016 / ISO 13320:2009.

[0170] 2. Test method for the mass content of alkaline sodium salt in positive electrode active materials

[0171] The mass content of alkaline sodium salts in the positive electrode active material can be determined using instruments and methods known in the art. For example, it can be determined with reference to the GB / T 9725-2007 standard.

[0172] In one example, the mass content of alkaline sodium salt in a ternary cathode active material can be represented by the sum of the mass content of sodium ions, the mass content of hydroxides, and the mass content of sodium carbonate. The following illustrates a possible testing procedure; it should be understood that this procedure is merely an example and does not constitute a limitation on testing procedures.

[0173] At 25℃, a suitable amount of the positive electrode active material (ternary positive electrode active material) to be tested was taken and treated with deionized water to fully dissolve the alkaline sodium salt on the surface of the positive electrode active material. Then, an acid-base titration method was used, with hydrochloric acid standard solution as the titrant, to titrate the lithium carbonate and lithium hydroxide in the filtrate, and then the Na content in the material was calculated. +Mass content, NaOH mass content and Na2CO3 mass content.

[0174] Specifically, Na + Mass content (Na) + The mass content of NaOH (NaOH%) and the mass content of Na2CO3 (Na2CO3%) can be calculated using the following formula.

[0175] Na + %=V²×C×2³×n×100 / (m×1000)

[0176] NaOH%=[V2-2×(V2-V1)]×C×40×n×100 / 1000m

[0177] Na2CO3%=(V2-V1)×C×105.99×n×100 / 1000m

[0178] Where V1 represents the volume of titrant corresponding to the first titration endpoint in mL; V2 represents the volume of titrant corresponding to the second titration endpoint in mL; C represents the concentration of the hydrochloric acid standard solution in mol / L; n represents the ratio of the total solution volume to the volume of solution required for the test; m represents the mass of the sample in g; V2-V1 represents the volume of titrant consumed by NaHCO3, 2×(V2-V1) represents the volume of titrant consumed by Na2CO3; V2-2×(V2-V1) represents the volume of titrant consumed; 23, 40, and 105.99 represent the molecular weights of Na, NaOH, and Na2CO3, respectively.

[0179] 3. Test methods for the cycle performance of sodium-ion batteries

[0180] Under normal temperature conditions, charge and discharge tests were conducted on sodium-ion batteries. The battery charge and discharge voltage range was maintained between 1.5V and 3.9V. The batteries were cycled at a current density of 0.33C / 1C, and the number of cycles was recorded when the SOC% decayed to 80%.

[0181] 4. DCR Testing Method

[0182] The DCR test method can refer to the method in "Performance Test Specification for High-Power Lithium-ion Power Batteries for HEVs", with slight adjustments to the test parameters to test the DCR of sodium-ion batteries.

[0183] For example, discharge the sodium-ion battery at a constant current of 1C to the cutoff voltage of 2.0V, let it rest for 1 hour, then charge it at a constant current of 1C for 18 minutes, adjust the SOC to 30%, let it rest for 1 hour, then charge it at a constant current of 3C for 1.5 minutes, and let it rest for 1 hour. Next, discharge it at a current of 9C for 0.5 minutes, let it rest for 1 hour, then charge it at a constant current of 1C for 6 minutes, adjust the SOC of the sodium-ion battery to 40%, and let it rest for 1 hour.

[0184] Repeat the above process until the SOC reaches 70%, and calculate the DCR data of the sodium-ion battery using the following formula.

[0185] R = ΔU / ΔI

[0186] Wherein, represents the voltage drop within 5 seconds of the start of discharge, and represents the current change within 5 seconds of the start of discharge.

[0187] Although this application has been described with reference to preferred embodiments, various modifications can be made thereto and components can be replaced with equivalents without departing from the scope of this application. In particular, the technical features mentioned in the various embodiments can be combined in any manner, provided there is no structural conflict. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A positive electrode material, characterized in that, include: Positive electrode active materials and additives; The additives include inorganic salts that can react with the alkaline sodium salts in the positive electrode active material; The mass content 'a' of the additive in the cathode material satisfies the following condition: 0.05% ≤ a ≤ 2.0%; The average volume particle size Dv50 of the additive satisfies: 2 μm ≤ Dv50 ≤ 9 μm; The additives include at least one of pyrophosphate, phosphate, borate, and metaborate.

2. The cathode material according to claim 1, characterized in that, The average volumetric particle size Dv50 of the additive satisfies: 2 μm ≤ Dv50 ≤ 5 μm.

3. The cathode material according to claim 1, characterized in that, The additives include pyrophosphates.

4. The cathode material according to claim 1, characterized in that, The pyrophosphates include magnesium pyrophosphate, calcium pyrophosphate, iron pyrophosphate, and potassium pyrophosphate.

5. The positive electrode material according to claim 3, characterized in that, The pyrophosphate includes calcium pyrophosphate.

6. The cathode material according to claim 1, characterized in that, The phosphate includes at least one of: calcium hydrogen phosphate, magnesium hydrogen phosphate, and potassium hydrogen phosphate.

7. The cathode material according to claim 1, characterized in that, The positive electrode active material includes at least one of polyanionic compounds, transition metal oxides, and Prussian blue compounds.

8. The cathode material according to claim 7, characterized in that, The positive electrode active material includes at least one of polyanionic compounds and transition metal oxides.

9. The cathode material according to any one of claims 1-8, characterized in that, The mass content b of the alkaline sodium salt in the positive electrode active material satisfies: 0.01% ≤ b ≤ 1.5%.

10. The cathode material according to any one of claims 1-8, characterized in that, The mass content c of the positive electrode active material in the positive electrode material satisfies: 90% ≤ c ≤ 98%.

11. The cathode material according to claim 8, characterized in that, The transition metal oxide includes: NaFe 0.33 Mn 0.33 Ni 0.33 O2, NaFe 0.2 Mn 0.4 Ni 0.4 At least one of O2.

12. A positive electrode plate, characterized in that, include: Positive current collector and positive electrode film; The positive electrode film layer is disposed on at least one side of the surface of the positive electrode current collector; The positive electrode film layer comprises the positive electrode material according to any one of claims 1-11.

13. The positive electrode sheet according to claim 12, characterized in that, The positive electrode film layer also includes at least one of sodium calcium pyrophosphate, sodium magnesium pyrophosphate, and sodium potassium pyrophosphate.

14. A single battery cell, characterized in that, The battery cell includes the positive electrode sheet as described in claim 12 or 13.

15. The battery cell according to claim 14, characterized in that, The internal pressure P of the battery cell after 1000 cycles satisfies: P≤0.4 MPa.

16. The battery cell according to claim 14 or 15, characterized in that, The DC internal resistance (DCR) of the battery cell satisfies: 0.5 mΩ ≤ DCR ≤ 5 mΩ.

17. The battery cell according to claim 16, characterized in that, The DC internal resistance (DCR) of the battery cell satisfies: 0.5 mΩ ≤ DCR ≤ 3 mΩ.

18. A sodium-ion battery, characterized in that, The sodium-ion battery comprises a battery cell as described in any one of claims 14-17.

19. An electrical appliance, characterized in that, The electrical device includes the sodium-ion battery as described in claim 18.

Images