Positive electrode active material, method for manufacturing the same, positive electrode sheet, battery, and electric device

Abstract

The application discloses a positive electrode active material and a preparation method thereof, a positive electrode sheet, a battery and an electric device. The positive electrode active material comprises a core and a coating layer. The core comprises a sodium ion transition metal oxide containing an iron element and / or a nickel element. In the sodium ion transition metal oxide, the molar amount of the iron element is denoted as b, the molar amount of the nickel element is denoted as c, 0<=b<=0.4, and 0<=c<=0.4. The coating layer is arranged on at least part of the surface of the core. The coating layer contains an alkaline sodium compound. The mass percentage of the alkaline sodium compound in the total amount of the positive electrode active material is w%, and the following condition is met: 0.1<= (b+c) / w<=0.5. The positive electrode active material is structurally stable at a high voltage, thereby improving the cycle stability and energy density of a battery containing the same at a high voltage.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of secondary batteries, and particularly relates to a positive electrode active material, a preparation method thereof, a positive electrode sheet, a battery and an electric device. BACKGROUND

[0002] Secondary batteries are widely used in various consumer electronic products and electric vehicles due to their light weight, no pollution and no memory effect.

[0003] Sodium-ion batteries are a kind of secondary batteries, and layered transition metal oxides are commonly used positive electrode active materials for sodium-ion batteries. Layered transition metal oxides can deintercalate more sodium ions at high voltage, and have a higher specific capacity. However, the existing layered transition metal oxides are unstable in structure at high voltage, resulting in low cycle stability of the battery at high voltage.

[0004] DISCLOSURE

[0005] In view of the technical problems in the background art, the application provides a positive electrode active material, aiming to solve the problem of instability of the positive electrode active material in structure at high voltage, thereby improving the cycle stability and energy density of the battery containing the same at high voltage.

[0006] To achieve the above-mentioned purpose, the first aspect of the application provides a positive electrode active material, which comprises:

[0007] a core, the core comprising a sodium-ion transition metal oxide containing iron elements and / or nickel elements, in the sodium-ion transition metal oxide, the molar amount of iron elements is denoted as b, and the molar amount of nickel elements is denoted as c, 0≤b≤0.4, 0≤c≤0.4;

[0008] a coating layer, the coating layer being arranged on at least a part of the surface of the core, the coating layer containing an alkaline sodium compound, the mass fraction of the alkaline sodium compound in the total amount of the positive electrode active material being w%, and satisfying: 0.1≤(b+c) / w≤0.5.

[0009] The positive electrode active material of the application is stable in structure at high voltage, thereby improving the cycle stability and energy density of the battery containing the same at high voltage.

[0010] In some embodiments, 0.2≤(b+c) / w≤0.4. In this way, the stability of the positive electrode active material in structure at high voltage can be improved, thereby improving the cycle stability and energy density of the battery containing the same at high voltage.

[0011] In some embodiments, the mass percentage w% of the basic sodium compound is 0.3wt%-5wt%, optionally 0.5wt%-2wt%. In this way, the structural stability of the positive electrode active material at high voltage can be improved, thereby improving the cycle stability and energy density of the battery containing the same at high voltage.

[0012] In some embodiments, the basic sodium compound includes at least one of sodium hydroxide and sodium carbonate, optionally sodium carbonate. In this way, the structural stability of the positive electrode active material at high voltage can be improved, thereby improving the cycle stability and energy density of the battery containing the same at high voltage.

[0013] In some embodiments, the mass percentage of the sodium carbonate is higher than or equal to 80% based on the total mass of the coating layer. In this way, the structural stability of the positive electrode active material at high voltage can be improved, thereby improving the cycle stability and energy density of the battery containing the same at high voltage.

[0014] In some embodiments, the mass percentage of the sodium hydroxide is lower than or equal to 10% based on the total mass of the coating layer. In this way, the structural stability of the positive electrode active material at high voltage can be improved, thereby improving the cycle stability and energy density of the battery containing the same at high voltage.

[0015] In some embodiments, the sodium ion transition metal oxide includes: Na x Mn a Fe b Ni c Q d O 2-e+δ F e , 0.5≤x≤1.2, 0

[0016] In some embodiments, the sodium ion transition metal oxide includes: Na x Mn a Fe b Ni c Q d O 2-e+δ F e0.7≤x≤1.2, 0 The mass ratio of the basic sodium compound is 1wt%-2wt% based on the total amount of the positive electrode active material. In this way, the structural stability of the positive electrode active material at high voltage can be improved, thereby improving the cycle stability and energy density of the battery containing the same at high voltage.

[0017] In some embodiments, at least one of the following conditions is satisfied: 0.3≤a≤0.6; 0.15≤b≤0.35; 0.15≤c≤0.35; 0.1≤d≤0.2.

[0018] In some embodiments, 0.5≤(b+c) / a≤2, and optionally 0.5≤(b+c) / a≤1.5. In this way, the structural stability of the positive electrode active material at high voltage can be improved, thereby improving the cycle stability and energy density of the battery containing the same at high voltage.

[0019] In some embodiments, the phase state of the sodium ion transition metal oxide includes O3 phase, and the space group includes The interlayer spacing is 0.53nm-0.55nm. In this way, the capacity of the battery can be improved.

[0020] In some embodiments, the sodium ion transition metal oxide includes: Na x Mn a Ni c Q d O 2-e+δ F e0.5≤x≤1.2, 0

[0021] In some embodiments, at least one of the following conditions is satisfied: 0.5≤a≤0.8; 0.15≤c≤0.25; 0.05≤d≤0.15.

[0022] In some embodiments, 0.125≤c / a≤0.45, and optionally 0.2≤c / a≤0.3. Thereby, the structural stability of the positive electrode active material at high voltage can be improved, and thus the cycle stability and energy density of the battery containing the same at high voltage can be improved.

[0023] In some embodiments, the phase state of the sodium ion transition metal oxide includes P2 phase, the space group includes P63 / mmc, and the interlayer distance is 0.55nm-0.57nm. Thereby, the rate performance and cycle stability of the battery can be improved.

[0024] In some embodiments, the BET specific surface area of the positive electrode active material is Sm 2 / g, and S and w satisfy the relationship: 0.3≤w / S≤3, and optionally 0.5≤w / S≤2. Thereby, the cycle stability of the battery can be improved.

[0025] In some embodiments, the positive electrode active material satisfies at least one of the following conditions: the D v 50 is 2μm-20μm, and optionally 4μm-15μm; the BET specific surface area of the positive electrode active material is 0.2m 2 / g-2m 2 / g, and optionally 0.3m 2 / g-2m 2 / g; the compaction density of the positive electrode active material under a pressure of 300MPa is 3.1g / cm 3 -3.8g / cm 3 , and optionally 3.2g / cm 3 -3.6g / cm 3.

[0026] Thus, when the D of the positive electrode active material is 0.5-1.5 A / cm2 v 50、When at least one of the specific surface area and the compaction density under a pressure of 300 MPa is in the above range, the conduction distance of Na ions in the positive electrode active material is small, the surface side reaction is less, the capacity of the positive electrode active material is promoted to play, and the capacity retention rate of the battery containing the same is improved.

[0027] The second aspect of the present application provides a method for preparing the positive electrode active material of the first aspect, comprising:

[0028] A sodium ion transition metal oxide containing iron elements and / or nickel elements is provided, wherein the molar amount of the iron elements is denoted as b, the molar amount of the nickel elements is denoted as c, 0≤b≤0.4, 0≤c≤0.4;

[0029] The sodium ion transition metal oxide and the basic sodium compound are mixed and sintered to obtain a positive electrode active material,

[0030] Wherein, based on the total amount of the positive electrode active material, the mass percentage of the basic sodium compound is w%, 0.1≤(b+c) / w≤0.5.

[0031] Thus, the positive electrode active material with stable structure at high voltage described above can be prepared, thereby improving the cycle stability and energy density of the battery containing the same at high voltage.

[0032] The third aspect of the present application provides a positive electrode tab, which comprises the positive electrode active material of the first aspect of the present application or the positive electrode active material prepared by the method of the second aspect of the present application.

[0033] The fourth aspect of the present application provides a battery, which comprises the positive electrode tab of the third aspect of the present application.

[0034] The fifth aspect of the present application provides a power utilization device, which comprises the battery of the fourth aspect of the present application.

[0035] Additional aspects and advantages of the present application will be in part apparent and in part pointed out hereinafter. BRIEF DESCRIPTION OF DRAWINGS

[0036] Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description, with reference to the accompanying drawings in which:

[0037] Figure 1is a sectional view of a positive electrode active material according to an embodiment of the present application;

[0038] Figure 2 is a structural schematic diagram of a battery according to an embodiment of the present application;

[0039] Figure 3 is a structural schematic diagram of a battery module according to an embodiment of the present application;

[0040] Figure 4 is a structural schematic diagram of a battery pack according to an embodiment of the present application;

[0041] Figure 5 is a sectional view of Figure 4

[0042] Figure 6 is a schematic diagram of a use device using a battery as a power source according to an embodiment of the present application;

[0043] Figure 7 is a surface morphology diagram of a positive electrode active material prepared for Example 1;

[0044] Figure 8 is a surface morphology diagram of a positive electrode active material prepared for Comparative Example 1;

[0045] Figure 9 is a surface morphology diagram of a positive electrode active material disassembled after a coin cell of Example 1 was cycled for 50 cycles;

[0046] Figure 10 is a surface morphology diagram of a positive electrode active material disassembled after a coin cell of Comparative Example 1 was cycled for 50 cycles.

[0047] BRIEF DESCRIPTION OF DRAWINGS

[0048] 1000: positive electrode active material; 100: inner core; 200: coating layer; 1: secondary battery; 2: battery module; 3: battery pack; 4: upper case; 5: lower case. DETAILED DESCRIPTION

[0049] The embodiments of the technical solutions of the present application will be described in detail below. The following examples are only used to more clearly illustrate the technical solutions of the present application, and therefore only serve as examples, and cannot limit the protection scope of the present application.

[0050] Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the present application. The appearance of the phrase in various places in the specification does not necessarily all refer to the same embodiment, nor does it necessarily refer to a particular embodiment in an exclusive sense. It is explicitly and implicitly understood that the embodiments described herein can be combined. ​

[0051] For the sake of brevity, only some numerical ranges are specifically disclosed herein. However, any upper limit can be combined with any lower limit to create a range not explicitly recited; and any lower limit can be combined with any other lower limit to create a range not explicitly recited, as well as any upper limit can be combined with any other upper limit to create a range not explicitly recited. Further, each individual disclosed point or singular number can be combined as a lower limit or an upper limit with any other point or singular number or with other lower limits or upper limits to create a range not explicitly recited.

[0052] In the description of the embodiments of the present application, the term "and / or" is only a description of an association relationship of associated objects, which means that there can be three relationships, for example, A and / or B, which can represent the three cases of A existing alone, A and B existing together, and B existing alone. In addition, the character " / " in this paper generally represents that the front and rear associated objects are in an "or" relationship.

[0053] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used in this paper is only for the purpose of describing specific embodiments and is not intended to limit the application; the terms "include" and "have" in the specification and claims of this application and the above description of drawings are intended to cover non-exclusive inclusion.

[0054] Secondary batteries are not only applied to energy storage power systems such as hydroelectric, thermal, wind and solar power stations, but also widely used in electric bicycles, electric motorcycles, electric vehicles and other electric vehicles, military equipment, aerospace and other fields. Sodium-ion batteries have strong price advantage compared with traditional lithium-ion batteries, and have wide application prospect in large-scale energy storage systems.

[0055] Layered transition metal oxides have become one of the popular positive active materials of sodium-ion batteries due to high conductivity, high energy density, large capacity and long cycle life. Under high-voltage charging conditions, more sodium ions are removed from the layered transition metal oxides, which makes them have a higher specific capacity. However, the activity of oxygen in the layered transition metal oxides is high, which easily reacts with the metal in the transition metal oxides to cause the metal to migrate to the electrolyte, and the high-activity oxygen also easily reacts with the electrolyte, leading to the dissolution of the metal in the transition metal oxides and the loss of oxygen, causing the layered transition metal oxides to crack, reducing the structural stability of the layered transition metal oxides, thereby making the battery have low cycle stability at high voltage.

[0056] In the present application, the positive electrode active material comprises an inner core and a coating layer arranged on at least part of the surface of the inner core, the inner core comprises a sodium ion transition metal oxide containing iron elements and / or nickel elements, wherein the molar amount of iron elements is denoted as b, the molar amount of nickel elements is denoted as c, 0≤b≤0.4, 0≤c≤0.4, since the nickel and iron in the sodium ion transition metal oxide have high activity, they are easy to induce the increase of oxygen activity of the adjacent oxygen sites, thus the present application controls the molar amount b of iron elements and the molar amount c of nickel elements to be within the above range, which can reduce the content of high-activity oxygen in the transition metal oxide. At the same time, the coating layer contains an alkaline sodium compound, the mass percentage of the alkaline sodium compound based on the total amount of the positive electrode active material is w%, and the iron elements and / or nickel elements in the sodium ion transition metal oxide in the inner core and the alkaline sodium compound in the coating layer satisfy: 0.1≤(b+c) / w≤0.5, the inner core and the coating layer satisfying the composition can increase the specific capacity of the positive electrode active material while reducing the surface activity of the sodium ion transition metal oxide, and the coating layer can also effectively isolate the sodium ion transition metal oxide from the electrolyte, reduce the side reaction between the electrolyte and the surface of the transition metal oxide, reduce metal dissolution and oxygen deficiency, improve the structural stability of the positive electrode active material at high voltage, thereby improving the cycle stability and energy density of the battery containing it at high voltage.

[0057] The positive electrode active material disclosed in the embodiments of the present application is suitable for secondary batteries, and the battery disclosed in the embodiments of the present application can be used in an electric device using a battery as a power source or a variety of energy storage systems using a battery as an energy storage element. The electric device can include, but is not limited to, a mobile phone, a tablet, a notebook computer, an electric toy, an electric tool, an electric vehicle, an electric automobile, a ship, a spacecraft, etc. Among them, the electric toy can include a fixed or mobile electric toy, for example, a game console, an electric automobile toy, an electric ship toy, and an electric aircraft toy, etc., and the spacecraft can include an airplane, a rocket, a space shuttle, a spacecraft, etc.

[0058] The first aspect of the present application provides a positive electrode active material, referring to Figure 1 The positive electrode active material 1000 comprises an inner core 100 and a coating layer 200, the inner core 100 comprises a sodium ion transition metal oxide containing iron elements and / or nickel elements, in the sodium ion transition metal oxide, the molar amount of iron elements is denoted as b, the molar amount of nickel elements is denoted as c, 0≤b≤0.4, 0≤c≤0.4; the coating layer 200 is arranged on at least part of the surface of the inner core 100, the coating layer 200 contains an alkaline sodium compound, the mass percentage of the alkaline sodium compound based on the total amount of the positive electrode active material 1000 is w%, and satisfies: 0.1≤(b+c) / w≤0.5.

[0059] The positive electrode active material 1000 of the present application comprises an inner core 100 and a coating layer 200 arranged on at least a part of the surface of the inner core 100, the inner core 100 comprises a sodium ion transition metal oxide containing iron element and / or nickel element, wherein the molar amount of iron element is denoted as b, the molar amount of nickel element is denoted as c, 0≤b≤0.4, 0≤c≤0.4, since the nickel and iron in the sodium ion transition metal oxide have high activity, they are easy to induce the increase of oxygen activity of the adjacent oxygen sites, thus the present application controls the molar amount b of iron element and the molar amount c of nickel element to be in the above range, which can reduce the content of high-activity oxygen in the transition metal oxide. At the same time, the coating layer 200 contains an alkaline sodium compound, the mass fraction of the alkaline sodium compound based on the total amount of the positive electrode active material is w%, and the iron element and / or nickel element in the sodium ion transition metal oxide in the inner core 100 and the alkaline sodium compound in the coating layer 200 satisfy: 0.1≤(b+c) / w≤0.5, the inner core 100 and the coating layer 200 satisfying the composition can improve the specific capacity of the positive electrode active material 1000 while reducing the surface activity of the sodium ion transition metal oxide, and the coating layer 200 can also effectively isolate the sodium ion transition metal oxide from the electrolyte, reduce the side reaction between the electrolyte and the surface of the sodium ion transition metal oxide, reduce metal dissolution and oxygen deficiency, improve the structural stability of the positive electrode active material 1000 at high voltage, thereby improving the cycle stability and energy density of the battery containing it at high voltage.

[0060] In some embodiments of the present application, the core 100 comprises a sodium ion transition metal oxide containing iron element and / or nickel element, wherein the molar amount of the iron element is denoted as b, and the molar amount of the nickel element is denoted as c, 0≤b≤0.4, 0≤c≤0.4, for example, 0.001≤b≤0.4, 0.005≤b≤0.4, 0.01≤b≤0.4, 0.015≤b≤0.4, 0.02≤b≤0.4, 0.05≤b≤0.4, 0.07≤b≤0.4, 0.1≤b≤0.4, 0.12≤b≤0.4, 0.15≤b≤0.4, 0.17≤b≤0.4, 0.2≤b≤0.4, 0.22≤b≤0.4, 0.25≤b≤0.4, 0.27≤b≤0.4, 0.3≤b≤0.4, 0.32≤b≤0.4, 0.35≤b≤0.4, 0.37≤b≤0.4, etc.; 0.001≤c≤0.4, 0.005≤c≤0.4, 0.01≤c≤0.4, 0.015≤c≤0.4, 0.02≤c≤0.4, 0.05≤c≤0.4, 0.07≤c≤0.4, 0.1≤c≤0.4, 0.12≤c≤0.4, 0.15≤c≤0.4, 0.17≤c≤0.4, 0.2≤c≤0.4, 0.22≤c≤0.4, 0.25≤c≤0.4, 0.27≤c≤0.4, 0.3≤c≤0.4, 0.32≤c≤0.4, 0.35≤c≤0.4, 0.37≤c≤0.4, etc. Specifically, since the nickel and iron in the sodium ion transition metal oxide have high activity, they can easily induce the increase of the activity of the adjacent oxygen sites. Therefore, by controlling the molar amount b of the iron element and the molar amount c of the nickel element within the above range, the content of the high-activity oxygen in the transition metal oxide can be reduced, thereby reducing the metal dissolution and oxygen deficiency in the transition metal oxide, and improving the structural stability of the positive active material 1000 at high voltage.

[0061] In some embodiments of the present application, the mass percentage of the basic sodium compound is w%, and satisfies: 0.1≤(b+c) / w≤0.5, for example, 0.15≤(b+c) / w≤0.45, 0.2≤(b+c) / w≤0.4, 0.25≤(b+c) / w≤0.35, 0.25≤(b+c) / w≤0.3, etc., based on the total amount of the positive electrode active material 1000. In some other embodiments of the present application, the mass percentage of the basic sodium compound is w%, and satisfies: 0.2≤(b+c) / w≤0.4. In this way, the core 100 and the coating layer 200 satisfying the composition can improve the specific capacity of the positive electrode active material 1000 while reducing the surface activity of the sodium ion transition metal oxide, and the coating layer 200 can also effectively isolate the sodium ion transition metal oxide from the electrolyte, reduce the side reaction between the electrolyte and the surface of the sodium ion transition metal oxide, reduce metal dissolution and oxygen deficiency, improve the structural stability of the positive electrode active material 1000 at high voltage, thereby improving the cycle stability and energy density of the battery containing the same at high voltage.

[0062] In some embodiments of the present application, the mass percentage of the basic sodium compound is w%, and satisfies: 0.1≤(b+c) / w≤0.5, for example, 0.15≤(b+c) / w≤0.45, 0.2≤(b+c) / w≤0.4, 0.25≤(b+c) / w≤0.35, 0.25≤(b+c) / w≤0.3, etc., based on the total amount of the positive electrode active material 1000. In some other embodiments of the present application, the mass percentage of the basic sodium compound is w%, and satisfies: 0.2≤(b+c) / w≤0.4. In this way, the core 100 and the coating layer 200 satisfying the composition can improve the specific capacity of the positive electrode active material 1000 while reducing the surface activity of the sodium ion transition metal oxide, and the coating layer 200 can also effectively isolate the sodium ion transition metal oxide from the electrolyte, reduce the side reaction between the electrolyte and the surface of the sodium ion transition metal oxide, reduce metal dissolution and oxygen deficiency, improve the structural stability of the positive electrode active material 1000 at high voltage, thereby improving the cycle stability and energy density of the battery containing the same at high voltage.

[0063] In some embodiments of the present application, the basic sodium compound includes at least one of sodium hydroxide and sodium carbonate. In some other embodiments of the present application, the basic sodium compound includes sodium carbonate. In this way, the coating layer 200 including the basic sodium compound described above can effectively isolate the sodium ion transition metal oxide from the electrolyte, reduce the side reaction between the electrolyte and the surface of the sodium ion transition metal oxide, reduce metal dissolution and oxygen deficiency, improve the structural stability of the positive electrode active material 1000 at high voltage, thereby improving the cycle stability and energy density of the battery containing the same at high voltage.

[0064] In some embodiments of the present application, the mass percentage of sodium carbonate in the total mass of the coating layer 200 is higher than or equal to 80%, for example, 80%-100%, 82%-98%, 85%-95%, 87%-92%, 90%-92%, etc. In this way, the sodium carbonate is uniformly distributed on the surface of the core 100 in the coating layer 200, and the coating layer 200 formed by the conversion is more uniform, which can effectively isolate the sodium ion transition metal oxide from contacting the electrolyte, reduce the side reaction between the electrolyte and the surface of the sodium ion transition metal oxide, reduce metal dissolution and oxygen deficiency, improve the structural stability of the positive active material 1000 at high voltage, thereby improving the cycle stability and energy density of the battery containing the same at high voltage.

[0065] In some embodiments of the present application, the mass percentage of sodium hydroxide in the total mass of the coating layer 200 is less than or equal to 10%, for example, 9%-10%, 8%-8.5%, 7%-7.8%, 6%-6.8%, 5%-5.8%, 4%-4.8%, 3%-3.8%, 2%-2.8%, 1%-1.8%, 0%-1%, etc. Specifically, the sodium hydroxide in the coating layer 200 is prone to side reactions with the binder in the positive electrode slurry, causing severe gelation of the slurry. Moreover, sodium hydroxide is prone to generate water molecules during the conversion to form the coating layer 200, and the water molecules are prone to react with lithium salt sodium hexafluorophosphate in the battery electrolyte to form HF, thereby reducing the cycle stability of the battery. Therefore, the mass percentage of sodium hydroxide in the coating layer 200 of the present application is in the above range, which can reduce the gelation of the positive electrode slurry while improving the cycle stability of the battery containing the same at high voltage.

[0066] In some embodiments of the present application, the sodium ion transition metal oxide in the above-mentioned core 100 comprises:

[0067] Na x Mn a Fe b Ni c Q d O 2-e+δ F e ,

[0068] 0.5≤x≤1.2, 0

[0069] In some specific embodiments of the present application, the sodium ion transition metal oxide in the above-mentioned core 100 includes:

[0070] Na x Mn a Fe b Ni c Q d O 2-e+δ F e ,

[0071] 0.7 ≤ x ≤ 1.2, 0 < a, 0.1 ≤ b ≤ 0.4, 0.1 ≤ c ≤ 0.4, 0 ≤ d ≤ 0.3, a + b + c + d = 1, 0 ≤ e ≤ 0.2, -0.1 ≤ δ ≤ 0.1, Q includes at least one of Li, B, Mg, Al, Si, K, Ca, Ti, Co, Cu, Zn, Ga, Y, Zr, Nb, Mo, In, Sn, Sb, La, Ce, Ta, W, and Bi, optionally at least one of B, Mg, Al, Si, Ca, Ti, Co, Cu, Zn, Zr, Nb, Mo, La, and Bi. Based on the total amount of the positive electrode active material 1000, the mass ratio of the alkaline sodium compound is 1 wt% - 2 wt%, such as 1.2 wt% - 2 wt%, 1.5 wt% - 2 wt%, 1.8 wt% - 2 wt%, etc. Thus, the mass ratio of the alkaline sodium compound in the coating layer 200 on the surface of the sodium ion transition metal oxide core 100 composed in the present application satisfies the above range, which can effectively isolate the sodium ion transition metal oxide from contacting with the electrolyte, reduce the side reaction between the electrolyte and the surface of the sodium ion transition metal oxide, reduce metal dissolution and oxygen deficiency, improve the structural stability of the positive electrode active material 1000 at high voltage, and thus improve the cycle stability and energy density of the battery containing it at high voltage.

[0072] In some embodiments of the present application, in the above-mentioned sodium ion transition metal oxide Na x Mn a Fe b Ni c Q d O 2-e+δ F e x can take 0.7 ≤ x ≤ 1.2, such as 0.7 ≤ x ≤ 1.1, 0.8 ≤ x ≤ 1, 0.85 ≤ x ≤ 1, 0.88 ≤ x ≤ 1, 0.9 ≤ x ≤ 1, 0.95 ≤ x ≤ 1, 0.98 ≤ x ≤ 1, etc. Thus, the inclusion of this content of sodium element in the sodium ion transition metal oxide enables the battery to have a relatively high capacity.

[0073] It should be noted that in the positive electrode sheet, the battery or the electric device, due to the processes such as formation and cycle of the battery, the sodium ions will be consumed, and thus the measured sodium element content x in the sodium ion transition metal oxide is less than 1. At the same time, if the positive electrode sheet and the negative electrode sheet use a sodium supplement agent, after the processes such as formation and cycle of the battery, the measured sodium element content x in the sodium ion transition metal oxide is greater than 1.

[0074] In some embodiments of the present application, the above-mentioned sodium ion transition metal oxide Na x Mn a Fe b Ni c Q d O 2-e+δ F e a can be taken as a>0, for example, 0.001≤a<1, 0.005≤a≤0.9, 0.1≤a≤0.8, 0.2≤a≤0.7, 0.3≤a≤0.6, 0.4≤a≤0.5, etc. Thus, the sodium ion transition metal oxide includes the content of manganese, which can effectively improve the structural stability of the sodium ion transition metal oxide, and improve the cycle stability of the battery containing it. In other embodiments of the present application, the above-mentioned sodium ion transition metal oxide Na x Mn a Fe b Ni c Q d O 2-e+δ F e a can be taken as 0.3≤a≤0.6.

[0075] In some embodiments of the present application, the above-mentioned sodium ion transition metal oxide Na x Mn a Fe b Ni c Q d O 2-e+δ F e b can be taken as 0.1≤b≤0.4, for example, 0.1≤b≤0.35, 0.15≤b≤0.3, 0.2≤b≤0.25, 0.22≤b≤0.25, etc. Thus, the sodium ion transition metal oxide Na x Mn a Fe b Ni c Q d O 2-e+δ F e includes the content of Fe, which not only can reduce the high activity oxygen content in the sodium ion transition metal oxide, but also can improve the specific capacity of the positive active material 1000. In other embodiments of the present application, the above-mentioned sodium ion transition metal oxide Na x Mna Fe b Ni c Q d O 2-e+δ F e In some embodiments of the present application, the sodium ion transition metal oxide Na

[0076] In some embodiments of the present application, the sodium ion transition metal oxide Na x Mn a Fe b Ni c Q d O 2-e+δ F e In some embodiments of the present application, the sodium ion transition metal oxide Na x Mn a Fe b Ni c Q d O 2-e+δ F e In some embodiments of the present application, the sodium ion transition metal oxide Na x Mn a Fe b Ni c Q d O 2-e+δ F e In some embodiments of the present application, the sodium ion transition metal oxide Na

[0077] In some embodiments of the present application, the sodium ion transition metal oxide Na x Mn a Fe b Ni c Q d O 2-e+δ F e In some embodiments of the present application, the sodium ion transition metal oxide Na x Mn a Fe b Ni c Q d O 2-e+δ F eQ includes at least one of B, Mg, Al, Si, Ca, Ti, Co, Cu, Zn, Zr, Nb, Mo, La, and Bi.

[0078] In some embodiments of the present application, the above-mentioned sodium ion transition metal oxide Na x Mn a Fe b Ni c Q d O 2-e+δ F e d takes 0≤d≤0.3, for example, 0.001≤d≤0.3, 0.005≤d≤0.3, 0.01≤d≤0.3, 0.05≤d≤0.3, 0.1≤d≤0.3, 0.15≤d≤0.3, 0.17≤d≤0.27, 0.2≤d≤0.25, 0.2≤d≤0.22, and the like. Thus, the sodium ion transition metal oxide Na x Mn a Fe b Ni c Q d O 2-e+δ F e In the above-mentioned sodium ion transition metal oxide Na x Mn a Fe b Ni c Q d O 2-e+δ F e d takes 0.1≤d≤0.2.

[0079] In some embodiments of the present application, the above-mentioned sodium ion transition metal oxide Na x Mn a Fe b Ni c Q d O 2-e+δ F e δ takes -0.1≤δ≤0.1 and e takes 0≤e≤0.2, for example, -0.09≤δ≤0.09, -0.08≤δ≤0.08, -0.07≤δ≤0.07, -0.06≤δ≤0.06, -0.05≤δ≤0.05, -0.04≤δ≤0.04, -0.03≤δ≤0.03, -0.02≤δ≤0.02, -0.01≤δ≤0.01, -0.01≤δ≤0, 0≤δ≤0.01, and the like, 0.01≤e≤0.2, 0.02≤e≤0.18, 0.05≤e≤0.15, 0.08≤e≤0.12, 0.1≤e≤0.12, and the like.

[0080] Specifically, the sodium ion transition metal oxide Na x Mn a Fe b Ni c Q d O 2-e+δ F e The oxygen site in the sodium ion transition metal oxide is doped with the content of F, which can effectively stabilize the oxygen in the sodium ion transition metal oxide, thereby reducing the structural damage caused by the lattice oxygen release in the sodium ion transition metal oxide, improving the stability of the positive electrode active material 1000, and further improving the cycle stability of the battery.

[0081] It should be noted that in the positive electrode sheet, the battery or the electrical equipment, due to the cycle process of the battery, the oxygen element in the sodium ion transition metal oxide is lost, so the measured content of the oxygen element in the sodium ion transition metal oxide is less than 2+δ-e.

[0082] In some embodiments of the present application, the above-mentioned sodium ion transition metal oxide Na x Mn a Fe b Ni c Q d O 2-e+δ F e 0.5≤(b+c) / a≤2, for example, 0.8≤(b+c) / a≤2, 1≤(b+c) / a≤1.8, 1.2≤(b+c) / a≤1.6, 1.5≤(b+c) / a≤1.6, etc. In other embodiments of the present application, the above-mentioned sodium ion transition metal oxide Na x Mn a Fe b Ni c Q d O 2-e+δ F e 0.5≤(b+c) / a≤1.5. Specifically, Ni can contribute capacity, but Fe and Ni are prone to cause structural instability when they change valence, while Mn can stabilize the structure of the sodium ion transition metal oxide, so that the molar amount a of Mn and the molar amount b of Fe and the molar amount c of Ni in the sodium ion transition metal oxide of the present application satisfy the above relationship, which can improve the specific capacity of the sodium ion transition metal oxide while improving its structural stability at high voltage, thereby improving the cycle stability and energy density of the battery containing it at high voltage.

[0083] In some embodiments of the present application, the above-mentioned sodium ion transition metal oxide Na x Mn a Fe b Ni c Q d O2-e+δ F e The phase states include the O3 phase, and the space group includes... The interlayer spacing is 0.53nm-0.55nm, for example, it can be 0.532nm-0.55nm, 0.535nm-0.548nm, 0.537nm-0.545nm, 0.540nm-0.542nm, etc. Specifically, the high sodium ion transition metal oxide (Na) content in the formed O3 phase results in a high battery capacity.

[0084] It should be noted that the sodium ion transition metal oxide Na in this application x Mn a Fe b Ni c Q d O 2-e+δ F e The phase state, space group, and interlayer spacing can be characterized using X-ray diffraction.

[0085] Specifically, sodium ions in transition metal oxides (Na) x Mn a Fe b Ni c Q d O 2-e+δ F e The interlayer spacing d of the 003 crystal plane 003 The space group testing method includes: grinding the sample to be tested in an agate mortar and pestle in a drying room or glove box, then passing it through a 350-mesh sieve. A suitable amount of the sieved sample is placed in the center of the sample holder groove, ensuring the loose sample powder is slightly higher than the sample holder plane. A glass slide is then gently pressed against the sample surface to level it with the frame plane, and excess powder is scraped off. After sample preparation, a Brucker D8A_A25 X-ray powder diffractometer from Brucker AxS (Germany) is used with CuK... α X-rays are the radiation source, and the wavelength of the X-rays is... The 2θ angle was scanned within the range of 5°-60° at a scanning rate of 4° / min. After the test, the interlayer spacing d of the 003 crystal plane was obtained by using the angle corresponding to the 003 crystal plane and applying Bragg's equation 2d·sinθ=λ, as well as the fact that each unit cell of the 003 crystal plane contains three transition metal layers. 003 By comparing the XRD diffraction peaks of the sample with the standard card of the XRD analysis software, the space group and crystal phase of the sample can be confirmed.

[0086] In some further embodiments of this application, the sodium ion transition metal oxide described in core 100 above includes:

[0087] Na x Mn aNi c Q d O 2-e+δ F e ,

[0088] 0.5≤x≤1.2, 0 0.1≤c≤0.3, 0≤d≤0.3, a+c+d=1, 0≤e≤0.2, -0.1≤δ≤0.1, Q comprises at least one of Li, B, Mg, Al, Si, K, Ca, Ti, Co, Cu, Zn, Ga, Y, Zr, Nb, Mo, In, Sn, Sb, La, Ce, Ta, W and Bi, and optionally at least one of B, Mg, Al, Si, Ca, Ti, Co, Cu, Zn, Zr, Nb, Mo, La and Bi, the mass ratio of the basic sodium compound in the total amount of the positive electrode active material 1000 is 0.5wt%-1.5wt%, for example, 0.5wt%-1.3wt%, 0.7wt%-1wt%, 0.9wt%-1wt% and the like. Thus, the mass ratio of the basic sodium compound in the coating layer 200 on the surface of the sodium ion transition metal oxide core 100 composed of the present application meets the above range, which can effectively isolate the sodium ion transition metal oxide from the electrolyte, reduce the side reaction between the electrolyte and the surface of the sodium ion transition metal oxide, reduce metal dissolution and oxygen deficiency, improve the structural stability of the positive electrode active material 1000, thereby improving the cycle stability and energy density of the battery containing it at high voltage.

[0089] In some embodiments of the present application, the above-mentioned sodium ion transition metal oxide Na x Mn a Ni c Q d O 2-e+δ F e x can be taken as 0.5≤x≤1.2, for example, 0.5≤x≤1.1, 0.6≤x≤1.1, 0.8≤x≤1, 0.85≤x≤1, 0.88≤x≤1, 0.9≤x≤1, 0.95≤x≤1, 0.98≤x≤1 and the like. Thus, the sodium element in the sodium ion transition metal oxide includes the content, so that the battery has higher capacity.

[0090] It should be noted that in the positive electrode sheet, the battery or the electric device, due to the formation and cycle of the battery and the like, the sodium ion will be consumed, so the measured sodium element content x in the sodium ion transition metal oxide will be less than 1. At the same time, if the positive electrode sheet and the negative electrode sheet use sodium supplement agent, after the formation and cycle of the battery and the like, the measured sodium element content x in the sodium ion transition metal oxide will be greater than 1.

[0091] In some embodiments of the present application, the above-mentioned sodium ion transition metal oxide Nax Mn a Ni c Q d O 2-e+δ F e In this case, 'a' can be greater than 0, for example, 0.001 ≤ a < 1, 0.005 ≤ a ≤ 0.9, 0.1 ≤ a ≤ 0.8, 0.2 ≤ a ≤ 0.7, 0.3 ≤ a ≤ 0.6, 0.4 ≤ a ≤ 0.5, etc. Therefore, including this amount of manganese in the sodium ion transition metal oxide can effectively improve the structural stability of the sodium ion transition metal oxide and improve the cycle stability of batteries containing it. In other embodiments of this application, the above-mentioned sodium ion transition metal oxide Na... x Mn a Ni c Q d O 2-e+δ F e In this case, 'a' can be 0.5 ≤ a ≤ 0.8.

[0092] In some embodiments of this application, the above-mentioned sodium ion transition metal oxide Na x Mn a Ni c Q d O 2-e+δ F e In this case, c takes values ​​of 0.1 ≤ c ≤ 0.3, for example, 0.15 ≤ c ≤ 0.3, 0.2 ≤ c ≤ 0.25, 0.22 ≤ c ≤ 0.25, etc. Therefore, this sodium ion transition metal oxide Na... x Mn a Fe b Ni c Q d O 2-e+δ F e Including this amount of Ni not only reduces the content of highly reactive oxygen species in sodium ion transition metal oxides, but also increases the specific capacity of the positive electrode active material 1000. In other embodiments of this application, the aforementioned sodium ion transition metal oxide Na... x Mn a Ni c Q d O 2-e+δ F e In this case, c is set to 0.15 ≤ c ≤ 0.25.

[0093] In some embodiments of this application, the above-mentioned sodium ion transition metal oxide Na x Mn a Ni c Q d O 2-e+δ F eQ includes at least one of Li, B, Mg, Al, Si, K, Ca, Ti, Co, Cu, Zn, Ga, Y, Zr, Nb, Mo, In, Sn, Sb, La, Ce, Ta, W, and Bi. In other embodiments of the present application, the above-mentioned sodium-ion transition metal oxide Na x Mn a Ni c Q d O 2-e+δ F e Q includes at least one of B, Mg, Al, Si, Ca, Ti, Co, Cu, Zn, Zr, Nb, Mo, La, and Bi.

[0094] In some embodiments of the present application, the above-mentioned sodium-ion transition metal oxide Na x Mn a Ni c Q d O 2-e+δ F e d takes 0≤d≤0.3, for example, 0.001≤d≤0.3, 0.005≤d≤0.3, 0.01≤d≤0.3, 0.05≤d≤0.3, 0.1≤d≤0.3, 0.15≤d≤0.3, 0.17≤d≤0.27, 0.2≤d≤0.25, 0.2≤d≤0.22, and the like. Thereby, the sodium-ion transition metal oxide Na x Mn a Ni c Q d O 2-e+δ F e In the above-mentioned sodium-ion transition metal oxide Na x Mn a Ni c Q d O 2-e+δ F e d takes 0.05≤d≤0.15.

[0095] In some embodiments of the present application, the above-mentioned sodium-ion transition metal oxide Na x Mn a Ni c Q d O 2-e+δ F eThe middle δ is in the range of -0.1≤δ≤0.1, and e is in the range of 0≤e≤0.2, for example, -0.09≤δ≤0.09, -0.08≤δ≤0.08, -0.07≤δ≤0.07, -0.06≤δ≤0.06, -0.05≤δ≤0.05, -0.04≤δ≤0.04, -0.03≤δ≤0.03, -0.02≤δ≤0.02, -0.01≤δ≤0.01, -0.01≤δ≤0, 0≤δ≤0.01, and the like, 0.01≤e≤0.2, 0.02≤e≤0.18, 0.05≤e≤0.15, 0.08≤e≤0.12, 0.1≤e≤0.12, and the like.

[0096] Specifically, the sodium ion transition metal oxide Na x Mn a Ni c Q d O 2-e+δ F e The middle oxygen site doped F can effectively stabilize the oxygen in the sodium ion transition metal oxide, thereby reducing the structural damage caused by the lattice oxygen release in the sodium ion transition metal oxide, improving the stability of the positive electrode active material 1000, and further improving the cycle stability of the battery.

[0097] It should be noted that in the positive electrode sheet, the battery or the electrical equipment, due to the cycle process of the battery, the oxygen element in the sodium ion transition metal oxide is lost, and thus the measured content of the oxygen element in the sodium ion transition metal oxide 2+δ-e is less than 2.

[0098] In some embodiments of the present application, the above-mentioned sodium ion transition metal oxide Na x Mn a Ni c Q d O 2-e+δ F e The middle 0.125≤c / a≤0.45, for example, 0.15≤c / a≤0.45, 0.175≤c / a≤0.425, 0.2≤c / a≤0.4, 0.225≤c / a≤0.375, 0.25≤c / a≤0.35, 0.275≤c / a≤0.325, 0.3≤c / a≤0.325, and the like. In some other embodiments of the present application, the above-mentioned sodium ion transition metal oxide Na x Mn a Ni c Q d O 2-e+δ F eIn this application, 0.2 ≤ c / a ≤ 0.3. Specifically, Ni contributes to capacity, but Ni's valence changes can easily lead to structural instability. Mn, on the other hand, can stabilize the structure of sodium-ion transition metal oxides. Therefore, in this application, the molar amount of Mn, a, and the molar amount of Ni, c, in the sodium-ion transition metal oxide satisfy the above relationship. This can improve the specific capacity of the sodium-ion transition metal oxide while simultaneously enhancing its structural stability at high voltage, thereby improving the high-voltage cycle stability and energy density of batteries containing it.

[0099] In some embodiments of this application, the above-mentioned sodium ion transition metal oxide Na x Mn a Ni c Q d O 2-e+δ F e The phase states include P2 phase, the space group includes P63 / mmc, and the interlayer spacing is 0.55nm-0.57nm, for example, the interlayer spacing can be 0.552nm-0.57nm, 0.555nm-0.568nm, 0.557nm-0.565nm, 0.56nm-0.562nm, etc. Specifically, the large interlayer spacing of the formed P2 phase sodium ion transition metal oxide can improve the Na ion transport rate, maintain the integrity of the layered structure, and enable the battery to have excellent rate performance and cycle performance.

[0100] It should be noted that the sodium ion transition metal oxide Na in this application x Mn a Ni c Q d O 2-e+δ F e The phase state, space group, and interlayer spacing can be characterized using X-ray diffraction.

[0101] Specifically, sodium ions in transition metal oxides (Na) x Mn a Ni c Q d O 2-e+δ F e The interlayer spacing d of the 003 crystal plane 003 The space group testing method includes: grinding the sample to be tested in an agate mortar and pestle in a drying room or glove box, then passing it through a 350-mesh sieve. A suitable amount of the sieved sample is placed in the center of the sample holder groove, ensuring the loose sample powder is slightly higher than the sample holder plane. A glass slide is then gently pressed against the sample surface to level it with the frame plane, and excess powder is scraped off. After sample preparation, a Brucker D8A_A25 X-ray powder diffractometer from Brucker AxS (Germany) is used with CuK... α X-rays are the radiation source, and the wavelength of the X-rays is... The test is performed at a scanning 2θ angle range of 5°-60° and a scanning rate of 4° / min. After the test, the interlayer spacing d of the 003 crystal face can be obtained according to the Bragg equation 2d·sinθ = λ and the fact that each unit cell of the 003 crystal face contains three transition metal layers. 003 The space group and crystal phase of the sample can be confirmed by comparing the XRD diffraction peak of the sample with the standard card of the XRD analysis software.

[0102] In some embodiments of the present application, the BET specific surface area of the positive electrode active material 1000 is Sm 2 / g, and S and w satisfy the relationship: 0.3≤w / S≤3, for example, 0.5≤w / S≤2.8, 0.7≤w / S≤2.5, 1≤w / S≤2.2, 1.3≤w / S≤2, 1.5≤w / S≤1.8, etc. In other embodiments of the present application, S and w in the positive electrode active material 1000 satisfy the relationship: 0.5≤w / S≤2. As such, when S and W in the positive electrode active material 1000 of the present application satisfy the above relationship, the contact between the sodium ion transition metal oxide and the electrolyte can be effectively prevented, the side reaction between the electrolyte and the surface of the transition metal oxide can be reduced, the metal dissolution and oxygen deficiency can be reduced, and the structural stability of the positive electrode active material 1000 can be improved, thereby improving the cycle stability and energy density of the battery containing the same at high voltage.

[0103] In some embodiments of the present application, the D v 50 of the positive electrode active material 1000 is 2 μm-20 μm, for example, the D v 50 of the positive electrode active material can be 2 μm-19 μm, 4 μm-18 μm, 5 μm-15 μm, 6 μm-14 μm, 8 μm-13 μm, 9 μm-12 μm, 10 μm-11 μm, etc. In other embodiments of the present application, the D v 50 of the positive electrode active material 1000 is 4 μm-15 μm.

[0104] In the present application, the D v 50 refers to the particle size corresponding to the cumulative volume percentage of 50%, which can be determined by using a laser particle size analyzer (for example, Malvern Master Size 3000) according to the standard GB / T 19077-2016.

[0105] In some embodiments of the present application, the BET specific surface area of the positive electrode active material 1000 is 0.2 m 2 / g-2 m 2 / g, for example, the specific surface area of the positive electrode active material can be 0.2 m 2 / g-1.5 m2 / g, 0.2m 2 / g-1m 2 / g, 0.3m 2 / g-0.8m 2 / g, 0.3m 2 / g-0.5m 2 / g, etc. In some embodiments of the present application, the specific surface area of the positive electrode active material 1000 is 0.3m 2 / g-2m 2 / g.

[0106] In the present application, the BET specific surface area of the positive electrode active material 1000 is the meaning known in the art, and can be measured by using the instruments and methods known in the art, for example, the BET specific surface area of the positive electrode active material 1000 can be measured by using the American Micromeritics Gemini VII 2390 full-automatic specific surface area and pore analyzer, about 7g of sample is placed in a 9cc long tube with a ball bubble, degassed at 200°C for 2h, and then placed in the main machine to measure the BET specific surface area data of the positive electrode active material 1000.

[0107] In some embodiments of the present application, the compaction density of the positive electrode active material 1000 under a pressure of 300MPa is 3.1g / cm 3 -3.8g / cm 3 , for example, the compaction density of the positive electrode active material 1000 under a pressure of 300MPa can be 3.0g / cm 3 -3.8g / cm 3 , 3.2g / cm 3 -3.5g / cm 3 , 3.2g / cm 3 -3.4g / cm 3 , etc. In some embodiments of the present application, the compaction density of the positive electrode active material 1000 under a pressure of 300MPa is 3.2g / cm 3 -3.6g / cm 3 .

[0108] In the present application, the compaction density is the meaning known in the art, and can be measured by using the instruments and methods known in the art, for example, the following test method can be used: a certain amount of powder is placed in a compaction special mold, the mold is placed on a compaction density instrument, a pressure of 300MPa is set, the thickness volume v of the powder under a pressure of 300MPa is measured on the device, and the compaction density is calculated by density=mass m / volume v; (for reference, GB / T24533-2009).

[0109] Specifically, when the D v50、When at least one of the specific surface area and the compaction density under a pressure of 300 MPa is in the above range, the conduction distance in the positive electrode active material 1000 is small, the surface side reaction is less, and the capacity of the positive electrode active material is promoted to exert its capacity, and the capacity retention rate of the battery containing the same is improved.

[0110] In the present application, the elemental composition of the positive electrode active material 1000 can be determined by using instruments and methods known in the art, for example, by using inductively coupled plasma atomic emission spectrometry, instrument standard reference EPA6010D-2014 "Inductively Coupled Plasma Atomic Emission Spectrometry". The sample is treated by chemical method to be digested into solution, atomized into plasma to be excited to emit characteristic spectrum of elements, and the element content is qualitatively and quantitatively analyzed according to the wavelength and intensity (proportional to concentration) of the spectrum.

[0111] The content of the basic sodium compound Na2CO3 in the coating layer 200 of the positive electrode active material 1000 can be determined by using instruments and methods known in the art, for example, by testing according to the GB / T 9736-2008 standard. Under an atmosphere excluding carbon dioxide, 30 g of the obtained positive electrode active material powder is added with 100 ml of pure water and stirred for 30 min, and after standing for 10 min, a certain amount of filtrate is removed after filtration, 0.05 mol / L hydrochloric acid standard solution is selected for titration, and Mettler T5 titrator is used.

[0112] The content of the basic sodium compound NaOH in the coating layer 200 of the positive electrode active material 1000 can be determined by using instruments and methods known in the art, for example, by testing according to the GB / T 9736-2008 standard. Under an atmosphere excluding carbon dioxide and dehumidification, 30 g of the obtained layered oxide powder is added with 100 ml of anhydrous ethanol and stirred for 30 min, and after standing for 10 min, 10 mL of the filtrate is removed after filtration, and then 50 mL of ultrapure water is used for dilution, and then 0.05 mol / L hydrochloric acid standard solution is selected for titration, and Mettler T5 titrator is used.

[0113] In the present application, the content of sodium element in the composition of the sodium ion transition metal oxide in the core 100 can be calculated by subtracting the total amount of the basic sodium compounds NaOH and Na2CO3 in the coating layer obtained by the above-mentioned test method from the total amount of sodium element obtained by the above-mentioned inductively coupled plasma atomic emission spectrometry, and the content of other elements in the composition of the sodium ion transition metal oxide can be obtained by the above-mentioned inductively coupled plasma atomic emission spectrometry, thereby obtaining the composition of the sodium ion transition metal oxide. The mass percentage w% of the basic sodium compound in the above-mentioned positive electrode active material 1000 can be obtained by adding the contents of the basic sodium compounds NaOH and Na2CO3 in the coating layer.

[0114] The second aspect of the present application provides a method for preparing the positive electrode active material of the first aspect, comprising:

[0115] S100: providing a sodium-ion transition metal oxide containing an iron element and / or a nickel element

[0116] In some embodiments of the present application, in the sodium-ion transition metal oxide, the molar amount of the iron element is denoted as b, the molar amount of the nickel element is denoted as c, 0≤b≤0.4, and 0≤c≤0.4.

[0117] In the present application, the sodium-ion transition metal oxide can include: Na x Mn a Fe b Ni c Q d O 2-e+δ F e For example, the sodium-ion transition metal oxide includes the above Na x Mn a Fe b Ni c Q d O 2-e+δ F e , 0.7≤x≤1.2, 0<a, 0.1≤b≤0.4, 0.1≤c≤0.4, 0≤d≤0.3, a+b+c+d=1, 0≤e≤0.2, -0.1≤δ≤0.1, Q includes at least one of Li, B, Mg, Al, Si, K, Ca, Ti, Co, Cu, Zn, Ga, Y, Zr, Nb, Mo, In, Sn, Sb, La, Ce, Ta, W and Bi; and for another example, the sodium-ion transition metal oxide includes the above Na x Mn a Ni c Q d O 2-e+δ F e , 0.5≤x≤1.2, 0<a, 0.1≤c≤0.3, 0≤d≤0.3, a+c+d=1, 0≤e≤0.2, -0.1≤δ≤0.1, Q includes at least one of Li, B, Mg, Al, Si, K, Ca, Ti, Co, Cu, Zn, Ga, Y, Zr, Nb, Mo, In, Sn, Sb, La, Ce, Ta, W and Bi.

[0118] In some embodiments of the present application, the preparation method of the above-mentioned sodium ion transition metal oxide can comprise: mixing a Na source, a Fe source, a Mn source, a Ni source and a Q source according to the composition of the above-mentioned sodium ion transition metal oxide, pre-milling in an agate mortar, and then ball milling in a planetary ball mill for 1 h-8 h, such as 2 h-7 h, 3 h-6 h, 4 h-5 h, etc., to obtain a precursor mixture I; uniformly placing the obtained precursor mixture I in an open crucible, and then heating from room temperature to 900 ℃-1000 ℃, such as 910 ℃-990 ℃, 920 ℃-980 ℃, 930 ℃-970 ℃, 940 ℃-960 ℃, 940 ℃-950 ℃, at a heating rate of 2 ℃ / min-5 ℃ / min, such as 2 ℃ / min-3 ℃ / min, 2 ℃ / min-3 ℃ / min, etc., in a muffle furnace, and keeping constant temperature for 10 h-20 h, such as 11 h-19 h, 12 h-18 h, 13 h-17 h, 14 h-16 h, 14 h-15 h, etc., and the atmosphere used is air without moisture and carbon dioxide, and after natural cooling, a sodium ion transition metal oxide is obtained.

[0119] It should be noted that due to the loss of Na source in the subsequent calcination process, the amount of Na added will be slightly higher than the required content of Na in the above-mentioned sodium ion transition metal oxide composition.

[0120] The Na source, Fe source, Mn source, Ni source and Q source in the present application are conventional materials in the art, which can be selected by the skilled person according to the actual situation, for example, the Na source can include at least one of Na2CO3, NaHCO3, NaOH and Na2O2; the Fe source can include at least one of FeO, Fe2O3 and Fe3O4; the Mn source can include at least one of Mn2O3, Mn3O4, MnO and MnO2; the Ni source can include NiO; and the Q source can include at least one of an oxide of Q, a salt containing Q and other compounds.

[0121] It should be noted that if it is necessary to dope F elements in the positive active material, at least one of the Na source, the Fe source, the Mn source, the Ni source and the Q source adopts at least one of its corresponding fluorine-containing salt and other compounds, such as sodium fluoride, iron fluoride, manganese fluoride, fluorinated Ni and fluorinated Q (fluorinated salt of Q).

[0122] S200: mixing and sintering the sodium ion transition metal oxide and the basic sodium compound

[0123] In some embodiments of the present application, the sodium ion transition metal oxide and the basic sodium compound described above are mixed according to 0.1≤(b+c) / w≤0.5 (the molar amount of iron in the sodium ion transition metal oxide is denoted as b, the molar amount of nickel is denoted as c, and the mass percentage of the basic sodium compound based on the total amount of the positive electrode active material is w%), pre-milled in an agate mortar, and then added to a planetary ball mill for ball milling for 1h-8h, such as 2h-7h, 3h-6h, 4h-5h, etc., to obtain a precursor mixture II. The obtained precursor mixture II is uniformly placed in an open crucible, and then heated from room temperature to 300℃-600℃, such as 350℃-550℃, 400℃-500℃, 450℃-500℃, etc., at a heating rate of 2℃ / min-5℃ / min, such as 2℃ / min-3℃ / min, 2℃ / min-3℃ / min, etc., and held at a constant temperature for 1h-3h, such as 1h-2h, 2h-3h, 1h-1.5h, etc., in an atmosphere of air with dehumidification and de-carbon dioxide. After natural cooling, the positive electrode active material is obtained. This sintering process can make the basic sodium compound more uniformly distributed on the surface of the sodium ion transition metal oxide and better combined with each other, thereby forming a stable coating layer on the surface of the sodium ion transition metal oxide, improving the structural stability of the positive electrode active material at high voltage, and thereby improving the cycle stability and energy density of the battery containing the same at high voltage.

[0124] Thus, the method of the present application can be used to prepare the positive electrode active material described above with structural stability at high voltage, thereby improving the cycle stability and energy density of the battery containing the same at high voltage.

[0125] The third aspect of the present application provides a positive electrode tab, which comprises the positive electrode active material of the first aspect of the present application or the positive electrode active material prepared by the method of the second aspect of the present application.

[0126] The positive electrode tab generally comprises a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, and the positive electrode active material layer comprises the positive electrode active material.

[0127] The positive electrode current collector can be a conventional metal foil or a composite current collector (a metal material can be disposed on a polymer substrate to form a composite current collector). As an example, the positive electrode current collector can comprise at least one of a copper foil, an aluminum foil, a nickel foil, a stainless steel foil, a stainless steel mesh, and a carbon-coated aluminum foil.

[0128] The positive electrode active material layer can further comprise a conductive agent and a binder. The conductive agent is used to improve the conductivity of the positive electrode active material layer, and the binder is used to firmly bond the positive electrode active material and the binder to the positive electrode current collector. The present application does not make specific limitations on the types of conductive agents and binders, which can be selected according to actual needs.

[0129] As an example, the conductive agent can include at least one of super P, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers; the binder can include at least one of styrene butadiene rubber (SBR), water-based acrylic resin, carboxymethyl cellulose (CMC), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), and polyvinyl alcohol (PVA).

[0130] These materials can all be obtained through commercial channels.

[0131] The fourth aspect of the present application provides a battery comprising the positive electrode sheet of the third aspect of the present application. Thus, the battery has excellent cycle stability and energy density at high voltage.

[0132] The battery refers to a battery that can be activated by charging after discharging and continue to be used.

[0133] It can be understood that the battery proposed in the present application is a sodium ion battery.

[0134] Generally, the battery comprises a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte. During the charging and discharging process of the battery, active ions are embedded and extracted between the positive electrode sheet and the negative electrode sheet. The separator is arranged between the positive electrode sheet and the negative electrode sheet and plays a role of isolation. The electrolyte plays a role of ion conduction between the positive electrode sheet and the negative electrode sheet.

[0135] [Negative electrode sheet]

[0136] In the battery, the negative electrode sheet generally comprises a negative electrode current collector and a negative electrode active material layer arranged on the negative electrode current collector, and the negative electrode active material layer comprises a negative electrode active material.

[0137] The negative electrode current collector can adopt a conventional metal foil or a composite current collector (for example, a metal material can be arranged on a polymer substrate to form a composite current collector). As an example, the negative electrode current collector can adopt a copper foil.

[0138] The specific type of the negative active material is not limited, and any active material known in the art that can be used in the negative electrode of a sodium-ion battery can be used, and a person skilled in the art can select according to actual needs. As an example, the negative active material can include, but is not limited to, at least one of sodium metal, a carbon material, an alloy material, a transition metal oxide and / or sulfide, a phosphorus-based material, and a titanate material. Specifically, the carbon material can include at least one of hard carbon, soft carbon, amorphous carbon, and nanostructured carbon material; the alloy material can include an alloy material formed by at least one of Si, Ge, Sn, Pb, and Sb; the transition metal oxide and sulfide can have a general formula of M x N y , wherein M includes at least one of Fe, Co, Ni, Cu, Mn, Sn, Mo, Sb, and V, and N includes O or S; the phosphorus-based material can include at least one of red phosphorus, white phosphorus, and black phosphorus; and the titanate material can include at least one of Na2Ti3O7, Na2Ti6O 13 , Na4Ti5O 12 , Li4Ti5O 12 , and NaTi2(PO4)3. These materials can be obtained through commercial channels.

[0139] The negative active material layer can also optionally include a binder and a conductive agent. The conductive agent is used to improve the conductivity of the negative active material layer, and the binder is used to firmly bond the negative active material and the binder to the negative current collector. The type of the conductive agent and the binder is not limited in the present application, and can be selected according to actual needs.

[0140] As an example, the conductive agent can include at least one of super P, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0141] As an example, the binder can include at least one of SBR (styrene butadiene rubber), SBCs (styrene butadiene rubber), water-based acrylic resin, and CMC (carboxymethyl cellulose).

[0142] The negative active material layer can also optionally include a thickening agent, such as CMC (carboxymethyl cellulose). However, the present application is not limited thereto, and other materials that can be used as a thickening agent for the negative electrode sheet of a sodium-ion battery can also be used.

[0143] [Electrolyte]

[0144] The electrolyte can include an electrolyte salt and a solvent.

[0145] As an example, the electrolyte salt can include at least one of sodium hexafluorophosphate, sodium difluoro oxalate borate, sodium tetrafluoroborate, sodium bisoxalate borate, sodium perchlorate, sodium hexafluoroarsenate, sodium bis(fluorosulfonyl)imide, sodium trifluoromethylsulfonate, and sodium bis(trifluoromethylsulfonyl)imide.

[0146] As an example, the solvent can include at least one of ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0147] In some embodiments, an additive is further included in the electrolyte. For example, the additive can include a negative electrode film-forming additive, a positive electrode film-forming additive, or an additive capable of improving certain performance of the battery, such as an additive capable of improving overcharge performance of the battery, an additive capable of improving high-temperature performance of the battery, or an additive capable of improving low-temperature performance of the battery.

[0148] [Separator]

[0149] As the separator described above, the present application is not particularly limited, and any known porous structure separator having electrochemical stability and mechanical stability can be used according to actual needs. For example, the separator can include a single layer or a multi-layer film including at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride.

[0150] The shape of the battery according to the embodiments of the present application is not particularly limited, and the battery can be in a cylindrical shape, a square shape, or any other shape. For example, Figure 2 is a secondary battery 1 in a square shape as an example.

[0151] In some embodiments, the battery can include an outer package. The outer package is used to package the positive electrode sheet, the negative electrode sheet, and the electrolyte.

[0152] In some embodiments, the outer package can include a housing and a cover plate. The housing can include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The housing has an opening communicating with the receiving cavity, and the cover plate can be arranged on the opening to close the receiving cavity.

[0153] The positive electrode sheet, the negative electrode sheet, and the separator film can be formed into an electrode assembly through a winding process or a stacking process. The electrode assembly is packaged in the accommodation cavity. The number of electrode assemblies contained in the battery can include one or several, which can be adjusted according to requirements.

[0154] In some embodiments, the outer package of the battery can include a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell.

[0155] The outer package of the battery can also include a soft package, such as a pouch-type soft package. The material of the soft package can be plastic, which can include at least one of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0156] In some embodiments, the battery can be assembled into a battery module, and the number of batteries contained in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.

[0157] Figure 3 The battery module 2 is an example. Referring to Figure 3 In the battery module 2, a plurality of secondary batteries 1 can be arranged in sequence along the length direction of the battery module 2. Of course, other arbitrary arrangements can also be used. Further, the plurality of secondary batteries 1 can be fixed by fasteners.

[0158] The battery module 2 can also include a housing having an accommodation space, and the plurality of secondary batteries 1 are accommodated in the accommodation space. In some embodiments, the above-mentioned battery module can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0159] Figure 4 And 5 The battery pack 3 is an example. Referring to Figure 4 And 5 The battery pack 3 can include a battery box and a plurality of battery modules 2 arranged in the battery box. The battery box includes an upper box body 4 and a lower box body 5, and the upper box body 4 can be arranged on the lower box body 5 to form a closed space for accommodating the battery modules 2. The plurality of battery modules 2 can be arranged in the battery box in any manner.

[0160] The fifth aspect of the present application provides a power consuming device including the battery of the fourth aspect. Specifically, the battery can serve as a power source of the power consuming device, or as an energy storage unit of the power consuming device. The power consuming device can include but is not limited to mobile devices (such as mobile phones, notebook computers), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks), electric trains, ships and satellites, energy storage systems.

[0161] Figure 6 The electric device is taken as an example. The electric device includes a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle.

[0162] The electric device taken as another example can include a mobile phone, a tablet computer, and a notebook computer. The electric device usually requires thinning and can adopt a battery as a power source.

[0163] In order to make the technical problems, technical solutions and beneficial effects solved by the embodiments of the present application clearer, further detailed description will be made in combination with the embodiments and drawings. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. The description of the at least one exemplary embodiment is actually only illustrative, but not as any limitation on the present application and its application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0164] Embodiment 1

[0165] Preparation of the positive electrode active material.

[0166] Na2CO3, Mn2O3, Fe2O3, and NiO are weighed in a total amount of 30 g with a molar ratio of Na:Mn:Fe:Ni being 1:0.4:0.3:0.3, and the obtained sample is pre-ground in an agate mortar and then added to a planetary ball mill for ball milling for 1 h to obtain a precursor mixture I. The obtained precursor mixture I is uniformly placed in an open crucible, and then heated from room temperature to 950 ℃ at a heating rate of 5 ℃ / min in a muffle furnace, and kept at 950 ℃ for 15 h. The atmosphere used is air with dehumidification and de-carbon dioxide. After natural cooling, a sodium ion transition metal oxide with a composition of Na 0.89 Mn 0.4 Fe 0.3 Ni 0.3 O2is obtained. Then, the obtained sodium ion transition metal oxide is pre-ground with 0.5 g of Na2CO3 in an agate mortar and then added to a planetary ball mill for ball milling for 1 h to obtain a precursor mixture II. The obtained precursor mixture II is uniformly placed in an open crucible, and then heated from room temperature to 500 ℃ at a heating rate of 5 ℃ / min in a muffle furnace, and kept at 500 ℃ for 2 h. The atmosphere used is air with dehumidification and de-carbon dioxide. After natural cooling, a positive electrode active material with a coating layer on the surface is obtained.

[0167] Preparation of the positive electrode tab

[0168] The positive electrode active material, the conductive agent carbon black (Super P), and the binder polyvinylidene fluoride (PVDF) obtained above were mixed in a solvent NMP (N-methyl pyrrolidone) in a mass ratio of 80:15:5 by sufficient stirring to form a uniform positive electrode slurry. The positive electrode slurry was uniformly coated on the upper and lower surfaces of the positive electrode current collector aluminum foil, and after drying and cold pressing, punched into a circular sheet with a diameter of 14 mm to obtain a positive electrode sheet.

[0169]

Preparation of the negative electrode sheet

[0170] The negative electrode sheet used a metal sodium sheet.

[0171]

Preparation of the electrolyte

[0172] Ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed in equal volumes to obtain an organic solvent, and then NaClO4 was dissolved in the organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0173]

Separator film

[0174] A porous polyethylene film was used as the separator film.

[0175]

Preparation of the button cell

[0176] The positive electrode sheet, the separator film, and the negative electrode sheet were stacked in order with the separator film between the positive electrode sheet and the negative electrode sheet to play a role of isolation, and the electrolyte prepared above was added to obtain a button cell.

[0177] The button cell containing the positive electrode active material of Example 2-30 was the same as Example 1 except that the parameters in the preparation of the positive electrode active material were different (see Tables 1-6), and the element Q was added in the form of an oxide of Q, and the F source was added in the form of a sodium source NaF.

[0178] The button cell containing the positive electrode active material of Comparative Example 1 was the same as Example 1 except that the preparation process of the positive electrode active material was different.

[0179] The preparation process of the positive electrode active material of Comparative Example 1 included: Na2CO3, Mn2O3, Fe2O3, and NiO were weighed in a total amount of 30 g in a molar ratio of Na:Mn:Fe:Ni of 1:0.4:0.3:0.3, and the obtained sample was pre-ground in an agate mortar and then ball-milled in a planetary ball mill for 1 h to obtain a precursor mixture I. The obtained precursor mixture I was uniformly placed in an open crucible, and then heated from room temperature to 950℃ at a heating rate of 5℃ / min in a muffle furnace, and kept at 950℃ for 15 h in an atmosphere of air with dehumidification and de-carbon dioxide. After natural cooling, a positive electrode active material with a composition of Na 0.89 Mn 0.4 Fe0.3 Ni 0.3 O2 cathode active material.

[0180] The coin cells containing cathode active materials of Comparative Examples 2-3 and 6 are the same as Comparative Example 1 except for the parameters in the preparation of the cathode active materials (see Tables 1-6), and the element Q is added as an oxide of Q, and the F source is added in the form of a sodium source NaF.

[0181] The coin cells containing cathode active materials of Comparative Examples 4-5 are the same as Example 1 except for the parameters in the preparation of the cathode active materials (see Tables 1-6).

[0182] It is considered that the sodium element will be lost in the sintering process, so if you want to obtain a sodium ion transition metal oxide with the index x of the Na element being 1, the Na source needs to be excessive by 0.05-0.2 in the mixing stage, for example, if you want to obtain NaMn 0.4 Fe 0.3 Ni 0.3 O2 sodium ion transition metal oxide, Na2CO3, Mn2O3, Fe2O3, NiO are added in a molar ratio of Na:Mn:Fe:Ni of 1.05-1.2:0.4:0.3:0.3. It should be noted that the basic sodium compound in Examples 1-30 and Comparative Examples 4-5 is sodium carbonate.

[0183] The composition of the cathode active material in the batteries of Examples 1-30 and Comparative Examples 1-6 of the present application is shown in Tables 1-6.

[0184]

[0185]

[0186]

[0187]

[0188]

[0189]

[0190]

[0191]

[0192]

[0193]

[0194]

[0195] The surface morphology of the positive electrode active materials in Examples 1-30 and Comparative Examples 1-6, the BET specific surface area, the composition of the sodium ion transition metal oxide, the phase state, the space group and the interlayer distance, and the proportion of the basic sodium compound were characterized, and the results are shown in Tables 1-6. The first cycle discharge specific capacity of the positive electrode active materials obtained in Examples 1-30 and Comparative Examples 1-6 and the cycle performance of the coin cells were characterized, and the results are shown in Table 7.

[0196] Test means:

[0197] (1) Surface morphology characterization of the positive electrode active material:

[0198] The surface morphology of the positive electrode active material was characterized by scanning electron microscopy (SEM), for example, using a field emission scanning electron microscope (Zeiss Gemini 360) according to the JY / T010-1996 standard.

[0199] (2) Characterization of the BET specific surface area of the positive electrode active material:

[0200] The BET specific surface area data of the positive electrode active material 1000 were obtained using a U.S. Micromeritics full-automatic specific surface area and pore analyzer Gemini VII 2390, about 7g of sample was placed in a 9cc long tube with a ball bubble, degassed at 200°C for 2h, and then placed in the main machine for testing.

[0201] (3) Composition characterization of the sodium ion transition metal oxide:

[0202] Inductively coupled plasma emission spectrometry was used for testing: the instrument standard reference was EPA6010D-2014 "Inductively Coupled Plasma Atomic Emission Spectrometry". The sample was treated by chemical method to be digested into solution, atomized into plasma to be excited to the characteristic spectrum of the element, and the element content was qualitatively and quantitatively analyzed according to the wavelength and intensity (proportional to the concentration) of the spectrum.

[0203] The content of the basic sodium compound Na2CO3 in the coating layer of the positive electrode active material can be determined by instruments and methods known in the art, for example, tested according to the GB / T 9736-2008 standard. Under an atmosphere free of carbon dioxide, 30g of the obtained positive electrode active material powder was weighed, 100ml of pure water was added and stirred for 30min, and then filtered after standing for 10min. A certain amount of filtrate was removed and titrated with 0.05mol / L hydrochloric acid standard solution. The instrument used was Mettler T5 titrator.

[0204] The content of alkaline sodium compounds (NaOH) in the coating layer of the positive electrode active material can be determined using instruments and methods known in the art, such as referring to the GB / T 9736-2008 standard. Under a dehumidified atmosphere free of carbon dioxide, 30g of the obtained layered oxide powder was weighed, 100ml of anhydrous ethanol was added, and the mixture was stirred for 30min. After standing for 10min, the mixture was filtered, and 10mL of the filtrate was transferred and diluted with 50mL of ultrapure water. Then, a 0.05mol / L hydrochloric acid standard solution was used for titration using a Mettler T5 titrator.

[0205] The sodium content in the composition of sodium ion transition metal oxides can be calculated by subtracting the total amount of basic sodium compounds NaOH and Na2CO3 in the coating layer obtained by the above-mentioned inductively coupled plasma atomic emission spectrometry (ICP-AES). The contents of other elements in the composition of sodium ion transition metal oxides can be obtained by the above-mentioned inductively coupled plasma atomic emission spectrometry (ICP-AES). Thus, the composition of sodium ion transition metal oxides can be obtained.

[0206] (4) Test of the mass percentage w% of alkaline sodium compounds in the positive electrode active material: The content of alkaline sodium compounds NaOH and Na2CO3 in the above coating layer is added together to obtain the result.

[0207] (5) Phase state of sodium ion transition metal oxides and interlayer spacing d of 003 crystal plane 003 and space group testing:

[0208] Grind the sample to be tested into a fine powder in an agate mortar and pestle in a drying room or glove box, then pass it through a 350-mesh sieve. Take an appropriate amount of the sieved sample and place it in the center of the sample holder groove, ensuring the loose sample powder is slightly higher than the sample holder plane. Gently press a glass slide onto the sample surface to level it with the frame plane, and scrape off any excess powder. After sample preparation, use a Brucker D8A_A25 X-ray powder diffractometer (Brucker AxS, Germany) with CuK... α X-rays are the radiation source, and the wavelength of the X-rays is... The 2θ angle was scanned within the range of 5°-60° at a scanning rate of 4° / min. After the test, the interlayer spacing d of the 003 crystal plane was obtained by using the angle corresponding to the 003 crystal plane and applying Bragg's equation 2d·sinθ=λ, as well as the fact that each unit cell of the 003 crystal plane contains three transition metal layers. 003 By comparing the XRD diffraction peaks of the sample with the standard card of the XRD analysis software, the space group and crystal phase of the sample can be confirmed.

[0209] (6) Initial discharge specific capacity and battery cycle performance testing of positive electrode active material

[0210] 25℃, the button cell was charged to 4.2V at a current density of 10mA / g, then discharged to 1.5V at a current density of 10mA / g, to obtain the initial discharge specific capacity C0 of the button cell, then cycled 50 times at a current density of 10mA / g, and the discharge specific capacity C1 of the 50th cycle was taken. The capacity retention rate of the battery after 50 cycles = C1 / C0 x 100%.

[0211] Figure 7 The surface morphology of the positive electrode active material prepared in Example 1, Figure 8 The surface morphology of the positive electrode active material prepared in Comparative Example 1, from Figures 7-8 It can be seen that the surface of the positive electrode active material of Example 1 has a uniform coating layer, and the surface of the positive electrode active material of Comparative Example 1 is relatively clean and does not have a significant continuous coating layer. In addition, the surfaces of the positive electrode active materials of Comparative Examples 2-3 and 6 do not have a significant continuous coating layer. Figure 9 The surface morphology of the positive electrode active material of the button cell of Example 1 after 50 cycles, Figure 10 The surface morphology of the positive electrode active material of the button cell of Comparative Example 1 after 50 cycles, from Figures 9-10 It can be seen that the surface of the positive electrode active material of the button cell of Example 1 still has a uniform coating layer and no obvious cracks after 50 cycles, while the surface of the positive electrode active material of the button cell of Comparative Example 1 has obvious cracks after 50 cycles, which indicates that the positive electrode active material of Example 1 has higher structural stability at high voltage than the positive electrode active material of Comparative Example 1, thereby improving the cycle performance and energy density of the battery of Example 1.

[0212] Table 7

[0213]

[0214]

[0215] Conclusion: From the data of Tables 1-6, it can be seen that sodium carbonate and sodium hydroxide are detected in the positive electrode active materials of Examples 1-31 and Comparative Examples 5-7, and the sodium hydroxide may be obtained from the water absorption reaction of oxidized sodium on the surface of the positive electrode active material. Sodium carbonate and sodium hydroxide are also detected in the positive electrode active materials of Comparative Examples 1-4, and the sodium carbonate is derived from the sodium source in the mixing process, and the sodium hydroxide may also be obtained from the water absorption reaction of oxidized sodium on the surface of the positive electrode active material. From the data of Table 7, it can be seen that the batteries of Examples 1-30 have excellent capacity retention at high voltage compared to Comparative Examples 1-6, indicating that the positive electrode active materials of the present application can improve the cycle stability of the batteries. At the same time, the initial specific discharge capacity of the positive electrode active materials of Examples 1-30 is not less than 158 mAh / g, indicating that the batteries of the present application have excellent energy density at high voltage. In summary, the positive electrode active materials of the present application can simultaneously improve the cycle stability and energy density of the batteries at high voltage.

[0216] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application, and they should be covered in the scope of the claims and the specification of the present application. In particular, as long as there is no structural conflict, each technical feature mentioned in each embodiment can be combined in any way. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A positive electrode active material, characterized in that, Comprising: A core, the core comprising a sodium-ion transition metal oxide containing iron element and / or nickel element. In the sodium-ion transition metal oxide, the molar amount of iron element is denoted as b, the molar amount of nickel element is denoted as c, and 0 ≤ b ≤ 0.4, 0 ≤ c ≤ 0.4; A coating layer, the coating layer being provided on at least a part of the surface of the core. The coating layer contains an alkaline sodium compound, and based on the total amount of the positive electrode active material, the mass proportion of the alkaline sodium compound is w%, and it satisfies: 0.1 ≤ (b + c) / w ≤ 0.5; The sodium-ion transition metal oxide includes: So x Mr a Feb b Ni c Q d O 2-e+δ F e , 0.5 ≤ x ≤ 1.2, 0 < a, 0 ≤ b ≤ 0.4, 0 ≤ c ≤ 0.4, 0 ≤ d, a + b + c + d = 1, 0 < e ≤ 0.2, -0.1 ≤ δ ≤ 0.1, Q includes at least one of Li, B, Mg, Al, Si, K, Ca, Ti, Co, Cu, Zn, Ga, Y, Zr, Nb, Mo, In, Sn, Sb, La, Ce, Ta, W, and Bi.

2. The positive electrode active material according to claim 1, characterized in that, 0.2 ≤ (b + c) / w ≤ 0.

4.

3. The positive electrode active material according to claim 1 or 2, characterized in that, The mass proportion w% of the alkaline sodium compound is 0.3 wt% - 5 wt%.

4. The positive electrode active material according to claim 3, characterized in that, The mass proportion w% of the alkaline sodium compound is 0.5 wt% - 2 wt%.

5. The positive electrode active material according to claim 1, characterized in that, The alkaline sodium compound includes at least one of sodium hydroxide and sodium carbonate.

6. The positive electrode active material according to claim 5, characterized in that, The alkaline sodium compound is sodium carbonate.

7. The positive electrode active material according to claim 6, based on the total mass of the coating layer, the mass proportion of sodium carbonate is higher than or equal to 80%.

8. The positive electrode active material according to claim 5 or 7, based on the total mass of the coating layer, the mass proportion of sodium hydroxide is lower than or equal to 10%.

9. The positive electrode active material according to claim 1 or 2, characterized in that, The sodium-ion transition metal oxide includes: So x Mr a Feb b Ni c Q d O 2-e+δ F e , 0.7 ≤ x ≤ 1.2, 0 < a, 0.1 ≤ b ≤ 0.4, 0.1 ≤ c ≤ 0.4, 0 ≤ d ≤ 0.3, a + b + c + d = 1, 0 < e ≤ 0.2, -0.1 ≤ δ ≤ 0.1, Q includes at least one of B, Mg, Al, Si, Ca, Ti, Co, Cu, Zn, Zr, Nb, Mo, La, and Bi, Based on the total amount of the positive electrode active material, the mass proportion of the alkaline sodium compound is 1 wt% - 2 wt%.

10. The positive electrode active material according to claim 9, characterized in that, Satisfying at least one of the following conditions: 0.3≤a≤0.6； 0.15≤b≤0.35； 0.15≤c≤0.35； 0.1≤d≤0.2。 11. The positive electrode active material according to claim 8, characterized in that, 0.5 ≤ (b + c) / a ≤ 2.

12. The positive electrode active material according to claim 11, characterized in that, 0.5 ≤ (b + c) / a ≤ 1.

5.

13. The positive electrode active material according to claim 8, characterized in that, The sodium ion transition metal oxide includes the O3 phase in the space group. The interlayer spacing is 0.53nm-0.55nm.

14. The positive electrode active material according to claim 1 or 2, characterized in that, The sodium-ion transition metal oxide includes: That x Mn a By c Q d Or 2-e+δ F e , 0.5 ≤ x ≤ 1.2, 0 < a, 0.1 ≤ c ≤ 0.3, 0 ≤ d ≤ 0.3, a + c + d = 1, 0 < e ≤ 0.2, -0.1 ≤ δ ≤ 0.1, Q includes at least one of B, Mg, Al, Si, Ca, Ti, Co, Cu, Zn, Zr, Nb, Mo, La, and Bi, Based on the total amount of the positive electrode active material, the mass proportion of the alkaline sodium compound is 0.5 wt% - 1.5 wt%.

15. The positive electrode active material according to claim 14, characterized in that, Satisfying at least one of the following conditions: 0.5≤a≤0.8； 0.15≤c≤0.25； 0.05≤d≤0.15。 16. The positive electrode active material according to claim 12, characterized in that, 0.125 ≤ c / a ≤ 0.

45.

17. The positive electrode active material according to claim 16, characterized in that, 0.2 ≤ c / a ≤ 0.

3.

18. The positive electrode active material according to claim 11, characterized in that, The phase of the sodium-ion transition metal oxide includes the P2 phase, the space group includes P63 / mmc, and the interlayer spacing is 0.55 nm - 0.57 nm.

19. The positive electrode active material according to claim 1, characterized in that, The BET specific surface area of ​​the positive electrode active material is Sm 2 / g, S and w satisfy the relationship: 0.3≤w / S≤3.

20. The positive electrode active material according to claim 19, characterized in that, 0.5 ≤ w / S ≤ 2.

21. The positive electrode active material according to claim 1, characterized in that, The positive electrode active material satisfies at least one of the following conditions: The positive electrode active material D v 50 is 2μm-20μm; The BET specific surface area of ​​the positive electrode active material is 0.2 m². 2 / g-2m 2 / g; The compaction density of the positive electrode active material under a pressure of 300 MPa is 3.1 g / cm³. 3 -3.8g / cm 3 .

22. The positive electrode active material according to claim 21, characterized in that, The positive electrode active material satisfies at least one of the following conditions: The positive electrode active material D v 50 is 4μm-15μm; The BET specific surface area of ​​the positive electrode active material is 0.3 m². 2 / g-2m 2 / g; The compaction density of the positive electrode active material under a pressure of 300 MPa is 3.2 g / cm³. 3 -3.6g / cm 3 .

23. A method for preparing a positive electrode active material, characterized in that, including: Provided is a sodium-ion transition metal oxide containing iron element and / or nickel element. In the sodium-ion transition metal oxide, the molar amount of the iron element is denoted as b, and the molar amount of the nickel element is denoted as c, where 0 ≤ b ≤ 0.4 and 0 ≤ c ≤ 0.4; Mix and sinter the sodium-ion transition metal oxide and the alkaline sodium compound to obtain the positive electrode active material, where, based on the total amount of the positive electrode active material, the mass percentage of the alkaline sodium compound is w%, and 0.1 ≤ (b + c) / w ≤ 0.5; The sodium-ion transition metal oxide includes: So x Mr a Feb b Ni c Q d O 2-e+δ F e , 0.5 ≤ x ≤ 1.2, 0 < a, 0 ≤ b ≤ 0.4, 0 ≤ c ≤ 0.4, 0 ≤ d, a + b + c + d = 1, 0 < e ≤ 0.2, -0.1 ≤ δ ≤ 0.1, and Q includes at least one of Li, B, Mg, Al, Si, K, Ca, Ti, Co, Cu, Zn, Ga, Y, Zr, Nb, Mo, In, Sn, Sb, La, Ce, Ta, W, and Bi.

24. A positive electrode plate, characterized in that, The positive electrode sheet includes the positive electrode active material described in any one of claims 1 - 22 or the positive electrode active material prepared by the method described in claim 23.

25. A battery, characterized in that, The battery includes the positive electrode sheet described in claim 24.

26. An electrical appliance, characterized in that, including the battery described in claim 25.

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