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

Abstract

The embodiment of the invention discloses a positive electrode material, a positive electrode plate, a battery monomer, a sodium ion battery and an electric device. The positive electrode material comprises a positive electrode active material and an additive, wherein the additive comprises inorganic salt capable of reacting with alkaline sodium salt in the positive electrode active material; and the mass content a of the additive in the positive electrode active material is more than or equal to 0.05% and less than or equal to 2.0%. When the positive electrode material is applied to the sodium-ion battery, the influence of alkaline sodium salt on the performance of the sodium-ion battery can be effectively improved, and the cycle performance and the capacity retention rate of the sodium-ion battery are improved.

Description

Technical Field

[0001] The present 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 Art

[0002] With the rapid development of social economy, energy and environment have become the focus of people's increasing attention. Among them, sodium-ion batteries, which are rich in element reserves, have been deeply studied 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. In the process of preparing the positive electrode active material of sodium-ion batteries, it is inevitable that alkaline sodium salt, i.e., residual alkali, will be left on the surface of the positive electrode material. The residual alkali has a great influence on the performance of the positive electrode active material, and side reactions and gas production occur during the cycle of the sodium-ion battery, which has an adverse effect on the capacity retention rate and cycle performance of the sodium-ion battery. Therefore, how to improve the influence of residual alkali on the performance of sodium-ion batteries has become a technical problem that needs to be solved urgently. Summary of the invention

[0004] The present application is made in view of the above technical problems, and its purpose is to provide a positive electrode material, a positive electrode plate, a battery cell, a sodium ion battery and an electrical device. The positive electrode material is applied to a sodium ion battery to effectively improve the effect of alkaline sodium salt on the performance of the sodium ion battery, and improve the cycle performance and capacity retention rate of the sodium ion battery.

[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 that can react with an alkaline sodium salt in the positive electrode active material, and a mass content a of the additive in the positive electrode material satisfies: 0.05%≤a≤2.0%.

[0006] In the embodiment of the present application, an additive capable of reacting with an alkaline sodium salt is introduced into the positive electrode material. When the positive electrode material is applied to a sodium ion battery, the additive can react with the alkaline sodium salt during the electrochemical process of the battery, consuming the alkaline sodium salt in the positive electrode active material, thereby improving the problem of easy gas production of the alkaline sodium salt during the cycle of the sodium ion battery, and helping to improve the cycle performance of the sodium ion battery. At the same time, by controlling the content of the alkaline sodium salt within a suitable range, the effect of the additive on the energy density of the sodium ion battery can be reduced while improving the gas production problem.

[0007] In a possible implementation, the average volume particle size Dv50 of the additive satisfies: Dv50≤9 μm; optionally, 2 μm≤Dv50≤5 μm.

[0008] In the embodiments of the present 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 a possible implementation, the additive includes at least one of pyrophosphate, phosphate, oxalate, and borate. Optionally, the additive includes pyrophosphate.

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

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

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

[0013] In a 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 a 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 a possible implementation, the mass content c of the positive electrode active material in the positive electrode material satisfies: 90%≤c≤98%.

[0016] In a possible implementation, 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.

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

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

[0019] In a third aspect, a battery cell is provided, wherein the battery cell comprises the positive electrode plate in any possible implementation manner of the second aspect.

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

[0021] In a possible implementation, the DC internal resistance DCR of the battery cell satisfies: 0.5 mΩ≤DCR≤5 mΩ, and may be 0.5 mΩ≤DCR≤3 mΩ.

[0022] In a fourth aspect, a sodium ion battery is provided, wherein the sodium ion battery comprises a battery cell according to any possible implementation of the third aspect.

[0023] In a fifth aspect, an electrical device is provided, wherein the electrical device comprises a sodium ion battery according to any possible implementation of the fourth aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments of the present application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the drawings without paying creative work.

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

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

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

[0028] Figure 4 Another schematic diagram of a sodium ion battery according to an embodiment of the present application. DETAILED DESCRIPTION

[0029] Hereinafter, the embodiments of the positive electrode material, positive electrode sheet, sodium ion battery and electric device of the present application are specifically disclosed with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following descriptions are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0030] "Scope" disclosed in the present application is limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope limited in this way can be including end values ​​or not including end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following scope can be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0031] In the description of this application, it should be noted that, unless otherwise specified, "multiple" means more than two; the terms "upper", "lower", "left", "right", "inner", "outer", etc., indicating directions 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 direction, be constructed and operated in a specific direction, and therefore cannot be understood as limiting this application. In addition, the terms "first", "second", "third", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0032] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0033] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0034] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

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

[0036] Where mentioned, "basic sodium salt" refers to a sodium salt that is basic in solution, such as sodium hydroxide, sodium carbonate, sodium bicarbonate, and the like.

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

[0038] As mentioned, "polyanionic compounds" refer to a class of compounds containing tetrahedral or octahedral anionic units. According to the type of anion, it can be divided into a variety of different systems. For example, phosphate system, pyrophosphate system, fluoropyrophosphate system, sulfate system, mixed anion system, etc.

[0039] As mentioned, "transition metal oxide" refers to a compound composed of sodium and an oxide containing a transition metal element, such as one or more of Fe, Co, Ni, Cu, Zn, V, Cr, and Mn. Structurally, the sodium transition metal oxide can have a layered structure, a tunnel structure, and the like.

[0040] Where mentioned, "Prussian blue type compounds" refers to a series of compounds containing a ferrocyanide structure.

[0041] Typically, a battery cell includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During the charge and discharge process of the battery cell, active ions are embedded and removed back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is arranged between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, and at the same time to allow active ions to pass through. In some embodiments, the above-mentioned battery cell is also called a secondary battery.

[0042] During the charging process of sodium-ion batteries, sodium ions are released from the positive electrode active material, moved and embedded in the negative electrode material; while during the discharging process, sodium ions are released from the negative electrode material, moved and embedded in the positive electrode active material.

[0043] It should be understood that the "embedding" process described in this application refers to the process in which sodium ions are embedded in the positive electrode active material and the negative electrode material due to an electrochemical reaction, and the "extraction" and "de-intercalation" processes described in this application refer to the process in which sodium ions are extracted from the positive electrode active material and the negative electrode material due to an electrochemical reaction.

[0044] Similar to lithium-ion batteries, the positive electrode material is one of the key factors that restrict the performance of sodium-ion batteries. In the current process of preparing positive electrode active materials, it is inevitable that alkaline sodium salts will remain or be produced on the surface of the positive electrode active materials, that is, there will be residual alkali in the positive electrode active materials. Alkaline sodium salts will produce side reactions and generate gases during the cycle of sodium-ion batteries, destroying the structure of the positive electrode materials and affecting the cycle performance of sodium-ion batteries. This gas production problem is particularly important in high-energy-density sodium-ion batteries.

[0045] Generally, after the positive electrode active material is prepared, the positive electrode active material can be treated by sintering, pickling and other steps to remove the residual alkali. This process is complicated, and in order to avoid the impact of the treatment process on the positive electrode active material, the effect of removing the residual alkali is limited, that is, the residual alkali cannot be completely removed. With the increase in the energy density of sodium ions, the positive electrode active material with some residual alkali can no longer meet the application requirements of high energy density sodium ion batteries.

[0046] In view of this, the present application provides a positive electrode material, into which an additive that can react with the alkaline sodium salt in the positive electrode active material is introduced, and the content of the additive is controlled within an appropriate range. When applied to a sodium ion battery, the additive can fully react with the alkaline sodium salt in the residual alkali, and consume the alkaline sodium salt in the positive electrode active material without affecting the energy density of the sodium ion battery, thereby improving the problem of gas production of the alkaline sodium salt during the sodium ion circulation process, and effectively improving the cycle performance and capacity retention rate of the sodium ion battery.

[0047] First, an embodiment of the present application provides a positive electrode material, including a positive electrode active material and an additive, wherein the additive includes an inorganic salt that can react with the 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%.

[0048] Specifically, the mass content a of the additive in the positive electrode 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%, 2.0%, or its value is within the range obtained by combining any two of the above values.

[0049] It should be understood that in some other examples, “mass content” may also be expressed as “mass percentage.” The mass content of the additive in the positive electrode material may be regulated by controlling the amount of the additive added.

[0050] In the positive electrode material provided by the present application, the additive can react with the alkaline sodium salt in the positive electrode active material, thereby consuming the alkaline sodium salt during the cycle of the sodium ion battery, and improving the adverse effects of the gas production of the alkaline sodium salt during the cycle on the cycle performance and capacity of the sodium ion battery. At the same time, the mass content of the additive is controlled within a suitable range. On the one hand, the mass content of the additive is too high, and the excess of the additive is not conducive to improving the energy density of the sodium ion battery; on the other hand, the mass content of the additive is too low, which is not conducive to the full reaction of the additive with the alkaline sodium salt. Thus, by controlling the mass content of the additive in the positive electrode material within a suitable range, it is possible to effectively improve the gas production problem of the alkaline sodium salt while reducing the effect of the additive on the energy density of the sodium ion battery, so that the positive electrode material can be applied to sodium ion batteries with high energy density.

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

[0052] Specifically, since the additive can react with alkaline sodium salt, when it is used in a sodium ion battery, it can consume the alkaline sodium salt in the positive electrode active material; the average volume particle size of the additive is controlled within a range of less than or equal to 9 μm, so that the additive can fully enter the structure of the positive electrode active material and fully react with the alkaline sodium salt, and the effect of removing the alkaline sodium salt is better than that of treating the positive electrode active material. Therefore, by introducing an inorganic salt with a specific average volume particle size that can react with the alkaline sodium salt into the positive electrode material, the alkaline sodium salt is more fully consumed when the positive electrode material is used in a sodium ion battery, effectively improving the problem of alkaline sodium salt gas generation destroying the structure of the positive electrode material and affecting the battery cycle, thereby improving the cycle performance and capacity retention rate of the sodium ion battery.

[0053] The average volume particle size Dv50 of the additive can be 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm, 5.5μm, 6μm, 6.5μm, 7μm, 7.5μm, 8μm, 8.5μm, 9μm, or its value is within the range obtained by combining any two of the above 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 be introduced into the positive electrode material as at least part of the additive. In the case where the additive includes pyrophosphate, the reaction between the additive and the pyrophosphate helps to form a SEI film with high ionic conductivity on the surface of the positive electrode film layer, 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, potassium pyrophosphate; alternatively, the pyrophosphate includes calcium pyrophosphate. In another embodiment, the phosphate includes calcium hydrogen phosphate, magnesium hydrogen phosphate, potassium hydrogen phosphate.

[0057] Specifically, alkaline sodium salts are usually based on sodium carbonate and sodium hydroxide. Phosphates and pyrophosphates can react with sodium carbonate and sodium hydroxide to consume alkaline sodium salts. Taking calcium hydrogen phosphate as an example, calcium hydrogen phosphate can react with sodium carbonate and sodium hydroxide to consume alkaline sodium salts, and calcium hydrogen phosphate can also decompose to form calcium pyrophosphate, which can continue to react with sodium carbonate and sodium hydroxide to further consume alkaline sodium salts. The specific reaction is as follows: 2CaHPO4+Na2CO3→2NaCaPO4+H2O+CO2 2CaHPO4+2NaOH→2NaCaPO4+2H2O 4CaHPO4→2CaP2O7+2H2O Ca2P2O7+Na2CO3→2NaCaPO4+CO2 Ca2P2O7+NaOH→2NaCaPO4+2H2O It can be seen that pyrophosphate and phosphate can effectively consume alkaline sodium salts. Especially hydrogen phosphate, which can react with alkaline sodium salts, and the pyrophosphate formed after decomposition can further consume alkaline sodium salts. Compared with the gas produced by the side reaction of residual alkali during the battery cycle, the small amount of gas (such as CO2) produced by the consumption of residual alkali by additives can be discharged during the formation process, and its impact on the battery cycle stability can be ignored.

[0058] 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.

[0059] Specifically, since alkaline sodium salts are more likely to remain or be produced during the preparation of polyanionic compounds and transition metal oxides, when the positive electrode active material includes polyanionic compounds and / or transition metal oxides, the positive electrode material provided in the present application has a more obvious improvement in the adverse effects of alkaline sodium salts.

[0060] In one embodiment, 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.

[0061] It should be understood that in the embodiments of the present application, the positive electrode material may be selected from the above-mentioned types of compounds, but the application is not limited thereto.

[0062] In one embodiment, the mass content b of the alkaline sodium salt in the positive electrode active material satisfies: 0.01%≤b≤1.5%.

[0063] Specifically, the mass content b of the 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 its value is within the range obtained by combining any two of the above values.

[0064] In one embodiment, the mass content c of the positive electrode active material in the positive electrode material satisfies: 90%≤c≤98%.

[0065] 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 its value is within the range obtained by combining any two of the above values.

[0066] In one embodiment, the positive electrode material further includes other substances such as a conductive agent and a binder.

[0067] Next, the electrode materials, positive electrode sheets, negative electrode sheets, separators and electrolytes in sodium-ion batteries are introduced in detail.

[0068] [Positive electrode]

[0069] The positive electrode plate includes a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector. The positive electrode film layer includes a positive electrode material, and the positive electrode material includes a positive electrode active material.

[0070] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer can be disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

[0071] Alternatively, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0072] Optionally, the positive electrode active material may include a positive electrode active material for sodium ion batteries known in the art. As described above, the positive electrode active material may include one or more of a polyanionic compound, a transition metal oxide, and a Prussian blue compound. As an example, a polyanionic compound may be a class of compounds having sodium ions, transition metal ions, and tetrahedral anion units, such as sodium iron phosphate (NaFePO4), sodium vanadium phosphate (Na3V2(PO4)3), and the like. The transition metal oxide may be a transition metal oxide having sodium ions, such as sodium copper iron manganate, sodium iron nickel manganate, and the like. The Prussian blue compound may be a class of compounds having sodium ions, transition metal ions, and cyanide ions. However, the present 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.

[0073] Alternatively, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0074] 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.

[0075] In some embodiments, the positive electrode sheet can be prepared in the following manner: the components for preparing the positive electrode sheet, such as the positive electrode active material, additives, conductive agent, binder and any other components are dispersed in a solvent (such as NMP) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0076] [Negative electrode]

[0077] The negative electrode sheet generally includes a negative electrode current collector, or includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, the negative electrode film layer includes a negative electrode material, and the negative electrode material includes a negative electrode active material.

[0078] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer may be disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

[0079] Alternatively, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, a copper foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0080] Optionally, the negative electrode active material may be a negative electrode active material for sodium ion batteries known in the art. For example, the negative electrode active material may include at least one of the following materials: natural graphite, artificial graphite, mesophase microcarbon beads (MCMB), hard carbon and soft carbon. For another example, in a sodium metal battery, the negative electrode active material may include at least one of the following materials: sodium metal, a carbon-based material or metal deposited with sodium metal, an alloy material, a composite material containing sodium metal, an alloy material containing sodium metal, and the like. However, the present 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 two or more materials may be used in combination.

[0081] In one embodiment, the sodium ion battery can be a sodium metal battery, that is, the negative electrode plate of the sodium ion battery is the negative electrode current collector. In other words, the negative electrode current collector directly serves as the negative electrode plate of the battery, and this type of sodium ion battery can also be called a "negative electrode-free battery". During the charging process, the sodium ions released from the positive electrode plate are deposited on the negative electrode current collector to form a sodium metal negative electrode. In the sodium metal negative electrode, sodium metal is the negative electrode active material. In other embodiments, in order to ensure the normal use of the negative electrode plate, or to facilitate the deposition of sodium metal on the negative electrode current collector, a conductive film layer can be provided on the negative electrode current collector.

[0082] Optionally, the negative electrode material further includes a conductive agent, and 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.

[0083] Optionally, the negative electrode material also includes a binder, which may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylate resin.

[0084] The negative electrode sheet can be prepared according to conventional methods in the art. For example, a copper foil or a 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).

[0085] For another example, the above-mentioned components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, can also be dispersed in a solvent to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0086] [Electrolytes]

[0087] The electrolyte plays the role of conducting ions between the positive electrode and the negative electrode. The present application has no specific restrictions on the type of electrolyte, which can be selected according to needs. For example, the electrolyte can be liquid, gel or all-solid.

[0088] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0089] Optionally, the electrolyte salt includes NaPF6, NaBCl4, NaSO3CF3 and Na(CH3)C6H4SO3, etc.

[0090] Optionally, the solvent includes carbonate or ether solvents. Carbonate solvents include cyclic ethylene carbonate (EC), propylene carbonate (PC), fluoroethylene carbonate (FEC) and chain 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-dioxolane, etc.

[0091] Optionally, the electrolyte may further include electrolyte additives. For example, the electrolyte additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.

[0092] [Isolator]

[0093] In some embodiments, the sodium ion battery further includes a separator. The present application has no particular restrictions on the type of separator, for example, the separator may be a separator membrane. The separator membrane may be any known porous structure separator membrane with good chemical stability and mechanical stability.

[0094] Optionally, the material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation membrane can be a single-layer film or a multi-layer composite film, without particular limitation. When the isolation membrane is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0095] In some embodiments, the positive electrode sheet, the negative electrode sheet and the separator may be formed into an electrode assembly by a winding process or a lamination process.

[0096] In some embodiments, the battery cell may include an outer packaging, which may be used to encapsulate the electrode assembly and the electrolyte.

[0097] In some embodiments, the outer packaging of the battery cell may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the battery cell may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0098] The present application has no particular restrictions on the shape of the battery cell, which can be cylindrical, square or any other shape. For example, Figure 1 The battery cell 100 of a sodium ion battery having a square structure is used as an example.

[0099] In one embodiment, the internal pressure P of the battery cell 100 after 1000 cycles satisfies: P≤0.4 MPa.

[0100] Figure 2 2 is a battery module 200 of a sodium ion battery as an example. Figure 2 In the battery module 200, the plurality of battery cells 100 may be arranged in sequence along the length direction of the battery module 200. Of course, they may also be arranged in any other manner. Further, the plurality of battery cells 100 may be fixed by fasteners.

[0101] Optionally, in one embodiment, the battery module 200 may further include a housing having an accommodation space, and the plurality of battery cells 100 are accommodated in the accommodation space.

[0102] Optionally, in one embodiment, the battery modules 200 may also be assembled into a sodium ion battery. The number of battery modules 200 contained in the sodium ion battery may be one or more, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery.

[0103] Figure 3 and Figure 4 300 is a sodium ion battery as an example. Figure 3 and Figure 4 In the sodium ion battery 300, a battery box and a plurality of battery modules 200 disposed in the battery box may be included. The battery box includes an upper box body 301 and a lower box body 302, and the upper box body 301 can be covered on the lower box body 302 to form a closed space for accommodating the battery module 200. The plurality of battery modules 200 may be arranged in the battery box in any manner.

[0104] It should be understood that in other embodiments, the sodium ion battery 300 is also referred to as a sodium ion battery pack. The battery cells 100 may first form a battery module 200, and the sodium ion battery 300 is composed of the battery module 200. The sodium ion battery 300 may also be directly formed of the battery cells 100, omitting the intermediate form of the battery module 200.

[0105] In addition, the present application also provides an electrical device, which includes at least one of the battery cell 100 of the sodium ion battery, the battery module 200 of the sodium ion battery, or the sodium ion battery 300 provided in the present application. The battery cell 100, the battery module 200, or the sodium ion battery 300 can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.

[0106] As an electric device, the number of battery cells 100, battery modules 200, or sodium ion batteries 300 can be selected according to its usage requirements.

[0107] As an example of an electric device, the electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the electric device's requirements for high power and high energy density of secondary batteries, a sodium ion battery 300 or a battery module 200 may be used.

[0108] As another example, the device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be light and thin, and the battery cell 100 may be used as a power source.

[0109] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If no specific techniques or conditions are indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. If the manufacturer is not indicated in the reagents or instruments used, they are all conventional products that can be obtained commercially.

[0110] [Examples 1-12 and Comparative Examples 1-2]

[0111] Example 1

[0112] (1) Preparation of positive electrode sheet

[0113] The positive electrode active material NaFe 0.33 Mn 0.33 Ni 0.33 O2, magnesium pyrophosphate additive with Dv50 of 3μm, conductive carbon black and adhesive polyvinylidene fluoride (PVDF) are fully stirred in a proper amount of NMP in a mass ratio of 94:1:3:2 to form a positive electrode slurry, and the positive electrode slurry is coated on the positive electrode collector aluminum foil, and the positive electrode sheet is obtained after drying and rolling.

[0114] The thickness h of the positive electrode film layer on the positive electrode current collector in the embodiments and comparative examples of the present application is in the range of 100 μm to 180 μm; 2 The loading amount of positive active material on the positive electrode sheet is in the range of 260mg to 350mg; under a pressure of 3T, the powder compaction density of the positive electrode sheet is 2.6g / cm 3 ~3.2g / cm 3 within the range.

[0115] Among them, the positive electrode active material NaFe 0.33 Mn 0.33 Ni 0.33 O2 was used for detection, and the mass content of alkaline sodium salt was b=0.7%.

[0116] (2) Preparation of negative electrode sheet

[0117] Carbon nanotubes and sodium alginate are added to deionized water and stirred to form a uniform slurry, which is then coated on a copper foil with a thickness of 8 μm. After drying and cold pressing, a "negative electrode-free" negative electrode sheet is obtained.

[0118] Alternatively, further, the above-mentioned "negative electrode-free" electrode sheet after drying and cold pressing is cut, and the electrode sheet is assembled into a battery cell with the positive electrode sheet and the isolation membrane, and the assembled battery cell is charged to 3.8V at a constant current of 0.5C, so as to pre-deposit sodium metal on the electrode sheet; after the battery cell is fully charged, the fully charged electrode sheet is removed in the glove box and used as the negative electrode sheet.

[0119] (3) Assembly of sodium ion battery cells

[0120] The positive electrode sheet, PE isolation film and negative electrode sheet are stacked in order so that the isolation film is between the positive electrode sheet and the negative electrode sheet. After the lamination process, an electrode assembly is formed. The electrode assembly is loaded into a packaging shell, and a NaPF6 electrolyte with a concentration of 1 mol / L is added. After packaging, formation, standing and other processes, a battery cell of a sodium ion battery is obtained.

[0121] Therefore, in Example 1, 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%.

[0122] Example 2

[0123] Compared with Example 1, in Example 2, c=93.0% and a=1.5%.

[0124] Example 3

[0125] Compared with Example 1, in Example 3, c=94.9% and a=1.8%.

[0126] Example 4

[0127] Compared with Example 1, in Example 4, a=0.1%.

[0128] Example 5

[0129] Compared with Example 1, in Example 5, a=2.0%.

[0130] Example 6

[0131] Compared with Example 1, in Example 6, Dv50=5 μm.

[0132] Example 7

[0133] Compared with Example 1, in Example 7, Dv50=2 μm.

[0134] Example 8

[0135] Compared with Example 1, in Example 8, Dv50=1 μm.

[0136] Example 9

[0137] Compared with Example 1, in Example 9, calcium pyrophosphate with a Dv50 of 3 μm is selected as the additive.

[0138] Example 10

[0139] Compared with Example 1, in Example 10, calcium hydrogen phosphate with a Dv50 of 3 μm is selected as the additive.

[0140] Embodiment 11

[0141] Compared with Example 1, in Example 11, calcium borate with a Dv50 of 3 μm is selected as the additive.

[0142] Example 12

[0143] Compared with Example 1, in Example 12, the positive electrode active material is NaFe 0.2 Mn 0.4 Ni 0.4 O2, the additive is magnesium pyrophosphate.

[0144] Comparative Example 1

[0145] Compared with Example 1, no additive is used in the positive electrode material of Comparative Example 1.

[0146] Comparative Example 2

[0147] Compared with Example 1, in the positive electrode material of Comparative Example 2, the mass content of magnesium pyrophosphate in the positive electrode material is a=0.02%.

[0148] Table 1 Product parameters of the embodiments and comparative examples 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 Embodiment 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

[0149] In Table 1, "a" represents the mass content of the additive in the positive electrode material, "c" represents the mass content of the positive electrode active material in the positive electrode material, and "Dv50" represents the average volume particle size of the additive.

[0150] The performance test results of the sodium ion batteries of the above embodiments and comparative examples are shown in Table 2.

[0151] Table 2 Battery performance test results of different embodiments and comparative examples

[0152] In Table 2, “1.5V-3.9V cycle number” indicates the cycle number of the sodium-ion battery in the charge and discharge voltage range of 1.5V-3.9V, and “DCR” indicates the DC internal resistance of the sodium-ion battery after 1000 cycles.

[0153] According to the comparative analysis of Examples 1-12 and Comparative Examples 1-2, the number of cycles of the sodium ion battery in Examples 1-12 is better than that in Comparative Examples 1-2. This shows that by introducing additives that can react with alkaline sodium salts into the positive electrode material, the problem of gas production by alkaline sodium salts during the cycle of the sodium ion battery can be improved, thereby effectively improving the cycle performance of the sodium ion battery. The DCR of the battery in Examples 1-12 after 1000 cycles is less than that in Comparative Examples 1-2.

[0154] According to the data comparison of Examples 1-3, as the mass content c of the positive electrode active material in the positive electrode material increases, the mass content a of the additive in the positive electrode material can be increased accordingly, so that the alkaline sodium salt in the positive electrode active material fully reacts with the additive. In Examples 1-5, as the mass content of the additive increases, magnesium pyrophosphate fully reacts with the alkaline sodium salt, and the reaction product can participate in the formation of the SEI film during the cycle of the sodium ion battery, thereby forming a SEI film with high ion conductivity, while improving the cycle performance of the sodium ion battery, reducing the DCR of the sodium ion battery.

[0155] According to the data comparison of Examples 1, 6-8, the smaller the average volume particle size of the additive, the better the cycle performance of the sodium ion battery. The possible mechanism is that the smaller the average volume particle size of the additive, the more complete its reaction with the alkaline sodium salt, the better the effect of improving the gas generation problem of the alkaline sodium salt during the cycle, and thus the better the cycle performance of the sodium ion battery.

[0156] According to the data of Examples 9-11, in addition to phosphates, calcium hydrogen phosphate and calcium borate can also be used as additives, which can also have a similar effect to pyrophosphate and improve the cycle performance of sodium ion batteries.

[0157] Example 12 gives an example of another positive electrode active material, illustrating that the improvement of the gas generation problem of alkaline sodium salt by additives is applicable to different positive electrode active materials.

[0158] Next, the testing methods of the physical parameters and performance parameters involved in the embodiments of the present application are introduced.

[0159] 1. Test method for average volume particle size (Dv50)

[0160] The average volume particle size of the material can be tested using the Malvern 2000 laser particle size analyzer. Take an appropriate amount of the sample to be tested (the sample concentration is sufficient to ensure 8-12% shading), add 20 ml of deionized water, and simultaneously operate the analyzer for 5 minutes (53KHz / 120W) to ensure that the sample is completely dispersed, and then measure the sample according to the GB / T19077-2016 / ISO 13320:2009 standard.

[0161] 2. Test method for mass content of alkaline sodium salt in positive electrode active material

[0162] The mass content of the alkaline sodium salt in the positive electrode active material can be measured using instruments and methods known in the art, for example, by referring to the GB / T 9725-2007 standard.

[0163] In one example, the mass content of the alkaline sodium salt in the ternary positive electrode active material can be represented by the sum of the mass content of sodium ions, the mass content of hydroxide, and the mass content of sodium carbonate. A possible test process is shown below. It should be understood that the test process is only used as a possible example and does not limit the test process.

[0164] At 25°C, take an appropriate amount of the positive electrode active material to be tested (ternary positive electrode active material), treat it with deionized water, and fully dissolve the alkaline sodium salt on the surface of the positive electrode active material in the deionized water. Then use the acid-base titration method, and the titrant is a standard hydrochloric acid solution to titrate the lithium carbonate and lithium hydroxide in the filtrate, and then calculate the Na + Mass content, NaOH mass content and Na2CO3 mass content.

[0165] Specifically, Na + Mass content (Na +%), NaOH mass content (NaOH%) and Na2CO3 mass content (Na2CO3%) can be calculated by the following formula. Na + % = V2×C×23×n×100 / (m×1000) NaOH%=[V2-2×(V2-V1)]×C×40×n×100 / 1000m Na2CO3%=(V2-V1)×C×105.99×n×100 / 1000m

[0166] Among them, V1 represents the volume of the titrant corresponding to the first titration endpoint, in mL; V2 represents the volume of the 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 volume of the solution to the volume of the solution required for the test; m represents the mass of the sample, in g; V2-V1 represents the volume of the titrant consumed by NaHCO3, 2×(V2-V1) represents the volume of the titrant consumed by Na2CO3; V2-2×(V2-V1) represents the volume of the consumed titrant; 23, 40, and 105.99 represent the molecular weights of Na, NaOH, and Na2CO3, respectively.

[0167] 3. Test method for sodium ion battery cycle performance

[0168] Under normal temperature conditions, the sodium ion battery was charged and discharged. The battery charge and discharge voltage range was maintained at 1.5V-3.9V. The battery was cycled at a current density of 0.33C / 1C, and the number of battery cycles was recorded when the SOC% decayed to 80%.

[0169] 4.DCR test method

[0170] The DCR test method can refer to the method in the "Performance Test Specification for High-Power Lithium-ion Power Batteries for HEV" and slightly adjust the test parameters to test the DCR of sodium-ion batteries.

[0171] For example, the sodium ion battery is discharged at a constant current of 1C to a cut-off voltage of 2.0V, and after being left for 1 hour, it is charged at a constant current of 1C for 18 minutes to adjust the SOC to 30%. After being left for 1 hour, it is charged at a constant current of 3C for 1.5 minutes, and then left for 1 hour. Then it is discharged at a current of 9C for 0.5 minutes, and after being left for 1 hour, it is charged at a constant current of 1C for 6 minutes to adjust the SOC of the sodium ion battery to 40%, and left for 1 hour.

[0172] The above process is repeated until the SOC reaches 70%, and the DCR data of the sodium ion battery is calculated by the following formula. R=ΔU / ΔI

[0173] Here, represents the voltage drop within 5 s after the discharge starts, and represents the current change value within 5 s after the discharge starts.

[0174] Although the present application has been described with reference to preferred embodiments, various modifications may be made thereto and parts thereof may be replaced with equivalents without departing from the scope of the present application. In particular, the various technical features mentioned in the various embodiments may be combined in any manner as long as there are no structural conflicts. The present 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 additive includes an inorganic salt that can react with the 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%.

2. The positive electrode material according to claim 1, characterized in that The average volume particle size Dv50 of the additive satisfies: Dv50≤9μm; optionally, 2μm≤Dv50≤5μm.

3. The positive electrode material according to claim 1 or 2, characterized in that The additive includes at least one of pyrophosphate, phosphate, borate, and metaborate. Optionally, the additive includes pyrophosphate.

4. The positive electrode material according to claim 3, characterized in that The pyrophosphate includes magnesium pyrophosphate, calcium pyrophosphate, iron pyrophosphate, potassium pyrophosphate; optionally, the pyrophosphate includes calcium pyrophosphate.

5. The positive electrode material according to claim 3 or 4, characterized in that: The phosphate includes at least one of calcium hydrogen phosphate, magnesium hydrogen phosphate and potassium hydrogen phosphate.

6. The positive electrode material according to any one of claims 1 to 5, characterized in that 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.

7. The positive electrode material according to any one of claims 1 to 6, characterized in that The mass content b of the alkaline sodium salt in the positive electrode active material satisfies: 0.01%≤b≤1.5%.

8. The positive electrode material according to any one of claims 1 to 7, characterized in that The mass content c of the positive electrode active material in the positive electrode material satisfies: 90%≤c≤98%.

9. The positive electrode material according to claim 6, characterized in that The transition metal oxides include: NaFe 0.33 Mn 0.33 Ni 0.33 O2、NaFe 0.2 Mn 0.4 Ni 0.4 At least one of O2.

10. A positive electrode sheet, characterized in that: include: Positive electrode current collector and positive electrode film layer; The positive electrode film layer is disposed on the surface of at least one side of the positive electrode current collector; The positive electrode film layer includes the positive electrode material described in any one of claims 1 to 9.

11. The positive electrode sheet according to claim 10, characterized in that: The positive electrode film layer also includes at least one of sodium calcium pyrophosphate, sodium magnesium pyrophosphate, and sodium potassium pyrophosphate.

12. A battery cell, characterized in that: The battery cell comprises the positive electrode sheet as claimed in claim 11.

13. The battery cell according to claim 12, characterized in that: The internal pressure P of the battery cell after 1000 cycles satisfies: P≤0.4 MPa.

14. The battery cell according to claim 12 or 13, characterized in that: The DC internal resistance DCR of the battery cell satisfies: 0.5 mΩ≤DCR≤5 mΩ, and may be 0.5 mΩ≤DCR≤3 mΩ.

15. A sodium ion battery, characterized in that: The sodium ion battery comprises the battery cell according to any one of claims 12 to 14.

16. An electrical device, characterized in that: The electrical device comprises the sodium ion battery as claimed in claim 15.

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