Sodium ion battery, composite positive electrode material, battery pack and energy storage system

Abstract

The invention provides a sodium ion battery, a composite positive electrode material, a battery pack and an energy storage system. According to the sodium ion battery, the composite positive electrode material in the positive electrode material layer comprises the layered oxide and the polyanion material, in an initial state, the half-peak width of a (003) crystal face diffraction peak in an XRD spectrum of the layered oxide is smaller than or equal to 0.15 degree, after the sodium ion battery is subjected to charging and discharging circulation for 50 circles, the half-peak width of the (003) crystal face diffraction peak in the XRD spectrum of the layered oxide is smaller than or equal to 0.2 degree, and the polyanion material is a polyanion material. Therefore, the cycling stability of the sodium-ion battery is improved.

Description

Technical Field

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

[0002] Sodium-ion batteries have broad application prospects in the fields of energy storage and low-speed vehicles due to advantages such as rich resources and low theoretical cost. A sodium-ion battery mainly consists of four parts: a cathode material, an anode material, an electrolyte, and a separator, among which the cathode material is the most critical one. Currently, the main cathode materials for sodium-ion batteries are layered oxides, polyanions, and Prussian blue-based materials. As one of the three main cathode materials for sodium-ion batteries, layered oxide materials are considered to be the first sodium-ion battery cathode materials to achieve commercial application due to their advantages such as high specific capacity, simple synthesis process, and high tap density. However, the charge and discharge process of layered oxide materials is a sodium ion deintercalation reaction. Since the radius of sodium ions is larger than that of lithium ions, the lattice volume of the cathode material changes greatly during the charge and discharge process, resulting in a low cycle life of sodium-ion batteries with layered oxides, especially severe cycle life attenuation in high-temperature environments. Summary of the Invention

[0003] This application provides a sodium-ion battery, a composite cathode material, a battery pack, and an energy storage system to improve the cycle stability of sodium-ion batteries.

[0004] In a first aspect, this application provides a sodium-ion battery, including a positive electrode plate and a negative electrode plate. The positive electrode plate includes a positive current collector and a positive electrode material layer provided on at least one surface of the positive current collector. The composite cathode material in the positive electrode material layer includes a layered oxide and a polyanion material; in an initial state, the full width at half maximum (FWHM) of the diffraction peak of the (003) crystal plane in the XRD pattern of the layered oxide is ≤ 0.15°. After the sodium-ion battery undergoes 50 charge-discharge cycles, the full width at half maximum (FWHM) of the diffraction peak of the (003) crystal plane in the XRD pattern of the layered oxide is ≤ 0.2°.

[0005] For the composite cathode material in the sodium-ion battery provided in this application, in the initial state, the full width at half maximum (FWHM) of the diffraction peak of the (003) crystal plane in the layered oxide in the composite material is ≤ 0.15°, which can ensure that the layered oxide has a high crystallinity, and its lattice structure is not prone to slip and cracking, with higher stability. After the sodium-ion battery undergoes 50 charge-discharge cycles, the full width at half maximum (FWHM) of the diffraction peak of the (003) crystal plane in the XRD pattern of the layered oxide satisfies ≤ 0.2°. Thus, after the layered oxide in this application undergoes charge-discharge cycles, its lattice structure has not changed significantly, which can ensure that the sodium-ion battery can still maintain a high structural stability after multiple cycles and improve the cycle capacity retention rate of the sodium-ion battery.

[0006] In an alternative implementation, after 100 charge-discharge cycles of the sodium-ion battery, the full width at half maximum of the diffraction peak of the (003) crystal plane in the XRD pattern of the layered oxide is ≤ 0.25°. After 100 charge-discharge cycles, the lattice structure of the layered oxide can still maintain high stability, which can further improve the structural stability of the sodium-ion battery after multiple cycles and enhance the cycle capacity retention rate of the sodium-ion battery.

[0007] In an alternative implementation, the composite cathode material includes a core and a coating layer. The core includes a layered oxide, and the coating layer includes a polyanion material. Coating the polyanion material on the periphery of the layered oxide can limit the deformation of the layered oxide during the charge-discharge cycle and improve its structural stability.

[0008] In an alternative implementation, the conductivity of the polyanion material is greater than or equal to 9 MΩ·cm. By selecting a polyanion material with a conductivity greater than or equal to 9 MΩ·cm to make the coating layer, the interfacial resistance between the composite cathode materials can be reduced, thereby optimizing the cycle performance of the sodium-ion battery.

[0009] In an alternative implementation, the polyanion material accounts for 8% - 35% of the total mass of the layered oxide material and the polyanion material. When the content of the polyanion material is in the range of 8% - 35%, the cycle stability of the sodium-ion battery can be further improved.

[0010] In an alternative implementation, the chemical formula of the polyanion material is Na β N γ (PO 4 ) 2 P 2 O 7 ; wherein, N is selected from at least one of Fe, Mn, Co, 3 ≤ β ≤ 5, 2 ≤ γ ≤ 3, and the values of β and γ satisfy the chemical formula balance. The above polyanion material can be of NASICON structure, and the polyanion material with this chemical structure can have a three-dimensional ion transport channel and a small volume change during the sodium-ion transport process. By coating the above polyanion material on the surface of the layered oxide, the expansion of the layered oxide can be reduced, and the structural damage of the layered oxide during the charge-discharge process can be avoided, thereby improving the structural stability of the cathode material layer.

[0011] In an alternative implementation, the polyanion material is selected from NaFeSO 4 、NaFePO 4 、Na 2 FeP 2 O 7 、Na 3 Fe 2 (PO 4)P 2 O 7 , Na 3 V 2 Fe(PO4) 3 , Na 3 VMn 2 Fe(PO 4 ) 3 , Na 3 VTiFe(PO 4 ) 3 , Na 3 Fe 2 Fe(PO 4 ) 3 , Na 3 MnTiFe(PO 4 ) 3 and Na 4 Fe 3 (PO 4 ) 2 P 2 O 7 at least one of the above. The above polyanion materials can achieve multi-directional transport of sodium ions, enable fast conduction of sodium ions, improve the transport rate of sodium ions, and thus help improve the rate performance and cycling performance of sodium-ion batteries. At the same time, the composite cathode material can obtain better structural stability and sodium-ion transport efficiency, and further improve the cycling performance and rate performance of sodium-ion batteries.

[0012] In an alternative implementation, the particle size D50 of the polyanion material is 1 - 3 μm, and the particle size D50 of the layered oxide material is 7 - 13 μm. The layered oxide has a planar conduction structure and can achieve fast in-plane conduction during the sodium-ion conduction process. The polyanion material has a three-dimensional conduction structure and can achieve fast conduction in different directions. When the particle size of the layered oxide and the particle size of the polyanion satisfy the above relationship, particle grading of the layered oxide and the polyanion can be achieved, and fast in-plane conduction in the transverse plane of the cathode material layer can be improved while enhancing conduction in the longitudinal direction. At the same time, the above grading relationship can utilize the polyanion to relieve the swelling of the layered oxide, improve the stability of the composite cathode material, and thus improve the cycling performance of sodium-ion batteries.

[0013] In an alternative implementation, the thickness of the coating layer is 5 - 10 μm. If the thickness of the coating layer is too thin, it is prone to cracking and cannot achieve the purpose of preventing the layered oxide from cracking. If the thickness of the coating layer is too thick, it will affect the transport of sodium ions and reduce the cycling performance of sodium-ion batteries.

[0014] In an alternative implementation, the coating layer contains a conductive agent, which is a particulate conductive agent or a linear conductive agent, and the conductive agent accounts for 0.2-1.5% of the total mass of the layered oxide material and the polyanion material. The addition of the conductive agent can reduce the interfacial resistance between the composite cathode material particles, improve the electron transfer efficiency, and thus improve the rate performance of the sodium-ion battery.

[0015] In an alternative implementation, the chemical formula of the layered oxide material is Na α (M x Fe y Mn z )O 2 , where the value range of α is 0.8 ≤ α ≤ 1.1; the values of x, y, and z are 0 < x < 1, 0 < y < 1, 0 < z < 1, and x + y + z = 1; M is selected from at least one of Ni, Cu, Co, Ti, Mg, Li, Al, Zn, and Ca. The layered oxide is a transition metal layered oxide. The layered oxide that satisfies the above chemical formula can have a relatively high specific capacity to improve the energy density of the composite cathode material.

[0016] In a second aspect, the present application provides a composite cathode material, which includes a layered oxide and a polyanion material; in the initial state, the full width at half maximum (FWHM) of the diffraction peak of the (003) crystal plane in the XRD pattern of the layered oxide ≤ 0.15°, and after 50 charge-discharge cycles, the FWHM of the diffraction peak of the (003) crystal plane in the XRD pattern of the layered oxide ≤ 0.2°.

[0017] In the initial state, the FWHM of the diffraction peak of the (003) crystal plane in the XRD pattern of the layered oxide in the composite material ≤ 0.15°, which can ensure that the layered oxide has a relatively high crystallinity, and its lattice structure is not prone to slip or cracking, and has higher stability. After 50 charge-discharge cycles, the FWHM of the diffraction peak of the (003) crystal plane in the XRD pattern of the layered oxide satisfies ≤ 0.2°. Thus, after the layered oxide of the present application undergoes charge-discharge cycles, its lattice structure does not change significantly, which can ensure that the sodium-ion battery can still maintain a relatively high structural stability after multiple cycles and improve the cycle capacity retention rate of the sodium-ion battery.

[0018] In an alternative implementation, after 100 charge-discharge cycles, the FWHM of the diffraction peak of the (003) crystal plane in the XRD pattern of the layered oxide ≤ 0.25°. After the layered oxide undergoes 100 charge-discharge cycles, its lattice structure can still maintain relatively high stability, which can further ensure that the sodium-ion battery can still maintain a relatively high structural stability after multiple cycles and improve the cycle capacity retention rate of the sodium-ion battery.

[0019] In an alternative implementation, the composite cathode material includes a core and a coating layer. The core includes a layered oxide, and the coating layer includes a polyanion material. The polyanion material coats the periphery of the layered oxide, which can limit the deformation of the layered oxide during the charge-discharge cycle and improve the stability of its structure.

[0020] In a third aspect, the present application provides a battery pack, which includes a plurality of batteries connected in series or in parallel; the batteries are the sodium-ion batteries of the present application.

[0021] In a fourth aspect, the present application provides an energy storage system, which includes a power converter and at least one battery pack of the present application; the power converter is used to perform power conversion on the voltage output by the battery pack and output it to the power grid or load, and / or perform power conversion on the voltage output by an external power source and output it to the battery pack.

[0022] Among them, for the data in the above possible implementation manners of the present application, such as the full width at half maximum of the diffraction peak, the content of the polyanion material, the particle size of the polyanion material, the thickness of the coating layer, etc., during measurement, the values within the range of engineering measurement error should be understood as being within the range defined by the present application.

[0023] The technical effects that can be achieved in the above third aspect to fourth aspect can be referred to the corresponding effect descriptions in the above first aspect, and will not be repeated here. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic structural diagram of a sodium-ion battery;

[0025] Figure 2 It is a schematic structural diagram of a positive electrode plate of an embodiment;

[0026] Figure 3 It is a schematic structural diagram of a composite cathode material;

[0027] Figure 4 It is a schematic connection structure diagram of an energy storage system.

[0028] REFERENCE SIGNS:

[0029] 11 - positive electrode plate; 12 - negative electrode plate; 13 - separator; 14 - electrolyte; 21 - positive current collector; 22 - positive electrode material layer;

[0030] 221 - layered oxide; 222 - polyanion material. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0031] In order to make the objectives, technical solutions, and advantages of the present application clearer, the present application will be further described in detail below with reference to the accompanying drawings.

[0032] The terms used in the following embodiments are only for the purpose of describing specific embodiments and are not intended to limit this application. As used in the specification and appended claims of this application, the singular forms "a", "an", "the above", "the", and "this" are also intended to include expressions such as "one or more", unless the context clearly indicates otherwise.

[0033] Reference to "one embodiment" or "some embodiments" described in this specification means that a specific feature, structure, or characteristic described in connection with that embodiment is included in one or more embodiments of this application. Thus, statements such as "in one embodiment", "in some embodiments", "in other some embodiments", "in still other embodiments", etc. that appear in different places in this specification do not necessarily all refer to the same embodiment, but mean "one or more but not all embodiments", unless otherwise specifically emphasized. The terms "comprising", "including", "having", and their variants all mean "including but not limited to", unless otherwise specifically emphasized.

[0034] Layered oxide materials, generally sodium transition metal layered oxides, have the problem of volume swelling during cycling. As the number of charge-discharge cycles increases, the lattice structure of the layered oxide is prone to change, thereby reducing the capacity of the layered oxide and the cycling performance of the sodium-ion battery. Aiming at the problem of low cycle life of sodium-ion batteries using layered oxide materials as the positive electrode material, this application provides a composite positive electrode material. By using a layered oxide with a more stable lattice structure and coating a polyanion material on the surface of the layered oxide material particles, the problems of cracking and transition metal dissolution of the layered oxide material during the charge-discharge cycle can be reduced, and the cycling stability of the sodium-ion battery can be improved.

[0035] Figure 1 It is a schematic structural diagram of a sodium-ion battery. As Figure 1 shown, the sodium-ion battery includes a positive electrode plate 11, a negative electrode plate 12, a separator 13, and an electrolyte 14. The separator 13 is disposed between the positive electrode plate 11 and the negative electrode plate 12, and the electrolyte 14 infiltrates the positive electrode plate 11, the separator 13, and the negative electrode plate 12.

[0036] Among them, the main function of the separator 13 is not only to prevent direct contact between the positive and negative electrodes from causing a short circuit, but also to provide a porous channel for the transport of sodium ions. The separator can be a polyolefin separator and a glass fiber separator. The polyolefin separator can be, for example, a polyethylene separator or a polypropylene separator, etc.

[0037] The electrolyte 14 is a carrier for ion transport in a sodium-ion battery and is usually composed of a sodium salt, a solvent, and an additive. The sodium salt can be, for example, one or more of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium hexafluoroarsenate, sodium perchlorate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide, sodium bis(oxalato)borate, and sodium difluoro(oxalato)borate. The solvent can be an aqueous solvent or a non-aqueous solvent, and can be specifically selected according to the types of the sodium salt and the additive. The additive can include, for example, one or more of vinylene carbonate, 1,3-propane sultone, fluoroethylene carbonate, fluoromethyl carbonate, dimethyl sulfate, and ethylene methyl sulfate.

[0038] The negative electrode sheet 12 includes a negative electrode current collector and a negative electrode coating provided on the surface of the negative electrode current collector. The negative electrode current collector can be, for example, a metal foil such as copper foil or aluminum foil. The negative electrode coating can include a negative electrode active material, a conductive agent, and a binder. The negative electrode active material can be, for example, hard carbon, soft carbon, or conductive carbon black and other substances.

[0039] Among them, the present application does not specifically limit the compositions of the separator, the electrolyte, and the negative electrode sheet, and can be adjusted according to actual applications.

[0040] Figure 2 It is a schematic structural diagram of a positive electrode sheet of an embodiment. As Figure 2 shown, in one embodiment, the positive electrode sheet 11 includes a positive electrode current collector 21 and a positive electrode material layer 22. The positive electrode current collector 21 can be a metal foil such as copper foil or aluminum foil. The thickness of the positive electrode current collector 21 can be, for example, 5 μm to 15 μm. Exemplarily, the thickness of the positive electrode current collector 21 can be 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, or 15 μm, etc., or any value between any two of the above values.

[0041] Among them, the positive electrode material layer 22 is provided on at least one side surface of the positive electrode current collector 21. As Figure 2 shown, in some embodiments, both side surfaces of the positive electrode current collector 21 are coated with the positive electrode material layer 22. Among them, the thickness of a single positive electrode material layer 22 can be 30 μm to 140 μm. Exemplarily, the thickness of the positive electrode material layer 22 can be, for example, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 80 μm, 100 μm, 110 μm, 120 μm, 130 μm, or 140 μm, etc., or any value between any two of the above values.

[0042] In the embodiments of the present application, the positive electrode material layer 22 includes a composite positive electrode material capable of achieving sodium intercalation and deintercalation. Figure 3 It is a schematic structural diagram of a composite positive electrode material. As Figure 3As shown, the composite cathode material has a core-shell structure. The inner core includes a layered oxide 221, and the outer shell is a coating layer including a polyanion material 222. Among them, the layered oxide 221 is a transition metal oxide, such as an iron-manganese-based layered oxide. The iron-manganese-based layered oxide can have a higher specific capacity and a good match with the polyanion material 222, and can act together with the polyanion material 222 to improve the stability of the positive electrode sheet of the sodium-ion battery.

[0043] In some embodiments, the molecular formula of the layered oxide is Na α (M x Fe y Mn z )O 2 . Among them, the value range of α is 0.8 ≤ α ≤ 1.1. Exemplarily, the value of α can be, for example, 0.8, 0.85, 0.9, 0.95, 1.0, 1.05 or 1.1, etc., or any value between any two of the above values. The values of x, y, and z are 0 < x < 1, 0 < y < 1, 0 < z < 1, and x + y + z = 1. M can be selected from at least one of Ni, Cu, Co, Ti, Mg, Li, Al, Zn, and Ca. The transition metal layered oxide can be, for example, Na(Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 )O 2 .

[0044] In the embodiments of the present application, when the layered oxide is in the initial state, that is, when the sodium-ion battery has not undergone charge-discharge cycles, the full width at half maximum of the diffraction peak of the (003) crystal plane in its XRD pattern ≤ 0.15°. After using this layered oxide as the cathode material to prepare a sodium-ion battery, at room temperature, that is, in an environment of 25 ± 5 °C, after the sodium-ion battery has been charged and discharged 50 cycles, the full width at half maximum of the diffraction peak of the (003) crystal plane in its XRD pattern ≤ 0.2°. In some embodiments, after the sodium-ion battery has been charged and discharged 100 cycles, the full width at half maximum of the diffraction peak of the (003) crystal plane in the XRD pattern ≤ 0.25°. Among them, the charge-discharge cycles can meet the above requirements at 0.5C, 1C, 2C, and 3C. Among them, the full width at half maximum of the diffraction peak of the (003) crystal plane is the width of the peak corresponding to half of the peak height of the diffraction peak at the (003) crystal plane in the XRD pattern.

[0045] In some embodiments, the conductivity of the polyanion material is greater than or equal to 9 MΩ*cm to improve the transport efficiency of sodium ions, reduce the transport resistance, and improve the cycle performance of sodium ions.

[0046] In some embodiments, the polyanion material is a phosphate compound having a NASICON crystal structure. The phosphate compound with a NASICON crystal structure has excellent sodium ion conductivity, which can reduce the occurrence of side reactions during conduction, reduce heat generation, and improve the safety performance of the battery.

[0047] In some embodiments, the chemical formula of the polyanion material is Na β N γ (PO 4 ) 2 P 2 O 7 ; wherein, N is selected from at least one of Fe, Mn, and Co, 3 ≤ β ≤ 5, 2 ≤ γ ≤ 3, and the values of β and γ satisfy the chemical formula balance. Exemplarily, the polyanion material may be selected from those with the molecular formulas of NaFeSO 4 , NaFePO 4 , Na 2 FeP 2 O 7 , Na 3 Fe 2 (PO 4 )P 2 O 7 , Na 3 V 2 Fe(PO4) 3 , Na 3 VMn 2 Fe(PO 4 ) 3 , Na 3 VTiFe(PO 4 ) 3 , Na 3 Fe 2 Fe(PO 4 ) 3 , Na 3 MnTiFe(PO 4 ) 3 , and Na 4 Fe 3 (PO 4 ) 2 P 2 O 7 at least one of them. When the polyanion material is the above compound, it can be combined with the transition metal layered oxide to further improve the stability of the positive electrode sheet.

[0048] In some embodiments of the present application, the polyanion material accounts for 8% to 35% of the total mass of the layered oxide material and the polyanion material. Exemplarily, in the layered oxide and the polyanion material, the mass percentage of the polyanion material can be, for example, 8%, 9%, 10%, 11%, 12%, 13%, 14%, or 15%, 18%, 20%, 22%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, or 35%, or any value between any two of the above values.

[0049] Among them, the particle size D50 of the polyanion material is 1 to 3 μm. The particle size D50, also known as the median particle size, is the particle size corresponding to when the cumulative particle size distribution percentage in the sample reaches 50%. Exemplarily, the particle size D50 of the polyanion material can be 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2.0 μm, 2.1 μm, 2.2 μm, 2.3 μm, 2.4 μm, 2.5 μm, 2.6 μm, 2.7 μm, 2.8 μm, 2.9 μm, 3.0 μm, or any value between any two of the above values. The particle size D50 of the layered oxide material is 7 to 13 μm. Exemplarily, the particle size D50 of the layered oxide material can be, for example, 7 μm, 7.5 μm, 7.8 μm, 8.0 μm, 8.2 μm, 8.5 μm, 8.8 μm, 9 μm, 9.2 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm, or any value between any two of the above values. The polyanion material particles with the above particle sizes can effectively adhere to the surface of the layered oxide particles to form a coating layer. The contact voids between the two are smaller, and the effective contact area is larger, thereby improving the transport of sodium ions between the layered oxide and the polyanion.

[0050] Among them, the thickness of the coating layer can be 5 to 10 μm. The coating layer with this thickness can effectively resist the volume expansion of the layered oxide material and can promote the transport of sodium ions between the polyanion material and the layered oxide material. Exemplarily, the thickness of the coating layer can be, for example, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, or any value between any two of the above values.

[0051] In addition to the polyanion material, the outer shell may further include a certain proportion of conductive agent. By adding the conductive agent, the conductivity of the composite cathode material can be improved, and the interfacial resistance between the composite cathode material particles can be reduced. The conductive agent can be a particulate conductive agent or a linear conductive agent. The particulate conductive agent can be, for example, conductive substances such as carbon black, graphite, soft carbon, and hard carbon. The linear conductive agent can be, for example, conductive materials such as carbon nanofibers and carbon nanotubes. Among them, the particle size of the particulate conductive agent is larger than the particle size D50 of the polyanion material. The length of the linear conductive agent is greater than the particle size D50 of the polyanion material. When the particle size of the conductive agent satisfies the above relationship, the interfacial resistance between the polyanion material particles can be effectively increased, thereby improving the conductivity of the coating layer.

[0052] In some embodiments, the conductive agent accounts for 0.2-1.5% of the total mass of the layered oxide material and the polyanion material. Exemplarily, based on the total mass of the layered oxide material and the polyanion material, the addition amount of the conductive agent can be 0.2%, 0.4%, 0.6%, 0.8%, 1.0%, 1.1%, 1.3%, 1.5% or any value between any two of the above values.

[0053] In some embodiments, the thickness of the cathode material layer is h1, and the thickness of the cathode current collector is h2. The ratio of h1 to h2 satisfies 1.1≤h1 / h2≤12.0. Exemplarily, the ratio of h1 / h2 can be, for example, 1.1, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0, 11.0, 12.0 or any value between any two of the above values. The thickness of the cathode material layer should be greater than the thickness of the cathode current collector, which can achieve high energy density coating. And due to the mutual cooperation of the layered oxide and the polyanion, the cycle performance of the sodium ion battery can be improved on the basis of improving the energy density of the sodium ion battery.

[0054] In some embodiments, the composite cathode material of the embodiments of the present application can be prepared by the following method:

[0055] Disperse the polyanion material, the layered oxide material, and the optional conductive agent in a solvent to obtain a mixed material; perform a fusion treatment on the mixed material in a mechanical fusion machine, and then perform a drying treatment to obtain a cathode composite material. Among them, the rotation speed of the mechanical fusion machine is 4000-7000r / min, and the fusion treatment time is 10-30min. The drying temperature in the drying treatment can be 80-120°C, such as 90-110°C, more such as 95-105°C; the drying time can be 0.5-2.5h, such as 1-2h.

[0056] The composite positive electrode slurry of the embodiments of the present application is placed in a solvent to form a positive electrode slurry, and the positive electrode slurry is coated on the surface of a positive electrode current collector to form a positive electrode sheet. Among them, the solvent for forming the positive electrode slurry can typically but not restrictively be selected from one or a combination of at least two of N-methylpyrrolidone (n-Methylpyrrolidone, NMP), N,N-dimethylformamide (N,N-dimethylformamide, DMF), dimethyl sulfoxide (dimethyl sulfoxide, DMSO), acetone, absolute ethanol, isopropanol, etc.

[0057] The positive electrode sheet, negative electrode sheet, separator, and electrolyte are assembled to form a sodium ion battery. When preparing the positive electrode slurry, a conductive agent can be added to the positive electrode slurry. The conductive agent in the positive electrode slurry can be the same as or different from the conductive agent in the composite positive electrode material.

[0058] The sodium ion batteries of the embodiments of the present application can be applied to related scenarios such as energy storage and power batteries, including low-speed electric vehicles, electric two-wheelers, electric three-wheelers, outdoor mobile power supplies, household energy storage, site energy backup power, data center backup power, and intelligent photovoltaic backup power scenarios, etc.

[0059] The sodium ion batteries of the embodiments of the present application can be assembled into a battery module or a battery pack. In addition to the sodium ion batteries of the embodiments of the present application, the battery module or battery pack can also include a BMS management system.

[0060] The sodium ion battery of the present application will be further described in detail below in conjunction with specific embodiments.

[0061] Embodiment

[0062] 1. Preparation of composite positive electrode material:

[0063] Weigh Na 2 CO 3 , Ni(OH) 2 , Fe 2 O 3 , MnO 2 materials according to the molar ratio of 1:1 / 3:1 / 3:1 / 3, dissolve and mix them evenly with deionized water and then dry. Sinter them at 910 - 980 °C under a compressed air atmosphere or an oxygen atmosphere for 18 - 24 h, and then cool them to room temperature over 12 - 48 h. Among them, the inlet flow rates of oxygen and compressed air are 5 L - 15 L / min. Then heat the sintered product to within the range of 400 - 500 °C for secondary sintering, and the time for secondary sintering is 100 - 400 min. Then cool it to room temperature, and the cooling time is 12 - 24 h. After cooling, obtain Na(Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 )O2 Material

[0064] Disperse the polyanion Na 4 Fe 3 (PO 4 ) 3 P 2 O 7 and the layered oxide Na(Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 )O 2 in the solvent (N-methylpyrrolidone (NMP)) in a mass ratio of 1-3:9-7 to obtain a mixed material. The drying temperature is 80-120 °C, and the drying time can be 0.5-2.5 h.

[0065] Fuse the mixed material in a mechanical fusion machine and then perform a drying treatment to obtain a composite cathode material. The rotation speed of the mechanical fusion machine is 4000-7000 r / min, and the fusion time is 10-30 min.

[0066] 2. Battery preparation:

[0067] Mix the composite cathode material with a conductive agent (a mixture of conductive carbon black (super-P, SP) and carbon nanotubes (CNT)), polyvinylidene difluoride (PVDF), and N-methylpyrrolidone (n-methylpyrrolidone, NMP) in a certain proportion, and stir to obtain a positive electrode paste; the ratio of the positive electrode active material: conductive agent: binder is 95:2.5:2.5.

[0068] Coat the positive electrode paste on both sides of the positive electrode current collector to form a positive electrode coating, and the thickness of the positive electrode paste coated on both sides of the positive electrode current collector is the same.

[0069] Stack the positive electrode plate, negative electrode plate, and separator to prepare a dry battery cell, and perform liquid injection and formation and grading to obtain a sodium-ion battery.

[0070] The composition parameters of the composite cathode materials of different examples and comparative examples are listed in Table 1.

[0071] Table 1

[0072]

[0073]

[0074] Test the cycle capacity retention rate of the sodium-ion batteries of different examples and comparative examples, and the test data are listed in Table 2.

[0075] Table 2

[0076]

[0077] As shown in Table 2, for the sodium-ion batteries of Embodiments 1-5 of the present application, their capacity retention rates after 100 cycles, 300 cycles, 500 cycles, and 700 cycles are all higher than those of the sodium-ion batteries of Comparative Example 1 and Comparative Example 2. And compared with the data of Comparative Examples 1-2, the sodium-ion batteries of Embodiments 1-5 have higher cycling performance both at room temperature and at 45°C than those of Comparative Examples 1 and 2. It shows that when the initial half-peak width of the layered oxide ≤ 0.15°, the half-peak width after 50 cycles ≤ 0.2°, and the half-peak width after 100 cycles ≤ 0.25°, it can help improve the cycling performance of the sodium-ion battery.

[0078] From the relevant test data of Embodiment 1, Comparative Example 1, and Comparative Example 2, it can be seen that when the initial half-peak width of the layered oxide meets the requirements but the 50-cycle and 100-cycle ones do not meet the scope defined in the present application, the corresponding cycling performance of the sodium-ion battery is also relatively low.

[0079] Based on the same technical purpose, the present application provides a battery pack, which includes a plurality of batteries connected in series or in parallel; the battery is the sodium-ion battery of the embodiment of the present application.

[0080] Based on the same technical purpose, an embodiment of the present application provides an energy storage system. Figure 4 It is a schematic diagram of the connection structure of an energy storage system. As Figure 4 shown, the energy storage system includes the battery pack of the present application and a power converter. The power converter is used to perform power conversion on the voltage output by the battery pack and then output it to the power grid or an external load, and / or the power converter is used to perform power conversion on the voltage output by an external power supply and then output it to the battery pack. Among them, the battery pack can be connected to a photovoltaic module to charge the battery pack by using the photovoltaic module.

[0081] The above is only the specific implementation manner of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present application, and all should be covered by the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A sodium-ion battery, characterized in that, it includes a positive electrode sheet and a negative electrode sheet. The positive electrode sheet includes a positive electrode current collector and a positive electrode material layer provided on at least one surface of the positive electrode current collector. The composite positive electrode material in the positive electrode material layer includes a layered oxide and a polyanion material; in the initial state, the full width at half maximum of the diffraction peak of the (003) crystal plane in the XRD pattern of the layered oxide ≤ 0.15°. After the sodium-ion battery undergoes 50 charge-discharge cycles, the full width at half maximum of the diffraction peak of the (003) crystal plane in the XRD pattern of the layered oxide ≤ 0.2°.

2. The sodium-ion battery according to claim 1, characterized in that, after the sodium-ion battery undergoes 100 charge-discharge cycles, the full width at half maximum of the diffraction peak of the (003) crystal plane in the XRD pattern of the layered oxide ≤ 0.25°.

3. The sodium-ion battery according to claim 1 or 2, characterized in that, the composite positive electrode material includes a core and a coating layer. The core includes a layered oxide, and the coating layer includes a polyanion material.

4. The sodium-ion battery according to any one of claims 1-3, characterized in that, the conductivity of the polyanion material is greater than or equal to 9 MΩ*cm.

5. The sodium-ion battery according to any one of claims 1-4, characterized in that, the polyanion material accounts for 8% - 35% of the sum of the masses of the layered oxide material and the polyanion material.

6. The sodium-ion battery according to any one of claims 1-5, characterized in that, The chemical formula of the polyanionic material is Na β N γ (PO 4 ) 2 P 2 O 7 ; wherein, N is selected from at least one of Fe, Mn, and Co, 3 ≤ β ≤ 5, 2 ≤ γ ≤ 4, and the values of β and γ satisfy the chemical formula balance.

7. The sodium-ion battery according to any one of claims 1-6, characterized in that, The polyanion material is selected from NaFeSO 4 , NaFePO 4 , Na 2 FeP 2 O 7 , Na 3 Fe 2 (PO 4 )P 2 O 7 , Na 3 V 2 Fe(PO4) 3 , Na 3 VMn 2 Fe(PO 4 ) 3 , Na 3 VTiFe(PO 4 ) 3 , Na 3 Fe 2 Fe(PO 4 ) 3 , Na 3 MnTiFe(PO 4 ) 3 and at least one of Na 4 Fe 3 (PO 4 ) 2 P 2 O 7 .

8. The sodium-ion battery according to any one of claims 1-7, characterized in that, the particle size D50 of the polyanion material is 1 - 3 μm, and the particle size D50 of the layered oxide material is 7 - 13 μm.

9. The sodium-ion battery according to any one of claims 1-8, characterized in that, the thickness of the coating layer is 5 - 10 μm.

10. The sodium-ion battery according to any one of claims 1-9, characterized in that, the coating layer further contains a conductive agent. The conductive agent is a particulate conductive agent or a linear conductive agent, and the conductive agent accounts for 0.2% - 1.5% of the total mass of the layered oxide material and the polyanion material.

11. The sodium-ion battery according to any one of claims 1-10, characterized in that, The chemical formula of the layered oxide material is Na α (M x Fe y Mn z )O 2 , where the value range of α is 0.8 ≤ α ≤ 1.1; the values of x, y, and z are 0 < x < 1, 0 < y < 1, 0 < z < 1, respectively, and x + y + z = 1; M is selected from at least one of Ni, Cu, Co, Ti, Mg, Li, Al, Zn, and Ca.

12. A composite positive electrode material, characterized in that, it includes a layered oxide and a polyanion material; in the initial state, the full width at half maximum of the diffraction peak of the (003) crystal plane in the XRD pattern of the layered oxide ≤ 0.15°. After undergoing 50 charge-discharge cycles, the full width at half maximum of the diffraction peak of the (003) crystal plane in the XRD pattern of the layered oxide ≤ 0.2°.

13. The composite positive electrode material according to claim 12, characterized in that, after undergoing 100 charge-discharge cycles, the full width at half maximum of the diffraction peak of the (003) crystal plane in the XRD pattern of the layered oxide ≤ 0.25°.

14. The composite positive electrode material according to claim 12 or 13, characterized in that, The composite cathode material includes a core and a coating layer, the core includes a layered oxide, and the coating layer includes a polyanion material.

15. A battery pack, characterized in that the battery pack includes a plurality of batteries, and the plurality of batteries are connected in series or in parallel; the battery is a sodium ion battery as described in any one of claims 1-11.

16. An energy storage system, characterized in that the energy storage system includes a power converter and at least one battery pack as described in claim 15; the power converter is used to perform power conversion on the voltage output by the battery pack and output it to the power grid or load, and / or perform power conversion on the voltage output by an external power source and output it to the battery pack.

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