Positive electrode material and preparation method therefor, positive electrode, sodium battery and electric device

Abstract

A positive electrode material and a preparation method therefor, a positive electrode, a sodium battery and an electric device. The positive electrode material comprises a layered oxide represented by chemical formula NaaNibFecMndMeOf, wherein 0.8≤a≤1, 0≤b≤0.2, 0.25≤c≤0.5, 0.26≤d≤0.6, 0≤e≤0.1, 1.8≤f≤2, and M is a doped metal element. The preparation method for the positive electrode material comprises the step of sintering a NaaNibFecMndMeOf precursor. The positive electrode contains the layered oxide represented by the chemical formula, and the sodium battery contains the positive electrode. The electric device comprises the sodium battery. The layered oxide contained in the positive electrode material has high structure stability, gram capacity and energy density and good cycle performance. The sodium battery has high energy density and good cycle performance.

Description

Positive electrode material and preparation method thereof, positive electrode, sodium battery and electrical device

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on November 2, 2023, with application number 202311450733.0, and application name "Positive electrode material and preparation method thereof, positive electrode, sodium battery and electrical device", all contents of which are incorporated by reference in this application. Technical Field

[0002] The present application belongs to the technical field of sodium batteries, and specifically relates to a positive electrode material and a preparation method thereof, a positive electrode, a sodium battery, and an electrical device. Background Art

[0003] Sodium-ion batteries, with their abundant raw material reserves, low cost, relatively stable chemical properties, and excellent safety, are expected to replace lithium-ion batteries in the market. The continued development of new energy vehicles and the increasing proportion of clean energy are placing higher demands on the energy density and cycle stability of sodium-ion batteries.

[0004] Among sodium-ion battery cathode materials, layered oxides have become a research hotspot due to their relatively high specific capacity. To further increase the specific capacity of layered oxides, metal doping is generally used. However, it has been found that the presence of some doping metals can reduce the stability of the layered oxide's crystal structure, thereby reducing the specific capacity and cycling performance of the layered oxide. Technical issues

[0005] In view of the above problems, the present application provides a positive electrode material and a preparation method thereof, a positive electrode containing the positive electrode material, and a sodium battery containing the positive electrode, so as to solve the technical problem that the existing layered oxides have poor structural stability, resulting in reduced specific capacity and cycle life. Technical Solutions

[0006] In a first aspect, the present invention provides a positive electrode material. The positive electrode material of the present invention comprises a layered oxide as shown in the following chemical formula: Na a Ni b Fe c Mn d M e O f ;

[0007] Among them, 0.8≤a≤1, 0≤b≤0.2, 0.25≤c≤0.5, 0.26≤d≤0.6, 0≤e≤0.1, 1.8≤f≤2, b+c+d+e≤1; M is an active and / or inert doping metal element.

[0008] The positive electrode material of the embodiment of the present application optimizes the structure of the transition metal layer (TMO6) of the layered oxide shown in the chemical formula by adding the Fe element or further using a doping metal element as shown in M, thereby effectively improving the specific capacity and energy density of the layered oxide. Controlling the content of the Fe element and the Mn element within the stoichiometric ratio range shown in d and c, or further controlling the stoichiometric ratio range shown in the doping metal element shown in M, can also effectively alleviate the migration phenomenon of the Fe element during the sodium intercalation and deintercalation process of the layered oxide, thereby improving the structural stability of the layered oxide and thus improving the cycle performance of the layered oxide.

[0009] The positive electrode material of the embodiment of the present application effectively adjusts the arrangement of metal elements in the transition metal layer contained in the layered oxide shown in the chemical formula and the distance between the transition metal layer and the sodium layer by including Fe and Mn elements or further controlling the content range of the element shown in M, thereby improving the structural stability of the layered oxide during the process of sodium insertion and extraction and fully utilizing the specific capacity, thereby improving the specific capacity and cycle performance of the layered oxide.

[0010] In some embodiments, at least one of a, b, c, d, and e is within the following value ranges:

[0011] 0.85≤a≤1, 0≤b≤0.18, 0.3≤c≤0.5, 0.3≤d≤0.6, 0.02≤e≤0.1.

[0012] By further selecting and controlling the stoichiometric ratio of at least one element among Ni, Mn, and Fe or at least one element among Ni, Mn, Fe, and M within this range, the doping of the transition metal layer in the layered oxide represented by the chemical formula with the Fe element or the doping metal element represented by M can be further optimized to further adjust the arrangement between the metal elements in the transition metal layer, thereby further reducing the migration of the Fe element, improving the structural stability of the layered oxide during the sodium insertion and deinsertion process, and improving the specific capacity and cycle performance of the layered oxide.

[0013] In some embodiments, the stoichiometric ratio of the total stoichiometric amount of the Ni element, the Mn element, the Fe element and the doping metal element to the stoichiometric ratio of the Na element is 1:(0.85-0.95).

[0014] In some embodiments, the stoichiometric ratio of the total stoichiometric amount of the Ni element, the Mn element, the Fe element and the doping metal element to the Na element is 1:(0.86-0.94).

[0015] By controlling the stoichiometric ratio of the Na element to other metal elements contained in the layered oxide represented by the chemical formula within this range, the specific capacity and cycle performance of the layered oxide can be improved.

[0016] In some embodiments, the total stoichiometric ratio of the Mn element and the M element to the Fe element is 0.9 to 1.5:1.

[0017] In some embodiments, the total stoichiometric ratio of the Mn element and the M element to the Fe element is 1 to 1.2:1.

[0018] At this time, when e=0 in the chemical formula (I), that is, when the content of M is equal to 0, it refers to the stoichiometric ratio of the Mn element to the Fe element; when e>0 in the chemical formula (I), that is, when the content of M is greater than 0, it refers to the stoichiometric ratio of the total stoichiometric ratio of the Mn element and the doping metal element represented by M to the Fe element. Controlling the stoichiometric ratio of the Fe element to the Mn element contained in the layered oxide represented by the chemical formula, or further to the doping metal element represented by M, within this range can further adjust the arrangement of the metal elements in the transition metal layer and the distance between the transition metal layer and the sodium layer, so as to further alleviate the migration phenomenon of the Fe element during the sodium intercalation and deintercalation process of the layered oxide, further improve the structural stability of the layered oxide, and improve the specific capacity.

[0019] In some embodiments, the doping metal element includes at least one of Zn, V, Cr, Al, Sc, Sn, Sb, Zr, Nb, Ti, Mg, Cu, Ru, and Ir. Controlling the doping metal element represented by M within the range of these elements can effectively adjust the arrangement of metal elements in the transition metal layer and the distance between the transition metal layer and the sodium layer, assisting the Mn element in further reducing the migration of the Fe element, thereby further improving the structural stability of the layered oxide represented by the chemical formula during the sodium insertion and extraction process. When the doping metal element represented by M is an active doping metal element, the specific capacity of the layered oxide is further improved.

[0020] In some embodiments, the layered oxide includes Na 0.87 Ni 0.2 Fe 0.3 Mn 0.45 O2、Na 0.87 Ni 0.2 Fe 0.35 Mn 0.45 O2、Na 0.85 Ni 0.1 Fe 0.387 Mn 0.43 O2、Na 0.85 Ni 0.05 Fe 0.45 Mn 0.45 O2、Na 0.87 Ni 0.05 Fe 0.5 Mn 0.45 O2、Na 0.85 Ni0.1 Feb 0.38 Mr 0.437 Zn 0.082 O2、Na 0.85 Ni 0.1 Feb 0.38 Mr 0.437 V 0.082 O2、Na 0.85 Ni 0.1 Feb 0.38 Mr 0.437 Cr 0.082 O2、Na 0.85 Ni 0.1 Feb 0.38 Mr 0.437 Al 0.082 O2、Na 0.85 Ni 0.1 Feb 0.38 Mr 0.437 Sc 0.082 O2、Na 0.85 Ni 0.1 Feb 0.38 Mr 0.437 Mr 0.082 O2、Na 0.85 Ni 0.1 Feb 0.38 Mr 0.437 Sb 0.082 O2、Na 0.85 Ni 0.1 Feb 0.38 Mr 0.437 Zr 0.082 O2、Na 0.85 Ni 0.1 Feb 0.38 Mr 0.437 No 0.082 O2、Na 0.85 Ni 0.1 Feb 0.38 Mr 0.437 Tea 0.082 O2、Na 0.85 Ni 0.2 Feb 0.28 Mr 0.437 Mg 0.082 O2、Na 0.85 Ni 0.1 Feb 0.38 Mr 0.437 Ru 0.082 O2、Na 0.85 Ni 0.1 Feb 0.38 Mr 0.437 Ir 0.082 O2、Na0.85 Ni 0.1 Fe 0.38 Mn 0.437 Al 0.04 Zn 0.04 O2、Na 0.85 Ni 0.1 Fe 0.38 Mn 0.267 Zn 0.082 O2、Na 0.85 Fe 0.4 Mn 0.6 O2、Na 0.92 Ni 0.15 Fe 0.34 Mn 0.45 O2、Na 0.92 Ni 0.15 Fe 0.41 Mn 0.44 O2、Na 0.92 Ni 0.05 Fe 0.5 Mn 0.45 O2、Na 0.92 Fe 0.38 Mn 0.6 O2、Na 0.92 Ni 0.1 Fe 0.38 Mn 0.437 Zn 0.082 O2、Na 0.92 Ni 0.1 Fe 0.38 Mn 0.367 Zn 0.082 O2、Na 0.92 Ni 0.1 Fe 0.494 Mn 0.395 At least one of O2, etc.

[0021] In the layered oxides represented by these molecular formulas, a specific arrangement is formed between the metal elements in the transition metal layer contained in the layered oxide. When the Mn element or the doped metal element represented by M is controlled, it can further exert a stabilizing effect on the Fe element, reduce the migration of the Fe element, further improve the stability of the iron element in the metal transition layer, and improve the specific capacity and cycle performance of the layered oxide. At the same time, this can further reduce the content of Ni in the layered oxide represented by chemical formula (I), while improving the specific capacity and cycle performance of the layered oxide represented by chemical formula (I), and reduce the economic cost of the layered oxide. In addition, the electrochemical properties and processing properties of the layered oxide, such as sheet resistance, can also be further improved.

[0022] In some embodiments, the layered oxide includes at least one of the following features (1) to (3):

[0023] (1) The crystal structure includes an O3 phase layered metal oxide, and the O3 phase layered metal oxide accounts for more than 95% of the total weight of the layered oxide;

[0024] (2) Dv50 particle size is 3 to 9 μm;

[0025] (3) It includes a single crystal, and the morphology of the single crystal is block-shaped.

[0026] In some embodiments, the layered oxide has a Dv50 particle size of 4.2 to 8.5 μm.

[0027] In some embodiments, the layered oxide includes at least one of the following features (1) to (3):

[0028] (1) The powder compaction density under 2 tons of pressure is higher than 2.7g / cm 3 ;

[0029] (2) The powder compaction density under 3 tons of pressure is higher than 3.0g / cm 3 ;

[0030] (3) Specific surface area is 0.4 to 1.5 m 2 / g.

[0031] In some embodiments, the layered oxide includes at least one of the following features (1) to (3):

[0032] (1) The compacted density of the powder under 2 tons of pressure is 2.7 to 3.0 g / cm 3 ;

[0033] (2) The compacted density of the powder under 3 tons of pressure is 3.0 to 3.3 g / cm 3 ;

[0034] (3) Specific surface area is 0.5 to 0.95 m 2 / g.

[0035] The layered oxides represented by chemical formula (I) in the above embodiments are mainly O3 phase layered metal oxides and include a single crystal structure, with a high compaction density and a specific surface area within a suitable range.

[0036] In some embodiments, the layered oxide comprises at least one of the following (1) to (3) at 1.5-4.2 V and 0.1 C:

[0037] (1) The charging capacity is 130-150 mAh / g;

[0038] (2) Discharge capacity is 129-145 mAh / g;

[0039] (3) The initial efficacy is higher than 92%.

[0040] In some embodiments, the layered oxide comprises at least one of the following (1) to (3) at 1.5-4.2 V and 0.1 C:

[0041] (1) Charge capacity is 132~150mAh / g;

[0042] (2) Discharge capacity is 130-144 mAh / g;

[0043] (3) The initial efficacy is 92% to 98%.

[0044] The structural stability of the layered oxide represented by the above chemical formula (I) is significantly improved, and the structural stability during the sodium insertion and extraction process is high in gram capacity and energy density.

[0045] In a second aspect, the present invention provides a method for preparing a positive electrode material. The method for preparing a positive electrode material in the present invention comprises the following steps:

[0046] Provides Na a Ni b Fe c Mn d M e O f precursors;

[0047] The precursor is sintered to obtain a chemical formula of Na a Ni b Fe c Mn d M e O f layered oxides;

[0048] Among them, 0.8≤a≤1, 0≤b≤0.2, 0.25≤c≤0.5, 0.26≤d≤0.6, 0≤e≤0.1; 1.8≤f≤2, b+c+d+e≤1; M is an active and / or inert doping metal element.

[0049] The positive electrode material preparation method of the present application embodiment is to a Ni b Fe c Mn d M e O f The precursor is sintered to prepare the chemical formula Na a Ni b Fe c Mnd M e O f The layered oxide shown. Therefore, the stoichiometric ratio of Fe and Mn in the layered oxide prepared by the positive electrode material preparation method of the present application embodiment can effectively reduce the migration of iron elements, improve the structural stability of the layered oxide during the sodium insertion and extraction process, so that the prepared layered oxide has high gram capacity and energy density and good cycle performance. At the same time, it also has properties such as high sodium ion diffusion rate, thereby improving the DCR growth of the battery cell. In addition, by adjusting the Na a Ni b Fe c Mn d M e O f The sintering conditions of the precursor can be effectively controlled to improve the chemical formula of Na a Ni b Fe c Mn d M e O f The stability of the structure and electrochemical properties of layered oxides.

[0050] In some embodiments, the doping metal element includes at least one of Zn, V, Cr, Al, Sc, Sn, Sb, Zr, Nb, Ti, Mg, Cu, Ru, and Ir.

[0051] These doping metal elements can be used together with elements such as Fe to further dope the transition metal layer contained in the layered oxide shown in the chemical formula, adjust the arrangement of the metal elements in the transition metal layer, and, depending on the type of the doping metal element, further improve the structural stability and / or gram capacity of the layered oxide shown in the chemical formula during the sodium insertion and extraction process.

[0052] In some embodiments, at least one of a, b, c, d, and e is within the following value ranges:

[0053] 0.85≤a≤1, 0≤b≤0.18, 0.3≤c≤0.5, 0.3≤d≤0.6, 0.02≤e≤0.1.

[0054] By adding Na a Ni b Fe c Mn d M e The ratio of these metal elements in the O2 precursor is further controlled within this range, which can further adjust the arrangement of the metal elements in the prepared layered oxide, thereby further improving the structural stability of the prepared layered oxide during the sodium insertion and deinsertion process, and improving the specific capacity of the layered oxide and the cyclic stability of the reversible capacity.

[0055] In some embodiments, the sintering process includes at least one of the following conditions (1) to (3):

[0056] (1) Temperature is 700-980°C;

[0057] (2) Duration: 3 to 20 hours;

[0058] (3) The temperature is raised to the sintering temperature at a heating rate of 2 to 15°C / min.

[0059] In some embodiments, the sintering process includes at least one of the following conditions (1) to (2):

[0060] (1) Temperature is 750-950℃;

[0061] (2) The duration is 5 to 12 hours.

[0062] By controlling the sintering conditions within the above range, the Na a Ni b Fe c Mn d M e O f The structural stability of layered oxides during the process of sodium insertion and removal further improves the high specific capacity, energy density and cycle performance of layered oxides. a Ni b Fe c Mn d M e O f The content of O3 phase layered metal oxide and the single crystal content in the layered oxide control the single crystal size and the particle size of the layered oxide, thereby improving the compaction density and other properties of the layered oxide.

[0063] In some embodiments, the Na a Ni b Fe c Mn d M e O f The precursor is prepared according to a method comprising the following steps:

[0064] According to Na a Ni b Fe c Mn d M e O f The precursor is obtained by solid-phase mixing the sodium source, nickel source, manganese source, iron source and M source in the stoichiometric ratio of the elements contained.

[0065] The solid-phase method was used to prepare Naa Ni b Fe c Mn d M e O f The precursor can effectively control the stoichiometric ratio of each element and improve the preparation effect of the precursor.

[0066] In some embodiments, the Na a Ni b Fe c Mn d M e O f The precursor is prepared according to a method comprising the following steps:

[0067] According to Na a Ni b Fe c Mn d M e O f A soluble nickel source, a soluble manganese source, a soluble iron source and a soluble doping element source represented by M are prepared into a mixed solution in a stoichiometric ratio of elements, and at least one of a precipitant and a complexing agent is added to perform a coprecipitation treatment to obtain a precipitated mixture;

[0068] The precipitation mixture is mixed with a sodium source to obtain the precursor.

[0069] The coprecipitation method was used to prepare Na a Ni b Fe c Mn d M e O f It is a precursor to improve the stoichiometric ratio accuracy of each element.

[0070] In a third aspect, embodiments of the present application provide a positive electrode. The positive electrode of the present application embodiment includes a current collector and a positive electrode active material layer disposed on a surface of the current collector, wherein the positive electrode active material layer includes the positive electrode material of the present application embodiment or a positive electrode material prepared by the positive electrode material preparation method of the present application embodiment.

[0071] The positive electrode active material layer of the positive electrode of the present embodiment contains the positive electrode material of the above embodiment of the present invention. The positive electrode has a high gram capacity, a high film coating surface density, and a high electrode compaction density, which is conducive to improving the energy density of the battery.

[0072] In some embodiments, the content of the positive electrode active material layer on the single surface of the current collector, that is, the film coating density (abbreviated as CW) is 250-330 mg / 1540.25 mm 2 .

[0073] In some embodiments, the content of the positive electrode active material layer on the single surface of the current collector, that is, the film coating density (abbreviated as CW) is 280-320 mg / 1540.25 mm 2 .

[0074] The positive electrode active material layer having a content within this range is beneficial for improving the energy density of the battery.

[0075] In some embodiments, the positive electrode has a compaction density of 2.6 to 3.2 g / cm 3 .

[0076] In some embodiments, the compaction density of the positive electrode is 2.8 to 3.0 g / cm 3 .

[0077] The compaction density in this range is beneficial to improving the energy density of the battery, and the contact interface with the electrolyte is stable.

[0078] In some embodiments, the porosity of the positive electrode active material layer is 35% to 65%.

[0079] In some embodiments, the porosity of the positive electrode active material layer is 40% to 58%.

[0080] The porosity within this range enables the positive electrode active material layer to have the above-mentioned compaction density, which is beneficial to improving the energy density of the battery and enhancing the wettability of the electrolyte.

[0081] In some embodiments, the positive electrode is a pole piece, and the pole piece has a sheet resistance of 0.5 to 5 mΩ.

[0082] In some embodiments, the positive electrode is a pole piece, and the pole piece has a sheet resistance of 0.5 to 3 mΩ.

[0083] The sheet resistance in this range can effectively improve battery performance such as efficiency and life.

[0084] In some embodiments, the positive electrode is a pole piece, and the ratio of the thickness from one surface of the pole piece to the other opposite surface to the thickness of the current collector is 7 to 16:1.

[0085] In some embodiments, the positive electrode is a pole piece, and the ratio of the thickness from one surface of the pole piece to the other opposite surface to the thickness of the current collector is 8 to 15:1.

[0086] By controlling the total thickness of the electrode and the thickness of the current collector within the above ratio range, the bonding strength between the positive electrode active material layer and the current collector can be improved, the mechanical strength of the electrode structure can be improved, the cycle performance of the electrode can be improved, and it is also beneficial to improve the energy density of the battery.

[0087] In some embodiments, the conductive agent contained in the positive electrode active material layer includes a linear conductive agent.

[0088] In an embodiment, the mass content of the linear conductive agent in the positive electrode active material layer is 0.1% to 2.5%.

[0089] In an embodiment, the linear conductive agent has a mass content of 0.2 to 0.8% in the positive electrode active material layer.

[0090] In the embodiment, the linear conductive agent has an aspect ratio of 40 to 3000:1.

[0091] In the embodiment, the linear conductive agent has an aspect ratio of 50 to 2500:1.

[0092] In an embodiment, the length of the linear conductive agent is 0.5-5 μm.

[0093] In an embodiment, the length of the linear conductive agent is 0.5-2 μm.

[0094] In an embodiment, the diameter of the linear conductive agent is 2-10 nm.

[0095] In an embodiment, the diameter of the linear conductive agent is 3-7 nm.

[0096] In an exemplary embodiment, the linear conductive agent includes at least one of carbon nanotubes, carbon fibers, and conductive oxide nanowires.

[0097] By adding a linear conductive agent to the positive electrode active material layer, and controlling the linear conductive agent content within the above-mentioned range, and selecting and controlling the linear conductive agent's type, aspect ratio, length, and diameter within the above-mentioned ranges, the linear conductive agent can form a rich conductive network structure within the positive electrode active material layer, and the linear conductive agent can also be entangled on the surface of the flat single crystal particles. When a particulate conductive agent is also added to the positive electrode active material layer, the particulate conductive agent can be effectively dispersed in the gaps within the positive electrode material. In this way, the linear conductive agent forms a long-range conductive network structure within the positive electrode active material layer, while the particulate conductive agent forms a short-range conductive structure. Therefore, the conductive synergistic effect of the linear conductive agent and the particulate conductive agent in the positive electrode active material layer effectively improves the conductivity of the positive electrode active material layer and can significantly reduce the internal resistance of the positive electrode.

[0098] In a fourth aspect, an embodiment of the present application provides a sodium battery. The sodium battery of the embodiment of the present application includes the positive electrode of the embodiment of the present application.

[0099] Since the sodium battery of the embodiment of the present application contains the positive electrode of the embodiment of the present application, the sodium battery of the embodiment of the present application has high energy density and good cycle performance.

[0100] In some embodiments, the sodium battery is a sodium battery cell, and the operating voltage of the sodium battery cell is 1.5 to 4.0V.

[0101] In a fifth aspect, an embodiment of the present application provides an electrical device, and the embodiment of the present application includes a sodium battery according to an embodiment of the present application.

[0102] The electrical device in the embodiment of the present application has a long standby or battery life and a long service life.

[0103] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0104] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiment below. The accompanying drawings are for illustration purposes only and are not to be considered as limiting the present application. The same reference numerals are used throughout the drawings to represent the same components. In the drawings:

[0105] FIG1 is a scanning electron microscope (SEM) image of a layered oxide provided in Example A3 of the present application;

[0106] FIG2 is a schematic structural diagram of a positive electrode in some embodiments of the present application;

[0107] FIG3 is another schematic structural diagram of a positive electrode according to some embodiments of the present application;

[0108] FIG4 is a schematic structural diagram of an embodiment of a sodium battery cell according to an embodiment of the present application;

[0109] FIG5 is an exploded schematic diagram of the sodium battery cell shown in FIG4 ;

[0110] FIG6 is a schematic structural diagram of an embodiment of a battery module according to the present application;

[0111] FIG7 is a schematic structural diagram of an embodiment of a battery pack according to the present application;

[0112] FIG8 is a schematic diagram of the exploded structure of the battery pack shown in FIG7 ;

[0113] FIG9 is a schematic diagram of an embodiment of an electrical device including a battery according to an embodiment of the present application as a power source.

[0114] The accompanying drawings in the specific implementation manner are as follows:

[0115] 10-positive electrode, 11 current collector, 12-positive electrode active material layer;

[0116] 20-battery cell, 21-housing, 22-electrode assembly, 23-cover plate;

[0117] 30-battery module;

[0118] 40-battery pack, 41-upper box, 42-lower box. DETAILED DESCRIPTION

[0119] The following embodiments of the technical solution of the present application will be described in detail with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application and are therefore only examples and are not intended to limit the scope of protection of the present application.

[0120] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above-mentioned figure descriptions are intended to cover non-exclusive inclusions.

[0121] In the description of the embodiments of this application, the technical terms "first" and "second" are used only to distinguish different objects and should not be understood to indicate or imply relative importance or implicitly specify the quantity, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, the meaning of "plurality" is more than two, unless otherwise clearly and specifically defined.

[0122] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0123] In the description of the embodiments of this application, the term "and / or" is simply a description of the association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent the following three situations: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0124] In the description of the embodiments of the present application, the term "multiple" refers to more than two (including two). Similarly, "multiple groups" refers to more than two groups (including two groups), and "multiple pieces" refers to more than two pieces (including two pieces).

[0125] In the description of the embodiments of the present application, the technical terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the embodiments of the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the embodiments of the present application.

[0126] In the description of the embodiments of the present application, unless otherwise expressly specified or limited, technical terms such as "installed," "connected," "connected," and "fixed" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integration; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; internal connections between two components or interactions between two components. Those skilled in the art can understand the specific meanings of the above terms in the embodiments of the present application based on specific circumstances.

[0127] Sodium-ion batteries (SIBs) are ideal candidates for energy storage systems due to their abundant raw material reserves and low cost. They also have enormous potential for application in the new energy vehicle market. With the rapid development of energy storage systems and new energy vehicles, the requirements for the energy density and cycle stability of sodium-ion batteries are becoming increasingly stringent.

[0128] For sodium-ion batteries, cathode materials are an important component of sodium-ion batteries, providing active sodium ions. They are also one of the key factors affecting the energy density and cycle performance of sodium-ion batteries. Among sodium-ion battery cathode materials, layered oxides have attracted much attention due to their high gram capacity and structure similar to that of lithium-ion battery cathode materials.

[0129] According to the arrangement and stacking order of oxygen atoms in layered oxides, the layered oxides are currently mainly divided into P2 type and O3 type. Among them, compared with P2 type layered oxides, O3 type layered oxides can store more Na + , can also exert a high reversible specific capacity within the same voltage range, and therefore has better commercial application prospects. Although layered oxides have relatively high specific capacity, as the market's requirements for battery energy density continue to increase, existing batteries have gradually failed to meet the current market's application requirements, thus placing higher requirements on the specific capacity of layered oxides.

[0130] In order to effectively improve the gram capacity of layered oxides, it is currently reported that transition metals are used to dope layered oxides, such as iron elements are used to dope layered oxides, specifically manganese-nickel-based layered oxides are doped with iron elements. Through research, it is found that although iron doping can improve the gram capacity of layered oxides such as manganese-nickel-based layered oxides, the iron element will migrate during the process of sodium intercalation and deintercalation of the layered oxide, such as from the transition layer to the sodium ion layer, resulting in a decrease in the structural stability of layered oxides such as manganese-nickel-based layered oxides, thereby reducing the gram capacity and cycle performance of the layered oxide. Further research found that the higher the doping amount of iron element, the more obvious the migration phenomenon of iron element, especially at higher voltages such as higher than 4.0V, the more obvious the migration phenomenon of iron element, resulting in a further decrease in the structural stability of layered oxides such as manganese-nickel-based layered oxides, thereby further reducing the gram capacity and cycle performance of the layered oxide.

[0131] In order to improve the structural stability of iron-containing layered oxides, it was unexpectedly discovered through research that by controlling and adjusting the content ratio of iron and manganese elements in manganese-nickel-based layered oxides, or further doping with active and / or inert doping metal elements and controlling the content ratio of doped metal elements, the arrangement of metal elements in the transition metal layer can be changed, thereby significantly reducing the migration of iron elements and improving the structural stability of manganese-nickel-based layered oxides, thereby significantly improving the gram capacity and cycle performance of manganese-nickel-based layered oxides. Based on the above research, the following technical solutions are proposed in the embodiments of this application.

[0132] cathode materials

[0133] In one aspect, the present invention provides a cathode material. In some embodiments, the cathode material comprises a layered oxide represented by the following chemical formula (I): Na a Ni b Fe c Mn d M e O2;

[0134] Among them, 0.8≤a≤1, 0≤b≤0.2, 0.25≤c≤0.5, 0.26≤d≤0.6, 0≤e≤0.1, 1.8≤f≤2, b+c+d+e≤1; M is an active and / or inert doping metal element.

[0135] In the chemical formula (I) of the layered oxide contained in the positive electrode material of the embodiment of the present application, a, b, c, d, e and f represent the stoichiometric content ratios of the doping metal elements represented by Na, Ni, Fe, Mn and M and the O element in the layered oxide, respectively. Therefore, the stoichiometric content ratio of Na, Ni, Fe, Mn and M and the O element contained in the layered oxide can be 0.8~1:0~0.2:0.25~0.5:0.26~0.6:0~0.1:1.8~2. In addition, the stoichiometric ratio of the doping metal elements represented by Na, Ni, Fe, Mn and M and the O element can be a molar ratio or a mass ratio converted according to the molar ratio. The active doping metal element represented by M refers to a type of metal element that has electrochemical redox activity in the layered oxide and mainly contributes to the gram capacity of the layered oxide. The inert doping metal element represented by M, relative to the active doping metal element, refers to a type of metal element that has relatively stable electrochemical redox activity in the layered oxide and primarily contributes to the stability of the layered oxide's crystal structure. The layered oxide is a cathode material composed of alternating transition metal layers (TMO6) and sodium layers (NaO6) containing Ni, Mn, and Fe, or further containing the doping metal element represented by M.

[0136] The Fe element contained in the layered oxide contained in the positive electrode material of the present application embodiment has a redox charge of Fe 2+ / Fe 3+ By optimizing the structure of the transition metal layer (TMO6) of the layered oxide represented by chemical formula (I) by using the Fe element or further using an active doping metal element as represented by M, the arrangement of the metal elements in the transition metal layer is adjusted (mainly disordered arrangement), effectively improving the specific capacity of the layered oxide. On this basis, controlling the content of the Fe and Mn elements within the stoichiometric ratio range represented by d and c, or further controlling the content of the doping metal element (active or / inert) represented by M within the stoichiometric ratio range represented by e (when e≠0), can also effectively alleviate the migration phenomenon of the Fe element during the sodium insertion and extraction process of the layered oxide under high voltage, thereby improving the structural stability of the layered oxide represented by chemical formula (I). Therefore, the layered oxide represented by chemical formula (I) effectively adjusts the arrangement of metal elements in the transition metal layer contained in the layered oxide represented by chemical formula (I) and the distance between the transition metal layer and the sodium layer by controlling the stoichiometric ratio of the Fe element and the Mn element or further controlling the doped metal element represented by M, thereby improving the gram capacity of the layered oxide and alleviating the migration phenomenon of the iron element during the process of sodium insertion and deinsertion, thereby improving the structural stability of the layered oxide and improving the cycle performance of the layered oxide.

[0137] Furthermore, the layered oxide shown in the chemical formula (I) is optimized by adjusting the stoichiometric ratio of Fe and Mn, and adding Fe or further doping with the metal element shown in M ​​to the transition metal layer (TMO6) containing Mn or Ni, which can effectively inhibit the Na formation during the charge and discharge process of the layered oxide. + and vacancies, reducing the Na + The diffusion barrier of the layered oxide increases the diffusion rate of sodium ions contained in the layered oxide, thereby improving the DCR growth of the battery cell. It also effectively reduces the Ni content, as shown in the stoichiometric content range (b), reducing the economic cost of the layered oxide.

[0138] In the exemplary embodiment, in the chemical formula (I) of the layered oxide contained in the positive electrode material of the present application, the stoichiometric content a of the Na element can be further 0.85≤a≤1. Based on the value range of a in chemical formula (I), in the exemplary embodiment, a can be a typical but non-limiting stoichiometric content such as 0.8, 0.85, 0.9, 0.95, 1.0, or a range between any two stoichiometric content values. The Na element in this content range increases the reversible capacity of the layered oxide represented by chemical formula (I).

[0139] In some embodiments, in the chemical formula (I) of the layered oxide contained in the positive electrode material of the embodiment of the present application, the stoichiometric content b of the Ni element can be 0≤b≤0.18, further 0.05≤b≤0.18. Based on the value range of b in chemical formula (I), in the exemplary embodiment, b can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.2, etc., or a range between any two stoichiometric content values. On the one hand, the Ni element in this content range can effectively reduce the content of inactive impurity phases such as NiO in the layered oxide under the co-doping of Mn element or further with the doping metal element represented by M, thereby further improving the structural stability of the layered oxide during the sodium insertion and extraction process. At the same time, the Fe element or the active doping metal element shown in M, especially the Fe element, can also replace part of the Ni element to reduce the content of the Ni element, such as making the content of the Ni element within the stoichiometric content range shown in b, thereby reducing the cost of the layered oxide without reducing the gram capacity of the layered oxide shown in chemical formula (I) and correspondingly increasing the energy density of the battery.

[0140] In some embodiments, in the layered oxide of the positive electrode material of the present invention, the stoichiometric content c of the Fe element can be further 0.3 ≤ c ≤ 0.5. Based on the value range of c in the chemical formula (I), in exemplary embodiments, c can be a typical but non-limiting stoichiometric content such as 0.25, 0.3, 0.3, 0.35, 0.35, 0.4, 0.4, 0.45, 0.45, 0.48, 0.5, or a range between any two stoichiometric content values. The Fe element in this stoichiometric content range can jointly optimize the structure of the transition metal layer in the layered oxide shown in chemical formula (I) with the stoichiometric content of the Mn element shown in c or further with the doping metal element shown in M, further reduce the migration of the Fe element, and improve the structural stability of the layered oxide shown in chemical formula (I) during the process of sodium insertion and extraction; at the same time, the Fe element replaces part of the Ni element, thereby reducing the content of the Ni element on the basis of improving the gram capacity and energy density of the layered oxide shown in chemical formula (I), thereby reducing the cost of the layered oxide shown in chemical formula (I).

[0141] In some embodiments, in the chemical formula (I) of the layered oxide contained in the positive electrode material of the present application, the stoichiometric content d of the Mn element can be 0.3≤d≤0.6, and further 0.3≤d≤0.45. Based on the value range of d in chemical formula (I), in exemplary embodiments, d can be 0.26, 0.27, 0.28, 0.29, 0.3, 0.31, 0.32, 0.33, 0.34, 0.35, 0.36, 0.37, 0.38, 0.39, 0.4, 0.41, 0.42, 0.43, 0.44, 0.45, 0.5, 0.55, 0.6, or other typical but non-limiting stoichiometric contents or a range between any two stoichiometric content values. On the one hand, the Mn element in this stoichiometric content range can adjust the arrangement between the metal elements in the transition metal layer under the co-doping of the Fe element or further with the doping metal element shown by M, so as to further inhibit the migration of the Fe element during the sodium intercalation and deintercalation process, while reducing the Jahn-Teller effect brought by the Mn element and the Ni element, further improving the structural stability of the layered oxide during the sodium intercalation and deintercalation process; on the other hand, it can also adjust the average oxidation state and lattice space of the layered oxide shown in chemical formula (I), improve the diffusion rate of Na ions, and thus improve the DCR growth of the battery cell.

[0142] In some embodiments, in the chemical formula (I) of the layered oxide contained in the positive electrode material of the present application, the stoichiometric content e of the doping metal element represented by M can be 0.02≤e≤0.1, and further 0.03≤e≤0.1. Based on the value range of e in chemical formula (I), e can be a typical but non-limiting stoichiometric content such as 0, 0.01, 0.02, 0.03, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, or a range between any two stoichiometric content values. When e>0, that is, when the layered oxide shown in chemical formula (I) contains the doping metal element shown in M, the doping metal element shown in M ​​in the stoichiometric content range can further dope the transition metal layer contained in the layered oxide shown in chemical formula (I), and further adjust the arrangement between the metal elements in the transition metal layer and the distance between the transition metal layer and the sodium layer together with metal elements such as Mn element and Fe element, so as to further reduce the migration of Fe element, improve the structural stability of the layered oxide during the process of sodium insertion and deinsertion, so as to further improve the cycle stability of the layered oxide; when the doping metal element shown in M ​​is an active doping metal element, it can further increase the gram capacity of the layered oxide together with the Fe element, thereby improving the energy density of the battery.

[0143] In an embodiment, the doping metal element shown in M ​​may include at least one of Zn, V, Cr, Al, Sc, Sn, Sb, Zr, Nb, Ti, Mg, Cu, Ru, Ir, etc. Among them, the active doping metal element shown in M ​​may include at least one metal element among Zn, V, Cr, Nb, Cu, Sc, Sn, Sb, etc., and the inert doping metal element shown in M ​​may be at least one metal element among Zr, Al, Ru, Ir, Mg, Ti, etc. The doping metal element shown in M ​​is selected and controlled in these element types, and together with elements such as Fe, the transition metal layer structure contained in the layered oxide shown in chemical formula (I) is optimized, the arrangement between the metal elements in the transition metal layer and the distance between the transition metal layer and the sodium layer are adjusted, and the Mn element is assisted to further reduce the migration of the Fe element, so as to further improve the structural stability of the layered oxide shown in chemical formula (I) during the sodium insertion and extraction process, and further improve the specific capacity and cycle performance of the layered oxide. When the doping metal element shown in M ​​is an active doping metal element, it can also further improve the specific capacity of the layered oxide with the Fe element, thereby improving the energy density of the battery.

[0144] In an exemplary embodiment, in the chemical formula (I) of the layered oxide contained in the positive electrode material of the embodiment of the present application, the stoichiometric content f of O can be a typical but non-limiting stoichiometric content such as 1.8, 1.9, 2, or a range between any two stoichiometric content values.

[0145] Based on the value ranges of a, b, c, d, and e in the above embodiments, in some embodiments, a, b, c, d, and e in the chemical formula (I) of the layered oxide can simultaneously have the following value ranges:

[0146] 0.85≤a≤1, 0≤b≤0.18, 0.3≤c≤0.5, 0.3≤d≤0.6, 0.02≤e≤0.1. At this time, the stoichiometric content ratio of the doping metal elements represented by Na, Ni, Mn, Fe and M contained in the layered oxide represented by chemical formula (I) can be 0.85-1:0-0.18:0.3-0.5:0.3-0.6:0.02-0.1. By selecting and controlling the stoichiometric ratio of the doping metal elements represented by Na, Ni, Mn, Fe and M within this range, the arrangement of the metal elements in the transition metal layer and the distance between the transition metal layer and the sodium layer in the layered oxide represented by chemical formula (I) can be further adjusted, the migration of the Fe element can be further alleviated, the structural stability of the layered oxide during the sodium insertion and extraction process can be improved, and the specific capacity and cycle performance of the layered oxide can be improved. In addition, the electrochemical properties and processing properties of the layered oxide can be further improved.

[0147] Based on the value ranges of a, b, c, d, and e in the above embodiments, in some embodiments, the stoichiometric ratio of the total stoichiometric amount of Ni, Mn, and Fe, or the total stoichiometric amount of Ni, Mn, Fe, and the doping metal element represented by M, to the stoichiometric ratio of Na in the chemical formula (I) of the layered oxide is 1:(0.85-0.95), optionally 1:(0.86-0.94), and in exemplary embodiments, can be 1:0.85, 1:0.86, 1:0.88, 1:0.9, 1:0.92, 1:0.93, 1:0.94, 1:0.95, or a range between any two molar ratios. The stoichiometric amount can be in terms of moles or mass converted based on the moles. By controlling the stoichiometric ratio of the Na element to other metal elements contained in the layered oxide represented by chemical formula (I) within this range, the content of sodium ions that can be inserted and removed from the layered oxide can be further increased, thereby increasing the gram capacity of the layered oxide; moreover, the sodium ions in this content range can increase the O3 crystal phase content of the layered oxide represented by chemical formula (I), so that the layered oxide represented by chemical formula (I) mainly presents O3 crystals, thereby improving the structural stability of the layered oxide represented by chemical formula (I) and improving its cycle performance.

[0148] In some embodiments, the stoichiometric ratio of the total stoichiometric amount of the Mn element and the doping metal element represented by M in the chemical formula (I) of the layered oxide to the Fe element is 0.9 to 1.5:1, and can be optionally 1 to 1.2:1. In exemplary embodiments, it can be a typical but non-limiting molar ratio such as 0.9:1, 0.95:1, 1.05:1, 1.1:1, 1.15:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, or a range between any two molar ratios. The stoichiometric amount can still be a molar number and a mass converted based on the molar number. At this time, when e=0 in the chemical formula (I), that is, when the content of M is equal to 0, it refers to the stoichiometric ratio of the Mn element to the Fe element; when e>0 in the chemical formula (I), that is, when the content of M is greater than 0, it refers to the stoichiometric ratio of the total stoichiometric amount of the Mn element and the doping metal element represented by M to the Fe element. By controlling the stoichiometric ratio of the Mn element or the further doped metal element shown in M ​​to the Fe element within this range, the arrangement of the metal elements in the transition metal layer and the distance between the transition metal layer and the sodium layer can be further adjusted, the role of the Mn element can be further exerted, the migration of the Fe element can be further alleviated, the stability of iron in the metal transition layer can be improved, the structural stability of the layered oxide during the sodium insertion and extraction process can be improved, and the specific capacity and cycle performance of the layered oxide can be improved.

[0149] Based on the value ranges of a, b, c, d and e in the above embodiments, in the embodiments, the layered oxides represented by chemical formula (I) in the above embodiments may include Na 0.87 Ni 0.2 Fe 0.3 Mn 0.45 O2、Na 0.87 Ni 0.2 Fe 0.35 Mn 0.45 O2、Na 0.85 Ni 0.1 Fe 0.387 Mn 0.43 O2、Na 0.85 Ni 0.05 Fe 0.45 Mn 0.45 O2、Na 0.87 Ni 0.05 Fe 0.5 Mn 0.45 O2、Na 0.85 Ni 0.1 Fe 0.38 Mn 0.437 Zn 0.082 O2、Na 0.85 Ni 0.1 Fe 0.38 Mn 0.437 V 0.082O2、Na 0.85 Ni 0.1 Feb 0.38 Mr 0.437 Cr 0.082 O2、Na 0.85 Ni 0.1 Feb 0.38 Mr 0.437 Al 0.082 O2、Na 0.85 Ni 0.1 Feb 0.38 Mr 0.437 Sc 0.082 O2、Na 0.85 Ni 0.1 Feb 0.38 Mr 0.437 Mr 0.082 O2、Na 0.85 Ni 0.1 Feb 0.38 Mr 0.437 Sb 0.082 O2、Na 0.85 Ni 0.1 Feb 0.38 Mr 0.437 Zr 0.082 O2、Na 0.85 Ni 0.1 Feb 0.38 Mr 0.437 No 0.082 O2、Na 0.85 Ni 0.1 Feb 0.38 Mr 0.437 Tea 0.082 O2、Na 0.85 Ni 0.2 Feb 0.28 Mr 0.437 Mg 0.082 O2、Na 0.85 Ni 0.1 Feb 0.38 Mr 0.437 Ru 0.082 O2、Na 0.85 Ni 0.1 Feb 0.38 Mr 0.437 Ir 0.082 O2、Na 0.85 Ni 0.1 Feb 0.38 Mr 0.437 Al 0.04 Zn 0.04 O2、Na 0.85 Ni 0.1 Feb 0.38 Mr0.267 Zn 0.082 O2、Na 0.85 Fe 0.4 Mn 0.6 O2、Na 0.92 Ni 0.15 Fe 0.34 Mn 0.45 O2、Na 0.92 Ni 0.15 Fe 0.41 Mn 0.44 O2、Na 0.92 Ni 0.05 Fe 0.5 Mn 0.45 O2、Na 0.92 Fe 0.38 Mn 0.6 O2、Na 0.92 Ni 0.1 Fe 0.38 Mn 0.437 Zn 0.082 O2、Na 0.92 Ni 0.1 Fe 0.38 Mn 0.367 Zn 0.082 O2、Na 0.92 Ni 0.1 Fe 0.494 Mn 0.395 At least one of O2, etc. In the layered oxides represented by these molecular formulas, the Mn element or when containing the doping metal element represented by M, can further play a stabilizing role on the Fe element, further reduce the migration phenomenon of the Fe element, further improve the stability of the iron element in the metal transition layer, and improve the specific capacity and cycle performance of the layered oxide. At the same time, the content of the Ni element in the layered oxide represented by chemical formula (I) can be further reduced, and on the basis of improving the specific capacity and cycle performance of the layered oxide represented by chemical formula (I), the economic cost of the layered oxide can be reduced. In addition, the electrochemical properties and processing properties of the layered oxide can be further improved.

[0150] After testing, in some embodiments, the crystal structure of the layered oxide represented by chemical formula (I) in the above embodiments includes O3-phase layered metal oxide. The O3-phase layered metal oxide refers to a layered oxide with a crystal structure in which the oxygen contained therein is stacked in an ABCABC type. In the embodiments, the layered oxide represented by chemical formula (I) in the above embodiments is mainly O3-phase layered metal oxide. Mainly O3-phase layered metal oxide means that in the layered oxide represented by chemical formula (I), the weight proportion of O3-phase layered metal oxide, that is, the O3-phase layered metal oxide accounts for more than 95% of the total weight of the layered oxide represented by chemical formula (I), and further more than 98%. Of course, the weight proportion of O3-phase layered metal oxide in the layered oxide represented by chemical formula (I) can reach 100%. The higher the weight proportion of the O3-phase layered metal oxide in the layered oxide represented by chemical formula (I), the more desirable it is. The layered oxide represented by chemical formula (I) is primarily present as an O3-phase layered metal oxide or a pure O3-phase layered metal oxide, further enhancing the stability of the Fe element and resulting in the layered oxide having relatively high structural stability, such as that compared to a P2-phase layered metal oxide, and exhibiting higher specific capacity and cycle performance. The crystalline phase of the layered oxide can be analyzed using an XRD diffractometer as described below.

[0151] In some embodiments, electron microscopic analysis shows that the layered oxide crystals represented by Chemical Formula (I) in each of the above embodiments include single crystals, and may also include polycrystals. The single crystals are in bulk form, as shown in Figure 1. Because the layered oxide is primarily an O3-phase layered metal oxide, the O3-phase layered metal oxide is a single crystal and has high structural stability. The crystal morphology of the layered oxide can be analyzed using the micron-scale scanning electron microscopy measurement method described in GB / T 16594-1996.

[0152] In the embodiments, it has been tested that the Dv50 particle size of the layered oxide represented by chemical formula (I) in the above embodiments is 3 to 9 μm, and can be optionally 4.2 to 8.5 μm. In the exemplary embodiments, the Dv50 particle size can be 3 μm, 4 μm, 4.2 μm, 5 μm, 6 μm, 7 μm, 8 μm, 8.5 μm, 9 μm, and other typical but non-limiting particle sizes or a range between any two particle size values. Among them, the Dv50 particle size refers to the particles of the layered oxide powder represented by chemical formula (I). The Dv50 particle size can be the particle size of the layered oxide represented by chemical formula (I) of the above single crystal, or it can be the particle size of the layered oxide represented by chemical formula (I) of the above polycrystalline. Of course, it can also be the particle size of the mixture of the single crystal and polycrystalline particles. The Dv50 particle size of the layered oxide can be measured according to the specific method in GB / T16418, or can be measured with reference to the method in GB / T19077-2016 (Particle Size Distribution by Laser Diffraction Method, pages 4-10).

[0153] The Dv50 particle size of the layered oxide represented by Chemical Formula (I) in each of the above-mentioned embodiments and the size distribution range of the O3 phase layered metal oxide single crystals therein provide the layered oxide with a high compaction density, thereby increasing the compaction density of the positive electrode material of the present application embodiment and improving the energy density of the battery. This also provides the layered oxide with a suitable specific surface area.

[0154] After testing, in the embodiments, the specific surface area (BET) of the layered oxide represented by chemical formula (I) in the above embodiments is 0.4 to 1.5 m 2 / g, optional range is 0.5~0.95m 2 / g, in the example, it can be 0.4m 2 / g, 0.5m 2 / g, 0.6m 2 / g, 0.7m 2 / g, 0.8m 2 / g, 0.9m 2 / g, 0.95m 2 / g、1m 2 / g, 1.1m 2 / g, 1.2m 2 / g, 1.3m 2 / g, 1.4m 2 / g, 1.5m 2 Typical but non-limiting specific surface areas such as 1000 nm / g, or a range between any two specific surface area values, can be used. A specific surface area within this range can improve properties such as the stability of the interface between the layered oxide and the electrolyte, thereby improving electrochemical properties such as battery cycling performance. The specific surface area of ​​the layered oxide can be measured according to the method described in the GB / T19587-2017 standard below.

[0155] After testing, the layered oxides represented by chemical formula (I) in the above embodiments have a powder compaction density of more than 2.7 g / cm under a pressure of 2 tons. 3 , can be selected as 2.7~3.0g / cm 3 In this example, the powder compaction density under 2 tons of pressure can be 2.7g / cm 3 , 2.8g / cm 3 , 2.9g / cm 3 , 3g / cm 3 Typical but non-limiting compacted densities or ranges between any two compacted density values.

[0156] In the embodiments, the layered oxides represented by chemical formula (I) in the above embodiments have a powder compaction density higher than 3.0 g / cm2 under a pressure of 3 tons. 3 , can be selected as 3.0~3.3g / cm 3 In this example, the powder compaction density under 3 tons of pressure can be 3.0g / cm 3 , 3.1g / cm 3 、3.2g / cm 3 , 3.3g / cm 3 Typical but non-limiting compacted densities or ranges between any two compacted density values.

[0157] The above-mentioned powder compaction density should be understood as being greater than or equal to. The above-mentioned powder compaction density range can improve the specific capacity and corresponding electrochemical performance of the battery containing the layered oxide represented by the above chemical formula (I). The powder compaction density can be tested according to the method described in the GB / T24533-2019 standard below.

[0158] Based on the morphology, crystal form, particle size, and compacted density of the layered oxide represented by chemical formula (I) in the above embodiments, in the embodiments, the layered oxide has a charge capacity of 130 to 150 mAh / g at 1.5 to 4.2 V and 0.1 C, and can be optionally 132 to 150 mAh / g; a discharge capacity of 129 to 140 mAh / g, and can be optionally 130 to 144 mAh / g. In other embodiments, the first efficiency of the layered oxide at 1.5 to 4.2 V and 0.1 C is higher than, that is, greater than or equal to 92%, and can be optionally 92 to 98%.

[0159] The charge capacity and discharge capacity in grams, as well as the first efficiency of the layered oxide, refer to the capacity and first efficiency of the layered oxide. Specifically, the layered oxide is prepared as a positive electrode for sodium ion buckle battery and assembled with the negative electrode into a sodium ion buckle battery. The capacity and first efficiency are obtained by testing the sodium ion buckle battery. The capacity and first efficiency of the layered oxide indicate that the structural stability of the layered oxide crystal has been significantly improved, the structural stability is good during the sodium insertion and extraction process, and the layered oxide has high capacity and cycle performance.

[0160] In the embodiment, the sodium ion button cell used to test the charge gram capacity and discharge gram capacity of the layered oxide and the first effect is assembled according to the following method:

[0161] Positive electrode sheet: The layered oxide represented by the above chemical formula (I) is used as the positive electrode active material, and is thoroughly stirred and mixed with a conductive agent carbon nanotube, a conductive agent carbon black, and a binder polyvinylidene fluoride (PVDF) in a weight ratio of 95:0.5:2:2.5 in an appropriate amount of solvent NMP to form a uniform positive electrode slurry; the positive electrode slurry is evenly coated on the surface of a 13 μm positive electrode current collector aluminum foil, and after drying and cold pressing, a positive electrode sheet is obtained;

[0162] Negative electrode sheet: Add hard carbon, conductive agent SP, and CMC binder to deionized water in a weight ratio of 8:1:1 and stir thoroughly to form a uniform negative electrode slurry. The negative electrode slurry is evenly coated on the surface of a 6μm copper foil, dried, and cold pressed to obtain a negative electrode sheet.

[0163] Electrolyte: 1 M NaPF6 / (EC / DEC, volume ratio 1:1);

[0164] Diaphragm: Glass fiber;

[0165] Sodium ion button cell assembly: The above-mentioned positive electrode sheet, glass fiber film and negative electrode sheet are stacked in order to form a button cell assembly after assembly. The electrode assembly is placed in a packaging shell, and 1M NaPF6 / (EC / DEC, volume ratio 1:1) electrolyte is added. After packaging, formation, and static standing, a sodium ion battery is obtained.

[0166] Based on the above embodiments, the positive electrode material of the present application can only contain the layered oxide represented by chemical formula (I) in the above embodiments. Of course, it can also further include other positive electrode materials, such as one or more of polyanion compounds, Prussian blue compounds, and other layered oxides.

[0167] In an exemplary embodiment, the polyanion compound may include at least one of sodium vanadium phosphate, sodium iron pyrophosphate, sodium iron phosphate, sodium fluoroferric phosphate, and the like.

[0168] In an exemplary embodiment, the Prussian blue compound may include at least one of Na2Fe[Fe(CN)6], Na2Mn[Fe(CN)6], Na2Mn[Mn(CN)6], etc.

[0169] The above-mentioned other positive electrode materials can, together with the layered oxide represented by the above-mentioned chemical formula (I), further improve the electrochemical properties such as energy density, reversible capacity, and cycle performance of the battery containing the positive electrode material of the embodiment of the present application.

[0170] Preparation method of positive electrode material

[0171] In a second aspect, the present invention provides a method for preparing the positive electrode material of the above-mentioned embodiment. In some embodiments, the method for preparing the positive electrode material of the present invention comprises the following steps:

[0172] S10: Provides Na a Ni b Fe c Mn d M e O f precursors;

[0173] S20: The precursor is sintered to obtain a chemical formula of Na a Ni b Fe c Mn d M e O f layered oxides.

[0174] In step S10 of the method for preparing the positive electrode material according to the embodiment of the present application, Na a Ni b Fe c Mn d M e O f The precursor of is the precursor of the layered oxide represented by the chemical formula (I) contained in the positive electrode material of the above-mentioned embodiment of the application. a Ni b Fe c Mn d M e O f The ranges of a, b, c, d, e and f are as follows:

[0175] 0.8≤a≤1, optionally 0.85≤a≤1; 0≤b≤0.2, optionally 0≤b≤0.18, further 0.05≤b≤0.2; 0.25≤c≤0.5, optionally 0.3≤c≤0.5; 0.26≤d≤0.6, optionally 0.3≤d≤0.6; 0≤e≤0.1, optionally 0.02≤e≤0.1, further 0.03≤e≤0.1; 1.8≤f≤2, b+c+d+e≤1; M is an active or / and inert doping metal element, in an exemplary embodiment, the doping metal element includes at least one of Zn, V, Cr, Al, Sc, Sn, Sb, Zr, Nb, Ti, Mg, Cu, Ru, and Ir. The sintering treatment in step S20 is to make the Na in step S10 a Ni b Fe c Mn d M e O f The precursor is reacted to generate the layered oxide represented by the chemical formula (I) contained in the positive electrode material of the above application embodiment.

[0176] The positive electrode material preparation method of the present application embodiment is to a Ni b Fe c Mn d M e O f The precursor is sintered to generate the positive electrode material of the above-mentioned embodiment of the application containing the chemical formula Na a Ni b Fe c Mn d M e O f The layered oxide shown. Therefore, the stoichiometric ratio of Fe and Mn in the layered oxide prepared by the positive electrode material preparation method of the present application embodiment can effectively reduce the migration of iron elements, improve the structural stability of the layered oxide during the sodium insertion and extraction process, so that the prepared layered oxide has high gram capacity and energy density and good cycle performance. At the same time, it also has properties such as high sodium ion diffusion rate, thereby improving the DCR growth of the battery cell. In addition, for Na a Ni b Fe c Mn d M e O f The sintering conditions of the precursor can be effectively controlled, thereby improving the chemical formula Na a Ni b Fe c Mn d M e O fThe stability of the structure and electrochemical properties of layered oxides.

[0177] Step S10:

[0178] Na in step S10 a Ni b Fe c Mn d M e O f The precursor can be based on Na a Ni b Fe c Mn d M e O f The sodium source, nickel source, manganese source, iron source and the doping element source represented by M are prepared by a solid phase method or a precipitation method according to the stoichiometric amount of the elements contained, such as moles or the mass ratio converted according to moles.

[0179] When the solid phase method was used to prepare Na a Ni b Fe c Mn d M e O f When the precursor is Na a Ni b Fe c Mn d M e O f The precursor can be prepared according to a method comprising the following steps:

[0180] Step S11: According to Na a Ni b Fe c Mn d M e O f The sodium source, nickel source, manganese source, iron source and the doping element source shown in M ​​are solid-phase mixed to obtain Na a Ni b Fe c Mn d M e O f precursor.

[0181] In step S11, solid phase mixing treatment is relative to liquid phase mixing, which generally means that no solvent is added during the mixing process, such as no water is added. The sodium source, nickel source, manganese source, iron source and the doping element source solid shown in M ​​are dry mixed under solvent-free conditions.

[0182] In order to improve the uniformity of mixing of the sodium source, nickel source, manganese source, iron source, and doping element source shown in M ​​during the solid-phase mixing process, in an embodiment, the nickel source, manganese source, iron source, and doping element source shown in M ​​can be mixed first, and then the sodium source can be added and mixed again. This improves the mixing uniformity of the sources and improves the safety of the solid-phase mixing process.

[0183] In the embodiment, the mixing treatment can be covered but not limited to ball milling treatment, as long as it can improve the uniformity of mixing of the sodium source, nickel source, manganese source, iron source and the doping element source shown in M, it is within the scope disclosed in the embodiment of the present application. In the embodiment, when the mixing treatment is ball milling treatment, the ball milling rate can be controlled to be 300 to 1000 rpm, optionally 400 to 600 rpm; the ball milling time can be 1h to 6h, optionally 2h to 4h. By ball milling treatment, the mixing uniformity of each source can be improved, thereby ultimately improving the Na a Ni b Fe c Mn d M e O f The stability of the structure and electrochemical properties of layered oxides.

[0184] In an exemplary embodiment, the sodium source may be a sodium salt, such as at least one of sodium carbonate, sodium hydroxide, and the like.

[0185] In an exemplary embodiment, the nickel source may be a soluble or insoluble nickel compound, such as nickel oxide (NiO) or a nickel salt, etc. The nickel salt may include at least one of nickel nitrate, nickel carbonate, nickel hydroxide, nickel sulfate, etc.

[0186] In an exemplary embodiment, the manganese source may be a soluble or insoluble manganese compound, such as manganese oxide (Mn2O3) or a manganese salt, etc. The manganese salt may include at least one of manganese nitrate, manganese carbonate, manganese hydroxide, manganese sulfate, etc.

[0187] In an exemplary embodiment, the iron source may be a soluble or insoluble iron compound, such as iron oxide (eg, Fe2O3) or an iron salt, etc. The iron salt may include at least one of iron nitrate, iron carbonate, iron hydroxide, iron sulfate, etc.

[0188] In an exemplary embodiment, the source of the doping metal element shown in M ​​may be a soluble or insoluble compound of the doping metal element shown in M, such as an oxide of the doping metal element shown in M ​​or a salt of the doping metal element shown in M. The salt of the doping metal element shown in M ​​may include at least one of a nitrate, carbonate, hydroxide, sulfate, etc. of the doping metal element shown in M.

[0189] The types of the above sodium source, nickel source, manganese source, iron source and doping element source shown in M ​​can be effectively mixed uniformly during the mixing process to improve Na a Ni b Fe c Mn d M e O f The precursor to generate Na a Ni b Fe c Mn d M e O f Structure and chemical stability of layered oxides.

[0190] The Na prepared by the solid phase method a Ni b Fe c Mn d M e O f After the precursor is sintered in step S20, the generated Na a Ni b Fe c Mn d M e O f Layered oxides are mostly single crystals.

[0191] When the precipitation method is used to prepare Na a Ni b Fe c Mn d M e O f When the precursor is Na a Ni b Fe c Mn d M e O f The precursor can be prepared according to a method comprising the following steps:

[0192] Step S12: According to Na a Ni b Fe c Mn d M e O f A soluble nickel source, a soluble manganese source, a soluble iron source and a soluble doping element source represented by M are prepared into a mixed solution in a stoichiometric ratio of elements, and at least one of a precipitant and a complexing agent is added thereto for co-precipitation to obtain a precipitated mixture;

[0193] Step S13: Mixing the precipitated mixture with a sodium source to obtain Na a Ni bFe c Mn d M e O f precursor.

[0194] In step S12, at least one of the precipitant and the complexing agent should be a compound that can precipitate nickel, manganese, iron and the doping metal element shown in M ​​in the nickel source, soluble manganese source, soluble iron source and the soluble doping element source shown in M. For example, in the embodiment, the precipitant may include at least one of alkali metal hydroxides, carbonates, etc.

[0195] In an embodiment, the complexing agent may include an inorganic or organic complexing agent. In a demonstration example, the inorganic complexing agent may include at least one of ammonia water, ammonium bicarbonate, ammonium sulfate, ammonium carbonate, etc.; the organic complexing agent may include at least one of citric acid, tartaric acid and disodium ethylenediaminetetraacetic acid, ethylenediaminetetraacetic acid (EDTA), aminotriacetic acid (NTA), etc.

[0196] These types of precipitants and complexing agents can effectively precipitate nickel, manganese, iron and the doping elements represented by M.

[0197] In the embodiment, at least one of the precipitant and the complexing agent should be in excess relative to the total amount of metal elements contained in the mixed solution, such as the total molar amount, to ensure that all metal elements contained in the mixed solution are fully precipitated to increase the Na a Ni b Fe c Mn d M e O f When the organic complexing agent is added in step S12, the prepared Na a Ni b Fe c Mn d M e O f After the precursor is sintered in step S20, the generated Na a Ni b Fe c Mn d M e O f The layered oxides are mostly polycrystalline; when no organic complexing agent is added in step S12, the prepared Na a Ni b Fe c Mn d M e O f After the precursor is sintered in step S20, the generated Na a Ni b Fec Mn d M e O f Layered oxides are mostly single crystals.

[0198] In an exemplary embodiment, the soluble nickel source may include at least one of nickel acetate, nickel chloride, nickel nitrate, and nickel sulfate.

[0199] In an exemplary embodiment, the soluble manganese source may include at least one of manganese nitrate, manganese sulfate, and manganese halide.

[0200] In an exemplary embodiment, the soluble iron source may include at least one of iron nitrate, manganese sulfate, and halide.

[0201] In an exemplary embodiment, the soluble doping metal element source M may include at least one of nitrates, manganese sulfate, halides, and the like of the doping metal element M.

[0202] The types of the above-mentioned soluble nickel source, soluble manganese source, soluble iron source and soluble doping element source represented by M all have good solubility and can quantitatively control the stoichiometric ratio of each metal element in the precipitation mixture.

[0203] The mixing ratio between the sodium source and the precipitation mixture in step S13 should satisfy Na a Ni b Fe c Mn d M e O f The mixing process can be a solid phase mixing process or a process in which a soluble sodium source is dissolved and mixed with the precipitation mixture, and then the solvent is removed.

[0204] In an exemplary embodiment, the sodium source may be a sodium salt, such as at least one of sodium carbonate, sodium hydroxide, and the like.

[0205] In addition, there is no sequential order between the above step S11, step S12 and step S13.

[0206] Step S20:

[0207] In step S20, Na in step S10 is a Ni b Fe c Mn d M e O f After the precursor is sintered, a chemical formula of Na a Ni b Fe c Mn d M e O fThe study found that the sintering conditions have a great influence on the formation of Na a Ni b Fe c Mn d M e O f The structural stability and electrochemical performance of the layered oxide are affected to a certain extent. In some embodiments, the sintering temperature can be controlled within a range of 700°C to 980°C, optionally 750°C to 950°C. In exemplary embodiments, the sintering temperature can be 700°C, 750°C, 800°C, 850°C, 900°C, 950°C, 980°C, or any other typical but non-limiting temperature range, or any temperature range between any two values.

[0208] At the above sintering temperature, the sintering treatment time can be 3 to 20 hours, optionally 5 to 12 hours. In the exemplary embodiment, it can be 3 hours, 4 hours, 5 hours, 8 hours, 10 hours, 12 hours, 15 hours, 18 hours, 20 hours and other typical but non-limiting hours or any range between two hours.

[0209] By controlling the stability and time of the sintering process within the above range, the Na a Ni b Fe c Mn d M e O f The precursor reacts to generate Na a Ni b Fe c Mn d M e O f layered oxides, and can further increase the Na a Ni b Fe c Mn d M e O f The structural stability of layered oxides during the process of sodium insertion and removal further improves the high specific capacity, energy density and cycle performance of layered oxides. a Ni b Fe c Mn d M e O f The content of O3 phase layered metal oxide and the single crystal content in the layered oxide control the single crystal size and the particle size of the layered oxide, thereby improving the compaction density and other properties of the layered oxide.

[0210] In an embodiment, the temperature of the sintering process can be increased to the temperature of the sintering process at a heating rate of 2 to 15°C / min. The heating rate can be further controlled to be 4 to 10°C / min. In an exemplary embodiment, the heating rate can be a typical but non-limiting rate such as 2°C / min, 4°C / min, 6°C / min, 8°C / min, 10°C / min, 12°C / min, 15°C / min, 17°C / min, 18°C / min, 20°C / min, or a range between any two rate values. By controlling the heating rate of the sintering process, such as controlling it within this heating rate range, the Na a Ni b Fe c Mn d M e O f The crystals of the layered oxide are perfect and complete, such as improving the uniformity of the crystal morphology.

[0211] In addition, the sintering process in the above step S20 should be understood to be carried out in an oxygen environment. For example, in the embodiment, the sintering process can be carried out in air or in an oxygen-containing protective atmosphere, such as oxygen-containing nitrogen or other inert atmospheres.

[0212] positive electrode

[0213] In a third aspect, embodiments of the present application provide a positive electrode. In some embodiments, the positive electrode of the present application includes a current collector and a positive electrode active material layer. The positive electrode active material layer is disposed on the surface of the current collector, and the positive electrode active material layer contains the positive electrode material of the above-mentioned embodiments of the present application.

[0214] In the positive electrode of the embodiment of the present application, the current collector refers to a structure for collecting current and for transmitting electrons. The positive electrode active material layer refers to a layer structure containing a positive electrode active material, which is a key substance participating in the battery chemical reaction in the positive electrode. Among them, the positive electrode active material includes the positive electrode material of the embodiment of the present application. The positive electrode active material layer is combined with the current collector, which means that the positive electrode active material layer is at least combined with the surface of the current collector. In addition, the positive electrode can be a pole piece, which means that the positive electrode has a sheet-like morphology. Of course, it can also be set to other morphologies as needed.

[0215] Since the positive electrode active material layer of the positive electrode of the embodiment of the present application contains the positive electrode material of the embodiment of the present application, the positive electrode has a relatively high gram capacity and good cycle performance.

[0216] In the embodiments, the current collector contained in the positive electrode of the present application includes, but is not limited to, a metal current collector, a carbon current collector, a conductive resin current collector, a metal and resin composite current collector, and more specifically, aluminum, copper, nickel, titanium, iron, and their respective alloys, stainless steel, carbon fiber, carbon nanotubes (CNTs), graphite, and the like. In the embodiments, the current collector can also be a dense film layer or a porous film layer. In the embodiments, the current collector can be, but is not limited to, aluminum foil or porous aluminum foil.

[0217] In the embodiments, the positive electrode active material layer contained in the positive electrode of the present application and the current collector can be at least laminated on the surface of the current collector. When the surface layer of the current collector has a porous structure or the current collector itself has a porous structure, the positive electrode active material layer can be at least partially embedded in the current collector.

[0218] In some embodiments, the positive electrode active material layer is provided at least on the surface of the current collector, and the structure may be as shown in FIG2 , where the positive electrode active material layer 12 is laminated on one surface of the current collector 11. When the surface of the current collector 11 has a porous structure or the current collector 11 is a porous structure as a whole, the positive electrode active material layer 12 may not only be laminated on the surface of the current collector 11 but also further extend into the porous structure of the current collector 11.

[0219] In other embodiments, the positive electrode active material layer is provided at least on the surface of the current collector, and the structure can be as shown in Figure 3. The current collector 11 has two surfaces arranged opposite to each other, and the positive electrode active material layer 12 is laminated on the two opposite surfaces of the current collector 11. When at least one of the two surfaces of the current collector 11 has a porous structure or the current collector 11 is a porous structure as a whole, the positive electrode active material layer 12, in addition to being laminated on the two surfaces of the current collector 11, can also further extend into the porous structure of the current collector 11.

[0220] As an embodiment of the present application, in the above-mentioned positive electrode active material layer, the mass content of the layered oxide represented by chemical formula (I) contained in the positive electrode material of the above-mentioned embodiment of the present application in the positive electrode active material layer can be 90% to 99%, optionally 94% to 98%. In exemplary embodiments, it can be 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% and other typical but non-limiting contents or a range between any two content values. The layered oxide in this content range can effectively improve the energy density of the positive electrode and has good cyclability.

[0221] The positive electrode active material layer contained in each of the above-mentioned embodiments generally includes, in addition to the above-mentioned positive electrode active material components, a binder, a conductive agent, and other components. The binder can enhance the mechanical properties between the positive electrode active material layer itself and the current collector. The conductive agent can effectively improve the conductivity of the positive electrode, such as reducing the resistance of the positive electrode.

[0222] In an embodiment, the mass content of the binder contained in the above-mentioned positive electrode active material layer can be 0.5% to 5%, optionally 1% to 3%. In a demonstration example, it can be 0.5%, 0.8%, 1%, 1.3%, 1.5%, 1.8%, 2%, 2.3%, 2.5%, 2.8%, 3% and other typical but non-limiting contents or a range between any two content values.

[0223] In an embodiment, the binder may include one or more of an oil-soluble binder, a water-soluble binder, an emulsion-type binder, etc. In an exemplary embodiment, the oil-soluble binder may include one or more of polyvinylidene fluoride, polyimide, polytetrafluoroethylene, polybutyl acrylate, polyacrylonitrile, etc.; in an exemplary embodiment, the water-soluble binder may include one or more of carboxymethyl cellulose, carboxymethyl cellulose salt, polyacrylic acid, polyacrylic acid salt, polyvinyl alcohol, sodium alginate, cyclodextrin, etc.; in an exemplary embodiment, the emulsion-type binder may include one or more of styrene-butadiene rubber, vinyl acetate resin, acrylic resin, and chlorinated rubber.

[0224] The content within this range and the above-mentioned types of binders can effectively enhance the mechanical properties of the positive electrode active material layer and the bonding strength between the positive electrode active material layer and the current collector, and can effectively improve the cycle performance of the positive electrode.

[0225] In an embodiment, the mass content of the conductive agent contained in the above-mentioned positive electrode active material layer can be 0.5% to 5%, optionally 1% to 3%. In a demonstration example, it can be 0.5%, 0.8%, 1%, 1.3%, 1.5%, 1.8%, 2%, 2.3%, 2.5%, 2.8%, 3% and other typical but non-limiting contents or a range between any two content values.

[0226] In an embodiment, the conductive agent may include at least one of a granular conductive agent and a linear conductive agent. The granular conductive agent may include one or more of acetylene black (SP), conductive carbon black (super-P), Ketjen black, graphene, and the like. The linear conductive agent may include one or more of carbon nanotubes, carbon fibers, and conductive oxide nanowires. The granular conductive agent is a conductive agent with a nonlinear particle morphology, as opposed to a linear conductive agent. A linear conductive agent is a conductive agent with a one-dimensional fiber morphology.

[0227] The content within this range and the above-mentioned type of conductive agent can effectively improve the conductivity of the positive electrode active material layer.

[0228] In the embodiments, the conductive agent contained in the positive electrode active material layer of each of the above embodiments includes a linear conductive agent and a granular conductive agent. The linear conductive agent has a mass content in the positive electrode active material layer of 0.1% to 2.5%, optionally 0.2% to 0.8%. In exemplary embodiments, the linear conductive agent may be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 1%, 1.3%, 1.5%, 1.8%, 2%, 2.3%, 2.5%, or any other typical but non-limiting content, or a range between any two content values. Since the crystals of the layered oxide represented by chemical formula (I) contained in the positive electrode material of the above-mentioned embodiment of the application include single crystals, and the morphology of the single crystals is blocky, a linear conductive agent is added to the positive electrode active material layer, and the content of the linear conductive agent is controlled within this range, so that the linear conductive agent can form a rich conductive network structure in the positive electrode active material layer, and the linear conductive agent can also be entangled on the surface of the blocky single crystal particles. In some embodiments, when the positive electrode active material layer also includes a particulate conductive agent, the particulate conductive agent can be effectively dispersed in the gaps of the positive electrode material. In this way, the linear conductive agent constructs a long-range conductive network structure in the positive electrode active material layer, and the particulate conductive agent constitutes a short-range conductive structure. Therefore, the conductive synergistic effect played by the linear conductive agent and the particulate conductive agent in the positive electrode active material layer effectively improves the conductivity of the positive electrode active material layer and can significantly reduce the internal resistance of the positive electrode.

[0229] In an embodiment, the aspect ratio of the linear conductive agent can be controlled to be 40 to 3000:1, or optionally 50 to 2500:1. In exemplary embodiments, typical but non-limiting aspect ratios such as 40:1, 50:1, 100:1, 500:1, 1000:1, 1500:1, 2000:1, 2500:1, and 3000:1 can be used, or ranges between any two aspect ratios. The aspect ratio refers to the ratio of the length of the linear conductive agent to its diameter.

[0230] In a further embodiment, the length of the linear conductive agent can be selected to be 0.5 to 5 μm, or optionally 0.5 to 2 μm. In the exemplary embodiment, the length can be 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, or other typical but non-limiting lengths, or a range between any two length values.

[0231] In a further embodiment, the diameter of the linear conductive agent can be selected to be 2 to 10 nm, or optionally 3 to 7 nm. In the exemplary embodiment, the diameter can be 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, or other typical but non-limiting diameters, or a range between any two diameter values.

[0232] By selecting and controlling the length, diameter and / or aspect ratio of the above-mentioned linear conductive agent within the above-mentioned range, the linear conductive agent can construct a richer long-range conductive network structure in the positive electrode active material layer; further adding a particulate conductive agent can enhance the conductive synergistic effect of the linear conductive agent and the particulate conductive agent, thereby further improving the conductivity of the positive electrode active material layer.

[0233] In the embodiments, the positive electrode active material layer in the positive electrode of each embodiment above may contain other additives in addition to the positive electrode active material, binder, conductive agent and other components. In the embodiments, the additives may include but are not limited to functional components such as sodium supplement additives.

[0234] In some embodiments, the content of the positive electrode active material layer on a single surface of the current collector in each of the above embodiments, that is, the coating weight (CW), is 250-330 mg / 1540.25 mm 2 , optional: 280~320mg / 1540.25mm 2 In the example, it can be 250mg / 1540.25mm 2 、260mg / 1540.25mm 2 、270mg / 1540.25mm 2 、280mg / 1540.25mm 2 、290mg / 1540.25mm 2 、300mg / 1540.25mm 2 、310mg / 1540.25mm 2 、320mg / 1540.25mm 2 、330mg / 1540.25mm 2 Typical but non-limiting contents or ranges between any two content values ​​are provided. The coating weight refers to the weight of the positive electrode active material layer per unit area. A coating weight within this range can help improve the energy density of the battery.

[0235] In some embodiments, the compaction density of the positive electrode in the above embodiments can be 2.6 to 3.2 g / cm 3 , can be selected as 2.8~3.0g / cm 3 In the example, it can be 2.6g / cm 3 , 2.7g / cm 3 , 2.8g / cm 3 , 2.9g / cm 3 , 3.0g / cm 3 , 3.1g / cm 3 、3.2g / cm 3Typical but non-limiting compacted densities, such as [ 0.05 ], or a range between any two compacted density values, are provided. The compacted density refers to the weight of the positive electrode active material layer per unit volume. A compacted density within this range can improve the energy density of the battery and provide good interfacial stability with the electrolyte.

[0236] In some embodiments, the porosity of the positive electrode active material layer in the above embodiments can be 35% to 65%, optionally 40% to 58%. In exemplary embodiments, it can be 35%, 38%, 40%, 43%, 45%, 48%, 50%, 53%, 55%, 58%, 60%, 63%, 65%, or other typical but non-limiting porosities or a range between any two porosity values. The porosity refers to the percentage of the total volume of pores contained in the unit volume of the positive electrode active material layer to the unit volume of the positive electrode active material layer. The porosity in this range enables the positive electrode sheet to have the above-mentioned compaction density, which is beneficial to improving the energy density of the battery and improving the wettability of the electrolyte.

[0237] In some embodiments, the positive electrode in each of the above embodiments is a pole piece. The sheet resistance of the positive electrode active material layer in each of the above embodiments can be 0.5 to 5 mΩ, optionally 0.5 to 3 mΩ. In exemplary embodiments, it can be a typical but non-limiting sheet resistance such as 0.5 mΩ, 1 mΩ, 1.5 mΩ, 2 mΩ, 2.5 mΩ, 3 mΩ, 3.5 mΩ, 4 mΩ, 4.5 mΩ, 5 mΩ, or a range between any two sheet resistance values. The pole piece has a sheet-like morphology as described above, and therefore has two opposing surfaces. The sheet resistance refers to the resistance value between one surface of the sheet-like positive electrode and the other opposing surface. A sheet resistance in this range can effectively improve battery performance such as efficiency and lifespan.

[0238] In some embodiments, the positive electrode is a pole piece in each of the above embodiments, and the ratio of the thickness from one surface of the pole piece to the other opposite surface to the thickness of the current collector is 7 to 16:1, optionally 8 to 15:1. In exemplary embodiments, it can be a typical but non-limiting ratio such as 7:1, 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, or a range between any two ratios. The thickness refers to the vertical distance from one surface of the layer structure to the other opposite surface. When a positive electrode active material layer is provided on one surface of the current collector as shown in FIG2 , the thickness from one surface of the pole piece to the other opposite surface refers to the sum of the thickness of one positive electrode active material layer plus the thickness of the current collector; when both surfaces of the current collector as shown in FIG3 contain positive electrode active material layers, the thickness from one surface of the pole piece to the other opposite surface refers to the sum of the thickness of two positive electrode active material layers plus the total thickness of the current collector.

[0239] In an embodiment, the thickness of the positive electrode active material layer contained in the electrode sheet can be controlled to be 91 to 156 μm, and further can be 95 to 150 μm. In exemplary embodiments, the thickness can be 91 μm, 95 μm, 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, 150 μm, 156 μm, or other typical but non-limiting thicknesses, or a range between any two thickness values. In an embodiment, the thickness of the current collector can be, but is not limited to, 13 to 15 μm.

[0240] By controlling the total thickness of the electrode and the thickness of the current collector within the above ratio range or specific thickness range, the bonding strength between the positive electrode active material layer and the current collector can be improved, the mechanical strength of the electrode structure can be improved, the cycle performance of the electrode can be improved, and at the same time, it is beneficial to improve the energy density of the battery.

[0241] Preparation method of positive electrode:

[0242] The present application also provides a method for preparing the positive electrode of the above embodiment. In some embodiments, the method for preparing the positive electrode of the above embodiment includes the following steps:

[0243] S30: Mixing the components including the positive electrode active material, the binder, the conductive agent and the like in a solvent in proportion to prepare a positive electrode slurry;

[0244] S40: The positive electrode slurry is subjected to a film-forming treatment on the current collector to form a positive electrode active material layer to obtain a positive electrode.

[0245] Step S30:

[0246] The positive electrode active material in step S30 includes the positive electrode material of the above-mentioned embodiment of the application, specifically, includes the layered oxide represented by the above-mentioned chemical formula (I).

[0247] In step S30, the positive electrode active material, binder, conductive agent and other components can be mixed according to the content ratio of the corresponding components in the positive electrode active material layer of the positive electrode. The solvent can be an organic solvent or water suitable for preparing positive electrode slurry.

[0248] The mixing process in step S30 can be performed according to conventional electrode slurry preparation methods, such as, but not limited to, stirring, until the components are evenly dispersed to form a stable positive electrode slurry. Of course, the viscosity and other properties of the positive electrode slurry should meet the requirements of the film forming process so that a positive electrode active material layer that meets the quality requirements can be formed on the current collector.

[0249] Step S40:

[0250] Based on the positive electrode slurry components prepared in step S30, the positive electrode active material layer prepared in step S40 is the positive electrode active material layer contained in the positive electrode of the embodiment of the present application.

[0251] The positive electrode slurry is formed into a film on the current collector in step S40 according to conventional methods for forming a positive electrode active material layer. For example, in the embodiment, the electrode slurry may be first formed into a wet film on the current collector; then, a drying process is performed to evaporate the solvent, thereby drying the wet film; and then, the dried film layer is roller-pressed to form a positive electrode active material layer, thereby obtaining a positive electrode.

[0252] Of course, the positive electrode active material layer can also be prepared by improving the conventional positive electrode active material layer preparation method, or by adopting a new method. As long as the electrode slurry in step S30 is used to prepare the positive electrode active material layer on the current collector, it is within the scope of the embodiments disclosed in the present application.

[0253] In addition, the film forming processing conditions in S40 can be controlled and adjusted, such as the conditions for forming a wet film on the current collector of the positive electrode slurry configured in step S30, the conditions for the roller pressing process, etc., and the related properties of the formed positive electrode active material layer can be controlled and adjusted, such as controlling and adjusting the content of the positive electrode active material layer on the single side of the current collector to 250-330 mg / 1540.25 mm as mentioned above. 2 Range, compaction density control and adjustment to 2.6 ~ 3.2g / cm 3 range, the porosity is controlled and adjusted to the range of 35% to 65% as mentioned above, and the diaphragm resistance of the electrode is controlled and adjusted to the range of 0.5 to 5 mΩ as mentioned above.

[0254] Battery

[0255] In a fourth aspect, an embodiment of the present application also provides a sodium battery.

[0256] In an embodiment, the sodium battery of the present application may include any one of a sodium battery cell, a battery module, and a battery pack.

[0257] Sodium battery cells:

[0258] A sodium battery cell, also known as a sodium battery cell, refers to a battery cell that includes the outer packaging of the battery and the electrode assembly encapsulated within the outer packaging. The number of electrode assemblies contained in a battery cell can be one or more, and can be adjusted according to actual needs.

[0259] The outer packaging of the sodium battery cell can be a hard shell, such as a hard plastic shell, aluminum shell, or steel shell; or a soft shell, such as a bag-type soft shell. The soft shell can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate. The outer packaging can be cylindrical, square, or any other shape. The outer packaging shape embodies the shape of the sodium battery cell, so the shape of the sodium battery cell can also be cylindrical, square, or any other shape that corresponds to the outer packaging. In this example, the sodium battery cell can be a square-shaped battery cell 20 as shown in Figure 4.

[0260] In some embodiments, as shown in FIG5 , the outer packaging of a battery cell 20 may include a housing 21 and a cover plate 23 . The housing 21 may include a bottom plate and side plates connected to the bottom plate, which together form a receiving cavity. The housing 21 has an opening communicating with the receiving cavity, and the cover plate 23 is used to cover the opening, thereby sealing the receiving cavity. One or more electrode assemblies 22 are enclosed in the receiving cavity.

[0261] In the embodiment, the sodium battery cell may be a sodium battery cell containing an electrolyte, or a sodium battery cell containing a solid electrolyte.

[0262] In the case of a sodium battery cell containing an electrolyte, the electrode assembly contained in the sodium battery cell generally includes a positive electrode, a negative electrode, and a separator. The positive and negative electrodes are alternately stacked, and the separator is stacked between the positive and negative electrodes to isolate the positive and negative electrodes. The positive electrode, separator layer, and negative electrode can be formed into a laminated electrode assembly through a lamination process, or a wound electrode assembly through a winding process. The separator-containing electrode assembly is placed in an outer packaging, and the electrolyte is injected to soak the electrode assembly. After packaging, the sodium battery cell is obtained.

[0263] In the case of a sodium battery cell containing a solid electrolyte, the electrode assembly typically includes a positive electrode, a negative electrode, and a solid electrolyte. The positive and negative electrodes are alternately stacked, with the solid electrolyte layered between them to act as an insulator, separating the positive and negative electrodes. The electrode assembly containing the solid electrolyte is placed in an outer packaging, and encapsulated to form a sodium battery cell.

[0264] In each of the above-mentioned sodium battery cells, the positive electrode contained in the electrode assembly is the positive electrode of the embodiment of the above-mentioned application, that is, its positive electrode active material layer contains the positive electrode material of the embodiment of the above-mentioned application, specifically, the layered oxide represented by the above-mentioned chemical formula (I).

[0265] In this way, the sodium battery cell has high energy density and good cycle performance.

[0266] For example, in the embodiments, the sodium battery cell has been tested to have an energy density of 120-150 Wh / kg. At 25°C and 0.33°C / 1°C, the capacity retention rate per 1000 cls can reach 70%-85%. In other embodiments, the sodium battery cell can have an operating voltage of 1.5-4.0V while maintaining good cycle performance.

[0267] In each of the above-mentioned sodium battery cells, the negative electrode contained in the electrode assembly includes a negative electrode current collector and, optionally, a negative electrode active material layer disposed on the surface of the negative electrode current collector, wherein the negative electrode active material layer contains a negative electrode active material. In embodiments, the negative electrode current collector may include, but is not limited to, a metal or a composite current collector. For example, the metal may include sodium, sodium alloys, copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, silver alloys, etc. When sodium or a sodium alloy is used as the negative electrode current collector, since the sodium or sodium alloy itself can also serve as the negative electrode active material, the negative electrode plate may not contain a negative electrode active material layer, and the sodium or sodium alloy serves as both the current collector and the negative electrode active material.

[0268] The composite current collector may include a composite material of a polymer and a metal. The polymer may include, but is not limited to, polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc., and the metal may include, but is not limited to, sodium, copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. The composite current collector may be obtained by blending the polymer and the metal, or may be coated on at least one side of the polymer by electroplating, coating, or other methods.

[0269] When the negative electrode includes a negative electrode active material layer, the negative electrode active material in the negative electrode active material layer may include, but is not limited to, a mixture or composite material of any one or more of a carbon-based material, an alloy material, a titanium-based material, and sodium metal. Carbon-based materials include, but are not limited to, one or more of graphite, soft carbon, hard carbon, carbon microspheres, and carbon fibers; alloy materials include, but are not limited to, one or more of sodium-tin alloy, sodium-germanium alloy, and sodium-antimony alloy; and titanium-based materials include, but are not limited to, one or more of titanium dioxide, titanates, and titanium phosphates.

[0270] The mass content of the negative electrode active material in the negative electrode active material layer can be 85% to 98%, optionally 95% to 98%. In the exemplary embodiment, it can be 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% and other typical but non-limiting contents or a range between any two content values.

[0271] The negative electrode active material layer may also include at least one of a conductive agent and a binder. The conductive agent is used to collect current between the negative electrode active materials and between the active materials and the current collector, improving electronic conductivity. It also promotes electrolyte wetting of the negative electrode sheet. The binder improves the bonding strength between the various substances in the negative electrode active material layer and between the active layer and the current collector.

[0272] In an embodiment, the conductive agent may comprise 0.5% to 10% by weight of the negative electrode active material layer. In exemplary embodiments, the conductive agent may comprise 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any other typical but non-limiting content, or a range between any two content values. Other content values ​​may also be used as needed. In exemplary embodiments, the conductive agent comprises one or more of acetylene black (SP), carbon nanotubes, conductive carbon black (super-P), Ketjen black, carbon fiber, and graphene.

[0273] In an embodiment, the binder content in the negative electrode active material layer may be 0.5% to 10% by weight. In exemplary embodiments, the binder content may be 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or other typical but non-limiting content, or a range between any two content values. Other content values ​​may also be set as needed. In exemplary embodiments, the binder includes, but is not limited to, one or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, polyimide, polytetrafluoroethylene, polybutyl acrylate, polyacrylonitrile, carboxymethyl cellulose, carboxymethyl cellulose salt, polyacrylic acid, polyacrylate, polyvinyl alcohol, sodium alginate, cyclodextrin, styrene-butadiene rubber, vinyl acetate resin, acrylic resin, and chlorinated rubber.

[0274] In an embodiment, the negative electrode active material layer may optionally include a thickener, such as, but not limited to, carboxymethyl cellulose (CMC). The mass content of the thickener in the negative electrode active layer may be set to 0.5% to 5%. In exemplary embodiments, the content may be 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or other typical but non-limiting content, or a range between any two content values.

[0275] In the embodiments, when each of the aforementioned sodium battery cells includes a separator, the separator, as described above, is disposed between the positive and negative electrodes to separate them. The separator prevents electrons from freely passing through the battery, preventing contact and short circuits between the electrodes, while allowing sodium ions in the electrolyte to freely pass between the positive and negative electrodes. The separator can be any known porous structure separator with electrochemical and mechanical stability. In exemplary embodiments, the separator comprises a single or multilayer film of at least one of glass fiber, non-woven fabric, polyethylene (PE), polypropylene (PP), and polyvinylidene fluoride (PVDF).

[0276] In an embodiment, when each of the sodium battery cells contains a solid electrolyte, the solid electrolyte, as described above, is disposed between the positive electrode and the negative electrode to separate the positive electrode and the negative electrode. The solid electrolyte may include at least one of a polymer solid electrolyte, an oxide electrolyte, a sulfide electrolyte, a borohydride electrolyte, a composite solid electrolyte, and the like.

[0277] Battery Module:

[0278] When the sodium battery in the embodiment of the present application is a battery module, the battery module refers to being assembled from the above-mentioned sodium battery cells, that is, it can contain multiple of the above-mentioned sodium battery cells, and the specific number can be adjusted according to the application and capacity of the battery module.

[0279] In some embodiments, FIG6 is a schematic diagram of an exemplary battery module 30. As shown in FIG6 , within the battery module 30, multiple sodium battery cells 20 may be arranged sequentially along the length of the battery module 30. Of course, any other arrangement is also possible. Furthermore, the multiple battery cells 20 may be secured together using fasteners.

[0280] Optionally, the battery module 30 may further include a housing having an accommodation space, and the plurality of sodium battery cells 20 are accommodated in the accommodation space.

[0281] Battery Pack:

[0282] When the sodium battery in the embodiments of the present application is a battery pack, the battery pack is assembled from the aforementioned sodium battery cells, that is, it may contain multiple sodium battery cells, and the multiple sodium battery cells are assembled into the aforementioned battery module. The specific number of battery cells or battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0283] In some embodiments, Figures 7 and 8 are schematic diagrams of an exemplary battery pack 40. The battery pack 40 may include a battery box and multiple battery modules 30 disposed within the battery box. The battery box includes an upper box body 41 and a lower box body 42. The upper box body 41 covers the lower box body 42 and forms an enclosed space for accommodating the battery modules 30. The multiple battery modules 30 may be arranged in any manner within the battery box.

[0284] Electrical devices

[0285] In a fifth aspect, the embodiments of the present application also provide an electric device. The electric device of the embodiments of the present application includes a power supply unit or an energy storage unit, and of course may also include other auxiliary components or necessary components. Among them, the power supply unit or energy storage unit contains the sodium battery of the above-mentioned embodiments of the present application. For example, it can be the above-mentioned sodium battery monomer, battery module or battery pack. Since the electric device of the embodiments of the present application contains the sodium battery of the above-mentioned embodiments of the present application, the power supply unit or energy storage unit of the electric device of the embodiments of the present application has high energy density, good cycle performance, long service life, and the electric device of the embodiments of the present application has a long standby or battery life.

[0286] In the embodiments, the electrical device may include, but is not limited to, a mobile phone, a tablet, a laptop computer, an electric toy, an electric tool, a battery-powered vehicle, an electric car, a ship, a spacecraft, and the like. The electric toy may include a fixed or mobile electric toy, such as a game console, an electric car toy, an electric ship toy, and an electric airplane toy, and the spacecraft may include an airplane, a rocket, a space shuttle, and a spacecraft. The battery may be a single cell, a battery module, or a battery pack, depending on the intended use of the electrical device.

[0287] FIG9 is a schematic diagram of an exemplary electric device. The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the electric device, a battery pack or battery module may be used.

[0288] In the embodiment, when the electrical device contains an energy storage unit, the electrical device can be an energy storage device, and the energy storage device includes the energy storage unit, and of course can also include other auxiliary components or necessary components. Among them, the energy storage unit contains the battery of the embodiment of the above text application. The battery contained in the energy storage unit can be one or more. When there are multiple batteries, multiple batteries can form a battery module or battery pack. Since the energy storage device of the embodiment of the present application contains the battery of the embodiment of the above text application, the energy storage device has high energy density, good cycle performance, long service life, and further high energy density.

[0289] Example

[0290] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0291] 1. Examples of positive electrode materials and preparation methods thereof

[0292] Example A1

[0293] This embodiment provides a positive electrode material and a preparation method thereof. The positive electrode material includes a molecular formula of Na 0.92 Ni 0.15 Fe 0.34 Mn 0.45 Layered oxides of O2.

[0294] The positive electrode material preparation method comprises the following steps:

[0295] S1: According to Na 0.92 Ni 0.15 Fe 0.34 Mn 0.45 The molar ratio of the metal elements contained in O2 is 500 rpm, and NiO, Mn2O3, and Fe2O3 are ball-milled for 3 hours, and then sodium carbonate is added in proportion to mix them to obtain a precursor;

[0296] S2: The precursor is sintered in a muffle furnace and crushed to obtain Na 0.92 Ni 0.15 Fe 0.34 Mn 0.45 O2 layered oxide; wherein, the sintering treatment conditions are: temperature: 850 ℃; time: 5h; heating rate: 5 ℃ / min; oxygen atmosphere.

[0297] Example A2

[0298] This embodiment provides a positive electrode material and a preparation method thereof. The positive electrode material includes a molecular formula of Na 0.92 Ni 0.15 Fe 0.41 Mn 0.44 Layered oxides of O2.

[0299] The positive electrode material preparation method comprises the following steps:

[0300] S1: According to Na 0.92 Ni 0.15 Fe 0.41 Mn 0.44The molar ratio of the metal elements contained in O2 is 500 rpm for 3 hours by ball milling NiO, Mn2O3 and Fe2O3, and then sodium carbonate is added in proportion for mixing to obtain a precursor;

[0301] S2: The precursor is sintered in a muffle furnace and crushed to obtain Na 0.92 Ni 0.15 Fe 0.41 Mn 0.44 O2 layered oxide; wherein the sintering conditions are: temperature: 850 ° C; time: 5h; heating rate: 5 ° C / min; oxygen atmosphere.

[0302] Example A3

[0303] This embodiment provides a positive electrode material and a preparation method thereof. The positive electrode material includes a molecular formula of Na 0.92 Ni 0.05 Fe 0.5 Mn 0.45 Layered oxides of O2.

[0304] The positive electrode material preparation method comprises the following steps:

[0305] S1: According to Na 0.92 Ni 0.05 Fe 0.5 Mn 0.45 The molar ratio of the metal elements contained in O2 is 500 rpm for 3 hours by ball milling NiO, Mn2O3 and Fe2O3, and then sodium carbonate is added in proportion for mixing to obtain a precursor;

[0306] S2: The precursor is sintered in a muffle furnace and crushed to obtain Na 0.92 Ni 0.05 Fe 0.5 Mn 0.45 O2 layered oxide; wherein, the sintering treatment conditions are: temperature: 850 ℃; time: 5h; heating rate: 5 ℃ / min; oxygen atmosphere.

[0307] Example A4

[0308] This embodiment provides a positive electrode material and a preparation method thereof. The positive electrode material includes a molecular formula of Na 0.92 Fe 0.38 Mn 0.6 Layered oxides of O2.

[0309] The positive electrode material preparation method comprises the following steps:

[0310] S1: According to Na 0.92 Fe 0.38Mn 0.6 The molar ratio of the metal elements contained in O2 was 500 rpm for 3 hours by ball milling Mn2O3 and Fe2O3, and then sodium carbonate was added in proportion for mixing to obtain a precursor;

[0311] S2: The precursor is sintered in a muffle furnace and crushed to obtain Na 0.92 Fe 0.38 Mn 0.6 O2 layered oxide; wherein, the sintering treatment conditions are: temperature: 850 ℃; time: 5h; heating rate: 5 ℃ / min; oxygen atmosphere.

[0312] Example A5

[0313] This embodiment provides a positive electrode material and a preparation method thereof. The positive electrode material includes a molecular formula of Na 0.92 Ni 0.1 Fe 0.38 Mn 0.437 Zn 0.082 Layered oxides of O2.

[0314] The positive electrode material preparation method comprises the following steps:

[0315] S1: According to Na 0.92 Ni 0.1 Fe 0.38 Mn 0.437 Zn 0.082 The molar ratio of the metal elements contained in O2 is 500 rpm for 3 hours by ball milling NiO, Mn2O3, Fe2O3 and ZnO, and then sodium carbonate is added in proportion for mixing to obtain a precursor;

[0316] S2: The precursor is sintered in a muffle furnace and crushed to obtain Na 0.92 Ni 0.1 Fe 0.38 Mn 0.437 Zn 0.082 O2 layered oxide; wherein, the sintering treatment conditions are: temperature: 850 ℃; time: 5h; heating rate: 5 ℃ / min; oxygen atmosphere.

[0317] Example A6

[0318] This embodiment provides a positive electrode material and a preparation method thereof. The positive electrode material includes a molecular formula of Na 0.92 Ni 0.1 Fe 0.38 Mn 0.367 Zn 0.082 Layered oxides of O2.

[0319] The positive electrode material preparation method comprises the following steps:

[0320] S1: According to Na 0.92 Ni 0.1 Fe 0.38 Mn 0.367 Zn 0.082 The molar ratio of the metal elements contained in O2 is 500 rpm for 3 hours by ball milling NiO, Mn2O3, Fe2O3 and ZnO2, and then sodium carbonate is added in proportion for mixing to obtain a precursor;

[0321] S2: The precursor is sintered in a muffle furnace and crushed to obtain Na 0.92 Ni 0.1 Fe 0.38 Mn 0.367 Zn 0.082 O2 layered oxide; wherein, the sintering treatment conditions are: temperature: 850 ℃; time: 5h; heating rate: 5 ℃ / min; oxygen atmosphere.

[0322] Example A7

[0323] This embodiment provides a positive electrode material and a preparation method thereof. The positive electrode material includes a molecular formula of Na 0.92 Ni 0.1 Fe 0.494 Mn 0.395 Layered oxides of O2.

[0324] The positive electrode material preparation method comprises the following steps:

[0325] S1: According to Na 0.92 Ni 0.1 Fe 0.494 Mn 0.395 The molar ratio of the metal elements contained in O2 is 500 rpm for 3 hours by ball milling NiO, Mn2O3 and Fe2O3, and then sodium carbonate is added in proportion for mixing to obtain a precursor;

[0326] S2: The precursor is sintered in a muffle furnace and crushed to obtain Na 0.92 Ni 0.1 Fe 0.494 Mn 0.395 O2 layered oxide; wherein, the sintering treatment conditions are: temperature: 850 ℃; time: 5h; heating rate: 5 ℃ / min; oxygen atmosphere.

[0327] Example A8

[0328] This embodiment provides a positive electrode material and a preparation method thereof. The positive electrode material includes a molecular formula of Na 0.85Ni 0.1 Fe 0.38 Mn 0.437 Al 0.082 Layered oxides of O2.

[0329] The positive electrode material preparation method comprises the following steps:

[0330] S1: According to Na 0.85 Ni 0.1 Fe 0.38 Mn 0.437 Al 0.082 The molar ratio of the metal elements contained in O2 was 500 rpm for 3 hours by ball milling NiO, Mn2O3, Fe2O3 and Al2O3, and then sodium carbonate was added in proportion for mixing to obtain a precursor;

[0331] S2: The precursor is sintered in a muffle furnace and crushed to obtain Na 0.85 Ni 0.1 Fe 0.38 Mn 0.437 Al 0.082 O2 layered oxide; wherein, the sintering treatment conditions are: temperature: 850 ℃; time: 5h; heating rate: 5 ℃ / min; oxygen atmosphere.

[0332] Example A9

[0333] This embodiment provides a positive electrode material and a preparation method thereof. The positive electrode material includes a molecular formula of Na 0.85 Ni 0.1 Fe 0.38 Mn 0.437 Mg 0.082 Layered oxides of O2.

[0334] The positive electrode material preparation method comprises the following steps:

[0335] S1: According to Na 0.85 Ni 0.1 Fe 0.38 Mn 0.437 Mg 0.082 The molar ratio of the metal elements contained in O2 is 500 rpm for 3 hours by ball milling NiO, Mn2O3, Fe2O3 and MgO, and then sodium carbonate is added in proportion for mixing to obtain a precursor;

[0336] S2: The precursor is sintered in a muffle furnace and crushed to obtain Na 0.85 Ni 0.1 Fe 0.38 Mn 0.437 Mg 0.082O2 layered oxide; wherein, the sintering treatment conditions are: temperature: 850 ℃; time: 5h; heating rate: 5 ℃ / min; oxygen atmosphere.

[0337] Comparative Example A1

[0338] This embodiment provides a positive electrode material and a preparation method thereof. The positive electrode material includes a molecular formula of Na 0.92 Ni 0.05 Fe 0.22 Mn 0.632 Layered oxides of O2.

[0339] The positive electrode material preparation method comprises the following steps:

[0340] S1: According to Na 0.92 Ni 0.05 Fe 0.22 Mn 0.632 The molar ratio of the metal elements contained in O2 is 500 rpm for 3 hours by ball milling NiO, Mn2O3 and Fe2O3, and then sodium carbonate is added in proportion for mixing to obtain a precursor;

[0341] S2: The precursor is sintered in a muffle furnace and crushed to obtain Na 0.92 Ni 0.05 Fe 0.22 Mn 0.632 O2 layered oxide; wherein, the sintering treatment conditions are: temperature: 850 ℃; time: 5h; heating rate: 5 ℃ / min; oxygen atmosphere.

[0342] Comparative Example A2

[0343] This embodiment provides a positive electrode material and a preparation method thereof. The positive electrode material includes a molecular formula of Na 0.92 Ni 0.05 Fe 0.75 Mn 0.2 Layered oxides of O2.

[0344] The positive electrode material preparation method comprises the following steps:

[0345] S1: According to Na 0.92 Ni 0.05 Fe 0.75 Mn 0.2 The molar ratio of the metal elements contained in O2 is 500 rpm for 3 hours by ball milling NiO, Mn2O3 and Fe2O3, and then sodium carbonate is added in proportion for mixing to obtain a precursor;

[0346] S2: The precursor is sintered in a muffle furnace and crushed to obtain Na 0.92 Ni0.05 Fe 0.75 Mn 0.2 O2 layered oxide; wherein, the sintering treatment conditions are: temperature: 850 ℃; time: 5h; heating rate: 5 ℃ / min; oxygen atmosphere.

[0347] Comparative Example A3

[0348] This embodiment provides a positive electrode material and a preparation method thereof. The positive electrode material includes a molecular formula of Na 0.85 Ni 0.1 Fe 0.24 Mn 0.65 Layered oxides of O2.

[0349] The positive electrode material preparation method comprises the following steps:

[0350] S1: According to Na 0.85 Ni 0.1 Fe 0.24 Mn 0.65 The molar ratio of the metal elements contained in O2 is 500 rpm for 3 hours by ball milling NiO, Mn2O3 and Fe2O3, and then sodium carbonate is added in proportion for mixing to obtain a precursor;

[0351] S2: The precursor is sintered in a muffle furnace and crushed to obtain Na 0.85 Ni 0.1 Fe 0.24 Mn 0.65 O2 layered oxide; wherein, the sintering treatment conditions are: temperature: 850 ℃; time: 5h; heating rate: 5 ℃ / min; oxygen atmosphere.

[0352] 2. Examples of positive electrodes and sodium-ion battery cells

[0353] Example B1 to Example B9

[0354] Embodiments B1 to B9 each provide a sodium ion battery cell. Each sodium ion battery cell includes an electrode assembly formed by a positive electrode sheet, a separator, and a negative electrode sheet, and also includes an electrolyte.

[0355] The sodium ion battery cells in Examples B1 to B9 are assembled as follows:

[0356] Positive electrode sheet: Sodium ion positive electrode active material, conductive agent carbon nanotubes, conductive agent carbon black, and binder polyvinylidene fluoride (PVDF) are thoroughly stirred and mixed in an appropriate amount of solvent NMP in a weight ratio of 95:0.5:2:2.5 to form a uniform positive electrode slurry; the positive electrode slurry is evenly coated on the surface of 13μm positive electrode current collector aluminum foil, and after drying and cold pressing, a positive electrode sheet is obtained; wherein, the sodium ion positive electrode active material is the positive electrode material in the above-mentioned Examples A1 to A9 respectively.

[0357] Negative electrode sheet: Add hard carbon, conductive agent SP, and CMC binder to deionized water in a weight ratio of 8:1:1 and stir thoroughly to form a uniform negative electrode slurry; evenly apply the negative electrode slurry on the surface of a 6μm copper foil, dry, and cold press to obtain a negative electrode sheet.

[0358] Electrolyte: In an environment with a water content of less than 10 ppm, the non-aqueous organic solvents ethylene carbonate (EC) and diethyl carbonate (DMC) are mixed in a volume ratio of 1:1 to obtain an electrolyte solvent. Subsequently, sodium hexafluorophosphate and the mixed solvent are mixed to prepare an electrolyte with a sodium salt concentration of 1 mol / L.

[0359] Isolation membrane: porous polyethylene (PE) film is used as the isolation membrane.

[0360] Battery Assembly: The aforementioned positive electrode sheets, separators, and negative electrode sheets are stacked in sequence, with the separators positioned between the positive and negative electrodes to provide isolation. The electrode assemblies are then laminated to obtain an electrode assembly. Each electrode assembly is placed in an outer packaging, dried, and then injected with electrolyte. After vacuum packaging, standing, forming, and shaping, the sodium-ion battery cells of Examples B1 to B9 are obtained. The sodium-ion positive electrode active material in Example B1 is the positive electrode material of Example A1, the sodium-ion positive electrode active material in Example B2 is the positive electrode material of Example A2, and so on. The sodium-ion positive electrode active material in Example B9 is the positive electrode material of Example A9.

[0361] Example B10 to Example B15

[0362] Embodiments B10 to B15 provide a sodium ion battery cell, respectively. Each sodium ion battery cell includes an electrode assembly formed by a positive electrode sheet, a separator, and a negative electrode sheet, and also includes an electrolyte.

[0363] The sodium ion battery monomers in Examples B10 to B15 were prepared with reference to the sodium ion battery monomer in Example B1, except that:

[0364] In the sodium ion battery cells of Examples B10 to B12, the content (CW) of the positive electrode active material layer on one side of the current collector contained in the positive electrode sheet of each sodium ion battery cell is controlled as shown in Table 2.

[0365] In the sodium ion battery cells of Example B13 to Example B14, the electrode sheet compaction density of the positive electrode sheet of each sodium ion battery cell is controlled as shown in Table 2.

[0366] In the sodium-ion battery cell of Example B15, the carbon nanotubes contained in the positive electrode sheet of the sodium-ion battery cell are replaced with carbon fibers, and the carbon nanotube content is controlled to 2%, as shown in Table 2. The total content of the conductive agent contained in the positive electrode sheet of Example B15 is the same as the total content of the conductive agent contained in the positive electrode sheet of Example B1.

[0367] Comparative Examples B1 to B3

[0368] Comparative Examples B1 to B3 provide a sodium ion battery cell, respectively. Each sodium ion battery cell includes an electrode assembly formed by a positive electrode sheet, a separator, and a negative electrode sheet, and also includes an electrolyte.

[0369] The sodium ion battery monomers in Comparative Examples B1 to B3 were prepared with reference to the sodium ion battery monomer in Example B1. The differences were:

[0370] In the sodium ion battery monomers of Comparative Examples B1 to B3, the sodium ion positive electrode active materials contained in the positive electrode sheets of the sodium ion battery monomers are the positive electrode materials in Comparative Example A1, Comparative Example A2 and Comparative Example A3, respectively. Specifically, the sodium ion positive electrode active material contained in Comparative Example B1 is the positive electrode material in Comparative Example A1, the sodium ion positive electrode active material contained in Comparative Example B2 is the positive electrode material in Comparative Example A2, and the sodium ion positive electrode active material contained in Comparative Example B3 is the positive electrode material in Comparative Example A3.

[0371] 2. Relevant performance tests of layered oxides and sodium ion battery monomers in each embodiment:

[0372] 2.1 Characterization of layered oxides and related performance tests in each example:

[0373] The layered oxides provided in Examples A1 to A9 and Comparative Examples A1 to A3 were tested for the relevant characteristics listed in Table 1 according to the following methods. The test results are shown in Table 1:

[0374] Method for detecting the element content of layered oxides: Inductively coupled plasma emission spectroscopy (ICP) was obtained using an Agilent ICP-OES730. The content of each metal element was then calculated from the ICP results, and the mass percentage of each component was then calculated.

[0375] Single Crystal Morphology Testing Method: Scanning electron microscopy (SEM) was performed on the layered oxides provided in each example using the micron-scale SEM measurement method in accordance with GB / T 16594-1996. Single crystal length, width, and height dimensions can be derived based on the SEM images. An SEM image of the layered oxide provided in Example A3 is shown in Figure 1.

[0376] Crystalline phase characterization method: The layered oxides were analyzed using an XRD diffractometer at a scanning rate of 0.5°C / min.

[0377] Dv50 detection method: Detect each layered oxide according to the method steps in GB / T16418.

[0378] BET specific surface area detection method: The specific surface area of ​​each layered oxide was detected according to the method steps in GB / T19587-2017.

[0379] Powder compacted density test method:

[0380] Refer to the GB / T24533-2019 standard test method for testing. Please refer to the following test steps for details:

[0381] (1) Use a clean soft cloth (paper towel) to wipe the upper and lower gaskets, top column and metal cylindrical sleeve of the compaction density meter. If necessary, wipe them with a soft cloth dipped in anhydrous ethanol and air dry them;

[0382] (2) Place the gasket, top column, metal cylindrical sleeve, and pad in the order of the test and place them on the digital thickness gauge, and press the zero key;

[0383] (3) Remove the top column and upper gasket, weigh 1g of sample in the sleeve to the nearest 0.0001g, and record the weight as m;

[0384] (4) Slowly slide the gasket and the top column down from the hole, install them together with the pad on the compaction density meter, and tighten the pressure control knob;

[0385] (5) Shake the pressure bar and observe the value on the digital pressure gauge on the compaction density meter at the same time. Start the stopwatch after reaching the specified value of 2200Ib; loosen the pressure control knob after 30 seconds to remove the pressure, lower the pad to a certain height, and then tighten the pressure control knob;

[0386] (6) Take out the top post, sleeve and film together with the pad, place them on the digital thickness gauge, and read the value on the digital thickness gauge within 10 seconds, which is recorded as H; r = 10m / (S×H);

[0387] Then calculate the powder compaction density r of the sample according to the above formula r=10m / (S×H).

[0388] Where mm is the sample weight in grams (g); HH is the thickness of the sample after compaction in millimeters (mm); SS is the cross-sectional area of ​​the top column in square centimeters (cm 2 ).

[0389] Charge / discharge gram capacity and first effect detection method: The detection was carried out according to the layered oxide detection method of the above application example.

[0390] 2.2 Performance tests of sodium ion battery cells and the positive electrode sheets contained therein in each embodiment:

[0391] The sodium ion battery cells and the positive electrode sheets contained therein provided in the above-mentioned Examples B1 to B15 and Comparative Examples B1 to B3 were respectively subjected to the relevant performance tests listed in Table 2 below according to the following methods. The test results are shown in Table 2:

[0392] CW detection method: the electrode is punched into 1540.25mm 2 The electrode is weighed minus the weight of the aluminum foil.

[0393] Positive electrode sheet compaction density test method: The specific compaction density of the positive electrode sheet can refer to the first discharge specific capacity and first charge and discharge efficiency test method of lithium manganese oxide, the positive electrode material of lithium-ion batteries, for details, see GB / T 39864-2021 or GB / T 42161-2022. For specific reference, please refer to the test steps of the following parameters:

[0394] Obtain battery electrodes that meet the machinability requirements, use a punch to punch out positive electrodes with a diameter of 14 mm, and use an electronic balance and a desktop digital thickness gauge to measure the mass m of the positive electrodes. c , thickness d c Use a punching machine to punch out a sufficient number of aluminum foil substrates with a diameter of 14 mm, and use an electronic balance and a desktop digital thickness gauge to measure the mass m of the aluminum foil substrates respectively Al , thickness d Al ; Calculate the positive electrode compaction density according to the following formula:

[0395] Positive electrode compaction density ρ c =(m c -m Al )×10 6 ÷[π(φ / 2)×(d c -d Al )];

[0396] Where: c is the compacted density of the positive electrode, in grams per cubic centimeter (g / cm 3 );

[0397] mc is the mass of the positive electrode, in grams (g);

[0398] m Al is the mass of the aluminum foil substrate, in grams (g);

[0399] φ is the diameter of the positive electrode sheet, in millimeters (mm);

[0400] d c is the thickness of the positive electrode sheet, in micrometers (μm);

[0401] d Al is the thickness of the aluminum foil substrate, in micrometers (μm).

[0402] The electrode porosity detection method is carried out by gas replacement method, with specific reference to GB / T24586-2009. The specific steps of the electrode porosity detection method are as follows: the electrode is immersed in ethyl methyl carbonate (EMC) for cleaning, and then the specific equipment specified in GB / T24586-2009 is used to measure the electrode porosity by gas replacement method; wherein, the percentage of the pore volume in the electrode to the total volume of the electrode is the electrode porosity, and the calculation formula is: porosity = (V-V0) / V×100%, wherein V0 is the true volume and V is the apparent volume.

[0403] Diaphragm resistance test method: Refer to GB / T 30835-2014 or T / CASAS 019-2021 for testing; for tester verification procedures, refer to JJG 508-2004. The four-probe method is used: clean the electrode by immersing it in ethyl methyl carbonate (EMC). Using the equipment specified in GB / T 30835-2014 or T / CASAS 019-2021, four copper plates (1.5 cm long, 1 cm wide, and 2 mm thick) are fixed equidistantly in a line. The spacing between the two center plates is L (1 cm to 2 cm). The substrate used to secure the plates is insulating material. During testing, the lower ends of the four copper plates are pressed against the electrode to be tested. A DC current I is applied to the two end plates. A voltage V is measured at the two center plates. The I and V values ​​are read three times, and the average of I and V is calculated. V / I is the electrode resistance at the test point.

[0404] Sodium ion battery monomer related performance testing methods:

[0405] Cycle Retention (%): At 25°C, a secondary battery is charged at a constant current of 0.33C to 3.85V, then charged at a constant voltage of 3.85V to a current of 0.05C, and then discharged at a constant current of 1C to 1.5V. This is considered one charge-discharge cycle. Taking the initial discharge capacity as 100%, calculate the capacity retention after 500 cycles. Capacity retention (%) after 1000 cycles = discharge capacity at the 1000th cycle / initial discharge capacity × 100%.

[0406] Energy density: Measure the discharge energy S0 of each battery cell at room temperature by charging it at a rate of 0.33C to a voltage of 4.2V, then discharging it at a rate of 0.33C to a voltage of 2.0V. Then, measure the mass M of the battery cell corresponding to S0, and calculate the battery cell energy density (mass energy density) using the formula S0 / M.

[0407] Table 1

[0408] Table 2

[0409] As shown in Table 1, the crystal form of the layered oxides with low nickel and high iron content provided in Examples A1 to A9 is O3. Further testing shows that the specific surface areas of the layered oxide particles provided in Examples A1 to A9 are respectively 0.4 to 1.5 m 2 / g, further 0.5~0.95m 2 The charge / discharge gram capacity of the layered oxides in Examples A1 to A9 is significantly improved compared to Comparative Examples A1 and A3, respectively.

[0410] Combining Table 1 and Table 2, it can be seen that the iron content of the layered oxide shown in Chemical Formula (I) is controlled within an appropriate range, which is beneficial to improving the gram capacity of the oxide material and the energy density and cycle retention rate of the corresponding sodium ion battery monomer. When the iron content c of the layered oxide shown in Chemical Formula (I) is lower than 0.25, such as as low as 0.22 in Comparative Example A1, the gram capacity of the layered oxide material is significantly reduced relative to when c is higher than 0.25, and the cycle retention rate and energy density of the corresponding sodium ion battery monomer are significantly reduced. When the iron content c of the layered oxide shown in Chemical Formula (I) is higher than 0.5, such as when it is increased to 0.75 in Comparative Example A2, the gram capacity of the oxide material is also significantly reduced relative to when c is lower than 0.5, and the cycle retention rate and energy density of the corresponding sodium ion battery monomer are significantly reduced.

[0411] Combining Table 1 and Table 2, it can be seen that in Comparative Examples A5 / B5 to A6 / B6 and Comparative Examples A2 / B2 to A3 / B3, the manganese element contained in the layered oxide shown in Chemical Formula (I) is controlled within an appropriate range, which is beneficial to improving the gram capacity of the oxide material and the energy density and cycle retention rate of the corresponding sodium-ion battery monomer. When the manganese element content d in Chemical Formula (I) is higher than 0.6, such as when it increases to 0.65 in Comparative Example A3, the gram capacity of the oxide material is significantly reduced, and the energy density and cycle retention rate of the corresponding sodium-ion battery monomer are also significantly reduced. When the manganese element content d in Chemical Formula (I) is higher than 0.26, such as when it is as low as 0.22 in Comparative Example A2, the cycle retention rate of the corresponding sodium-ion battery monomer is significantly reduced.

[0412] Combining Table 1 and Table 2, it can be seen from the comparison of Examples A1 / B1 to A7 / B7 that the total stoichiometric ratio of the Mn element and the doping metal element represented by M contained in the layered oxide represented by chemical formula (I) to the stoichiometric ratio of the Fe element must meet an appropriate range, such as between 0.9 and 1.5:1. The gram capacity of the layered oxide represented by chemical formula (I) is improved, and the comprehensive performance of the energy density and cycle performance of the corresponding battery cell can be improved. Moreover, when the ratio is between 0.9 and 1.5:1, the cycle retention rate of the battery cell has a certain increasing trend as the ratio increases, but when the ratio increases to about 1.37, the increasing trend of the cycle retention rate of the battery cell slows down, and the energy density of the battery cell also decreases; when it continues to increase to 1.58, the cycle retention rate and energy density of the battery cell decrease. Further comparison of Examples A3 / B3 with Examples A7 / B7 shows that when the stoichiometric ratio of the total stoichiometric amount of the Mn element and the doping metal element represented by M contained in the layered oxide represented by Chemical Formula (I) to the stoichiometric ratio of the Fe element is less than 0.9:1, such as 0.8:1 in Example A7, the specific capacity of the layered oxide decreases, and the energy density and cycle performance of the corresponding battery cell also decrease, especially the cycle performance decreases significantly. Further comparison of Examples A4 / B4 with Examples A5 / B5 shows that when the stoichiometric ratio of the total stoichiometric amount of the Mn element and the doping metal element contained in the layered oxide represented by Chemical Formula (I) to the stoichiometric ratio of the Fe element is higher, such as 1.58:1 in Example A4, the specific capacity of the layered oxide represented by Chemical Formula (I) decreases, and the energy density and cycle performance of the corresponding battery cell also decrease, especially the energy density decreases significantly. Therefore, on the basis of adjusting the stoichiometry of iron and manganese elements contained in the layered oxide represented by chemical formula (I), further regulating the stoichiometric ratio of the total stoichiometry of Mn element and doping metal elements to the stoichiometric ratio of Fe element can improve the structural stability of the layered oxide represented by chemical formula (I) and improve the performance of gram capacity.

[0413] Combining Table 1 and Table 2, it can be seen from the comparison of Examples A5 / B5, A8 / B8 to A9 / B9 that when the layered oxide represented by the chemical formula (I) is doped with the doping metal element represented by M, its type also has a certain influence on the specific capacity and structural stability of the layered oxide. Specifically, when M is an active metal element such as zinc relative to an inert metal element such as aluminum, the specific capacity of the layered oxide is improved; the energy density of the corresponding battery cell doped with active metals is also improved relative to that doped with inert metals. Therefore, the doping metal element represented by M participates in the disordered arrangement of the metal elements in the transition metal layer contained in the layered oxide, and can contribute to the specific capacity and / or structural stability of the layered oxide, and can also contribute to the energy density or cycle performance of the battery cell.

[0414] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application, and they should all be included in the scope of the claims and specification of the present application. In particular, as long as there is no structural conflict, the various technical features mentioned in the various embodiments can be combined in any way. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions that fall within the scope of the claims.

Claims

1. A positive electrode material, wherein: Includes layered oxides of the following chemical formula: Na a Ni b Fe c Mn d M e O f ; Among them, 0.8≤a≤1, 0≤b≤0.2, 0.25≤c≤0.5, 0.26≤d≤0.6, 0≤e≤0.1, 1.8≤f≤2, b+c+d+e≤1; M is an active and / or inert doping metal element.

2. The positive electrode material according to claim 1, wherein At least one of a, b, c, d and e is in the following value range: 0.85≤a≤1, 0≤b≤0.18, 0.3≤c≤0.5, 0.3≤d≤0.6, 0.02≤e≤0.

1.

3. The positive electrode material according to claim 1 or 2, wherein The stoichiometric ratio of the total stoichiometric amount of the Ni element, the Mn element, the Fe element and the doping metal element to the stoichiometric ratio of the Na element is 1:(0.85-0.95); and / or The e>0, and the total stoichiometric ratio of the Mn element and the doping metal element to the Fe element is 0.9-1.5:

1.

4. The positive electrode material according to claim 1 or 2, wherein The total stoichiometric ratio of the Mn element, the Fe element and the doping metal element to the Na element is 1:(0.86-0.94) and / or The e>0, and the total stoichiometric ratio of the Mn element and the doping metal element to the Fe element is 1-1.2:

1.

5. The positive electrode material according to any one of claims 1 to 4, wherein The doping metal element includes at least one of Zn, V, Cr, Al, Sc, Sn, Sb, Zr, Nb, Ti, Mg, Cu, Ru, and Ir.

6. The positive electrode material according to any one of claims 1 to 5, characterized in that The above-mentioned lamellar compound inclusive Na 0.87 Ni 0.2 Fe 0.3 Mn 0.45 O2, Na 0.87 Ni 0.2 Fe 0.35 Mn 0.45 O2, Na 0.85 Ni 0.1 Fe 0.387 Mn 0.43 O2, Na 0.85 Ni 0.05 Fe 0.45 Mn 0.45 O2, Na 0.87 Ni 0.05 Fe 0.5 Mn 0.45 O2, Na 0.85 Ni 0.1 Fe 0.38 Mn 0.437 Zinc 0.082 O2, Na 0.85 Ni 0.1 Fe 0.38 Mn 0.437 V 0.082 O2, Na 0.85 Ni 0.1 Fe 0.38 Mn 0.437 Cr 0.082 O2, Na 0.85 Ni 0.1 Fe 0.38 Mn 0.437 Al 0.082 O2, Na 0.85 Ni 0.1 Fe 0.38 Mn 0.437 Sc 0.082 O2, Na 0.85 Ni 0.1 Fe 0.38 Mn 0.437 Sn 0.082 O2, Na 0.85 Ni 0.1 Fe 0.38 Mn 0.437 Sb 0.082 O2, Na 0.85 Ni 0.1 Fe 0.38 Mn 0.437 Zr 0.082 O2, Na 0.85 Ni 0.1 Fe 0.38 Mn 0.437 No 0.082 O2、Na 0.85 Ni 0.1 Feb 0.38 Mr 0.437 Tea 0.082 O2、Na 0.85 Ni 0.2 Feb 0.28 Mr 0.437 Mg 0.082 O2、Na 0.85 Ni 0.1 Feb 0.38 Mr 0.437 Ru 0.082 O2、Na 0.85 Ni 0.1 Feb 0.38 Mr 0.437 Ir 0.082 O2、Na 0.85 Ni 0.1 Feb 0.38 Mr 0.437 Al 0.04 Zn 0.04 O2、Na 0.85 Ni 0.1 Feb 0.38 Mr 0.267 Zn 0.082 O2、Na 0.85 Feb 0.4 Mr 0.6 O2、Na 0.92 Ni 0.15 Feb 0.34 Mr 0.45 O2、Na 0.92 Ni 0.15 Feb 0.41 Mr 0.44 O2、Na 0.92 Ni 0.05 Feb 0.5 Mr 0.45 O2、Na 0.92 Feb 0.38 Mr 0.6 O2、Na 0.92 Ni 0.1 Feb 0.38 Mr 0.437 Zn 0.082 O2、Na 0.92 Ni 0.1 Feb 0.38 Mr 0.367 Zn 0.082 O2、Na 0.92 Ni 0.1 Feb 0.494 Mr 0.395 At least one of O2.

7. The positive electrode material according to any one of claims 1 to 6, wherein The layered oxide includes at least one of the following features (1) to (6): (1) The crystal structure includes an O3 phase layered metal oxide, and the O3 phase layered metal oxide accounts for more than 95% of the total weight of the layered oxide; (2) Dv50 particle size is 3 to 9 μm; (3) It includes a single crystal, and the single crystal has a block-like morphology.

8. The positive electrode material according to any one of claims 1 to 6, wherein The Dv50 particle size of the layered oxide is 4.2 to 8.5 μm.

9. The positive electrode material according to any one of claims 1 to 8, wherein The layered oxide includes at least one of the following features (1) to (3): (1) The compacted density of the powder under 2 tons of pressure is higher than 2.7g / cm 3 ; (2) The compacted density of the powder under 3 tons of pressure is higher than 3.0g / cm 3 ; (3) Specific surface area is 0.4 to 1.5 m 2 / g.

10. The positive electrode material according to any one of claims 1 to 8, wherein The layered oxide includes at least one of the following features (1) to (3): (1) The compacted density of the powder under 2 tons of pressure is 2.7 to 3.0 g / cm 3 ; (2) The compacted density of the powder under 3 tons of pressure is 3.0-3.3 g / cm 3 ; (3) Specific surface area is 0.5 to 0.95 m 2 / g.

11. The positive electrode material according to any one of claims 1 to 10, wherein The layered oxide comprises at least one of the following (1) to (3) at 1.5 to 4.0 V and 0.1 C: (1) The charging capacity is 130-150 mAh / g; (2) The discharge capacity is 129-140 mAh / g; (3) The initial efficacy is higher than 92%.

12. The positive electrode material according to any one of claims 1 to 10, wherein The layered oxide comprises at least one of the following (1) to (3) at 1.5 to 4.0 V and 0.1 C: (1) The charging capacity is 132-150 mAh / g; (2) The discharge capacity is 130-144 mAh / g; (3) The initial efficacy is 92% to 98%.

13. A method for preparing a positive electrode material, wherein: The steps include: Provide Na a Ni b Fe c Mn d M e O f Precursor of The precursor is sintered to obtain a product having a chemical formula of Na a Ni b Fe c Mn d M e O f Layered oxides; Among them, 0.8≤a≤1, 0.05≤b≤0.2, 0.25≤c≤0.5, 0.26≤d≤0.6, 0≤e≤0.1; M is an active and / or inert doping metal element.

14. The preparation method according to claim 13, wherein: The doping metal element includes at least one of Zn, V, Cr, Al, Sc, Sn, Sb, Zr, Nb, Ti, Mg, Cu, Ru, and Ir; and / or At least one of a, b, c, d and e is in the following value range: 0.85≤a≤1, 0≤b≤0.18, 0.3≤c≤0.5, 0.3≤d≤0.6, 0.02≤e≤0.

1.

15. The preparation method according to claim 13 or 14, wherein: The sintering process includes at least one of the following conditions (1) to (3): (1) Temperature is 700~980℃; (2) Duration: 3 to 20 hours; (3) The temperature is raised to the sintering temperature at a heating rate of 2 to 15°C / min.

16. The preparation method according to claim 13 or 14, wherein: The sintering process includes at least one of the following conditions (1) to (2): (1) Temperature is 750~950℃; (2) The duration is 5 to 12 hours.

17. The preparation method according to any one of claims 13 to 16, wherein: The Na a Ni b Fe c Mn d M e O f The precursor is prepared according to a method comprising the following steps: According to Na a Ni b Fe c Mn d M e O f The precursor is obtained by solid phase mixing the sodium source, the nickel source, the manganese source, the iron source and the M source according to the stoichiometric ratio of the elements contained therein; and / or The Na a Ni b Fe c Mn d M e O f The precursor is prepared according to a method comprising the following steps: According to Na a Ni b Fe c Mn d M e O f A soluble nickel source, a soluble manganese source, a soluble iron source and a soluble doping element source represented by M are prepared into a mixed solution according to the stoichiometric ratio of the elements, and at least one of a precipitant and a complexing agent is added to perform a coprecipitation treatment to obtain a precipitated mixture; The precipitation mixture is mixed with a sodium source to obtain the precursor.

18. A positive electrode, comprising a current collector and a positive electrode active material layer disposed on the surface of the current collector, wherein: The positive electrode active material layer comprises the positive electrode material according to any one of claims 1 to 12 or the positive electrode material prepared by the preparation method according to any one of claims 13 to 17.

19. The positive electrode according to claim 18, characterized in that: The content of the positive electrode active material layer on the single surface of the current collector is 250-330 mg / 1540.25 mm 2 ; and / or The compaction density of the positive electrode is 2.6-3.2 g / cm 3 .

20. The positive electrode according to claim 18, characterized in that: The content of the positive electrode active material layer on the single surface of the current collector is 280-320 mg / 1540.25 mm 2 ; and / or The compaction density of the positive electrode is 2.8-3.0 g / cm 3 .

21. The positive electrode according to any one of claims 18 to 20, wherein The porosity of the positive electrode active material layer is 35% to 65%; and / or The positive electrode is a pole piece, and the membrane resistance of the pole piece is 0.5-5 mΩ.

22. The positive electrode according to any one of claims 18 to 20, wherein The porosity of the positive electrode active material layer is 40% to 58%; and / or The positive electrode is a pole piece, and the membrane resistance of the pole piece is 0.5-3 mΩ.

23. The positive electrode according to any one of claims 18 to 22, wherein The positive electrode is a pole piece, and the ratio of the thickness from one surface of the pole piece to the other opposite surface to the thickness of the current collector is 7 to 16:

1.

24. The positive electrode according to any one of claims 18 to 22, wherein The positive electrode is a pole piece, and the ratio of the thickness from one surface of the pole piece to the other opposite surface to the thickness of the current collector is 8 to 15:

1.

25. The positive electrode according to any one of claims 18 to 24, wherein The conductive agent contained in the positive electrode active material layer includes a linear conductive agent.

26. The positive electrode according to claim 25, wherein The mass content of the linear conductive agent in the positive electrode active material layer is 0.1% to 2.5%; and / or The linear conductive agent has an aspect ratio of 40 to 3000:1; and / or The length of the linear conductive agent is 0.5 to 5 μm; and / or The diameter of the linear conductive agent is 2 to 10 nm; and / or The linear conductive agent includes at least one of carbon nanotubes, carbon fibers, and conductive oxide nanowires.

27. The positive electrode according to claim 25 or 26, wherein The mass content of the linear conductive agent in the positive electrode active material layer is 0.2% to 0.8%; and / or The linear conductive agent has an aspect ratio of 50 to 2500:1; and / or The length of the linear conductive agent is 0.5 to 2 μm; and / or The diameter of the linear conductive agent is 3-7 nm.

28. A sodium battery, wherein: The positive electrode comprises the positive electrode according to any one of claims 18 to 27.

29. The sodium battery according to claim 28, wherein: The sodium battery comprises a sodium battery cell, and the operating voltage of the sodium battery cell is 1.5-4.0V.

30. An electrical device, wherein: Includes the sodium battery as described in claim 28 or 29.

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